Report on the Radiolaria Collected by H.M.S. Challenger During the Years 1873-1876, First Part: Porulosa (Spumellaria and Acantharia) Report on the Scientific Results of the Voyage of H.M.S. Challenger During the Years 1873-76, Vol. XVIII

CHAPTER XI.--LITERATURE AND HISTORY.

Chapter 12288,673 wordsPublic domain

251. _List of Publications from 1834 to 1884_:--

_Note._--In the text the references to the following publications are indicated by the letters L. N.

1. 1834. MEYEN, F., Palmellaria (Physematium, Sphærozoum), in Beiträge zur Zoologie, gesammelt auf einer Reise um die Erde. _Nova Acta Acad. Cæs. Leop.-Carol._, vol. xvi., Suppl., p. 160, Taf. xxviii. figs. 1-7.

2. 1838. EHRENBERG, G., Polycystina (Lithocampe, Cornutella, Haliomma) in Ueber die Bildung der Kreidefelsen und des Kreidemergels durch unsichtbare Organismen. _Abhandl. d. k. Akad. d. Wiss. Berlin_, p. 117.

3. 1839. EHRENBERG, G., Ueber noch jetzt lebende Thierarten der Kreidebildung (Haliomma radians). _Abhandl. d. k. Akad. d. Wiss. Berlin_, p. 154.

4. 1844-1873. EHRENBERG, G., Vorläufige Mittheilungen über Beobachtungen von Polycystinen. _Monatsber. d. k. preuss. Akad. d. Wiss. Berlin_. Republished with illustrations in the Mikrogeologie (L. N. 6) and in the two treatises of 1872 (L. N. 24) and 1875 (L. N. 25). Compare the _Monatsberichte_ of 1844 (pp. 57, 182, 257), of 1846 (p. 382), of 1847 (p. 40), of 1850 (p. 476), of 1854 (pp. 54, 205, 236), of 1855 (pp. 292, 305), of 1856 (pp. 197, 425), of 1857 (pp. 142, 538), of 1858 (pp. 12, 30), of 1859 (p. 569), of 1860 (pp. 765, 819), of 1861 (p. 222), of 1869 (p. 253), of 1872 (pp. 300-321), of 1873 (pp. 214-263). Only one of these small papers is of permanent value, The First Systematic Arrangement of the Polycystina in 7 families, 44 genera, and 282 species (_Monatsber. d. k. preuss. Akad. d. Wiss. Berlin_, 1847, p. 54). Compare my Monograph (1862, L. N. 16), pp. 3-12, 214-219.

5. 1851. HUXLEY, TH., Upon Thalassicolla, a new Zoophyte. _Ann. and Mag. Nat. Hist._, ser. 2, vol. viii. pp. 433-442, pl. xvi.

6. 1854. EHRENBERG, G., Mikrogeologie. Figures of numerous Polycystina on 8 plates; Taf. xviii. figs. 110, 111; Taf. xix. figs. 48-56, 60-62; Taf. xx. Nr. i., figs. 20-25, 42; Taf. xxi. figs. 51-56; Taf. xxii. figs. 20-40; Taf. xxxv. A., Nr. xix. A. fig. 5; Taf. xxxv. B. figs. 16-23; Taf. xxxvi. figs. 1-33.

7. 1855. BAILEY, J. W., Notice of Microscopic Forms of the Sea of Kamtschatka. _Amer. Journ. Sci. and Arts_, vol. xxii. p. 1, pl. i.

8. 1855. MÜLLER, JOHANNES, Ueber Sphærozoum und Thalassicolla. _Monatsber. d. k. preuss. Akad. d. Wiss. Berlin_, p. 229.

9. 1855. MÜLLER, JOHANNES, Ueber die im Hafen von Messina beobachteten Polycystinen (Haliomma, Eucyrtidium, Dictyospyris, Podocyrtis). _Monatsber. d. k. preuss. Akad. d. Wiss. Berlin_, p. 671.

10. 1856. MÜLLER, JOHANNES, Ueber die Thalassicollen, Polycystinen und Acanthometren des Mittelmeeres. _Monatsber. d. k. preuss. Akad. d. Wiss. Berlin_, p. 474.

11. 1858. MÜLLER, JOHANNES, Erläuterung einiger bei St. Tropez am Mittelmeer beobachteter Polycystinen und Acanthometren. _Monatsber. d. k. preuss. Akad. d. Wiss. Berlin_, p. 154.

12. 1858. MÜLLER, JOHANNES, Ueber die Thalassicollen, Polycystinen und Acanthometren des Mittelmeeres, _Abhandl. d. k. Akad. d. Wiss. Berlin_, pp. 1-62, Taf. i.-xi. (The fundamental treatise on the Radiolaria.)

{clxxvii}13. 1858. SCHNEIDER, ANTON, Ueber zwei neue Thalassicollen von Messina. _Archiv f. Anat. u. Physiol._, p. 38, Taf. iii. B, figs. 1-4.

14. 1858. CLAPARÈDE et LACHMANN, Echinocystida (Plagiacantha et Acanthometra). Études sur les Infusoires et les Rhizopodes, p. 458, pl. xxii. figs. 8, 9; pl. xxiii. figs. 1-6.

15. 1860. HAECKEL, ERNST, Ueber neue lebende Radiolarien des Mittelmeeres. _Monatsber. d. k. preuss. Akad. d. Wiss. Berlin_, pp. 794, 835.

16. 1862. HAECKEL, ERNST, Die Radiolarien (Rhizopoda radiaria). Eine Monographie. 572 pp. fol. with an Atlas of 35 Copperplates.

17. 1862. BURY, Mrs., Polycystins, figures of remarkable forms in the Barbados Chalk Deposit. Ed. ii. By M. C. Cooke, 1868. 25 quarto plates, photographed from drawings by hand, containing many forms overlooked by Ehrenberg from Barbados.

18. 1863 HARTING, PAUL, Bijdrage tot de Kennis der mikroskopische Fauna en Flora van de Banda-Zee (Diep-Zee-Polycystinen). _Verhandl. d. Kon. Akad. van. Wetensch. Amsterdam_, vol. ix. p. 30, pls. i.-iii.

19. 1865. HAECKEL, ERNST, Ueber den Sarcode-Körper der Rhizopoden (Actinelius, Acanthodesmia, Cyrtidosphæra, &c.). _Zeitschr. f. wiss. Zool._, Bd. xv. p. 342, Taf. xxvi.

20. 1867. SCHNEIDER, ANTON, Zur Kenntniss des Baues der Radiolarien (Thalassicolla). _Archiv f. Anat. u. Physiol._, 1867, p. 509.

21. 1870. HAECKEL, ERNST, Beiträge zur Plastiden Theorie (Myxobrachia; Amylum in den gelben Zellen). _Jenaische Zeitschr. für Naturw._, Bd. v. p. 519-540, Taf. xviii.

22. 1871. CIENKOWSKI, L., Ueber Schwärmer-Bildung bei Radiolarien. _Archiv f. mikrosk. Anat._, Bd. vii. p. 372-381, Taf. xxix.

23. 1872. WAGNER, N., Myxobrachia Cienkowskii. _Bull. d. Acad. St. Petersburg_, vol. xvii. p. 140.

24. 1872. EHRENBERG, GOTTFRIED, Mikrogeologische Studien über das kleinste Leben der Meeres-Tiefgründe aller Zonen und dessen geologischen Einfluss. _Abhandl. d. k. Akad. d. Wiss. Berlin_, 1872. Mit 12 Tafeln. (The Latin diagnoses of 113 new species here mentioned are given in the _Monatsberichte_ of April 25, 1872, pp. 300-321.)

25. 1875. EHRENBERG, GOTTFRIED, Polycystinen-Mergel von Barbados (Fortsetzung der Mikrogeologischen Studien). _Abhandl. d. k. Akad. d. Wiss. Berlin_, 1875, 168 pag. mit 30 Tafeln. (The Latin diagnoses of 265 species here recorded are given in Namensverzeichniss der fossilen Polycystinen von Barbados. _Monatsber. d. k. preuss. Akad. d. Wiss. Berlin_, Jan. 30, 1873, pp. 213-263.)

26. 1876. HERTWIG, RICHARD, Zur Histologie der Radiolarien. Untersuchungen über den Bau und die Entwickelung der Sphærozoiden und Thalassicolliden. 91 pp. with 5 plates.

27. 1876. MURRAY, JOHN, Challengerida. Preliminary Reports on Work done on board the Challenger. _Proc. Roy. Soc. Lond._, vol. xxiv. pp. 471-536, pl. xxiv.

28. 1876. ZITTEL, KARL, Palæozoologie, Bd. i. pp. 114-126, figs. 46-56.

29. 1876. ZITTEL, KARL, Ueber fossile Radiolarien der oberen Kreide. _Zeitschr. d. deutsch. geol. Gesellsch._, Bd. xxviii. pp. 75-96, Taf. ii. (with figures of six Cretaceous species).

30. 1877. MIVART, ST. GEORGE, Notes touching recent researches on the Radiolaria. _Journ. Linn. Soc. Lond._ (Zool.), vol. xiv. pp. 136-186. (Historical sketch of previous literature.)

31. 1877. WYVILLE THOMSON, The Voyage of the Challenger--The Atlantic, vol. i. pp. 231-237, figs. 51-54; vol. ii. pp. 340-343, figs. 58, 59, &c.

32. 1878. HAECKEL, ERNST, Das Protistenreich, eine populäre Uebersicht über das Formengebiet der niedersten Lebewesen, pp. 101-104.

33. 1879. HERTWIG, RICHARD, Der Organismus der Radiolarien. _Jenaische Denkschriften_, Bd. ii. Taf. vi.-xvi. pp. 129-277.

34. 1879. HAECKEL, ERNST, Ueber die Phæodarien, eine neue Gruppe kieselschaliger mariner Rhizopoden. _Sitzungsb. med.-nat. Gesellsch. Jena_, December 12, 1879.

35. 1880. STÖHR, EMIL, Die Radiolarien-Fauna der Tripoli von Grotte (Provinz Girgenti in Sicilien). _Palæontographica,_ Bd. xxvi. pp. 71-124, Taf. xvii.-xxiii. A preliminary communication regarding this fauna from the tripoli is given in _Tagebl. d. Naturf. Versamml. München_, 1877.

{clxxviii}36. 1880. PANTANELLI, DANTE, I Diaspri della Toscana e i loro fossili. _Real. Accad. dei Lincei_, ser. 3, vol. vii. pp. 13-34, Tab. i. Radiolaria di Calabria. _Atti. Soc. Tosc._, p. 59.

37. 1881. HAECKEL, ERNST, Prodromus Systematis Radiolarium, Entwurf eines Radiolarien-Systems auf Grund von Studien der Challenger-Radiolarien. _Jenaische Zeitschr. für Naturw._, Bd. xv. pp. 418-472.

38. 1881. BRANDT, KARL, Untersuchungen an Radiolarien. _Monatsber. d. k. preuss. Akad. d. Wiss. Berlin_, (April 21), pp. 388-404, Taf. i.

39. 1882. BRANDT, KARL, Ueber die morphologische und physiologische Bedeutung des Chlorophylls bei Thieren. I. Artikel. _Archiv f. Anat. u. Physiol._, pp. 125-151, Taf. i. II. Artikel. _Mittheil. a. d. Zool. Station zu Neapel_, Bd. iv. pp. 193-302, Taf. xix., xx.

40. 1882. BÜTSCHLI, OTTO, Beiträge zur Kenntniss der Radiolarien-Skelette, insbesondere der der Cyrtida. _Zeitschr. f. wiss. Zool._, Bd. xxxvi. pp. 485-540, Taf. xxxi.-xxxiii.

41. 1882. BÜTSCHLI, OTTO, Radiolaria. In Bronn's Klassen und Ordnungen des Thierreichs. Bd. i., Protozoa, pp. 332-478, Taf. xvii.-xxxii.

42. 1882. GEDDES, PATRICK, Further Researches on Animals containing Chlorophyll. _Nature_, pp. 303-305.

43. 1882. GEDDES, PATRICK, On the Nature and Functions of the "Yellow Cells" of Radiolarians and Coelenterates. _Proc. Roy. Soc. Edin._, p. 377.

44. 1882. DUNIKOWSKI, EMIL, Die Spongien, Radiolarien und Foraminiferen der Unter-Liassischen Schichten vom Schafberg bei Salzburg. _Denkschr. d. k. Akad. d. Wiss. Wien_, Bd. xlv. pp. 22-34. Taf. iv.-vi.

45. 1882. PANTANELLI, DANTE, Fauna miocenica di Radiolari del Appennino settentrional. _Boll. Soc. Geol. Ital._

46. 1883. HAECKEL, ERNST, Die Ordnungen der Radiolarien (Acantharia, Spumellaria, Nassellaria, Phæodaria). _Sitzungsb. med.-nat. Gesellsch. Jena_, February 16, 1883.

47. 1883. HERTWIG, OSCAR, Die Symbiose oder das Genossenschaftsleben im Thierreich. 56. _Versamml. Deutscher Naturf. u. Aerzte_, Freiburg i/B.

48. 1883. RÜST, WILHELM, Ueber das Vorkommen von Radiolarien-Resten in kryptokrystallinischen Quarzen aus dem Jura und in Koprolithen aus dem Lias. 56. _Versamml. Deutscher Naturf. u. Aerzte_, Freiburg i/B.

49. 1884. CAR, LAZAR, Acanthometra hemicompressa (= Zygacantha semicompressa). _Zool. Anzeiger_, p. 94.

50. 1884. HAECKEL, ERNST, Ueber die Geometrie der Radiolarien (Promorphologie). _Sitzungsb. med.-nat. Gesellsch. Jena_, November 22, 1883.

251 A. _Supplementary List of Works Published in_ 1885:--

51. 1885. D. RÜST, Beiträge zur Kenntniss der fossilen Radiolarien aus Gesteinen des Jura. 45 pp. 4to, and 20 plates. _Palæontographica_, Bd. xxxi. (oder iii. Folge, vii. Band).

52. 1885. KARL BRANDT, Die koloniebildenden Radiolarien (Sphærozoeen) des Golfes von Neapel und der angrenzenden Meeres-Abschnitte. 276 pp. 4to, and 8 plates.

53. 1885. JOHN MURRAY, Narrative of the Cruise of H.M.S. Challenger, with a general account of the scientific results of the Expedition. Vol i. First part, pp. 219-227, pl. A. Second part, pp. 915-926, pl. N. fig. 2.

54. 1885. ERNST HAECKEL, System der Acantharien. _Sitzungsb. med.-nat. Gesellsch. Jena_, November 13.

Since the printing of this Report began in 1884 and was far advanced in 1885, it was impossible to include the important works of Rüst and Brandt (L. N. 51, 52) in the descriptive portion, so that they are only referred to in the Introduction.

251 B. _Phaulographic Appendix_:--

A list of absolutely worthless literature, which contains either only long known facts or false statements, and may hence be entirely neglected with advantage. Compare § 252, and also L. N. 26, p. 9.

55. 1865. WALLICH, G. C., On the structure and affinities of Polycystina. _Trans. Micr. Soc. Lond._, vol. xiii. pp. 57-84. (Compare L. N. 26, p. 9.)

{clxxix}56. 1879. WALLICH, G. C., Observations on the Thalassicollidæ. _Ann. and Mag. Nat. Hist._, ser. 4, vol. iii. p. 97.

57. 1866. STUART, ALEXANDER, Ueber Coscinosphæra ciliosa, eine neue Radiolarie (= Globigerina echinoides!!). _Zeitschr. f. wiss. Zool._, Bd. xvi. p. 328, Taf. xviii. (Compare L. N. 26, p. 9.)

58. 1870. STUART, ALEXANDER, Neapolitanische Studien. _Göttinger Nachr._, p. 99, and _Zeitschr. f. wiss. Zool._, Bd. xxii. p. 290 ("Blue Siliceous Crystals" in Collozoum inerme!).

59. 1871. MACDONALD, JOHN DENIS, Remarks on the Structure of Polycystina (Astromma Yelvertoni = Euchitonia Mülleri). _Ann. and Mag. Nat. Hist._, ser. 4, vol. viii. p. 226.

60. 1871. DOENITZ, W., Beobachtungen über Radiolarien. _Archiv f. Anat. u. Physiol._, 1871, p. 71, Taf. ii. (Compare L. N. 26, p. 7.)

252. _Progress of our Knowledge of the Radiolaria from_ 1862 _to_ 1885.--The history of our scientific knowledge of the Radiolaria extends over about half a century (from 1834 to 1885). A historical and critical discussion of the works which appeared within the first twenty-eight years of this period (from 1834 to 1862) is contained in the historical introduction to my Monograph (L. N. 16, pp. 1-24); I shall therefore give here only a brief survey of the investigations published during the last twenty-three years (from 1862 to 1885). The most important steps in our progress during this period we owe to the following naturalists:--Cienkowski (1871), Ehrenberg (1872 and 1875), Richard Hertwig (1876 and 1879), Karl Brandt (1881 and 1885), Bütschli (1882), and Rüst (1885). To the valuable works of these authors must be added a number of smaller contributions, which are recorded in the foregoing Bibliography. Some communications from dilettanti, written with insufficient knowledge of the subject, and hence of no value, are mentioned for the sake of completeness in the "Phaulographic Appendix" (compare L. N. 55-60, also L. N. 26, p. 9).

The first important advance in our knowledge of the organisation of the Radiolaria, made after the publication of my Monograph (1862), was the demonstration of the nature of the extracapsular "yellow cells." In the year 1870 I showed that these yellow cells contain starch (L. N. 21, p. 519). I regarded them, as did all authors up to that time, as integral parts of the Radiolarian organism, and hence considered this to be multicellular; for no doubt was possible regarding the true cellular nature of these remarkable, nucleated, yellow globules, which I had thoroughly studied in 1862. It was first shown by Cienkowski in 1871 that the yellow cells of the #Collodaria# remain unchanged even after the death of these organisms, "that they continue to grow uninterruptedly, and eventually multiply by division" (L. N. 22, pp. 378-380, Taf. xix. figs. 30-36). Cienkowski concluded from these important observations that the yellow cells are not integral parts of the Radiolarian body, but "parasitic structures," independent, unicellular organisms, which live only as parasites in the body of the Radiolaria (compare § 90).

This important recognition underwent ten years later a further development and complete establishment by the extensive investigations of Karl Brandt (L. N. 38, 39) {clxxx}and Patrick Geddes (L. N. 42, 43). This arrangement was compared by Brandt to the remarkable symbiosis of the Algoid gonidia and Fungoid hyphæ in the organisation of the Lichens, which had been recently discovered, and since he recognised the independent nature of the yellow cells, as unicellular Algæ, in all divisions of the Radiolaria, he founded for them the genus _Zooxanthella_. Geddes named them _Philozoon_, and showed experimentally that they give out oxygen under the influence of sunlight (compare § 90). The great physiological importance of the yellow cells in the metastasis of the Radiolaria, and, when they are developed in large quantities, in the economy of marine organisms in general, has recently been insisted upon by Brandt (see § 205 and L. N. 52, pp. 65-71, 86-94).

The proof that the yellow cells do not belong to the Radiolarian organism itself, but only live parasitically in it, was a necessary preliminary to the very important step which next took place in our knowledge of the organisation of the Radiolaria. This step consisted in the demonstration that the whole body of the Radiolaria, like that of all other Protista, is only a single cell. It was Richard Hertwig who in two remarkable works (L. N. 26, 33) firmly established this fundamental theorem of the unicellular nature of the Radiolaria. In his treatise on the histology of the Radiolaria (L. N. 26, 1876) he published complete investigations into the structure and development of the Sphærozoida and Thalassicollida. Since he made use of the modern methods of histological examination, and especially of staining fluids, which he was the first to apply to the study of the Radiolaria, he was able to show that no true cells (apart from the parasitic yellow cells) are to be found in their bodies, but rather that all their morphological components are to be regarded as differentiated parts of a single true cell, and in particular that the central capsule includes a genuine nucleus.

A wider foundation for this important discovery and its applicability to all divisions of this extensive class, was given by Hertwig in a second work on the organisation of the Radiolaria (L. N. 33, 1879). Among the numerous discoveries by which this work enriched the natural history of the Radiolaria must be specially mentioned the recognition of the fundamental differences exhibited by the main divisions of the class in the structure of their central capsule. Hertwig first observed that the capsular membrane is double in the PHÆODARIA but single in the other Radiolaria (§ 56); the former he named "TRIPYLEA" because he discovered in their capsular membrane a large, peculiarly constructed main opening and two small accessory openings. The NASSELLARIA, in which he found a single porous area at the basal pole of the main axis, with a cone of pseudopodia rising from it, he called on this account "MONOPYLEA"; whilst the other Radiolaria, whose capsular membrane is perforated on all sides with fine pores, were termed "PERIPYLEA." Besides the central capsule, Hertwig laid stress upon the significance of the gelatinous envelope as a constant and important constituent of the body. He also devoted attentive consideration to the morphology of the skeleton, and on the basis of certain {clxxxi}phylogenetic conclusions which he drew from it, he arrived at an improved systematic arrangement in which he distinguished six orders:--(1) #Thalassicollea#, (2) #Sphærozoea#, (3) #Peripylea#, (4) #Acanthometrea#, (5) #Monopylea#, (6) #Tripylea#. The numerous isolated discoveries with which Hertwig enriched the morphology of the Radiolaria, have been already alluded to in the appropriate paragraphs in the anatomical portion of this Introduction (see L. N. 42, pp. 340, 341).

The new and interesting group, which was thus erected into an order under the name TRIPYLEA, I had already a year previously separated from the other Radiolaria as "_Pansolenia_" in my Protistenreich (L. N. 32, p. 102). Since, however, neither the three capsular openings of the TRIPYLEA nor the skeletal tubes of the Pansolenia are present in all the families of this extensive order, I substituted in 1879 the more suitable name PHÆODARIA, which is applicable to all members of the group (L. N. 34). In the preliminary memoir then published regarding the Phæodaria, a New Group of Siliceous Marine Rhizopods, I distinguished four orders, ten families, and thirty-eight genera. The great majority of these new forms (among which were no less than 465 different species) were first discovered by the deep-sea investigations of the Challenger. John Murray was the first who called attention to the great abundance in the deep sea of these remarkable Rhizopods, and to the constant presence of their peculiar, dark, extracapsular pigment body (phæodium); even in 1876 he described a portion of them as Challengerida (L. N. 27, p. 536; L. N. 53, p. 226). The earliest observations on the PHÆODARIA were made at Messina in 1859, where I examined five genera of this remarkable group alive (compare p. 1522 and L. N. 16).

By the discovery that the PHÆODARIA, although differing in important respects from the other Radiolaria, still conform to the definition of the class, a new and extensive series of forms was added to this latter, and by their closer investigation a fresh source of interesting morphological problems was disclosed. In other groups, however, morphology was advanced by comparative anatomical studies. In addition to the smaller contributions of various authors, mentioned in the foregoing bibliography, I may specially refer to the valuable Beiträge zur Kenntniss der Radiolarien-Skelete, insbesondere der der Cyrtida by O. Bütschli (L. N. 40, 1882). On the basis of careful comparative anatomical studies, investigations into the skeletal structure of a number of fossil #Cyrtoidea# and critical application of the recently published researches of Ehrenberg into the Polycystina of Barbados (L. N. 25), Bütschli attempted to derive the complicated relations of the Monopylean skeletons phylogenetically from a simple primitive form,--the primary sagittal ring. Even if this attempt did not actually solve the very difficult morphological problem in question, still the critical and synthetic mode in which it was carried out deserves full recognition, and furnishes the proof that the comparative anatomy of the skeleton in the Radiolaria not less than in the Vertebrata, is a most interesting and fruitful field of phylogenetic investigation. A {clxxxii}further demonstration of this was furnished by Bütschli in the general account of the organisation of the Radiolaria which he published in 1882 in Bronn's Klassen und Ordnungen des Thierreichs (L. N. 41).

In our knowledge of the developmental history of these Protista the last two decades have witnessed less progress than in their comparative anatomy. The most important advance in this direction has been the proof that in all the main groups of the class the contents of the central capsule are used in the formation of swarm-spores. The movements of these zoospores in the central capsule had indeed been observed by several previous authors in the case of the SPUMELLARIA and ACANTHARIA (L. N. 10, 13, 16; compare also § 142, Note A). The origin of the flagellate spores from the contents of the central capsule and their peculiar constitution were, however, first described fully by Cienkowski in 1871 (L. N. 22, p. 372). Soon after this, R. Hertwig discovered that in the social Radiolaria (Polycyttaria or Sphærozoea) two different forms of zoospores are formed, one with, the other without crystals, and that the latter are also divided into macrospores and microspores (compare L. N. 26, and § 142). Recently this sexual differentiation has been shown by Karl Brandt to exist in all the groups of Sphærozoea, and its regular interchange with the formation of crystal-spores has been interpreted as a true "alternation of generations" (compare L. N. 52 and also § 216). The other forms of development also, especially reproduction by cell-division (§ 213) and gemmation (§ 214), have been elucidated by the recent investigations of the same author.

The palæontology of the Radiolaria has of late made important and interesting advances. Until ten years ago fossil remains of this class were known exclusively from the Tertiary period; almost the only source of our information was to be found in the researches of Ehrenberg, commenced in 1838, continued in his Mikrogeologie in 1854, and concluded in his last work (L. N. 25) published in 1875 (compare L. N. 16, pp. 3-9, 191-193). In the year 1876 a number of Mesozoic Radiolaria from the chalk were described by Zittel (L. N. 28), and afterwards others from the Jura by Dunikowski (L. N. 44). That fossil Radiolaria occur in Mesozoic formations, especially in the Jura, as well preserved and as abundantly as in the Tertiary rocks of Barbados, was shown in 1883 by Rüst (L. N. 48). By the examination of numerous thin sections he discovered that in all the main divisions of the Jurassic formation (Lias, Dogger, Malm) there are distributed jaspers, flints, cherts, and other quartzites, which consist largely of the siliceous shells of Polycystina; the same is true also of many Coprolites found in the Jura. The full account of these and the descriptions and figures of 234 Jurassic species, distributed in 76 genera, are contained in the Beiträge zur Kenntniss der fossilen Radiolarien aus Gesteinen des Jura (L. N. 51, 1885). But even in the older rocks, the Trias, the Permian, and Carboniferous systems, and even as far downwards as the Silurian and Cambrian formations, Rüst has recently shown the existence of fossil Radiolaria, {clxxxiii}and thus increased the known period of the developmental history of the class by many millions of years (§ 244).

The great significance of the Radiolaria in geology and palæontology has been brought into new light not only by these extensive discoveries, but also by the important relations which have been shown to exist between the Radiolarian rocks and the deep-sea deposits of the present day. In this direction the wonderful discoveries of the Challenger, and especially the investigation of the deep-sea deposits by Wyville Thomson (L. N. 31) and John Murray (L. N. 27), have furnished us with new and valuable information (compare §§ 236-239, and §§ 245-250). The Tertiary Polycystine formations of Barbados and the Nicobar Islands, with which we have been acquainted for the last forty years, as also the Mesozoic Radiolarian quartzes, which have only recently been made known to us from the Jura, are ascertained to be fossil representatives of the same deep-sea deposits which now occur in the form of Radiolarian ooze (§ 237), and to some extent also of Globigerina ooze and red clay (§§ 238, 239), on the bottom of the ocean, at depths of from 2000 to 4500 fathoms.

These investigations into fossil Radiolaria and their comparison with recent deep-sea forms have a further general significance, inasmuch as the identity of many living and fossil species from the Tertiary formation has been shown beyond all doubt. In this direction the numerous measurements and accurate comparisons which I have made during the last ten years of the abyssal forms in the Challenger collection, and of fossil species from Barbados and Caltanisetta, have brought to light many important facts. In this I had the able assistance of my friend, Dr. Reinhold Teuscher (compare § 250, and p. 1760). Further valuable contributions in this direction are found in the careful observations and comparative measurements recently published by Emil Stöhr (L. N. 35, 1880), regarding the Radiolarian fauna of the Tripoli of Grotte in the province of Girgenti, Sicily. From these it appears that the number of Miocene species which are still extant, is much greater than would appear from the results of Ehrenberg.

Ehrenberg himself, towards the end of his long and laborious life, collected the results of the systematic and palæontological researches, which he had begun thirty-seven years previously (L. N. 16, pp. 3-12) into the Polycystina, in two large works (L. N. 24, 25). The first treatise (L. N. 24, 1872) contains the Mikrogeologische Studien über das Kleinste Leben der Meeres-Tiefgründe aller Zonen und dessen geologischen Einfluss, with a list of 279 Polycystina observed by him from the deep-sea, as well as figures of 127 species. The second work (L. N. 25, 1875) contains the Fortsetzung der Mikrogeologischen Studien, mit specieller Rücksicht auf den Polycystinen-Mergel von Barbados; the list of fossil Polycystina observed by him includes 325 species, of which 26 are still extant; 282 of them are figured on the thirty plates accompanying the memoir. By means of these numerous figures, as well as by the appended systematic and chorological tables, Ehrenberg furnished a welcome {clxxxiv}supplement to the numerous communications regarding the Polycystina, which he had made to the Berlin Academy since 1838, and which he had published in his Mikrogeologie in 1854. It will always be the merit of this zealous and indefatigable microscopist that he first called attention to the great wealth of forms existing in this class; he separated systematically about 500 species, and published drawings of about 400; in addition to which he was the first to lay stress upon the great chorological and geological importance of the Radiolaria.

With these systematic and descriptive, chorological and palæontological works, however, which relate exclusively to the Polycystina, the merits of the famous naturalist of Berlin are exhausted as regards this class of animals. Of the organisation of the Radiolaria, Gottfried Ehrenberg remained entirely ignorant up till his death in 1876. All that a number of famous naturalists had observed during a quarter of a century as to the structure and life-history of the Radiolaria, all the important discoveries of Huxley (1851), Johannes Müller (1858), Claparède (1858), Cienkowski (1871), and many others (L. N. 1-22), and all that I had published in my Monograph (1862) on the basis of three years' study of their anatomy and physiology--all this Ehrenberg ignored, or rather, he regarded it all as worthless rubbish of science, as a chaos of devious errors, resting upon incomplete observations and false conclusions. His strange "special considerations regarding the Polycystina" (L. N. 24, pp. 339-346) and the general "concluding remarks" (L. N. 25, pp. 146-147) leave no room for doubt on this point. Ehrenberg indeed doubted to the last whether any observer had seen living Radiolaria at all (L. N. 25, p. 108).

The invincible obstinacy with which Ehrenberg maintained his preconceived opinion of the high organisation of the Radiolaria, and entirely ignored the contrary observations of other naturalists, is explained by the consistency with which he held to the end the "principle peculiar to himself of the universally equal development of the animal kingdom" (L. N. 16, p. 7). From the complicated arrangement of their siliceous shells he concluded that the animals inhabiting them must possess a structure correspondingly complex, and nearly related to that of the Echinodermata (Holothuria). Like all other animals the Radiolaria must possess systems of organs for locomotion, sensation, nutrition, circulation, and reproduction. Whilst Ehrenberg originally interpreted the Polycystina as siliceous Infusoria polygastrica, and regarded them as compound Arcellina, he afterwards classed them sometimes with the Echinodermata (Holothuria), sometimes with the Bryozoa, sometimes with the Oscillaria (see L. N. 41, p. 336). Although a decided opponent of the cell-theory he called them "multicellular animalcules" (Polycystina), interpreting the pores of the siliceous shell as cells. To-day the opposite term (Monocystina) might be adopted to express their unicellular organisation. It was a remarkable irony of fate that in the self-same year (1838) in which Schwann of Berlin made by his foundation of the cell theory the greatest advance in the whole {clxxxv}of Biological Science, that Ehrenberg, all his life the most zealous opponent of that theory, published his great work on the Infusoria, and at the same time established the "family of multicellular animalcules or Polycystina" (L. N. 16, p. 4).

The "short systematic survey of the genera of cellular animalcules" given by Ehrenberg in 1875 (L. N. 25, p. 157), is only a new edition, increased by sixteen genera, of his first systematic arrangement of the Polycystina of 1847 (L. N. 4, p. 53). Since I have already given a full discussion of this in my Monograph (L. N. 16, pp. 214-219), I need only here remark that a correct understanding of his very inadequate generic diagnoses is only possible by the aid of his figures. Relying upon these I have retained almost all Ehrenberg's genera, although entirely new definitions of most of them have been necessary.

The same is true also of the two orders which Ehrenberg distinguished in his class of "Zellenthierchen." The first order is constituted by his "Netzkörbchen" (Monodictya or NASSELLARIA) formerly known as "Polycystina solitaria"; they include our #Cyrtoidea#, the greater part of Hertwig's Monopylea. Ehrenberg's second order is the "Schaumsternchen" (Polydictya or SPUMELLARIA), previously called "Polycystina composita"; they include the Peripylea of Hertwig, as well as the Spyridina (our #Spyroidea#), which belong properly to the NASSELLARIA. Although Ehrenberg's statements regarding the organisation of both these orders were quite erroneous, and his knowledge even of the structure of their shells very defective, I still thought it advisable to retain his names for the groups, since they constituted his one successful effort in the systematic treatment of the Radiolaria (compare L. N. 41, p. 336).

The sketch of a systematic arrangement of the Radiolaria (L. N. 37), which I published in 1881 on the basis of the study of the Challenger Radiolaria, resembles, in respect of seven orders being distinguished, the new system which R. Hertwig founded in 1879, in consequence of the variations which he discovered in the structural relations of the central capsule (L. N. 33, p. 133). It differs, however, inasmuch as his Sphærozoea (my Polycyttaria) are here divided into two orders, Symbelaria (#Collosphærida#) and Syncollaria (#Sphærozoida#). In that sketch too I separated for the first time the two subclasses Holotrypasta (Porulosa) and Merotrypasta (Osculosa). The fifteen families established by Hertwig were then raised to twenty-four. The six hundred and thirty genera, which I then distinguished, are still for the most part retained, some, however, in a restricted sense, or with amended definitions.

The differential characters of the orders and families of the Radiolaria, given in the Prodromus in 1881, were amended in a further communication which I gave in 1883 regarding the orders of the Radiolaria (L. N. 46, p. 17). There I reduced the seven orders to four, the structural relations of the central capsule being precisely the same in the Polycyttaria and #Collodaria# as in the #Peripylea#. The survey of the affinities of the class was thus rendered much simpler and clearer, and the {clxxxvi}hypothetical genealogical tree, which I then published, has been still further carried out in Chapter VI. of the present Introduction (see §§ 153-200).

253. _General Survey of the Growth of our Systematic Acquaintance with the Radiolaria from 1834 to 1885._

1834. MEYEN (L. N. 1) describes 2 genera and species of #Collodaria#:--_Sphærozoum fuscum_ and _Physematium atlanticum_.

1838. EHRENBERG (L. N. 2) founds the family Polycystina upon 3 fossil genera (with 6 species):--_Lithocampe_, _Cornutella_, _Haliomma_.

1847. EHRENBERG (L. N. 4) publishes his preliminary communications regarding the fossil Polycystina of Barbados and distinguishes 282 species, distributed in 44 genera and 7 families. In the tabular view of the genera he distinguishes two orders:--I. #Solitaria#--(1) Halicalyptrina, (2) Lithochytrina, (3) Eucyrtidina; and II. #Composita#--(4) Spyridina, (5) Calodictya, (6) Haliommatina, (7) Lithocyclidina (compare L. N. 16, pp. 214-219).

1851. HUXLEY (L. N. 5) gives the first accurate account of living Radiolaria, and describes 2 species of the genus _Thalassicolla_ (_nucleata_ and _punctata_); under the latter are included 4 genera of #Sphærozoea#:--_Collozoum_, _Sphærozoum_, _Collosphæra_, _Siphonosphæra_ (compare L. N. 16, pp. 12-14).

1854. EHRENBERG (L. N. 6) publishes in his Mikrogeologie, figures of seventy-two species of fossil Polycystina (without descriptions).

1855. JOHANNES MÜLLER (L. N. 8, p. 248) describes the first _Acanthometra_, and elucidates its affinity to Huxley's _Thalassicolla_ and Ehrenberg's Polycystina.

1858. JOHANNES MÜLLER (L. N. 12) establishes the new group Radiolaria as a special order of the Rhizopoda, and includes in it the Thalassicolla, Polycystina, and Acanthometra as closely related families. He opposes these radiate Rhizopoda to the Polythalamia, and describes 50 species observed by him living in the Mediterranean, these he arranges in 20 genera, of which 10 are new. The figures are contained in eleven plates (see L. N. 16, pp. 22-24).

1858. CLAPARÈDE (L. N. 14) describes the first #Plectoidean# (_Plagiacantha arachnoides_) and two species of _Acanthometra_, which he had observed living in Norway (see L. N. 16, p. 18).

1860. EHRENBERG (L. N. 4) gives a short diagnosis of 22 new genera of Polycystina, based on the investigation of numerous deep-sea species brought up by Brooke from the depths of the Pacific Ocean. The number of his genera is thus increased to 66 (compare L. N. 16, pp. 10, 11).

1862. ERNST HAECKEL (L. N. 16) embraces in his Monograph of the Radiolaria all the species hitherto known either by figures or descriptions, and arranges them in 15 families and 113 genera; of which latter 46 are new. The number of new species observed living amounts to 144. In a "survey of the Radiolarian fauna of Messina" (p. 565) he records 72 genera and 169 species. Most of these are figured in the accompanying atlas of thirty-five plates.

{clxxxvii}1862. BURY (L. N. 17) gives in an atlas of twenty-five plates, photographed from drawings, the figures of numerous fossil Polycystina of Barbados (without descriptions), of which many are new species overlooked by Ehrenberg (compare § 242, above).

1872. EHRENBERG (L. N. 24) gives a list of names (without description) of all the Polycystina observed by him from the bottom of the sea, 279 species, of which 127 are figured on twelve plates.

1875. EHRENBERG (L. N. 25) gives a list of names of all the fossil Polycystina observed by him (from Barbados, the Nicobar Islands and Sicily), 326 species, of which 282 are figured (compare § 242 above). In a new "Systematic Survey of the Genera" the number of these is given as 63. The 7 families are the same as given in 1847 (see above), as also the two orders (NASSELLARIA = Solitaria, SPUMELLARIA = Composita).

1876. ZITTEL (L. N. 29) describes the first fossil Radiolaria from the chalk (6 species) and establishes the new Cyrtoid genus _Dictyomitra_.

1876. JOHN MURRAY (L. N. 27) establishes the new family Challengerida, and figures 6 new generic types of PHÆODARIA.

1879. RICHARD HERTWIG (L. N. 33) first describes the fundamental differences in the structure of the central capsule, and in accordance with them divides the Radiolaria into six orders:--(1) Thalassicollea, (2) Sphærozoea, (3) Peripylea, (4) Acanthometrea, (5) Monopylea, (6) Tripylea (p. 133). These are subdivided into 18 families, and their phylogenetic affinities discussed (p. 137). On the ten plates, several new species from Messina are figured, among them the types of several new genera (_Cystidium_, _Coelacantha_, _Echinosphæra_) (compare § 252).

1879. ERNST HAECKEL (L. N. 34) founds the order PHÆODARIA as a "new group of marine siliceous Rhizopods," and distinguishes in it 4 suborders, 10 families and 38 genera.

1880. EMIL STÖHR (L. N. 35) describes the Miocene "Radiolarian fauna of the tripoli from Grotte in Sicily," 118 species, of which 78 are new; among them is the new genus _Ommatodiscus_, the type of a new family, Ommatodiscida. The new species are figured on seven plates.

1880. DANTE PANTANELLI (L. N. 36) describes 30 species of fossil Polycystina from the jaspers of Tuscany, which he regarded as Eocene, but which were probably of Jurassic origin (compare § 243, note B, above).

1881. ERNST HAECKEL (L. N. 37) publishes a "Sketch of a classification of the Radiolaria on the basis of the study of the Challenger Collection," and distinguishes in his "conspectus ordinum" (p. 421) 2 subclasses and 7 orders, and in the "prodromus systematis Radiolarium" (pp. 423-472) 24 families with 630 genera, among which are more than 2000 new species.

1882. BÜTSCHLI (L. N. 40) on the basis of studies of the fossil Monopylea of Barbados, investigates the "mutual relations of the Acanthodesmida, Zygocyrtida and Cyrtida," and gives a critical revision of the genera of these "Cricoidea;" a number of new species are described and figured (Tafs. xxxii., xxxiii.), and some new genera of Stichocyrtida established (_Lithostrobus_, _Lithomitra_, &c.).

1882. DUNIKOWSKI (L. N. 44) describes 18 new fossil Polycystina from the lower lias of the Salzburg Alps, among them the types of 3 new genera (_Ellipsoxiphus_, _Triactinosphæra_, and _Spongocyrtis_).

{clxxxviii}1883. ERNST HAECKEL (L. N. 46) revises the 4 orders and 32 families of Radiolaria, and gives more accurate definitions of them, as well as of the 2 subclasses (I. _Holotrypasta_ = ACANTHARIA and SPUMELLARIA; II. _Merotrypasta_ = NASSELLARIA and PHÆODARIA).

1885. D. RÜST (L. N. 51) describes 234 new species of fossil Radiolaria from the Jura, and illustrates them by twenty plates. Among them are 103 SPUMELLARIA, 130 NASSELLARIA, and 1 PHÆODARIA; these are contained in 35 genera, of which 20 belong to the Porulosa, and 15 to the Osculosa.

254. _Statistical Synopsis of the Twenty Orders_:--

(a) Number of Families. (b) Number of Genera. (c) Number of Species. (d) Previously known Species. (e) New Species. (f) Fossil Species. (g) Pelagic Abundance. (h) Abyssal Abundance. (i) Figured on Plates

+-----+-----+------+-----+------+-----+-----+-----+-------------------+ | | | | | | | | | Figured on | | (a) | (b) | (c) | (d) | (e) | (f) | (g) | (h) | Plates. | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | I. Legion SPUMELLARIA (Porulosa peripylea) | +-----+---------------------------------------------------------------+ | | I. COLLODARIA (Spumellaria palliata) | +-----+-----+---------------------------------------------------------+ | | 1. Colloidea | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | 2 | 6 | 36 | 9 | 27 | 0 | A | E | 1, 3 | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | | 2. Beloidea | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | 2 | 8 | 56 | 9 | 47 | 0 | A | D | 2, 4 | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | | II. SPHÆRELLARIA (Spumellaria loricata) | +-----+-----+---------------------------------------------------------+ | | 3. Sphæroidea | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | 6 | 107 | 660 | 105 | 555 | 66 | A | B | { 5-8 | | | | | | | | | | { 11-30 | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | | 4. Prunoidea | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | 7 | 53 | 280 | 35 | 245 | 36 | B | B | { 16, 17 | | | | | | | | | | { 39, 40 | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | | 5. Discoidea | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | 6 | 91 | 503 | 126 | 376 | 102 | B | A | { 31-38 | | | | | | | | | | { 41-48 | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | | 6. Larcoidea | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | 9 | 51 | 260 | 8 | 252 | 0 | E | B | { 9, 10 | | | | | | | | | | { 49, 50 | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | II. Legion ACANTHARIA (Porulosa actipylea) | +-----+---------------------------------------------------------------+ | | III. ACANTHOMETRA (Acantharia palliata) | +-----+-----+---------------------------------------------------------+ | | 7. Actinelida | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | 3 | 6 | 22 | 6 | 16 | 0 | E | E | 129 (figs. 1-3) | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | | 8. Acanthonida | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | 3 | 21 | 138 | 50 | 88 | 0 | A | C | 130-132 | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | | IV. ACANTHOPHRACTA (Acantharia loricata) | +-----+-----+---------------------------------------------------------+ | | 9. Sphærophracta | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | 3 | 27 | 149 | 9 | 140 | 0 | B | B | 133-138 | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | | 10. Prunophracta | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | 3 | 11 | 63 | 5 | 58 | 0 | D | B | 139, 140 | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | III. Legion NASSELLARIA (Osculosa monopylea) | +-----+---------------------------------------------------------------+ | | V. PLECTELLARIA (Nassellaria palliata) | +-----+-----+---------------------------------------------------------+ | | 11. Nassoidea | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | 1 | 2 | 5 | 1 | 4 | 0 | E | E | 91 (fig. 1) | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | | 12. Plectoidea | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | 2 | 17 | 61 | 5 | 56 | 0 | D | C | 91 (figs. 2-12) | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | | 13. Stephoidea | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | 4 | 40 | 205 | 14 | 191 | 17 | C | B | { 81, 82 | | | | | | | | | | { 92-94 | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | | VI. CYRTELLARIA (Nassellaria loricata) | +-----+-----+---------------------------------------------------------+ | | 14. Spyroidea | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | 4 | 45 | 239 | 51 | 188 | 53 | C | A | 83-90 | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | | 15. Botryodea | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | 3 | 10 | 55 | 15 | 40 | 10 | E | C | 96 | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | | 16. Cyrtoidea | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | 12 | 160 | 1122 | 328 | 794 |250 | C | A | 51-80 | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | IV. Legion PHÆODARIA (Osculosa cannopylea) | +-----+---------------------------------------------------------------+ | | VII. PHÆOCYSTINA (Phæodaria palliata) | +-----+-----+---------------------------------------------------------+ | | 17. Phæocystina | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | 3 | 15 | 112 | 30 | 82 | 24 | C | B | 101-105 | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | | VIII. PHÆOCOSCINA (Phæodaria loricata) | +-----+-----+---------------------------------------------------------+ | | 18. Phæosphæria | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | 4 | 22 | 121 | 5 | 116 | 0 | C | A | 106-112 | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | | 19. Phæogromia | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | 5 | 27 | 159 | 5 | 154 | 0 | C | A | { 99, 100 | | | | | | | | | | { 113-120 | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | | 20. Phæoconchia | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | 3 | 20 | 73 | 4 | 69 | 0 | D | B | 121-128 | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | Total, | +-----+-----+------+-----+------+-----+-----+-----+-------------------+ | 85 | 739 | 4318 | 810 | 3508 | 558 | ... | ... | 140 | +-----+-----+------+-----+------+-----+-----+-----+-------------------+

_Note._--In the tenth and eleventh columns the relative abundance of each order at or near the surface and near the bottom is approximately indicated by the letters A-E, which have the following significance:--A, abundant; B, very numerous; C, many (medium quantity); D, few; E, very few.

{1}SYSTEMATIC PART.

----

CLASS RADIOLARIA.

RADIOLARIA, Johannes Müller, 1858. RHIZOPODA RADIARIA, Johannes Müller, 1858. POLYCYSTINA (_pro parte_), Ehrenberg, 1838. ECHINOCYSTIDA, Claparède, 1858. RHIZOPODA CAPSULARIA, Haeckel, 1861. CYTOPHORA, Haeckel, 1862.

_Definition of the Class:_--#Rhizopoda with unicellular body, divided by a porous membrane into an internal or intracapsular part (with nucleus), and an external or extracapsular part (with calymma); propagating by flagellated spores.#

The RADIOLARIA or CAPSULATE RHIZOPODA, first constituted by Johannes Müller in the year 1858 as a separate group of the Rhizopoda, form a peculiar class of the PROTISTA, or unicellular organisms. This class is exclusively marine, and has in general the characteristic organisation of the Rhizopoda, with the development of numerous _pseudopodia_ from the surface of the cell; but it differs from all other Rhizopoda in the possession of a peculiar _membrane_, dividing the cell-body into two different parts; the _central capsule_ or the internal part with the _nucleus_, and the external part or _extracapsulum_ with the _calymma_; propagation by flagellated spores produced in the central capsule; the sarcode or the _protoplasm_ of both parts communicates by fine _pores_, piercing the separating membrane, which is called the _capsule-membrane_.

The _Central Capsule_ or the inner part of the Radiolarian body is constantly composed of three essential parts, viz.:--

1. _The Central Nucleus_ (a true cell-nucleus).

2. _The Intracapsular Sarcode_ (endosarc) or surrounding internal protoplasm.

3. _The Capsule Membrane_ or enveloping porous membrane.

{2}Besides these constant and essential elements, the central capsule contains very commonly (but not constantly) some other enclosed structures, viz.:--

4. An internal or intracapsular skeleton.

5. Intracapsular vacuoles or alveoli.

6. Fat-granules or oil-globules.

7. Crystals of different composition.

8. Pigment-granules.

_The Extracapsulum_, or the outer part of the Radiolarian body is also constantly composed of three essential elements,--

1. _The Calymma_, or the thick extracapsular _jelly-veil_, completely enveloping the whole central capsule.

2. _The Matrix_, or the maternal tissue of the external protoplasm, enveloping immediately the capsule-membrane as a thin continuous layer of _extracapsular sarcode_ (ectosarc).

3. _The Pseudopodia_, or the very numerous thread-like filaments of protoplasm, which radiate from the matrix; whilst their inner part is enclosed in the calymma, their outer part floats freely in the sea-water.

Besides these three constant and essential elements, the extracapsulum contains very commonly (but not constantly) some other enclosed structures, viz.:--

4. An external or extracapsular skeleton.

5. Extracapsular vacuoles or alveoli.

6. Fat-granules or oil-globules.

7. Pigment-granules or a peculiar large body of dark extracapsular pigment, the "phæodium."

8. "Xanthellæ" or "zooxanthellæ," peculiar yellow cells, which contain starch and are unicellular yellow Algæ, living as "Symbiontes" in true Symbiosis with a great many Radiolaria.

_The Nucleus_ of the Radiolaria is a large true simple cell-nucleus, originally a solid spherical, roundish or longish body of nuclein. It is placed either in the centre of the capsule (in most Peripylea) or excentrically (in most other Radiolaria). Originally solid, the nucleus is commonly differentiated later into an outer dense nuclear-membrane and an inner softer or fluid content; either with one single nucleolus or with a variable number of nucleoli. Originally always simple, the nucleus becomes afterwards constantly divided into numerous small nuclei, each of which, together with a part of the surrounding {3}protoplasm, forms a vibratile-spore or "flagellate-spore." This division in the Acantharia and in the social (or colonial) Peripylea begins very early, in all other Radiolaria much later, immediately before propagation.

_The Endoplasm_ or "endosarc," or "intracapsular protoplasm" or "inner sarcode," in all Radiolaria originally fills that space within the capsule, which is not taken up by the nucleus. It seems to be employed mainly for the purpose of propagation, becoming divided earlier or later into numerous small particles, each of which surrounds a small particle of the nucleus and forms together with it a flagellate-spore. Besides this the endoplasm of the Radiolaria seems to have a great significance for the nutrition, mainly for the interchange of materials. It becomes very often vacuolate or alveolate, filled with smaller or larger spherical drops of fluid; it produces very commonly smaller fat-granules or larger oil-globules, and further pigment-granules of different colours, more rarely crystals and other peculiar enclosed parts.

_The Membrane_ or "capsule-membrane" is the most typical and characteristic part of the body of a Radiolarian, sufficient of itself to separate this class from all other Rhizopoda. At the same time, by its different shape it presents the best means for the systematic distinction of the four subclasses or "legions" of the class. The membrane is composed of a special organic matter (probably nearly related to chitin) and combines density with elasticity to a high degree. Observed with a high power of the microscope its margin (or section) appears commonly simple-edged, but often in larger forms distinctly double-edged.

The legion PHÆODARIA is distinguished by a double membrane (the thinner inner and thicker outer membranes being separated by an interval); in the three other legions it is simple. The membrane completely separates the intracapsular from the extracapsular body, both communicating only by certain pores or openings in the membrane. With reference to this important communication, the whole class can be divided into two subclasses, Holotrypasta and Merotrypasta: the HOLOTRYPASTA contain the Peripylea and Actipylea, in which the membrane is pierced by innumerable very small pores; the MEROTRYPASTA consist of the Monopylea and the Cannopylea, in which the membrane exhibits only one large main opening, distinguished in the former by a peculiar "porous area," in the latter by an "osculum" or a prolonged tubule.

_The Calymma_ or "jelly-veil" is the most characteristic part of the extracapsular body in all Radiolaria; in the majority of the class it is the most voluminous part of the whole body, being much more voluminous than all the other parts taken together. The calymma is a structureless, clear, and transparent jelly-envelope which always includes the whole central capsule and often also the whole extracapsular skeleton. Owing to the high degree of its consistence, this jelly-veil takes a very important part in the formation of the extracapsular skeleton, furnishing the matrix for the deposition of its tangential parts.

{4}_The Matrix_ or the "maternal tissue of the pseudopodia" is formed in all Radiolaria by the thin layer of exoplasm or of extracapsular sarcode, which immediately envelops the central capsule and is itself enclosed by the calymma. This continuous sarcode-cover of the capsule communicates by its pores or openings with the endoplasm or the intracapsular sarcode; whilst from its outer surface arise the pseudopodia. The morphological signification of the matrix is very small, but the physiological importance is very great, for it seems to be the chief organ of many vital functions.

_The Pseudopodia_ or the very fine, long, thread-like filaments of exoplasm arise in all Radiolaria in very great numbers from the surface of the matrix, and exhibit in general the same characteristic shape as in the other Rhizopoda. Their inner or proximal part is enclosed within the jelly-veil or calymma, whilst their outer or distal part floats freely in the sea-water. Their special motions and modifications exhibit considerable variations in different groups, their tendency to ramify, anastomose, and form networks being in some cases very small, in others very great. Also the characteristic motion of granules in the pseudopodia is very different. In general those most important exoplasmatic filaments serve as organs both for the vegetative functions of nutrition, and for the animal functions of motion and sensation.

_The class_ Radiolaria can be divided according to its varying structure into four different legions or subclasses, the characters of which are the following:--

I. PERIPYLEA OR SPUMELLARIA.

Membrane of the central capsule simple, perforated by innumerable very fine pores. Fundamental form originally homaxon or spherical. Skeleton wanting or siliceous. No phæodium in the extracapsular calymma. The Peripylea comprise two orders:--

A. COLLODARIA (without lattice-shell). B. SPHÆRELLARIA (with lattice-shell).

II. ACTIPYLEA OR ACANTHARIA.

Membrane of the central capsule simple, perforated by innumerable fine pores. Fundamental form originally homaxon or spherical. Skeleton acanthinic (not siliceous). No phæodium in the extracapsular calymma. The Actipylea consist of two orders:--

A. ACANTHOMETRA (without complete lattice-shell). B. ACANTHOPHRACTA (with complete lattice-shell).

{5}III. MONOPYLEA OR NASSELLARIA.

Membrane of the central capsule simple, perforated by a porous-area, or by one single large opening, divided into numerous very fine pores. Fundamental form originally monaxon or egg-shaped. Skeleton siliceous. No phæodium in the extracapsular calymma. The Monopylea comprise two orders:--

A. PLECTELLARIA (without complete lattice-shell). B. CYRTELLARIA (with complete lattice-shell).

IV. CANNOPYLEA OR PHÆODARIA.

Membrane of the central capsule double, perforated by one simple main-opening, prolonged into a tubulus, and besides this commonly by one or two (rarely more) small accessory openings. Fundamental form originally monaxon or egg-shaped. Skeleton siliceous. Constantly a peculiar dark pigment-body or "phæodium" in the extracapsular calymma. The Cannopylea comprise two orders:--

A. PHÆOCYSTINA (without lattice-shell). B. PHÆOCOSCINA (with lattice-shell).

_Synopsis of the four Subclasses or Legions of Radiolaria._

{6}LEGION I. #SPUMELLARIA#,

VEL PERIPYLEA, VEL PERIPYLARIA (PLS. 1-50).

_Spumellaria_ (_exclusis_ Spyridinis), Ehrenberg, 1875. _Peripylea_ (_inclusis_ Thalassicollis et Sphærozois), Hertwig, 1879. _Peripylaria_ (_inclusis_ Collodariis et Polycyttariis), Haeckel, 1881.

_Definition._--Radiolaria with simple membrane of the central capsule, which is everywhere perforated by innumerable very fine pores. Extracapsulum without phæodium. Skeleton wanting or siliceous. Fundamental form originally spherical.

The legion SPUMELLARIA vel PERIPYLEA, in the extent here defined, was constituted by me in 1883 in my paper on Die Ordnungen der Radiolarien.[2] I propose to retain for this legion either the name SPUMELLARIA of Ehrenberg (1875) or PERIPYLEA of Hertwig (1879), although both groups have not quite the same extension. We exclude from the SPUMELLARIA the Spyridina (united with them by Ehrenberg) and include the Collodaria. With the Peripylea of Hertwig we unite his Thalassicollea and Sphærozoea. To avoid any confusion it would perhaps be better to name this legion "Peripylaria."

The SPUMELLARIA agree with the ACANTHARIA in the structure of the simple capsule-membrane, which is perforated by numerous small pores (but devoid of the large main opening, which the NASSELLARIA and PHÆODARIA possess), whence we unite both the former as Holotrypasta, both the latter as Merotrypasta.

The difference between the two legions of Holotrypasta is determined by the skeleton, which in the SPUMELLARIA is either siliceous or wanting, whilst in the Acantharia it consists of the peculiar organic substance, acanthin.

The legion SPUMELLARIA is by far the largest and most important of the four legions of Radiolaria, as well with respect to the number of different forms, as to the enormous masses of individuals, which we encounter living and fossil. We distinguish in this legion not less than thirty-two different families, three hundred and sixteen genera, and more than seventeen hundred species.

The classification of this large group requires for its better comprehension a careful division into larger and smaller groups. We divide it therefore first of all into two orders, #Collodaria# and #Sphærellaria#, as proposed in the paper mentioned above.[3]

The #Collodaria# have no perfect latticed skeleton, and comprise two suborders or sections: in the #Colloidea# the skeleton is entirely wanting, in the #Beloidea# it is represented by a variable number of siliceous needles or spicules, scattered in the calymma around the central capsule.

{7}The #Sphærellaria# differ from the #Collodaria# in the possession of a perfect siliceous skeleton, which is originally a latticed spherical shell, enveloping the central capsule. By modification of this fenestrated sphere arises an enormous mass of different forms, which we dispose in twenty-eight families, and these in four larger groups, suborders or sections,--#Sphæroidea#, #Prunoidea#, #Discoidea#, and #Larcoidea#.

The #Sphæroidea#, the common ancestral group of the #Sphærellaria#, possess a skeleton which is either a simple fenestrated sphere, or composed of two or more concentric latticed spheres, which are united by radial beams; more rarely it becomes more or less spongy.

The #Prunoidea# are derived from the #Sphæroidea# by prolongation of the latticed sphere in one axis; the skeleton therefore becomes here ellipsoidal or cylindrical (often with annular transversal constrictions).

The #Discoidea# on the contrary must be derived from the #Sphæroidea# by shortening in one axis; here therefore the fenestrated shell becomes more or less lenticular or iscoidal (often with radial spines or arms in the equatorial plane, on the circular margin).

The #Larcoidea#, the fourth section, differ from the three foregoing sections by the different growth of the shell in three different dimensions of space; therefore here the fenestrated shell becomes "lentelliptical," or a "triaxial ellipsoid," its length, breadth, and height being different.

_The Skeleton_ consists in all SPUMELLARIA either of pure _silica_ or of a peculiar silicate. The siliceous bars and beams constituting it are invariably _solid_, as also in the NASSELLARIA, never hollow, as in the PHÆODARIA. Never is the skeleton composed of acanthin, as in all ACANTHARIA. Whilst in the first order of SPUMELLARIA, #Collodaria#, the form of the spicula, or the scattered needles, composing the skeleton, is very simple, _never latticed_, in the second order, the #Sphærellaria#, it is constantly latticed or fenestrated, often also spongy.

The geometrical fundamental form of the lattice-shell in the #Sphærellaria# is originally spherical (homaxon), as preserved in all #Sphæroidea#; in the #Prunoidea# and #Discoidea# it becomes monaxon, with one single axis (prolonged in the former, shortened in the latter); in the #Larcoidea# it becomes triaxon, by different growth in three principal axes, perpendicular one to another. The further development of radial parts of the skeleton in these three axes is very important for the "promorphology" of the Radiolaria.

_The Malacoma_, or the whole soft body of the SPUMELLARIA as opposed to the skeleton, exhibits some differences of structure in two different groups, which were separated formerly (1862) as Monocyttaria and Polycyttaria, corresponding to the "Radiolaria monozoa and polyzoa" of Johannes Müller (1858).

The #Monocyttaria# (or the Spumellaria solitaria) live isolated as single cells--like {8}all other Radiolaria--and are never aggregated in colonies; the calymma includes one single central capsule, and this again one central nucleus, which does not become divided until full maturity.

The #Polycyttaria# on the contrary (or the Spumellaria socialia) live aggregated in large colonies; the calymma includes a variable number of associated central capsules and each of these commonly one central oil-globule, whilst the original simple nucleus commonly becomes very early divided into numerous small nuclei.

_The Nucleus_ of the SPUMELLARIA is originally constantly _central_, placed quite in the centre of the concentric capsule, and it retains this central position in all Monocyttaria or solitary Peripylea; whereas in the Polycyttaria--in consequence of its early division--its place is commonly taken by a central oil-globule. Whilst the numerous nuclei of the latter are very small, the single nucleus of the former is comparatively large, extremely large (more than a millimeter in diameter) in some gigantic #Collodaria#.

_The Endoplasm_ or the intracapsular sarcode exhibits in the greater number of SPUMELLARIA a more or less distinct radial striation. It encloses a great variety of different parts; vacuoles, oil-globules, pigment-granules, crystals, &c.

_The Membrane_ of the capsule in all SPUMELLARIA is simple (never double as in the _Phæodaria_) and everywhere equally perforated by innumerable small pores; in the thick, double-edged membrane of many large #Collodaria# these pores appear (in the optical section of the capsule-wall) as distinct fine radial canals, very densely and regularly disposed.

_The Central Capsule_ in the SPUMELLARIA is originally a _geometrical sphere_, and this simple globular form is preserved in all #Sphæroidea#, and in the greatest part of #Colloidea# and #Beloidea#. By prolongation of one axis the form becomes _ellipsoidal_ (or even cylindrical) in the #Prunoidea#, and in some few forms of #Colloidea#. By shortening of one axis it becomes _lenticular_ (or even discoidal) in the _Discoidea_, and in some few forms of #Colloidea#. By unequal growth in three different axes, perpendicular one to another, the capsule becomes _lentelliptical_ in all #Larcoidea#. Very rarely the capsule assumes in the SPUMELLARIA a polyhedral or irregular (sometimes even amoeboid) form, only in a few #Colloidea#.

_The Calymma_, or the jelly-veil including the central capsule, is very voluminous in many SPUMELLARIA of gigantic size, mainly in the large #Colloidea#, and in all Polycyttaria or social Radiolaria. It includes here a considerable number of large vacuoles or "alveoli." The calymma never exhibits in this legion the dark voluminous phæodium, possessed by all PHÆODARIA.

_Xanthellæ_ or "zooxanthellæ" are numerous in the calymma of most SPUMELLARIA, but by no means constant; they are very variable in number and size.

_The Matrix_, placed between the calymma and central capsule, is, in the majority of the SPUMELLARIA, a rather thick layer of granular exoplasm.

_The Pseudopodia_ arising from it are very numerous, equally disposed over the whole {9}surface, and are in general rather fluid, exhibiting a considerable tendency to ramify, anastomose, and form networks. The movement of granules is commonly lively. In the Polycyttaria all capsules of one colony or "coenobium" are connected by the dense variable network of anastomosing pseudopodia.

_Synopsis of the Orders and Suborders of_ SPUMELLARIA.

I. COLLODARIA. { Skeleton entirely wanting, 1. #Colloidea.# Skeleton wanting or { quite imperfect, { Skeleton represented by not latticed. { numerous scattered spicules, 2. #Beloidea.#

II. SPHÆRELLARIA. { Lattice-shell spherical or { composed of concentric spheres, 3. #Sphæroidea.# Skeleton a perfect { shell of lattice { Lattice-shell ellipsoidal or work, or spongy and { prolonged in one axis, 4. #Prunoidea.# resembling { wicker-work. { Lattice-shell discoidal or { shortened in one axis, 5. #Discoidea.# { { Lattice-shell lentelliptical, { with different extent of growth { in three axes, 6. #Larcoidea.#

----

Order I. COLLODARIA, Haeckel, 1881.

_Collodaria_, Haeckel, Prodromus, 1881, p. 469. _Collida_ et _Sphærozoida_, Haeckel, 1862, Monogr. d. Radiol., pp. 246, 522.

_Definition._--SPUMELLARIA without latticed shell.

The order #Collodaria#, the first order of Radiolaria, comprises all those SPUMELLARIA in which the skeleton is either entirely wanting, or represented by numerous single, solid, siliceous needles or spicules, loosely scattered in the calymma around the central capsule. Never in this order is there any trace of the latticed or fenestrated shell, which characterises the second order, #Sphærellaria#. The skeleton exhibits no trace of phylogenetic connection in the two orders.

In my monograph (1862) two families appertaining to this order are described, the Collida (p. 244) and the Sphærozoida (p. 521). Both families contain forms with and without a skeleton. Of the solitary or monozous Collida the Thalassicollida are devoid of a skeleton, whilst the Thalassosphærida are provided with a skeleton. Of the social or polyzous Sphærozoida the Collozoida are without a skeleton, the Rhaphidozoida provided with one. As the special form in both skeletophorous subfamilies is exactly the same, I prefer now to associate them in the suborder #Beloidea#, and to oppose them to the other two skeletonless subfamilies, which are united under the name of #Colloidea#.

{10}_Synopsis of the four Families of Collodaria._

Suborder I. { Solitary cells, living COLLOIDEA. { as isolated individuals { (_Colloidea monozoa_), 1. THALASSICOLLIDA. Skeleton entirely { wanting. { Associated cells, living { in colonies or coenobia { (_Colloidea polyzoa_), 2. COLLOZOIDA.

Suborder II. { Solitary cells, living as BELOIDEA. { isolated individuals { (_Beloidea monozoa_), 3. THALASSOSPHÆRIDA. Skeleton composed { of numerous { Associated cells, living in needles or { colonies or coenobia spicula, scattered { (_Beloidea polyzoa_), 4. SPHÆROZOIDA. in the calymma. {

----

Suborder I. COLLOIDEA, Haeckel.

_Definition._--SPUMELLARIA without skeleton.

The suborder #Colloidea# comprises all those SPUMELLARIA in which no skeleton is developed. The whole body is therefore soft--a true malacoma--and is composed only of two essential parts, the central capsule and the enveloping extracapsulum. The suborder contains only two different families, the solitary #Thalassicollida# (or Colloidea monozoa) and the associated #Collozoida# (or Colloidea polyzoa). Both families are very nearly allied, and differ only in one single essential character: the solitary life of the former, the social union of the latter. It seems to be merely in consequence of this difference that the cleavage of the nucleus commonly takes place very late in the former, very early in the latter.

Therefore the full-grown Thalassicollida (till immediately before propagation) commonly exhibit one single nucleus in the centre of the capsule, whilst in the Collozoida the capsule is distended by numerous small nuclei. In these latter the centre of the capsule usually contains one large oil-globule, whilst in the former oil-globules are either wanting, or scattered in large numbers in the endoplasm, or disposed in one layer on the inside of the capsule membrane.

In the solitary Thalassicollida each capsule is enclosed in its own peculiar spherical calymma, whilst in the associated Collozoida all capsules of the colony are united in one common, very voluminous calymma.

Family I. #THALASSICOLLIDA#, Haeckel, 1862.

_Thalassicollida_, Haeckel, 1862, Monogr. d. Radiol., p. 246. _Thalassicollida_, Haeckel, 1881, Prodromus, p. 469.

_Definition._--#Colloidea# solitaria.

The family Thalassicollida comprises all solitary SPUMELLARIA without a skeleton. The oldest and best known form of this family is the genus _Thalassicolla_, as restricted by {11}Johannes Müller.[4] The most common representative of it, the cosmopolitan _Thalassicolla nucleata_, was first described by Huxley in 1851. But as early as 1834 another large Radiolarian, appertaining either to this or to a nearly allied family, had been described by Meyen as _Physematium atlanticum_. A third genus was detected by me in 1859 at Messina and figured under the name _Thalassolampe margarodes_.[5] A very accurate histological description of these forms was given in 1876 by Richard Hertwig.[6] The same author figured in his Organismus in 1879 a very interesting simpler form under the name _Thalassolampe primordialis_ (Taf. iii. fig. 5). Some similar forms had already been observed by me, and are here united with it to form the first genus _Actissa_.[7]

_Actissa_ is of the highest general interest as the most simple and typical form of all Radiolaria, and as the common ancestral form, from which all other forms of this large class may be derived. Its unicellular body exhibits neither the extracapsular alveoli of _Thalassicolla_, nor the intracapsular alveoli of _Thalassolampe_, and shows all essential characters of the Radiolarian type in its most simple form (Pl. 1, figs. 1 to 1_c_). The simple cell-body is composed of a spherical central capsule and a concentric, spherical, enveloping calymma, both separated by a thin membrane which is perforated by innumerable pores. The capsule includes the endoplasm and in the centre a simple spherical nucleus with nucleolus; at the time of propagation this latter becomes cleft into numerous small nuclei, each of which, together with a small piece of the surrounding endoplasm, forms a flagellated zoospore (fig. 1_c_). The extracapsulum is formed by the large, structureless, spherical calymma or concentric jelly-veil enveloping the capsule, and by the thin granular matrix or the layer of exoplasm which separates the calymma from the membrane. From this matrix or maternal tissue arise innumerable very long and thin pseudopodia, as simple radiating filaments, the proximal part of which is included in the calymma, whilst the distal part floats freely in the sea-water (Pl. 1, fig. 1).

The other Thalassicollida differ from their common ancestral form, _Actissa_, mainly by the higher histological differentiation of the unicellular body. Whilst in _Thalassicolla_ and _Thalassolampe_ the nucleus remains a single sphere as in _Actissa_, it becomes branched or covered with radial blind saccules in _Thalassopila_ and _Thalassophysa_; also the intracapsular protoplasm develops here a great variety of peculiar different corpuscles, as oil-globules, pigment-granules, concentric concretions, crystals, &c. But the most striking peculiarity by which the other Thalassicollida differ from _Actissa_ is the development of large vesicular alveoli, either within or without the capsule; the unicellular body reaches by this inflation the extraordinary size of 5 to 10 mm. or more.

{12}_Synopsis of the Genera of Thalassicollida._

A. Alveoli neither { Nucleus spherical within nor without { (sometimes ellipsoidal), the central capsule. { not branched, 1. _Actissa_.

B. Numerous large { Nucleus spherical, 2. _Thalassolampe_. alveoli within the { central capsule (not { Nucleus branched or in the calymma). { covered with radial { sacs, 3. _Thalassopila_.

C. Numerous large { Nucleus spherical, 4. _Thalassicolla_. alveoli without the { central capsule, { Nucleus branched, or within the jelly-veil { covered with radial or calymma. { sacs, 5. _Thalassophysa_.

Genus 1. _Actissa_,[8] n. gen.

_Definition._--#Thalassicollida# with simple spherical nucleus, without any alveoli (either within or outside the central capsule).

The genus _Actissa_ is the most simple and typical form of all Radiolaria, and may be regarded as the common ancestral form of the whole class. The spherical body is composed of a simple spherical capsule and a concentric spherical calymma or jelly-envelope. Neither the former nor the latter contains alveoli. The central capsule possesses a strong membrane perforated by small pores, and contains in the intracapsular sarcode numerous small pellucid vacuoles, and in its middle a simple, concentric, spherical nucleus (often with some nucleoli); sometimes also one or more oil-globules. The extracapsularium forms a soft, voluminous, structureless calymma or enveloping jelly-sphere, perforated by the numberless, fine pseudopodia, which radiate outwards from the matrix or the thin granulated sarcode-layer, surrounding the capsule. Often (but not constantly) xanthellæ or yellow cells are scattered in it. _Actissa_ differs from the following skeletonless genera in the absence of all alveoli; it has neither intracapsular alveoli (like _Thalassolampe_) nor extracapsular alveoli (like _Thalassicolla_). The first observed species of this genus is that which I found in 1866 at the Canary Islands, _Actissa prototypus_; the second is that which Hertwig accurately described in 1879, from the Mediterranean (Messina), _Actissa primordialis_; the third I observed in 1881 at Ceylon, frequent and sporiparous, _Actissa princeps_. A fourth species (_Actissa radiata_) exhibited a distinct radial segmentation of the capsule-contents. These four species are quite spherical. Six other species, occurring in different preparations from the Challenger, are distinguished by modifications of the spherical capsule-form and may represent three different subgenera (or, perhaps better, genera?)--_Actiprunum_ ellipsoidal, _Actidiscus_ lenticular, _Actilarcus_ lentelliptical; perhaps these are the ancestral forms of the three sections: #Prunoidea#, #Discoidea#, #Larcoidea#.

{13}Subgenus 1. _Procyttarium_, Haeckel, 1879.

_Procyttarium_, Haeckel, Natürl. Schöpfungsgeschichte, ed. vii. p. 705.

_Definition._--Central capsule spherical.

1. _Actissa princeps_, n. sp. (Pl. 1, fig. 1).

Central capsule spherical, colourless or a little reddish, transparent, with a thick double-edged membrane. Nucleus central, spherical, one-third as broad as the central capsule, containing a single, central, glossy nucleolus. Protoplasm finely granulated, without oil-globules, with numerous clear spherical vacuoles of equal size and at equal distances; the superficial layer of protoplasm (immediately below the membrane) radially striated (fig. 1). In some older specimens the nucleus was divided into numerous small nuclei (fig. 1_a_), which by further division gave the nuclei of the flagellated spores (fig. 1_b_); each spore with a very thin lateral flagellum (fig. 1_c_). Jelly-like calymma twice as broad as the enclosed capsule, without xanthellæ or yellow cells, pierced by innumerable, very thin and long, undivided pseudopodia, which arise from the sarcode-matrix on the outside of the membrane (six to eight times longer than shown in fig. 1).

_Dimensions._--Diameter of the central capsule 0.1 to 0.12, of the nucleus 0.03 to 0.04, of the jelly calymma 0.2 to 0.3.

_Habitat._--Indian Ocean, Ceylon, Belligemma, Haeckel, 1881; also in a preparation from Station 271, Central Pacific, surface.

2. _Actissa primordialis_, Haeckel.

_Thalassolampe primordialis_, R. Hertwig, 1879, Organismus der Radiolarien, p. 32, Taf. iii. fig. 5.

_Procyttarium primordiale_, Haeckel, 1879, Natürl. Schöpf., ed. vii. p. 705, Taf. xvi. fig. 1.

Central capsule spherical, dim-yellowish, with a thin, simple-edged but compact membrane. Nucleus large, central (about half as broad), with one or two dark nucleoli; on its side an excentric oil-globule, nearly of the same size. Protoplasm between nucleus and membrane, in the younger specimens finely granulated and radially striped; in the older specimens with numerous hyaline globules (vacuoles). Jelly-envelope or calymma very voluminous, ten to twelve times as broad as the central capsule, structureless, containing numerous yellow bodies (xanthellæ?), pierced by very numerous simple pseudopodia.

_Dimensions._--Diameter of the central capsule 0.11 to 0.18, of the nucleus 0.04 to 0.09, of the jelly-like calymma 1.2 to 1.5.

_Habitat._--Mediterranean, Messina, Hertwig, 1878, surface.

3. _Actissa prototypus_, n. sp.

Central capsule spherical, red-coloured, with a thick, double-edged membrane. Nucleus central, spherical, half as large as the radius of the capsule, containing a large number (forty to sixty) of small {14}dark nucleoli. Protoplasm filled up with numerous small clear vacuoles, and between them fine red pigment granules; on the inside of the membrane one layer of dark oil-globules. Jelly-like calymma four times as broad as the enclosed capsule, with very numerous small xanthellæ.

_Dimensions._--Diameter of the capsule 0.2, of the nucleus 0.05, of the calymma 0.8.

_Habitat._--Atlantic, Canary Islands (Lanzerote, Haeckel), 1866; also at Station 348, surface.

4. _Actissa radiata_, n. sp.

Central capsule spherical, dark, with a thick, double-edged membrane. Nucleus central, spherical, half as large as the capsule, transparent. Protoplasm divided into numerous cuneiform radial pieces which are separated by clear intervals, and filled with very fine dark granules (darker in the distal half). The equatorial optical section exhibits around the circular clear nucleus a coronal of twenty-five such wedge-shaped pieces (mother-cells of spores?) No oil-globules in the central capsule. Jelly-like calymma one and a half times as broad as the enclosed capsule, with numerous small xanthellæ.

_Dimensions._--Diameter of the capsule 0.15, of the nucleus 0.07, of the calymma 0.24.

_Habitat._--North Pacific, Station 241, surface.

Subgenus 2. _Actiprunum_, Haeckel, 1882.

_Definition._--Central capsule ellipsoidal, with one prolonged axis.

5. _Actissa prunoides_, n. sp.

_Actiprunum prunoideum_, Haeckel, 1882, Manuscript.

Central capsule ellipsoidal, colourless, with a thin, simple-edged membrane. Proportion of its major axis to the minor 4 : 3. Nucleus spherical, its diameter equal to one-third of the minor axis, in its centre a large, dark, spherical nucleolus. Protoplasm clear, containing numerous small vacuoles, separated by regular distances, and on the inside of the capsule-membrane, numerous (forty to fifty) small oil-globules. Calymma (or jelly-veil) ellipsoidal, with a thin sarcode-stratum on the outside of the capsule; its diameter twice as large as that of the central capsule.

_Dimensions._--Major axis of the capsule 0.16, minor 0.12; diameter of the nucleus 0.04; major axis of the calymma 0.32, minor 0.24.

_Habitat._--Central Pacific, Station 274, surface.

6. _Actissa ellipsoides_, n. sp.

_Actiprunum ellipsoides_, Haeckel, 1882, Manuscript.

Central capsule ellipsoidal, red-coloured, with a thick, double-edged membrane. Proportion of its major axis to the minor 5 : 3. Nucleus ellipsoidal, one-third as large as the capsule, containing eight small dark nucleoli. Protoplasm dusky, filled with dark pink pigment-granules; in the {15}major axis, on both poles of the nucleus-axis, two large oil-globules, half as large as the nucleus. Calymma ellipsoidal, with numerous xanthellæ; its diameter four times as large as that of the capsule.

_Dimensions._--Major axis of the capsule 0.2, minor 0.12; major axis of the nucleus 0.07, minor 0.04; major axis of the calymma 0.8, minor 0.5.

_Habitat._--Mediterranean, Corfu, 1877, Haeckel, surface.

Subgenus 3. _Actidiscus_, Haeckel, 1882.

_Definition._--Central capsule lenticular, with one shortened axis.

7. _Actissa discoides_, n. sp.

_Actidiscus discoides_, Haeckel, 1882, Manuscript.

Central capsule lenticular, red-coloured, about twice as broad as high, with a thick, double-edged membrane. Nucleus spherical, one-third as broad as the capsule, with one single, large central nucleolus. Protoplasm dusky, filled with scarlet pigment; granules and small oil-globules between them. Calymma lenticular, three times as broad as the capsule.

_Dimensions._--Major axis of the capsule 0.16, minor 0.08; diameter of the nucleus 0.05; breadth of the calymma 0.5.

_Habitat._--North Pacific, Station 236, surface.

8. _Actissa lenticularis_, n. sp.

Central capsule lenticular, flattened, about three times as broad as high, with a thin, simple-edged membrane. Nucleus lenticular, one-third as large as the capsule, with ten small dark nucleoli. Protoplasm transparent, colourless, filled with small vacuoles at regular distances; on the inside of the membrane in the circular periphery of the lens twenty dark oil-globules. Calymma lenticular, twice as broad as the capsule.

_Dimensions._--Major axis of the capsule 0.15, minor 0.05; breadth of the nucleus 0.05, height 0.02; breadth of the calymma 0.03.

_Habitat._--East Pacific, Station 272, surface.

9. _Actissa phacoides_, n. sp.

_Actidiscus phacoides_, Haeckel, 1882, Manuscript.

Central capsule lenticular, strongly flattened, about four times as broad as high, with a thin, simple-edged membrane. Nucleus lenticular, one-fourth as broad as the capsule, with numerous (twenty or more) small nucleoli. Protoplasm filled with dark pigment-granules; on the inside of the membrane in the circular periphery of the lens thirty-two dark oil-globules. Calymma lenticular, three times as broad as the capsule.

{16}_Dimensions._--Major axis of the capsule 0.2, minor 0.05; breadth of the nucleus 0.05, height 0.015; breadth of the calymma 0.6.

_Habitat._--Tropical Atlantic, Station 347, surface.

Subgenus 4. _Actilarcus_, Haeckel.

_Definition._--Central capsule lentelliptical, with three different axes.

10. _Actissa larcoides_, n. sp.

Central capsule lentelliptical; with three different axes, bearing the proportion 4 : 3 : 2. Nucleus spherical; its diameter equal to the shortest radius of the capsule. No nucleoli visible. Protoplasm transparent, with small vacuoles; on the inside of the thin capsule-membrane numerous (fifty to sixty) small oil-globules, regularly disposed. Calymma lentelliptical, twice as large as the central capsule.

_Dimensions._--Major axis or length of the capsule 0.2, middle axis or breadth 0.15, minor axis or height 0.1; diameter of the nucleus 0.05, of the calymma 0.3-0.4.

_Habitat._--Central Pacific, Station 266, surface.

Genus 2. _Thalassolampe_,[9] Haeckel, 1862, Monogr. d. Radiol., p. 253.

_Definition._--#Thalassicollida# without extracapsular alveoles, but with large roundish or globular alveoles within the central capsule, with a simple spherical, not branched nucleus in the centre.

The genus _Thalassolampe_ is, next to _Actissa_, the most simple of all Radiolaria, but differs from it by the large intracapsular alveoles. By these the central capsule is inflated to an extraordinary size, which in _Thalassolampe maxima_ exceeds that of most other Radiolaria. From the nearly allied _Thalassopila_ it differs by the simple spherical nucleus, from _Physematium_ by the absence of spicula. Of the two species of the genus the first observed _Thalassolampe margarodes_, 1862, is Mediterranean, the second, _Thalassolampe maxima_, 1882, is Indian.

1. _Thalassolampe margarodes_, Haeckel.

_Thalassolampe margarodes_, Haeckel, 1862, Monogr. d. Radiol., p. 253, Taf. ii. figs. 4, 5.

_Thalassolampe margarodes_, R. Hertwig, 1876, Histologie d. Radiol., p. 68, Taf. iii. figs. 1-5.

Spherical body very soft and limpid, somewhat pearl-like opalescent, yellowish or bluish. Central capsule with a very thin structureless membrane, its diameter six to eight times as large as that of the central spherical nucleus. Wall of the vesicular nucleus thick, perforated by fine {17}pore-canals; on its inside often numerous oval nucleoli. In the movable protoplasmic network between the large alveoles a considerable number of large yellowish or orange oil-globules. Extracapsular jelly-envelope very thin, contains small yellow bodies (zooxanthellæ). (Compare the accurate description of this Mediterranean species in my monograph and in Hertwig's work.) In the Canary Islands I found very often a large variety of it, of double and triple the size, distinguished by the delicate orange colour of the intracapsular oil-globules. This may be distinguished as _Thalassolampe aurantiaca_.

_Dimensions._--Diameter of the whole jelly-sphere 2 to 4 mm., of the central capsule 2 to 3 mm., of its nucleus 0.2 to 0.4 mm.

_Habitat._--Mediterranean, Messina, Haeckel, Hertwig; Canary Islands, Lanzerote, Haeckel; surface.

2. _Thalassolampe maxima_, n. sp. (Pl. 1, fig. 2).

Spherical body quite pellucid, like a glass globule, colourless. Central capsule with a moderately thick, but quite transparent, structureless membrane, its diameter ten to twelve times as large as that of the central spherical nucleus. Wall of the vesicular nucleus thick, perforated by fine pore-canals; on its inside numerous small spherical nucleoli. No large oil-globules in the movable protoplasmic network between the large alveoles. Extracapsular jelly-envelope very thin, containing no yellow bodies. This differs from the preceding nearly allied species in the want of the intracapsular oil-globules and of the extracapsular yellow bodies. It possesses the largest central capsule of all known Radiolaria. I found them living and floating in water taken from the surface of the Indian Ocean by a bucket.

_Dimensions._--Diameter of the whole jelly-body 12 to 15 mm., of the central capsule 10 to 12 mm., of the nucleus 0.8 to 1.2 mm.

_Habitat._--Indian Ocean, near the Maldive Islands, Haeckel, 1882, surface.

Genus 3. _Thalassopila_,[10] Haeckel, 1881, Prodromus, p. 469.

_Definition._--Thalassicollida without extracapsular alveoles, but with large roundish or globular alveoles within the central capsule, with a papillate or branched nucleus in its centre.

The genus _Thalassopila_ has, like _Thalassolampe_, a voluminous foamy central capsule, inflated by numerous large alveoles; but it differs in the complicated form of the nucleus, which is like that of _Thalassophysa_, and is either branched or occupied by conical or roundish papillæ.

1. _Thalassopila cladococcus_, n. sp. (Pl. 1, fig. 3).

Spherical body dark-spotted, with a thin yellowish jelly-envelope. Central capsule with a thick and firm membrane, perforated by pores; its diameter three times that of the central nucleus, {18}three-fourths that of the whole jelly-sphere. Nucleus profusely branched or papillated, its spherical surface covered with numerous (more than a hundred) finger-shaped obtuse blind sacs, about as long as its radius. Protoplasm of the central capsule forming a loose network between the large roundish alveoles, in the cortical zone radially striped and containing one layer of large dark oil-globules. These are regularly distributed on the inside of the capsule-membrane and separated by intervals, twice as broad as its diameter, giving to the capsule-surface a spotted appearance. Extracapsular jelly-envelope thin, yellowish, with very numerous and small xanthellæ.

_Dimensions._--Diameter of the whole jelly-sphere 5 mm., of the central capsule 4 mm., of the nucleus 1.3 mm.

_Habitat._--Antarctic Ocean, Station 154 (south of Kerguelen), surface.

Genus 4. _Thalassicolla_,[11] Huxley, 1851, Ann. and Mag. Nat. Hist., ser. 2, vol. viii. p. 433.

_Definition._--Thalassicollida without intracapsular alveoles, but with large roundish or globular alveoles within the extracapsular calymma. Nucleus in the centre of the capsule simple spherical, not branched.

The genus _Thalassicolla_ was proposed by Huxley in 1851, for a certain number of different voluminous jelly-like Radiolaria, which he had observed living during his voyage in the "Rattlesnake" through the tropical seas, and of which he gives an excellent description--the first accurate observations on living Radiolaria. Johannes Müller afterwards removed from this genus the social genera _Sphærozoum_ and _Collosphæra_ (formerly _Thalassicolla punctata_), and retained as type of the genus _Thalassicolla nucleata_. In 1862 in my Monograph I added two other species, _Thalassicolla pelagica_ and _Thalassicolla zanclea_, and later (1870) _Thalassicolla sanguinolenta_. Now I think it better to separate the last two species as a new genus, _Thalassophysa_, characterised by the papillate or branched nucleus, and to retain in _Thalassicolla_ only those forms with simple spherical nucleus. For both genera the extracapsular, voluminous, spherical calymma or jelly-envelope, with numerous large alveoles, is characteristic. The membrane of the central capsule in _Thalassicolla_ is now structureless (subgenus _Thalassicollarium_, with three species), now characterised by a peculiar structure, prominent ridges on the inside of the membrane, which form a network with polygonal plates, resembling an epithelium (Pl. 1, fig. 5_b_; subgenus _Thalassicollidium_, with four species). Of the seven species here described, two are cosmopolitan, widely distributed, and common; one is Mediterranean, one Atlantic, and three Pacific.

Subgenus 1. _Thalassicollarium_, Haeckel.

_Definition._--Membrane of the central capsule structureless, only perforated by innumerable very small radial pores.

{19}1. _Thalassicolla pellucida_, n. sp.

Spherical body very soft, transparent, clear and colourless, without any pigment. Central capsule soft, hyaline, with a thin, structureless, not areolated membrane. Diameter of the central capsule about three times that of the nucleus, one-fourth to one-sixth that of the jelly-envelope. Nucleus delicate, transparent, with one single central nucleolus, about one-third its diameter. Protoplasm of the central capsule contains only small, pellucid, densely packed globules (vacuoles?), no oil-globules. Extracapsular body quite transparent, without pigment or oil-globules, only composed of the large alveoles imbedded in the jelly-cover, and of the fine protoplasmic network between them. No xanthellæ.

_Dimensions._--Diameter of the central capsule 0.8 to 1.2, of the nucleus 0.3 to 0.4, of the calymma 3 to 6 mm.

_Habitat._--Cosmopolitan, Canary Islands, Haeckel; Cape, Australia, Pacific, Challenger; surface.

2. _Thalassicolla spumida_, n. sp.

Spherical body nearly transparent, yellowish, without dark pigment. Central capsule pellucid, with a thick, structureless, not areolated membrane. Diameter of the central capsule about twice that of the nucleus, one-sixth to one-eighth that of the jelly-cover. Nucleus delicate, somewhat opaque, with numerous small nucleoli. Protoplasm of the central capsule contains small pellucid globules (vacuoles?), and immediately under its membrane (on its inside) one single layer of large, dark, refractive oil-globules. Extracapsular body very voluminous, foamy, with innumerable alveoles in the jelly, and many xanthellæ between them.

_Dimensions._--Diameter of the central capsule 0.6 to 0.8, of the nucleus 0.3 to 0.4, of the calymma 3 to 5 mm.

_Habitat._--Atlantic, Canary Islands, Haeckel; Cape Verde Islands, Challenger Station 350; Brazil, Rabbe; surface.

3. _Thalassicolla zanclea_, Haeckel.

_Thalassicolla zanclea_, Haeckel, 1862, Monogr. d. Radiol., p. 252, Taf. ii. fig. 3.

Spherical body opaque, transparent only in the periphery, with colourless central capsule, but with brown or black pigment-powder scattered everywhere through the extracapsular alveolated jelly-cover. Central capsule soft, transparent, colourless, with a thin structureless, not areolated membrane. Diameter of the central capsule about one and a half times that of the nucleus, one-half or one-third that of the jelly-cover. Nucleus delicate, transparent, with a thin, finely punctated membrane, with one or more nucleoli. Protoplasm of the central capsule contains only small, pellucid, densely packed globules (vacuoles?), no oil-globules. Extracapsular body very dark and opaque, with a great mass of brown or blackish-brown pigment between the alveoles of the jelly-cover. Numerous xanthellæ.

_Dimensions._--Diameter of the central capsule 0.1 to 0.12, of the nucleus 0.07 to 0.08, of the calymma 0.2 to 0.4.

_Habitat._--Mediterranean, Messina, Haeckel.

{20}Subgenus 2. _Thalassicollidium_, Haeckel.

_Definition._--Membrane of the central capsule areolated, with small polygonal plates, resembling an epithelial cell-tissue, spotted by innumerable fine radial pores.

4. _Thalassicolla australis_, n. sp.

Spherical body nearly transparent, without dark pigment. Central capsule colourless, somewhat opaque, with a thick and firm, very elastic membrane, areolated by polygonal, punctated figures resembling cells. Diameter of the central capsule about three times that of the nucleus, one-third that of the jelly-cover. Nucleus thin-walled, with many small nucleoli. Protoplasm of the central capsule finely granulated, containing numerous hyaline globules (vacuoles?) of different size, and in each of these one single roundish, dark refringing corpuscle, concentrically lamellated like an amylum grain. Extracapsular body without pigment or oil-globules, only composed of the large alveoles imbedded in the jelly-cover, and of the fine protoplasmic network between them. No xanthellæ.

_Dimensions._--Diameter of the central capsule 1 to 2, of its nucleus 0.3 to 0.4, of the nucleoli 0.12 to 0.16, of the hyaline globules in the protoplasm of the capsule 0.02 to 0.05; calymma, 4 to 6 mm.

_Habitat._--South-west Pacific, east coast of Australia, New Zealand, &c.; Challenger Stations 163, 171; surface.

5. _Thalassicolla nucleata_, Huxley.

_Thalassicolla nucleata_, Huxley, 1851, Ann. and Mag. Nat. Hist., ser. 2, vol. viii. p. 435, pl. xvi. fig. 4.

_Thalassicolla nucleata_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 28.

_Thalassicolla coerulea_, Schneider, 1858, Archiv f. Anat. u. Physiol., p. 40, Taf. iii. Bd. i. figs. 5-7.

_Thalassicolla nucleata_, Haeckel, 1862, Monogr. d. Radiol., p. 249, Taf. iii. figs. 1-5.

_Thalassicolla nucleata_, R. Hertwig, 1876, Histologie d. Radiol., p. 43, Taf. iii. figs. 61-5, Taf. iv., v.

_Thalassicolla nucleata_, R. Hertwig, 1879, Organismus d. Radiol., p. 34.

Spherical body in the central part opaque, black or dark coloured, in the periphery transparent, whitish, or yellowish. Central capsule rather compact, yellowish, opaque, with a thick and firm, very elastic membrane, areolated by polygonal, punctated figures resembling cells. Diameter of the central capsule about twice as large as that of the nucleus, one-half to one-fourth that of the jelly-cover. Nucleus with a very thick, finely punctated membrane, containing a viscous fluid (when coagulated finely granular), and sometimes one large, central, spherical, or ramified nucleolus, sometimes a variable number of smaller roundish nucleoli. Protoplasm of the central capsule containing many very variable corpuscles, mostly pellucid (albuminous?) spherules, containing oil-globules, or concentric amyloid concretions, or crystals, &c. Extracapsular body with dark pigment-powder of variable colour (black, brown, violet, blue, &c.), densely aggregated around the central capsule, more loosely dissipated between the alveoles of the outer jelly-cover. Xanthellæ very numerous.

{21}_Dimensions._--Diameter of the central capsule 0.4 to 0.8, of the nucleus 0.02 to 0.05, of the calymma 1 to 5 mm.

_Habitat._--Cosmopolitan; common in all warmer seas; Mediterranean, Atlantic, Indian Ocean, Pacific, mainly between lat. 40° N. and lat. 40° S.; surface.

6. _Thalassicolla maculata_, n. sp. (Pl. 1, fig. 4).

Spherical body in the central part opaque, black or dark coloured, in the periphery semi-transparent, spotted. Central capsule compact, yellowish, opaque, with a thick and firm, very elastic membrane, areolated by polygonal, punctated figures resembling cells. Diameter of the central capsule about twice that of the nucleus, one-third to one-fifth that of the jelly-cover. Nucleus thin-walled, with one large spherical nucleolus. Protoplasm of the central capsule contains innumerable very small, hyaline, spherical vesicles of equal size (or vacuoles?), two to four times as broad as the separating bridges of protoplasm. Extracapsular body with dark pigment-powder of black or brown colour, densely accumulated around the central capsule (in the matrix), loosely scattered between the alveoles of the outer jelly-cover. The latter appears spotted by numerous large, roundish lumps of protoplasm, scattered between the alveoles. No xanthellæ.

_Dimensions._--Diameter of the central capsule 0.3 to 0.6, of the nucleus 0.2 to 0.3, of the hyaline globules in the protoplasm of the capsule 0.02 to 0.03; calymma, 2 to 3 mm.

_Habitat._--South Pacific, Challenger Station 289.

7. _Thalassicolla melacapsa_, n. sp. (Pl. 1, fig. 5).

Spherical body in the central part opaque, black or dark coloured, in the periphery semi-transparent, spotted. Central capsule compact, black, with a thick and firm, very elastic membrane, areolated by polygonal, punctated figures resembling cells. Diameter of the central capsule about twice that of the nucleus, one-third or half that of the jelly-cover. Nucleus thin-walled, transparent, containing very numerous and small nucleoli. Protoplasm of the central capsule filled with small black pigment-granules, quite intransparent, contains densely packed hyaline (albuminous?) globules of equal size; every pellucid globule includes a smaller globule (one-third or one-fourth its diameter), which appears to be composed of aggregated oil-bubbles. Extracapsular body without pigment, contains between its alveoles in the inner half numerous, dark refractive oil-globules, in the outer half numerous amoeboid lumps of protoplasm, irregularly scattered. No xanthellæ.

_Dimensions._--Diameter of the central capsule 2 to 2.5, of the nucleus 1 to 1.5, of the hyaline globules in the protoplasm of the capsule 0.03 to 0.04; calymma, 3 to 5 mm.

_Habitat._--South-east Pacific (near Valparaiso), Challenger Station 300, surface.

Genus 5. _Thalassophysa_,[12] Haeckel, 1881, Prodromus, p. 470.

{22}The genus _Thalassophysa_ contains those species of Thalassicollida formerly associated with _Thalassicolla_, which are distinguished by the complicated, ramose, or papillate form of the large nucleus. All three species here described are found in the Mediterranean and the Atlantic. To this genus appertains also that strange form of Radiolaria which I described in 1870 as _Myxobrachia_ (compare _Thalassophysa sanguinolenta_).

1. _Thalassophysa papillosa_, n. sp.

_Thalassicolla papillosa_, Haeckel, 1867, Manuscript.

Spherical body transparent, colourless, or somewhat yellowish. Central capsule soft, colourless, with a very thin but firm, elastic, structureless membrane. Diameter of the central capsule about twice that of the nucleus, one-fourth to one-sixth that of the jelly-envelope. Nucleus papillated, its spherical surface covered with a great number (50 to 80) of conical or finger-like protuberances or blind sacs, not longer than half its radius. Protoplasm of the central capsule filled with very small and numerous spherical vacuoles, without oil-globules. Extracapsular jelly-body, without dark pigment, oil-globules, and large protoplasmic lumps, contains between its alveoles very numerous xanthellæ.

_Dimensions._--Diameter of the whole jelly sphere 4 to 5 mm., of the central capsule 0.8 to 1 mm., of its nucleus 0.4 to 0.5.

_Habitat._--Canary Islands, Lanzerote, common, Haeckel; Cape Verde Islands, Challenger; surface.

2. _Thalassophysa sanguinolenta_, Haeckel.

_Thalassicolla sanguinolenta_, Haeckel, 1870, Jenaische Zeitschr., Bd. v. p. 526, Taf. 18.

_Thalassicolla sanguinolenta_, Haeckel, 1870, Biolog. Studien, i. p. 113, Taf. iv.

_Thalassicolla sanguinolenta_, R. Hertwig, 1879, Organismus d. Radiol., p. 37, Taf. iii. fig. 1.

_Myxobrachia rhopalum_, Haeckel, 1870, Jenaische Zeitschr., Bd. v. p. 519, Taf. 18 (et in Biol. Stud., _loc. cit._).

_Myxobrachia pluteus_, Haeckel, 1870, Jenaische Zeitschr., Bd. v. p. 520, Taf. 18 (et in Biol. Stud., _loc. cit._).

Spherical body in the central part opaque, reddish, in the periphery transparent, yellowish. Central capsule compact, white, red spotted, with a thick elastic membrane, perforated by pores, but not areolated. Diameter of the central capsule three times that of the nucleus, one-fifth to one-eighth that of the jelly-envelope. Nucleus papillated, its spherical surface covered with numerous (80 to 120) conical or finger-like protuberances not longer than one-fourth or one-third of its radius. On the inside of these blind sacs lie numerous small roundish nucleoli. Protoplasm of the central capsule in the outer (cortical) zone (on the inside of the membrane) radially striped, with one layer of very numerous red oil-globules of equal size, producing its blood-spotted appearance; in the inner (medullary) zone foamy, with numerous small spherical vacuoles. Extracapsular jelly-body without dark pigment, contains between its alveoles no large protoplasmic lumps (as in _Thalassophysa pelagica_), but numerous small oil-globules and xanthellæ. This species sometimes amasses in its jelly-envelope large accumulations of Coccoliths and Coccospheres, {23}which are much heavier than the jelly-body, and produce arm-like protuberances of it; this modified form, often of very regular and peculiar appearance, I formerly described as _Myxobrachia_ (compare my Biolog. Studien, _loc. cit._, and Hertwig, _loc. cit._, p. 37). Compare also _Myxobrachia cienkowski_, Wagner, 1872, L. N. 23.

_Dimensions._--Diameter of the whole jelly-sphere 5 to 8 mm., of the central capsule 1 to 1.2 mm., of its nucleus 0.3 to 0.4.

_Habitat._--Canary Islands, Lanzerote; common, Haeckel; Mediterranean, Messina, Hertwig; surface.

3. _Thalassophysa pelagica_, Haeckel.

_Thalassicolla pelagica_, Haeckel, 1862, Monogr. d. Radiol., p. 247, Taf. i.

_Thalassicolla pelagica_, R. Hertwig, 1879, Organismus d. Radiol., p. 35, Taf. iii. fig. 4.

Spherical body in the central part opaque, yellowish, in the periphery semi-transparent, spotted. Central capsule compact, yellowish-white, with a thick and compact membrane, perforated by pores, but not areolated. Diameter of the central capsule about twice that of the nucleus, one-half to one-sixth that of the jelly-envelope. Nucleus papillated, its spherical surface covered with numerous (20 to 60) conical, roundish, or finger-like protuberances, not longer than its radius (commonly only one-half or one-third as long). Enclosed in the semi-fluid substance of the nucleus are very long and thin cylindrical nucleoli snake-like, contorted, and penetrating into the protuberances of the nucleus. Protoplasm of the central capsule in the outer (cortical) zone (on the inside of the membrane) radially striped, with one layer of large oil-globules of different sizes; in the inner (medullary) zone foamy, with numerous small spherical vacuoles, mostly of equal size. Extracapsular jelly-body without dark pigment, contains between its alveoles a large number of large roundish or amoeboid lumps of protoplasm, and very numerous yellow cells or xanthellæ (compare the detailed description in my Monograph, and in R. Hertwig's work).

_Dimensions._--Diameter of the whole jelly-sphere 1 to 4 mm., of the central capsule 0.5 to 0.6, of the nucleus 0.2 to 0.3.

_Habitat._--Mediterranean--Messina, Corfu, Nizza, Genoa, Haeckel; Messina, R. Hertwig; surface.

Family II. #COLLOZOIDA#, Haeckel, 1862 (Pl. 3).

_Collozoida_, Haeckel, 1862, Monogr. d. Radiol., p. 522.

_Definition._--#Colloidea# socialia.

The family Collozoida comprises all associated or colony-building Radiolaria without skeleton. We unite here all these skeletonless Radiolarian colonies into one single genus _Collozoum_, constituted (1862) in my Monograph (p. 522). The oldest known form of it was the _Collozoum inerme_, described firstly by Johannes Müller (1856) as _Sphærozoum inerme_. Two other species of the genus were figured (1862) in my Monograph (p. 522, Tafn. xxxii., xxxv.). A most accurate description of its histological structure and {24}development was given in 1876 by Richard Hertwig in his Histologie der Radiolarien (pp. 12-42, Tafn. i., ii.). A number of other very remarkable forms of _Collozoum_ have been observed by me during the last few years, and partly figured in Pl. 3.

_Collozoum_, as the only representative of this family, is sufficiently distinguished from all other Radiolaria by the definition "_Skeletonless Radiolarian Colonies._" These occur floating on the surface of all warmer seas, often in astonishing masses, and may be easily confounded, owing to their external resemblance, with the jelly-like egg-masses of certain Mollusca. _Collozoum_ is derived either from _Actissa_ or from _Thalassicolla_, simply by multiplication of the unicellular body and by reunion of the associated capsules in one common calymma or jelly-veil; this is constantly alveolated, as in _Thalassicolla_. As in _Actissa_, the form of the central capsule remains either spherical, or it becomes ellipsoidal or discoidal, rarely polyhedral or amoeboid. In _Collozoum_ as in all colonial Radiolaria, the original central nucleus commonly undergoes cleavage very early into numerous small nuclei, whilst its place is usually taken by a central oil-globule. This peculiarity may serve often (but not constantly) for the distinction of isolated capsules of _Collozoum_ from _Actissa_.

Genus 6. _Collozoum_,[13] Haeckel, 1862, Monogr. d. Radiol., p. 522.

_Definition._--Skeletonless colonies of Radiolaria.

The genus _Collozoum_, as already mentioned, is the only representative of its family, and comprises all Radiolaria living associated in colonies, and having no skeleton. Therefore _Collozoum_ possesses all the peculiarities described above. Although the floating colonies of this genus occur in enormous masses on the surface of all warmer seas, nevertheless the number of different species in this genus is not great, and amounts only to thirteen. If this number increase by further investigations, the subgenera distinguished in the following description can be advanced to the range of genera; in which case _Collodinium_ (or _Collozoum_ sensu restricto) will be characterised by the spherical form of its central capsules, _Colloprunum_ by the ellipsoidal form (Pl. 3, fig. 9), _Collophidium_ by the cylindrical, very prolonged form (figs. 2, 3), _Collodiscus_ by the lenticular or discoidal form, and _Collodastrum_ by the indefinite, polyhedral, or amoeboid form (figs. 4, 5).

Subgenus 1. _Collodinium_, Haeckel.

_Definition._--Form of the central capsules spherical or subspherical, never polyhedral, ellipsoidal, or cylindrical.

{25}1. _Collozoum inerme_, Haeckel (Pl. 3, figs. 10-12).

_Collozoum inerme_, Haeckel, 1862, Monogr. d. Radiol., p. 522, Taf. xxxv.

_Collozoum inerme_, Cienkowski, 1871, Archiv. f. mikrosk. Anat., vol. vii. p. 376, Taf. xxix. figs. 18-36.

_Collozoum inerme_, R. Hertwig, 1876, Histologie der Radiol., p. 12, Taf. i., ii.

_Collozoum inerme_, R. Hertwig, 1879, Organismus d. Radiol., p. 31, Taf. iii. fig. 12.

_Sphærozoum inerme_, J. Müller, 1856, Monatsber. d. k. Akad. d. Wiss. Berlin, p. 478; Abhandl., p. 54.

_Sphærozoum bicellulare_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 54, Taf. viii. fig. 5.

_Thalassicolla punctata_, Huxley (_pro parte_), 1851, Ann. and Mag. Nat. Hist., ser. 2, vol. viii. p. 433.

Central capsules spherical, with thin, simple-edged membrane, with one single oil-globule in the centre. (If the capsules multiply by division, the spherical form becomes violin-shaped, constricted in the middle; and in this condition the number of oil-globules increases; but in the ordinary mature state the capsule of this species remains spherical, and its oil-globule solitary. In quite young capsules the oil-globules are wanting; Pl. 3, fig. 12.)

_Dimensions._--Diameter of the central capsules 0.04 to 0.16.

_Habitat._--Cosmopolitan, common in all warmer seas (Mediterranean, Atlantic, Indian, and Pacific), surface.

2. _Collozoum nostochinum_, n. sp.

Central capsules spherical, very large, opaque, distended with red pigment-granules and with very numerous (two hundred to three hundred) small oil-globules. Membrane thick, double-edged.

_Dimensions._--Diameter of the central capsules 0.3 to 0.5.

_Habitat._--Indian Ocean, off Socotra, surface, Haeckel.

3. _Collozoum volvocinum_, n. sp.

Central capsules spherical, very large, opaque, containing a great number (ten to thirty) of large oil-globules, and between them densely packed masses of dark pigment. Membrane thick, double-edged. This species differs from _Collozoum inerme_, mainly by the great size of the central capsules (three to five times as big as in the former) and the great number of oil-globules in them.

_Dimensions._--Diameter of the central capsules 0.2 to 0.3.

_Habitat._--Central Pacific, Station 272, surface.

Subgenus 2. _Colloprunum_, Haeckel.

_Definition._--Form of the central capsules ellipsoidal, with one prolonged axis.

4. _Collozoum ovatum_, n. sp.

_Colloprunum ovatum_, Haeckel, 1882, Manuscript.

Central capsules ovate or ellipsoidal, its longer diameter twice to three times as large as the shorter. In the centre of every capsule one single oil-globule.

{26}_Dimensions._--Length of the central capsules 0.2 to 0.3, breadth of them 0.1 to 15.

_Habitat._--North Pacific, Station 244, surface.

5. _Collozoum ellipsoides_, n. sp. (Pl. 3, figs. 8, 9).

_Colloprunum ellipsoides_, Haeckel, 1882, Manuscript.

Central capsules regularly ellipsoidal, very large; their longer diameter once and a half to twice as large as the shorter. In every capsule fifty to eighty oil-globules.

_Dimensions._--Length of the central capsules 0.3 to 4, breadth of them 0.2.

_Habitat._--North Atlantic, Færöe Channel (Gulf Stream), surface, John Murray.

Subgenus 3. _Collophidium_, Haeckel.

_Definition._--Form of the central capsules cylindrical, often snake-like, contorted, with one axis much prolonged, several times longer than the transverse axis.

6. _Collozoum contortum_, n. sp.

_Collophidium contortum_, Haeckel, 1882, Manuscript.

Central capsules cylindrical, three to four times as long as broad, C- or S-like curved, transparent, without oil-globules.

_Dimensions._--Length of the central capsules 0.2 to 0.3, breadth 0.06 to 0.08.

_Habitat._--Tropical Atlantic, Station 347, surface.

7. _Collozoum serpentinum_, n. sp. (Pl. 3, figs. 1-3).

_Collophidium serpentinum_, Haeckel, 1882, Manuscript.

Central capsules cylindrical, filiform, much elongated, ten to one hundred times, sometimes two hundred to four hundred times as long as broad, snake-shaped or worm-shaped, curved and contorted in the most irregular manner, often spiral or twisted into a large nodule. Numerous oil-vesicles constantly present, forming one series of globules in the axis of every capsule; distance of the globules, one from another, and also from the capsule-membrane, about equal to their diameter. (This interesting and very curious form was very frequently observed living by me in the Canary Islands, in January 1867; the jelly-colonies were commonly spherical, and contained fifty to two hundred or more capsules of very different size and form.)

_Dimensions._--Length of the central capsules 1 to 10, sometimes 20 to 40 mm.; average breadth 0.1 mm.

_Habitat._--Canary Islands, Lanzerote, Haeckel, surface.

{27}8. _Collozoum vermiforme_, n. sp. (Pl. 3, figs. 6, 7).

_Collophidium vermiforme_, Haeckel, 1882, Manuscript.

Central capsules cylindrical, much elongated, five to ten times (sometimes twenty to fifty times) as long as broad, snake-shaped or worm-shaped, very irregularly curved and contorted. Numerous oil-globules constantly present, forming in the axis of every capsule a double series of alternating rose-coloured globules. (This species is nearly allied to the preceding; but its capsules are thicker and shorter, and the oil-vesicles in them are arranged not in a single, but in a double row.)

_Dimensions._--Length of the central capsules 0.6 to 1.2 mm., sometimes 3 to 6 mm.; breadth 0.12.

_Habitat._--Tropical Atlantic, near the west coast of Africa, Station 349, Canary Islands, surface.

Subgenus 4. _Collodiscus_, Haeckel.

_Definition._--Form of the central capsules discoidal or lenticular, with one shortened axis.

9. _Collozoum coeruleum_, Haeckel.

_Collozoum coeruleum_, Haeckel, 1862, Monogr. d. Radiol., p. 523, Taf. xxxii. figs. 6-8.

_Collodiscus coeruleus_, Haeckel, 1882, Manuscript.

Central capsule lenticular or discoidal, flattened, blue coloured, with one single oil-globule in the centre. Protoplasm containing numerous crystals and dark blue pigment-granules. Membrane very thick, double-edged. (Whilst at Messina in 1859 I found this form not constantly discoidal, in 1867 in the Canary Islands I observed it constantly lenticular.)

_Dimensions._--Breadth of the central capsules 0.1 to 0.15, height 0.04 to 0.08.

_Habitat._--Mediterranean (Messina), Atlantic (Canary Islands), surface.

10. _Collozoum discoideum_, n. sp.

_Collodiscus discoideus_, Haeckel, 1882, Manuscript.

Central capsule discoidal, flattened, transparent, with a ring of twenty to twenty-five oil-globules in its circular periphery (on the inside of the thin membrane).

_Dimensions._--Breadth of the central capsules 0.2, height 0.05.

_Habitat._--South Pacific (Juan Fernandez), Station 300, surface.

Subgenus 5. _Collodastrum_, Haeckel.

_Definition._--Form of the central capsules irregular and indefinite, variable, commonly polyhedral or polygonal, or amoeboid, often with irregular, finger-like processes.

{28}11. _Collozoum pelagicum_, Haeckel.

_Collozoum pelagicum_, Haeckel, 1862, Monogr. d. Radiol., p. 525, Taf. xxxii. figs. 4, 5.

_Sphærozoum pelagicum_, Haeckel, 1860, Monatsber. d. k. Akad. d. Wiss. Berlin, 1860, p. 845.

Central capsules small, quite irregularly formed, roundish-polyhedral or depressed-polygonal, transparent, without oil-globules. Often many extracapsular oil-vesicles in the common jelly-body between the central capsules. Membrane very thin and delicate.

_Dimensions._--Diameter of the central capsules 0.02 to 0.08.

_Habitat._--Mediterranean, Messina, Haeckel; Naples, Brandt; surface.

12. _Collozoum stellatum_, n. sp.

_Collodastrum stellatum_, Haeckel, 1882, Manuscript.

Central capsules star-shaped, irregularly radiating, with a great number (eight to twenty or more) of radial, short, conical, acute processes, very variable in size and number. Membrane thin. In every capsule several (four to eight) oil-globules.

_Dimensions._--Diameter of the central capsules 0.12 to 0.2.

_Habitat._--Central Pacific, Station 274, surface.

13. _Collozoum amoeboides_, n. sp. (Pl. 3, figs. 4, 5).

_Collodastrum amoeboides_, Haeckel, 1882, Manuscript.

Central capsules amoebiform, of moderate size, quite irregularly formed, with a variable number of finger-like, obtuse, irregular prolongations (commonly three to six), very variable in size and form. Membrane thin. In the centre of every capsule one single oil-globule.

_Dimensions._--Diameter of the central capsules 0.04 to 0.08.

_Habitat._--Indian Ocean, Ceylon, Haeckel; Madagascar, Rabbe; surface.

----

Suborder II. BELOIDEA, Haeckel.

_Definition._--SPUMELLARIA with an imperfect skeleton, composed of numerous solid needles or spicula, scattered irregularly in the calymma.

The suborder #Beloidea# comprises all those SPUMELLARIA which possess an imperfect or rudimentary skeleton, composed of a variable number of isolated spicula scattered in the extracapsulum. The suborder contains only two different families, the solitary Thalassosphærida (or Beloidea monozoa) and the associated Sphærozoida (or Beloidea polyzoa). Both families are very nearly allied, and differ only in one single character: the solitary life of the former, the social union of the {29}latter. It seems to be merely a consequence of this difference that the cleavage of the nucleus commonly takes place very late in the former, very early in the latter.

Commonly, therefore, the full-grown Thalassosphærida (until immediately before their propagation) exhibit one single nucleus in the centre of the capsule, whilst in the Sphærozoida the capsule is distended with numerous small nuclei. In these latter the centre of the capsule usually contains one large oil-globule, whilst in the former oil-globules are either wanting or scattered in large numbers in the endoplasm, or disposed in one layer on the inside of the capsule membrane.

In the solitary Thalassosphærida each capsule is enclosed in its own peculiar spherical calymma, whilst in the associated Sphærozoida all the capsules of the colony are united into one common, very voluminous, alveolated calymma.

Family III. #THALASSOSPHÆRIDA#, Haeckel, 1862, (Pl. 2).

_Thalassosphærida_, Monogr. d. Radiol., p. 255.

_Definition._--#Beloidea# solitaria.

The family Thalassosphærida comprises all solitary SPUMELLARIA with an imperfect skeleton, composed of numerous solid needles or spicula, scattered around the central capsule in the calymma. The structure of the unicellular soft body is quite the same as in the Thalassicollida; it differs from these only in the possession of the extracapsular skeleton. All needles of this skeleton are solid siliceous spicula, never hollow, as in the similar Cannorrhaphida among the PHÆODARIA. In the special structure and form of the skeleton the Thalassosphærida agree perfectly with the well-known, colony-building Sphærozoida; they differ from these only by their hermit-like life and by some peculiarities derived from this solitary development.

The oldest known form of this family is probably the first Radiolarian, observed in the living state, described in 1834 by Meyen as _Physematium atlanticum_ (see p. 35). A second form was figured in my Monograph (1862) as _Thalassosphæra bifurca_ (p. 260, Taf. xii. fig. 1). A third form was there described under the name _Thalassosphæra morum_; this remarkable form was first observed by Johannes Müller, and figured under the name _Thalassicolla morum_ (1858, Abhandl., p. 28, Taf. vii. figs. 1, 2). The same form was afterwards observed living by myself in the Mediterranean, as well as in the Atlantic, and in great numbers by the late Sir Wyville Thomson in the Pacific. The latter gave a good figure of it with some valuable remarks in his excellent work, The Atlantic (1877, vol. i. p. 233, fig. 51). He called this peculiar Rhizopod _Calcaromma calcarea_, on account of the very peculiar _calcareous_ bodies "looking in outline like the rowels of spurs," which are accumulated in great quantity around the central capsule, in the calymma. Further investigations have convinced me that these peculiar stellate {30}bodies of carbonate of lime, for which we propose the name "Calcastrella," are not parts of the skeleton produced by the Radiolarian, but foreign bodies picked up by its extracapsular sarcode (in the same way as the Coccoliths are picked up by _Thalassicolla sanguinolenta = Myxobrachia!_). These Calcastrella occur also in the calymma of some Discoidea and other Radiolaria; they are either unicellular calcareous Algæ, or foreign bodies of other origin. The _Collodarium_, however, described as _Thalassicolla morum_ and _Calcaromma calcarea_, seems to be a simple _Actissa_, which has picked up a number of Calcastrella.

The Challenger collection has yielded a number of other true Thalassosphærida, which partly agree with _Thalassosphæra_ in the simple structure of the unicellular body (resembling _Actissa_), and partly differ from it in the development of alveoles, either within or without the central capsule (similar to _Thalassolampe_ and _Thalassicolla_). The solid siliceous spicula, which occur in great numbers scattered in the calymma, agree perfectly in form with the spicula of the colony-building Sphærozoida. A characteristic difference between the social and the solitary #Beloidea# seems to be determined by the cleavage of the nucleus, which takes place in the latter very late, in the former very early. Therefore in the large central capsule of the mature solitary Thalassosphærida, we commonly find one large nucleus in the centre, and a number of oil-globules around it in the endosarc, or disposed in one layer on the inside of the capsule-membrane (Pl. 2, figs. 2, 5); whereas in the much smaller associated capsules of the Sphærozoida one large oil-globule is placed commonly in the centre, and a great number of small nuclei scattered in the endoplasm (compare above, p. 24).

_Synopsis of the Genera of Thalassosphærida._

A. Alveoles neither within { Spicula simple, 7. _Thalassosphæra_. nor without the { central capsule. { Spicula branched, 8. _Thalassoxanthium_.

B. Numerous large alveoles } within the central } Spicula simple, 9. _Physematium_. capsule (not in the } calymma). }

C. Numerous large alveoles { Spicula simple, 10. _Thalassoplancta_. within the calymma (not { in the central capsule). { Spicula branched, 11. _Lampoxanthium_.

Genus 7. _Thalassosphæra_,[14] Haeckel, 1862, Monogr. d. Radiol., p. 259.

_Definition._--Thalassosphærida without alveoles, with simple, unbranched, needle-shaped spicula in the calymma.

The genus _Thalassosphæra_ was founded by me in 1862 for those solitary #Collodaria# in which the simple central capsule is surrounded by scattered solid spicula. {31}I described these two different species, the new _Thalassosphæra bifurca_ and the _Thalassosphæra morum_, which J. Müller had formerly called _Thalassicolla morum_. This latter form is characterised by peculiar _calcareous_ bodies "looking in outline like the rowels of spurs, scattered irregularly in the gelatinous envelope," and was therefore afterwards called "_Calcaromma calcarea_" by Sir Wyville Thomson.[15] As already mentioned above, these calcareous rowels are foreign bodies, picked up by an _Actissa_ (see p. 29). I here confine the genus _Thalassosphæra_ to those solitary #Beloidea# in which the body exhibits no alveoles, and the siliceous solid spicula in the calymma are quite simple needles.

_Thalassosphæra belonium_, n. sp.

Spicula thin cylindrical rods, more or less curved, pointed at both ends, with smooth surface (similar to the needles of _Rhaphidozoum italicum_). Central capsule spherical, three times as large as the central nucleus, without larger oil-globules.

_Dimensions._--Diameter of the central capsule 0.1 to 0.12, length of the spicula 0.04 to 0.08.

_Habitat._--Central Pacific, Station 272, surface.

_Thalassosphæra rhaphidium_, n. sp.

Spicula thick cylindrical rods, more or less curved, pointed at both ends, covered with numerous strong conical thorns, perpendicular to the axis. Central capsule spherical, four times as broad as the central nucleus, with twenty to thirty large oil-globules on the inside of the membrane.

_Dimensions._--Diameter of the central capsule 0.2, length of the spicula 0.12 to 0.16.

_Habitat._--Tropical Atlantic, Station 347, surface.

Genus 8. _Thalassoxanthium_,[16] Haeckel, 1881, Prodromus, p. 470.

_Definition._--Thalassosphærida without alveoles, with numerous branched or compound spicula in the calymma.

The genus _Thalassoxanthium_ differs from the foregoing _Thalassosphæra_, by the ramification of the spicula, and has therefore the same relation to it as _Sphærozoum_ to _Belonozoum_. The soft unicellular body is as simple as in _Actissa_, and exhibits alveoles neither in the capsule nor in the calymma.

Subgenus 1. _Thalassoxanthella_, Haeckel.

_Definition._--Spicula not geminate, but simply radiate, consisting of three, four, or more needles or shanks, radiating in different directions from one and the same point; shanks now simple or needle-like, now furcate or branched.

{32}1. _Thalassoxanthium triactinium_, n. sp.

Spicula all (or nearly all) triradiate, composed of three (or sometimes in a few spicula four) needle-like shanks of equal length, diverging from one common point. Shanks straight or somewhat curved, smooth, pointed. Central capsule pellucid, twice as broad as its dark nucleus, without larger oil-globules. Jelly-envelope very thin, with numerous xanthellæ.

_Dimensions._--Diameter of the central capsule 0.1, of its nucleus 0.05, length of the spicule-shanks 0.6 to 0.8.

_Habitat._--Central Pacific, Station 266, surface.

2. _Thalassoxanthium triradiatum_, n. sp.

Spicula all (or nearly all) triradiate, composed of three (or sometimes in a few spicula four) needle-like shanks of different length, diverging from one common point. Shanks curved or bent, covered with small conical thorns. Central capsule dark, three times as large as the nucleus, with numerous large oil-globules. Jelly-envelope thick, without xanthellæ.

_Dimensions._--Diameter of the capsule 0.2, of the nucleus 0.07, length of the spicule-shanks 0.1 to 0.15.

_Habitat._--South Pacific, Station 302, surface.

3. _Thalassoxanthium medusinum_, n. sp. (Pl. 2, fig. 5).

Spicula all (or nearly all) quadriradiate, irregular, composed of four (or sometimes in a few spicula three) needle-like shanks (mostly of unequal length), diverging from one common point. Shanks curved, pointed, thorny, covered with small spinules. Central capsule dusky, twice to three times as large as its dark central nucleus. On the inside of the membrane numerous large oil-globules. Jelly-envelope thin, with numerous xanthellæ.

_Dimensions._--Diameter of the central capsule 0.45 to 0.5, of its nucleus 0.18 to 0.2.

_Habitat._--North Pacific, Station 244, surface.

4. _Thalassoxanthium hexactinium_, n. sp.

Spicula all (or nearly all) hexaradiate, composed of six (or sometimes in a few spicula three) needle-like shanks, diverging in two opposite hemispheres (three needles upwards, three needles downwards). Shanks somewhat curved, pointed, smooth. Central capsule yellowish-brown, dark, four times as broad as its dark central nucleus. Jelly-envelope thick (about twice as broad as the capsule), with very numerous xanthellæ.

_Dimensions._--Diameter of the central capsule 0.3 to 0.4, of its nucleus 0.1 to 0.12.

_Habitat._--South Atlantic, Station 325, surface.

{33}5. _Thalassoxanthium cervicorne_, n. sp. (Pl. 2, figs. 3, 4).

Spicula all triradiate, trichotomously branched, with three equal shanks, which diverge from one common point, and are again provided each with three branches on the distal end. These nine branches are commonly once or twice forked (each fork rarely provided with three ramules). The ramules are thin, unequal, curved, or bent, and the ramification nearly resembles a stag's horn. Central capsule transparent, without oil-globules, two to three times as broad as the dark nucleus, which contains one single long central nucleolus. Calymma thin, scarcely as thick as the radius of the nucleus.

_Dimensions._--Diameter of the central capsule 0.2 to 0.25, of the nucleus 0.08 to 0.1, length of the spicula 0.05 to 0.15.

_Habitat._--Central Pacific, Stations 271, 274, surface.

Subgenus 2. _Thalassoxanthomma_, Haeckel.

_Definition._--Spicula all or partly geminate, consisting of one middle or axial rod, from the two poles of which diverge two, three, or more shanks in different directions. Shanks or needle-rays sometimes simple, needle-like, sometimes bifurcated or branched.

6. _Thalassoxanthium furcatum_, n. sp.

Spicula all (or nearly all) geminate and simply forked, composed of a simple axial rod and two simple, needle-like shanks on each end of it. Shanks straight, pointed, smooth, somewhat shorter than the middle rod. Central capsule yellowish, dark, three times as broad as its central dark nucleus; besides this a single oil-globule, nearly of the same size.

_Dimensions._--Diameter of the central capsule 0.1, of its nucleus 0.03; length of the axial rod of the spicula 0.04, of its shanks 0.03.

_Habitat._--Cape Verde Islands.

7. _Thalassoxanthium bifurcum_, Haeckel.

_Thalassosphæra bifurca_, Haeckel, 1862, Monogr. d. Radiol., p. 260, Taf. xii. fig. 1.

_Sphærozoum bifurcum_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 845.

Spicula all geminate and double forked, composed of a simple axial rod and two forked branches on each end; these branches are again forked, so that each spiculum exhibits eight thin distal ends. All branches are thin, slender and straight. Central capsule red, four times as broad as the central nucleus, containing between the red pigment-granules numerous, peculiar, violin-shaped bodies (fat-corpuscles?). Compare fig. 1, _loc. cit._

_Dimensions._--Diameter of the central capsule 0.08, of the nucleus 0.02, length of the spicula 0.05 to 0.08.

_Habitat._--Mediterranean (Messina), surface, Haeckel.

{34}8. _Thalassoxanthium ovodimare_, n. sp.

Spicula all geminate, composed of a simple, very short axial rod and three diverging shanks or branches on each end of it; the shanks are very thin, straight, or little curved, and eight to ten times as long as the axial rod. The spicula are quite smooth, as in the similar _Sphærozoum ovodimare_ (in which, however, the axial rod is much longer). Central capsule transparent, without oil-globules, twice as broad as the nucleus.

_Dimensions._--Diameter of the capsule 0.4, of the nucleus 0.2, length of the spicula 0.1 to 0.2.

_Habitat._--Central Pacific, Station 273, surface.

9. _Thalassoxanthium punctatum_, n. sp.

Spicula all geminate-triradiate, composed of a simple middle rod and of three diverging shanks on each end of it; the shanks are thorny with small spinules and shorter than the axial rod, very similar to the common _Sphærozoum punctatum_. Central capsule dark, with numerous (twenty to thirty) oil-globules on the inside of the membrane, three times as broad as the nucleus.

_Dimensions._--Diameter of the capsule 0.3, of the nucleus 0.1, length of the spicula 0.05 to 0.2.

_Habitat._--Central Pacific, Station 274, surface.

10. _Thalassoxanthium octoceras_, n. sp. (Pl. 2, fig. 6).

Spicula all geminate-quadriradiate, composed of a simple short middle rod and of four diverging shanks on each end of it; the shanks are quite smooth, irregularly curved or bent, and four to eight times as long as the middle rod. Central capsule dark, filled with pigment-granules, without oil-globules, four times as large as the nucleus.

_Dimensions._--Diameter of the capsule 0.5, of the nucleus 0.12, length of the spicula 0.2 to 0.4.

_Habitat._--Indian Ocean, Madagascar, Rabbe.

Genus 9. _Physematium_,[17] Meyen, 1834, Nova Acta Acad. Nat. Curios., vol. xvi., Suppl., p. 286 (p. 162).

_Definition._--#Thalassosphærida# with large numerous alveoles within the central capsule (not in the calymma), and with numerous simple, needle-shaped spicula in the calymma.

The genus _Physematium_ is, together with the colony-forming _Sphærozoum_, the first Radiolarian which was observed in the living state, described in 1834 by Meyen. It is most nearly allied to _Thalassolampe_, and has the same large roundish alveoles within the central capsule, which reaches therefore an extraordinary size, 5 to 10 mm. It {35}differs from the latter by the possession of spicula in the calymma. The peculiar "centripetale Zell-gruppen" on the inside of the capsule-membrane are probably due to radial cleavages of the endoplasm; as also occurs in other #Collodaria#.

1. _Physematium mülleri_, Schneider.

_Physematium mülleri_, Schneider, 1858, Archiv. f. Anat. u. Physiol., p. 38, Taf. iii. B, figs. 1-5.

_Physematium mülleri_, Haeckel, 1862, Monogr. d. Radiol., p. 256, Taf. iii. figs. 6-9.

Spherical body limpid, somewhat opalescent, sometimes a little yellowish or brownish, rather soft. Central capsule with a thin, but firm, transparent membrane, its diameter eight to ten times as large as that of the central spherical nucleus. Membrane of the nucleus thick, porous, on its inside with some nucleoli. In the protoplasmic network between the large intracapsular alveoles, numerous large, pale, yellowish, or orange oil-globules. On the inside of the membrane numerous conical bodies, centripetally directed with the apex towards the centre; every conical body ("kegelförmige centripetale Zellgruppe") composed of three to nine (commonly four or five) nucleated cells (mother-cells of the spores?); in the axis of the cone there is often a yellowish, orange, or brown oil-globule. Extracapsular jelly-envelope thin, with short pseudopodia. Xanthellæ scarce or wanting. Spicula scattered in the jelly numerous, small, simple needles, commonly C- or S-like curved, smooth.

_Dimensions._--Diameter of the whole jelly-sphere 3 to 6 mm., of the central capsule 1 to 5 mm., of the nucleus 0.1 to 0.5, length of the spicula 0.05 to 0.1.

_Habitat._--Mediterranean, Messina; Schneider, Haeckel; surface.

2. _Physematium atlanticum_, Meyen.

_Physematium atlanticum_, Meyen, 1834, Nova Acta Acad. Nat. Curios., vol. xvi., Suppl., p. 286 (162), Taf. xxxviii. (xxviii.) figs. 1-3.

Spherical body opalescent, pearl-like, with a violet or purple lustre, very soft. Central capsule with a strong, semi-transparent membrane, its diameter six to eight times as large as that of the central spherical nucleus. Membrane of the nucleus very thick, porous, on its inside with many small nucleoli. In the protoplasmic network between the alveoles very numerous, small, purple oil-globules. On the inside of the membrane a continuous simple layer of small nuclei, enclosed in radially striped protoplasm (mother-cells of the spores?). No centripetal conical bodies. Extracapsular jelly-envelope very thin, with short pseudopodia. No xanthellæ. Spicule scattered in the jelly numerous, small needles, straight or slightly curved, thorny owing to numerous small vertical spinules. This species and _Thalassolampe maxima_ (p. 17) possess the largest central capsule.

_Dimensions._--Diameter of the whole jelly-sphere 8 to 12 mm., of the central capsule 5 to 10 mm., of the nucleus 1 to 2 mm., length of the spicula 0.1 to 0.3.

_Habitat._--Eastern Atlantic, between Canary Islands and Cape Verde Islands, Meyen; Lanzerote, Haeckel.

{36}Genus 10. _Thalassoplancta_,[18] Haeckel, 1862, Monogr. d. Radiol., p. 261.

_Definition._--#Thalassosphærida# with numerous large alveoles in the calymma (but not in the central capsule), and with numerous simple, needle-shaped spicula around the central capsule.

The genus _Thalassoplancta_ was founded by me in 1862 for a Radiolarian with simple hollow needles in the calymma, which was afterwards recognised as a Phæodarium, belonging to _Cannorrhaphis_. We here retain this name for a true Thalassosphærid, very similar to the latter, but distinguished by the absence of the phæodium and the solid--not hollow--needle-shaped spicula, which are scattered in the alveolated calymma. _Thalassoplancta_ can be regarded as the solitary form of the social _Belonozoum_.[19]

1. _Thalassoplancta longispicula_, n. sp.

Spicula long and thin, cylindrical, smooth, more or less bent, pointed at both ends, similar to those of _Thalassoplancta cavispicula_. Central capsule thin-walled, without oil-globules, four times as broad as the nucleus, which encloses one single nucleolus.

_Dimensions._--Diameter of the capsule 0.6, of the nucleus 0.15, of the calymma 4 mm.

_Habitat._--North Atlantic, Færöe Channel (Gulf Stream), John Murray.

2. _Thalassoplancta brevispicula_, n. sp. (Pl. 2, fig. 2).

_Lampoxanthium brevispiculum_, Haeckel, 1882, Atlas.

Spicula short and thick, thorny, irregularly curved, pointed at both ends, very numerous. In the observed specimen all spicula were aggregated in the outer part of the voluminous calymma, whilst the inner alveolated part was devoid of them. Central capsule thick walled, with a layer of large oil-globules on its inner surface, twice as broad as the large nucleus which contains numerous nucleoli.

_Dimensions._--Diameter of the central capsule 0.5, of the nucleus 0.2, of the calymma 2.5.

_Habitat._--South Atlantic, Station 334, surface.

Genus 11. _Lampoxanthium_,[20] n. gen.

_Definition._--#Thalassosphærida# with numerous large alveoles in the calymma (but not in the central capsule), and with numerous branched or compound spicula in the calymma.

{37}The genus _Lampoxanthium_ differs from the foregoing, _Thalassoplancta_, by the composite form of the spicula, which are not simple needles, but radiate or geminate, or branched in different forms; the former stands therefore in the same relation to the latter as the social _Belonozoum_ to _Sphærozoum_. The spicula of some species of _Lampoxanthium_ are identical with those of some species of _Sphærozoum_, so that the latter may be derived from the former by forming colonies. The large central capsule is enveloped by a very voluminous alveolated calymma, and includes a large central nucleus with numerous nucleoli.

Subgenus 1. _Lampoxanthella_, Haeckel.

_Definition._--Spicula all (or nearly all) of one kind, radiate.

1. _Lampoxanthium tetractinium_, n. sp.

Spicula all (or nearly all) tetraradiate, with four thorny, straight, pointed shanks, radiating from one common point. (Intermingled with these are often some few, thorny, triradiate spicula.) On the inside of the capsule a layer of large oil-globules as in _Thalassoplancta_, Pl. 2, fig. 2.

_Dimensions._--Diameter of the central capsule 0.2, of the nucleus 0.08, of the calymma 0.8.

_Habitat._--South Pacific, Station 288, surface.

Subgenus 2. _Lampoxanthomma_, Haeckel.

_Definition._--Spicula all (or nearly all) of one kind, geminate-radiate, with a simple middle rod and two to four diverging shanks on each end of it.

2. _Lampoxanthium punctatum_, n. sp.

Spicula all geminate-triradiate, thorny, of the same form as in the common _Sphærozoum punctatum_, of which this species is the large solitary representative. The spicula are aggregated in a very condensed layer on the surface of the large calymma.

_Dimensions._--Diameter of the capsule 0.8, of the nucleus 0.6, of the calymma 2.0.

_Habitat._--North Pacific, Station 248, surface.

3. _Lampoxanthium octoceras_, n. sp.

Spicula all geminate-quadriradiate, with a very short simple middle rod and four very long divergent shanks on both ends of it; the shanks are smooth, five to ten times as long as the middle {38}rod, irregularly bent and curved. (Differs from the similar _Thalassoxanthium octoceras_, Pl. 2, fig. 6, by slender, more curved shanks, and by the voluminous calymma, there entirely wanting.)

_Dimensions._--Diameter of the capsule 0.5, of the nucleus 0.2, of the calymma 3.0.

_Habitat._--South Atlantic, Station 331, surface.

Subgenus 3. _Lampoxanthura_, Haeckel.

_Definition._--Spicula of two or three different kinds, simple, radiate, and geminate-radiate mixed.

4. _Lampoxanthium pandora_, n. sp. (Pl. 2, fig. 1).

Spicula mixed, of three different kinds--simple, radiate and geminate-radiate; all three kinds partly smooth, partly thorny. The simple needles short, thin spindle-shaped, often curved. The radiate spicula commonly with three or four, rarely five or six, unequal rays, straight or curved. The radiate-geminate spicula commonly with three, rarely four, shanks on each end, often different on both ends of the middle rod. The size, number, and form of the irregular spicula are here quite as variable as in the social _Rhaphidozoum pandora_, of which it is the solitary representative. The wall of the large central capsule is very thick, with evident pore-canals, separated by a clear interval from the coagulated and vacuolated endoplasm, which contains no oil-globules. Nucleus with numerous nucleoli.

_Dimensions._--Diameter of the central capsule 0.5 to 0.6, of the nucleus 0.1 to 0.2, of the calymma 2 to 4 mm.

_Habitat._--North Pacific, Station 244, surface.

Family IV. #SPHÆROZOIDA#, Haeckel (Pl. 4).

_Sphærozoida_, Haeckel, 1862, Monogr. d. Radiol., p. 521.

_Definition._--#Beloidea# socialia.

The family #Sphærozoida# comprises all associated or colony-forming Radiolaria, which are provided with an imperfect skeleton, composed of numerous solid needles or spicula, scattered around the central capsule in the calymma. The structure and form of this skeleton is quite the same as in the preceding solitary Thalassosphærida, but on the other hand, the structure and form of the colonies and of the included numerous central capsules is the same as in the skeletonless Collozoida.

The oldest well-known form of Sphærozoida is the common cosmopolitan _Sphærozoum punctatum_, probably first observed in 1834 by Meyen, and called _Sphærozoum fuscum_, afterwards more accurately described by Huxley in 1851.

{39}Other forms were afterwards described by Müller and by myself in 1862.[21] Further investigations have shown me that some species of this family are among the most common Radiolaria, and occur in astonishing numbers on the surface of all warmer seas. But the number of species is comparatively small, and their distinction is very difficult, as all the different forms are very variable and connected by intermediate forms--a truly "_transformistic_" group.

The only character sufficient for the constitution of genera in this transformistic group is found in the form and composition of the spicula; the very variable form of the jelly-calymma and the enclosed central capsule being without value for this purpose. But also the form of the spicula is very variable, and not always constant. In some species the particular form of the spicula is transmitted by constant heredity, whilst in others it is very inconstant, even in one and the same individual. (Compare the remarks on variability in the general introduction.)

As the number of various forms is rather great, it seems to be advisable to distinguish the three following genera.

_Synopsis of the Genera of Sphærozoida._

A. Spicula all of one kind, simple or needle-shaped, 12. _Belonozoum_. B. Spicula all of one kind, branched or radiate, or geminate, 13. _Sphærozoum_. C. Spicula of two more different kinds, partly simple, partly branched, 14. _Rhaphidozoum_.

Genus 12. _Belonozoum_,[22] n. gen.

_Definition._--#Sphærozoida# with simple needle-shaped spicula, which are neither radiate nor branched.

The genus _Belonozoum_ comprises the Sphærozoida with simple needle-shaped spicula, and may be regarded as the colonial form of _Thalassosphæra_ or _Thalassoplancta_, derived from these solitary #Beloidea# by multiplication of the capsules and union in a common calymma.

1. _Belonozoum bacillosum_, n. sp.

_Sphærozoum bacillosum_, Haeckel, 1881, Manuscript.

Spicula all simple rods, straight cylindrical, obtuse at both ends, quite smooth. Central capsule pellucid, with one single central oil-globule.

_Dimensions._--Diameter of the central capsule 0.08 to 0.12, length of the spicula 0.05 to 0.08.

_Habitat._--Central Pacific, Station 271, surface.

{40}2. _Belonozoum spinulosum_, Haeckel.

_Sphærozoum spinulosum_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 54, Taf. viii. fig. 4.

_Sphærozoum spinulosum_, Haeckel, 1862, Monogr. d. Radiol., p. 527, Taf. xxxiii. figs. 3, 4.

Spicula all simple rods, straight cylindrical, obtuse on both ends, thorny with numerous small spines, placed vertically on the rods.

_Dimensions._--Diameter of the central capsule 0.08 to 0.1, length of the spicula 0.05 to 0.2.

_Habitat._--Mediterranean, Nice, J. Müller; Messina, Haeckel; Naples, Brandt; surface.

3. _Belonozoum italicum_, Haeckel.

_Sphærozoum italicum_, Haeckel, 1862, Monogr. d. Radiol., p. 526, Taf. xxxiii. figs. 1, 2.

Spicula all simple rods, more or less curved or bent, pointed at both ends, quite smooth. Central capsule with a variable number (commonly five to twenty) of oil-globules.

_Dimensions._--Diameter of the central capsule 0.1 to 0.3, length of the spicula 0.05 to 0.2.

_Habitat._--Mediterranean, Nice, Naples, Messina, Haeckel, surface.

4. _Belonozoum atlanticum_, n. sp.

_Sphærozoum atlanticum_, Haeckel, 1881, Manuscript.

Spicula all together simple rods, more or less curved or bent, pointed at both ends, thorny from numerous small spines, placed vertically on the rods.

_Dimensions._--Diameter of the central capsule 0.1 to 0.2, length of the spicula 0.07 to 0.15.

_Habitat._--Tropical Atlantic, Station 348, surface.

Genus 13. _Sphærozoum_,[23] Meyen, 1834, Nova Acta Acad. Nat. Curios., Bd. xvi., Suppl., p. 287 (p. 163).

_Definition._--#Sphærozoida# with branched or radiate spicula of one kind.

The genus _Sphærozoum_, with _Physematium_ one of the two oldest Radiolaria, observed in the living state, was founded 1834 by Meyen for one of the social #Beloidea#, which was probably the common cosmopolitan _Sphærozoum punctatum_, the true type of this genus. Johannes Müller described a number of species, which were partly skeletonless (_Collozoum_), partly armed with simple or with compound spicula. The species with simple spicula we refer here to _Belonozoum_, the species with two or more different kinds of spicula to _Rhaphidozoum_, while we unite in _Sphærozoum_ all species with one kind of branched or compound spicula. The two following species are incompletely known:--_Sphærozoum orientale_, Dana, 1863, _Ann. and Mag. Nat. Hist._, vol. xii. p. 54. _Sphærozoum sanderi_, Doenitz, 1871, L. N. 60, p. 71.

{41}Subgenus 1. _Sphærozonactis_, Haeckel.

_Definition._--Spicula radiate, not geminate, consisting of three, four, or more needles or shanks, radiating in different directions from one common central point.

1. _Sphærozoum triactinium_, n. sp.

Spicula all (or nearly all) triradiate, composed of three (or sometimes in few spicula four) needle-like shanks, diverging from one common point. Shanks straight or somewhat curved, smooth, pointed. Central capsules spherical, with one central oil-vesicle. This species may be regarded as the social form of _Thalassoxanthium triactinium_.

_Dimensions._--Diameter of the central capsules 0.1 to 0.12, length of the spicula-shanks 0.05 to 0.1.

_Habitat._--South Pacific, Station 295, surface.

2. _Sphærozoum medusinum_, n. sp.

Spicula all (or nearly all) quadriradiate, composed of four (or sometimes in few spicula three) needle-like shanks (mostly of unequal length), diverging from one common point. Shanks slightly curved, pointed, thorny, covered with small spinules. Central capsules ellipsoidal, containing several (four to eight) oil-vesicles. This species may be regarded as the social form of the solitary _Thalassoxanthium medusinum_ (Pl. 2, fig. 5).

_Dimensions._--Diameter of the central capsules 0.15 to 0.18, length of the spicula-shanks 0.08 to 0.12.

_Habitat._--North Pacific, Station 236, surface.

3. _Sphærozoum hamatum_, n. sp.

Spicula all (or nearly all) quadriradiate, composed of four (or sometimes in few spicula three) needle-like shanks, mostly of very different size, diverging from one common point. Shanks strong, straight, curved, or hook-like; thorny, covered with small spinules on the distal extremity. Central capsules ellipsoidal, large, containing many (ten to twenty) oil-globules. This large species is distinguished by the very irregular form and size of the spicula.

_Dimensions._--Diameter of the central capsules 0.2 to 0.25, length of the spicula-shanks 0.12 to 0.18.

_Habitat._--Central Pacific, Station 265, surface.

4. _Sphærozoum hexactinium_, n. sp.

Spicula all (or nearly all) hexaradiate, composed of six (or sometimes in few spicula five or seven) needle-like shanks, mostly of equal size, diverging from one common point in two opposite hemispheres (three needles upwards, three needles downwards). Shanks somewhat curved, pointed, {42}smooth. Central capsules spherical, small, with one central oil-globule. This species may be regarded as the social form of _Thalassoxanthium hexactinium_.

_Dimensions._--Diameter of the central capsule 0.06 to 0.08, length of the spicula-shanks 0.05 to 0.06.

_Habitat._--North Atlantic, Færöe Channel (Gulf Stream), John Murray.

Subgenus 2. _Sphærozonoceras_, Haeckel.

_Definition._--Spicula all geminate-radiate, consisting of one middle rod, which bears an equal and constant number of rays (two, three, or four) at each end.

5. _Sphærozoum furcatum_, n. sp.

Spicula all (or nearly all) geminate and simply forked, composed of a simple axial rod and two simple needle-like shanks on each end of it. Shanks straight, pointed, smooth, commonly somewhat longer than the middle rod.

_Dimensions._--Diameter of the central capsules 0.1 to 0.15, length of the axial rod of the spicula 0.03, of its shanks 0.04 to 0.06.

_Habitat._--Tropical zone of the Atlantic, near Ascension Island, Station 344, surface.

6. _Sphærozoum furculosum_, n. sp.

Spicula all (or nearly all) geminate and simply forked, composed of a simple axial rod and two simple needle-like shanks on each end of it. Shanks curved or bent, pointed, thorny, with many small spinules, commonly somewhat shorter than the middle rod.

_Dimensions._--Diameter of the central capsules 0.2 to 0.25, length of the axial rod of the spicula 0.1, of its shanks 0.05 to 0.08.

_Habitat._--South Atlantic, near Tristan da Cunha, Station 334, surface.

7. _Sphærozoum ovodimare_, Haeckel.

_Sphærozoum ovodimare_, Haeckel, 1862, Monogr. d. Radiol., p. 527, Taf. xxxiii. figs. 5, 6.

_Sphærozoum punctatum_, var., Brandt, 1881, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, Taf. i. fig. 54.

Spicula all (or nearly all) geminate and triradiate, composed of a long simple axial rod and three simple needle-like shanks on each end of it. Shanks straight, pointed, smooth, commonly shorter than the middle rod. (Often few furcate or four-rayed spicula are intermixed, or few spicula are not smooth, but thorny.)

_Dimensions._--Diameter of the central capsules 0.05 to 0.2, length of the middle rod of the spicula 0.02 to 0.06, of its shanks 0.01 to 0.04.

_Habitat._--Mediterranean, Naples, Messina, Haeckel; Atlantic, Canary Islands, Cape Verde Islands, West Coast of Africa, Stations 351 to 354; surface.

{43}8. _Sphærozoum trigeminum_, n. sp.

Spicula all (or nearly all) geminate-triradiate, composed of a short simple axial middle rod and three simple needle-like shanks on each end of it. Shanks curved or bent, very thin, smooth, commonly much longer than the middle rod. (Often few quadriradiate or few thorny triradiate spicules are interspersed among the others.)

_Dimensions._--Length of the middle rod of the spicula 0.02 to 0.04, of its shanks 0.03 to 0.09.

_Habitat._--North Pacific, Stations 244 to 248, surface.

9. _Sphærozoum punctatum_, J. Müller.

_Sphærozoum punctatum_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 54, Taf. viii. figs. 1, 2.

_Sphærozoum punctatum_, Haeckel, 1862, Monogr. d. Radiol., p. 528, Taf. xxxiii. figs. 7-9.

_Sphærozoum fuscum_, Meyen, 1834, Nova Acta Acad. Nat. Cur., vol. xvi. Taf. xxxviii. fig. 7.

_Thalassicolla punctata_, Huxley, 1851, Ann. and Mag. Nat. Hist., ser. 2, vol. viii. p. 434, pl. xvi. figs. 1, 2, 3.

Spicula all (or nearly all) geminate-triradiate, composed of a long simple axial middle rod and three simple needle-like shanks on each end of it. Shanks straight, pointed, thorny, with many small spines, commonly somewhat shorter than the middle rod. (Often few furcate or four-rayed spicula are intermingled, or some of the spicula are smooth.) This cosmopolitan species is extremely variable, and produces interesting transitional forms to many other species of the genus. Compare also the general remarks on the genus, and the chapter on "Transformation" in the general introduction.

_Dimensions._--Length of the middle rod of the spicula 0.02 to 0.06, of its shanks 0.01 to 0.05.

_Habitat._--Cosmopolitan, common in nearly all warmer seas, Mediterranean, Atlantic, Indian Ocean, Pacific; surface.

10. _Sphærozoum armatum_, n. sp. (Pl. 4, fig. 9).

Spicula all geminate-triradiate, with a stout and short middle rod and three arborescent shanks on each end of it. Shanks longer than the middle rod, very stout, straight, pine-shaped, with six to twelve irregular, spinulated, lateral branches.

_Dimensions._--Diameter of the central capsules 0.04 to 0.08, length of the middle rod of the spicula 0.02 to 0.03, of its shanks 0.05 to 0.08.

_Habitat._--North Pacific, Japan, Station 239, surface.

11. _Sphærozoum alveolatum_, n. sp. (Pl. 4, figs. 2, 3).

Spicula all together geminate-triradiate, with a simple stout middle rod and three arborescent shanks on each end of it. Shanks more or less curved, slender, pine-shaped, with four to eight short, thorny lateral branches. In all coenobia of this remarkable species the central capsules are enclosed in large thick-walled alveoles (of three times their breadth), and in each alveole is placed besides {44}the capsule one single very large spiculum, whilst the others are much smaller (fig. 3). All the alveolated capsules are placed in one single stratum on the surface of the jelly-like spherical coenobium, comparable to the blastoderm-cells of a blastula.

_Dimensions._--Diameter of the central capsules 0.08 to 0.1, of the alveoles 0.2 to 0.4, length of the spicula 0.1 to 0.3.

_Habitat._--South Pacific (Juan Fernandez), Station 300, surface.

12. _Sphærozoum verticillatum_, n. sp. (Pl. 4, fig. 7).

Spicula all geminate-triradiate, with a short simple middle rod and three much longer arborescent shanks on each end of it. Shanks straight, slender, pine-shaped, each in the distal half with three to four elegant verticils of thorny lateral branches.

_Dimensions._--Diameter of the capsules 0.1 to 0.12, middle rod of the spicula 0.03 to 0.05, shanks 0.1 to 0.15.

_Habitat._--Indian Ocean, Ceylon, Haeckel; Madagascar, Rabbe; surface.

13. _Sphærozoum octoceras_, n. sp.

Spicula all geminate-quadriradiate, with a short simple middle rod and four diverging shanks on each end of it. Shanks smooth, irregularly curved or bent, three to six times as long as the middle rod. It may be regarded as the social form of _Thalassoxanthium octoceras_ (Pl. 2, fig. 6).

_Dimensions._--Diameter of the capsules 0.12 to 0.16, middle rod of the spicula 0.02, shanks 0.01.

_Habitat._--Australia, south coast, Faber; Station 163, surface.

14. _Sphærozoum quadrigeminum_, n. sp.

Spicula all geminate-quadriradiate, with a long thick middle rod and four shorter diverging shanks on each end of it. Shanks straight, thorny.

_Dimensions._--Diameter of the capsules 0.06 to 0.08, length of the spicula 0.05 to 0.15.

_Habitat._--North Atlantic, Azores, Station 354, surface.

15. _Sphærozoum araucaria_, n. sp.

Spicula all geminate-quadriradiate, with stout straight middle rod and four longer diverging shanks on each end of it. Shanks arborescent, with six to twelve thorny lateral branches.

_Dimensions._--Diameter of the capsules 0.1 to 0.15, length of the spicula 0.05 to 0.1.

_Habitat._--South Atlantic, coast of Brazil, Rabbe; surface.

16. _Sphærozoum arborescens_, n. sp. (Pl. 4, fig. 8).

Spicula all geminate-quadriradiate, with a stout straight middle rod and four longer diverging shanks on each end of it. Shanks arborescent, pine-shaped, with four to six verticils of lateral branches, which again are ramified and thorny.

{45}_Dimensions._--Diameter of the capsules 0.16 to 0.18, length of the spicula 0.1 to 0.2.

_Habitat._--South Atlantic (Tristan da Cunha), Station 332, surface.

Subgenus 3. _Sphærozonura_, Haeckel.

_Definition._--Spicula all geminate-radiate, but with a different and variable number of shanks on each end of the middle rod.

17. _Sphærozoum stellatum_, n. sp.

Spicula all geminate-radiate, with a strong middle rod and a variable number of shorter radiating shanks on the two ends of it. Shanks straight, nearly conical, smooth; for the most part three or four shanks on each end, but sometimes also five or six; very often this number is unequal on the two ends.

_Dimensions._--Diameter of the central capsules 0.1 to 0.2, length of the spicula 0.05 to 0.15.

_Habitat._--Central Pacific, Station 270, surface.

18. _Sphærozoum geminatum_, n. sp. (Pl. 4, fig. 4).

Spicula all geminate-radiate, with a strong middle rod and a variable number of longer radiant shanks on each end of it. Shanks straight, conical, in the distal half thorny; commonly either three or four shanks on each end of the middle rod, often also three on one end, four on the other end; rarely five or six rays on one end.

_Dimensions._--Diameter of the capsules 0.15 to 0.2, length of the spicula 0.05 to 0.1.

_Habitat._--Indian Ocean, Ceylon, Haeckel; surface.

19. _Sphærozoum circumtextum_, n. sp.

Spicula all geminate-radiate, with a very variable number of rays (two to six) on each end of the thin middle rod. All spicula very thin and delicate, smooth, with curved or bent shanks, densely covering the central capsule like a cobweb. The number of rays on each end is usually different, generally four or five, often also two or three, rarely six.

_Dimensions._--Diameter of the capsule 0.1 to 0.2, length of the spicula 0.04 to 0.12.

_Habitat._--Southeast part of the Indian Ocean, Station 160, surface.

20. _Sphærozoum variabile_, n. sp. (Pl. 4, fig. 5).

Spicula all geminate-radiate, with a short middle rod and a variable number of shanks on each end of it. Shanks four to eight times as long as the middle rod, curved or bent, in the distal half thorny; their number is commonly different on the two ends of it, three or five, often also four or six, rarely two; their size and form very variable.

{46}_Dimensions._--Diameter of the capsules 0.1 to 0.3, length of the spicula 0.1 to 0.2.

_Habitat._--North Pacific, Station 248, surface.

Genus 14. _Rhaphidozoum_,[24] Haeckel, 1862, Monogr. d. Radiol., p. 529.

_Definition._--Sphærozoida with two or more different kinds of spicula; one kind simple, needle-shaped; the other kinds compound, radiate, or branched.

The genus _Rhaphidozoum_ differs from _Sphærozoum_ by the composition of the skeleton of two or more different kinds of spicula, and has therefore the same relation to it as the solitary _Lampoxanthura_ to _Lampoxanthella_.

In some species nearly all the different forms, which characterise the numerous species of #Beloidea#, may be united in one and the same individual.

Subgenus 1. _Rhaphidonactis_, Haeckel.

_Definition._--Spicula of two different kinds; one kind simple, needle-shaped, the other radiate (composed of three, four, or more shanks, diverging from one common point).

1. _Rhaphidozoum pelagicum_, n. sp.

Spicula of two different kinds; one kind simple thin needles, a little curved or bent, the other kind triradiate, with three thin, curved shanks. Both kinds smooth, without thorns. Resembles a combination of _Belonozoum italicum_ and _Sphærozoum triactinium_.

_Dimensions._--Diameter of the central capsules 0.1 to 0.12, length of the spicula 0.05 to 0.15.

_Habitat._--Central Pacific, Station 267, surface.

2. _Rhaphidozoum pacificum_, n. sp.

Spicula of two different kinds; one kind simple needles, stout and straight, pointed at both ends, the other kind triradiate, with three straight and stout shanks. Both kinds thorny.

_Dimensions._--Diameter of the central capsule 0.06 to 0.08, length of the spicula 0.05 to 0.1.

_Habitat._--Central Pacific, Station 271, surface.

3. _Rhaphidozoum acuferum_, Haeckel.

_Rhaphidozoum acuferum_, Haeckel, 1862, Monogr. d. Radiol., p. 529, Taf. xxxii. figs. 9-11.

_Sphærozoum acuferum_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 54, Taf. viii. fig. 3.

_Thalassicolla acufera_, J. Müller, 1855, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 237.

Spicula of two different kinds, simple needles and quadriradiate; both strong, thorny, covered with small spinules. Simple needles mostly curved, C-shaped. Four shanks of the quadriradiate {47}spicula now straight, now curved, commonly of very different size. (Often one single quadriradiate spiculum is distinguished by its extraordinary size.) For the detailed description of this species compare my Monograph (_loc. cit._).

_Dimensions._--Diameter of the central capsules 0.05 to 0.35, length of the simple needles 0.05 to 0.25, shanks of the quadriradiate spicula 0.05 to 0.15.

_Habitat._--Mediterranean, Messina, Naples, Nice.

4. _Rhaphidozoum arachnoides_, n. sp.

Spicula of two different kinds; one kind simple, needle-like, the other quadriradiate; both very thin and slender, smooth, without spicules. Simple needles curved, C-shaped. Four shanks of the quadriradiate spicula also curved, commonly of nearly equal size. The numerous thread-like spicula of this species are so densely packed around the central capsule, that they extend all around its surface like the network round a balloon.

_Dimensions._--Diameter of the central capsules 0.12 to 0.15, length of the simple needles 0.1 to 0.12, shanks of the quadriradiate spicula 0.06 to 0.08.

_Habitat._--Tropical Atlantic, Station 345, surface.

5. _Rhaphidozoum asperum_, n. sp.

Spicula of two different kinds; one kind simple, needle-shaped, stout, and straight, the other kind hexaradiate; its six shanks about half as long as the former, conical. Both kinds very thorny, covered with short conical spinules.

_Dimensions._--Diameter of the capsules 0.06 to 0.08, length of the simple needles 0.05 to 0.07, shanks of the hexaradiate spicula 0.03 to 0.04.

_Habitat._--South Pacific, Station 288, surface.

Subgenus 2. _Rhaphidoceras_, Haeckel.

_Definition._--Spicula of two different kinds; one kind simple, needle-shaped, the other kind geminate-radiate, with rays on both poles of a middle rod.

6. _Rhaphidozoum neapolitanum_, Haeckel.

_Sphærozoum neapolitanum_, C. Brandt, 1881, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 390, Taf. i. figs. 14, 16-18.

Spicula mixed, of two different kinds; simple needles and geminate-forked. Simple rods, like those of _Belonozoum italicum_, more or less curved, pointed at both ends, smooth (sometimes a little thorny at both ends). Geminate spicula simply forked, like those of _Sphærozoum furcatum_, composed of a short, simple, axial rod, and two simple, smooth, straight shanks on each end of it, commonly somewhat longer than the middle rod. This species, which I have observed myself in Spezzia in great quantity, is quite as variable as all the other species of the genus, and has not more claim to specific rights than the others. Commonly the simple needles are much more numerous {48}than the geminate-forked, but sometimes the contrary is the case. On their variability compare the general remarks on the genus, and the chapter on "Transformation" in the general introduction.

_Dimensions._--Length of the simple spicula 0.05 to 0.1, of the middle rod of the forked spicule 0.05 to 0.08, of their shanks 0.01 to 0.03.

_Habitat._--Mediterranean, Naples, Spezzia, surface.

7. _Rhaphidozoum patagonicum_, n. sp.

Spicula mixed, of two different kinds, simple needles and geminate-triradiate. Simple rods, like those of _Belonozoum spinulosum_, straight, thorny, pointed at both ends. Geminate spicula double-triradiate, like those of _Sphærozoum punctatum_, composed of a simple, short, axial rod and three simple pointed shanks on each end of it. Shanks straight, thorny, with many small spinules, commonly somewhat longer than the middle rod. (Often some of the spicula of both kinds are smooth, not thorny, or not straight, but a little curved, or a few forked or four-radiated geminate spicula are mingled with the others.)

_Dimensions._--Diameter of the central capsules 0.08 to 0.2, length of the simple spicula 0.1 to 0.15, of the geminate 0.08 to 0.16.

_Habitat._--South Pacific, west coast of Patagonia, Station 302, surface.

8. _Rhaphidozoum ascensionis_, n. sp.

Spicula mixed, of two different kinds, simple needles and geminate-triradiate; both kinds thin, smooth, without spinules. Simple needles somewhat curved, C- or S-shaped. Geminate spicula double-triradiate, composed of a simple, short, straight axial rod and three slender curved shanks on each end of it. Shanks two to four times longer than the middle rod. (Sometimes few simple hexaradiate and geminate tetraradiate spicula are mingled.)

_Dimensions._--Diameter of the central capsules 0.12 to 0.15, length of the simple spicula 0.1, of the double-triradiate 0.05 to 0.2.

_Habitat._--South Atlantic, off Ascension Island, Station 342, surface.

9. _Rhaphidozoum capense_, n. sp.

Spicula of two different kinds; one kind simple, needle-shaped, straight, pointed at both ends, the other kind geminate-quadriradiate, with a stout short middle rod and four longer bent shanks on each end of it. Both kinds smooth.

_Dimensions._--Diameter of the capsules 0.2 to 0.25, length of the simple needles 0.01 to 0.3, of the geminate spicula 0.05 to 0.15.

_Habitat._--Cape of Good Hope (Agulhas), Station 142, surface.

10. _Rhaphidozoum australe_, n. sp.

Spicula of two different kinds; one kind simple, needle-shaped, curved, thin; the other kind geminate, with a variable number of shanks on both ends of the shorter middle rod, often {49}different on the two poles of it. The prevalent number of rays on each end is three or four, often also two or five, rarely six. All spicula smooth, more or less bent.

_Dimensions._--Diameter of the capsules 0.1 to 0.2, length of the spicula 0.05 to 0.15.

_Habitat._--South West Pacific, Station 165, surface.

Subgenus 3. _Rhaphidonura_, Haeckel.

_Definition._--Spicula of three different kinds: one kind simple, needle-shaped; the second kind radiate, with three to six shanks radiating from a common central point; the third kind geminate-radiate, with rays on both poles of a middle rod.

11. _Rhaphidozoum polymorphum_, n. sp.

Spicula of three different kinds; simple needles, radiate, and geminate mixed. The simple needles straight and stout. The radiate spicula commonly with three or six, rarely four or five, rays. The geminate-radiate spicula prevalent, with three or four, rarely two or five, shanks on each end of the middle rod. Number very variable. All shanks straight and smooth.

_Dimensions._--Diameter of the capsule 0.1 to 0.2, length of the spicula 0.05 to 0.15.

_Habitat._--South Pacific, Station 295, surface.

12. _Rhaphidozoum pandora_, n. sp. (Pl. 4, fig. 6).

Spicula of three different kinds; simple needles, radiate and geminate mixed. The simple needles thin spindle-shaped, often curved. The radiate spicula commonly with three or four, rarely five or six, curved rays. The geminate-radiate spicula commonly with three or four, rarely two or five, shanks on each end, often different on the two ends of the middle rod. Number and form very variable. All or most of the shanks more or less bent and thorny.

_Dimensions._--Diameter of the capsule 0.1 to 0.3, length of the spicula 0.05 to 0.2.

_Habitat._--South Atlantic (near Ascension Island), Station 343, surface.

----

Order II. SPHÆRELLARIA, Haeckel, 1881.

_Sphærellaria_, Haeckel, 1881, Prodromus, p. 421. _Sphæridea_ vel _Peripylea_, Hertwig, 1879, Organismus der Radiol., p. 133.

_Definition._--SPUMELLARIA with latticed or spongy shell.

The order #Sphærellaria#, the second order of Radiolaria, comprises all those SPUMELLARIA in which the skeleton is a latticed or fenestrated, often more or less spongy, siliceous shell. Originally this shell is a simple extracapsular lattice-sphere, in which the central capsule is included; from this simple ancestral form an enormous {50}mass of different and often very complicated forms is derived; this order is by far the largest, and in morphological respects the most important and most interesting, of all Radiolaria. It contains not less than twenty-eight different families, three hundred and five genera, and more than sixteen hundred species.

In my Monograph (1862) seven families appertaining to this group are described--the Ethmosphærida, Cladococcida, Ommatida, Spongurida, Discida, Lithelida, and Collosphærida. The astonishing increase of this group by the detection of a large series of new and interesting forms, and particularly of important connecting forms between very different branches of it, now enables me to give a much better arrangement. I discern now four suborders or sections of #Sphærellaria#, according to the different geometrical form of the central capsule and of the latticed shell enveloping it. The first of these, and the common ancestral group of the whole order, is the #Sphæroidea#, with spherical capsule; in the #Prunoidea# it becomes ellipsoidal or cylindrical by prolongation of one axis; in the #Discoidea# lenticular or discoidal by shortening of one axis; in the #Larcoidea# lentelliptical, or triaxon-ellipsoid, by different growth of the capsule in three different "dimensive axes."

_Synopsis of the Four Suborders of_ #Sphærellaria#.

Central capsule { Shell a simple sphere or a spherical. { system of concentric spheres, 1. #Sphæroidea#.

Central capsule { Shell a simple ellipsoid or a ellipsoidal or { cylinder with annular cylindrical. { transverse constrictions, 2. #Prunoidea#.

Central capsule lenticular or { Shell a biconvex lens or a discoidal. { flat disk, 3. #Discoidea#.

Central capsule lentelliptical or { Shell a triaxon-ellipsoid, with triaxon. { three different axes, 4. #Larcoidea#.

----

Suborder I. SPHÆROIDEA, Haeckel.

_Sphæroida_, _Sphæridea_, _Sphærida_, Haeckel, 1878, Protistenreich, p. 103. _Sphæridea_, R. Hertwig, 1879, Organismus der Radiol., p. 39.

_Definition._--SPUMELLARIA with spherical central capsule (very rarely somewhat modified, or allomorphous); with spherical fenestrated siliceous shell (often an endospherical polyhedron, very rarely of more modified, subspherical form or allomorphous). Growth of the shell in the three dimensive axes equal.

The suborder #Sphæroidea#, the first and most important of the four of the #Sphærellaria#, comprises those SPUMELLARIA in which the original geometrical {51}spherical form is quite constantly preserved in the central capsule, and commonly also in the fenestrated shell enveloping the latter, although in many forms the sphere is more or less modified; very frequently it is an "endospherical polyhedron," _i.e._, a polyhedron all the angles (or the nodes of the network) of which lie upon the surface of a geometrical sphere; more rarely the spherical form is more or less modified and irregular. In the great majority of #Sphæroidea# there is no external indication of the three dimensive axes; but in many forms they are indicated by the regular position of certain external radial spines or internal radial beams. However, in no case are those three axes expressed in the form of the shell itself and of the enclosed spherical central capsule; this is the main character by which the #Sphæroidea# differ from the following sections:--#Prunoidea#, #Discoidea#, #Larcoidea#, all three of which arise from them.

The section #Sphæroidea#, in the sense here restricted, was founded by me in my Protistenreich (1878, p. 103) and adopted by Hertwig (1879) in his Organismus der Radiolarien (p. 39). The different groups appertaining to this large section were characterised more accurately in my Prodromus (1881, pp. 448-456); there I gave the characters of six subfamilies with thirty tribes, containing ninety-three genera. Formerly, in my Monograph (1862), the #Sphæroidea# were disposed in five different families:--Ethmosphærida, Cladococcida, Ommatida, Spongosphærida, Collosphærida. At that time I could not separate them sufficiently from some ACANTHARIA and PHÆODARIA, which have a similar spherical lattice-shell.

As the number of different genera and species in the #Sphæroidea# is much greater than in all other sections of SPUMELLARIA, many forms were already described by former authors. In the oldest system of Ehrenberg (1847, _loc. cit._, p. 53) they represent one part of his Haliommatina (with four genera, _Haliomma_, _Chilomma_, _Stylosphæra_, _Spongosphæra_). Most species, however, of these genera are #Discoidea#. Also in the latest system of Ehrenberg (1875, _loc. cit._, p. 157) his Haliommatina are a confused conglomeration of different SPUMELLARIA (#Sphæroidea#, #Discoidea#, and #Prunoidea#).

The section #Sphæroidea# is the largest division of #Sphærellaria#, comprising not less than one hundred and seven genera and six hundred and fifty species. This enormous number (easily to be augmented by further investigations) requires a careful disposition in different families and subfamilies. For this disposition two different principles only can be employed: firstly, the number and disposition of the _radial spines_; secondly, the number of the _concentric latticed spheres_, which are connected by radial beams. I give here the preference to the first principle, whilst in my Prodromus (1881) I had preferred the second. The question, which of the two principles is more important for the classification of #Sphæroidea#, is very difficult to answer; probably in many cases the former, in many the latter is more important for their phylogeny.

{52}Regarding the number of the concentric shells which compose the latticed carapace of the #Sphæroidea#, we can distinguish six families, viz.:--

I. Monosphærida (with one single shell). II. Dyosphærida (with two concentric shells). III. Triosphærida (with three concentric shells). IV. Tetrasphærida (with four concentric shells). V. Polysphærida (with five or more concentric shells). VI. Spongosphærida (with spongy shells).

On the other hand, regarding the number of the radial spines and their regular disposition on the shell-surface, we can distinguish five families, viz.:--

I. Liosphærida (without radial spines). II. Stylosphærida (with two radial spines, opposite in one axis). III. Staurosphærida (with four radial spines, opposite in pairs in two axes, perpendicular one to another). IV. Cubosphærida (with six radial spines, opposite in pairs in the three dimensive axes). V. Astrosphærida (with numerous--eight, twelve, twenty, or more--radial spines, often more than a hundred).

All five latter groups contain representatives of all six former groups; therefore we get together not less than thirty different subfamilies of #Sphæroidea#, already enumerated in my Prodromus, 1881, p. 449. I repeat them here to give a better survey of the system there employed.

{53}The #Monosphærida# comprise all those #Sphæroidea# in which the carapace is represented only by one single lattice-shell. Originally this shell is probably everywhere an extracapsular or "cortical shell," which is developed on the outside of the jelly-veil enveloping the central capsule, and serves as a protective carapace for these soft enclosed parts. But with the progress of growth the central capsule becomes larger than the including shell, and sends out through its pores club-shaped prolongations or cæcal-sacs (Pl. 11, figs. 1, 5; Pl. 19, figs. 2, 3, 5; Pl. 20, fig. 1_a_; Pl. 27, fig. 3). These protruded sacs may fuse together again outside the shell and form a spherical bladder, now enveloping the smaller shell; the latter now becomes an intracapsular or "medullary shell."

As #Pliosphærida# (or _Sphæroidea concentrica_) we can oppose to the simple Monosphærida all other #Sphæroidea#, the lattice-shell of which is composed of two or more concentric shells, connected by radial beams. Probably all Pliosphærida (or at least the greater part of them) arise from the Monosphærida by centrifugal growth; two or more radial spines are developed from the surface of the simple lattice-sphere, and are united together by communicating lateral branches, developed at equal distances from the centre; and this same process may be repeated, two, three, four, or more times. In this way originate the characteristic systems of concentric spheres, all united by piercing radial beams which arise from the surface of the innermost sphere (not from its centre). Regarding this mode of growth, we can distinguish the innermost as "original" or "primary" shell, and all subsequent ones as "apposed" or "secondary" shells; if the number of concentric shells amount to three or more, commonly both innermost shells lie within the central capsule and are medullary shells, whilst all others lie outside it and are therefore cortical shells. This difference can be commonly recognised also in the isolated shell, without its central capsule; the distance between the cortical and the medullary shells being commonly much larger than the distance between the two medullary shells.

The #Dyosphærida#, or the #Sphæroidea# with two concentric shells, are the most numerous among the Pliosphærida. Commonly in this group the inner or primary shell lies within the central capsule as a true "medullary shell," whilst the outer lies outside it as a "cortical shell"; therefore the radial beams, connecting both, pierce the wall of the capsule. But in several forms, mainly in the peculiar group of Diplosphærida, both concentric shells remain outside the central capsule, and both are therefore "cortical shells."

The #Triosphærida#, or the #Sphæroidea# with three concentric shells, are also very rich in different forms, though not so numerous by far as the Dyosphærida. Commonly in the Triosphærida both inner shells lie within the central capsule as "medullary shells," whilst the third lies outside it as a "cortical shell"; therefore the central capsule remains intermediate in size between the outer and the middle shell. But in some genera (_e.g._, _Rhodosphæra_) both outer shells are cortical and only the {54}innermost is a medullary shell. In this case the size of the capsule remains intermediate between the inner and the middle shell.

The #Tetrasphærida#, or the #Sphæroidea# with four concentric shells, are in general not frequent, and not rich in different forms. In most of the observed species two inner shells are medullary, two outer cortical shells, the former within, the latter without, the central capsule; and the wall of the capsule, pierced by the connecting radial beams, lies between the two middle shells. But there are some Tetrasphærida in which all four shells seem to be external or cortical shells.

The #Polysphærida#, or the #Sphæroidea# with five or more concentric shells, seem of course to offer the greatest possibility for the development of very different forms; but in reality this group is the poorest and smallest of all; and only one part of it, the Arachnosphærida, is rather common. In this peculiar division the shell is composed of five to ten or more, very delicate, cobweb-like concentric shells, which are connected by radial beams; all are cortical shells, and lie outside the central capsule. Much more rare are those Polysphærida, in which both innermost shells, as true medullary shells, lie within the central capsule, all others being outside it. The total number of concentric shells in this group is commonly between five and ten, rarely more.

The #Spongosphærida# are distinguished from all other #Sphæroidea# by the spongy structure of the spherical shell, which is composed wholly or partially of an irregular spongy framework. The relation of this group to the other groups of #Sphæroidea# is probably rather complicated, for in some Spongosphærida the whole shell is composed of massive spongy reticulation, whilst in others it contains a spherical central cavity, and in a third group this cavity is filled up by one or two concentric lattice-shells, connected by radial beams. Many of these Spongosphærida are very common, and of considerable size.

The #Collosphærida# form a peculiar separate group of #Sphæroidea#, distinguished from all others by their social life or aggregation in colonies (coenobia). They represent the only group of #Sphærellaria# in which this association of numerous individual capsules or cells is realised. The shell is almost constantly simple, without regularly disposed radial spines; therefore they may be called "social Monosphærida," or better "polyzoic Ethmosphærida." Only in one small group (Clathrosphærida) the shell, enveloping every central capsule, is double or surrounded by an external mantle; these may be compared to the Diplosphærida (or better to a part of the Carposphærida, _Liosphæra_, p. 76). In most of the Collosphærida the lattice-shell is more or less irregular in form and structure.

_The Lattice Work_ of the fenestrated shells is in the #Sphæroidea# of the greatest variability, and its innumerable modifications serve mainly for the distinction of species. In general we can distinguish as the most important modifications a _regular_ network (with equal size, form, and distance of the pores or meshes) and an _irregular_ network (with {55}differences in the size, form, or distance of the meshes or pores). In both groups the pores may be either angular or round; so that there may exist together four different main forms of network--(A) regular lattice with equal hexagonal pores; (B) regular lattice with equal circular pores; (C) irregular lattice with unequal polygonal pores; (D) irregular lattice with unequal roundish pores. Besides these modifications, the pores may be prolonged into tubules which are directed radially towards the outside (rarely towards the inside) of the sphere. In other cases they are surrounded by elevated or honeycomb-like frames.

_The Radial Spines_ exhibit in the #Sphæroidea# the greatest variety in form, size, disposition, &c., and their numerous modifications serve mainly for the distinction of genera, their peculiar formation and size also for the distinction of species. In general we may distinguish as the most important modifications primary and secondary spines. The primary spines or "main spines" are commonly direct outward prolongations of the internal radial beams, connecting the concentric shells. The secondary or "by-spines" arise only from the surface of the lattice-shell, without reference to the internal beams. The by-spines are commonly smaller, and much more numerous than the main spines. Regarding the form, the radial spines are either roundish (cylindrical or conical, often also club-shaped, rarely spindle-shaped) or angular (commonly three-sided, prismatic or pyramidal). The spines are constantly solid, never hollow; the "internal canals," described by some authors, are only microscopic views of the transparent edges. In many cases the spines are branched or forked. The most important difference in the variable shape of the spines is their regular or irregular number and disposition, which afford characters for the distinction of our five families.

_The Three Dimensive Axes_--or the three diameters of the sphere, perpendicular one to another--are in the great majority of the #Sphæroidea# significant in the promorphological consideration of the body, and are indicated either by the position of the external radial spines, or at least of the internal radial beams, connecting the concentric spheres. Commonly two radial spines are placed opposite in each axis. The most perfect group in this respect seems to be that of the Cubosphærida, in which the three axes are represented by three pairs of spines. Next come the Staurosphærida, in which two axes in cross-form are exhibited by two pairs of spines. The most simple group are the Stylosphærida, in which only one pair of spines is developed, indicating one single axis. These three families form together a continuous natural series,--the #Sphæroidea# with real dimensive axes,--and exhibit at the same time relations to the three other suborders of #Sphærellaria#, the #Larcoidea#, #Discoidea#, and #Prunoidea# respectively. At both ends of this series stand two other families, on one side the Liosphærida, without any radial spines on the surface of the sphere, on the other side the Astrosphærida, in which the radial spines are developed in great and variable numbers, at least eight to twelve, commonly twenty to forty, often more than a hundred or even a thousand.

{56}The #Liosphærida# comprise all those #Sphæroidea# in which the surface of the shell is smooth, without radial spines (Pls. 12, 20). The simplest of these are the Ethmosphærida, with one single lattice-shell, enveloping the spherical central capsule. _Cenosphæra_, the most simple form of the Ethmosphærida, may be regarded as the common ancestral form of all #Sphæroidea#, in an ontogenetical as well as in a phylogenetical and morphological sense. From this simple lattice sphere all other #Sphæroidea# can be derived either by radial or by tangential growth. If the radial beams, arising from the surface of the simple fenestrated sphere, become connected (at equal distances from the centre) by tangential beams, we get the compound shells of the "Liosphærida concentrica" (with two, three, four, or more concentric spheres). The radial beams connecting these exhibit in many Liosphærida the same regular disposition and number as the external radial spines in the Astrosphærida. Perhaps these forms in a "natural system" would be better united (_e.g._, Liosphærida with twelve or twenty internal radial beams, and Astrosphærida with twelve or twenty external radial spines); but in many cases (mainly for higher numbers) the certain determination of their number and disposition is very difficult or quite impossible.

The #Cubosphærida# (Pls. 21-25) represent the large and very important family of #Sphæroidea#, in which all three dimensive axes are equally distinguished by pairs of spines, corresponding to three axes of a cube or of a regular octahedron, agreeing therefore also with the three axes of the cubic or regular crystalline system. In the majority of the Cubosphærida the six radial spines are accurately opposite each other in pairs in three axes, perpendicular one to another, and commonly they are of equal size and form; but in some genera the three pairs of spines become differentiated, whilst both spines of each pair remain equal. Either one pair is larger than the two others (which are equal), corresponding to the axes of the quadratic crystalline system; or all three pairs are different (corresponding to the three unequal axes of the rhombic crystalline system); the former nearer to the #Discoidea#, the latter to the #Larcoidea#. We may suppose with some probability, that the Cubosphærida are for the most part the common ancestral group of those #Sphæroidea#, in which a certain number of radial spines or beams is disposed in a regular order; the Staurosphærida may be derived from them by loss of one pair of spines, the Stylosphærida by loss of two pairs of spines, and most Astrosphærida by multiplying the radial spines, six to fourteen or more secondary spines being added to the six primary "dimensive spines." However, in many Astrosphærida (_e.g._, in those with eight spines, _Centrocubus_, _Octodendron_, &c.) the regular geometrical disposition of the radial spines seems to follow another mathematical order, quite independent of the Cubosphærida.

The #Staurosphærida# (Pl. 15) are distinguished by the possession of four radial spines, opposite in pairs in two axes, perpendicular one to another. This rectangular cross determines a certain plane, the "equatorial plane," and this brings the Staurosphærida near {57}to the #Discoidea#, mainly to those which also bear on the periphery of the circular equatorial plane four crossed spines (such as _Staurodisculus_, _Stethostaurus_, _Staurodictya_, &c.). But in these cruciform #Discoidea# the shell and the enclosed central capsule are discoidal or lenticular, whilst in the Staurosphærida they remain spherical. Commonly the cross is quite regular, with four right angles and four equal beams; but often also it becomes more or less irregular. In some genera one pair of equal opposite spines is larger than the other pair. These forms represent the three different axes of the rhombic crystal system, whilst the common regular Staurosphærida represent those of the quadratic crystal system. The latter can be derived from the Cubosphærida (representing the regular crystal system) by reduction of one axis and loss of its pair of spines. In general the number of species (and particularly of the individuals) is much smaller in the Staurosphærida than in all other families of #Sphæroidea#.

The #Stylosphærida# (Pls. 13-17) can be derived from the Cubosphærida by reduction of two dimensive axes and loss of two pairs of spines. Therefore, here one pair of spines only is developed, opposite in one single axis. This "monaxonial" form brings the Stylosphærida very near to the ellipsoidal #Prunoidea# (mainly to many two-spined forms of Ellipsida and Druppulida); but they differ from these by the spherical (not ellipsoidal) form of the central capsule and of the enclosing lattice-shell. In the greater part of the Stylosphærida both spines are of equal size and form, accurately opposite in the "main axis." But in many forms both spines become unequal in size or form, often very different. More rarely they are not accurately opposed, but placed in two different axes, intersecting at a small variable angle. The small group of Saturnalida presents a very remarkable and peculiar structure, in which both spines (at equal distances from the centre) are united by a circular or elliptical ring (Pl. 13, figs. 15, 16; Pl. 16, figs. 16, 17).

The #Astrosphærida# are distinguished from the other #Sphæroidea# by the great and variable number of their external radial spines (Pls. 11, 18-20, 26-30). Commonly this number amounts to from twelve to twenty, rarely to only eight to ten, very often to thirty-two to forty or more; in many species more than one hundred are present. As already mentioned above, it would be important to distinguish between primary spines (as outer prolongations of the inner radial beams) and secondary spines (developed from the surface of the shell), but in many cases this distinction is difficult or impossible. More practical is the distinction between larger "main spines" and smaller "by-spines." The size and form of the radial spines is extremely variable. Much more important is their number and disposition. In general we can here distinguish the following different cases:--(A) radial spines are developed from all the nodal points of the network on the shell surface; (B) the number of the spines is smaller than that of the nodal points, but they are irregularly scattered; (C) the radial spines exhibit a limited number and a certain regular disposition. In this latter case the following modes of distribution seem to be the most important:--(_a_) eight spines placed in the four diagonal axes of the {58}regular cube (Pl. 18, figs. 1-3); (_b_) twelve spines (placed in the corner axes of the regular icosahedron); (_c_) fourteen spines (six placed in the three dimensive axes of the regular octahedron, eight in the centres of its eight faces); (_d_) twenty spines (placed either in the same order as in many #Larcoidea# and ACANTHARIA [?], or in the twenty corners of the regular dodecahedron); (_e_) thirty-two spines (twelve placed in the twelve corners of the regular icosahedron, twenty in the centre of its triangular faces). Besides these most important and quite geometrical modes of disposition there also seem to occur in the Astrosphærida the following subregular (or symmetrical?) modes: 9, 10, 16, 18, 24, 40, 60, 80. But it is very difficult to give a correct account of these modes. In every case this manifold and regular disposition of the radial spines is of the highest interest for the study of general "Promorphology."

_The Central Capsule_ is in all #Sphæroidea# (without any exception) a perfect sphere in the geometrical sense, even in those forms in which the enclosing lattice-shell is more or less irregular (_i.e._, many Collosphærida). This is the most important character, which separates the #Sphæroidea# from all other #Sphærellaria#. For in the #Prunoidea# the capsule is ellipsoidal, with one prolonged axis; in the #Discoidea# lenticular, with one shortened axis; in the #Larcoidea# lentelliptical, with three different dimensive axes. The central capsule is originally always enclosed by the lattice-shell; but in many cases with increasing growth this relation becomes inverted; the capsule sending out many club-shaped blind sacs through the meshes of the lattice-shell, and these melting together outside the latter, a new membrane is formed, enclosing a "medullary shell."

_The Nucleus_ of the cell exhibits a very different shape in the solitary and the social #Sphæroidea#. In the solitary or monozoic #Sphæroidea# the centre of the central capsule is occupied by a large spherical concentric nucleus, with or without nucleoli; also this nucleus is originally always within the innermost lattice-shell, but with increasing size may overgrow and enclose it. A short time before the formation of the vibratile spores the central nucleus becomes resolved into many small nuclei. In the social or polyzoic #Sphæroidea#--the Collosphærida--commonly the simple central nucleus very early (a long time before the formation of the spores) is divided into a great number of small nuclei, whilst the centre of the capsule becomes filled with a large oil-globule. Therefore we find the same difference between the solitary and social forms in the #Sphæroidea# as in the #Colloidea#. Here also the calymma, or the jelly-mantle, enveloping the central capsule, is in the social forms very large and voluminous, differentiated into alveoles, whilst in the solitary forms it is much smaller, without alveoles.

{59}_Synopsis of the Families of_ #Sphæroidea#.

{ A. Liosphærida { Spherical shell { monozoa. { commonly { Single cells { quite regular, { (each with shell) { simple, or Surface of { living solitary. { composed of the spherical { { two or more shell smooth, { { concentric rough, or { { spheres, 5. LIOSPHÆRIDA. thorny, but { not armed { B. Liosphærida { Spherical shell with radial { polyzoa. { commonly spines. { Aggregated cells { more or less { (each with { irregular, { shell) living { simple (rarely { in colonies. { composed of { { two concentric { { spheres), 6. COLLOSPHÆRIDA.

Surface of { Two radial main-spines, opposite in the spherical { one axis of the shell 7. STYLOSPHÆRIDA. shell armed { with two, { Four radial main-spines, opposite in four, or six { pairs in two dimensive axes, radial main { perpendicular one to another, 8. STAUROSPHÆRIDA. spines, { opposite in { Six radial main-spines, opposite in pairs in one, { pairs in three dimensive two, or three { axes (perpendicular one to dimensive { another), 9. CUBOSPHÆRIDA. axes (always { solitary). {

Surface of the spherical shell covered with numerous (commonly irregularly disposed) radial spines, often also twelve to twenty, more or less regularly disposed, 10. ASTROSPHÆRIDA.

Family V. #LIOSPHÆRIDA#, Haeckel, 1881.

_Liosphærida_, Haeckel, 1881, Prodromus, p. 449.

_Definition._--#Sphæroidea# without radial spines on the surface of the spherical shell; living solitary (not associated in colonies).

The family #Liosphærida# comprises all those solitary #Sphæroidea# in which the surface of the spherical shell is not armed with radial spines. Nearly the half of this large group is formed by the Ethmosphærida, in which the carapace is a quite simple, spherical lattice-shell; this subfamily is probably the common ancestral group from which all other #Sphæroidea#, or even all #Sphærellaria#, can be derived in a phylogenetical as well as in a morphological sense. The central capsule in this first subfamily is constantly enclosed by the fenestrated shell, and separated from it by the jelly-veil. The shell is therefore an extracapsular or medullary shell.

To these simple Ethmosphærida all other subfamilies can be opposed as "Liosphærida concentrica," as their carapace is composed of two or more concentric lattice-shells; two in the Carposphærida, three in the Thecosphærida, four in the Cromyosphærida, five or more in the Caryosphærida. In all these four subfamilies the concentric shells are simple (not spongy) fenestrated shells. In a sixth subfamily, in the Plegmosphærida, the shell is wholly or partially composed of spongy wicker-work, with or without a latticed medullary shell in the centre.

The internal radial beams, in the "Liosphærida composita" connecting the concentric spheres, exhibit in their number and disposition similar important differences, such as the external radial spines in the Astrosphærida. The following eight {60}different cases of regular disposition were observed:--(A) two opposite beams in one axis; (B) four beams, opposite in pairs in two axes perpendicular one to another; (C) six beams, opposite in pairs in the three dimensive axes; (D) eight beams, opposite in pairs in the four diagonals of the regular cube; (E) twelve beams corresponding to the twelve axes of the regular icosahedron; (F) fourteen beams quite regularly disposed (six corresponding to the three axes of the regular octahedron, eight to the central points of its faces); (G) twenty beams (probably corresponding to the twenty corners of a regular dodecahedron); (H) thirty-two beams, regularly disposed. Rarely the number of the radial beams is intermediate between these eight cases, and rarely it is higher; then commonly the disposition is irregular. The regularity of their disposition in the great majority of cases is very remarkable and evident.

_Synopsis of the Genera of Liosphærida._

------------------------------------------------------------------------- I. Subfamily Ethmosphærida. (Shell one single latticed sphere.) ------------------------------------------------------------------------- {Shell cavity { simple, 15. _Cenosphæra_. Pores of the { shell simple, {Shell cavity not prolonged { with radial into free tubuli. { beams united { in the { centre, 16. _Stigmosphæra_.

Pores prolonged {Tubuli external, into free { centrifugal, 17. _Ethmosphæra_. conical or { cylindrical {Tubuli internal, tubuli. { centripetal, 18. _Sethosphæra_. ------------------------------------------------------------------------- II. Subfamily Carposphærida. (Two concentric spheres.) ------------------------------------------------------------------------- One shell medullary (intracapsular), the other cortical (extracapsular), 19. _Carposphæra_.

Both shells cortical (near together), 20. _Liosphæra_. ------------------------------------------------------------------------- III. Subfamily Thecosphærida. (Three concentric spheres.) ------------------------------------------------------------------------- Two shells medullary (intracapsular), one shell cortical (extracapsular), 21. _Thecosphæra_.

One shell medullary (intracapsular), two shells cortical (extracapsular), 22. _Rhodosphæra_. ------------------------------------------------------------------------- IV. Subfamily Cromyosphærida. (Four concentric spheres.) ------------------------------------------------------------------------- Two inner medullary shells (intracapsular), and two outer cortical shells (extracapsular), 23. _Cromyosphæra_. ------------------------------------------------------------------------- V. Subfamily Caryosphærida. (Five or more concentric spheres.) ------------------------------------------------------------------------- Two inner medullary shells, and three or more outer cortical shells, 24. _Caryosphæra_. ------------------------------------------------------------------------- VI. Subfamily Plegmosphærida. (Spherical shell wholly or partially of spongy structure.) ------------------------------------------------------------------------- Spongy sphere {Sphere solid, 25. _Styptosphæra_. without latticed { medullary shell {Sphere with a in the centre. { central cavity, 26. _Plegmosphæra_.

Spongy sphere with {One single one or two { medullary shell, 27. _Spongoplegma_. latticed { medullary shells {Two concentric in the centre. { medullary { shells, 28. _Spongodictyon_.

{61}Subfamily ETHMOSPHÆRIDA,[25] Haeckel, 1862, Monogr. d. Radiol., p. 348 (_sensu restricto_).

_Definition._--#Liosphærida# with one single spherical lattice-shell; living solitary, not aggregated in colonies.

Genus 15. _Cenosphæra_,[26] Ehrenberg, 1854, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 237.

_Definition._--#Liosphærida# with one single latticed sphere, with simple shell-pores (not prolonged into free tubuli) and with simple shell-cavity (without internal radial beams).

The genus _Cenosphæra_ is the most simple form of all SPHÆROIDEA, and may be regarded as the common ancestral form of this order. The siliceous latticed shell, in which the central capsule is enclosed, represents a simple regular sphere, with simple cavity. The pores of the shell-wall are simple, not prolonged into radial tubuli (as in _Ethmosphæra_ and _Sethosphæra_). According to the different form of the pores, the numerous species of this genus can be disposed in four different subgenera. Some species may be easily confounded with isolated shells of the corresponding social _Collosphæra_; but in this latter the spherical shell-form is commonly more or less irregular, in _Cenosphæra_ quite regular.

Subgenus 1. _Phormosphæra_, Haeckel, 1881, Prodromus, p. 448.

_Definition._--Pores of the shell regular or subregular, hexagonal or circular, with hexagonal frames or lobes; all nearly of equal size and form.

1. _Cenosphæra primordialis_, n. sp.

Shell very thin walled, smooth. Pores hexagonal, regular, or subregular; twelve to fifteen on the half meridian of the shell; bars between them extremely delicate (only visible when three hundred or four hundred times enlarged). Diameter of the shell nine to ten times that of the meshes. This species is remarkable for the extreme delicacy of the arachnoidal network of the simple spherical shell; it may be regarded as the common ancestral form of all #Sphæroidea#. The shell equals that of _Heliosphæra tenuissima_ (figured in my Monograph, 1862, pl. ix. fig. 2), but differs from it by the smooth surface and the absence of all spines or thorns. I observed this species living in the Indian Ocean, near Ceylon, in 1882; the spherical diameter of the central capsule is about one-third of that of the shell; the contents of the central capsule are colourless {62}and transparent, except the central dark globular nucleus. The same shells also occur in some mounted preparations of surface organisms from the Challenger.

_Dimensions._--Diameter of the shell 0.12, of the pores 0.012.

_Habitat._--Indian Ocean, Ceylon, Haeckel; Central Pacific, Stations 266, 271, surface.

2. _Cenosphæra inermis_, Haeckel.

_Heliosphæra inermis_, Haeckel, 1862, Monogr. d. Radiol., p. 351, Taf. ix. fig. 1.

Surface of the thin-walled shell smooth. Pores regular, hexagonal, twelve to fifteen times as broad as the bars, seven to nine on the quadrant.

_Dimensions._--Diameter of the shell 0.08 to 0.12, pores 0.012 to 0.015, bars 0.001.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface.

3. _Cenosphæra hexagonalis_, n. sp.

Surface of the thick-walled shell smooth. Pores regular, hexagonal, five to six times as broad as the bars, six to eight on the quadrant.

_Dimensions._--Diameter of the shell 0.1 to 0.15, pores 0.01 to 0.012, bars 0.002.

_Habitat._--Central Pacific, Stations 265 to 274, at various depths.

4. _Cenosphæra mellifica_, n. sp. (Pl. 12, fig. 9).

Surface of the thick-walled shell smooth. Pores regular, circular, with thin hexagonal frames, four times as broad as the bars, six to eight on the quadrant.

_Dimensions._--Diameter of the shell 0.2, pores 0.12, bars 0.003.

_Habitat._--South Pacific, Station 288, surface.

5. _Cenosphæra favosa_, n. sp. (Pl. 12, fig. 10).

Surface of the thick-walled shell rough. Pores regular, circular, with thin hexagonal frames, three times as broad as the bars, ten to twelve on the quadrant.

_Dimensions._--Diameter of the shell 0.2, pores 0.09, bars 0.003.

_Habitat._--North Atlantic, Færöe Channel (Gulf Stream), John Murray, surface.

6. _Cenosphæra vesparia_, n. sp. (Pl. 12, fig. 11).

Surface of the thick-walled shell smooth. Pores regular, circular, with thick hexagonal frames, twice as broad as the bars, ten to twelve on the quadrant.

_Dimensions._--Diameter of the shell 0.25, pores 0.016, bars 0.008.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms, and surface.

{63}7. _Cenosphæra bombus_, n. sp.

Shell thick walled, rough. Pores regular, circular, with thin hexagonal frames, of the same breadth as the bars, twenty to twenty-two on the quadrant.

_Dimensions._--Diameter of the shell 0.3, pores and bars 0.005.

_Habitat._--Tropical Atlantic, Station 347, depth 2250 fathoms.

8. _Cenosphæra melecta_, n. sp.

Shell thick walled, papillate. Pores regular, circular, double-edged, with thick hexagonal frames, of the same breadth as the bars; a short conical papilla in the corner of each hexagon; fourteen to sixteen pores on the quadrant.

_Dimensions._--Diameter of the shell 0.2, pores and bars 0.008.

_Habitat._--Fossil in Barbados.

9. _Cenosphæra anthophora_, n. sp.

Shell thick walled, papillate. Pores regular, circular, with an elegant six-lobed frame and a coronal of six short papillæ; the latter alternating with the six lobes (quite as in Pl. 28, fig. 1_b_). Pores twice as broad as the bars, ten to twelve on the quadrant.

_Dimensions._--Diameter of the shell 0.13, pores 0.01, bars 0.005.

_Habitat._--Central Pacific, Station 271, surface.

10. _Cenosphæra rosetta_, n. sp.

Shell thin walled, smooth. Pores regular, circular, with an elegant six-lobed outer opening, without papillæ. Pores of the same breadth as the bars, six to eight on the quadrant.

_Dimensions._--Diameter of the shell 0.1, pores and bars 0.006.

_Habitat._--South Atlantic, Station 323, depth 1900 fathoms.

Subgenus 2. _Circosphæra_, Haeckel.

_Definition._--Pores of the spherical shell regular or subregular, circular, without hexagonal frames or lobes, all nearly of equal size and form.

11. _Cenosphæra porophæna_, Ehrenberg.

_Cenosphæra porophæna_, Ehrenberg, 1858, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 31.

Shell thin walled, smooth. Pores regular, circular, six to eight times as broad as the bars, five to six on the quadrant.

_Dimensions._--Diameter of the shell 0.1, pores 0.012, bars 0.002.

_Habitat._--Mediterranean (Crete, depth 1100 fathoms; Corfu, surface).

{64}12. _Cenosphæra setosa_, Ehrenberg.

_Cenosphæra setosa_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 287, Taf. vii. fig. 1.

Shell thin walled, covered with very short and numerous bristles. Pores regular, circular, five to six times as broad as the bars, six to eight on the quadrant.

_Dimensions._--Diameter of the shell 0.17, pores 0.2, bars 0.03.

_Habitat._--West Tropical Pacific, 3300 fathoms; Philippine Sea, Station 200, depth 250 fathoms.

13. _Cenosphæra plutonis_, Ehrenberg.

_Cenosphæra plutonis_, Ehrenberg, 1854, Mikrogeol., Taf. xxxv. B, B. iv. fig. 20.

Shell thin walled, covered with short conical papillæ. Pores regular, circular, twice as broad as the bars, eight to nine on the quadrant.

_Dimensions._--Diameter of the shell 0.09, pores 0.006, bars 0.003.

_Habitat._--North Atlantic, Station 353, depth 2965 fathoms.

14. _Cenosphæra proserpinæ_, n. sp.

Shell thin walled, smooth. Pores regular, circular, four times as broad as the bars, five to six on the quadrant.

_Dimensions._--Diameter of the shell 0.08, pores 0.008, bars 0.002.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

15. _Cenosphæra eridani_, n. sp.

Shell thin walled, smooth. Pores regular, circular, three times as broad as the bars, eleven to twelve on the quadrant.

_Dimensions._--Diameter of the shell 0.16, pores 0.01, bars 0.003.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

16. _Cenosphæra lethe_, n. sp.

Shell thick walled, smooth. Pores regular, circular, double-edged, five times as broad as the bars, sixteen to eighteen on the quadrant.

_Dimensions._--Diameter of the shell 0.25, pores 0.01, bars 0.002.

_Habitat._--North Atlantic, Station 64, depth 2700 fathoms.

17. _Cenosphæra elysia_, n. sp. (Pl. 12, fig. 8).

Shell thick walled, rough. Pores regular, circular, double-edged, twice as broad as the bars, twelve to fourteen on the quadrant.

_Dimensions._--Diameter of the shell 0.2, pores 0.01, bars 0.005.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

{65}18. _Cenosphæra nirwana_, n. sp.

Shell thick walled, smooth. Pores regular, circular, twice as broad as the bars, twenty-four to twenty-five on the quadrant.

_Dimensions._--Diameter of the shell 0.25, pores 0.004, bars 0.002.

_Habitat._--Indian Ocean, Belligemma, Ceylon, surface; Haeckel.

19. _Cenosphæra maxima_, n. sp.

Shell thick walled, smooth. Pores regular, circular, twice as broad as the bars, thirty to thirty-three on the quadrant.

_Dimensions._--Diameter of the shell 0.3 to 0.4, pores 0.012, bars 0.006.

_Habitat._--West Tropical Pacific, Station 225, depth 4475; also fossil in Barbados.

20. _Cenosphæra compacta_, n. sp. (Pl. 12, fig. 7).

Shell very thick walled, rough (its wall one-fourth to one-third as thick as the radius). Pores subregular, circular, of the same breadth as the bars, seven to eight on the quadrant.

_Dimensions._--Diameter of the shell 0.15, pores and bars 0.012.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

_Cenosphæra radiata_, Zittel, 1876 (L. N. 29, p. 84, Taf. ii. figs. 7, 8), a fossil Cretaceous species, is closely allied to _Cenosphæra compacta_.

21. _Cenosphæra crassa_, n. sp.

Shell very thick walled, rough (its wall nearly half as thick as the radius). Pores tubular, double-edged, regular, circular, ten times as broad as the thin united bars, twelve to fourteen on the quadrant.

_Dimensions._--Diameter of the shell 0.14, pores 0.01, bars 0.001.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

22. _Cenosphæra solida_, n. sp.

Shell very thick walled, covered with innumerable short bristles (its wall one-third as thick as the radius). Pores regular, circular, four times as broad as the bars, tubular, eight to ten on the quadrant.

_Dimensions._--Diameter of the shell 0.2, pores 0.02, bars 0.005.

_Habitat._--Antarctic Ocean, Station 157, depth 1950 fathoms.

Subgenus 3. _Cyrtidosphæra_, Haeckel, 1862, Monogr. d. Radiol., p. 348.

_Definition._--Pores of the spherical shell irregularly polygonal, of unequal size or form, sometimes roundish with polygonal frames.

{66}23. _Cenosphæra reticulata_, Haeckel.

_Cyrtidosphæra reticulata_, Haeckel, 1862, Monogr. d. Radiol., p. 349, Taf. xi. fig. 2.

Shell very thin walled, smooth. Pores irregular, polygonal, two to eight times as broad as the bars, fifteen to twenty on the quadrant (groups of four to eight smaller meshes are scattered on the surface, and separated by reticular rows of larger meshes).

_Dimensions._--Diameter of the shell 0.16, pores 0.004 to 0.016, bars 0.002.

_Habitat._--Mediterranean (Messina), surface.

24. _Cenosphæra tenerrima_, n. sp.

Shell extremely thin walled, smooth, like a cobweb. Pores very irregular and small, polygonal with thread-like bars, thirty to forty on the quadrant.

_Dimensions._--Diameter of the shell 0.25, pores 0.002 to 0.008, bars under 0.001.

_Habitat._--Central Pacific, Station 271, surface.

25. _Cenosphæra polygonalis_, n. sp.

Shell thin walled, smooth, with irregular, polygonal pores, three to four times as broad as the bars, eight to ten on the quadrant.

_Dimensions._--Diameter of the shell 0.2, pores 0.012 to 0.02, bars 0.005.

_Habitat._--North Pacific, Station 236, surface.

26. _Cenosphæra papillata_, n. sp.

Shell thick walled, covered with short conical papillæ. Pores irregular, polygonal, three to five times as broad as the bars, fourteen to sixteen on the quadrant.

_Dimensions._--Diameter of the shell 0.12, pores 0.004 to 0.007, bars 0.0015.

_Habitat._--South Atlantic, Station 325, surface.

27. _Cenosphæra cristata_, n. sp.

Shell thick walled, rough. Pores irregular, roundish, surrounded by polygonal crested frames two to three times as broad as the bars, eight to twelve on the quadrant.

_Dimensions._--Diameter of the shell 0.16, pores 0.006 to 0.01, bars 0.003.

_Habitat._--North Pacific, Station 254, surface.

28. _Cenosphæra perforata_, n. sp. (Pl. 26, fig. 10).

_Ceriosphæra perforata_, Haeckel, 1881, Prodromus et Atlas, _loc. cit._

Shell thick walled, rough. Pores irregular, roundish, surrounded by high polygonal funnel-shaped frames, which are solid in the inner half, perforated by numerous very small pores in the {67}outer half, sieve-shaped. Pores one to three times as broad as the bars, of very different size, four to six on the quadrant.

_Dimensions._--Diameter of the shell 0.15, pores 0.01 to 0.02, bars 0.005 to 0.01.

_Habitat._--Tropical Atlantic, Station 347, depth 2250 fathoms.

29. _Cenosphæra coronata_, n. sp. (Pl. 26, fig. 11).

Shell thick walled, rough. Pores irregular, roundish, surrounded by high polygonal frames bearing on their sharp crest a series of small papillæ, so that each pore is surrounded by a coronal of such spinules. Pores four to eight times as broad as the bars, four to five on the quadrant.

_Dimensions._--Diameter of the shell 0.15, pores 0.01 to 0.03, bars 0.002 to 0.008.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

Subgenus 4. _Porosphæra_, Haeckel.

_Definition._--Pores of the spherical shell irregular, roundish, without polygonal frames, of unequal size or form.

30. _Cenosphæra antiqua_, Haeckel.

_Cenosphæra plutonis_, var., Dunikowski, 1882, Denkschr. d. k. Akad. d. Wiss. Wien, Bd. xlv. p. 25, Taf. iv. figs. 47, 48.

_Cenosphæra plutonis_, var., Stöhr, 1880, Palæontogr. xxvi. p. 85, Taf. i. fig. 1.

Shell thin walled, smooth. Pores irregular, roundish, two to eight times as broad as the bars, ten to fifteen on the quadrant.

_Dimensions._--Diameter of the shell 0.15 to 0.2, pores 0.007 to 0.015, bars 0.002 to 0.008.

_Habitat._--Fossil in the Jurassic, Cretaceous, and Tertiary formations; living in the depths of the Atlantic and Pacific; Station 332, depth 2200 fathoms; Station 225, depth 4475 fathoms, &c.

31. _Cenosphæra gigantea_, n. sp.

Shell thick walled, smooth. Pores irregular, roundish, two to five times as broad as the bars, thirty to forty on the quadrant.

_Dimensions._--Diameter of the shell 0.4 to 0.5, pores 0.004 to 0.01, bars 0.002.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms; also fossil in Barbados.

32. _Cenosphæra marginata_, n. sp.

Shell very thick walled, smooth. Pores irregular, roundish, double-edged, three to eight times as broad as the bars, six to eight on the quadrant.

{68}_Dimensions._--Diameter of the shell 0.12, pores 0.01 to 0.03, bars 0.004.

_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.

33. _Cenosphæra aspera_, Stöhr.

_Cenosphæra aspera_, Stöhr, 1880, Palæontogr. Bd. xxvi. p. 85, Taf. i. fig. 2.

Shell thick walled, rough, covered with short conical papillæ. Pores irregular, roundish, of about the same breadth as the bars, eight to twelve on the quadrant.

_Dimensions._--Diameter of the shell 0.17, pores and bars 0.01 to 0.04.

_Habitat._--Fossil in Tertiary rocks of Sicily; Grotte, Stöhr.

34. _Cenosphæra hirsuta_, Ehrenberg.

_Cenosphæra hirsuta_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss., Berlin, p. 287, Taf. x. fig. 18.

Shell thin walled, rough, covered with innumerable very short bristles. Pores very irregular, roundish, of about the same breadth as the bars.

_Dimensions._--Diameter of the shell 0.11, pores and bars 0.002 to 0.012.

_Habitat._--Indian Ocean, Zanzibar, Pullen; depth 2200 fathoms.

Genus 16. _Stigmosphæra_,[27] Haeckel, n. gen.

_Definition._--#Liosphærida# with one single latticed sphere, with simple shell-pores (not prolonged into free tubuli); in the central point of the spherical shell-cavity are united a number of radial beams, which become forked and inserted into the inner surface of the shell by their distal ends.

The genus _Stigmosphæra_ differs from _Cenosphæra_ (and from all other Monosphærida) by internal radial beams, which are united in the centre of the simple spherical shell; these beams are branched, and the distal ends of the branches inserted on the internal surface of the shell. I have observed only two, nearly identical specimens of this genus, both with regular, hexagonal pores and thin bars; the beams were implanted in the corners of the hexagons. In one specimen the surface was covered with short radial bristles, whilst these in the other specimen were prolonged into radial spines (like _Acanthosphæra_). Possibly this peculiar genus is derived from _Carposphæra_, by reduction and loss of a central medullary shell.

_Stigmosphæra actinocentra_, n. sp.

Shell very thin walled, rough, with regular circular, hexagonally framed pores, six times as broad as the bars, eight to ten on the quadrant; in the corner of each hexagon a small bristle. In {69}the central point of the shell are united about twelve (?) thin and straight radial beams, which are forked, with dichotomous branches; the distal ends of the branches are inserted in the corners of the hexagons on the inside of the shell.

_Dimensions._--Diameter of the shell 0.15, pores 0.02, bars 0.003.

_Habitat._--Central Pacific, Station 271, surface.

Genus 17. _Ethmosphæra_,[28] Haeckel, 1862, Monogr. d. Radiol., p. 349.

_Definition._--#Liosphærida# with one single latticed sphere, with simple shell-cavity; with shell-pores which are prolonged on the outside in centrifugal, conical, or cylindrical tubuli.

The genus _Ethmosphæra_ differs from the simple _Cenosphæra_, its ancestral form, by the peculiar formation of the shell-pores; in all observed species of the genus these are quite regular, of nearly equal size and form; their base in the spherical shell-face is hexagonal, but on the outside prolonged into centrifugal, external, radial tubuli, which are either conical or cylindrical (in the latter case both openings of the tubes being equal, in the former the outer opening being smaller than the inner). The solitary _Ethmosphæra_ corresponds to the social _Siphonosphæra_; but in the former the formation of the shell and of its tubuli is quite regular, in the latter more or less irregular.

Subgenus 1. _Ethmosphærella_, Haeckel.

_Definition._--Tubuli conical, their outer opening smaller than the inner.

1. _Ethmosphæra siphonophora_, Haeckel.

_Ethmosphæra siphonophora_, Haeckel, 1862, Monogr. d. Radiol., p. 350, Taf. xi. fig. 1.

Tubuli conical, their outer opening half as broad as the inner and three times as broad as their height. Five to six pores on the quadrant. Diameter of the outer pores one and a half times as large as their distance from each other.

_Dimensions._--Diameter of the shell 0.1, outer pores 0.01, their distance 0.007.

_Habitat._--Mediterranean (Messina), surface, Haeckel.

2. _Ethmosphæra conosiphonia_, n. sp. (Pl. 12, figs. 5, 5_a_).

Tubuli conical, their outer opening two thirds as broad as the inner, and scarcely broader than their height. Ten to twelve pores on the quadrant. Diameter of the outer pores twice as large as their distance from each other.

_Dimensions._--Diameter of the shell 0.17, outer pores 0.01, their distance 0.005.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

{70}3. _Ethmosphæra polysiphonia_, n. sp. (Pl. 12, fig. 6).

Tubuli conical, their outer opening three-fourths as broad as the inner and three times as broad as their height. Sixteen to eighteen pores on the quadrant. Diameter of the outer pores three times as large as their distance apart.

_Dimensions._--Diameter of the shell 0.2, outer pores 0.008, their distance 0.003.

_Habitat._--West Tropical Pacific, Station 225, depth 4475 fathoms; also fossil in Barbados and in Sicily.

Subgenus 2. _Ethmosphæromma_, Haeckel.

_Definition._--Tubuli cylindrical, their outer opening about as large as the inner.

4. _Ethmosphæra stenosiphonia_, n. sp.

Tubuli cylindrical, short, quite contiguous, so that their diameter is six times as large as their distance apart, but about equal to their height. Nine to ten pores on the quadrant.

_Dimensions._--Diameter of the shell 0.14, outer pores 0.012, their distance 0.002.

_Habitat._--Central Pacific, Station 271, surface.

5. _Ethmosphæra pachysiphonia_, n. sp.

Tubuli cylindrical, twice as long as broad, very thick-walled, and nearly contiguous, so that their diameter is five times as large as their distance apart. The thickness of their wall is equal to their lumen. Twelve to fourteen pores on the quadrant.

_Dimensions._--Diameter of the shell 0.16, outer pores 0.01, their distance 0.002.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

6. _Ethmosphæra leptosiphonia_, n. sp.

Tubuli cylindrical, short, about as long as broad, very thin-walled and fragile, separated by wide distances, which are three times as large as their diameter. Six to seven pores on the quadrant. (Very similar to _Siphonosphæra cyathina_, Pl. 6, fig. 10, but quite regular, all tubuli retaining the same size and distance.)

_Dimensions._--Diameter of the shell 0.12, outer pores 0.01, their distance 0.03.

_Habitat._--North Atlantic, Færöe Channel, John Murray; surface.

7. _Ethmosphæra macrosiphonia_, n. sp.

Tubuli cylindrical, very elongated, four times as long as broad; their bases separated by distances which are equal to their breadth. Eight to ten tubuli on the quadrant. (The tubes are similar to those of _Siphonosphæra serpula_, Pl. 6, fig. 6, but quite regular, straight, not curved, all of the same size and at equal distances apart.)

{71}_Dimensions._--Diameter of the shell 0.1, length of the tubes 0.04, breadth 0.01, basal distance 0.01.

_Habitat._--Indian Ocean, Cocos Islands, surface, Rabbe.

Genus 18. _Sethosphæra_,[29] Hæckel, 1881, Prodromus, p. 452 (_sensu emendato_).

_Definition._--#Liosphærida# with one single latticed sphere, with simple shell-cavity; with shell-pores, which are prolonged on the inside into centripetal, conical, or cylindrical tubuli.

The genus _Sethosphæra_ differs from its ancestral form, _Cenosphæra_, by the production of internal, centripetal, radial tubuli on the inside of the shell (the contrary of the preceding genus _Ethmosphæra_). It corresponds therefore to the social _Pharyngosphæra_; but in the latter the formation of the shell and its tubes is more or less irregular, whilst in the former each regular pore is prolonged into a regular tubule.

1. _Sethosphæra entosiphonia_, n. sp.

Shell with smooth surface and regular circular pores, separated by hexagonal frames, twice as broad as the bars. Six to eight on the quadrant. Each pore is prolonged on the inside of the shell in a short conical centripetal tube, twice as long as its diameter.

_Dimensions._--Diameter of the shell 0.15, outer pores 0.008, bars 0.004, length of the tubuli 0.015.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

2. _Sethosphæra entosolenia_, n. sp.

Shell with smooth surface and regular circular pores, without hexagonal frames, of about the same breadth as the bars. Ten to twelve on the quadrant. Each pore is prolonged on the inside of the shell into a thin cylindrical centripetal tube, three times as long as its diameter.

_Dimensions._--Diameter of the shell 0.2, outer pores and bars 0.006, length of the tubuli 0.02.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

Subfamily CARPOSPHÆRIDA,[30] Haeckel, 1881, Prodromus, p. 449.

_Definition._--#Liosphærida# with two concentric spherical lattice-shells, which are united by radial beams.

_Carposphæra_,[31] Haeckel, 1881, Prodromus, p. 451.

_Definition._--Liosphærida with one medullary (intracapsular) and one cortical (extracapsular) shell, both connected by radial beams piercing the central capsule.

{72}The genus _Carposphæra_ comprises a large number of double-shelled #Sphæroidea#, formerly united with _Haliomma_, but different from this genus by the absence of radial spines. The shell is composed of two concentric latticed spheres, the inner of which (or the medullary shell) is situated within the central capsule, the other (or the cortical shell) outside it. Both shells are connected by radial beams which pierce the wall of the central capsule. The distance between the shells is at least as large as (commonly much larger than) the radius of the inner shell, whilst in the following genus, _Liosphæra_, that distance is much smaller than this radius.

Subgenus 1. _Melittosphæra_, Haeckel, 1881, Prodromus, p. 451.

_Definition._--Pores of the cortical shell regular, hexagonal (or circular, with hexagonal frames or lobes), all of nearly equal size and form.

1. _Carposphæra capillacea_, n. sp.

Cortical shell very delicate, four times as broad as the similarly constructed medullary shell, with regular hexagonal meshes (twenty to twenty-five on the quadrant) and very thin thread-like bars. Both shells connected by twenty (?) very thin radial beams. (Similar to _Heliosoma radians_, Pl. 28, fig. 3, 3_a_, but with smooth surface, without any radial spines.)

_Dimensions._--Diameter of the outer shell 0.2, inner 0.05, pores 0.01, bars below 0.001.

_Habitat._--Central Pacific, Station 274, surface.

2. _Carposphæra cubaxonia_, n. sp.

Cortical shell smooth, three times as broad as the medullary shell, with regular hexagonal pores, four times as broad as the bars. Eight to ten pores on the quadrant. Medullary shell with regular circular pores, twice as broad as the bars. Both shells connected by six radial beams, which are three-sided prismatical, opposite in pairs in the three dimensive axes.

_Dimensions._--Diameter of the outer shell 0.15, inner 0.05; outer pores 0.01, inner 0.005.

_Habitat._--South Pacific, Station 291, surface.

3. _Carposphæra infundibulum_, Haeckel.

_Haliomma infundibuliforme_, Stöhr, 1880, Palæontogr. Bd. xxvi. p. 87, Taf. i. fig. 6.

Cortical shell very thick-walled, two and a half times as broad as the medullary shell, with rough surface and regular hexagonal, funnel-shaped pores, of about the same breadth as the bars. Five to six on the quadrant.

_Dimensions._--Diameter of the outer shell 0.1, inner 0.04, outer pores and bars 0.01.

_Habitat._--North Atlantic, Station 354; fossil in Tertiary rocks (Barbados and Sicily).

{73}4. _Carposphæra melissa_, n. sp.

Cortical shell thick walled, four times as broad as the medullary shell, with regular circular, hexagonally framed pores, three times as broad as the bars. Eight to ten pores on the quadrant. Medullary shell with simple circular pores.

_Dimensions._--Diameter of the outer shell 0.16, inner 0.04, outer pores 0.012, bars 0.004.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

5. _Carposphæra melitomma_, n. sp. (Pl. 20, fig. 4).

_Melitomma melittosphæra_, Haeckel, 1881; Prodromus et Atlas, _loc. cit._

Cortical shell thick walled, with thorny surface, two and a half times as broad as the medullary shell. Its pores regular, circular, twice as broad as the bars, elegantly six-lobed, separated by crested hexagonal frames; in each hexagon-corner a short conical papilla (alternating with a lobe). Eight to ten pores on the quadrant. Medullary shell with small simple circular pores.

_Dimensions._--Diameter of the outer shell 0.17, inner 0.07, outer pores 0.01, bars 0.005, inner pores 0.005.

_Habitat._--Central Pacific, Stations 266 to 274, in various depths.

Subgenus 2. _Cerasosphæra_, Haeckel, 1881, Prodromus, p. 451.

_Definition._--Pores of the cortical shell regular, circular, without hexagonal frames, all of nearly equal size and form.

6. _Carposphæra cerasus_, n. sp.

Cortical shell thin walled, smooth, twice as broad as the medullary shell; both with regular circular pores, six times as broad as the bars. Twelve to fifteen pores on the quadrant. Outer pores twice as large as the inner.

_Dimensions._--Diameter of the outer shell 0.24, inner 0.12; outer pores 0.016, inner 0.008.

_Habitat._--Central Pacific, Station 271, surface.

7. _Carposphæra apiculata_, Haeckel.

? _Haliomma apiculatum_, Ehrenberg, 1872; Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 313.

Cortical shell thin-walled, covered with numerous short conical thorns, three times as broad as the medullary shell. Pores regular, circular, four times as broad as the bars. Six to eight pores on the quadrant.

_Dimensions._--Diameter of the outer shell 0.15, inner 0.05, outer pores 0.012, bars 0.03.

_Habitat._--North Pacific, California, depth 2000 fathoms; Station 254, depth 3025 fathoms.

{74}8. _Carposphæra entactinia_, Haeckel.

_Haliomma entactinia_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxvi. fig. 4.

Cortical shell thick walled, rough, twice as broad as the medullary shell; both shells with regular circular pores, twice as broad as the bars. Six to eight pores on the quadrant. Outer pores half as broad as the inner. Both shells connected by very numerous (twenty-four to forty-eight or more) radial beams.

_Dimensions._--Diameter of the outer shell 0.12, inner 0.06, outer pores 0.008, bars 0.004, inner pores 0.004.

_Habitat._--Cosmopolitan; Atlantic and Pacific, in various depths; fossil in Barbados and Sicily.

9. _Carposphæra modesta_, Haeckel.

_Haliomma modestum_, Stöhr, 1880, Palæontogr. Bd. xxvi. p. 86, Taf. i. fig. 5.

Cortical shell thick walled, rough, three times as broad as the medullary shell, with regular circular pores of the same breadth as the bars. Eight to twelve pores on the quadrant. (Very common, like the preceding species, and connected with it by numerous intermediate forms.)

_Dimensions._--Diameter of the outer shell 0.12 to 0.2, inner 0.04 to 0.07, pores and bars 0.006 to 0.008.

_Habitat._--Atlantic and Pacific, from many Stations and at various depths; fossil in Barbados and Sicily.

10. _Carposphæra belladonna_, n. sp.

Cortical shell thick walled, smooth, five times as broad as the medullary shell, with regular circular pores of the same breadth as the bars. Twenty to twenty-two pores on the quadrant.

_Dimensions._--Diameter of the outer shell 0.3, inner 0.06, outer pores and bars 0.004.

_Habitat._--North Atlantic, Færöe Channel, John Murray.

11. _Carposphæra areca_, n. sp.

Cortical shell very thick walled, rough, twice as broad as the medullary shell, with regular circular pores half as broad as the bars. Eight to ten pores on the quadrant.

_Dimensions._--Diameter of the outer shell 0.12, inner 0.06, outer pores 0.03, bars 0.006.

_Habitat._--Indian Ocean, Ceylon, Haeckel, surface.

Subgenus 3. _Prunosphæra_, Haeckel, 1881, Prodromus, p. 451.

_Definition._--Pores of the cortical shell irregular polygonal, of unequal size or dissimilar form.

12. _Carposphæra prunulum_, n. sp.

Cortical shell thin walled, smooth, four times as broad as the medullary shell, with large irregular polygonal pores, four to eight times as broad as the bars. Connecting beams between them numerous.

{75}_Dimensions._--Diameter of the outer shell 0.24, inner 0.06, outer pores 0.008 to 0.016, bars 0.002.

_Habitat._--South Atlantic, Station 325, surface.

13. _Carposphæra corypha_, n. sp.

Cortical shell thin walled, rough, three times as broad as the medullary shell, with irregular polygonal pores, three to six times as broad as the bars. Connecting beams between the two shells twenty, regularly disposed.

_Dimensions._--Diameter of the outer shell 0.15, inner 0.05, outer pores 0.01 to 0.02, bars 0.003.

_Habitat._--South Pacific, Station 300, surface.

14. _Carposphæra borassus_, n. sp.

Cortical shell thick walled, smooth, three times as broad as the medullary shell, with irregular polygonal pores, two to four times as broad as the bars. Connecting beams between the two shells six, opposite by pairs in the three dimensive axes. (Similar to _Hexalonche aristarchi_, Pl. 22, fig. 3, but without external radial spines.)

_Dimensions._--Diameter of the outer shell 0.12, inner 0.04, outer pores 0.01 to 0.02, bars 0.005.

_Habitat._--Central Pacific, Station 268, surface.

Subgenus 4. _Phoenicosphæra_, Haeckel.

_Definition._--Pores of the cortical shell irregular roundish, of unequal size or form.

15. _Carposphæra nobilis_, Haeckel.

_Haliomma nobile_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 268; Abhandl., 1875, Taf. xxvii. fig. 6.

Cortical shell thin walled, rough, twice as broad as the medullary shell, with irregular roundish pores, two to four times as broad as the bars.

_Dimensions._--Diameter of the outer shell 0.1, inner 0.05, outer pores 0.01 to 0.02, bars 0.006.

_Habitat._--Cosmopolitan; Atlantic, Indian, Pacific, at various depths; fossil in Jurassic, Cretaceous, and Tertiary rocks.

16. _Carposphæra micrococcus_, n. sp.

Cortical shell thin walled, rough, seven times as broad as the medullary shell, with irregular roundish pores, three to six times as broad as the bars.

_Dimensions._--Diameter of the outer shell 0.2, inner 0.03, outer pores 0.012 to 0.025, bars 0.004.

_Habitat._--South Atlantic, Station 330, surface.

{76}17. _Carposphæra maxima_, n. sp.

Cortical shell thin walled, smooth, five times as broad as the medullary shell, with irregular roundish pores, of about the same breadth as the bars.

_Dimensions._--Diameter of the outer shell 0.4, inner 0.08, pores and bars 0.004 to 0.008.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

18. _Carposphæra nodosa_, n. sp. (Pl. 28, figs. 2, 2_a_).

_Anthomma nodosum_, Haeckel, 1879, Atlas, _loc. cit._

Cortical shell thick walled, covered with forty to fifty scattered pyramidal nodules, two and a half times as broad as the medullary shell, connected with it by very numerous thin radial beams. Outer and inner pores irregular roundish or polygonal, two to three times as broad as the bars. (This species in consequence of the cortical nodules may represent a peculiar genus, analogous to _Conosphæra_, called _Anthomma_.)

_Dimensions._--Diameter of the outer shell 0.13, inner 0.05, inner and outer pores 0.008 to 0.012, bars 0.004.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

Genus 20. _Liosphæra_,[32] Haeckel, 1881, Prodromus, p. 449.

_Definition._--#Liosphærida# with two cortical (extracapsular) shells (without a medullary or intracapsular shell).

The genus _Liosphæra_ agrees with the preceding _Carposphæra_ in the possession of two concentric latticed spheres; but whilst in the latter genus the inner sphere is a medullary one (intracapsular), the outer a cortical shell (extracapsular), both connected by radial beams piercing the capsule-wall, here in _Liosphæra_ the central capsule lies freely within the inner lattice shell and is not pierced by radial beams. Therefore both shells are here cortical shells, both separated by a distance, which is constantly much smaller than the radius of the inner shell; whereas in _Carposphæra_ this distance is at least as large as that radius (commonly much larger). In _Carposphæra_ the number of pores in both shells is never the same; in several species of _Liosphæra_ this number is the same, each outer regular hexagonal pore exactly corresponding to an inner; the six corners of each connected by six short radial beams.

Subgenus 1. _Melitomma_, Haeckel.

_Definition._--Pores of both shells regular, in each shell all of nearly equal size and form.

1. _Liosphæra hexagonia_, n. sp. (Pl. 20, fig. 3).

Both shells with the same number of pores, exactly corresponding, about ten on the quadrant. {77}All pores regular, or subregular, hexagonal; the outer twice as broad as the inner. Outer bars very thin, thread-like; inner bars thick, one-third as broad as the pores. Surface smooth. Both shells connected by numerous radial beams, their distance one-third as large as the radius of the inner shell.

_Dimensions._--Diameter of the outer shell 0.16, inner 0.12, distance of both 0.02; outer pores 0.014, inner pores 0.007.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

2. _Liosphæra rhodococcus_, n. sp.

Both shells with the same number of pores, exactly corresponding, about twelve on the quadrant. All pores regular or subregular; the inner circular, with elegant six-lobed frames, twice as broad as the bars; the outer hexagonal, with very thin thread-like bars. All corners of the outer and inner hexagons connected by thin, bristle-shaped radial beams. (Similar to _Haliomma rhodococcus_, Pl. 19, fig. 6; but with smooth surface and regular hexagonal pores of the outer shell.)

_Dimensions._--Diameter of the outer shell 0.2, inner 0.16, distance of both 0.02; outer pores 0.03, inner 0.01.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

3. _Liosphæra porulosa_, n. sp.

Both shells with regular hexagonal pores; their number in the outer shell seven times as great as in the inner. Pores of the stout inner shell large, three times as broad as the bars, about eight on the quadrant. From each hexagon-corner arises one bristle-shaped radial beam; their distal ends are united by threads (three from each), forming the large meshes of the delicate outer shell. Each of these is divided by very thin threads into seven small circular porules, one central and six around it.

_Dimensions._--Diameter of the outer shell 0.25, inner 0.2, distance of both 0.025; outer pores 0.04, their porules 0.012, inner pores 0.15.

_Habitat._--Indian Ocean, Sunda Strait, Rabbe; surface.

Subgenus 2. _Craspedomma_, Haeckel.

_Definition._--Pores of both shells irregular, in each shell differing either in form or size.

4. _Liosphæra peridromium_, n. sp.

Both shells with the same number of large, polygonal, very irregular pores, exactly corresponding (about eight to ten on the quadrant); both with a very delicate thin framework. From the thread-like bars of the inner, very large and thin-walled, sphere arise perpendicularly innumerable short bristles of equal length, which are united at equal distances by tangential thread-like bars, parallel to the former, composing the outer shell. Each mesh is, therefore, surrounded by a delicate ballister or rail.

{78}_Dimensions._--Diameter of the outer shell 0.42, inner 0.4, distance of both 0.01; diameter of the meshes 0.02 to 0.06.

_Habitat._--North Pacific, Station 250, surface.

5. _Liosphæra polypora_, n. sp. (Pl. 20, fig. 2).

Both shells with small irregular roundish pores, of about the same size as the bars between them; twenty to thirty on the quadrant. The pores of the outer shell somewhat smaller, therefore much more numerous than the pores of the inner shell. Distance between the two shells about one-third as great as the radius of the inner. Both shells connected by numerous thin radial beams. Surface smooth or a little rough.

_Dimensions._--Diameter of the outer shell 0.18, inner 0.14, distance of both 0.02; pores and bars 0.003 to 0.005.

_Habitat._--West Tropical Pacific, Station 225, depth 4475.

Subfamily THECOSPHÆRIDA,[33] Haeckel, 1881, Prodromus, pp. 449, 452.

_Definition._--#Liosphærida# with three concentric spherical lattice-shells, which are united by radial beams.

Genus 21. _Thecosphæra_,[34] Haeckel, 1881, Prodromus, p. 452.

_Definition._--#Liosphærida# with two medullary (intracapsular) shells and one cortical (extracapsular) shell.

The genus _Thecosphæra_ comprises a large number of triple-shelled #Sphæroidea#, formerly united with _Actinomma_, but different from this genus in the absence of radial spines. The latticed shell is composed of three concentric spheres, two of which lie within the central capsule (medullary shells), and one outside (cortical shell). This latter is connected with the former by radial beams piercing the wall of the central capsule. From the following _Rhodosphæra_ (with one medullary and two cortical shells) _Carposphæra_ differs also by the distance of the three shells. In the former the distance between the two outer shells is much smaller, in the latter much larger, than the distance between the inner shells.

Subgenus 1. _Thecosphærantha_, Haeckel.

_Definition._--Pores of the cortical shell regular, hexagonal, or circular, with hexagonal frames or lobes, all of nearly equal size and form.

{79}1. _Thecosphæra triplodictyon_, n. sp.

Cortical shell thin walled, smooth, with regular, hexagonal pores, four times as broad as the bars. Radial proportion of the three spheres = 1 : 2 : 8. Both medullary shells with regular circular pores, twice as broad as the bars, the inner half as broad as the outer. All three shells connected by six thin radial beams, opposite in pairs in the three dimensive axes.

_Dimensions._--Diameter of the outer shell 0.2, middle 0.05, inner 0.025; cortical pores 0.012, bars 0.003.

_Habitat._--Central Pacific, Station 271, surface.

2. _Thecosphæra phænaxonia_, n. sp.

Cortical shell thick walled, rough, with regular, circular, hexagonally framed pores, twice as broad as the bars. Radial proportion of the three spheres = 1 : 2 : 6. Both medullary shells with regular hexagonal pores and thin bars. All three shells connected by six prismatic radial beams, opposite in pairs in the three dimensive axes. (Shell similar to _Hexacontium sceptrum_, Pl. 24, fig. 1, 1_a_, but without external spines.)

_Dimensions._--Diameter of the outer shell 0.12, middle 0.04, inner 0.02; cortical pores 0.01, bars 0.005.

_Habitat._--North Pacific, Station 253, surface.

3. _Thecosphæra favosa_, n. sp.

Cortical shell thick walled, thorny, with regular, circular, hexagonally framed pores, of the same breadth as the bars. Radial proportion of the three spheres = 1 : 3 : 10. Both medullary shells with regular circular pores, connected with the former by twelve short prismatic, regularly disposed radial beams.

_Dimensions._--Diameter of the outer shell 0.2, middle 0.06, inner 0.02; cortical pores and bars 0.008.

_Habitat._--Central Pacific, Station 268, surface; also fossil in Barbados.

4. _Thecosphæra floribunda_, n. sp.

Cortical shell thick walled, smooth, with regular, elegantly six-lobed pores, three times as broad as the bars. Radial proportion of the three spheres = 1 : 2 : 4. Both medullary shells with simple regular circular pores, connected with the former by six dimensive radial beams. (Similar to _Hexacontium floridum_, Pl. 24, fig. 4, but without external spines.)

_Dimensions._--Diameter of the outer shell 0.12, middle 0.06, inner 0.03; cortical pores 0.01, bars 0.0033.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

{80}Subgenus 2. _Thecosphærella_, Haeckel.

_Definition._--Pores of the cortical shell regular, circular, without hexagonal frames or lobes, all of nearly equal size and form.

5. _Thecosphæra inermis_, Haeckel.

_Actinomma inerme_, Haeckel, 1862, Monogr. d. Radiol., p. 440, Taf. xxiv. fig. 5.

_Haliomma inerme_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 815.

Cortical shell thin walled, rough, with regular circular pores, twice as broad as the bars. Radial proportion of the three spheres and of their circular regular pores = 1 : 2 : 4. All three spheres connected by twelve regularly disposed radial beams.

_Dimensions._--Diameter of the outer shell 0.1, middle 0.05, inner 0.025; cortical pores 0.006, bars 0.003.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, at many Stations and at various depths.

6. _Thecosphæra æquorea_, Haeckel.

_Haliomma æquorea_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 83; Mikrogeol., 1854, Taf. xxii. fig. 35.

_Actinomma æquorea_, Haeckel, 1862, Monogr. d. Radiol., p. 443.

Cortical shell thick walled, smooth, with regular circular pores of the same breadth as the bars. Radial proportion of the three spheres and of their regular pores = 1 : 2 : 6 or = 1 : 3 : 9; they are connected by six radial beams, opposite by pairs in the three dimensive axes.

_Dimensions._--Diameter of the outer shell 0.08 to 0.12, middle 0.03 to 0.04, inner 0.09 to 0.12; cortical pores and bars about 0.006.

_Habitat._--Mediterranean, Corfu, surface; fossil in Greece and Sicily.

7. _Thecosphæra medusa_, Haeckel.

_Haliomma medusa_, Ehrenberg, 1838, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 130; Mikrogeol., 1854, Taf. xxii. figs. 33, 34.

_Actinomma medusa_, Haeckel, 1862, Monogr. d. Radiol., p. 444.

_Actinomma medusa_, Stöhr, 1880, Palæontogr., Bd. xxvi. p. 90, Taf. ii. fig. 3.

Cortical shell thick walled, rough or thorny, with regular circular pores of the same breadth as the bars. Radial proportion of the three spheres = 1 : 2 : 4 (or 1 : 2.5 : 6); they are connected by four radial beams, crossed by pairs in two diameters, perpendicular one to another.

_Dimensions._--Diameter of the outer shell 0.08 to 0.12, middle 0.04 to 0.06, inner 0.02 to 0.025; cortical pores and bars in average 0.005.

_Habitat._--Fossil in Tertiary rocks of Barbados and the Mediterranean.

{81}8. _Thecosphæra entactinia_, n. sp.

Cortical shell thick walled, smooth, with regular circular pores of the same breadth as the bars. Radial proportion of the three spheres = 1 : 3 : 12; they are connected by very numerous (forty to fifty, or more) thin radial beams.

_Dimensions._--Diameter of the outer shell 0.24, middle 0.06, inner 0.02; cortical pores and bars 0.008.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

9. _Thecosphæra micropora_, n. sp.

Cortical shell thin walled, smooth, with very small and numerous, regular, circular pores, half as broad as the bars. Radial proportion of the three shells = 1 : 2 : 5; they are connected by twenty regularly disposed radial beams.

_Dimensions._--Diameter of the outer shell 0.2, middle 0.08, inner 0.04; cortical pores 0.002, bars 0.004.

_Habitat._--South Pacific, Station 288, surface.

Subgenus 3. _Thecosphærina_, Haeckel.

_Definition._--Pores of the cortical shell irregular polygonal, of unequal size or dissimilar form.

10. _Thecosphæra capillacea_, n. sp.

Cortical shell thin walled, smooth, with irregular polygonal pores, three to six times as broad as the bars. Both medullary shells with similar, but smaller, pores. Radial proportion of the three spheres = 1 : 3 : 8; they are connected by very numerous (sixty to eighty or more) thin radial beams. (Similar to _Actinomma capillaceum_, Pl. 29, fig. 6, but without external spines.)

_Dimensions._--Diameter of the outer shell 0.2, middle 0.075, inner 0.025; cortical pores 0.006 to 0.012, bars 0.002.

_Habitat._--North Pacific, Station 250, surface.

11. _Thecosphæra diplococcus_, n. sp.

Cortical shell thick walled, rough, with large irregular polygonal pores, two to three times as broad as the bars. Both medullary shells with small regular circular pores. Radial proportion of the three spheres = 1 : 2 : 6; they are connected by twenty (?) stout radial beams.

_Dimensions._--Diameter of the outer shell 0.12, middle 0.04, inner 0.02; cortical pores 0.008 to 0.012, bars 0.004.

_Habitat._--South Atlantic, Station 330, surface.

Subgenus 4. _Thecosphæromma_, Haeckel.

_Definition._--Pores of the cortical shell irregular, roundish, of unequal size or dissimilar form.

{82}12. _Thecosphæra dodecactis_, n. sp.

Cortical shell thin walled, smooth, with large irregular roundish pores, two to eight times as broad as the bars. Both medullary shells with regular circular pores, twice as broad as the bars. Radial proportion of the three spheres = 1 : 2 : 5; they are connected by twelve regularly disposed stout radial beams.

_Dimensions._--Diameter of the outer shell 0.2, middle 0.08, inner 0.04; cortical pores 0.004 to 0.016, bars 0.002.

_Habitat._--Central Pacific, Station 263, depth 2650 fathoms.

13. _Thecosphæra icosactis_, n. sp.

Cortical shell thin walled, with small irregular roundish pores, two to four times as broad as the bars. Both medullary shells with similar but smaller pores. Radial proportion of the three spheres = 1 : 3 : 8; they are connected by twenty thin radial beams.

_Dimensions._--Diameter of the outer shell 0.32, middle 0.12, inner 0.04; cortical pores 0.005 to 0.012, bars 0.003.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

14. _Thecosphæra maxima_, n. sp.

Cortical shell thin walled, with small irregular roundish pores, two to six times as broad as the bars. Both medullary shells with similar, but smaller, pores. Radial proportion of the three spheres = 1 : 3 : 9; they are connected by numerous (forty to sixty or more) thin radial beams.

_Dimensions._--Diameter of the outer shell 0.45, middle 0.15, inner 0.05; cortical pores 0.008 to 0.024, bars 0.004.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

Genus 22. _Rhodosphæra_,[35] Haeckel, 1881, Prodromus, p. 452.

_Definition._--#Liosphærida# with one medullary (intracapsular) shell and two cortical (extracapsular) shells.

The genus _Rhodosphæra_ differs from the preceding _Thecosphæra_ in the same manner in which, among the Dyosphærida, _Liosphæra_ differs from _Carposphæra_. The cortical shell is double, composed of two not far distant shells, lying outside the central capsule. The distance between the shells is much smaller than the radius of the inner shell. This is connected by radial beams (piercing the central capsule) with the small central medullary shell.

Subgenus 1. _Rhodosphærella_, Haeckel.

_Definition._--Pores of both cortical shells regular, in each shell all of nearly equal size and form.

{83}1. _Rhodosphæra hexagonia_, n. sp.

Both cortical shells with the same number of regular hexagonal pores; the inner four times as broad as the bars, and half as broad as the outer pores, which are separated by thread-like bars. Medullary shell only one-fourth as broad as the inner cortical shell, with regular hexagonal pores of half the size. (Differs from the similar _Liosphæra hexagonia_, Pl. 20, fig. 3, by the possession of a medullary shell.)

_Dimensions._--Diameter of the outer shell 0.2, middle 0.16, inner 0.04; outer pores 0.013, middle 0.008, inner 0.004.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

2. _Rhodosphæra melitomma_, n. sp.

Both cortical shells with the same number of regular pores; the inner regular, circular, twice as broad as the bars, with elegant hexagonal frames and six roundish lobes alternating with the six radial spines which arise from the hexagon-corners; these short conical spines are connected at the distal end (at equal distances from the centre) by delicate threads (three from each spine), which form the delicate external shell. Medullary shell one-third as broad as the inner cortical shell, with small, simple, regular circular pores. (If in _Carposphæra melitomma_, Pl. 20, fig. 4, the distal ends of the spines became united by a cobweb-like outer shell, this species would be formed.)

_Dimensions._--Diameter of the outer shell 0.22, middle 0.18, inner 0.06; outer pores 0.025, middle 0.0125, inner 0.005.

_Habitat._--Central Pacific, Station 270, depth 2925 fathoms.

Subgenus 2. _Rhodosphæromma_, Haeckel.

_Definition._--Pores of both cortical shells irregular, in each shell of unequal size or dissimilar form.

3. _Rhodosphæra palliata_, n. sp.

Both cortical shells with an unequal number of irregular roundish pores; the outer pores somewhat smaller and much more numerous than the inner pores; the bars between the latter are thicker. Medullary shell about one quarter as broad as the inner cortical shell, with regular circular pores.

_Dimensions._--Diameter of the outer shell 0.4, middle 0.36, inner 0.08; outer pores on an average 0.008, middle 0.012, inner 0.004.

_Habitat._--Fossil in Barbados.

4. _Rhodosphæra pentaphylla_, n. sp.

Both cortical shells with unequal number of irregular roundish pores; the inner pores large, three to four times as broad as the bars; to each inner pore corresponds a group of five smaller {84}outer pores, like the five petals of a flower. Medullary shell half as broad as the inner cortical shell, with regular circular pores.

_Dimensions._--Diameter of the outer shell 0.25, middle 0.2, inner 0.1; outer pores on an average 0.006, middle 0.012, inner 0.004.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

Subfamily CROMYOSPHÆRIDA,[36] Haeckel, 1881, Prodromus, pp. 449, 453.

_Definition._--#Liosphærida# with four concentric spherical latticed shells, united by radial beams.

Genus 23. _Cromyosphæra_,[37] Haeckel, 1881, Prodromus, p. 453.

_Definition._--#Liosphærida# with two intracapsular (medullary) shells and two extracapsular (cortical) shells; the former united with the latter by radial beams piercing the wall of the central capsule.

The genus _Cromyosphæra_ is the only known genus of Cromyosphærida, or of such #Sphæroidea#, the smooth shell of which is composed of two medullary and two cortical shells. There may possibly be other Cromyosphærida, in which the shell is composed of one simple medullary and three cortical shells, or only of four extra-capsular cortical shells; but such have not as yet been observed. _Caryosphæra polysphærica_, Bütschli, 1882 (L. N. 41, Taf. xxiii. fig. 12) is probably a _Cromyosphæra_ (fossil in Barbados).

1. _Cromyosphæra quadruplex_, n. sp. (Pl. 30, fig. 9).

Radial proportion of the four spheres = 1 : 2 : 4 : 5. Outer cortical shell smooth, with large regular hexagonal pores, ten times as broad as the bars; inner cortical shell with irregular polygonal pores, five times as broad as the bars. Both medullary shells with regular circular pores of the same breadth as the bars.

_Dimensions._--Diameter of the four spheres--(A) 0.16, (B) 0.12, (C) 0.06, (D) 0.03.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

2. _Cromyosphæra rosetta_, n. sp.

Radial proportion of the four spheres = 1 : 2 : 8 : 10. Outer cortical shell smooth, with regular hexagonal pores and very thin bars; inner cortical shell with the same number of exactly corresponding, regular circular, hexagonally framed pores, twice as broad as the bars; the corners of the outer and inner hexagons united by radial bristles. Both medullary shells with regular circular pores, twice as broad as the bars.

_Dimensions._--Diameter of the four spheres--(A) 0.2, (B) 0.16, (C) 0.04, (D) 0.02.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

{85}3. _Cromyosphæra bigemina_, n. sp.

Radial proportion of the four spheres = 1 : 2 : 7 : 8. Outer cortical shell smooth, with regular hexagonal pores and very thin bars; inner cortical shell with the same number of exactly corresponding, regular circular pores. Both medullary shells with regular circular pores of the same breadth as the bars. (Somewhat similar to _Hexacromyon elegans_, Pl. 24, fig. 9, also with six inner radial beams, but without external radial spines.)

_Dimensions._--Diameter of the four spheres--(A) 0.2, (B) 0.17, (C) 0.05, (D) 0.025.

_Habitat._--North Pacific, Station 241, depth 2300 fathoms.

4. _Cromyosphæra cepa_, n. sp.

Radial proportion of the four spheres = 1 : 2 : 4 : 5. All four shells of the same structure, thick-walled, with regular circular pores, two to four times as broad as the bars; the size of the pores increases gradually from the inner to the outer shell. Surface thorny. Distance between the second and third shells twice as great as that between the others.

_Dimensions._--Diameter of the four spheres--(A) 0.125, (B) 0.1, (C) 0.05, (D) 0.025.

_Habitat._--Fossil in Barbados.

5. _Cromyosphæra scorodonium_, n. sp.

Radial proportion of the four spheres = 1 : 2 : 3 : 4. All four shells of the same structure, thin-walled, with irregular roundish pores, two to four times as broad as the bars; the size of the pores increasing gradually from the inner to the outer shell. Surface smooth. Distance between each two shells equal to the diameter of the innermost.

_Dimensions._--Diameter of the four spheres--(A) 0.12, (B) 0.09, (C) 0.06, (D) 0.03.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms; also fossil in Barbados.

6. _Cromyosphæra antarctica_, n. sp..

Radial proportion of the four spheres = 1 : 2 : 5 : 7. Both cortical shells with irregular polygonal roundish pores; the outermost with thinner bars and rough surface, the inner with thicker bars. Both medullary shells with irregular roundish pores.

_Dimensions._--Diameter of the four spheres--(A) 0.18, (B) 0.12, (C) 0.05, (D) 0.025.

_Habitat._--Antarctic Ocean; in very large number, together with _Rhizosphæra antarctica_, in the diatomaceous ooze of Station 157 (3rd March 1874); depth 1950 fathoms.

Subfamily CARYOSPHÆRIDA,[38] Haeckel, 1881, Prodromus, pp. 449, 454.

_Definition._--#Liosphærida# with numerous (five or more) concentric spherical latticed shells, united by radial beams.

{86}Genus 24. _Caryosphæra_,[39] Haeckel, 1881, Prodromus, p. 454.

_Definition._--#Liosphærida# with two intracapsular (medullary) shells and three or more extracapsular (cortical) shells; the former united with the latter by radial beams piercing the wall of the central capsule.

The genus _Caryosphæra_, the only observed form of this subfamily, comprises those #Liosphærida# in which the shell is composed of two medullary and three or more cortical shells. Such forms (without radial spines) are very rare; I observed only two species, one with five, the other with six shells. They are derived from _Cromyosphæra_ by further apposition of outer cortical shells.

1. _Caryosphæra pentalepas_, n. sp.

Shell composed of five concentric spheres, with radial proportion = 1 : 2 : 8 : 10 : 12. Both medullary shells with regular circular pores, twice as broad as the bars. First cortical shell with regular, circular, hexagonally framed pores, three times as broad as the bars; second cortical shell with regular hexagonal pores, four times as broad as the bars; third (outermost) cortical shell with regular hexagonal pores and very thin thread-like bars. Surface smooth.

_Dimensions._--Diameter of the five shells--(A) 0.02, (B) 0.04, (C) 0.16, (D) 0.2, (E) 0.24.

_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.

2. _Caryosphæra hexalepas_, n. sp.

Shell composed of six concentric spheres, with the radial proportion = 1 : 2 : 4 : 5 : 6 : 8. All six shells with regular circular pores, two to four times as broad as the bars, with increasing size from the centrum against the smooth surface.

_Dimensions._--Diameter of the six shells--(A) 0.025, (B) 0.05, (C) 0.1, (D) 0.13, (E) 0.16, (F) 0.2.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms; also fossil in Barbados.

Subfamily PLEGMOSPHÆRIDA,[40] Haeckel, 1881, Prodromus, p. 455.

_Definition._--#Liosphærida# with spongy spherical shell, with or without latticed medullary shell in the centre.

Genus 25. _Styptosphæra_,[41] Haeckel, 1881, Prodromus, p. 455.

_Definition._--#Liosphærida# forming a solid sphere of spongy framework, without enclosed medullary shell, and without central cavity.

{87}The genus _Styptosphæra_ presents a spherical shell with smooth or rough surface (without radial spines), the whole mass of which is composed of looser or denser spongy wicker-work.

1. _Styptosphæra spumacea_, n. sp.

Spongy framework of the solid sphere loose, with large polygonal meshes of slightly different size, ten to twenty times as broad as the bars. Structure of the whole spongy sphere the same. Central capsule filled with crystals. Surface smooth.

_Dimensions._--Diameter of the sphere 0.32, of the central capsule 0.26, meshes 0.01 to 0.02, bars 0.001.

_Habitat._--North Pacific, Station 236, surface.

2. _Styptosphæra spongiacea_, n. sp.

Spongy framework in the central part of the solid sphere much more compact than in the peripheral part, becoming gradually looser towards the rough surface. Meshes in the centre three to five times, in the periphery fifteen to twenty times as broad as the bent bars.

_Dimensions._--Diameter of the sphere 0.45, inner meshes 0.006 to 0.01, outer meshes 0.03 to 0.04, bars 0.002.

_Habitat._--Central Pacific, Station 271, surface.

3. _Styptosphæra stupacea_, n. sp.

Spongy framework of the solid sphere rather compact, everywhere of the same structure, with roundish, nearly equal meshes, six to eight times as broad as the bars. Surface rough with prominent thorns.

_Dimensions._--Diameter of the sphere 0.22, meshes 0.01 to 0.012, bars 0.0015.

_Habitat._--South Pacific, Station 291, surface.

Genus 26. _Plegmosphæra_, Haeckel,[42] 1881, Prodromus, p. 455.

_Definition._--#Liosphærida# forming a hollow sphere of spongy framework, without a medullary shell in the central cavity.

The genus _Plegmosphæra_ develops a large hollow sphere, the wall of which is composed of looser or denser spongy wicker-work. On the inner as well as on the outer face of the spongy shell-wall may be present a simple lattice-sphere from which the threads of the framework arise; but in some species these lattice-plates are quite absent.

{88}Subgenus 1. _Plegmosphærantha_, Haeckel.

_Definition._--Inside and outside of the spongy shell-wall smooth, closed by a lattice-plate with polygonal meshes.

1. _Plegmosphæra maxima_, n. sp.

Radius of the spherical shell-cavity eight to ten times as great as the thickness of the thin spongy wall. Inside and outside of the wall smooth, closed by a lattice-plate with irregular polygonal meshes. Only three or four meshes in the thickness of the wall.

_Dimensions._--Diameter of the spongy sphere 0.8 to 1.0 mm., of its inner cavity 0.7 to 0.8, meshes 0.01 to 0.02, bars 0.002 to 0.003, central capsule 0.5 to 0.6, nucleus 0.1 to 0.15.

_Habitat._--Central Pacific, Station 271, surface.

2. _Plegmosphæra coelopila_, n. sp.

Radius of the spherical shell-cavity eight to ten times as great as the thickness of the spongy wall. Inside and outside of the wall closed by a smooth lattice-plate with irregular polygonal meshes, five to ten times as broad as the bars.

_Dimensions._--Diameter of the shell 0.32, of its cavity 0.26, meshes 0.01 to 0.02, bars 0.002.

_Habitat._--North Atlantic, Færöe Channel, Gulf Stream, John Murray.

3. _Plegmosphæra pachypila_, n. sp.

Radius of the spherical shell-cavity about equal to the thickness of the spongy wall. Inside and outside of the wall closed by a smooth lattice-plate with irregular polygonal meshes, three to six times as broad as the bars.

_Dimensions._--Diameter of the shell 0.24, of its cavity 0.12.

_Habitat._--North Pacific, Station 250, surface.

Subgenus 2. _Plegmosphærella_, Haeckel.

_Definition._--Inside of the spongy shell-wall closed by a smooth lattice-plate, outside rough, spongy, with prominent thorns.

4. _Plegmosphæra entodictyon_, n. sp.

Radius of the spherical shell-cavity half as great as the thickness of the spongy wall. Inside of the wall closed by a smooth lattice-plate, outside rough, spongy.

_Dimensions._--Diameter of the shell 0.24, of its cavity 0.08.

_Habitat._--South Pacific, Station 300, surface.

{89}5. _Plegmosphæra leptodictyon_, n. sp.

Radius of the spongy shell-cavity six times as great as the thickness of the spongy wall. Inside of the wall closed by a smooth lattice-plate, outside rough spongy.

_Dimensions._--Diameter of the shell 0.44, of its cavity 0.36.

_Habitat._--Central Pacific, Station 266, surface.

Subgenus 3. _Plegmosphæromma_, Haeckel.

_Definition._--Inside of the spongy shell-wall rough spongy, without lattice-plate, outside closed by a smooth lattice-plate.

6. _Plegmosphæra exodictyon_, n. sp. (Pl. 18, fig. 8).

Radius of the spongy shell-cavity only one-fourth as great as the thickness of the spongy shell-wall. Outside of the wall closed by a smooth lattice-plate, inside rough, spongy.

_Dimensions._--Diameter of the shell 0.4, of its cavity 0.08.

_Habitat._--South Atlantic, Station 325, surface.

Subgenus 4. _Plegmosphærusa_, Haeckel.

_Definition._--Inside and outside of the spongy shell-wall rough, with spongy or spiny surface, without lattice-plate.

7. _Plegmosphæra leptoplegma_, n. sp.

Radius of the spherical shell-cavity half as great as the thickness of the loose spongy shell-wall. Inside and outside of the wall rough spongy, not closed by a lattice-plate. Meshes ten to twenty times as broad as the bars.

_Dimensions._--Diameter of the shell 0.3, of its cavity 0.088.

_Habitat._--North Atlantic, Station 253, surface.

8. _Plegmosphæra pachyplegma_, n. sp.

Radius of the spherical shell-cavity about equal to the thickness of the dark and dense spongy shell-wall. Inside and outside of the wall rough spongy, not closed by a lattice-plate. Meshes three to five times as broad as the bars.

_Dimensions._--Diameter of the shell 0.2, of its cavity 0.1.

_Habitat._--Central Pacific, Station 270, surface.

Genus 27. _Spongoplegma_,[43] Haeckel, 1881, Prodromus, p. 455.

_Definition._--#Liosphærida# forming a sphere of spongy framework, which encloses in the centre one single latticed medullary shell.

{90}The genus _Spongoplegma_ may be regarded as a _Carposphæra_, in which the simple latticed cortical shell is represented by an irregular spongy framework, immediately enclosing the simple latticed medullary shell.

1. _Spongoplegma antarcticum_, n. sp.

Cortical shell with loose spongy framework and rough surface, four to six times as broad as the enclosed simple medullary shell. Pores of the latter regular circular, twice as broad as the bars. From its surface arise numerous (forty to fifty or more) short radial beams, which become forked and compose, by communication of lateral branches, the spongy cortical shell.

_Dimensions._--Diameter of the spongy cortical shell 0.2 to 0.3 of the latticed medullary shell 0.05 to 0.06.

_Habitat._--Antarctic Ocean, in large number, together with _Cromyosphæra antarctica_; in the Diatom ooze of Station 157 (depth 1950 fathoms).

Genus 28. _Spongodictyon_,[44] Haeckel, 1862, Monogr. d. Radiol., p. 459.

_Definition._--#Liosphærida# forming a sphere of spongy framework, which encloses in the centre a double latticed concentric medullary shell.

The genus _Spongodictyon_ can be regarded as a _Thecosphæra_, in which the simple latticed cortical shell is represented by an irregular spongy framework, which immediately encloses the double latticed medullary shell. Sometimes this latter appears triple, the inner surface of the spongy cortical shell forming a smooth spherical lattice-plate, separated by an interval from the double medullary shell.

Subgenus 1. _Dictyoplegma_, Haeckel, 1862, Monogr. d. Radiol, p. 458.

_Definition._--Spongy cortical shell enveloping immediately the double medullary shell.

1. _Spongodictyon spongiosum_, Haeckel.

_Dictyosoma spongiosum_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 31, Taf. ii. figs. 9-11.

_Dictyoplegma spongiosum_, Haeckel, 1862, Monogr. d. Radiol., p. 458.

Spongy framework of the cortical shell loose, with large, polygonal roundish meshes, on an average as large as the double medullary shell, which is immediately enveloped by it. Both concentric medullary shells with subregular roundish pores, twice as broad as the bars.

_Dimensions._--Diameter of the cortical shell 0.2 to 0.3 or more; of the outer medullary shell 0.03, inner 0.01.

_Habitat._--Mediterranean (French south coast, surface), J. Müller.

{91}2. _Spongodictyon cavernosum_, n. sp.

Spongy framework of the cortical shell rather compact in the inner part, which immediately envelops the double medullary shell; very loose, with large caverns in the outer part, caverns of the surface larger than the medullary shell. Both medullary shells with regular circular pores, three times as broad as the bars.

_Dimensions._--Diameter of the cortical shell 0.3 to 0.4, outer medullary shell 0.1, inner 0.03.

_Habitat._--Tropical Atlantic, Station 338, surface.

Subgenus 2. _Spongodictyoma_, Haeckel.

_Definition._--Spongy cortical shell on the inner surface with a smooth lattice-plate (or third medullary shell), which is connected by radial beams with the inner double medullary shell.

3. _Spongodictyon trigonizon_, Haeckel.

_Spongodictyon trigonizon_, Haeckel, 1862, Monogr. d. Radiol., p. 459, Taf. xxvi. figs. 4-6.

_Dictyosoma trigonizon_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 841.

Spongy framework of the cortical shell very loose, with very large, for the most part triangular meshes, which are two to six times as large as the enclosed double medullary shell. From the surface of the latter arise numerous radial beams, which are connected by a spherical lattice-plate, forming the smooth inner surface of the spongy sphere (or a third medullary shell). The structure of the framework reminds one of the PHÆODARIUM _Sagena_ (Pl. 108). Pores of both medullary shells regular circular, twice as broad as the bars.

_Dimensions._--Diameter of the cortical shell 0.5 to 1.15, outer medullary 0.05, inner 0.035.

_Habitat._--Mediterranean, Messina, surface.

4. _Spongodictyon arcadophoron_, n. sp.

Spongy framework of the cortical shell in the inner part very loose, in the outer part more compact; outer meshes scarcely as large as the inner medullary shell (or only half as large), inner meshes two to four times as large. From the surface of the double medullary shell arise numerous radial beams, which are forked at equal distances from the centre; the fork branches are curved and united together by dichotomous branches, like elegant arcades; and these arcades form together the large polygonal meshes on the inside of the cortical shell (or a third medullary shell). Both medullary shells with regular circular pores, of the same breadth as the bars.

_Dimensions._--Diameter of the cortical shell 0.2, outer medullary shell 0.04, inner 0.02.

_Habitat._--Tropical Atlantic, Station 349, surface.

{92}Family VI. #COLLOSPHÆRIDA#, J. Müller[45] (Pls. 5-8).

_Definition._--#Sphæroidea# living associated in colonies, united by an alveolar jelly-body, and connected by the network of anastomosing pseudopodia.

The family #Collosphærida# comprises all polyzous or social #Sphæroidea#, and constitutes the only polyzoic group among the SPHÆRELLARIA. This group was first constituted by J. Müller as "_Radiolaria polyzoa_ with shells."[46] Formerly following his authority, in my Monograph I had separated them from the other #Sphæroidea# and united them with the social Collodaria (Sphærozoida).[47] Also R. Hertwig in his Organismus der Radiolarien[48] united them with his Sphærozoea. In my Prodromus[49] I had retained this isolated position. But a further careful study has convinced me that this isolation is not truly natural, and that the Collosphærida are only "social Ethmosphærida" which have arisen from this solitary subfamily by adaptation to colonial life. There are some forms of Collosphærida which are nearly identical with some forms of Ethmosphærida, only differing from the latter by their association in colonies; and in some forms of both groups it is quite impossible to decide whether the isolated shells appertain to one or to the other family.

The isolated shell of the Collosphærida is almost constantly (with few exceptions) a simple extracapsular lattice-shell, as in the Monosphærida; only the small group of Clathrosphærida (with the genera _Clathrosphæra_ and _Xanthiosphæra_) exhibit an exception, the simple lattice-shell being overgrown by an external mantle or veil of very thin, cobweb-like, irregular lattice-work (Pl. 8, figs. 6-11). Therefore these Clathrosphærida bear to the Acrosphærida (or the common simple Collosphærida) a relation similar to that which _Liosphæra_ (p. 76) bears to _Cenosphæra_; both shells are extracapsular "cortical shells" at a very short distance apart. In the Collosphærida true concentric medullary shells never occur; the central capsule always lies quite freely in the simple or double cortical shell, separated from it by a jelly-veil.

Although a well marked difference in the simple lattice-shell of the social Collosphærida and the solitary Ethmosphærida does not exist, nevertheless in most cases the two shells can be distinguished by a practiced observer. The simple fenestrated shells of the monozoic Ethmosphærida are commonly quite regular spheres in a mathematical sense, or regular "endospherical polyhedra"; whereas in the Collosphærida they are commonly more or less irregular, often to an extraordinary degree (Pls. 5-8). Some species of Collosphærida, however, also possess quite regular spherical shells. Another difference is often shown in the lattice-work of the shells, which in the Collosphærida is nearly always very irregular, and exhibits a peculiar tendency to the {93}production of radial, conical, or cylindrical tubules. These occur as well on the inside as on the outside of the shell, and the tubules are now more conical, now more cylindrical; their wall either solid or pierced by pores (Pls. 5-8). The tubules are commonly very irregular in form, size, and disposition; distinguished, however, by a number of hereditary peculiarities, which are sufficient for the distinction of genera. Similar tubules occur also in some genera of solitary Ethmosphærida (_Coscinomma_, _Ethmosphæra_, _Conosphæra_, &c., Pl. 12); but the tubules are here much more regular and not so highly developed.

Besides the tubules of the fenestrated shells, in some genera of Collosphærida the surface is armed with irregular thorns, rarely with more regular radial spines. But these spines obtain constantly the character of accessory by-spines, and remain short and thin. In this family typical radial spines never occur in a regular and characteristic disposition, corresponding to dimensive axes, as is the case in nearly all solitary #Sphæroidea#, only excepting the Liosphærida. Commonly these spines or thorns serve as protective arms for the shell-meshes, surrounding them often in the form of coronels. Often the lattice-plate of the irregular roundish shell is tubercular, elevated into irregular protuberances, bearing on the top a short spine or thorn (Pl. 8).

The _Central Capsule_ of the Collosphærida is always a regular sphere, as in all other #Sphæroidea#; it is constantly placed within the lattice-shell, and commonly much smaller than it, separated from it by a thick jelly-veil. A remarkable difference from the solitary #Sphæroidea# is shown in the early division of the nucleus. Commonly the central capsule of the Collosphærida contains in its centre a large oil-globule, surrounded by very numerous small nuclei. R. Hertwig estimated this difference as so important, that he separated the social "Sphærozoea" and the solitary "Peripylea" as two different orders. As already shown above (p. 7, 24), we cannot support this separation, and are now convinced that this difference in the development of the spores--just as in the #Collodaria#--is the consequence of an adaptation to social life.

The common jelly-body, in which the numerous central capsules and their enveloping shells are united, exhibits in the Collosphærida quite the same characters as in the other social Radiolaria, the Collozoida and Sphærozoida. The jelly-body is very voluminous, commonly spherical, often cylindrical, of considerable size; constantly containing numerous large alveoles. Often each shell is enclosed in a separate alveole with rather solid wall (Pl. 6, fig. 2). Sometimes in the dead colonies all shells are united in the central part of the jelly-body, whilst its peripheral part is composed of a stratum of large alveoles (Pl. 8, fig. 11); at other times no alveoles are visible (Pl. 7, fig. 11). In many living colonies I found a very large spherical alveole with thick wall in the centre of the spherical colony, surrounded by many strata of delicate thin-walled alveoles (Pl. 5, fig. 1). In this case often the inner younger capsules were naked, {94}without shells, the outer only surrounded by shells. Already in my Monograph I had described the same peculiar formation.[50]

_Synopsis of the Genera of Collosphærida._

------------------------------------------------------------------------- I. Subfamily Acrosphærida. (Lattice-shell simple, without an external mantle of network.) ------------------------------------------------------------------------- {Inside {Inside smooth, 29. _Collosphæra_. Outside of { without { the shell { tubuli. {Inside spiny, 30. _Tribonosphæra_. smooth, { without { {Tubuli spines or {Inside with { imperforated, 31. _Pharyngosphæra_. tubuli. { centripetal { { tubuli. {Tubuli { { fenestrated, 32. _Buccinosphæra_.

{Spines { irregularly { scattered on { the surface, 33. _Acrosphæra_. { Outside of the shell armed {Each larger with solid spines, but { pore with one with hollow tubuli. { single spine, 34. _Odontosphæra_. { {Each larger { pore with { a coronal of { spines, 35. _Choenicosphæra_.

{Mouth of the { tubuli { truncated, { smooth, 36. _Siphonosphæra_. { Outside of {Tubuli {Mouth with the shell { simple, not { one single with { branched. { large tooth, 37. _Mazosphæra_. irregular { { radial { {Mouth with a tubuli, { { coronal of the wall of { { teeth, 38. _Trypanosphæra_. which is { solid, not {Tubuli irregularly branched, fenestrated.{ each with two to four or { more openings, 39. _Caminosphæra_.

{Mouth of the { tubuli { truncated, { smooth, 40. _Solenosphæra_. Outside of the shell with { irregular radial tubuli, {Mouth with one open on both ends, { single large with fenestrated wall. { tooth, 41. _Otosphæra_. { {Mouth with a { coronal of { teeth, 42. _Coronosphæra_. ------------------------------------------------------------------------- II. Subfamily Clathrosphærida. (Lattice-shell double, with an external mantle of network.) ------------------------------------------------------------------------- Surface of the outer shell smooth, 43. _Clathrosphæra_.

Surface of the outer shell thorny, 44. _Xanthiosphæra_.

Subfamily ACROSPHÆRIDA, Haeckel, 1881, Prodromus, p. 471.

_Definition._--#Collosphærida# with one simple lattice-shell around every central capsule of the coenobium.

{95}Genus 29. _Collosphæra_,[51] J. Müller, 1855.

_Definition._--#Collosphærida# with simple shells, smooth on the inside and on the outside, without any spines or tubuli.

The genus _Collosphæra_ is the most simple form of all Collosphærida, and must be regarded as the common ancestral form of this family. As the lattice-shell is quite a simple sphere, without any spines, tubules, or other peculiar productions, it agrees perfectly with _Cenosphæra_, and represents the social or polyzoid aggregate of this solitary or monozoid genus. Therefore a certain distinction between the isolated shells of the two genera is often very difficult or even impossible; but commonly this distinction is possible owing to the circumstance, that in the majority of the _Collosphæræ_ the shell is more or less irregular roundish or polyhedral, not quite spherical, as in _Cenosphæra_. _Dermatosphæra_, Ehrenberg, is a _Collosphæra_ with small pores (compare L. N. 16, p. 533).

Subgenus 1. _Eucollosphæra_, Haeckel.

_Definition._--Shell a regular or subregular sphere.

1. _Collosphæra primordialis_, n. sp.

Shell a regular sphere, with very delicate and regular network of hexagonal meshes. Six to eight meshes in the half meridian of the shell. Diameter of the meshes ten to fifteen times as broad as the thin bars between them. Can be regarded as social form of _Cenosphæra primordialis_.

_Dimensions._--Diameter of the shell 0.1 to 0.12, of the pores 0.008.

_Habitat._--Central Pacific, Stations 271 to 274, surface.

2. _Collosphæra regularis_, n. sp.

Shell a regular sphere, with a perfectly regular network of circular meshes, all of the same size. Ten to twelve meshes in the half meridian of the shell. Diameter of the meshes the same as that of the bars between them.

_Dimensions._--Diameter of the shell 0.1 to 0.12, of the pores 0.005 to 0.006.

_Habitat._--Indian Ocean, Madagascar, surface, Rabbe.

3. _Collosphæra globularis_, n. sp.

Shell a regular sphere, with subregular network of circular meshes of different sizes; few large pores between many smaller pores. Ten to twenty meshes in the half meridian of the shell. Diameter of the meshes from half to twice as broad as that of the bars.

{96}_Dimensions._--Diameter of the shell 0.1 to 0.12, of the pores 0.002 to 0.008, breadth of the bars 0.004 to 0.008.

_Habitat._--Tropical and subtropical zone of both hemispheres, widely distributed; Canaries, Azores, Cape Verde Islands, Guinea Coast, Brazil Coast, Indian Ocean, Madagascar, Ceylon, surface.

Subgenus 2. _Dyscollosphæra_, Haeckel.

_Definition._--Shell not a regular sphere, but irregular roundish, in all degrees of variation between subspherical and polyhedral or quite irregular forms.

4. _Collosphæra huxleyi_, J. Müller.

_Collosphæra huxleyi_, J. Müller, 1855, Abhandl. d. k. Akad. d. Wiss. Berlin, pp. 55-59, Taf. viii. figs. 6-9.

_Collosphæra huxleyi_, Haeckel, 1862, Monogr. d. Radiol., p. 534, Taf. xxxiv.

_Collosphæra huxleyi_, Cienkowski, 1871, Archiv f. mikrosk. Anat., Bd. vii. p. 374, Taf. xxix. figs. 1-6.

_Collosphæra ligurina_, J. Müller, 1856, Monatsber. d. k. Akad. d. Wiss. Berlin, p. 481.

_Thalassicolla punctata_, var., Huxley, 1851, Ann. and Mag. Nat. Hist., ser. 2, vol. viii. p. 434, pl. xvi. fig. 6.

Shell subspherical, somewhat irregular, sometimes with more or less superficial impressions, with irregular network of roundish meshes. Eight to sixteen meshes in the half meridian of the shell, one to three times as broad as their bars. Very variable, with direct transition-forms to other species of this genus, especially to _Collosphæra globularis_, _Collosphæra tuberosa_, _Collosphæra pyriformis_, and _Collosphæra polyedra_.

_Dimensions._--Diameter of the shell 0.1 to 0.16, of the pores 0.004 to 0.012, of the bridges 0.003 to 0.006.

_Habitat._--Cosmopolitan; common in the greater part of the warmer seas, surface.

5. _Collosphæra polygona_, n. sp. (Pl. 5, fig. 13).

_Collosphæra huxleyi_ var., Haeckel, 1862, Monogr. d. Radiol., Taf. xxxiv. fig. 5.

Shell irregular polygonal, with very delicate, irregular network of polygonal meshes, four to twelve times as broad as the bars. Ten to twenty pores on the half meridian of the shell.

_Dimensions._--Diameter of the shell 0.1 to 0.2, of the pores 0.012 to 0.004, of the bars 0.001 to 0.002.

_Habitat._--Mediterranean, Atlantic, surface; Stations 348 to 354.

6. _Collosphæra pyriformis_, Haeckel, n. sp.

Shell irregular, rounded, ovate or pear-shaped, with irregular network of rounded or nearly polygonal meshes. Ten to twenty meshes in the half meridian of the shell, one to three times as broad as the bars. Commonly one large opening (two to three times as broad as the largest {97}meshes) on the thinner end of the ovate shell (corresponding to the insertion of a pear-stalk); sometimes two or three such large openings.

_Dimensions._--Diameter of the shell 0.1 to 0.15, of the pores 0.008 to 0.016, of the bridges 0.004 to 0.008.

_Habitat._--Tropical zone--Cape Verde Islands, Ceylon; Central Pacific, Stations 266 to 272, 348 to 352, &c.

7. _Collosphæra polyedra_, n. sp.

_Trisolenia zanguebarica_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 301, Taf. x. fig. 11.

Shell irregular, polyhedral, with even or somewhat vaulted sides, and obtuse ridges between them. Network more or less irregular, with small rounded meshes, quite as broad or twice as broad as their bars. Besides these small pores constantly some large round openings (commonly three to six), situated on the corners of the polyhedral shell, four to six times as large as the pores. Often an acute tooth on the edge of each large opening. Transition-form between _Collosphæra_ and _Solenosphæra_ or _Odontosphæra_.

_Dimensions._--Diameter of the shell 0.1 to 0.15, of the pores 0.004 to 0.008, of their bridges 0.004, of the large openings 0.24 to 0.032.

_Habitat._--Tropical zone of the Pacific and the Indian Ocean; Stations 266 to 272, surface.

8. _Collosphæra tuberosa_, n. sp.

_Collosphæra huxleyi_, var., Haeckel, 1862, Monogr. d. Radiol., Taf. xxxiv. figs. 3, 9.

Shell very irregular, between subspherical and polyhedral in form, but always with irregular impressions, boils or bosses, and between these different rounded prominent tubercles and ridges. Network irregular, strong, with rounded, subcircular or nearly polygonal meshes. Ten to thirty pores in the half meridian of the shell. Diameter of the meshes half to four times as broad as that of the thick bars.

_Dimensions._--Diameter of the shell very variable in the same coenobium, 0.05 to 0.2, of the pores 0.002 to 0.008, breadth of the bridges 0.004 to 0.006.

_Habitat._--Cosmopolitan, common in all warmer seas, surface.

9. _Collosphæra irregularis_, n. sp.

_Collosphæra huxleyi_, var., Haeckel, 1862, Monogr. d. Radiol., Taf. xxxiv. fig. 8.

Shell quite irregular, knotty or bulbous, with irregular impressions, and prominent knobs or bulbs between them. Network thin, fragile, quite irregular, with polygonal meshes of most unequal size and form. Five to twenty pores in the half meridian of the shell. Diameter of the meshes two to ten times as broad as that of the thin bars.

_Dimensions._--Diameter of the shell very variable in the same coenobium, 0.04 to 0.24, of the pores 0.005 to 0.05, of the bridges 0.002 to 0.004.

_Habitat._--Mediterranean, Atlantic, not common; Stations 348, 352, &c., surface.

{98}Genus 30. _Tribonosphæra_,[52] Haeckel, 1881, Prodromus, p. 471.

_Definition._--#Collosphærida# with simple shells, on the inside with radial centripetal beams.

The genus _Tribonosphæra_ differs from _Collosphæra_ by a very peculiar and rare character, the development of centripetal radial sticks on the internal face of the shell; these beams are not united in the centrum, but finish freely in a certain distance from it.

1. _Tribonosphæra centripetalis_, n. sp. (Pl. 5, fig. 12).

Shell roundish or subspherical, with numerous small circular or roundish pores, about twice as broad as the bars. Twenty to thirty pores on the half meridian of the shell. Outside of the shell smooth, inside a variable number (ten to twenty) of thin, radial, centripetal sticks or spines, one-third or one-half as long as the radius of the shell. (In the central capsule many very large crystals, resting after the destruction of the capsule.)

_Dimensions._--Diameter of the shell 0.1 to 0.12, of the pores 0.003 to 0.005, of the bridges 0.001 to 0.002; length of the inner centripetal sticks 0.02 to 0.03.

_Habitat._--Central Pacific, Station 271, surface.

Genus 31. _Pharyngosphæra_,[53] n. gen.

_Definition._--#Collosphærida# with simple shells, having on the inside radial centripetal tubes, the walls of which are solid.

The genus _Pharyngosphæra_ differs from _Collosphæra_ by the development of radial tubules on the inside of the shell, which are directed centripetally towards its centre. The wall of the tubule is solid, not latticed as in the following genus.

1. _Pharyngosphæra stomodæa_, n. sp. (Pl. 5, fig. 10).

Shell irregular polyhedral, with ten to fifteen polygonal faces and rounded edges. Pores very small, circular, irregularly scattered, smaller than the bars. Twelve to fifteen pores on the half meridian of the shell. On the inside of every shell-face one short, nearly cylindrical, centripetal tubule, twice as long as broad, and about one-third as long as the shell radius. Outer umbilical mouth of the tubules somewhat wider than the inner truncated mouth.

_Dimensions._--Diameter of the shell 0.11 to 0.12, of the pores 0.003 to 0.005, of the bars 0.01 to 0.02; length of the inner tubuli 0.02, breadth of them 0.01.

_Habitat._--South Pacific, Station 288, depth 2600 fathoms.

{99}Genus 32. _Buccinosphæra_,[54] n. gen.

_Definition._--#Collosphærida# with simple shells, having on the inside radial centripetal tubes, the walls of which are fenestrated.

The genus _Buccinosphæra_ exhibits, on the inner surface of the shell, radial centripetal tubules similar to those of the foregoing _Pharyngosphæra_; but the walls of these tubes are here latticed, not solid; they represent therefore true invaginations of the whole shell-wall.

1. _Buccinosphæra invaginata_, n. sp. (Pl. 5, fig. 11).

Shell irregular roundish or nearly polyhedral, with a variable number of umbilical depressions, which are prolonged on the inside into cylindrical or somewhat conical, centripetal, fenestrated tubes, about one-third as long as the shell radius. Inner mouth of the tubes narrower, scarcely half as broad as the outer mouth, about equal to one-fourth the shell radius, truncated. Pores of the tubes and of the shell small, roundish, irregular in size and distribution, about as broad as the bars. Twenty-five to thirty pores in the half meridian of the shell. In all observed specimens the spherical central capsule (half as broad as the shell) contained a large number of crystals.

_Dimensions._--Diameter of the shell 0.1 to 0.12, of the pores 0.001 to 0.003, of the bars 0.002 to 0.003; length of the tubuli 0.02; outer mouth 0.026, inner mouth 0.013; crystals in the central capsule 0.002 to 0.004, sometimes 0.008.

_Habitat._--Philippine Islands (Samboangan), Station 213, surface.

2. _Buccinosphæra tubaria_, n. sp.

Shell irregular polyhedral with rounded edges, with a variable number of umbilical depressions, which are prolonged on the inside into large, nearly cylindrical, centripetal, fenestrated tubes, half as long as the shell radius. In the middle the tubes are somewhat constricted and narrower. Inner mouth of the tubes dilated, nearly as broad as the outer mouth, about equal to one-half the shell-radius, truncated. Pores of the tubes and of the shell large, roundish polygonal, irregular in size and distribution, three to four times as broad as the bars. Fifteen to twenty pores in the half meridian of the shell.

_Dimensions._--Diameter of the shell 0.12 to 0.14, of the pores 0.008 to 0.012, of the bars 0.002 to 0.004; length of the tubuli 0.03; outer mouth 0.04, inner mouth 0.03.

_Habitat._--North coast of New Guinea, Station 217, surface.

Genus 33. _Acrosphæra_,[55] Haeckel, 1881, Prodromus, p. 471.

_Definition._--#Collosphærida# with simple shells, the outer surface of which is covered with radial, irregularly scattered spines.

{100}The genus _Acrosphæra_ differs from its ancestral genus _Collosphæra_ by the development of spines on the outer surface of the shell. These are either short, straight, radial spines, or oblique and often curved; their base is often inflated; they are irregularly scattered on the whole surface between the pores.

1. _Acrosphæra erinacea_, n. sp.

Shell a regular sphere, everywhere covered with small, very numerous, straight radial spines, regularly scattered between the pores. In the half meridian of the shell ten to twelve circular pores, all of the same form and size, double as broad as the bars. Spines bristle-shaped, very thin, solid, about as long as the diameter of the pores.

_Dimensions._--Diameter of the shell 0.1 to 0.12, of the pores 0.008 to 0.012; length of the spines 0.01.

_Habitat._--Tropical zone of the Atlantic, coast of Brazil, Rabbe, surface.

2. _Acrosphæra echinoides_, n. sp. (Pl 8, fig. 1).

Shell a regular sphere, covered with numerous, straight, radial spines, irregularly scattered over the whole surface. In the half meridian of the shell twenty to thirty irregular roundish pores of variable size, one to four times as broad as the bars. Spines conical, strong, quite radial, at the top of small conical elevations, which are perforated by from three to six pores.

_Dimensions._--Diameter of the shell 0.12 to 0.15, of the pores 0.002 to 0.008; length of the spines 0.015, of their basal zones 0.01.

_Habitat._--South-east corner of the Pacific, Valparaiso, Station 298, surface.

3. _Acrosphæra setosa_, Haeckel.

_Polysolenia setosa_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 299, Taf. viii. fig. 10.

Shell a regular sphere, covered with numerous bristle-shaped radial spines, irregularly scattered between the pores. In the half meridian of the shell two to four very large circular pores (equal to one-third the radius), and between them numerous very small, point-like pores.

_Dimensions._--Diameter of the shell 0.05 to 0.08, of the large pores 0.01, of the small 0.001; length of the spines 0.01 to 0.02.

_Habitat._--West Tropical Pacific, Philippine Sea, Station 206, depth 2100 fathoms.

4. _Acrosphæra spinosa_, Haeckel.

_Collosphæra spinosa_, Haeckel, 1862, Monogr. d. Radiol., p. 536, Taf. xxxiv. figs. 12, 13.

_Collosphæra spinosa_, Cienkowsky, 1871, Archiv f. mikrosk. Anat., vii. p. 374, Taf. xxix. figs. 7-17.

Shell a regular or subregular sphere, covered with numerous, obliquely standing spines, irregularly scattered over the surface. In the half meridian of the shell fifteen to twenty irregular {101}roundish pores of very different form and size, one to four times as broad as their bars. Spines conical, irregularly diverging and curved, their hollow base perforated by several pores, not longer than the diameter of the largest pores.

_Dimensions._--Diameter of the shell 0.1 to 0.2, of the pores 0.001 to 0.04; length of the spines 0.01 to 0.02.

_Habitat._--Mediterranean, Messina; Canary Islands, Haeckel.

5. _Acrosphæra collina_, n. sp. (Pl. 8, fig. 2).

Shell quite irregular, polyhedrical, hilly, with a variable number (eight to sixteen) of large conical hill-like prominences; every cone or hill about as high as broad, perforated by the same pores as the shell, on its top bearing a larger irregular roundish pore, and on its edge one single bristle-like spine, not larger than the diameter of this pore, obliquely inserted. In the half meridian of the shell twenty to thirty irregular roundish pores of very different size, one to six times as broad as the bars. A very characteristic species, closely resembling the following _Odontosphæra_.

_Dimensions._--Diameter of the shell 0.15 to 0.25, of the pores 0.005 to 0.02; length of the spines 0.01 to 0.02, height of the hills from which they rise 0.03 to 0.04.

_Habitat._--North coast of New Guinea, Station 218, surface.

6. _Acrosphæra inflata_, n. sp. (Pl. 5, fig. 7).

_Mazosphæra inflata_, Haeckel, 1879, Atlas, _loc. cit._

Shell more or less irregular, polyhedral, hilly, with a variable number (six to twelve) of large pyramidal, hill-like prominences; every hill about as high as broad, on the top a strong conical, radial, or obliquely inserted spine, inflated, with three to six very large polygonal meshes, much larger than the other pores between the hills, which are also polygonal, two to six times as broad as the bars. Ten to fifteen pores on the half meridian.

_Dimensions._--Diameter of the shell 0.1 to 0.14, of the largest pores 0.05, of the smallest 0.005; length of the spines 0.02 to 0.03.

_Habitat._--North Atlantic, Station 64, surface.

Genus 34. _Odontosphæra_,[56] n. gen.

_Definition._--#Collosphærida# with simple shells, the outside of which bears single scattered spines, one single spine on the margin of each larger pore.

The genus _Odontosphæra_ is distinguished from the foregoing _Acrosphæra_ by the peculiar disposition of the spines, which are not scattered on the outside of the shell between the pores, but so disposed that each larger pore is protected by one single spine, obliquely placed over it.

{102}1. _Odontosphæra monodon_, n. sp. (Pl. 5, fig. 5).

Shell spherical or subspherical, with very small and numerous circular pores, much smaller than the bars. Twelve to fifteen pores on the half meridian of the shell. Between them a variable number of larger roundish apertures (mostly twelve to sixteen) irregularly scattered, one-fourth to one-fifth as broad as the shell radius. On the margin of every larger aperture a single (rarely two or three) sharp conical tooth, about as long as the diameter of the aperture, and obliquely laid over them.

_Dimensions._--Diameter of the shell 0.1 to 0.13, of the pores 0.001 to 0.003, of the bars 0.01 to 0.02, of the larger apertures 0.01 to 0.02.

_Habitat._--Sunda Archipelago, Station 192, surface.

2. _Odontosphæra cyrtodon_, n. sp. (Pl. 5, fig. 6).

Shell spherical or subspherical, with numerous roundish pores of very irregular size and distribution, mostly larger than the bars. Ten to twelve pores on the half meridian of the shell. Between them a variable number (mostly six to nine) of large roundish pores, about half as broad as the shell radius, armed on one side of the margin with one single large tooth, about as long as the diameter of the aperture, hook-like, curved, and obliquely laid over them.

_Dimensions._--Diameter of the shell 0.12 to 0.14, of the pores 0.01 to 0.02, of the bars 0.003 to 0.006, of the larger apertures 0.03 to 0.04.

_Habitat._--Indian Ocean, near the Cocos Islands, Rabbe, surface.

Genus 35. _Choenicosphæra_,[57] n. gen.

_Definition._--#Collosphærida# with simple shells, armed on the outside with radial spines, forming elegant coronals around the larger pores.

The genus _Choenicosphæra_ is characterised by the peculiar disposition of its radial spines, which form protective coronals around the larger pores, or even around all pores of the shell.

Subgenus 1. _Choenicosphærula_.

_Definition._--A coronal of spines around every pore of the shell.

1. _Choenicosphæra murrayana_, n. sp. (Pl. 8, fig. 4).

Shell spherical, with large circular or roundish pores of unequal size, two to four times as broad as the bars. Ten to twelve pores in the half meridian of the shell. Margin of every pore {103}with a coronal of six to nine short and acute spines, not longer than the half diameter of the pore. No spines between the pores.

_Dimensions._--Diameter of the shell 0.16 to 0.2, of the pores 0.02 to 0.03; length of the spines 0.008 to 0.012.

_Habitat._--Færöe Channel (Gulf Stream), common. Expedition of H.M.S. "Triton," John Murray.

2. _Choenicosphæra flosculenta_, n. sp.

Shell spherical, with large circular or roundish pores of different size, three to six times as broad as the bars. Six to eight pores in the half meridian of the shell. Margin of every pore somewhat prominent, with a coronal of ten to twenty parallel acute spines of different length, the largest somewhat longer than the diameter of the pore. No spines between the pores.

_Dimensions._--Diameter of the shell 0.12 to 0.15, of the pores 0.02 to 0.04; length of the spines 0.02 to 0.05.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

Subgenus 2. _Choenicosphærium_.

_Definition._--A coronal of spines only around the larger pores, not around the smaller.

3. _Choenicosphæra nassiterna_, n. sp. (Pl. 8, fig. 3).

Shell spherical, with circular or roundish pores of very different size. The smaller pores very numerous, without coronal of spines, roundish, about as broad as the bridges. Twenty to thirty pores in the half meridian of the shell. Between them, irregularly scattered, a small number (eight to twelve) of very large circular pores, one-third to one-half as broad as the radius of the shell, armed with a coronal of six to nine parallel, straight, acute spines, about half as long as the radius of the shell.

_Dimensions._--Diameter of the shell 0.1 to 0.13, of the smaller pores 0.002 to 0.004, of the larger armed pores 0.02 to 0.03; length of the spines 0.03 to 0.04.

_Habitat._--Philippine Islands, Mindanao, Station 213, depth 2050 fathoms.

4. _Choenicosphæra flammabunda_, n. sp. (Pl. 8, fig. 5).

Shell spherical, with circular or roundish pores of very different size. The smaller pores very numerous and unequal, very irregularly scattered, hardly one-fourth to one-half as broad as the bridges between them. Twelve to twenty-four pores in the half meridian of the shell. Between them, irregularly scattered, a variable number (ten to twenty) of very large circular pores, about one-fourth as broad as the radius of the shell. The margin of these large pores is armed with a very irregular coronal of four to twelve unequal, curved acute spines, partly simple, partly branched like {104}a deer-horn, one-fourth to one-half as long as the radius of the shell. Some other small spines irregularly scattered over the shell.

_Dimensions._--Diameter of the shell 0.12 to 0.16, of the smaller pores 0.001 to 0.004, of the larger armed pores 0.016 to 0.024; length of the spines 0.02 to 0.04.

_Habitat._--Central area of the Tropical Pacific, Stations 266 to 272, depth 2425 to 2925 fathoms.

Genus 36. _Siphonosphæra_,[58] J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 59.

_Definition._--#Collosphærida# with simple shells, the pores of which are prolonged into external simple radial tubuli with solid wall; outer mouth of the tubuli truncated, smooth.

The genus _Siphonosphæra_ is, next to _Collosphæra_, the most common of all Collosphærida, and rich in different species; all agreeing in the tubular prolongation of the pores, and corresponding therefore to _Ethmosphæra_ among the simple Liosphærida.

Subgenus 1. _Holosiphonia_, Haeckel.

_Definition._--All the pores or apertures of the shell prolonged into tubules.

1. _Siphonosphæra pansiphonia_, n. sp.

Shell a regular sphere, everywhere occupied by short, regular cylindrical tubes, all of the same size and form. Length of the tubules equal to their breadth and to the intervals between them. Ten to twelve tubules in the half meridian of the shell. This most regular species is nearly allied to _Collosphæra regularis_, and may be derived from it by tubular prolongation of all the regular pores.

_Dimensions._--Diameter of the shell 0.1 to 0.12, length and breadth of the tubules 0.005 to 0.006.

_Habitat._--Indian Ocean, Sunda Strait, Rabbe, surface.

2. _Siphonosphæra marginata_, n. sp.

Shell a regular or subregular sphere, occupied by numerous short cylindrical tubules of different sizes. Six to eight tubules in the half meridian of the shell. Diameter of the tubules about equal to their distance apart, but two to four times as large as their length.

_Dimensions._--Diameter of the shell 0.1 to 14; length of the tubules 0.004 to 0.006, breadth of the tubules and the intervals 0.01 to 0.02.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

{105}3. _Siphonosphæra tubulosa_, J. Müller (Pl. 6, fig. 4).

_Siphonosphæra tubulosa_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 59.

_Siphonosphæra tubulosa_, Haeckel, 1862, Monogr. d. Radiol., p. 532.

_Collosphæra tubulosa_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 59.

_Thalassicolla punctata_, var., Huxley, 1851, Ann. and Mag. Nat. Hist., ser. 2, vol. viii. p. 435, pl. xvi. fig. 5.

Shell subspherical or roundish, somewhat irregular, occupied by a small number (five to ten) of short cylindrical tubules, irregularly scattered at great distances; intervals between the tubules very large, two to four times as broad as the length of the tubules, which is equal to their breadth and about one-fifth or one-sixth of the shell diameter. Only two or three tubules in the half meridian of the shell.

_Dimensions._--Diameter of the shell 0.12 to 0.15, length and breadth of the tubules 0.02 to 0.03.

_Habitat._--Equatorial zone of the Pacific, Stations 225, 265, 268, surface.

4. _Siphonosphæra cyathina_, n. sp. (Pl. 6, fig. 10).

Shell a regular sphere, everywhere occupied by short cup-like tubules of somewhat different size. In the half meridian of the shell about ten to twelve tubules, nearly cylindrical, but constricted in the middle. Inner and outer aperture of the tubule of the same size; their diameter equal to their length and distance.

_Dimensions._--Diameter of the shell 0.1 to 0.12, length and breadth of the tubules 0.005 to 0.01.

_Habitat._--West coast of Tropical Africa, Stations 348 to 352, surface.

5. _Siphonosphæra patinaria_, n. sp. (Pl. 6, figs. 7, 8).

Shell a regular or subregular sphere, occupied by numerous broad cup-like tubules of very different sizes. In the half meridian of the shell about six to eight tubules, very flat, circular or subcircular, much constricted in the middle. Diameter of the inner aperture larger than that of the middle stricture, smaller than that of the outer aperture of the tubule; outer diameter two to four times as great as their length.

_Dimensions._--Diameter of the shell 0.1 to 0.15, of the pores 0.01 to 0.04; length of the tubules 0.01, breadth 0.02 to 0.04.

_Habitat._--Tropical Atlantic, Station 348, depth 2450 fathoms.

6. _Siphonosphæra infundibulum_, n. sp.

Shell subspherical or irregular rounded, occupied by a small number (six to twelve) of large funnel-like tubules of very different size, scattered irregularly at great distances. Intervals between the tubules larger than their length, which surpasses the radius of the shell. Outer opening of the funnels three to four times as broad as the inner.

_Dimensions._--Diameter of the shell 0.15; length of the tubules 0.05 to 0.09.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

{106}7. _Siphonosphæra conifera_, n. sp. (Pl. 6, fig. 9).

Shell subspherical, everywhere occupied by irregular conical tubules, the length of which nearly reaches the shell radius. Inner aperture of the cones two to three times as large as the outer. Four to five tubules in the half meridian of the shell. Distances between the bases of the cones small and irregular.

_Dimensions._--Diameter of the shell 0.06 to 0.08, length of the tubules 0.03 to 0.04; inner aperture of the cones 0.01 to 0.02, outer aperture 0.008 to 0.01.

_Habitat._--Indian Ocean, Cocos Islands, Rabbe, surface.

8. _Siphonosphæra fragilis_, n. sp.

Shell quite irregular roundish or nearly ovate, very thin and fragile, everywhere occupied by irregular, short, and broad cylindrical or conical tubes. Six to ten tubes in the half meridian of the shell. Diameter of the tubules about one-eighth that of the shell, three to four times as large as the length of the tubules, and the distance apart of their bases.

_Dimensions._--Diameter of the shell 0.16 to 0.24, of the tubules 0.02 to 0.03; length of the tubules 0.006 to 0.008, distance of them 0.005 to 0.009.

_Habitat._--East coast of Australia, Sydney, Faber; Station 165, surface.

Subgenus 2. _Merosiphonia_, Haeckel.

_Definition._--Only part of the shell apertures prolonged in tubules, the others simple.

9. _Siphonosphæra socialis_, n. sp. (Pl. 6, figs. 1, 2).

Shell a regular or subregular sphere, bearing only a small number (one to four, commonly two to three) of short and broad cylindrical tubules, irregularly scattered. Between them many small circular or subcircular pores of different sizes, double as broad as their bars. Eight to ten pores in the half meridian of the shell. Tubules three to six times as broad as the pores, about as long as broad, now quite cylindrical, now somewhat dilated at the outer opening. (Although the shells and cells of this common species are among the smallest, their colonies are among the largest, often containing more than one hundred social individuals, often enclosed in alveoles.)

_Dimensions._--Diameter of the shell 0.04 to 0.05, of the pores 0.002 to 0.004, of the tubules 0.015 to 0.02; length of them about the same.

_Habitat._--Tropical and subtropical part of the Eastern Atlantic, Cape Verde Islands, Canaries, very common, Haeckel; Stations 338 to 353, surface.

10. _Siphonosphæra polysiphonia_, n. sp.

Shell a regular or subregular sphere, bearing twelve to sixteen circular pores in its half meridian. Nearly one half the pores simple, very small; the other half prolonged into short cylindrical tubules, {107}half as long as broad, two to four times as broad as the pores and their intervals. This species is nearly related to the foregoing, which it represents in the western tropical part of the Atlantic, but differs constantly in the double size of the shell and the much larger number of the tubules.

_Dimensions._--Diameter of the shell 0.06 to 0.09, of the pores 0.002 to 0.004, of the tubules 0.01 to 0.012; their length 0.006 to 0.008, surface.

_Habitat._--Tropical and subtropical part of the Western Atlantic, coast of Brazil, &c., Rabbe.

11. _Siphonosphæra macrosiphonia_, n. sp.

Shell a regular sphere, with numerous very small pores of equal size and distribution. Twelve to sixteen pores in its half meridian. Bars (between the pores) three to four times as broad as their diameter. Only a small number (two to four) of very long cylindrical tubes, irregularly scattered, nearly as long or somewhat longer than the shell diameter; now quite straight, now somewhat curved. Diameter of the cylinders four to six times as large as that of the pores.

_Dimensions._--Diameter of the shell 0.1 to 0.12, of the pores 0.002 to 0.004, of the tubules 0.015 to 0.018; length of the tubules 0.08 to 0.16.

_Habitat._--Central Tropical Pacific, Station 266 to 272, surface.

12. _Siphonosphæra serpula_, n. sp. (Pl. 6, fig. 6).

Shell a regular sphere, with numerous very small pores of equal size and distribution. Eight to ten pores in its half meridian; bars between them three to four times as broad as their diameter. Only a small number (six to eight) of very long and snake-like, contorted, cylindrical tubes, irregularly scattered. The shape of the latter is very much like that of the calcareous tubes of some species of _Serpula_; they are nearly as long as, or longer than, the shell diameter, and four to six times as broad as the pores.

_Dimensions._--Diameter of the shell 0.12 to 0.14, of the pores 0.003 to 0.005, of the tubules 0.02 to 0.022; length of the tubules 0.1 to 0.2.

_Habitat._--North Eastern Pacific, Station 252 to 262, Sandwich Islands, Haltermann.

13. _Siphonosphæra chonophora_, n. sp. (Pl. 6, fig. 5).

Shell a regular or subregular sphere, with numerous very small pores of equal size and distribution, ten to twelve in its half meridian. Bars between the pores four to six times their diameter. Only a small number (two to six) of very large funnel-like tubules, irregularly scattered. The inner half of these tubules is a short cylindrical tube, of the same thickness as the shell, three to four times as broad as the pores; the outer half is an irregular funnel, suddenly expanded, with siliceous walls of the utmost tenuity and fragility, often irregularly folded and contorted, like a decayed flower-calyx, often half as large as the shell.

_Dimensions._--Diameter of the shell 0.1 to 0.12, of the pores 0.003 to 0.005, inner half of the tubules 0.015 to 0.02, outer funnel-like half 0.05 to 0.08.

_Habitat._--South Pacific, Stations 285 to 295, surface.

{108}14. _Siphonosphæra pipetta_, n. sp. (Pl. 6, fig. 3).

Shell more or less irregularly roundish or subspherical, occupied in part by very small pores, in part by very large cylindrical tubules, inflated in the middle. Number, form, and size of the tubes very irregular; commonly there are five to ten, half as long or as long as the shell radius; their inner and outer aperture about half as broad as their inflated middle part; three to nine times as broad as the pores. A very irregular and variable species.

_Dimensions._--Diameter of the shell 0.1 to 0.15, of the pores 0.001 to 0.005, of the tubules 0.015 to 0.03; length of the tubules 0.03 to 0.08.

_Habitat._--North Pacific, Stations 242 to 253, surface.

Genus 37. _Mazosphæra_,[59] Ehrenberg, 1860.

_Mazosphæra_, Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 833.

_Definition._--#Collosphærida# with simple shells, the pores of which are prolonged into external simple radial tubuli with solid wall; outer mouth of each tubulus armed with a single tooth.

The genus _Mazosphæra_ is intermediate between _Siphonosphæra_ and _Odontosphæra_, agreeing with the former in the tubular prolongation of the pores, with the latter in the possession of a single large protective tooth on the outer opening.

1. _Mazosphæra hippotis_, n. sp. (Pl. 5, fig. 8).

Shell spherical, with circular pores of irregular size and distribution, scarcely half as broad as the bars; fifteen to twenty on the half meridian of the shell. Between them, irregularly distributed, a variable number (ten to fifteen) of short cylindrical radial tubules, about twice as long as broad, and half as long as the shell radius. Mouth of the tubuli obliquely truncated, having on one side a strong acute tooth.

_Dimensions._--Diameter of the shell 0.11 to 0.12, of the pores 0.002 to 0.004, of the bridges 0.006 to 0.009; length of the tubuli 0.03, breadth of them 0.01 to 0.015.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

2. _Mazosphæra lagotis_, n. sp. (Pl. 5, fig. 9).

Shell spherical, with circular pores of irregular size and distribution, about as broad as the bars; twelve to sixteen on the half meridian. Between them, irregularly distributed, a variable number (eight to twelve) of long, cylindrical, curved tubules, three to six times as long as broad, and about as long as the shell radius; their external mouth lateral, obliquely truncated, ovate, having on one side a strong conical tooth.

{109}_Dimensions._--Diameter of the shell 0.1 to 0.12, of the pores 0.002 to 0.01; length of the tubuli 0.05 to 0.07.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

3. _Mazosphæra lævis_, Ehrenberg.

_Mazosphæra lævis_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 297, Taf. vii. fig. 7.

Shell spherical, with very small pores, scarcely one-fourth as broad as the bars. Fifteen to twenty pores on the half meridian of the shell. Between them, irregularly distributed, a variable number (fifteen to twenty) of short conical tubules, about as long as broad, only one-fifth to one-sixth as long as the shell radius. Mouth of the tubuli truncated, with an obtuse short tooth on one side.

_Dimensions._--Diameter of the shell 0.08 to 0.09, of the pores 0.001 to 0.002, of the bridges 0.005 to 0.008; length of the tubuli 0.01 to 0.02, breadth of them the same.

_Habitat._--Philippine Islands (depth 3300 fathoms), Ehrenberg; Station 206, depth 2100 fathoms; Station 225, depth 4575 fathoms.

4. _Mazosphæra apicata_, Ehrenberg.

_Mazosphæra apicata_, Ehrenberg, 1872, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 316.

Shell spherical, without small pores, only with a variable number (ten to twenty) of short conical tubules, twice as long as broad, and half as long as the shell radius. Mouths of the tubuli obliquely truncated, with a strong acute tooth on one side. (This species differs from the two preceding by the want of the small pores between the tubules.)

_Dimensions._--Diameter of the shell 0.08 to 0.1, of the tubules 0.01.

_Habitat._--Philippine Islands (depth 3300 fathoms), Ehrenberg; north coast of New Guinea, depth 2000 fathoms; Station 217.

Genus 38. _Trypanosphæra_,[60] n. gen.

_Definition._--#Collosphærida# with simple shells, the pores of which are prolonged into external simple radial tubuli with solid walls; outer mouth of each tubulus armed with a coronal of spines.

The genus _Trypanosphæra_ is intermediate between _Siphonosphæra_ and _Choenicosphæra_ agreeing with the former in the tubular prolongation of the pores, with the latter in the possession of a coronal of teeth on their outer opening.

Subgenus 1. _Trypanosphærula_, Haeckel.

_Definition._--All pores of the shell prolonged into short coronated tubules.

{110}1. _Trypanosphæra trepanata_, n. sp. (Pl. 5, fig. 4).

Shell regular spherical, with regular circular pores of nearly equal size, at unequal distances, one to four times as broad as the bars. Eight to ten pores on the half meridian. All the pores prolonged into short cylindrical tubuli about as long as broad, armed on the external mouth with an elegant coronal of twenty to thirty straight bristle-shaped, parallel teeth.

_Dimensions._--Diameter of the shell 0.12 to 0.14, of the pores 0.015 to 0.02; length of the tubuli 0.02.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

2. _Trypanosphæra dentata_, n. sp.

Shell regular spherical, with regular circular pores of equal size, but at very different distances. Only three to four pores on the half meridian. All the pores prolonged into irregular curved, cylindrical tubuli, about as long as the shell radius, with a coronal of ten to twelve short conical teeth on the distal end.

_Dimensions._--Diameter of the shell 0.08 to 0.09; length of the tubuli 0.04, breadth 0.02.

_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.

Subgenus 2. _Trypanosphærium_, Haeckel.

_Definition._--Only part of the shell-pores prolonged into coronated tubules.

3. _Trypanosphæra coronata_, n. sp. (Pl. 5, fig. 3).

Shell regular spherical, with irregular roundish pores of very different sizes. On the half meridian four to six large and twelve to sixteen very small pores. About half of the large pores prolonged into short cylindrical tubuli, the outer mouth of each being armed with an elegant coronal of ten to twenty thin irregular teeth.

_Dimensions._--Diameter of the shell 0.1 to 0.12, of the large pores 0.01 to 0.02, of the small pores 0.001; length of the tubuli 0.012.

_Habitat._--North Pacific, Station 241, depth 2300 fathoms.

4. _Trypanosphæra terebrata_, n. sp.

Shell irregular roundish, with unequal, small, roundish pores. Sixteen to twenty pores on the half meridian. Six to eight larger pores are prolonged into curved cylindrical tubuli, about as long as the shell radius, with a coronal of ten to twelve strong conical straight teeth on the distal end.

_Dimensions._--Diameter of the shell 0.15, of the pores 0.001 to 0.003; length of the tubuli 0.08, breadth 0.02.

_Habitat._--West Tropical Pacific, Station 225, depth 4575 fathoms.

{111}5. _Trypanosphæra transformata_, n. sp. (Pl. 5, figs. 1, 2).

Shell quite irregular, of very variable, roundish, or polyhedral form, with small irregular roundish pores, two to four times as broad as the bars. Ten to thirty on the half meridian. The different form of the shell depends upon the variable number of tubuli, which arise at irregular distances from the shell; commonly three to four, often also five to six, more rarely one or two. The tubuli are now more conical, now more cylindrical, about as long as the shell radius, at other times scarcely one-half or one-third as long, with a coronal of ten to twenty more or less curved teeth on the narrower distal mouth. All the different forms are to be found in one and the same colony, as shown in fig. 1. This coenobium, which I observed living in Ceylon, exhibited the same peculiar formation as I figured in _Collosphæra huxleyi_ in my Monograph 1862 (Taf. xxxiv. fig. 1). In the centre of the jelly-sphere lies a large globular alveole, surrounded by numerous small, young central capsules without shell; whilst in the surface lies one layer of older capsules, enclosed in shells. Some of the younger capsules exhibit self-division.

_Dimensions._--Diameter of the shells 0.08 to 0.12, pores 0.002 to 0.006; length and breadth of the tubuli 0.03 to 0.05.

_Habitat._--Indian Ocean, Belligemma, Ceylon, surface.

Genus 39. _Caminosphæra_,[61] n. gen.

_Definition._--#Collosphærida# with simple shells, the pores of which are prolonged into external branched radial tubuli with solid wall.

The genus _Caminosphæra_ differs from _Siphonosphæra_ (and from all other Collosphærida) in the ramification of the tubuli, which arise from the pores; the walls of the tubuli are solid, not fenestrated.

1. _Caminosphæra furcata_, n. sp.

Shell spherical or subspherical, with a variable number (four to eight) of short cylindrical tubes, irregularly scattered, about as long as the radius of the shell. Every tube forked, with two cylindrical branches of the same size as the simple basal part of the tube. Mouth of the branches truncated, not dilated. Pores of the shell between the tubes very small, all of the same size, half as broad as their bars. Fifteen to twenty pores in the half meridian of the shell.

_Dimensions._--Diameter of the shell 0.1 to 0.12, of the pores 0.001 to 0.002; length of the tubules 0.05 to 0.06, breadth of them 0.012 to 0.015.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

2. _Caminosphæra elongata_, n. sp.

Shell spherical, with a large number (twelve to twenty) of long cylindrical tubes, irregularly formed and scattered, somewhat longer than the diameter of the shell. Every tube forked at {112}the distal end, with two or three short irregular branches of unequal size and form; branches much shorter than the undivided basal part of the tube. Mouth of the branches narrowed, truncated. Pores of the shell between the tubes about half as broad, irregularly roundish or polygonal, two to three times as broad as their bars. Ten to twelve pores in the half meridian of the shell.

_Dimensions._--Diameter of the shell 0.05 to 0.07, of the pores 0.006 to 0.009; length of the tubules 0.06 to 0.09, breadth of them 0.015 to 0.02.

_Habitat._--Tropical Central Pacific, Station 271, depth 2425 fathoms.

3. _Caminosphæra dichotoma_, n. sp. (Pl. 7, fig. 2).

Shell spherical, with a variable number (ten to fifteen) of cylindrical tubes, irregularly scattered, about as long as the radius of the shell. Every tube furcated, with two cylindrical branches of the same size as the simple basal part of the tube. Mouth of the branches dilated, funnel-like, twice as broad as the tube; the edges irregularly dentated or lacerated. Pores between the tubes small, one-third to one-sixth as broad as these, half as broad as their bars. Ten to twelve pores in the half meridian of the shell.

_Dimensions._--Diameter of the shell 0.12 to 0.14, of the pores 0.003 to 0.005; length of the tubules 0.06 to 0.08, breadth of them 0.02 to 0.03.

_Habitat._--Southern Pacific, Station 295, depth 1500 fathoms.

4. _Caminosphæra dendrophora_, n. sp. (Pl. 7, fig. 1).

Shell spherical, with a variable number (eight to twelve) of long cylindrical tubes, irregularly branched and scattered, nearly as long as the diameter of the shell. Every tube with two to six (commonly three to four) branches of different sizes. Mouth of the branches dilated, funnel-like; the edges irregularly dentated or lacerated. Pores between the tubes half as broad as these, irregularly roundish, twice as broad as their bars. Ten to twelve pores in the half meridian of the shell.

_Dimensions._--Diameter of the shell 0.12 to 0.15, of the pores 0.006 to 0.01; length of the tubules 0.1 to 0.13, breadth of them 0.02 to 0.025.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

Genus 40. _Solenosphæra_,[62] n. gen.

_Definition._--#Collosphærida# with simple shells, the pores of which are prolonged into external simple radial tubuli with fenestrated wall; outer mouth of the tubuli truncated, smooth.

The genus _Solenosphæra_ differs from _Siphonosphæra_ in the fenestration of the external radial tubes. A large number of shells, appertaining to this genus, were already described by Ehrenberg, and disposed in five different genera corresponding to the {113}different numbers of the tubuli:--_Disolenia_ with two tubes, _Trisolenia_ with three tubes, _Tetrasolenia_ with four tubes, _Pentasolenia_ with five tubes, _Polysolenia_ with six or more tubes. All these five genera are without value, as those different numbers of tubes occur frequently intermingled in the individual cells of one and the same colony, wherever the form and structure of the tubes is inherited with sufficient constancy to determine the species.

Subgenus 1. _Solenosphactra_, Haeckel.

_Definition._--Tubuli of the shell cylindrical or nearly cylindrical, the outer and inner apertures nearly of the same size.

1. _Solenosphæra variabilis_, Haeckel.

_Tetrasolenia quadrata_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. x. fig. 20.

Shell quite irregular roundish or polyhedral, with roundish pores of different size. Ten to fifteen pores in the half meridian of the shell, two to three times as broad as the bars. Porous tubuli of the shell in variable number (in one and the same colony), three to nine, mostly four to six; cylindrical or subcylindrical or somewhat conical, two to three times as broad as long, not longer than the half radius of the shell. Inner aperture of the tubuli commonly as broad as the half radius of the shell (or somewhat smaller), about as large as the truncated outer aperture. This species is closely related to _Collosphæra polyedra_ (p. 97), and may be derived from it by a short tube-like prolongation of the larger apertures.

_Dimensions._--Diameter of the shell 0.1 to 0.16, of the pores 0.005 to 0.015; length of the tubules 0.02 to 0.03, breadth of them 0.04 to 0.06.

_Habitat._--Central area of the Tropical Pacific, Stations 270, 271, 272, depths 2425 to 2925 fathoms.

2. _Solenosphæra pandora_, n. sp. (Pl. 7, figs. 10, 11).

Shell irregular roundish or subglobular, with roundish pores of different sizes, mostly somewhat broader than the bars. About twelve to sixteen pores on the half meridian of the shell. Porous tubuli of the shell of variable number (in one and the same colony), one to six, mostly three to four; cylindrical or nearly cylindrical, somewhat longer than broad, not longer than the radius of the shell. Inner aperture of the tubuli commonly as broad as the half radius of the shell, and a little smaller than the truncated outer aperture.

_Dimensions._--Diameter of the shell 0.07 to 0.1, of the pores 0.003 to 0.006; length of the tubuli 0.03 to 0.05, breadth of them 0.02 to 0.03.

_Habitat._--Central area of the Tropical Pacific, Stations 266 to 274, depths 2350 to 2925 fathoms.

{114}3. _Solenosphæra megalactis_, Haeckel.

_Trisolenia megalactis_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 301, Taf. viii. fig. 19.

Shell irregularly polyhedrical, with very small roundish pores, scarcely half as broad as the bars. Only eight to ten pores on the half meridian of the shell. Porous tubuli of the shell of variable number (in one and the same colony), two to five, mostly three or four; cylindrical, about as long as the radius of the shell. Inner aperture of the tubuli commonly as broad as the half radius of the shell, and quite as broad as the truncated outer aperture.

_Dimensions._--Diameter of the shell 0.07 to 0.09, of the pores 0.002 to 0.004, of the bars 0.005 to 0.009; length of the tubuli 0.03 to 0.04, breadth of them 0.02.

_Habitat._--Pacific; California, Philippine Sea, Ehrenberg; Stations 256 to 285, depths 310 to 3000 fathoms.

4. _Solenosphæra serpentina_, n. sp. (Pl. 7, fig. 7).

Shell nearly spherical, with very small circular pores, scarcely one-third or one-fourth as broad as the bars. Only five to seven pores in the half meridian of the shell. Porous tubuli of the shell of variable number (in one and the same colony), two to nine, mostly seven or eight; cylindrical, somewhat curved or contorted, once and a half or twice as long as the diameter of the shell, with few very small and widely scattered pores. Inner and outer aperture of the tubuli have the same diameter, about one-fifth or one-fourth that of the shell. (This species is closely allied to _Siphonosphæra serpula_, but is distinguished from it by the long tortuous tubuli and the small scarce pores.)

_Dimensions._--Diameter of the shell 0.08 to 0.1, of the pores 0.001 to 0.002, of the bars 0.004 to 0.008; length of the tubuli 0.12 to 0.18, breadth of them 0.02 to 0.025.

_Habitat._--North-eastern Pacific, between Sandwich Islands and California, Haltermann, surface.

Subgenus 2. _Solenosphenia_, Haeckel.

_Definition._--Tubuli of the shell more or less conical, the inner aperture much larger than the outer aperture.

5. _Solenosphæra venosa_, Haeckel.

_Tetrasolenia venosa_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 301, Taf. vii. fig. 22.

Shell irregular polyhedral or roundish, with a delicate network of large irregular polyhedral meshes, five to ten times as broad as the thin bars. Eight to twelve meshes on the half meridian of the shell. Fenestrated tubuli of the shell of variable number (in one and the same colony), one to five, commonly three or four, shaped like a short truncated cone, about half as long as broad on its base, shorter than the radius of the shell. Inner aperture of the cone nearly as broad as the half radius of the shell, about twice as broad as the truncated outer aperture.

{115}_Dimensions._--Diameter of the shell 0.07 to 0.12, of the pores 0.008 to 0.016, of the bars 0.001; length of the tubuli 0.02 to 0.03, inner aperture 0.03 to 0.04, outer aperture 0.02 to 0.03.

_Habitat._--Indian Ocean, Sunda Strait, Rabbe.

6. _Solenosphæra ascensionis_, n. sp. (Pl. 7, fig. 9).

Shell somewhat irregular, subspherical, with polygonal pores of different size. Twelve to fifteen pores in the half meridian of the shell, two to eight times as broad as their bars. Porous tubuli of the shell of variable number (in one and the same colony), three to nine, mostly five to seven; conical or nearly cylindrical, irregular, about as long as broad at their base. Inner aperture of the tubuli two to four times as broad as the broadest pores, and double as broad as the truncated circular outer aperture.

_Dimensions._--Diameter of the shell 0.1 to 0.12, of the pores 0.004 to 0.018, of the bars 0.002, length of the tubuli 0.04, inner aperture 0.04, outer 0.02.

_Habitat._--South Atlantic, near Ascension Island, Station 343, surface.

Subgenus 3. _Solenosphyra_, Haeckel.

_Definition._--Tubuli of the shell funnel-like, the outer aperture much larger than the inner.

7. _Solenosphæra cornucopia_, n. sp. (Pl. 7, fig. 8).

Shell spherical or subspherical, with roundish pores of different size. Ten to twelve pores in the half meridian of the shell, two to three times as broad as the bars. Porous tubuli of the shell of variable number (in one and the same colony), four to eight, mostly five to seven, funnel-like, about as long as the diameter of the shell. Inner aperture of the tubuli commonly two-thirds or three-fourths as broad as the radius of the shell (or somewhat smaller), only one-half or two-thirds as broad as the dilated and truncated outer aperture.

_Dimensions._--Diameter of the shell 0.07 to 0.09, of the pores 0.006 to 0.018; length of the tubuli 0.06 to 0.08, diameter of the inner aperture 0.04 to 0.05, of the outer 0.06 to 0.08.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

8. _Solenosphæra amalthea_, n. sp.

Shell irregular roundish or spherical, with small circular pores of different size. Fifteen to twenty pores in the half meridian of the shell, but still not as broad as the bars. Porous tubuli of the shell of variable number (in one and the same colony), three to six, commonly four or five, funnel-like, about as long as the radius of the shell. Inner aperture of the tubuli about half as broad as the radius of the shell, only one-half or one-third as broad as the truncated outer aperture. (This species is intermediate between the preceding and _Siphonosphæra chonophora_, Pl. 6, fig. 5.)

{116}_Dimensions._--Diameter of the shell 0.09 to 0.11, of the pores 0.002 to 0.004, of the bars 0.003 to 0.006; length of the tubuli 0.05 to 0.06; diameter of the inner aperture 0.02 to 0.03, of the outer aperture 0.05 to 0.07.

_Habitat._--Western part of the South Atlantic, Station 325, surface.

Genus 41. _Otosphæra_,[63] n. gen.

_Definition._--#Collosphærida# with simple shells, the pores of which are prolonged into external simple radial tubuli with fenestrated walls; outer mouth of the tubuli armed with a single tooth.

The genus _Otosphæra_ differs from _Solenosphæra_ by the single tooth on the external mouth of the tubuli, from _Mazosphæra_ by the fenestration of the walls of the tubuli.

1. _Otosphæra polymorpha_, n. sp. (Pl. 7, fig. 6).

Shell quite irregular, polyhedral or roundish, very variable in size and form, with numerous very small pores, much smaller than the bars. Twenty to thirty pores in the half meridian of the shell. Porous tubuli of the shell commonly in variable number (one to four), but sometimes constant in number (one, two, three, or four) in the one and same colony. Tubuli irregular conical, commonly about as long as the radius of the shell; their outer aperture obliquely truncated, on one side prolonged into one large, prominent, bill-like, curved, acute tooth.

_Dimensions._--Diameter of the shell 0.12 to 0.15, of the pores 0.001 to 0.002; length of the tubuli 0.06 to 0.08, inner aperture 0.03, outer aperture 0.02.

_Habitat._--Indian Ocean, Madagascar, Rabbe, surface.

2. _Otosphæra auriculata_, n. sp. (Pl. 7, fig. 5).

Shell quite irregular, of extremely variable form, now inclining to roundish, now to polyhedral, with very numerous small pores, irregularly formed and distributed. Twelve to twenty-four pores in the half meridian of the shell, of very different size, for the most part larger than the bars. Porous tubuli of the shell of variable number (in one and the same colony), one to five, mostly three or four, of conical form, irregularly formed and scattered, commonly about half as long as the radius of the shell. Outer aperture of the tubuli obliquely truncated, with one large prominent, often curved, acute tooth.

_Dimensions._--Diameter of the shell 0.1 to 0.2, of the pores 0.003 to 0.005; length of the tubuli 0.01 to 0.05, inner aperture 0.04, outer aperture 0.03.

_Habitat._--Central Tropical Pacific, Stations 268 to 272, depths 2425 to 2925 fathoms.

{117}Genus 42. _Coronosphæra_,[64] n. gen.

_Definition._--#Collosphærida# with simple shells, the pores of which are prolonged into external simple radial tubuli with fenestrated walls; outer mouth of the tubuli armed with a coronal of spines.

The genus _Coronosphæra_ differs from _Solenosphæra_ by the coronated mouth of the tubuli, from _Trypanosphæra_ by the fenestration of the walls of the tubuli.

1. _Coronosphæra diadema_, n. sp. (Pl. 7, fig. 3).

Shell spherical or subspherical, with a variable number (fifteen to twenty) of short, coronal-like tubules, irregularly scattered, about half as long as the radius of the shell. Outer aperture of the tubuli irregularly dentated, a little dilated, and not much broader than the inner aperture, one-half or one-third as broad as the shell radius. Pores of the shell and of the tubuli circular or roundish, very irregularly scattered, mostly one-half or one-third as broad as the bars.

_Dimensions._--Diameter of the shell 0.11 to 14, of the pores 0.002 to 0.004, of the bars 0.006 to 0.012; length of the tubuli 0.03, inner aperture 0.02 to 0.03, outer aperture 0.03 to 0.04.

_Habitat._--Central Pacific, Stations 268 to 270, depths 2550 to 2925 fathoms.

2. _Coronosphæra calycina_, n. sp. (Pl. 7, fig. 4).

Shell spherical or subspherical, with a variable number (eight to twelve) of large, funnel-like tubules, irregularly scattered, about as long as the radius of the shell. Outer aperture of the tubuli irregularly dentated, much dilated, somewhat broader than the shell radius, three to four times as broad as the inner circular aperture. Pores of the shell and of the tubuli circular or roundish, of very different size, one to three times as broad as the bars.

_Dimensions._--Diameter of the shell 0.1 to 0.3, of the pores 0.003 to 0.01, of the bars 0.002 to 0.004; length of the tubuli 0.1, inner aperture 0.02 to 0.03, outer aperture 0.06 to 0.18.

_Habitat._--Central Pacific, Stations 271, 272, depths 2425 and 2600 fathoms respectively.

3. _Coronosphæra convolvulus_, n. sp.

Shell irregular roundish, with a variable number (five to ten) of long, curved tubules, about as long as the shell diameter. The inner half of the tubuli is narrow, cylindrical; the outer half funnel-like dilated, similar to the flower of _Convolvulus_. The outer aperture is elegantly dentated, five to six times as broad as the inner aperture. Pores of the shell and of the tubuli very irregular roundish, about as broad as the bars.

_Dimensions._--Diameter of the shell 0.08 to 0.09, of the pores and bars 0.004 to 0.008; length of the tubuli 0.07 to 0.1, inner aperture 0.01, outer aperture 0.05.

_Habitat._--Tropical Atlantic, Station 347, surface.

{118}Subfamily CLATHROSPHÆRIDA, Haeckel, 1881, Prodromus, p. 472.

_Definition._--#Collosphærida# with a double lattice-shell around every central capsule of the coenobium; both concentric shells connected by irregular or subradial beams, commonly solid or lamellar staffs, rarely hollow tubes.

Genus 43. _Clathrosphæra_,[65] Haeckel, 1881, Prodromus, p. 472.

_Definition._--#Collosphærida# with a double lattice-shell around every central capsule of the coenobium; surface of the outer shell smooth.

The genus _Clathrosphæra_ (with smooth surface) and the following _Xanthiosphæra_ (with spiny surface) form together the small subfamily, Clathrosphærida, different from the other Collosphærida by the double lattice-shell. From the surface of the inner primary shell arise either solid spines or hollow tubes, which unite by the anastomosis of irregular branches and so form the outer secondary shell, often very incomplete and irregular. All Clathrosphærida seem to inhabit great depths.

Subgenus 1. _Clathrosphærula_, Haeckel.

_Definition._--The connecting staffs between both shells are hollow tubes (derived from _Siphonosphæra_).

1. _Clathrosphæra circumtexta_, n. sp. (Pl. 8, fig. 6).

Inner shell spherical, with irregular roundish large meshes, now broader now smaller than their bars. Eight to ten meshes in the half meridian of the shell. All these meshes are prolonged into short cylindrical hollow tubes, about as long as broad, somewhat constricted in the middle. From the margins of the outer openings of these tubes proceed very numerous and delicate siliceous filaments, which all lie on the same spherical face, branch, anastomose, and twine over the openings and the intervals between them, forming a very thin, arachnoid spherical outer shell. The meshes of this are quite irregular polygonal, of very different size and form. The radius of the inner shell bears to that of the outer a ratio = 5 : 6.

_Dimensions._--Diameter of the inner shell 0.11 to 0.13, of the outer 0.13 to 0.16; meshes of the inner shell 0.005 to 0.02, of the outer 0.005 to 0.04.

_Habitat._--North Pacific, Stations 238 to 253, depths 2050 to 3950 fathoms.

Subgenus 2. _Clathrosphærium_, Haeckel.

_Definition._--The connecting staffs between the two shells are solid rods or lamellar spines (derived from _Acrosphæra_).

{119}2. _Clathrosphæra arachnoides_, n. sp. (Pl. 8, fig. 7).

Inner shell spherical, with irregular roundish meshes, two or three times as broad as the bars. Ten to twelve meshes in the half meridian of the shell. From its surface arise numerous conical radial spines (with base often fenestrated), which at equal distances from the surface send out lateral branches. All these branches lie on a spherical face, and form by communications the irregular, very delicate, arachnoid network of the outer shell, quite unlike that of the inner, with large polygonal meshes of very different size. Eight to sixteen meshes in the half meridian of the shell. Surface of the outer shell nearly spherical, somewhat uneven, like a spider's web. The radius of the inner shell bears to that of the outer a ratio = 3 : 4.

_Dimensions._--Diameter of the inner shell 0.12 to 0.14, of the outer 0.15 to 0.18; pores of the inner shell 0.003 to 0.02, of the outer 0.01 to 0.04.

_Habitat._--Central area of the Tropical Pacific, Station 268, depth 2900 fathoms.

3. _Clathrosphæra lamellosa_, n. sp. (Pl. 8, fig. 8).

Inner shell spherical or subspherical, with irregular roundish meshes, about half as broad as the bars. Twelve to sixteen meshes in the half meridian of the shell. From its surface arise numerous oblique irregular staffs or broad and thin lamellæ, which branch quite irregularly, and by communications of the branches form the thin outer shell. This is quite irregular roundish or subspherical, very unlike the inner, with large polygonal meshes of different size, six to twelve in the half meridian of the shell. Bridges between the meshes very variable, now very thin filamentous, now very broad lamellar. Outer surface very uneven or tuberculated, but not spinous. The radius of the inner shell bears to that of the outer a ratio = 5 : 6.

_Dimensions._--Diameter of the inner shell 0.1 to 0.13, of the outer 0.12 to 0.18; pores of the inner shell 0.003 to 0.009, of the outer 0.01 to 0.04.

_Habitat._--Central area of the Tropical Pacific, Stations 270 to 274, depths 2350 to 2925 fathoms.

Genus 44. _Xanthiosphæra_,[66] Haeckel, 1881, Prodromus, p. 472.

_Definition._--#Collosphærida# with a double lattice-shell around every central capsule of the coenobium; surface of the outer shell thorny or spiny.

The genus _Xanthiosphæra_ differs from the foregoing _Clathrosphæra_ by spines or thorns arising from the surface of the outer shell, commonly very irregular.

1. _Xanthiosphæra capillacea_, n. sp.

Inner shell spherical, with irregular polygonal meshes, three to five times as broad as their narrow bars. Six to eight meshes in the half meridian of the shell. From its surface arise at the nodes of the network numerous thin radial spines, which, at equal distances from the surface, {120}send out lateral branches. All these branches lie on a spherical face, and form by communications the irregular delicate network of the outer shell, very like that of the inner, with large polygonal meshes, six to eight meshes in the half meridian of the shell. Surface of the outer shell covered with numerous straight spines, prolongations of the inner spines, but only half as long as these. The radius of the inner shell bears to that of the outer a ratio = 3 : 5.

_Dimensions._--Diameter of the inner shell 0.1 to 0.12, of the outer 0.15 to 0.19; pores of the inner shell 0.02 to 0.04 to 0.06, of the outer 0.04 to 0.06 to 0.08; length of the outer spines 0.01 to 0.02.

_Habitat._--Central area of the Tropical Pacific, Station 263, depth 2650 fathoms.

2. _Xanthiosphæra erinacea_, n. sp. (Pl. 8, fig. 9).

Inner shell spherical, with irregular roundish meshes, one-half to two times as broad as the bars. Fifteen to twenty meshes in the half meridian of the shell. From its surface arise numerous thin radial spines, which at equal distances from the surface send out lateral branches. All these branches lie on the face of a sphere, and form by communications the irregular delicate network of the outer shell, very unlike that of the inner, with large polygonal meshes, twelve to twenty-four in the half meridian of the shell. Surface of the outer shell covered with numerous straight spines, prolongations of the inner spines, and of the same length. The radius of the inner shell bears to that of the outer a ratio = 3 : 4.

_Dimensions._--Diameter of the inner shell 0.1 to 0.12, of the outer 0.13 to 0.16; pores of the inner shell 0.002 to 0.008, of the outer 0.01 to 0.03; length of the outer spines 0.02 to 0.03.

_Habitat._--Central area of the Tropical Pacific, Stations 270, 272, depth 2925 and 2600 fathoms respectively.

3. _Xanthiosphæra lappacea_, n. sp. (Pl. 8, figs. 10, 11).

Inner shell spherical or subspherical, with very small roundish pores, quite irregularly scattered, one-fourth to three-fourth as broad as their bars. Ten to twenty pores in the half meridian of the shell. From its surface arise in an extremely irregular and variable manner numerous oblique spines, often curved, often lamellar, and perforated by pores, sometimes hollow, fenestrated cones. At different distances from the surface these spines send out lateral curved branches, which by communications form the delicate and very irregular network of the outer shell. This network is often incomplete and very unlike that of the inner shell, with large polygonal meshes, six to eighteen in the half meridian of the shell. Surface of the outer shell covered with numerous small, curved, and oblique spines, prolongations of the inner spines, but scarcely one-third to one-half as long as these. The radius of the inner shell bears to that of the outer a ratio = 3 : 4.

_Dimensions._--Diameter of the inner shell 0.08 to 0.12, of the outer 0.11 to 0.15; pores of the inner shell 0.001 to 0.009, of the outer 0.01 to 0.04; length of the outer spines 0.005 to 0.009.

_Habitat._--Central area of the Tropical Pacific, Stations 263 to 274, depths 2350 to 3000 fathoms.

{121}Family VII. #STYLOSPHÆRIDA#, Haeckel (Pls. 13-17).

_Stylosphærida_, Haeckel, 1881, Prodromus, p. 449.

_Definition._--#Sphæroidea# with two radial spines on the surface of the spherical shell, opposite in one axis; living solitary (not associated in colonies).

The family #Stylosphærida# comprises a large number of very common #Sphæroidea#, and is distinguished from all others by the possession of two radial spines which are placed in one axis of the spherical shell.[67] By the expression of this "main axis" as a solid rod they form the transition to the #Prunoidea#, in which the whole shell is more or less transformed according to this "monaxial growth." But in these latter the shell, as well as the central capsule, becomes ellipsoidal, prolonged in one axis, whilst in the former they remain spherical. However, the distinction of both nearly allied groups is sometimes difficult.

The most simple Stylosphærida are the _Xiphostylida_, with one single spherical lattice-shell. To this ancestral group all other subfamilies can be opposed as "Stylosphærida concentrica," as their carapace is composed of two or more concentric lattice-shells: two in the Sphærostylida, three in the Amphistylida, four in the Cromyostylida, five or more in the Caryostylida. In all these four subfamilies the concentric shells are simple (not spongy) fenestrated spheres. In a sixth subfamily, in the Spongostylida, the shell is wholly or partially composed of a spongy irregular wicker-work, with or without a medullary shell in the centre.

Both the radial spines in all Stylosphærida are opposed normally in one axis; but in many species besides the normal form occur individual abnormalities, in which the two spines are not accurately opposed in this main axis, but placed in two different axes, intersecting at a smaller or larger angle. In the majority of the Stylosphærida both opposite spines have the same size and form; but in some genera they are more or less different, often in a very striking degree. The same differences occur in the nearly allied groups of #Prunoidea#, in the Ellipsida and Druppulida.

The distal ends of both spines are commonly free; but in the small group of Saturnalida (_Saturnalis_ with one single shell, _Saturnulus_ with two concentric shells, _Saturninus_ with three concentric shells) the distal ends of both spines are united, at equal distances from the centre, by a circular or elliptical ring. This remarkable peculiarity occurs in no other group of #Sphæroidea#, and consequently brings the Saturnalida into close relation with the #Discoidea#.

{122}_Synopsis of the Genera of Stylosphærida._

{ {Both spines {Polar spines { equal, 45. _Xiphosphæra_. { free, without{ I. Subfamily { connecting {Spines Xiphostylida. { ring on the { different (Spherical shell{ distal ends. { in size simple.) { { or form, 46. _Xiphostylus_. { {Both polar spines united by { a circular or elliptical { ring, 47. _Saturnalis_.

{ {Both spines { { equal, 48. _Stylosphæra_. {Polar spines { II. Subfamily { free. {Spines Sphærostylida.{ { different in (Two concentric { { size or spheres.) { { form, 49. _Sphærostylus_. { {Both polar spines united by { a circular or elliptical { ring, 50. _Saturnulus_.

{ {Both spines { { equal, 51. _Amphisphæra_. {Polar spines { III. Subfamily { free. {Spines Amphistylida. { { different in (Three { { size or concentric { { form, 52. _Amphistylus_. spheres.) { {Both polar spines united by { a circular or elliptical { ring, 53. _Saturninus_.

IV. Subfamily } {Both spines Cromyostylida.}Polar spines { equal, 54. _Stylocromyum_. (Four concentric} free. { spheres.) } {Spines } { different, 55. _Cromyostylus_.

V. Subfamily } Caryostylida. }Polar spines {Both spines (Five or more } free. { equal, 56. _Caryostylus_. concentric } spheres.) }

{Shell a solid spongy sphere { without central medullary { shell, 57. _Spongolonchis_. VI. Subfamily { Spongostylida.{ {One central (Spherical shell{ { medullary partially or {In the centre { shell, 58. _Spongostylus_. wholly of a { of the spongy{ spongy { sphere one or{Two structure.) { two medullary{ concentric { shells. { medullary { { shells, 59. _Spongostylidium_.

Subfamily XIPHOSTYLIDA, Haeckel, 1881, Prodromus, pp. 449, 450.

_Definition._--#Stylosphærida# with one simple spherical lattice-shell.

Genus 45. _Xiphosphæra_,[68] Haeckel, 1881, Prodromus, p. 450.

_Definition._--#Stylosphærida# with one single lattice-sphere and two free spines of equal size and form.

The genus _Xiphosphæra_ is the most simple form of all Stylosphærida, and may be regarded as the common ancestral form of this family. On the surface of a simple {123}spherical lattice-shell, enclosing the central capsule, arise two equal, free, radial spines, opposite to each other on the poles of one axis.

Subgenus 1. _Xiphosphærantha_, Haeckel.

_Definition._--Pores of the spherical shell regular, of nearly equal size and form; surface smooth or a little rough, without spines or thorns (other than the two polar spines).

1. _Xiphosphæra planeta_, n. sp.

Pores regular, hexagonal, eight to nine times as broad as the thin bars. Ten to twelve pores on the half equator. Shell very thin walled; surface smooth. Polar spines three-sided pyramidal, about as long as the axis of the sphere, as broad at the base as one pore.

_Dimensions._--Diameter of the sphere 0.12 to 0.13, pores 0.016 to 0.018, bars 0.002; length of the polar spines 0.1 to 0.15, basal thickness 0.02.

_Habitat._--Pacific, central area, surface; Stations 271 to 274, depths 2425 to 2750 fathoms.

2. _Xiphosphæra gæa_, n. sp. (Pl. 14, fig. 5).

Pores regular, circular, with prominent hexagonal crests between them. On the half equator ten to twelve pores, of the same breadth as the crested bars. Shell thin walled; surface smooth. Polar spines three-sided prismatic, about twice as long as the axis of the sphere, twice as broad at the base as one pore.

_Dimensions._--Diameter of the sphere 0.07 to 0.09, pores and bars 0.005; length of the polar spines 0.15 to 0.2, basal thickness 0.01.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

3. _Xiphosphæra venus_, n. sp. (Pl. 14, fig. 2).

Pores regular, circular, with prominent hexagonal frames. On the half equator fifteen to eighteen pores, of the same breadth as the bars. Shell very thick walled; surface smooth, honeycomb-like. Polar spines conical, smooth, about as long as the axis of the shell, twice as broad at the base as one pore.

_Dimensions._--Diameter of the sphere 0.12 to 0.13, pores and bars 0.005; thickness of the shell wall 0.013; length of the polar spines 0.12 to 0.15, basal breadth 0.01.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

4. _Xiphosphæra luna_, n. sp.

Pores regular, circular, hexagonally lobed or rosette-shaped, three times as broad as the bars. Ten to twelve pores on the half equator. Shell thick walled; surface smooth. Polar spines three-sided pyramidal, one to two times as long as the axis of the shell, as broad at the base as one pore {124}(very similar to _Xiphostylus phasianus_, Pl. 13, fig. 9, but different in the equal size and similar form of the two large polar spines).

_Dimensions._--Diameter of the sphere 0.12, pores 0.015, bars 0.005; length of the polar spines 0.1 to 0.2, basal breadth 0.02.

_Habitat._--Indian Ocean, Cocos Islands, surface, Rabbe.

5. _Xiphosphæra hebe_, n. sp.

Pores regular, circular, three times as broad as the bars. On the half equator sixteen to twenty pores. Shell thick walled; surface smooth. Polar spines conical or nearly cylindrical, about as long as the axis of the sphere, as broad at the base as two pores.

_Dimensions._--Diameter of the sphere 0.1 to 0.13, pores 0.006, bars 0.002; polar spines 0.1 to 0.15 long, 0.01 thick.

_Habitat._--Pacific, central area, Stations 265 to 268, depths 2700 to 2900 fathoms.

6. _Xiphosphæra maxima_, n. sp.

Pores regular, circular, twice as broad as the bars, funnel-shaped. Twenty to thirty pores on the half equator. Shell very thick walled; surface smooth. Polar spines three-sided pyramidal, about as long as the radius of the sphere, as broad at the base as two pores.

_Dimensions._--Diameter of the sphere 0.22 to 0.35, pores 0.008 to 0.01, bars 0.005; polar spines 0.1 to 0.15 long, 0.02 thick.

_Habitat._--Equatorial Atlantic, Station 347, depth 2250 fathoms.

7. _Xiphosphæra euphrosyne_, n. sp.

Pores regular, circular, about as broad as the bars, double contoured. Eight to ten on the half equator. Shell thin walled; surface smooth. Polar spines conical, about as long as the radius of the sphere, as broad at the base as one pore.

_Dimensions._--Diameter of the sphere 0.12 to 0.15, pores and bars 0.02; polar spines 0.06 to 0.09 long, 0.02 thick.

_Habitat._--South Atlantic, Station 323, depth 1900 fathoms.

Subgenus 2. _Xiphosphærella_, Haeckel.

_Definition._--Pores of the spherical shell regular, of nearly equal size and form; surface thorny or spiny, covered with regularly distributed papillæ or thorns (in addition to the two large polar spines).

8. _Xiphosphæra pallas_, n. sp. (Pl. 14, fig. 4).

Pores regular, circular, separated by hexagonal elevated frames, the sharp crest of which is elegantly denticulated; in each corner of the hexagons (between three pores) is a short radial spine, {125}about as long as one pore. On the half equator sixteen to twenty pores, of the same breadth as the bars. Shell thick walled; whole surface spiny. Polar spines cylindrical, at the apex conical, about as long as the axis of the sphere, three to four times as broad as one pore.

_Dimensions._--Diameter of the sphere 0.1, pores and bars 0.005; length of the polar spines 0.07 to 0.11, thickness 0.015 to 0.02.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

9. _Xiphosphæra flora_, n. sp.

Pores regular, circular, with hexagonal frames, twice as broad as the bars. Ten to twelve pores on the half equator. Shell thin walled, with spiny surface; in each corner of the hexagons is one bristle-like radial spine twice as long as one pore. Polar spines three-sided prismatic, at the apex pyramidal, nearly twice as long as the axis of the sphere, as broad at the base as two pores (similar to _Ellipsoxiphus palliatus_, Pl. 14, fig. 7).

_Dimensions._--Diameter of the sphere 0.15, pores 0.01, bars 0.005; length of the polar spines 0.2 to 0.25, breadth 0.02.

_Habitat._--Tropical Atlantic, Station 342, depth 1445 fathoms.

10. _Xiphosphæra juno_, n. sp.

Pores regular, circular, as broad as the bars, funnel-shaped. Fifteen to twenty pores on the half equator. Shell thick walled, covered with bristle-like spines, about twice as long as one pore. Polar spines conical, thick, about as long as the axis of the sphere, twice as broad at the base as one pore.

_Dimensions._--Diameter of the sphere 0.12, pores and bars 0.01; length of the polar spines 0.14, basal breadth 0.02.

_Habitat._--Fossil in the Barbados rocks; living in the greatest depth of the Tropical Pacific, Station 225, depth 4475.

11. _Xiphosphæra gigantea_, n. sp.

Pores regular, circular, two to three times as broad as the bars; twenty-eight to thirty-two on the half equator. Shell thick walled, covered with short conical thorns. Polar spines three-sided pyramidal, about as long as the radius of the sphere, as broad at the base as three pores.

_Dimensions._--Diameter of the sphere 0.25 to 0.3, pores 0.01, bars 0.004; polar spines 0.1 to 0.15 long, 0.03 broad.

_Habitat._--Fossil in the Tertiary rocks of Barbados and Sicily (Cattanisetta).

Subgenus 3. _Xiphosphærissa_, Haeckel.

_Definition._--Pores of the spherical shell irregular, of different size or form; surface smooth or a little rough, without spines or thorns (other than the polar spines).

{126}12. _Xiphosphæra ceres_, n. sp.

Pores irregular, roundish, of different sizes, two to four times as broad as the bars. Sixteen to twenty pores on the half equator. Shell thin walled, with smooth surface. Polar spines conical, about as long as the axis of the sphere, very thick at the base.

_Dimensions._--Diameter of the sphere 0.15 to 0.2, pores 0.004 to 0.008, bars 0.002; polar spines 0.18 to 0.24 long, at the base 0.02 thick.

_Habitat._--North Atlantic, Station 353, surface.

13. _Xiphosphæra clavigera_, n. sp.

Pores irregular, roundish, double contoured, of very unequal size, two to seven times as broad as the bars; ten to twelve on the half equator. Shell thick walled; surface a little rough. Polar spines club-shaped, with prominent edges, about half as long as the axis of the sphere; thinner at both ends than in the middle. (Differs from _Ellipsoxiphus claviger_, Pl. 14, fig. 3, in the spherical shell and shorter spines.)

_Dimensions._--Diameter of the sphere 0.2, pores 0.005 to 0.02, bars 0.003; polar spines 0.06 long, 0.02 broad.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

Subgenus 4. _Xiphosphæromma_, Haeckel.

_Definition._--Pores of the spherical shell irregular, of different size or form; surface thorny or spiny (besides the two large polar spines).

14. _Xiphosphæra vesta_ n. sp. (Pl. 14, fig. 6).

Pores irregular, roundish, three to five times as broad as the bars; fourteen to sixteen on the half equator. Scattered on the surface of the thick-walled shell are from twenty to thirty strong three-sided pyramidal spines of unequal size, the largest twice as long as the largest pores. Polar spines very strong, nearly three-sided prismatic, with curved edges, nearly as long as the axis of the sphere and twice as broad as the largest pores.

_Dimensions._--Diameter of the sphere 0.17, pores 0.01 to 0.02, bars 0.004; length of the polar spines 0.13, thickness 0.02 to 0.03.

_Habitat._--Pacific, central area. Station 266, depth 2750 fathoms,

15. _Xiphosphæra astræa_, n. sp.

Pores irregular, roundish, one to two times as broad as the bars; ten to twelve on the half equator. Surface of the thick-walled shell covered with numerous short conical thorns. Polar spines cylindro-conical, one and a half to two times as long as the axis of the sphere.

{127}_Dimensions._--Diameter of the sphere 0.18, pores 0.01 to 0.015, bars 0.008; length of the polar spines 0.25 to 0.3, thickness 0.02.

_Habitat._--Indian Ocean, surface; Ceylon, Haeckel.

Genus 46. _Xiphostylus_,[69] Haeckel, 1881, Prodromus, p. 450.

_Definition._--#Stylosphærida# with one single lattice-sphere and two free spines of different size or form.

The genus _Xiphostylus_ differs from the foregoing _Xiphosphæra_ in the unequal size or form of both polar spines, which become more or less differentiated.

Subgenus 1. _Xiphostylantha_, Haeckel.

_Definition._--Pores of the spherical shell regular, of nearly equal size and form; surface smooth or a little rough, without spines or thorns.

1. _Xiphostylus alcedo_, n. sp. (Pl. 13, fig. 4).

Pores regular, circular, with elevated hexagonal frames, twice as broad as the bars. Eight to ten pores on the half equator. Surface smooth. Polar spines three-sided pyramidal, as broad at the base as one hexagon; the major spine four to five times as long as the minor, which is about equal to the radius of the sphere.

_Dimensions._--Diameter of the sphere 0.12, pores 0.012, bars 0.006; length of the major polar spine 0.16 to 0.2, of the minor 0.04 to 0.06, basal breadth 0.02.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475.

2. _Xiphostylus phasianus_, n. sp. (Pl. 13, fig. 9).

Pores regular, circular, twice as broad as the bars. Eight to ten pores on the half equator. Outer opening of each pore elegantly lobed, with eight indentations. Surface a little rough. Polar spines very unequal; major spine sword-like, sharply edged, about as long as the diameter of the sphere; minor spine scarcely half so long, pommel-shaped, with nine (?) wing-like edges.

_Dimensions._--Diameter of the sphere 0.13, inner circular opening of the pores 0.01, outer eight-lobed opening 0.015, bars 0.005; length of the major polar spine 0.14, of the minor 0.06, breadth 0.03.

_Habitat._--Australian Sea, Station 162, surface.

3. _Xiphostylus motacilla_, n. sp.

Pores regular, circular, three times as broad as the bars; sixteen to twenty on the half equator. Surface smooth. Polar spines compressed, two-edged, at the base three to four times as broad as {128}one pore; the major spine somewhat longer than the diameter of the shell, the minor scarcely one-third or one-half as long.

_Dimensions._--Diameter of the sphere 0.14, pores 0.006, bars 0.002; length of the major spine 0.16 to 0.18, of the minor 0.05 to 0.07, basal breadth 0.02.

_Habitat._--Indian Ocean, Zanzibar, 2200 fathoms, Pullen.

4. _Xiphostylus gallus_, n. sp.

Pores regular, circular, five times as broad as the bars. Twelve to sixteen pores on the half equator. Surface smooth. Polar spines very unequal; the major conical spine one and a half to three times as long as the diameter of the sphere; the minor pommel-shaped, scarcely one-third as long (length of both spines very variable).

_Dimensions._--Diameter of the sphere 0.13, pores 0.01, bars 0.002; length of the major spine 0.2 to 0.4, of the minor 0.05 to 0.08.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

5. _Xiphostylus alauda_, n. sp. (Pl. 14, fig. 15).

_Lithomespilus alauda_, Haeckel, 1881, Prodrom. et Atlas, _loc. cit._

Pores subregular, circular, three to four times as broad as the bars; fifteen to eighteen on the half equator. Surface a little rough. Polar spines irregularly conical or pyramidal, scarcely as long as the radius of the sphere; one spine simple, the other composed of a bunch of four or five spines united at the base.

_Dimensions._--Diameter of the sphere 0.11, pores 0.01, bars 0.003; length of the polar spines 0.03 to 0.05, basal breadth 0.02.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

6. _Xiphostylus anhinga_, Haeckel.

_Rhabdolithis pipa_, Bury, 1862, Polycystins of Barbados, pl. iii. fig. 4.

Pores subregular, circular, about the same breadth as the bars; eight to ten on the half equator. Surface smooth or a little rough. Polar spines cylindrical, very irregularly curved like S or contorted, the major three to six times as long as the diameter of the sphere, the minor scarcely one-fourth as long as the former, at the end truncated.

_Dimensions._--Diameter of the sphere 0.07, pores and bars 0.005; length of the major polar spine 0.2 to 0.4, of the minor 0.06 to 0.09, basal breadth 0.01.

_Habitat._--Fossil in the Barbados rocks.

Subgenus 2. _Xiphostyletta_, Haeckel.

_Definition._--Pores of the spherical shell regular, of nearly equal size and form; surface thorny or spiny (other than the two large polar spines).

{129}7. _Xiphostylus cuculus_, n. sp.

Pores regular, circular, hexagonally framed, three times as broad as the bars; ten to twelve on the half equator. Surface thorny, between every three pores a short conical thorn. Polar spines three-sided prismatic, the major somewhat longer than the diameter of the sphere, the minor scarcely one-third as long, pommel-shaped.

_Dimensions._--Diameter of the sphere 0.17, pores 0.012, bars 0.004; length of the major polar spine 0.2, of the minor 0.05, basal breadth 0.015.

_Habitat._--South Atlantic, surface; Station 335, depth 1425 fathoms.

8. _Xiphostylus trochilus_, n. sp. (Pl. 13, fig. 10).

Pores regular, circular, four times as broad as the bars; eight to nine on the half equator. Polar spines cylindrical, the major somewhat longer than the axis of the sphere, the minor shorter, surrounded by a group of from four to eight shorter conical spines. Surface of the opposite hemisphere smooth, without by-spines.

_Dimensions._--Diameter of the sphere 0.07 to 0.08, pores 0.01, bars 0.0025.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

9. _Xiphostylus picus_, n. sp. (Pl. 14, fig. 13).

_Lithomespilus picus_, Haeckel, 1881, Prodrom. et Atlas.

Pores regular, circular, twice as broad as the bars; sixteen to eighteen on the half equator. Polar spines cylindrical, conical at the apex, the major once and a half to twice as long as the diameter of the shell, the minor scarcely half so long; around the latter a group of twelve to twenty shorter conical spines, irregularly scattered. Surface of the other hemisphere smooth.

_Dimensions._--Diameter of the sphere 0.13, pores 0.006, bars 0.003; length of the major polar spine 0.2 to 0.24, of the minor 0.08 to 0.09, basal breadth 0.02.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

Subgenus 3. _Xiphostylissa_, Haeckel.

_Definition._--Pores of the spherical shell irregular, of unequal size or form; surface smooth or a little rough, without thorns.

10. _Xiphostylus trogon_, n. sp. (Pl. 14, fig. 12).

_Lithomespilus trogon_, Haeckel, 1881, Prodrom. et Atlas.

Pores irregular, roundish or subcircular, two to three times as broad as the bars; ten to twelve on the half equator. Surface smooth. Major polar spine three-sided prismatic, once and a half to twice as long as the axis of the sphere; minor spine quite rudimentary, scarcely longer than broad, but surrounded by a group of from three to six similar short spines.

{130}_Dimensions._--Diameter of the sphere 0.1, pores 0.005 to 0.015, bars 0.005 to 0.008; length of the major spine 0.15 to 0.18, of the minor 0.01 to 0.02, basal breadth 0.02.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

11. _Xiphostylus falco_, n. sp. (Pl. 13, fig. 14).

Pores irregular, roundish, two to five times as broad as the bars; sixteen to eighteen on the half equator. Surface smooth. Polar spines cylindrical, very stout, nearly half as thick as the radius of the shell; major spine two to four times as long as the diameter of the shell; minor spine obliquely inserted, scarcely longer than the diameter, divided at the end into two short, hook-shaped, curved branches.

_Dimensions._--Diameter of the sphere 0.08, pores 0.002 to 0.005, bars 0.001; breadth of the spines 0.02, length of the major spine 0.15 to 0.2, of the minor 0.09.

_Habitat._--South Pacific, Station 302, depth 1450 fathoms.

12. _Xiphostylus alca_, n. sp. (Pl. 13, fig. 13).

Pores irregular, roundish, two to six times as broad as the bars; six to eight on the half equator. Each pore with three to six lobes, composed of three to six confluent smaller pores. Surface smooth. Major spine conical, curved, somewhat longer than the axis of the sphere; minor spine somewhat shorter, pommel-like, edged.

_Dimensions._--Diameter of the sphere 0.07, pores 0.01 to 0.02, bars 0.003; length of the major spine 0.08, of the minor 0.06, basal thickness 0.02.

_Habitat._--Indian Ocean, Sunda Strait, Rabbe, surface.

13. _Xiphostylus edolius_, n. sp. (Pl. 13, fig. 5).

Pores irregular, roundish, composed of two to six smaller confluent pores. On the half equator six to eight large pores, and twenty to thirty small pores; bars between the smaller very thin. Surface a little rough. Major polar spine conical, S-shaped, about twice as long as the axis of the shell; minor spine pommel-shaped, edged, scarcely as long as its radius.

_Dimensions._--Diameter of the sphere 0.12, large pores 0.01 to 0.03, small pores 0.004 to 0.008, bars 0.001 to 0.004; length of the major spine 0.2, of the minor 0.05, basal breadth 0.02.

_Habitat._--Central Pacific, Station 273, surface.

Subgenus 4. _Xiphostylomma_, Haeckel.

_Definition._--Pores of the spherical shell irregular, of different size or form; surface thorny or spiny.

{131}14. _Xiphostylus emberiza_, n. sp. (Pl. 13, fig. 11).

Pores irregular, roundish, one to four times as broad as the bars; six to eight on the half equator. Polar spines very unequal; major cylindrical, twice as long as the axis of the sphere; minor scarcely half as long, obliquely inserted, like a bird's head, surrounded by a group of ten to twenty smaller conical spines. Opposite hemisphere smooth.

_Dimensions._--Diameter of the sphere 0.005, pores 0.002 to 0.008, bars 0.002; length of the major spine 0.09, of the minor 0.05, basal breadth 0.01.

_Habitat._--South Atlantic, Station 332, surface.

15. _Xiphostylus ardea_, n. sp.

Pores irregular, roundish, one to three times as broad as the bars; twelve to sixteen on the half equator. Whole surface spiny. Major polar spine three-sided pyramidal, somewhat longer than the diameter of the sphere; minor scarcely so long as its half radius, pommel-like, edged.

_Dimensions._--Diameter of the sphere 0.12, pores 0.003 to 0.01, bars 0.003; length of the major polar spine 0.15, of the minor 0.03, basal breadth 0.02.

_Habitat._--North Atlantic, Station 64, surface.

Genus 47. _Saturnalis_,[70] Haeckel, 1881, Prodromus, p. 450.

_Definition._--#Stylosphærida# with one single lattice-sphere and two equal opposite spines, connected at the distal end by a circular or elliptical ring.

The genus _Saturnalis_ (with simple lattice-sphere) and the two similar genera _Saturnulus_ (with two concentric spheres) and _Saturninus_ (with three spheres) form together the small peculiar group of Saturnalida, distinguished by a remarkable circular or elliptical ring, connecting the distal ends of the two equal opposite polar spines. This ring indicates a certain equatorial plane, and therefore brings these #Sphæroidea# into relation with the #Discoidea#.

Subgenus 1. _Saturnalina_, Haeckel.

_Definition._--Ring smooth, without spines or thorns.

1. _Saturnalis circularis_, n. sp.

Pores of the spherical shell regular, circular, hexagonally framed, twice as broad as the bars. Ten to twelve pores on the half equator. Ring circular, smooth, its diameter three times as great as that of the sphere.

{132}_Dimensions._--Diameter of the sphere 0.07, pores 0.005, bars 0.0025; diameter of the circular ring 0.2, thickness of the axial beams and the ring 0.01.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

2. _Saturnalis annularis_, n. sp. (Pl. 13, fig. 16).

Pores of the spherical shell regular, circular, with elevated hexagonal frames, of the same breadth as the bars. Sixteen to twenty pores on the half equator. Ring elliptical, smooth, somewhat constricted at the poles of the axis, its diameter three times as great as that of the sphere.

_Dimensions._--Diameter of the sphere 0.09, pores and bars 0.005, major axis of the elliptical ring 0.27 to 0.3, minor axis 0.19 to 0.2; thickness of the ring and of the axial beams 0.01.

_Habitat._--Pacific, central area, Stations 270 to 274, surface.

3. _Saturnalis cyclus_, n. sp.

_Lithocircus mesocena_, Bury, 1862, Polycystins of Barbados, pl. iii. fig. 1.

Pores of the spherical shell regular, circular, without hexagonal frames, twice as broad as the bars. Eight to ten pores on the half equator. Ring circular, smooth, its diameter four times as great as that of the sphere.

_Dimensions._--Diameter of the sphere 0.07, pores 0.006, bars 0.003; diameter of the circular ring 0.28, thickness of the ring and both axial beams 0.01.

_Habitat._--Fossil in the Barbados rocks.

4. _Saturnalis circoides_, n. sp. (Pl. 13, fig. 12).

Pores of the spherical shell irregular, roundish, often somewhat lobed, one to three times as broad as the bars; fifteen to twenty on the half equator. Ring circular, smooth, with four prominent edges, its diameter twice as great as that of the sphere. (The figured specimen is a young or not fully developed one; afterwards I found in the same locality other specimens with quite perfect rings, similar to the edged ring of _Saturnulus annulus_, Pl. 16, fig. 17.)

_Dimensions._--Diameter of the sphere 0.09 to 0.1, pores 0.003 to 0.01, bars 0.004; diameter of the circular ring 0.2 to 0.24, thickness of the ring and the polar beams 0.01.

_Habitat._--Indian Ocean; fossil in the Nicobar rocks; living at great depths near Zanzibar, 2200 fathoms, Pullen.

Subgenus 2. _Saturnalium_, Haeckel.

_Definition._--Ring armed on the periphery with numerous spines or thorns.

5. _Saturnalis trochoides_, n. sp.

_Haliomma_ species, Bury, 1862, Polycystins of Barbados, pl. xx. fig. 2.

Pores of the spherical shell subregular, circular, twice as broad as the bars. Twelve to sixteen pores on the half equator. Ring circular, armed with ten to twelve strong conical, irregular spines, its diameter twice as great as that of the sphere.

{133}_Dimensions._--Diameter of the sphere 0.08, pores 0.006, bars 0.003; diameter of the circular ring 0.16; length of the radial spines 0.02 to 0.04; thickness of the ring and the axial beams 0.01.

_Habitat._--Fossil in the Barbados rocks.

6. _Saturnalis rotula_, n. sp. (Pl. 13, fig. 15).

Pores of the spherical shell regular, circular, twice as broad as the bars; sixteen to twenty on the half equator. Ring circular, armed with fifteen to twenty strong, conical, irregular spines, partly simple, partly divided into two or three irregular branches; diameter of the ring two and a half times as great as that of the sphere.

_Dimensions._--Diameter of the sphere 0.08, pores 0.004, bars 0.002; diameter of the circular ring 0.2, length of its spines 0.02 to 0.03; thickness of the ring and the radial beams 0.01.

_Habitat._--North Pacific, Station 244, surface.

Subfamily SPHÆROSTYLIDA, Haeckel, 1881, Prodromus, pp. 449, 451.

_Definition._--#Stylosphærida# with two concentric, spherical lattice-shells.

Genus 48. _Stylosphæra_,[71] Ehrenberg, 1847, Monatsber. d. Berlin Akad., p. 54.

_Definition._--#Stylosphærida# with two concentric lattice-spheres and two free spines of equal size and similar form.

The genus _Stylosphæra_, the most simple form of the Sphærostylida, can be derived either from _Xiphosphæra_ by duplication of the spherical shell, or from _Carposphæra_ by development of two opposite polar spines. The inner or medullary shell is enclosed in the central capsule, whilst the outer or cortical shell lies outside it; the two are connected by two or more radial beams, piercing the wall of the capsule.

Subgenus 1. _Stylosphærantha_, Haeckel.

_Definition._--Pores of the cortical shell regular, of nearly equal size and similar form; surface smooth or a little rough, without spines or thorns.

1. _Stylosphæra musa_, n. sp.

Radial proportion of the two concentric spheres = 3 : 1. Cortical shell thin walled, smooth, with regular, hexagonal pores, three times as broad as the thin bars; twelve on the half equator. Polar spines three-sided pyramidal, as long as the axis of the cortical shell, one-tenth as broad at the base.

_Dimensions._--Diameter of the outer shell 0.2, pores 0.01, bars 0.003; diameter of the inner shell 0.06; length of the polar spines 0.2, basal breadth 0.02.

_Habitat._--Tropical Atlantic, Station 347, depth 2250 fathoms.

{134}2. _Stylosphæra urania_, n. sp.

Radial proportion of the two shells = 4 : 1. Cortical shell thin walled, smooth; pores regular, circular, hexagonally framed, twice as broad as the bars; ten on the half equator. Polar spines conical, as long as the radius of the outer shell.

_Dimensions._--Diameter of the cortical shell 0.24, pores 0.012, bars 0.006; medullary shell 0.06; length of the polar spines 0.12, basal breadth 0.024.

_Habitat._--South Pacific, Station 285, depth 2375 fathoms.

3. _Stylosphæra calliope_, n. sp. (Pl. 16, fig. 6).

Radial proportion of the two shells = 3 : 1. Cortical shell thick walled, smooth; pores regular, circular, three times as broad as the bars. Each pore on its outer opening with eight regular lobules, flower-like. Nine to ten pores on the half equator. Polar spines three-sided pyramidal, with three strong prominent edges, about as long as the axis, as broad as one pore. (Sometimes, as in the figured specimen, one spine is smaller than the other; this variety, otherwise identical, may be called _Sphærostylus calliope_.)

_Dimensions._--Diameter of the outer shell 0.12, pores 0.015, bars 0.005; inner shell 0.04; length of the polar spine 0.08 to 0.12, breadth 0.02.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

4. _Stylosphæra clio_, n. sp. (Pl. 16, fig. 7).

Radial proportion of the two shells = 2 : 1. Cortical shell thick walled, smooth; pores regular, circular, three times as broad as the bars; fourteen to sixteen on the half equator. Polar spines three-sided pyramidal, very robust, with thick prismatic edges, about as long as the axis of the cortical shell, one-third as broad at the base. (Sometimes, as in the figured specimen, one spine is greater than the other; this form may be called _Sphærostylus clio_.)

_Dimensions._--Diameter of the outer shell 0.12, pores 0.01, bars 0.003; inner shell 0.06; length of the polar spines 0.08 to 0.12, basal breadth 0.03 to 0.04.

_Habitat._--Pacific, central area; Station 272, depth 2600 fathoms.

5. _Stylosphæra polyhymnia_, n. sp.

Radial proportion of the two spheres = 3 : 1. Cortical shell very thin walled, smooth, with regular, circular pores, three times as broad as the bars; sixteen to twenty on the half equator. Polar spines cylindrical, pointed, once and a half to twice as long as the axis of the outer sphere, scarcely broader than one pore. The two spheres are connected only by the two opposite beams.

_Dimensions._--Diameter of the outer shell 0.12 to 0.16, pores 0.006 to 0.009, bars 0.002 to 0.003; inner shell 0.04 to 0.05; length of the polar spines 0.18 to 0.22, breadth 0.01.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface.

{135}6. _Stylosphæra dixyphos_, Haeckel.

_Haliomma dixyphos_, Ehrenberg, 1854, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 83; Mikrogeol., Taf. xxii. fig. 31.

_Haliomma dixyphos_, Haeckel, 1862, Monogr. d. Radiol. p. 433.

Radial proportion of the two spheres = 2 : 1. Cortical shell thin walled, smooth, with regular, circular pores, twice as broad as the bars; ten to twelve on the half equator. Polar spines about as long as the axis of the outer shell, three-sided pyramidal, at the base twice as broad as one pore. (The two spheres connected by four beams, two opposite in the main axis, two opposite in the equatorial axis.)

_Dimensions._--Diameter of the outer shell 0.1, pores 0.01, bars 0.05; inner shell 0.05; length of the polar spines 0.08 to 0.1, basal breadth 0.02.

_Habitat._--South Atlantic, Station 332, surface; fossil in Tertiary rocks of Sicily.

Subgenus 2. _Stylosphærella_, Haeckel.

_Definition._--Pores of the cortical shell regular, of nearly equal size and similar form; surface thorny or spiny.

7. _Stylosphæra setosa_, Ehrenberg, 1872.

_Stylosphæra setosa_, Ehrenberg, 1872, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 320; Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. viii. fig. 15.

Radial proportion of the two shells = 2 : 1. Cortical shell thin walled, spiny; pores regular, hexagonal, four times as broad as the bars. Six to eight pores on the half equator. Polar spines conical, thin, scarcely as long as the radius of the cortical shell.

_Dimensions._--Diameter of the cortical shell 0.1, pores 0.002, bars 0.005; medullary shell 0.05; length of the polar spines 0.04, basal breadth 0.01.

_Habitat._--Philippine Sea, depth 3300 fathoms, Ehrenberg; Station 206, depth 2100 fathoms.

8. _Stylosphæra euterpe_, n. sp.

Radial proportion of the two shells = 3 : 1. Cortical shell thin walled, spiny; pores regular, circular, with hexagonal frames, twice as broad as the bars; eight to ten on the half equator. Polar spines conical, as thick as one pore at the base, about as long as the axis of the cortical shell.

_Dimensions._--Diameter of the cortical shell 0.12, pores 0.012, bars 0.006; medullary shell 0.04; length of the polar spines 0.1, basal breadth 0.012.

_Habitat._--South Pacific, Station 302, depth 1450 fathoms.

9. _Stylosphæra melpomene_, n. sp. (Pl. 16, fig. 1).

Radial proportion of the two shells = 3 : 1. Cortical shell thin walled, spiny, with regular, circular pores, four times as broad as the bars; eight to ten on the half equator. Polar spines three-sided prismatic, pointed, as broad as one pore, only one-third as long as the axis of the sphere (the two shells connected by four thin beams, two opposite in the main axis, two in the equatorial axis).

{136}_Dimensions._--Diameter of the outer shell 0.12, pores 0.012, bars 0.003; inner shell 0.04; length of the polar spines 0.04, thickness 0.013.

_Habitat._--Indian Ocean, Cocos Islands, Rabbe.

10. _Stylosphæra hispida_, Ehrenberg, 1854.

_Stylosphæra hispida_, Ehrenberg, 1854, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 246; Mikrogeol, Taf. xxxvi. fig. 26.

_Haliomma hispidum_, Haeckel, 1862, Monogr. d. Radiol., p. 433.

Radial proportion of the two spheres = 3 : 1. Cortical shell thick walled, spiny, with regular, circular pores of the same breadth as the bars; ten to fifteen on the half equator. Polar spines three-sided prismatic, pointed, about as long as the axis of the outer sphere, nearly as broad at the base as the inner sphere. (Compare _Sphærostylus hispidus_; also Ehrenberg, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, 1874, p. 259.)

_Dimensions._--Diameter of the outer shell 0.1 to 0.12, pores and bars 0.004; inner shell 0.04; length of the polar spines 0.1 to 0.15, basal breadth 0.03.

_Habitat._--Fossil in the Tertiary rocks of Sicily, Barbados, Nicobars, &c.

11. _Stylosphæra liostylus_, Ehrenberg, 1875.

_Stylosphæra liostylus_, Ehrenberg, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxv. fig. 3.

Radial proportion of the two spheres = 3 : 1. Cortical shell thick walled, thorny, with regular, circular pores, three times as broad as the bars; eight to ten on the half equator. Polar spines conical, once and a half to twice as long as the axis of the outer sphere, half as broad at the base as its radius. (This species, common in the Barbados rocks, is different from _Sphærostylus liostylus_, _loc. cit._, fig. 2, which Ehrenberg believed identical.)

_Dimensions._--Diameter of the outer shell 0.1, pores 0.01, bars 0.0035; inner shell 0.03; length of the polar spines 0.14 to 0.18, basal breadth 0.02.

_Habitat._--Fossil in the Barbados rocks; living in the depths of the North Atlantic, Gulf Stream, Florida.

Subgenus 3. _Stylosphærissa_, Haeckel.

_Definition._--Pores of the cortical shell irregular, of different size or form; surface smooth or a little rough, without thorns or spines.

12. _Stylosphæra nana_, n. sp. (Pl. 16, figs. 12, 13).

Radial proportion of the two spheres = 2 : 1. Cortical shell thick walled, somewhat irregular, smooth, with irregular, roundish pores, one to three times as broad as the bars; eight to ten on the half equator. Polar spines three-sided pyramidal, scarcely as long as the axis of the outer sphere, and nearly as broad at the base as its radius. (A very variable and irregular form.)

_Dimensions._--Diameter of the outer shell 0.07 to 0.09, pores 0.003 to 0.009, bars 0.003; inner shell 0.03 to 0.04; length of the polar spines 0.04 to 0.07, basal breadth 0.03.

_Habitat._--North Pacific, Stations 241 to 253, surface.

{137}13. _Stylosphæra jugata_, n. sp.

Radial proportion of the two shells = 2 : 1. Cortical shell thick walled, smooth, with irregular, roundish, double-contoured pores, confluent in groups of two to six. On the half equator six to nine groups and fifteen to twenty pores; bars between them of very variable breadth. Polar spines very strong, three-sided pyramidal, twice as long as the axis of the outer sphere, half as broad at the base as its radius. (Nearly allied to _Lithatractus jugatus_, Pl. 16, fig. 2, but differs in the truly spherical form of both shells and the double length of the polar spines.)

_Dimensions._--Diameter of the outer shell 0.15, pores 0.005 to 0.02; inner shell 0.07; length of the polar spines 0.25 to 0.3, basal breadth 0.03.

_Habitat._--Western Tropical Pacific, Station 224, depth 1850 fathoms.

14. _Stylosphæra terpsichore_, n. sp.

Radial proportion of the two shells = 3 : 1 or 4 : 1. Cortical shell thick walled, smooth, with irregular, roundish pores, one to three times as broad as the bars; fifteen to twenty-five on the half equator. Polar spines conical, about as long as the axis of the outer sphere, as broad at the base as the inner shell.

_Dimensions._--Diameter of the outer shell 0.15 to 0.2, pores 0.005 to 0.02, bars 0.004 to 0.008; inner shell 0.05; length of the polar spines 0.15 to 0.25, basal breadth 0.05.

_Habitat._--Western Indian Ocean, Zanzibar, depth 2200 fathoms, Pullen.

Subgenus 4. _Stylosphæromma_, Haeckel.

_Definition._--Pores of the cortical shell irregular, of different size or form; surface spiny or thorny.

15. _Stylosphæra thalia_, n. sp.

Radial proportion of the two shells = 2 : 1. Cortical shell thin walled, thorny, with irregular, roundish pores, two to four times as broad as the bars; eight to twelve on the half equator. Polar spines conical, one to one and a half times as long as the axis of the outer sphere, one-fourth to one-sixth as thick at the base. (Resembles _Sphærostylus ophidium_, Pl. 16, fig. 14, but differs in the straight regular conical polar spines, both of equal length and similar form.)

_Dimensions._--Diameter of the outer shell 0.12, pores 0.01 to 0.02, bars 0.005; inner shell 0.06; polar spines 0.1 to 0.16 long, 0.03 broad.

_Habitat._--South Pacific, Station 302, depth 1450 fathoms.

16. _Stylosphæra erato_, n. sp.

Radial proportion of the two shells = 3 : 1. Cortical shell thick walled, thorny, with irregular, roundish pores, two to five times as broad as the bars; fourteen to eighteen on the half equator. {138}Polar spines three-sided pyramidal, about as long as the axis of the outer sphere, one-fourth as broad as its radius. (Similar to _Xiphosphæra vesta_, Pl. 14, fig. 6.)

_Dimensions._--Diameter of the outer shell 0.15, pores 0.008 to 0.015, bars 0.003; inner shell 0.05; polar spines 0.12 long, 0.02 broad.

_Habitat._--South Atlantic, Station 335, depth 1425 fathoms.

Genus 49. _Sphærostylus_,[72] Haeckel, 1881, Prodromus, p. 451.

_Definition._--#Stylosphærida# with two concentric lattice-spheres and two free spines, of different size or form.

The genus _Sphærostylus_ differs from _Stylosphæra_ in the different size or form of the two polar spines, and therefore has the same relation to it that _Xiphostylus_ bears to _Xiphosphæra_.

Subgenus 1. _Sphærostylantha_, Haeckel.

_Definition._--Pores of the cortical shell regular, of nearly equal size and similar form; surface smooth or a little rough, without thorns.

1. _Sphærostylus liostylus_, Haeckel.

_Stylosphæra liostylus_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. xxv. fig. 2.

Cortical shell thin walled, with rough surface, three times as broad as the medullary shell. Pores of the cortical shell regular, circular, twice as broad as the bars; ten to twelve on the half equator. Polar spines cylindrical, as broad as one pore, with conical apex; the minor spine about as long as the axis of the outer shell, the major three to four times as long.

_Dimensions._--Diameter of the outer sphere 0.12, pores 0.12, bars 0.006; diameter of the inner sphere 0.04; length of the major polar spine 0.3 to 0.4, of the minor 0.1 to 0.15, breadth 0.012.

_Habitat._--Fossil in the Barbados rocks.

2. _Sphærostylus flexuosus_, Haeckel.

_Stylosphæra flexuosa_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. xxv. fig. 5.

Cortical shell thick walled, with rough surface, three times as broad as the medullary shell. Pores of the cortical shell regular circular, of the same breadth as the bars; eight to ten on the half equator. Polar spines cylindrical, S-like curved, irregular; the minor scarcely as long as the axis of the outer sphere, the major two to three times as long. (In the figure of Ehrenberg the spines are broken off; I have found them myself constantly irregular and of unequal length, sometimes with conical apex.)

{139}_Dimensions._--Diameter of the outer sphere 0.08, pores and bars 0.006; inner sphere 0.03; length of the major polar spine 0.15 to 0.25, of the minor 0.07 to 0.09, breadth 0.02.

_Habitat._--Fossil in the Barbados rocks.

3. _Sphærostylus clio_, n. sp.

Cortical shell thick walled, with smooth surface, twice as broad as the medullary shell; its network has regular, circular pores, three times as broad as the bars; sixteen to twenty on the half equator. Polar spines very strong, three-sided pyramidal; the major nearly twice as long as the axis of the outer sphere, the minor scarcely as long as its radius. (Nearly related to _Stylosphæra clio_, Pl. 16, fig. 7, but differs in the slender form and unequal length of the polar spines.)

_Dimensions._--Diameter of the outer sphere 0.14, pores 0.01, bars 0.03; inner sphere 0.07; length of the major spine 0.25, of the minor 0.06, basal breadth 0.02.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

4. _Sphærostylus hippocampus_, n. sp. (Pl. 16, figs. 10, 11).

Cortical shell thick walled, with smooth surface and regular network; the pores circular, hexagonally-lobed, three times as broad as the bars; ten to twelve on the half equator. Medullary shell half as large, with very small circular pores, eight to ten on the half equator. Major polar spine scarcely as long as the axis of the outer shell, curved like a horn; minor spine scarcely half as long, pommel-like, edged. (Sometimes, by prolongation of the main axis, the spherical shells become ellipsoidal and thus the species is transformed into _Druppatractus hippocampus_.)

_Dimensions._--Diameter of the outer sphere 0.08, pores 0.009, bars 0.003; inner sphere 0.04; length of the major spine 0.07, of the minor 0.03, breadth 0.02.

_Habitat._--Pacific, central area, Station 270, depth 2925 fathoms.

Subgenus 2. _Sphærostyletta_, Haeckel.

_Definition._--Pores of the cortical shell regular, of nearly equal size and form; surface spiny or thorny.

5. _Sphærostylus diadema_, n. sp.

Cortical shell thick walled, spiny, twice as broad as the medullary shell, with regular, circular pores, twice as broad as the bars; eight to ten on the half equator. Major polar spine about as long as the axis of the outer sphere, three-sided pyramidal; minor spine scarcely half as long, pommel-shaped, edged. (Similar in general form to _Xiphatractus glyptodon_, Pl. 17, figs. 9, 10; but differs in the simple medullary shell, the spherical form of both shells, and the simple circular regular pores.)

{140}_Dimensions._--Diameter of the outer sphere 0.12, pores 0.014, bars 0.007; inner sphere 0.06; length of the major spine 0.13, of the minor 0.05, greatest breadth 0.04.

_Habitat._--Southern Pacific, surface, Station 289.

Subgenus 3. _Sphærostylissa_, Haeckel.

_Definition._--Pores of the cortical shell irregular, of different size or form; surface smooth or a little rough.

6. _Sphærostylus cottus_, n. sp.

Cortical shell thick walled, smooth, about twice as broad as the medullary shell, with irregular, roundish pores, scarcely larger than the bars; fifteen to twenty on the half equator. Polar spines conical, the major once and a half to twice as long as the axis of the outer sphere, the minor scarcely as long as its radius.

_Dimensions._--Diameter of the outer sphere 0.14, pores and bars 0.008 to 0.012; inner sphere 0.065; length of the major spine 0.2 to 0.3, of the minor 0.05 to 0.07, basal breadth 0.03.

_Habitat._--Northern Atlantic, Færöe Channel, surface, John Murray.

7. _Sphærostylus trigla_, n. sp.

Cortical shell thin walled, smooth, three times as broad as the medullary shell, with irregular, roundish pores, two to three times as broad as the bars; ten to twelve on the half equator. Polar spines very unequal; the major three-sided pyramidal, one and a half times as long as the axis of the outer sphere; the minor scarcely as long as its radius, edged, pommel-like.

_Dimensions._--Diameter of the outer sphere 0.12, pores 0.01 to 0.015, bars 0.005; inner sphere 0.04; length of the major spine 0.2, of the minor 0.05, breadth 0.03.

_Habitat._--Northern Pacific, Station 241, depth 2300 fathoms.

Subgenus 4. _Sphærostylomma_, Haeckel.

_Definition._--Pores of the cortical shell irregular, of different size or form; surface spiny or thorny.

8. _Sphærostylus ophidium_, n. sp. (Pl. 16, figs. 14, 15).

_Stylosphæra ophidium_, Haeckel, 1878, Atlas, _loc. cit._

Cortical shell thin walled, thorny, twice as broad as the medullary shell, with irregular, roundish pores; eight to ten on the half equator. Polar spines conical, more or less curved or S-shaped; the minor scarcely as long as the axis of the outer sphere, the major two to three times as long.

{141}_Dimensions._--Diameter of the outer sphere 0.11, pores 0.01 to 0.017, bars 0.003 to 0.007; diameter of the inner sphere 0.06, pores 0.005 to 0.008, bars 0.002 to 0.004; length of the major polar spine 0.25, of the minor 0.1, basal breadth 0.03.

_Habitat._--Indian Ocean, Madagascar, Rabbe, surface.

Genus 50. _Saturnulus_,[73] Haeckel, 1881, Prodromus, p. 451.

_Definition._--#Stylosphærida# with two concentric lattice-spheres and two equal opposite spines, the distal ends of which are connected by a circular or elliptical ring.

The genus _Saturnulus_ differs from the similar _Saturnalis_ by the duplication of the spherical lattice-shell; the inner lies within, the outer without the central capsule.

1. _Saturnulus circulus_, n. sp.

Cortical shell smooth, twice as broad as the medullary shell, with regular, circular, hexagonally framed pores, of the same breadth as the bars; fourteen to sixteen on the half equator. Ring circular, smooth, without edges, its diameter three times as great as that of the sphere.

_Dimensions._--Diameter of the outer sphere 0.08, pores and bars 0.004; of the inner sphere 0.04, of the ring 0.24.

_Habitat._--Central Pacific, Station 272, surface.

2. _Saturnulus annulus_, n. sp.

Cortical shell smooth, three times as broad as the medullary shell, with regular, circular, hexagonally framed pores, of the same breadth as the bars; eighteen to twenty on the half equator. Ring elliptical, smooth, without edges, somewhat constricted at the poles of the minor axis, its major diameter four times as great as that of the sphere. Differs from _Saturnalis annularis_, Pl. 13, fig. 16, mainly in the possession of a medullary shell.

_Dimensions._--Diameter of the outer sphere 0.1, pores and bars 0.005; inner sphere 0.033; major axis of the ring 0.4, minor 0.3.

_Habitat._--North Pacific, Station 244, surface.

3. _Saturnulus ellipticus_, n. sp. (Pl. 16, fig. 16).

Cortical shell smooth, three times as broad as the medullary shell, with regular, circular pores, three times as broad as the bars; sixteen to eighteen on the half equator. Ring elliptical, smooth, without edges, its major diameter three times as great as that of the sphere.

_Dimensions._--Diameter of the outer sphere 0.09, pores 0.006, bars 0.002; inner sphere 0.03; major axis of the elliptical ring 0.28, minor 0.24; thickness of the ring and the axial beams 0.008.

_Habitat._--South Pacific, Station 300, surface.

{142}4. _Saturnulus planetes_, n. sp. (Pl. 16, fig. 17).

Cortical shell smooth, twice as broad as the medullary shell, with regular, circular pores, of the same breadth as the bars; sixteen to eighteen on the half equator. Ring elliptical, smooth, with strong prominent edges, constricted at the poles of the minor axis, its major diameter three times as great as that of the outer sphere.

_Dimensions._--Diameter of the outer sphere 0.08, pores and bars 0.005; inner sphere 0.035; major axis of the ring 0.25, minor axis 0.2; thickness of the ring and the axial beams 0.012.

_Habitat._--Indian Ocean, Sunda Strait, Rabbe; Station 200, surface.

Subfamily AMPHISTYLIDA, Haeckel, 1881, Prodromus, pp. 449, 452.

_Definition._--#Stylosphærida# with three concentric spherical lattice-shells.

Genus 51. _Amphisphæra_, Haeckel,[74] 1881, Prodromus, p. 452.

_Definition._--#Stylosphærida# with three concentric lattice-spheres and two free spines of equal size and similar form.

The genus _Amphisphæra_ differs from its probable ancestral form, _Stylosphæra_, in the triple spherical lattice-shell. Commonly two of these lie within the central capsule (medullary shell), whilst the third lies outside it (cortical shell). But sometimes this order is inverted, the cortical shell being double, the medullary shell simple; and perhaps these forms may better represent a peculiar genus, _Amphisphæridium_.

Subgenus 1. _Amphisphærantha_, Haeckel.

_Definition._--Pores of the cortical shell regular, of nearly equal size and similar form; surface smooth or a little rough, without spines or thorns.

1. _Amphisphæra neptunus_, n. sp.

Radial proportion of the three concentric spheres = 4 : 2 : 1. Cortical shell thick walled, smooth, with regular, circular, hexagonally framed pores, of the same breadth as the bars; twelve to fifteen on the half equator. Polar spines three-sided pyramidal, with strong prominent edges, about as long as the radius of the outer shell, half as broad at the base. (Similar to _Stylatractus neptunus_, Pl. 17, fig. 6, but differs in the purely spherical form of the three concentric shells and the regular form of the network and of the polar spines.)

_Dimensions._--Diameter of the outer shell 0.16, middle shell 0.08, inner shell 0.04; pores and bars of the cortical shell 0.008; length of the polar spines 0.08, basal breadth 0.04.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

{143}2. _Amphisphæra uranus_, n. sp.

Radial proportion of the three spheres = 4 : 2 : 1. Cortical shell thick walled, smooth, with regular, circular pores, three times as broad as the bars; ten to twelve on the half equator. Polar spines three-sided pyramidal, about as long as the diameter of the outer shell, twice as broad at the base as one pore.

_Dimensions._--Diameter of the outer shell 0.12, middle 0.06, inner 0.03; pores of the cortical shell 0.012, bars 0.004; length of the polar spines 0.1, basal breadth 0.024.

_Habitat._--Western Indian Ocean, Zanzibar, 2200 fathoms, Pullen.

3. _Amphisphæra jupiter_, n. sp.

Radial proportion of the three spheres = 10 : 3 : 2. Cortical shell thick walled, smooth, with regular, circular pores, twice as broad as the bars; twenty to twenty-five on the half equator. Polar spines cylindro-conical, nearly as long as the axis of the outer shell, twice as broad at the base as one pore.

_Dimensions._--Diameter of the outer shell 0.2, middle 0.06, inner 0.04; pores of the cortical shell 0.01, bars 0.005; length of the polar spines 0.15 to 0.18, breadth 0.02.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

Subgenus 2. _Amphisphærella_, Haeckel.

_Definition._--Pores of the cortical shell regular, of nearly equal size and similar form; surface thorny or spiny.

4. _Amphisphæra apollo_, n. sp.

Radial proportion of the three spheres = 3 : 1.5 : 1. Cortical shell thick walled, spiny, with regular, circular, hexagonally framed pores, of the same breadth as the bars; twenty to twenty-two on the half equator. In each hexagon-corner (between three pores) a bristle-like radial spine. Polar spines cylindrical, with conical apex; one to one and a half times as long as the axis of the outer shell, as broad as three pores at the base. (Resembles closely _Xiphosphæra pallas_, Pl. 14, fig. 4, but differs in the presence of two medullary shells and the absence of the fine denticulations on the hexagonal crests.)

_Dimensions._--Diameter of the outer shell 0.12, middle 0.06, inner 0.04; pores and bars of the cortical shell 0.006; length of the polar spines 0.15, breadth 0.02.

_Habitat._--Western Tropical Pacific, Station 224, depth 1850 fathoms.

5. _Amphisphæra mercurius_, n. sp.

Radial proportion of the three spheres = 3 : 2 : 1. Cortical shell thin walled, spiny, with regular, circular pores, twice as broad as the bars; fifteen to eighteen on the half equator; between {144}them short bristle-like radial spines. Polar spines three-sided pyramidal, about as long as the radius of the outer shell, one-third as broad at the base.

_Dimensions._--Diameter of the outer shell 0.15, middle 0.09, inner 0.05; pores of the cortical shell 0.01, bars 0.005; length of the polar spines 0.09, basal breadth 0.03.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

Subgenus 3. _Amphisphærissa_, Haeckel.

_Definition._--Pores of the cortical shell irregular, of different size or form; surface smooth or a little rough, without spines or thorns.

6. _Amphisphæra cronos_, n. sp. (Pl. 17, fig. 5).

Radial proportion of the three spheres = 3 : 2 : 1. Cortical shell thin walled, smooth, with irregular, roundish pores, two to four times as broad as the bars; eight to ten on the half equator. Outer medullary shell similar, but with pores of half the size, connected with the cortical shell by numerous radial beams; inner medullary shell with very small pores. Polar spines three-sided pyramidal, as long as the axis of the inner medullary shell, half as broad at the base.

_Dimensions._--Diameter of the outer shell 0.12, middle 0.08, inner 0.04; pores of the cortical shell 0.01 to 0.02, bars 0.05; length of the polar spines 0.04, basal breadth 0.02.

_Habitat._--South Atlantic, Station 330, surface.

7. _Amphisphæra pluto_, n. sp. (Pl. 17, figs. 7, 8).

Radial proportion of the three spheres about = 4 : 2 : 1 (or 11 : 7 : 3). Cortical shell thick walled, smooth, with very irregular, roundish pores, two to four times as broad as the bars; eight to ten on the half equator; often two to four pores confluent. Margin of their outer aperture double. Polar spines conical, double contoured, as long as the radius of the outer shell, one-third as broad at the base.

_Dimensions._--Diameter of the outer shell 0.11, middle shell 0.07, inner shell 0.03; pores of the cortical shell 0.01 to 0.02, bars 0.06, length of the polar spines 0.06, basal breadth 0.02.

_Habitat._--Central Pacific, Station 268, surface.

Subgenus 4. _Amphisphæromma_, Haeckel.

_Definition._--Pores of the cortical shell irregular, of different size or form; surface spiny or thorny.

8. _Amphisphæra mars_, n. sp.

Radial proportion of the three spheres = 10 : 3 : 2. Cortical shell thin walled, thorny, with irregular, roundish pores, one to three times as broad as the bars; sixteen to twenty on the {145}half equator. Irregularly scattered between them short conical thorns. Polar spines conical, about as long as the axis of the outer shell, as broad at the base as the inner shell.

_Dimensions._--Diameter of the outer shell 0.2, middle shell 0.06, inner shell 0.04; pores of the cortical shell 0.005 to 0.02, bars 0.006; length of the polar spines 0.17, basal breadth 0.04.

_Habitat._--North Atlantic, Gulf Stream, near Florida, depth 1500 fathoms, Schaffner.

Genus 52. _Amphistylus_,[75] Haeckel, 1881, Prodromus, p. 452.

_Definition._--#Stylosphærida# with three concentric lattice-spheres and two free spines of different size or form.

The genus _Amphistylus_ differs from its ancestral form, _Amphisphæra_, by the differentiation of both polar spines, and exhibits therefore the same relation to it that _Sphærostylus_ bears to _Stylosphæra_.

1. _Amphistylus clio_, n. sp.

Radial proportion of the three spheres = 4 : 2 : 1. Cortical shell thick walled, smooth; its pores regular, circular, three times as broad as the bars; eighteen to twenty on the half equator. Polar spines three-sided pyramidal, very stout, as broad at the base as the inner medullary shell; major spine somewhat longer than the diameter of the cortical shell; minor spine scarcely half as long. (Similar to _Stylosphæra clio_, Pl. 16, fig. 7, but different in the double medullary shell and the different length of the polar spines.)

_Dimensions._--Diameter of the outer sphere 0.15, middle 0.08, inner 0.04; pores of the outer shell 0.01, bars 0.003; length of the major spine 0.17, minor 0.07, basal breadth 0.04.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

2. _Amphistylus hippocampus_, n. sp.

Radial proportion of the three spheres = 3 : 2 : 1. Cortical shell thick walled, smooth; its pores regular, circular, hexagonally lobed, three times as broad as the bars; twelve to fifteen on the half equator. Major polar spine three-sided pyramidal, about as long as the axis of cortical shell; minor spine pommel-like, edged, scarcely one-third as long. (Similar to _Sphærostylus hippocampus_, Pl. 16, figs. 10, 11, but differs in the larger size, the double medullary shell, and the straight, not curved, major spine.)

_Dimensions._--Diameter of the outer sphere 0.11, middle 0.07, inner 0.035; pores of the outer shell 0.011, bars 0.004; length of the major spine 0.12, of the minor 0.04, breadth 0.03.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

3. _Amphistylus glyptodon_, n. sp.

Radial proportion of the three spheres = 6 : 3 : 1. Cortical shell thick walled, spiny, with irregular, roundish pores, two to four times as broad as the bars; ten to twelve on the half equator. {146}Inner aperture of each pore closed by a thin fenestrated lamella with five to seven small pores. Major polar spine three-sided pyramidal, longer than the diameter of the outer sphere; minor polar spine scarcely as long as its radius, pommel-shaped. (Similar to _Xiphatractus glyptodon_, Pl. 17, figs. 9, 10, but differs in the spherical, not ellipsoidal, form of the three shells and the size of the polar spines.)

_Dimensions._--Diameter of the outer sphere 0.12, middle 0.06, inner 0.02; pores and spines of the outer shell 0.01 to 0.02, bars and porules 0.006; length of the major polar spine 0.15, of the minor 0.05, breadth 0.04.

_Habitat._--South Pacific, Station 285, depth 2375 fathoms.

Genus 53. _Saturninus_,[76] n. gen.

_Definition._--#Stylosphærida# with three concentric lattice-spheres and two equal opposite spines, connected at the distal end by a circular or elliptical ring.

The genus _Saturninus_ differs from the similar _Saturnulus_ by the triplication of the spherical lattice-shell; the inner shell is enclosed in the central capsule, whilst both the others lie outside it.

1. _Saturninus triplex_, n. sp.

Radial proportion of the three spheres = 4 : 3 : 1. Inner cortical shell with regular, circular pores, of the same breadth as the bars, sixteen to eighteen on the half equator; outer cortical shell connected with the inner by numerous bristle-like radial spines, network very delicate, cobweb-shaped, with irregular polygonal meshes. Ring elliptical, two and a half times as broad as the outer shell.

_Dimensions._--Diameter of the inner sphere 0.03, middle 0.09, outer 0.12; pores and bars of the middle shell 0.004; major axis of the elliptical ring 0.3, minor 0.25; thickness of the ring and the axial beams 0.008.

_Habitat._--Central Pacific, Station 272, surface.

Subfamily CROMYOSTYLIDA, Haeckel, 1881, Prodromus, pp. 449, 453.

_Definition._--#Stylosphærida# with four concentric spherical lattice-shells (two medullary and two cortical).

Genus 54. _Stylocromyum_,[77] Haeckel, 1881, Prodromus, p. 453.

_Definition._--#Stylosphærida# with four concentric lattice-spheres and two free spines of equal size and similar form.

{147}The genus _Stylocromyum_ differs from its probable ancestral form, _Amphisphæra_, by the duplication of the cortical shell; two opposite radial beams, piercing the wall of the central capsule, connect it with the double medullary shell, and are prolonged outside into two equal spines.

1. _Stylocromyum amphiconus_, n. sp.

Surface of the shell smooth. Radial proportion of the four spheres = 1 : 2 : 8 : 9. Two medullary shells inside the central capsule, two cortical shells outside it. Interval between the second and third shells the greatest. Pores of all the shells regular, circular, two to four times as broad as the bars. Both polar spines equal, conical, about as long as the axis of the outermost sphere, as broad at the base as the innermost.

_Dimensions._--Diameter of the four spheres--(A) inner medullary shell 0.03, (B) outer medullary shell 0.06, (C) inner cortical shell 0.25, (D) outer cortical shell 0.28; length of the polar spines 0.3, basal breadth 0.03.

_Habitat._--Central Pacific, Station 273, depth 2350 fathoms.

2. _Stylocromyum amphipyramis_, n. sp.

Surface of the shell smooth. Radial proportion of the four spheres = 2 : 3 : 6 : 8. Both medullary shells with regular, circular pores, twice as broad as the bars. Both cortical shells with irregular, roundish, much larger pores, three to six times as broad as the bars. Both polar spines equal or nearly equal, three-sided pyramidal, about as long as the axis of the third shell.

_Dimensions._--Diameter of the four spheres--(A) 0.04, (B) 0.06, (C) 0.12, (D) 0.16; length of the polar spines 0.11, basal breadth 0.02.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

Genus 55. _Cromyostylus_,[78] Haeckel, 1881, Prodromus, p. 453.

_Definition._--#Stylosphærida# with four concentric lattice-spheres and two free spines of different size or form.

The genus _Cromyostylus_ differs from its ancestral form, _Stylocromyum_, in the differentiation of the two unequal polar spines.

1. _Cromyostylus gladius_, n. sp.

Surface of the shell smooth. Radial proportion of the four spheres = 1 : 3 : 10 : 12. Both medullary shells with regular, circular, simple pores. Inner cortical shell with regular, circular, hexagonally framed pores, twice as broad as the bars. From each hexagon-corner arises a {148}bristle-shaped radial spine, which at the distal end gives off three thread-like branches; by communication of these threads (at equal distances from the centre) the delicate outer medullary shell is formed. The polar spines very different; major spine six-sided pyramidal, longer than the diameter of the shell; minor pommel-shaped, shorter than the radius (similar to _Xiphatractus glyptodon_, Pl. 17, figs. 9, 10, but different in the double spherical cortical shell).

_Dimensions._--Diameter of the four spheres--(A) 0.02, (B) 0.06, (C) 0.2, (D) 0.24; length of the major spine 0.3, of the minor 0.1.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

Subfamily CARYOSTYLIDA, Haeckel, 1881, Prodromus, pp. 449, 454.

_Definition._--#Stylosphærida# with five or more concentric, spherical lattice-shells.

Genus 56. _Caryostylus_, Haeckel, 1881, Prodromus, p. 454.

_Definition._--#Stylosphærida# with five to six or more concentric lattice-shells and two free opposite spines of equal size and similar form.

The genus _Caryostylus_ differs from its ancestral form, _Stylocromyum_, by the multiplication of the concentric spheres, the number of which amounts to five or six or more. I have only observed one single species of this genus. Some similar forms which in my Prodromus (1881, p. 454) were annexed to it, and disposed in three nearly allied genera (_Caryoxiphus_, _Caryodoras_, _Caryolonche_), have now been proved to belong to other groups, mainly ellipsoidal Druppulida.

1. _Caryostylus hexalepas_, n. sp.

Surface of the spherical shell smooth. Radial proportion of the component six concentric shells = 1 : 2 : 7 : 9 : 12 : 15. Both medullary shells connected only by six radial beams, opposite in pairs in the three dimensive axes. Between second and third shell numerous (twenty regularly disposed?) radial beams. Four cortical shells connected by very numerous (sixty to eighty or more?) short radial beams. Pores of all six shells regular, circular, the size increasing towards the surface, two to three times as broad as the bars. Two opposite polar spines very large, of equal size, three times as long as the shell radius, cylindrical, club-shaped at the thicker distal end. (The whole shell structure is similar to Pl. 15, fig. 2, but the shells are spherical, not ellipsoidal.)

_Dimensions._--Diameter of the six spheres--(A) 0.02, (B) 0.04, (C) 0.15, (D) 0.18, (E) 0.24, (F) 0.3; length of the spines 0.5.

_Habitat._--West Tropical Pacific, Station 225, depth 4475 fathoms.

Subfamily SPONGOSTYLIDA, Haeckel, 1881, Prodromus, pp. 449, 455.

_Definition._--#Stylosphærida# with spherical spongy shell (with or without enclosed latticed medullary shells).

{149}Genus 57. _Spongolonchis_,[79] Haeckel, 1881, Prodromus, p. 455.

_Definition._--#Stylosphærida# with a solid sphere of spongy framework, and with two opposite free radial spines.

The genus _Spongolonchis_ differs from its probable ancestral form, _Styptosphæra_, by the development of two opposite radial spines situated in one axis.

1. _Spongolonchis compacta_, n. sp.

Spongy framework of the spherical shell very compact, with small meshes, three to four times as broad as the bars. Surface rough, but not spiny. Two polar spines pyramidal, only as long as the radius of the shell, one-third as broad at the base.

_Dimensions._--Diameter of the shell 0.2; length of the spines 0.1, basal breadth 0.03.

_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.

2. _Spongolonchis laxa_, n. sp.

Spongy framework loose, with large meshes, ten to twelve times as broad as the bars. Surface spiny. Two polar spines three-sided prismatic, longer than the diameter of the shell (broken off in the observed specimen).

_Dimensions._--Diameter of the shell 0.5; length of the spine 0.6 and more, breadth 0.02.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

Genus 58. _Spongostylus_,[80] Haeckel, 1881, Prodromus, p. 455.

_Definition._--#Stylosphærida# with spongy spherical cortical shell, enclosing in the centre a simple latticed medullary shell, and with two opposite free radial spines.

The genus _Spongostylus_ may probably be derived from _Spongoplegma_ by development of two opposite radial spines in one axis.

1. _Spongostylus hastatus_, n. sp.

Spongy cortical shell with compact framework, twice as broad as the enclosed medullary shell, the pores of which are regular, circular, twice as broad as the bars. Two polar spines, three times as long as the radius of the shell, in the basal two-thirds cylindrical, in the distal third compressed, two-edged, spear-shaped.

_Dimensions._--Diameter of the cortical shell 0.1, medullary shell 0.05; length of the spines 0.15.

_Habitat._--South Atlantic, Station 335, depth 1425 fathoms.

{150}2. _Spongostylus gladiatus_, Haeckel.

_Stylosphæra holosphæra_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 299, Taf. viii. fig. 14.

Spongy cortical shell with rather compact framework, four times as broad as the enclosed medullary shell, the pores of which are irregular, roundish, three to four times as broad as the bars. Two polar spines sword-shaped, two-edged, as long as the shell diameter.

_Dimensions._--Diameter of the cortical shell 0.24, medullary shell 0.06; length of the spines 0.25.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms; Philippine Sea, depth 3300 fathoms.

3. _Spongostylus serratus_, n. sp.

Spongy cortical shell with lax framework, ten to twelve times as broad as the enclosed medullary shell, the pores of which are irregular, roundish, once and a half to twice as broad as the bars. Two polar spines longer than the shell diameter (broken off in the observed specimen), three-sided prismatical, with three straight serrated edges.

_Dimensions._--Diameter of the cortical shell 0.5, medullary shell 0.04; length of the spines 0.6 or more.

_Habitat._--South Pacific, Station 285, depth 2375 fathoms.

Genus 59. _Spongostylidium_,[81] Haeckel, 1881, Prodromus, p. 455.

_Definition._--#Stylosphærida# with spongy spherical cortical shell, enclosing two concentric spherical latticed medullary shells, and with two opposite, free radial spines.

The genus _Spongostylidium_ differs from _Spongostylus_ by duplication of the latticed medullary shell, and therefore bears the same relation to it as _Spongodictyon_ to _Spongoplegma_.

1. _Spongostylidium streptacanthum_, n. sp.

Both medullary shells spherical, with small, regular, circular pores, twice as broad as the bars (outer twice as broad as the inner). Spongy cortical shell enclosing it with dense framework, four times as broad as the outer medullary shell. Two polar spines very large, four times as long as the diameter of the outer shell; as broad as the inner medullary shell, with three dentated, spirally contorted edges. (Very similar to the common _Spongosphæra streptacantha_ and to _Hexadoridium streptacanthum_, but with only two opposite spines in one axis.)

_Dimensions._--Diameter of the cortical shell 0.16, of the outer medullary shell 0.04, inner 0.02; length of the spines 0.7 and more, breadth 0.02.

_Habitat._--Indian Ocean, Cocos Islands, Rabbe.

{151}Family VIII. #STAUROSPHÆRIDA#, Haeckel (Pl. 15).

_Staurosphærida_, Haeckel, 1881, Prodromus, p. 449.

_Definition._--#Sphæroidea# with four radial spines on the surface of the spherical shell, forming a regular cross, being opposite in pairs in two axes perpendicular to one another; living solitary (not associated in colonies).

The family #Staurosphærida# is distinguished from the other #Sphæroidea# by the possession of four radial spines, which are opposite in pairs in two perpendicularly crossed axes. By these "two main axes" an equatorial plane is determined, which approximates them to the #Discoidea#. But in the latter the shells as well as the central capsule become more or less flattened, lenticular, or discoidal, whilst in the former they remain spherical. However, some forms of both groups are very similar, and inspection from different sides (and mainly from the margin of the equatorial plane) is required to determine the spherical (not compressed) shell-form of the Staurosphærida. As a rule the species of this family are much rarer, and much less numerous, than those of all the other #Sphæroidea#.

The most simple Staurosphærida are the Staurostylida, with one single spherical lattice-shell. To this ancestral group all other subfamilies can be opposed as "Staurosphærida concentrica," since their carapace is composed of two or more concentric lattice-shells; two in the Staurolonchida, three in the Stauracontida, four in the Staurocromyida, five or more in the Staurocaryida. In all these four subfamilies the concentric shells are simple (not spongy) fenestrated spheres. In a sixth subfamily, in the Staurodorida, the shell is wholly or partially composed of irregular spongy wickerwork, with or without a medullary shell in the centre.

_The Four Radial Spines_ in all Staurosphærida are normally opposed in pairs in two axes perpendicular one to another, and therefore together form a rectangular cross. But in many species besides this normal form individual abnormalities occur, in which the four spines in the equatorial plane are not quite accurately opposed, so that the four angles between them are not right angles, but more or less unequal. More rarely also their position in the equatorial plane is not accurately retained, so that they are placed in two, three, or four different meridian planes, intersecting at very small variable angles.

In the greater part of Staurosphærida all four radial spines are quite equal, and of the same size and form. But in some genera there takes place a more or less considerable differentiation of the four spines, commonly in pairs, so that the two opposite spines of each pair are equal, but the pairs different (_Staurostylus_, _Staurolonchidium_). More rarely also both spines of one pair become unequal, whilst those of the other pair remain equal (_Stauroxiphos_). Very rarely all four spines assume a different size or form.

{152}_Synopsis of the Genera of Staurosphærida._

I. Subfamily {All four spines equal, 60. _Staurosphæra_. Staurostylida. { (Shell one single {Four spines different lattice-sphere.) { in pairs, 61. _Staurostylus_. { {One spine larger than the { three others, 62. _Stylostaurus_.

II. Subfamily {All four spines {Simple, 63. _Staurolonche_. Staurolonchida. { equal, { (Shell with { {Branched, 64. _Staurancistra_. two concentric { lattice-spheres.) {Four spines different 65. { in pairs, _Staurolonchidium_. { {One spine larger than { the three others, 66. _Stauroxiphos_.

III. Subfamily }All four spines equal, Stauracontida. } simple, 67. _Stauracontium_. (Shell with three } concentric spheres.) }

IV. Subfamily }All four spines {Simple, 68. _Staurocromyum_. Staurocromyida. } equal, { (Shell with four } {Branched, 69. _Cromyostaurus_. concentric spheres.) }

V. Subfamily }All four spines equal, 70. _Staurocaryum_. Staurocaryida. } (Shell with five } or more concentric } spheres.) }

VI. Subfamily }Solid spongy sphere Staurodorida. } without medullary shell, 71. _Staurodoras_. (Shell a spongy } sphere.) }

Subfamily STAUROSTYLIDA,[82] Haeckel, Prodromus, 1881, pp. 449, 450.

_Definition._--#Staurosphærida# with one single spherical lattice-shell.

Genus 60. _Staurosphæra_,[83] Haeckel, 1881, Prodromus, p. 450.

_Definition._--#Staurosphærida# with a single lattice-sphere and four crossed equal spines.

The genus _Staurosphæra_ may be regarded as the common ancestral form of this subfamily, since it represents their most simple and primitive form. From the surface of the simple lattice-sphere, enclosing the central capsule, arise four equal, simple, radial spines, opposite in pairs in two diameters, perpendicular one to another. _Staurosphæra_ may be derived phylogenetically either from _Cenosphæra_ by production of the four spines, or from _Hexastylus_ by reduction of two opposite spines.

{153}Subgenus 1. _Staurosphærantha_, Haeckel.

_Definition._--Pores regular, all of nearly equal size and similar form; surface smooth.

1. _Staurosphæra cruciata_, n. sp.

Shell thin walled, smooth, with regular, hexagonal pores, four times as broad as the bars; ten to twelve on the quadrant. Four crossed radial spines three-sided pyramidal, as long as the diameter of the shell, as broad at the base as one pore (very similar to _Hexastylus phænaxonius_, Pl. 21, fig. 3, but with only four spines).

_Dimensions._--Diameter of the shell 0.12, of the pores 0.008, bars 0.002.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

2. _Staurosphæra christiana_, n. sp.

Shell thick walled, smooth, with regular, circular, hexagonally framed pores, three times as broad as the bars; six to eight on the quadrant. Four crossed spines six-sided pyramidal, as long as the radius, as broad as one mesh.

_Dimensions._--Diameter of the shell 0.13, pores 0.012, bars 0.004.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

3. _Staurosphæra johannis_, n. sp.

Shell thick walled, smooth, with regular, circular pores, four times as broad as the bars; five to six on the quadrant. Four spines six-sided pyramidal, half as long as the radius, as broad as one mesh.

_Dimensions._--Diameter of the shell 0.15, pores 0.02, bars 0.005.

_Habitat._--North Pacific, Station 241, depth 2300 fathoms.

4. _Staurosphæra pauli_, n. sp.

Shell very thick walled, smooth, with regular, circular, double-edged pores, four times as broad as the bars; eight to ten on the quadrant. Four spines conical, as long as the radius, as broad as one mesh.

_Dimensions._--Diameter of the shell 0.15, pores 0.016, bars 0.004.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

5. _Staurosphæra petri_, n. sp.

Shell thin walled, smooth, with regular, circular pores, three times as broad as the bars; twenty to twenty-two on the quadrant. Four spines conical, half as long as the radius, as broad as one mesh.

_Dimensions._--Diameter of the shell 0.22, pores 0.006, bars 0.002.

_Habitat._--South Atlantic, Station 325, depth 2650 fathoms; also fossil in Barbados.

{154}6. _Staurosphæra jacobi_, n. sp.

Shell thick walled, smooth, with regular, circular pores, twice as broad as the bars; eleven to twelve on the quadrant. Four spines cylindrical, three times as long as the radius, three times as broad as one mesh.

_Dimensions._--Diameter of the shell 0.1, pores 0.006, bars 0.003.

_Habitat._--North Atlantic, Station 353, depth 2965 fathoms.

7. _Staurosphæra simonis_, n. sp.

_Haliomma_ with four spines, Bury, 1862, Polycystins of Barbados, pl. iv. fig. 4.

Shell thick walled, smooth, with regular, circular pores, of the same breadth as the bars; eight to ten on the quadrant. Four spines cylindrical, twice as long as the radius, five times as broad as one mesh.

_Dimensions._--Diameter of the sphere 0.1, pores and bars 0.003.

_Habitat._--Fossil in Barbados.

Subgenus 2. _Staurosphærella_, Haeckel.

_Definition._--Pores regular, all of nearly equal size and similar form; surface covered with by-spines or accessory thorns.

8. _Staurosphæra philippi_, n. sp. (Pl. 15, fig. 6).

Shell thin walled, covered with bristle-shaped by-spines, as long as the radius. Pores regular, circular, twice as broad as the bars; six to eight on the quadrant. Four main spines cylindrical, five to ten times as long as the radius, as broad as one mesh.

_Dimensions._--Diameter of the shell 0.08, pores 0.006, bars 0.003.

_Habitat._--Central Pacific, Station 272, surface.

9. _Staurosphæra andreæ_, n. sp.

Shell thick walled, with regular, circular, hexagonally framed pores, three times as broad as the bars; nine to ten on the quadrant. From each hexagon-corner arises a bristle-shaped by-spine, half as long as the radius. Four main spines three-sided pyramidal, with spirally contorted edges, as long as the radius (very similar to _Hexastylus solonis_, Pl. 21, fig. 11, but with only four spines).

_Dimensions._--Diameter of the shell 0.16, pores 0.01, bars 0.003.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

{155}10. _Staurosphæra thomæ_.

Shell thick walled, with regular, circular pores, twice as broad as the bars; twelve to fourteen on the quadrant; surface covered with short conical by-spines. Four main spines conical, twice as long as the radius, twice as broad as one mesh.

_Dimensions._--Diameter of the sphere 0.2, pores 0.012, bars 0.006.

_Habitat._--South Atlantic, Station 332, depth, 2200 fathoms.

Subgenus 3. _Staurosphærissa_, Haeckel.

_Definition._--Pores irregular, of different size or form; surface smooth.

11. _Staurosphæra judæ_, n. sp.

Shell thin walled, smooth, with irregular, polygonal pores, twice to four times as broad as the bars; six to ten on the quadrant. Four main spines three-sided pyramidal, as long as the radius.

_Dimensions._--Diameter of the sphere 0.15, pores 0.006 to 0.012, bars 0.003.

_Habitat._--Central Pacific, Station 273, depth, 2350 fathoms.

12. _Staurosphæra crassa_, Dunikowski.

_Staurosphæra crassa_, 1882, Denkschr. d. k. Akad. d. Wiss. Wien, Bd. xlv. p. 27, Taf. v. figs. 52-55.

Shell thick walled, smooth, with irregular, roundish pores, scarcely broader than the bars; eight to ten on the quadrant. Four spines three-sided pyramidal, nearly as long as the shell diameter.

_Dimensions._--Diameter of the sphere 0.19, pores and bars 0.015.

_Habitat._--Fossil in the Alpine Lias (Schafberg near Salzburg, Dunikowski).

13. _Staurosphæra apostolorum_, Haeckel.

? _Cenosphæra megapora_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. iii. fig. 1.

? _Cenosphæra micropora_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. iii. fig. 2.

Shell thin walled, smooth, with large, irregular, roundish pores, twice to six times as broad as the bars; four to six on the quadrant. Four spines conical, very stout, about as long as the shell diameter, often more or less irregularly disposed.

_Dimensions._--Diameter of the sphere 0.12 to 0.2, pores 0.01 to 0.03, bars 0.005.

_Habitat._--Fossil in Barbados.

{156}Subgenus 4. _Staurosphæromma_, Haeckel.

_Definition._--Pores irregular, of different size or form; surface covered with by-spines or accessory thorns.

14. _Staurosphæra bartholomæi_, n. sp.

Shell thin walled, with irregular, polygonal pores, three times as broad as the bars; six to eight on the quadrant; surface covered with short bristle-shaped by-spines. Four main spines three-sided pyramidal, twice as long as the radius.

_Dimensions._--Diameter of the shell 0.14, pores 0.008 to 0.016, bars 0.003 to 0.005.

_Habitat._--South Pacific, Station 285, depth 2375 fathoms.

15. _Staurosphæra thaddæi_, n. sp.

Shell thick walled, with irregular, roundish, polygonally framed pores, twice to three times as broad as the bars; five to seven on the quadrant; surface covered with bristle-shaped spines, half as long as the radius. Four main spines pyramidal, as long as the radius.

_Dimensions._--Diameter of the shell 0.12, pores 006 to 0.012, bars 0.004.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms; also fossil in Barbados.

16. _Staurosphæra matthæi_, n. sp.

Shell thick walled, with irregular, roundish pores, twice to five times as broad as the bars; ten to twelve on the quadrant; surface covered with short conical thorns or by-spines. Four main spines conical, as long as the radius.

_Dimensions._--Diameter of the shell 0.15, pores 0.004 to 0.01, bars 0.002.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

Genus 61. _Staurostylus_,[84] Haeckel, 1881, Prodromus, p. 450.

_Definition._--#Staurosphærida# with one single lattice-sphere and four crossed spines which are arranged in opposite pairs, one pair opposite being larger than the other.

The genus _Staurostylus_ has been developed from _Staurosphæra_ by differentiation of the four crossed spines in pairs; two opposite spines growing much more strongly than the other two.

1. _Staurostylus græcus_, n. sp.

Shell thick walled, smooth, with regular, circular, hexagonally framed pores, twice as broad as the bars; six to eight on the quadrant. Spines three-sided prismatic, pointed, as broad as {157}one mesh; two opposite larger spines as long as the diameter of the shell, two smaller only as long as the radius.

_Dimensions._--Diameter of the shell 0.15, pores 0.01, bars 0.005; length of the major spines 0.16, minor 0.08.

_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.

2. _Staurostylus latinus_, n. sp.

Shell thin walled, smooth, with regular, circular, double-edged pores, three times as broad as the bars; twelve to fourteen on the quadrant. Spines conical, twice as broad at the base as one mesh; two opposite larger spines as long as the radius of the shell, two smaller only one-third as long.

_Dimensions._--Diameter of the shell 0.24, pores 0.012, bars 0.004; length of the major spines 0.12, minor 0.04.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

3. _Staurostylus germanicus_, n. sp.

Shell thick walled, covered with bristle-shaped by-spines, half as long as the radius. Pores regular, circular, hexagonally framed, twice as broad as the bars; eight to ten on the quadrant. From each hexagon-corner arises one short by-spine. Four main spines three-sided pyramidal, as broad at the base as one mesh; two opposite larger spines one and a half times as long as the radius, two smaller two-thirds as long.

_Dimensions._--Diameter of the shell 0.16, pores 0.008, bars 0.004; length of the major spines 0.12, minor 0.08.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

Genus 62. _Stylostaurus_,[85] 1881, Prodromus, p. 450.

_Definition._--#Staurosphærida# with one single lattice-sphere and four crossed spines, one of which is much larger than the other three.

The genus _Stylostaurus_ differs from the preceding in the extraordinary development of one of the four spines, which is much longer than the other three; these may be equal or different.

1. _Stylostaurus caudatus_, n. sp. (Pl. 13, fig. 7).

Shell thick walled, smooth, with regular, circular, hexagonally framed pores, twice as broad as the bars; five to six on the quadrant. Spines three-sided pyramidal, as broad at the base as {158}one mesh; one of the spines longer than the shell diameter, the opposite spine nearly as long as the shell radius; both lateral spines scarcely one-third as long.

_Dimensions._--Diameter of the shell 0.1, pores 0.01, bars 0.005; length of the major spine 0.14, of the opposite 0.04, of both lateral spines 0.012.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

2. _Stylostaurus gladiatus_, n. sp.

Shell thick walled, smooth, with regular, circular pores, three times as broad as the bars; nine to ten on the quadrant. Spines three-sided prismatic, as broad at the base as one mesh; one of the spines longer than the shell diameter, and much larger than the other three, which are nearly equal (half as long as the radius).

_Dimensions._--Diameter of the shell 0.2, pores 0.015, bars 0.005; length of the major spine 0.25, of the three others 0.005.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

Subfamily STAUROLONCHIDA,[86] Haeckel, 1881, Prodromus, pp. 449, 451.

_Definition._--#Staurosphærida# with two concentric spherical lattice-shells.

Genus 63. _Staurolonche_,[87] Haeckel, 1881, Prodromus, p. 451.

_Definition._--#Staurosphærida# with two concentric lattice-spheres and four crossed, equal, simple spines.

The genus _Staurolonche_ may be derived either from _Staurosphæra_ by the duplication of the lattice-sphere, or from _Carposphæra_ by the production of four crossed radial spines, lying in one meridional plane, or from _Hexalonche_ by the reduction of two opposite spines.

Subgenus 1. _Staurolonchantha_, Haeckel.

_Definition._--Pores of the cortical shell regular, and of nearly equal size and similar form; surface smooth.

1. _Staurolonche hexagona_, n. sp.

_Haliomma hexagonum_, Ehrenberg, 1854, Mikrogeol., Taf. xxxvb., Bd. iv. fig. 17.

_Haliomma hexagonum_, Haeckel, 1862, Monogr. d. Radiol., p. 434.

Cortical shell thin walled, smooth, three times as broad as the medullary shell, with regular, hexagonal pores, four times as broad as the bars; seven to eight on the quadrant. Four spines three-sided pyramidal, somewhat longer than the radius, as broad at the base as one mesh.

{159}_Dimensions._--Diameter of the outer shell 0.12, inner 0.04; cortical pores 0.012, bars 0.003; length of the spines 0.08.

_Habitat._--North Atlantic, Station 64, depth 2700 fathoms.

2. _Staurolonche spinozæ_, n. sp.

Cortical shell thick walled, smooth, twice as broad as the medullary shell, with regular, circular, hexagonally framed pores, three times as broad as the bars; five to six on the quadrant. Four spines three-sided pyramidal, half as long as the radius, as broad at the base as one mesh.

_Dimensions._--Diameter of the outer shell 0.16, inner 0.08; cortical pores 0.012, bars 0.004; length of the spines 0.04.

_Habitat._--Central Pacific, Station 271, surface.

3. _Staurolonche aperta_, Haeckel.

_Haliomma apertum_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxviii. fig. 5.

Cortical shell thin walled, smooth, three times as broad as the medullary shell; pores regular, circular, five times as broad as the bars; four to five on the quadrant. Four spines conical, as long as the radius, as broad as one mesh.

_Dimensions._--Diameter of the outer shell 0.1, inner 0.03; cortical pores 0.015, bars 0.003; length of the spines 0.05.

_Habitat._--Fossil in Barbados.

4. _Staurolonche brunonis_, n. sp.

Cortical shell thick walled, smooth, twice as broad as the medullary shell, with regular, circular pores, three times as broad as the bars; eight to ten on the quadrant. Four spines cylindro-conical, longer than the diameter, twice as broad as one mesh.

_Dimensions._--Diameter of the outer shell 0.08, inner 0.04; cortical pores 0.006, bars 0.002; length of the spines 0.12.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

5. _Staurolonche pertusa_, n. sp. (Pl. 15, figs. 5, 5_a_).

Cortical shell thin walled, smooth, three times as broad as the medullary shell, with regular, circular pores, three times as broad as the bars; eight to ten on the quadrant. Pores of the medullary shell only one-third as large, also circular. Four spines three-sided prismatic, three times as long as the radius; each of their three thin wings perforated by a single row of small pores.

_Dimensions._--Diameter of the outer shell 0.1, inner 0.033; cortical pores 0.01, bars 0.003; length of the spines 0.15.

_Habitat._--North Atlantic, Station 353, surface.

{160}Subgenus 2. _Staurolonchella_, Haeckel.

_Definition._--Pores of the cortical shell regular, and of nearly equal size and similar form; surface covered with by-spines or thorns.

6. _Staurolonche straussii_, n. sp.

Cortical shell thin walled, four times as broad as the medullary shell, and covered with numerous bristle-shaped by-spines, half as long as the radius. Pores regular, circular, hexagonally framed, twice as broad as the bars; six to eight on the radius. On each hexagonal frame twelve by-spines (six at the corners, six in the middle between them). Four main spines six-sided pyramidal, about as long as the radius, twice as broad as one mesh.

_Dimensions._--Diameter of the outer shell 0.16, inner 0.04; cortical pores 0.016, bars 0.008; length of the spines 0.1.

_Habitat._--West Tropical Pacific, Station 225, depth 4475 fathoms.

7. _Staurolonche feuerbachii_, n. sp.

Cortical shell thick walled, five times as broad as the medullary shell, and covered with short conical by-spines. Pores regular, circular, twice as broad as the bars; twenty to twenty-two on the quadrant. Four main spines three-sided prismatic, with pyramidal apex, two to three times as long as the radius, twice as broad as one mesh.

_Dimensions._--Diameter of the outer shell 0.27, of the inner 0.055; cortical pores 0.008, bars 0.004; length of the spines 0.3 to 0.4.

_Habitat._--Fossil in Barbados.

8. _Staurolonche moleschottii_, n. sp.

Cortical shell thick walled, three times as broad as the medullary shell, and covered with short conical by-spines. Pores regular, circular, of the same breadth as the bars; fourteen to sixteen on the quadrant. Four main spines conical, as long as the radius, three times as broad at the base as one mesh.

_Dimensions._--Diameter of the outer shell 0.15, inner 0.05; cortical pores and bars 0.004; length of the spines 0.08.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

Subgenus 3. _Staurolonchissa_, Haeckel.

_Definition._--Pores of the cortical shell irregular, of different size or form; surface smooth.

9. _Staurolonche holbachii_, n. sp.

Cortical shell thin walled, with smooth surface, three times as broad as the medullary shell. Pores irregular, polygonal, twice to four times as broad as the bars. Four main spines three-sided prismatic, longer than the shell diameter.

{161}_Dimensions._--Diameter of the outer shell 0.12, inner 0.04; cortical pores 0.006 to 0.012, bars 0.003; length of the spines 0.15.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

10. _Staurolonche gassendii_, n. sp.

Cortical shell thick walled, with smooth surface, four times as broad as the medullary shell. Pores irregular, roundish, three to five times as broad as the bars. Four main spines conical, as long as the radius.

_Dimensions._--Diameter of the outer shell 0.2, inner 0.05; cortical pores 0.01 to 0.02, bars 0.004; length of the spines 0.1.

_Habitat._--North Atlantic, Station 353, depth 2965 fathoms.

Subgenus 4. _Staurolonchura_, Haeckel.

_Definition._--Pores of the cortical shell irregular, of different size or form; surface covered with by-spines or thorns.

11. _Staurolonche epicurii_, n. sp.

Cortical shell thick walled, five times as broad as the medullary shell, and covered with numerous bristle-shaped by-spines (half as long as the radius). Pores irregular, roundish, polygonally framed, twice to three times as broad as the bars. Four main spines pyramidal, as long as the radius.

_Dimensions._--Diameter of the outer shell 0.22, inner 0.044; cortical pores 0.02 to 0.04, bars 0.012; length of the spines 0.1.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

12. _Staurolonche lucretii_, n. sp.

Cortical shell thick-walled, three times as broad as the medullary shell, and covered with numerous short, conical thorns. Pores irregular, roundish, twice to four times as broad as the bars. Four main spines conical, half as long as the radius.

_Dimensions._--Diameter of the outer shell 0.15, inner 0.05; cortical pores 0.015 to 0.03, bars 0.008; length of the spines 0.04.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

Genus 64. _Staurancistra_,[88] Haeckel, 1881, Prodromus, p. 451.

_Definition._--#Staurosphærida# with two concentric lattice-spheres and four crossed, equal, branched spines.

{162}The genus _Staurancistra_ differs from its ancestral form, _Staurolonche_, in the ramification of the four crossed spines.

1. _Staurancistra quadricuspis_, n. sp.

Cortical shell thin walled, with rough, thorny surface, and irregular, roundish pores, twice to four times as broad as the bars; six to eight on the quadrant. Medullary shell one-third as large, with regular, circular pores; connected with the cortical shell by four crossed radial beams. These are prolonged outside into four strong three-sided prismatic spines, nearly as long as the shell diameter, each having three curved branches below the distal end. (Similar to _Hexancistra quadricuspis_, Pl. 22, fig. 11, but with only four spines.)

_Dimensions._--Diameter of the cortical shell 0.16, of the medullary shell 0.05; pores of the former 0.06 to 0.012, bars 0.003; length of the spines 0.14, breadth 0.012.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

Genus 65. _Staurolonchidium_,[89] n. gen.

_Definition._--#Staurosphærida# with two concentric lattice-spheres and four crossed simple spines which are disposed in two different pairs, two opposite being larger than the other two.

The genus _Staurolonchidium_ has arisen from _Staurolonche_ by the stronger growth of the two opposite spines, the other two remaining stationary; both spines of each pair equal.

1. _Staurolonchidium artioscelides_, n. sp.

Cortical shell thin walled, with smooth surface, three times as broad as the medullary shell. Pores regular, circular, hexagonally framed, twice as broad as the bars; eight to ten on the quadrant. Four radial spines three-sided pyramidal, as broad as one mesh; two opposite larger spines three times as long as the two smaller, which are about equal to the radius.

_Dimensions._--Diameter of the cortical shell 0.16, medullary shell 0.05; pores of the former 0.012, bars 0.006; length of the major spines 0.24, minor 0.08.

_Habitat._--Central Pacific, Station 265, surface.

2. _Staurolonchidium perspicuum_, Haeckel.

_Haliomma perspicuum_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxix. fig. 1.

Cortical shell thin walled, covered with small conical by-spines, five times as broad as the medullary shell. Pores regular, circular, eight times as broad as the bars; three to four on the quadrant. Four radial spines three-sided pyramidal, scarcely one-third as broad as one mesh; two opposite larger spines four times as long as the two smaller, which are about equal to half the radius.

{163}_Dimensions._--Diameter of the cortical shell 0.12, medullary shell 0.025; pores of the former 0.03, bars 0.004; length of the major spines 0.12, minor 0.03.

_Habitat._--Fossil in Barbados.

Genus 66. _Stauroxiphos_,[90] n. gen.

_Definition._--#Staurosphærida# with two concentric lattice-spheres and four crossed simple spines, one of which is much larger than the other three.

The genus _Stauroxiphos_ differs from its ancestral form, _Staurolonche_, in the greater development of one single spine, and exhibits therefore the same relation to it that _Stylostaurus_ bears to _Staurosphæra_.

1. _Stauroxiphos gladius_, n. sp. (Pl. 15, fig. 7).

Cortical shell thick walled, smooth, three times as broad as the medullary shell. Pores of the outer shell regular, circular, regularly six-lobed on the outer opening, four times as broad as the bars; about six on the quadrant. Pores of the inner shell only one-third as large, simple, circular. Three of the four radial spines of nearly equal size, pommel-shaped, with three prominent, dentated wings, somewhat shorter than the shell radius and about half as broad as long; the fourth spine much larger, sword-like, about three times as long as the shell radius.

_Dimensions._--Diameter of the outer shell 0.12, of the inner 0.04; pores of the former 0.01, bars 0.0025; pores of the latter 0.003, bars 0.001; length of the major spine 0.18, of the three minor 0.04.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

Subfamily STAURACONTIDA,[91] Haeckel, 1881, Prodromus, p. 52.

_Definition._--#Staurosphærida# with three concentric spherical lattice-shells.

Genus 67. _Stauracontium_,[92] Haeckel, 1881, Prodromus, p. 452.

_Definition._--#Staurosphærida# with three concentric lattice-spheres and four crossed, equal, simple spines.

The genus _Stauracontium_ differs from its probable ancestral form, _Staurolonche_, in the duplication of the cortical shell.

Subgenus 1. _Stauracontarium_, Haeckel.

_Definition._--Pores of the cortical shell regular, all of nearly equal size and similar form; surface smooth.

{164}1. _Stauracontium cruciferum_, n. sp.

Cortical shell thin walled, smooth, with regular, hexagonal pores, four times as broad as the bars; eight to ten on the quadrant. Radial proportion of the three spheres = 1 : 3 : 9. Connecting radial beams between them six (opposite in pairs in the three dimensive axes), but only four of them are prolonged outside into four stout three-sided prismatic spines, lying in one equatorial plane, as long as the shell diameter.

_Dimensions._--Diameter of the outer shell 0.22, middle 0.07, inner 0.025; cortical pores 0.012, bars 0.003; length of the spines 0.2.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

2. _Stauracontium tetracanthum_, Haeckel.

_Haliomma tetracanthum_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 295, Taf. x. figs. 7, 8.

Cortical shell thin walled, smooth, with regular, circular pores, three times as broad as the bars; five to six on the quadrant. Radial proportion of the three spheres = 1 : 3 : 12. Radial spines three-sided pyramidal, about as long as the shell diameter.

_Dimensions._--Diameter of the outer shell 0.12, middle 0.03, inner 0.01; cortical pores 0.01, bars 0.003; length of the spines 0.1.

_Habitat._--Indian Ocean, Zanzibar, depth 2200 fathoms, Pullen.

3. _Stauracontium tetracontium_, Haeckel.

_Actinomma tetracanthum_, Stöhr, 1880, Palæontogr. 26, p. 91, Taf. ii. fig. 6.

Cortical shell thin walled, rough, with regular, circular pores, of the same breadth as the bars; six to seven on the quadrant. Radial proportion of the three spheres = 1 : 2.5 : 8. Radial spines three-sided pyramidal, nearly as long as the shell diameter.

_Dimensions._--Diameter of the outer shell 0.1, middle 0.03, inner 0.013; cortical pores and bars 0.006; length of the spines 0.08.

_Habitat._--Fossil in Tertiary rocks of Sicily; Grotte, Caltanisetta.

Subgenus 2. _Stauracontellium_, Haeckel.

_Definition._--Pores of the cortical shell regular, and of nearly equal size and similar form; surface covered with numerous small thorns or by-spines.

4. _Stauracontium daturæforme_, Haeckel.

_Actinomma daturæforme_, Stöhr, 1880, Palæontogr. 26, p. 93, Taf. ii. fig. 13.

Cortical shell thick walled, covered with short thorns, and with regular, hexagonal pores, five times as broad as the bars; six to seven on the quadrant. Radial proportion of the three spheres = 1 : 3 : 3.5. Radial spines six-sided pyramidal, about half as long as the radius and one-fourth as broad.

{165}_Dimensions._--Diameter of the outer shell 0.15, middle 0.13, inner 0.04; cortical pores 0.017, bars 0.003; length of the spines 0.03.

_Habitat._--Fossil in Tertiary rocks of Sicily; Grotte, Stöhr.

5. _Stauracontium sparganium_, n. sp.

Cortical shell thick walled, covered with very numerous, short, conical spines, and with regular, circular pores, five times as broad as the bars; sixteen to eighteen on the quadrant. Radial proportion of the three spheres = 2 : 3 : 9. Radial main spines three-sided prismatic, as long as the radius or longer.

_Dimensions._--Diameter of the outer shell 0.275, middle 0.09, inner 0.06; cortical pores 0.01, bars 0.002; length of the spines 0.15.

_Habitat._--Fossil in Barbados.

Subgenus 3. _Stauracontidium_, Haeckel.

_Definition._--Pores irregular, of different size or form; surface smooth.

6. _Stauracontium antarcticum_, n. sp.

Cortical shell thin walled, smooth. Pores irregular, roundish, two to four times as broad as the bars. Radial proportion of the three spheres = 1 : 2 : 8. Radial spines conical, as long as the radius.

_Dimensions._--Diameter of the outer shell 0.2, middle 0.05, inner 0.025; cortical pores 0.006 to 0.012, bars 0.003; length of the spines 0.1.

_Habitat._--Antarctic Ocean, Station 157, depth 1950 fathoms.

Subgenus 4. _Stauracontonium_, Haeckel.

_Definition._--Pores irregular, of different size or form; surface covered with thorns or by-spines.

7. _Stauracontium setosum_, n. sp.

Cortical shell thin walled, covered with thin bristle-shaped by-spines, half as long as the radius. Pores irregular, polygonal, three to five times as broad as the bars. Proportion of the three spheres = 1 : 2 : 6. Radial main spines pyramidal, nearly as long as the shell diameter.

_Dimensions._--Diameter of the outer shell 0.15, middle 0.05, inner 0.025; cortical pores 0.01 to 0.015, bars 0.003; length of the spines 0.12.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

8. _Stauracontium papillosum_, n. sp.

Cortical shell thick walled, covered with short conical papillæ or by-spines. Pores irregular, roundish, two to four times as broad as the bars. Proportion of the three spheres = 1 : 3 : 12. Radial main spines conical, as long as the radius.

{166}_Dimensions._--Diameter of the outer shell 0.24, middle 0.06, inner 0.02; cortical pores 0.007 to 0.015, bars 0.004; length of the spines 0.12.

_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.

Subfamily STAUROCROMYIDA,[93] Haeckel, 1881, Prodromus, pp. 449, 453.

_Definition._--#Staurosphærida# with four concentric spherical lattice-shells.

Genus 68. _Staurocromyum_,[94] Haeckel, 1881, Prodromus, p. 453.

_Definition._--#Staurosphærida# with four concentric lattice-spheres and four crossed, equal, simple spines.

The genus _Staurocromyum_ has arisen probably from _Stauracontium_ by duplication of the cortical shell, two concentric shells lying within, two others outside the central capsule.

1. _Staurocromyum quadruplex_, n. sp.

Radial proportion of the four spheres = 1 : 2 : 8 : 10. Both medullary shells with very small, regular, circular pores. Inner cortical shell with regular, circular, hexagonally-framed pores, twice as broad as the bars; from each hexagon-corner arises a small by-spine, and these, connected by tangential branches at equal distances from the centre, form the delicate outer cortical shell, with spiny surface. Four main spines three-sided pyramidal, as long as the shell radius.

_Dimensions._--Diameter of the four shells--(A) 0.25, (B) 0.2, (C) 0.05, (D) 0.025; length of the spines 0.12.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

2. _Staurocromyum quadrispinum_, n. sp.

Radial proportion of the four spheres = 1 : 3 : 9 : 12. Both medullary shells with small, regular, circular pores. Both cortical shells with irregular, roundish pores. Surface covered with short, conical by-spines. Four main spines cylindro-conical, somewhat longer than the shell diameter.

_Dimensions._--Diameter of the four shells--(A) 0.24, (B) 0.18, (C) 0.06, (D) 0.02.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

Genus 69. _Cromyostaurus_,[95] Haeckel, 1881, Prodromus, p. 453.

_Definition._--#Staurosphærida# with four concentric lattice-spheres and four crossed, equal, branched spines.

{167}The genus _Cromyostaurus_ differs from the preceding _Staurocromyum_, its ancestral form, in the ramification of the four crossed spines.

1. _Cromyostaurus verticillatus_, n. sp.

Radial proportion of the four spheres = 1 : 3 : 11 : 13. Both medullary shells with small, regular, circular pores; inner cortical shell with regular, hexagonal pores; from the hexagon-corners arise small, radial by-spines, which at equal distances from the centre send out forked tangential branches, three from each spine, and by communication of these form the outer, delicate, cortical shell. Four main spines nearly as long as the shell diameter, three-sided prismatic, with four to six verticils of ramified lateral branches, each verticil composed of three forked branches, which ramify again.

_Dimensions._--Diameter of the four shells--(A) 0.26, (B) 0.22, (C) 0.06, (D) 0.02; length of the spines 0.24.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

Subfamily STAUROCARYIDA,[96] Haeckel, 1881, Prodromus, pp. 449, 454.

_Definition._--#Staurosphærida# with five or more concentric spherical lattice-shells.

Genus 70. _Staurocaryum_,[97] Haeckel, 1881, Prodromus, p. 454.

_Definition._--#Staurosphærida# with five or more concentric lattice-spheres and four crossed, equal spines.

The genus _Staurocaryum_ has arisen from the preceding _Staurocromyum_ by the further multiplication of the concentric spheres; in the only observed form there are six, at nearly equal distances apart.

1. _Staurocaryum arborescens_, n. sp. (Pl. 15, fig. 8).

Shell composed of six concentric latticed spheres, at nearly equal distances apart, and with somewhat regular, circular pores, the size of which gradually increases from the first to the sixth shell. The surface of the outermost shell is densely covered with numerous arborescent by-spines, which bifurcate from three to four times, and are three-sided pyramidal at the base, and twice as long as the distance between each two shells. The six shells are connected only by four crossed, conical, radial beams, which increase in diameter from the centre, and are prolonged outside into very stout cylindrical, radial spines, irregularly covered with small thorns and forked ramules, and nearly as long as the shell diameter. Only a single specimen was observed.

{168}_Dimensions._--Diameter of the whole shell 0.22; distance between each two shells 0.02; length of the by-spines 0.05, of the main spines 0.2.

_Habitat._--Indian Ocean, Cocos Islands, surface, Rabbe.

Subfamily STAURODORIDA,[98] Haeckel, 1881, Prodromus, pp. 449, 455.

_Definition._--#Staurosphærida# with spongy, spherical shell (with or without enclosed concentric lattice-shells).

Genus 71. _Staurodoras_,[99] Haeckel, 1881, Prodromus, p. 455.

_Definition._--#Staurosphærida# with solid, spongy, spherical shell and four crossed simple spines.

The genus _Staurodoras_ may be developed from _Styptosphæra_ by the production of four crossed spines on the simple, spongy, spherical shell, which is composed of looser or denser irregular wicker-work, without enclosed medullary shell.

1. _Staurodoras spongosphæra_, n. sp.

Four crossed spines, two to three times as long as the diameter of the spongy sphere, three-sided prismatic, with three dentated and spirally contorted edges. (Form of _Spongosphæra streptacantha_, but without medullary shell and with four equal spines, crossed regularly at right angles.)

_Dimensions._--Diameter of the sphere 0.25; length of the spines 0.4 to 0.7.

_Habitat._--Central Pacific, Station 271, surface.

2. _Staurodoras mojsisovicsi_, Dunikowski.

_Staurodoras mojsisovicsi_, Dunikowski, 1882, Denkschr. d. k. Akad. d. Wiss. Wien, Bd. xlv. p. 28, Taf. v. fig. 56.

Four crossed spines, one and a half times as long as the diameter of the spongy sphere, three-sided pyramidal, with three smooth edges. (What Dunikowski describes as "inner canals" of the spines are their edges.)

_Dimensions._--Diameter of the sphere 0.14; length of the spines 0.18 to 0.2. basal breadth 0.04.

_Habitat._--Fossil in the Alpine Lias (Schafberg near Salzburg).

3. _Staurodoras liassica_, Dunikowski.

_Staurodoras liassica_, Dunikowski, 1882, Denkschr. d. k. Akad. d. Wiss. Wien, Bd. xlv. p. 28, Taf. v. fig. 57.

Four crossed spines, shorter than the diameter of the spongy sphere, conical or pyramidal (?).

_Dimensions._--Diameter of the sphere 0.19; length of the spine 0.13, basal breadth 0.045.

_Habitat._--Fossil in the Alpine Lias (Schafberg near Salzburg).

{169}4. _Staurodoras wandae_, Dunikowski.

_Staurodoras wandae_, Dunikowski, 1882, Denkschr. d. k. Akad. d. Wiss. Wien, Bd. xlv. p. 28, Taf. v. fig. 58.

Four crossed spines shorter than the radius of the spongy sphere, conical. (May be the young form of the preceding species.)

_Dimensions._--Diameter of the sphere 0.14; length of the spines 0.06, basal breadth 0.05.

_Habitat._--Fossil in the Alpine Lias (Schafberg near Salzburg).

Family IX. #CUBOSPHÆRIDA#, Haeckel (Pls. 21-25).

_Cubosphærida_, Haeckel, 1881, Prodromus, p. 449.

_Definition._--#Sphæroidea# with six radial spines on the surface of the spherical shell, opposite in pairs in the three dimensive axes, perpendicular one to another; living solitary (not associated in colonies).

The family #Cubosphærida# is distinguished from the other #Sphæroidea# by the possession of six radial spines, which are opposite in pairs in three different axes, one perpendicular to the other two. These three axes are the typical "dimensive axes," which are more or less differentiated in the #Larcoidea#. But in these latter the shell itself and the enclosed central capsule become affected by the unequal growth in the three axes, whilst in the former the capsule constantly, and commonly also the shell, remains spherical. Sometimes the shell assumes the form of a regular octahedron, from the six corners of which arise the six radial spines, indicating its three axes.

The most simple Cubosphærida are the Hexastylida, with one single, spherical lattice-shell. To this ancestral group all other subfamilies can be opposed as "Cubosphærida concentrica," as their carapace is composed of two or more concentric lattice-shells--two in the Hexalonchida, three in the Hexacontida, four in the Hexacromyida, five or more in the Hexacaryida. In all these four subfamilies the concentric shells are simple (not spongy), fenestrated spheres. In a sixth subfamily, in the Hexadorida, the shell is wholly or partially composed of irregular, spongy wicker-work or loose reticulations, with or without a medullary shell in the centre.

The _Six Radial Spines_ of the Cubosphærida are normally opposite in pairs in the three dimensive axes, each of which is perpendicular to the other two. But in many species besides this normal form occur individual abnormalities, in which the six spines are not quite accurately opposed, but more or less divergent; and often also the three dimensive planes (determined each by two axes) are not quite regular, but more or less uneven. More rarely the six spines appear disposed in quite an irregular manner.

In the greater part of the Cubosphærida all six spines are quite equal, of the same size and form. But in some genera a more or less considerable differentiation takes place, so {170}that two pairs or all three pairs of spines become different; very rarely, also both spines of one pair become unequal (probably only an individual abnormality). Those variations correspond to the differences between the crystalline systems. The common Cubosphærida, with three equal spine-pairs, correspond to the regular or cubic system, with three equal axes. The rarer forms (_Hexastylarium_, _Hexaloncharium_, _Hexacontarium_) exhibit two equal pairs and one different pair; they correspond to the quadratic system, with three perpendicular axes, two of which are equal, the third unequal. Still more rare are those forms (_Hexastylidium_, _Hexalonchidium_), in which all three pairs of spines are different, corresponding to the three unequal axes of the rhombic crystalline system.

_Synopsis of the Genera of Cubosphærida._

{All six radial spines simple, I. Subfamily { of equal size, 72. _Hexastylus_. Hexastylida. { (Shell one {Six spines of {Two pairs equal, simple { different sizes,{ one pair latticed { all six simple. { different, 73. _Hexastylarium_. sphere.) { { { {All three pairs { { different, 74. _Hexastylidium_.

{All six radial {Spines simple, 75. _Hexalonche_. { spines of { II. Subfamily { equal size. {Spines branched, 76. _Hexancistra_. Hexalonchida. { (Shell composed {Six spines {Two pairs equal, of two { simple, in { one pair concentric { pairs of { different, 77. _Hexaloncharium_. latticed { different sizes. spheres.) { {All three pairs { { different, 78. _Hexalonchidium_.

{All six radial {Spines simple, 79. _Hexacontium_. III. Subfamily { spines of { Hexacontida. { equal size. {Spines branched, 80. _Hexadendron_. (Shell composed { of three {Six spines Two pairs equal, spheres.) { simple, of one pair { different sizes. different, 81. _Hexacontarium_.

IV. Subfamily }All six radial Spines simple, Hexacromyida. } spines of not branched, 82. _Hexacromyum_. (Four concentric} equal size. spheres.) }

V. Subfamily }All six radial {Spines simple, 83. _Cubosphæra_. Hexacaryida. } spines of { (Five or more } equal size. {Spines branched, 84. _Hexacaryum_. spheres.) }

{Without latticed { medullary VI. Subfamily }All six radial { shell, 85. _Cubaxonium_. Hexadorida. } spines of { (Shell a spongy } equal size, {With one single sphere, with } simple (not { medullary or without an } branched). { shell, 86. _Hexadoras_. enclosed } { central } {With two medullary } { medullary shell.) } { shells, 87. _Hexadoridium_.

{171}Subfamily HEXASTYLIDA,[100] Haeckel, 1881, Prodromus, pp. 449, 450.

_Definition._--#Cubosphærida# with one single spherical lattice-shell.

Genus 72. _Hexastylus_,[101] Haeckel, 1881, Prodromus, p. 450.

_Definition._--#Cubosphærida# with one simple lattice-sphere and six simple spines of equal size.

The genus _Hexalonche_ is the most simple form of all Cubosphærida, and may be regarded as the common ancestral form of this family. It can be derived phylogenetically from _Cenosphæra_, by development of six radial spines on the surface of the simple spherical lattice-shell. These six simple spines are of equal size and opposite in pairs in the three dimensive axes, corresponding to the three equal axes of a cubic crystal.

Subgenus 1. _Hexastylanthus_, Haeckel.

_Definition._--Pores regular or subregular, of nearly equal size and form; surface of the cortical shell smooth, without radial by-spines (other than the six main spines).

1. _Hexastylus phænaxonius_, n. sp. (Pl. 21, fig. 3).

Shell thin walled, with smooth surface. Pores subregular, hexagonal, five to six times as broad as the bars; nine to ten on the radius. Six spines triangular pyramidal, as long as the radius of the shell, as broad at the base as one pore.

_Dimensions._--Diameter of the shell 0.13, pores 0.008 to 0.01, bars 0.0015; length of the spines 0.07, basal breadth 0.008 to 0.012.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

2. _Hexastylus sapientum_, n. sp.

Shell thin walled, with smooth surface. Pores regular, hexagonal, eight to ten times as broad as the bars; six to seven on the radius. Six spines bristle-shaped, longer than the diameter of the shell. (Lattice-work and spines similar to those of _Heliosphæra actinota_, Monogr. d. Radiol., Taf. ix. fig. 3.)

_Dimensions._--Diameter of the shell 0.15, pores 0.016, bars 0.002; length of the spines 0.2, breadth 0.002.

_Habitat._--North Atlantic, Station 354, surface.

{172}3. _Hexastylus thaletis_, n. sp. (Pl. 21, fig. 4).

Shell thin walled, with smooth surface. Pores subregular, circular, hexagonally framed, somewhat funnel-shaped, of the same breadth as the bars; eight to nine on the radius. Six spines triangular pyramidal, with prominent edges, as long as the radius, three to four times as broad at the base as one pore.

_Dimensions._--Diameter of the shell 0.1, pores and bars 0.005; length of the spines 0.05, basal breadth 0.02.

_Habitat._--Tropical Pacific, Station 225, depth 4575 fathoms.

4. _Hexastylus favosus_, n. sp.

Shell thick walled, with smooth surface. Pores regular, circular, hexagonally framed, deep funnel-shaped, of the same breadth as the bars; six to seven on the radius. Six spines triangular pyramidal, as long as the diameter, twice as broad at the base as one pore.

_Dimensions._--Diameter of the shell 0.12, pores and bars 0.01; length of the spines 0.12, basal breadth 0.02.

_Habitat._--South Atlantic, Station 320, surface.

5. _Hexastylus longissimus_, n. sp.

Shell thick walled, with smooth surface. Pores regular, circular, hexagonally framed, of the same breadth as the bars; five to six on the radius. Six spines triangular prismatic, extremely elongated, ten to twenty times as long as the diameter of the shell, twice as broad as one pore.

_Dimensions._--Diameter of the shell 0.08, pores and bars 0.008; length of the spines 1.0 to 1.5, breadth 0.015.

_Habitat._--Tropical Atlantic, Station 347, surface.

6. _Hexastylus minimus_, n. sp. (Pl. 21, fig. 5).

Shell thin walled, with smooth surface. Pores subregular, circular, twice as broad as the bars; five to six on the radius. Six spines triangular pyramidal, scarcely as long as the radius, at the base half as broad as long.

_Dimensions._--Diameter of the shell 0.05, pores 0.004, bars 0.002; length of the spines 0.02, basal breadth 0.01.

_Habitat._--Tropical Pacific, Station 225, depth 4575 fathoms.

7. _Hexastylus biantis_, n. sp.

? _Haliphormis hexacantha_, Ehrenberg, 1872, L. N. 24, Taf. x. fig. 6.

Shell thin walled, smooth. Pores regular, circular, four times as broad as the bars; eight to nine on the radius. Six spines conical, as long as the radius, at the base as broad as one pore.

{173}_Dimensions._--Diameter of the shell 0.12, pores 0.012, bars 0.003; length of the spines 0.06, basal breadth 0.012.

_Habitat._--Indian Ocean, Madagascar, surface, Rabbe.

8. _Hexastylus pittaci_, n. sp.

Shell thin walled, smooth. Pores regular, circular, ten to twelve times as broad as the bars; six to seven on the radius. Six spines triangular pyramidal, as long as the radius, as broad as one pore.

_Dimensions._--Diameter of the shell 0.12, pores 0.02, bars 0.002; length of the spines 0.06, basal breadth 0.02.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

9. _Hexastylus maximus_, n. sp.

Shell thick walled, smooth. Pores regular, circular, twice as broad as the bars; twelve to sixteen on the radius. Six spines six-sided pyramidal, half as long as the radius, three times as broad as one pore.

_Dimensions._--Diameter of the shell 0.3, pores 0.01, bars 0.005; length of the spines 0.08, basal breadth 0.03.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

10. _Hexastylus periandri_, n. sp.

Shell thick walled, smooth. Pores regular, circular, double-edged, four times as broad as the bars; six to seven on the radius. Six spines conical, as long as the radius, twice as broad as one pore.

_Dimensions._--Diameter of the shell 0.2, pores 0.012, bars 0.003; length of the spines 0.1, basal breadth 0.025.

_Habitat._--Tropical Atlantic, Station 335, depth 1425 fathoms.

Subgenus 2. _Hexastylettus_, Haeckel.

_Definition._--Pores regular or subregular, of nearly equal size and form; surface of the spherical shell spiny, covered with numerous conical or bristle-shaped radial by-spines.

11. _Hexastylus solonis_, n. sp. (Pl. 21, fig. 11).

Shell thick walled, covered with numerous bristle-shaped radial spines (one-third to one-half as long as the six main spines, arising from the lattice-knots). Pores regular, circular, enclosed by prominent, hexagonal frames, four to six times as broad as the bars; seven to eight on the radius. {174}Six main spines triangular pyramidal, with spirally contorted prominent edges, as long as the radius, as broad at the base as one pore.

_Dimensions._--Diameter of the shell 0.13, pores 0.01, bars 0.002; length of the spines 0.06 to 0.8, basal breadth 0.01.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

12. _Hexastylus cochleatus_, n. sp. (Pl. 21, fig. 1).

Shell thick walled, covered with numerous short, conical spines (about as large as one pore). Pores regular, circular, three times as broad as the bars; eight to nine on the radius. Six main spines triangular pyramidal, with prominent, spirally-twisted edges, as long as the diameter of the shell, and twice as broad at the base as one pore.

_Dimensions._--Diameter of the shell 0.17, pores 0.015, bars 0.005; length of the spines 0.16, breadth 0.03.

_Habitat._--Mediterranean, Corfu, Haeckel, surface.

13. _Hexastylus setosus_, Haeckel.

_Acanthosphæra setosa_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 285, Taf. ix. fig. 11.

Shell thin walled, covered with numerous short, bristle-shaped spines (not larger than one pore). Pores regular, circular, four times as broad as the bars; thirteen to sixteen on the radius. Six main spines three-sided pyramidal, scarcely one-third as long as the radius. (In the figure of Ehrenberg, _loc. cit._, only four spines are in regular, crossed disposition, two others opposite in oblique direction; this is either an individual abnormality, or an error of drawing; the same species occurs with six spines exactly regularly disposed in the three dimensive axes.)

_Dimensions._--Diameter of the shell 0.15; pores 0.008, bars 0.002; length of the spines 0.02 to 0.03, basal breadth 0.005.

_Habitat._--Indian Ocean, Zanzibar, Pullen; Madagascar, Rabbe.

14. _Hexastylus chilonis_, n. sp.

Shell thin walled, covered with numerous bristle-shaped spines (as long as the radius). Pores regular, circular, twice as broad as the bars; eight to nine on the radius. Six main spines triangular pyramidal, with straight edges, as long as the diameter of the shell, as broad as two pores.

_Dimensions._--Diameter of the shell 0.2, pores 0.02, bars 0.01; length of the spines 0.2, basal breadth 0.05.

_Habitat._--South Atlantic, Station 325, surface.

15. _Hexastylus cleobuli_, n. sp.

Shell thick walled, covered with numerous short, conical spines (twice as large as one pore). Pores regular, circular, of the same breadth as the bars; twelve to thirteen on the radius. Six main spines conical, as long as the radius, three times as broad as one pore.

{175}_Dimensions._--Diameter of the shell 0.24, pores and bars 0.005; length of the spines 0.12, basal breadth 0.016.

_Habitat._--South Pacific, Station 300, depth 1375 fathoms.

Subgenus 3. _Hexastylissus_, Haeckel.

_Definition._--Pores irregular, of unequal size or form; surface of the spherical shell smooth, without radial by-spines (other than the six main spines).

16. _Hexastylus triaxonius_, n. sp. (Pl. 21, fig. 2).

Shell thin walled, with smooth surface. Pores irregular, polygonal, three to six times as broad as the bars; four to six on the radius. Six spines triangular pyramidal, as long as the diameter of the shell, as broad at the base as one pore.

_Dimensions._--Diameter of the shell 0.05, pores 0.004 to 0.008, bars 0.0015; length of the spines 0.04, basal breadth 0.006.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

17. _Hexastylus dimensivus_, n. sp. (Pl. 21, fig. 6).

Shell thin walled, with smooth surface. Pores irregular, polygonal, four to eight times as broad as the bars; eleven to thirteen on the radius. Six spines hexagonal pyramidal, as long as the radius, about three times as broad at the base as one pore.

_Dimensions._--Diameter of the shell 0.13, pores 0.006 to 0.009, bars 0.0012; length of the spines 0.06, basal breadth 0.025.

_Habitat._--North Pacific, Station 256, depth 2950 fathoms.

18. _Hexastylus brevispinus_, n. sp.

Shell thin walled, with smooth surface. Pores irregular, roundish, two to four times as broad as the bars; six to eight on the radius. Six spines triangular pyramidal, half as long as the radius, twice as broad as one pore.

_Dimensions._--Diameter of the shell 0.2, pores 0.008 to 0.016, bars 0.004; length of the spines 0.05, basal breadth 0.025.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

19. _Hexastylus longispinus_, n. sp.

Shell thick walled, smooth. Pores irregular, roundish, two to three times as broad as the bars; three to four on the radius. Six spines triangular prismatical, two to three times as long as the diameter of the shell.

{176}_Dimensions._--Diameter of the shell 0.08, pores 0.008 to 0.012, bars 0.004; length of the spines 0.2, breadth 0.01.

_Habitat._--North Atlantic, Station 353, surface.

20. _Hexastylus marginatus_, n. sp. (Pl. 21, fig. 10).

Shell thick walled, rough. Pores irregular, roundish, somewhat funnel-shaped double-edged, two to three times as broad as the bars; twelve to fourteen on the radius. Six spines three-sided pyramidal, somewhat longer than the radius, three times as broad as one pore.

_Dimensions._--Diameter of the shell 0.15, pores 0.007 to 0.01, bars 0.004; length of the spines 0.1, basal breadth 0.025.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

21. _Hexastylus conifer_, n. sp.

Shell thick walled, rough. Pores irregular, roundish, scarcely broader than the bars; fifteen to sixteen on the radius. Six spines conical, as long as the radius, five to seven times as broad as one pore.

_Dimensions._--Diameter of the shell 0.18, pores and bars 0.004 to 0.006; length of the spines 0.1, basal breadth 0.03.

_Habitat._--Indian Ocean, Sunda Strait, Rabbe, surface.

Subgenus 4. _Hexastylurus_, Haeckel.

_Definition._--Pores irregular, of unequal size or form; surface of the spherical shell spiny, covered with numerous conical or bristle-shaped by-spines.

22. _Hexastylus dictyotus_, n. sp. (Pl. 21, figs. 8, 9).

Shell thin walled, spiny; short spines conical, smaller than the pore-breadth. Pores irregular, polygonal, five to seven times as broad as the bars; four to six on the radius. Six spines triangular pyramidal, longer than the radius, about as broad as one smaller pore.

_Dimensions._--Diameter of the shell 0.09, pores 0.01 to 0.015, bars 0.002; length of the spines 0.06, basal breadth 0.01.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

23. _Hexastylus hirsutus_, n. sp.

Shell thin walled, densely covered with bristle-shaped, radial spines, half as long as the six main spines. Pores irregular, polygonal, three to four times as broad as the bars; eight to ten on the radius. Six spines triangular pyramidal, as long as the radius, twice as broad as one pore.

{177}_Dimensions._--Diameter of the shell 0.14, pores 0.005 to 0.008, bars 0.002; length of the spines 0.06, basal breadth 0.01.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

24. _Hexastylus contortus_, n. sp. (Pl. 21, fig. 12).

Shell thick walled, covered with bristle-shaped, radial spines, half as long as the radius. Pores irregular, roundish, two to three times as broad as the bars; seven to eight on the radius. Six spines triangular prismatic, in the distal half spirally twisted like a cork-screw (fig. 12); longer than the diameter of the shell, about as broad as one pore.

_Dimensions._--Diameter of the shell 0.12, pores 0.006 to 0.008, bars 0.003; length of the spines 0.15, breadth 0.015.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

25. _Hexastylus spiralis_, n. sp. (Pl. 21, fig. 7).

Shell thick walled, covered with short conical spines. Pores irregular, roundish, two to three times as broad as the bars; five to six on the radius. Six spines triangular prismatic, with three thin, spirally contorted edges, two to three times as long as the diameter of the shell, about as broad as one large pore.

_Dimensions._--Diameter of the shell 0.16, pores 0.01 to 0.02, bars 0.006; length of the spines 0.3 to 0.5, basal breadth 0.02.

_Habitat._--Tropical Western Pacific, Station 225, depth 4475 fathoms.

Genus 73. _Hexastylarium_,[102] n. gen.

_Definition._--#Cubosphærida# with one simple lattice-sphere and six simple spines of different sizes; one opposite pair larger than the other two.

The genus _Hexastylarium_ differs from its probable ancestral form, _Hexastylus_, by the unequal growth of the six simple spines; two opposite spines of one pair being more strongly developed than the four others, which are equal. They correspond therefore to the three axes of a quadratic crystal.

1. _Hexastylarium heteraxonium_, n. sp.

Cortical shell thin walled, smooth, with regular, hexagonal pores, three times as broad as the bars; eight to ten on the radius. Six spines three-sided pyramidal, at the base as broad as one pore. Two opposite major spines longer than the shell diameter; four others scarcely as long as {178}the radius. (Similar to _Hexastylus phænaxonius_, Pl. 21, fig. 3, but differing in the unequal length of the spines.)

_Dimensions._--Diameter of the shell 0.15, pores 0.12, bars 0.004; length of the two major spines 0.2, of the four minor 0.07.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

2. _Hexastylarium quadratum_, n. sp.

Shell very delicate, with smooth surface, and irregular, polygonal pores, separated by very thin bars. The form of the shell is not, as commonly, a sphere, but a geometrical square octahedron, one axis (with two opposite major spines) being nearly twice as long as the other two dimensive axes; four spines, opposite by pairs in the latter, are only half as long. The eight sides of the octahedral shell are even, equilateral-triangular. Spines angular, thin.

_Dimensions._--Diameter of the shell in the major axis 0.18, in the minor 0.1; length of the major spines 0.24, minor 0.12.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

3. _Hexastylarium elongatum_, n. sp.

Shell thick walled, with spiny surface, and with irregular, roundish pores, two to four times as broad as the bars; eight to ten on the radius. Two opposite major spines, three to four times as long as the shell diameter, whilst the four other spines are very short, scarcely as long as the radius. All six spines at the base three-sided pyramidal, the two longer being cylindrical.

_Dimensions._--Diameter of the shell 0.1; length of the major spines 0.3 to 0.4, of the minor 0.04, basal breadth 0.02.

_Habitat._--North Pacific, Station 244, surface.

Genus 74. _Hexastylidium_,[103] Haeckel, 1881, Prodromus, p. 450.

_Definition._--#Cubosphærida# with one simple lattice-sphere and six simple spines in pairs different; the two opposite spines of each pair equal, the three pairs unequal.

The genus _Hexastylidium_ differs from its probable ancestral form, _Hexastylus_, by the unequal growth of the six simple spines; the two spines of each pair reaching the same dimensions, whilst the three pairs are different. They correspond therefore to the three axes of a rhombic crystal.

1. _Hexastylidium rhomboides_, n. sp.

Shell thin walled, smooth, with irregular, polygonal pores and very thin bars. Its form is not, as commonly, a sphere, but a rhombic octahedron. The radial proportion of the three unequal {179}dimensive axes = 1 : 2 : 4. The radial proportion of the three pairs of spines = 1 : 3 : 8. Spines thin cylindrical, at the base angular.

_Dimensions._--Diameter of the major shell axis 0.2, middle 0.1, minor 0.05; length of the major spines 0.3, middle 0.12, minor 0.04.

_Habitat._--Indian Ocean, Madagascar, Rabbe, surface.

2. _Hexastylidium spirale_, n. sp.

Shell thick walled, spherical, thorny, with irregular, roundish pores, three to five times as broad as the bars; six spines very stout, prismatic (as broad as one large pore), with three ring-like, spirally convoluted edges. Two opposite major spines of extraordinary length, ten to twelve times as long as the shell diameter, the two middle opposite spines being about as long as the latter, the two minor scarcely one-third as long. (Similar to _Hexastylus spiralis_, Pl. 21, fig. 7, but distinguished by the very unequal length of the spines.)

_Dimensions._--Diameter of the shell 0.12; length of the major spines 1 to 1.5 mm., middle 0.15, minor 0.04.

_Habitat._--Central Pacific, Station 266, surface.

Subfamily HEXALONCHIDA,[104] Haeckel, 1881, Prodromus, pp. 449, 451.

_Definition._--#Cubosphærida# with two concentric spherical lattice-shells.

Genus 75. _Hexalonche_,[105] Haeckel, 1881, Prodromus, p. 451.

_Definition._--#Cubosphærida# with two concentric lattice-spheres and six simple spines of equal size.

The genus _Hexalonche_ is the most simple form, and probably the common ancestral form, of all Hexalonchida, or those Cubosphærida which possess two concentric latticed spheres, connected by six radial beams. Commonly one shell is intracapsular (medullary shell) and the other extracapsular (cortical shell); but sometimes also both shells are extracapsular, and these forms may perhaps be better separated as a peculiar genus _Hexadilemma_. In _Hexalonche_ all six simple spines are of equal size, and opposite by pairs in three equal dimensive axes, corresponding to the three equal axes of a tesseral crystal. It can be derived from _Hexastylus_ by duplication of the lattice-shell.

Subgenus 1. _Hexalonchara_, Haeckel.

_Definition._--Pores of the cortical shell regular or subregular, of nearly equal size and similar form; surface smooth, without radial by-spines (other than the six main spines).

{180}1. _Hexalonche phænaxonia_, n. sp.

Cortical shell thin walled, smooth; its pores regular, hexagonal, six to eight times as broad as the bars; eight to ten to twelve on the radius. Medullary shell one-third as broad, with regular, hexagonal pores of half size. Six spines triangular pyramidal, as long as the radius of the shell, at the base as broad as one pore. (Differs from _Hexastylus phænaxonius_, Pl. 21, fig. 3, only in the medullary shell and the six inner radial beams, connecting it with the cortical shell.)

_Dimensions._--Diameter of the outer shell 0.15, pores 0.01 to 0.015, bars 0.015 to 0.02; inner shell 0.05; length of the spines 0.08, basal breadth 0.01.

_Habitat._--Central Pacific, Stations 266 to 271, depth 2425 to 2925 fathoms.

2. _Hexalonche rosetta_, n. sp. (Pl. 25, figs. 3, 3_a_, 3_b_).

Cortical shell thick walled, smooth, two and a half time as broad as the medullary shell. Pores of the latter (fig. 3_a_) regular circular; eight to ten on the half meridian, about as broad as the bars between them. Pores of the outer shell regular, hexagonal, remarkable for a very peculiar form and arrangement. In the transverse section of the shell (fig. 3_b_) they appear as narrow, hexagonal prismatic canals, twice as high as broad, and four to five times as broad as the thin elevated bars between them. Every seven meshes form together a larger, regular hexagon (six pores surrounding one central pore). The periphery of these larger, rosette-like hexagons projects more strongly from the surface than the walls between the smaller hexagons. On the half meridian of the shell may be counted six to seven larger and eighteen to twenty smaller hexagons. The six radial beams between the two shells are thin, three-sided prismatic, not broader than the bars of the network, the prominent prolongations of which form six very strong spines of peculiar club-like shape (fig. 3), as long as the radius of the outer shell. The three wings of the club are lower in the inner, higher in the outer half; the broadest part of the spine (at the base and in the outer third) is as broad as a hexagonal rosette (equal to three meshes of the outer shell); its outer apex is pyramidal.

_Dimensions._--Diameter of the outer shell 0.13, pores 0.008 to 0.01, bars 0.02; inner shell 0.05; length of the spines 0.07, distal breadth 0.03.

_Habitat._--Tropical West Pacific, Station 225, depth 4475 fathoms.

3. _Hexalonche favosa_, n. sp.

Cortical shell thick walled, smooth, four times as broad as the medullary shell. Pores of the former regular circular, hexagonally framed, deep funnel-shaped, of the same breadth as the bars; six to eight on the radius. Six spines triangular-pyramidal, as long as the radius, at the base twice as broad as one pore. (Differs from the similar _Hexastylus favosus_ mainly in the possession of a medullary shell.)

_Dimensions._--Diameter of the outer shell 0.16, pores and bars 0.012; inner shell 0.04; length of the spines 0.08, basal breadth 0.025.

_Habitat._--Equatorial Atlantic, Station 348, depth 2450 fathoms; also fossil in Barbados.

{181}4. _Hexalonche octahedra_, n. sp. (Pl. 22, figs. 8, 8_a_).

Cortical shell a regular octahedron, thin walled, with twelve more or less rounded edges (between the bases of the spines), and with smooth surface, three times as broad as the spherical medullary shell. Pores of the former regular circular (three times as large as those of the latter), four times as broad as the bars; five to seven on the radius. Six spines three-sided prismatic, with thickened base and cuspidated end, somewhat longer than the radius, and once to twice as broad as one pore.

_Dimensions._--Diameter of the outer shell 0.11, pores 0.01, bars 0.0025; inner shell 0.04; length of the spines 0.08, bars 0.01.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

5. _Hexalonche conicornis_, n. sp. (Pl. 22, fig. 2).

Cortical shell thick walled, smooth, three times as broad as the medullary shell. Pores of both spheres regular circular, three to four times as broad as the bars; those of the thick walled outer shell six to seven on the radius, twice as large as those of the thin walled inner shell; six radial beams between the two spheres, very thin, cylindrical; six spines short, conical, scarcely as long as the radius of the outer shell, at the base twice as broad as one pore.

_Dimensions._--Diameter of the outer shell 0.12 to 0.14, pores 0.01, bars 0.003; inner shell 0.04 to 0.05; length of the spines 0.04 to 0.06, basal breadth 0.02.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

6. _Hexalonche curvicornis_, n. sp. (Pl. 25, fig. 4).

Cortical shell thick walled, smooth, not much larger than the medullary shell (= 4 : 3). Pores of both spheres regular circular, nearly of the same size, three times as broad as the bars between them; seven to nine on the radius. Six spines three-sided prismatic, inside and outside of the exterior shell of equal thickness, twice as broad as one pore, longer than the diameter of the outer shell, and in a singular manner curved like an ox horn; the three edges of each horn somewhat spirally twisted.

_Dimensions._--Diameter of the outer shell 0.16, pores 0.01, bars 0.003; inner shell 0.12; length of the spines 0.2, breadth 0.02.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

7. _Hexalonche brevicornis_, n. sp.

Cortical shell thin walled, smooth, three times as broad as the medullary shell. Pores of the former regular circular, double-edged, six to eight times as broad as the thin bars, five to six on the radius. Six spines triangular pyramidal, as broad as one pore and only twice as long.

_Dimensions._--Diameter of the outer shell 0.14, pores 0.02, bars 0.003; inner shell 0.045; length of the spines 0.05, basal breadth 0.02.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

{182}8. _Hexalonche grandis_, n. sp.

Cortical shell thick walled, smooth, four times as broad as the medullary shell. Pores of the outer shell regular circular, four times as broad as the bars; thirteen to fifteen on the radius. Six spines conical, scarcely half as long as the radius, at the base as broad as one pore.

_Dimensions._--Diameter of the outer shell 0.2 to 0.32, pores 0.01 to 0.02, bars 0.003 to 0.005; inner shell 0.06 to 0.08; length of the spines 0.06, breadth 0.02.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

Subgenus 2. _Hexalonchetta_, Haeckel.

_Definition._--Pores of the cortical shell regular or subregular, of nearly equal size and similar form; surface covered with numerous conical or bristle-shaped radial by-spines.

9. _Hexalonche amphisiphon_, n. sp. (Pl. 25, figs. 2, 2_a_, 2_b_).

Cortical shell thin walled, armed with very numerous bristle-shaped, radial by-spines, a quarter to a half as long as the six main spines. Pores regular hexagonal, twelve to fourteen on the radius, with very thin bars, prolonged on the outer as well as the inner surface into a short truncated conical tube (Pl. 25, fig. 2_b_). Medullary shell octahedral, with irregular polygonal meshes and very thin bars between them (fig. 2_a_), connected with the outer (six to eight times larger) shell by six very thin radial beams. These are prolonged outside into six strong pyramidal spines, nearly as long as the diameter of the outer shell, with sharp straight edges, at the base twice as broad as one pore.

_Dimensions._--Diameter of the outer shell 0.15, pores 0.01, bars 0.001; inner shell 0.02; length of the spines 0.12, basal breadth 0.02.

_Habitat._--Central Pacific, Station 271, surface.

10. _Hexalonche anaximandri_, n. sp. (Pl. 22, fig. 5).

Cortical shell thin walled, covered with short conical spines (smaller than the pores), three times as broad as the medullary shell. Pores of the outer shell subregular hexagonal, four times as broad as the bars; five to seven on the radius. Inner shell with regular hexagonal pores of half the size, connected with the outer by six strong, three-sided prismatic beams, which are prolonged outside into six very stout pyramidal spines, with three prominent edges, longer than the radius and twice as broad as one pore.

_Dimensions._--Diameter of the outer shell 0.12, pores 0.01, bars 0.0025; inner shell 0.04; length of the spines 0.07, basal breadth 0.02.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

{183}11. _Hexalonche octocolpa_, n. sp. (Pl. 22, figs. 6, 6_a_).

Cortical shell thin walled, nearly octahedral, with eight hemispherical or bosom-shaped vaultings, corresponding to the eight faces of a regular octahedron, the three axes of which are indicated by the six spines. Surface covered with short bristle-shaped spines. Pores regular hexagonal, ten to fifteen times as broad as the thin bars; seven to nine on the radius. Medullary shell (fig. 6_a_) spherical, with regular circular pores, one-third as broad as the cortical shell, and connected with it by six strong triangular radial beams, which are prolonged outside into pyramidal spines, one-third as long as the shell diameter.

_Dimensions._--Diameter of the outer shell 0.2, pores 0.03, bars 0.002; inner shell 0.06; length of the spines 0.06, breadth 0.02.

_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.

12. _Hexalonche cristata_, n. sp.

Cortical shell thick walled, four times as broad as the medullary shell, and covered with short conical spines arising from the nodal points of elevated crests which form regular hexagonal frames around the funnel-shaped circular pores. These are two to three times as broad as the crested bars; eight to ten on the radius. Six spines three-sided pyramidal, with strong prominent edges, about as long as the radius of the shell.

_Dimensions._--Diameter of the outer shell 0.16 to 0.2, pores 0.01 to 0.015, bars 0.003 to 0.005; inner shell 0.04 to 0.05; length of the spines 0.08 to 0.12, basal breadth 0.01 to 0.03.

_Habitat._--Central Pacific, Station 266 to 274, depth 2350 to 2925 fathoms.

13. _Hexalonche serrata_, n. sp.

Cortical shell thick walled, four times as broad as the medullary shell, with spiny surface. Pores regular circular, twice as broad as the bars, five to seven on the radius, funnel-shaped, separated by hexagonal frames, the sharp crests of which are serrated; at the nodal-points longer bristle-shaped by-spines. Six main spines triangular prismatic, longer than the diameter of the shell, twice as broad as one pore.

_Dimensions._--Diameter of the outer shell 0.15, pores 0.01, bars 0.005; inner shell 0.04; length of the spines 0.2, breadth 0.02.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

14. _Hexalonche anaximenis_, n. sp. (Pl. 25, fig. 5).

Cortical shell thin walled, twice as broad as the medullary shell, and covered with short conical by-spines. Pores regular circular, twice as broad as the bars; five to six on the radius. Circular pores of the medullary shell one-third as broad. Radial main spines conical, nearly as long as the radius of the shell.

_Dimensions._--Diameter of the outer shell 0.1, pores 0.01, bars 0.005; inner shell 0.05; length of the spines 0.04, basal breadth 0.015.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

{184}15. _Hexalonche aspera_, n. sp.

Cortical shell thin walled, three times as broad as the medullary shell, and covered with short conical spines. Pores regular circular, four to six times as broad as the bars; eight to ten on the radius. Radial spines conical, about as long as the diameter of the shell.

_Dimensions._--Diameter of the outer shell 0.12, pores 0.08, bars 0.0015; inner shell 0.04; length of the spines 0.1, basal breadth 0.02.

_Habitat._--South Pacific, Station 300, depth 1375 fathoms.

16. _Hexalonche castanella_, n. sp.

Cortical shell thick walled, five times as broad as the medullary shell, and covered with numerous short conical spines. Pores regular circular, twice as broad as the bars; ten to twelve on the radius. Radial spines triangular pyramidal, about as long as the radius of the shell.

_Dimensions._--Diameter of the outer shell 0.22, pores 0.01, bars 0.005; inner shell 0.045; length of the spines 0.12, basal breadth 0.02.

_Habitat._--North Atlantic, Station 353, depth 3125 fathoms.

Subgenus 3. _Hexalonchilla_, Haeckel.

_Definition._--Pores of the cortical shell irregular, of unequal size or form; surface smooth, without radial by-spines (other than the six main spines).

17. _Hexalonche hexacantha_, Haeckel.

_Haliomma hexacanthum_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 35, Taf. iv. fig. 5.

_Haliomma hexacanthum_, Haeckel, 1862, Monogr. d. Radiol., p. 430.

Cortical shell thin walled, smooth, with irregular polygonal pores (commonly hexagonal or pentagonal), two to three times as broad as the bars; eight to ten on the radius. Medullary shell one quarter as broad, connected with the former by six thin radial beams which are prolonged outside into six triangular pyramidal spines (not quadrangular, as Müller describes), longer than the radius of the shell.

_Dimensions._--Diameter of the outer shell 0.2, pores 0.01 to 0.015, bars 0.005; inner shell 0.05; length of the spines 0.15, basal breadth 0.015.

_Habitat._--Mediterranean (Messina, Nice, Genoa).

18. _Hexalonche geometrica_, n. sp.

Cortical shell thick walled, smooth, with very peculiar geometrical formation of its network, the pores of which are of very different size and form, but highly regular disposition. Each of the six {185}triangular spines is surrounded at the base by three small roundish pores (between the three wings of its base), and further by a coronal of six very large pores, three of which are pentagonal, and the other three (alternating) heptagonal. The six basal coronals are separated by irregular smaller pores. Medullary shell thin walled, with regular hexagonal pores (three on the radius) and thin bars, connected with the outer shell by six thin triangular prismatic radial beams, which are prolonged outside into short pyramidal spines (half as long as the radius).

_Dimensions._--Diameter of the outer shell 0.2, thirty-six larger pores of the coronals 0.03 to 0.04, smaller pores between them 0.01 to 0.02, bars 0.005; inner shell 0.05 (with pores of 0.008); length of the spines 0.05, basal breadth 0.03.

_Habitat._--South Atlantic, off Buenos Ayres, Station 323, depth 1900 fathoms.

19. _Hexalonche pythagoræa_, n. sp. (Pl. 22, fig. 1).

Cortical shell thick walled, smooth, three times as broad as the medullary shell. Pores irregular roundish, twice to eight times as broad as the bars, of very different size; usually in the space between every three spines are three or six larger pores, separated by numerous smaller pores (often the disposition of the larger pores is much more regular than in the figured specimen). Medullary shell with regular circular pores, connected with the outer by six very thin radial beams, which are prolonged outside into six short triangular pyramidal spines about as long and broad as the half radius.

_Dimensions._--Diameter of the outer shell 0.12, pores 0.008 to 0.03, bars 0.004; inner shell 0.04; length of the spines 0.04, basal breadth 0.03.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

20. _Hexalonche aristarchi_, n. sp. (Pl. 22, fig. 3).

Cortical shell thin walled, smooth, four times as broad as the medullary shell. Pores irregular polygonal, of very variable size and form, twice to six times as broad as the bars; six to ten on the radius. Medullary shell with regular hexagonal pores, connected with the outer by six very thin radial beams, which are prolonged outside into six triangular pyramidal spines, nearly as long as the radius.

_Dimensions._--Diameter of the outer shell 0.1, pores 0.005 to 0.02, bars 0.003; inner shell 0.025; length of the spines 0.05, basal breadth 0.01.

_Habitat._--North Pacific, Station 241, depth 2300 fathoms.

21. _Hexalonche ekphantæa_, n. sp.

Cortical shell thin walled, smooth, four times as broad as the medullary shell. Pores irregular roundish, of very variable size and form, twice to six times as broad as the bars, ten to fifteen on the radius. Six spines cylindro-conical, longer than the diameter of the shell.

_Dimensions._--Diameter of the outer shell 0.2, pores 0.004 to 0.012, bars 0.002; inner shell 0.05; length of the spine 0.3, basal breadth 0.01.

_Habitat._--Indian Ocean, Sunda Strait, surface, Rabbe.

{186}Subgenus 4. _Hexalonchusa_, Haeckel.

_Definition._--Pores of the cortical shell irregular, of different size or form; surface covered with numerous conical or bristle-shaped, radial by-spines.

22. _Hexalonche philosophica_, n. sp. (Pl. 22, fig. 4).

Cortical shell thin walled, covered with short conical spines, three times as broad as the medullary shell. Pores irregular polygonal, or more roundish, twice to six times as broad as the bars; six to eight on the radius. Inner shell of the same structure, pores three times smaller, connected with the outer by six very thin radial beams, which are prolonged outside into six strong, triangular pyramidal spines, as long as the radius. (Similar to _Hexalonche anaximandri_, Pl. 22, fig. 5, but different in the irregular network and the shorter by-spines.)

_Dimensions._--Diameter of the outer shell 0.11, pores 0.005 to 0.015, bars 0.0025; inner shell 0.04; length of the spines 0.06, breadth 0.02.

_Habitat._--North Atlantic, Færöe Channel, John Murray; Iceland, Krabbe, surface.

23. _Hexalonche seleuci_, n. sp.

Cortical shell thick walled, covered with numerous short, bristle-shaped spines. Pores of very different size and form, and of a peculiar, subregular disposition, similar to those of _Hexalonche geometrica_ (though in this case more regular). Each of the six triangular main spines (which reach nearly the length of the radius) is surrounded at the base by three small roundish pores, and these are further supplemented by a coronal of six very large polygonal pores; the six coronals are separated by irregular rows of smaller pores. Inner shell equal to one-third of the outer. Six main spines pyramidal, as long as the radius.

_Dimensions._--Diameter of the outer shell 0.16, larger pores 0.03 to 0.04, smaller pores 0.01 to 0.02, bars 0.05 to 0.01; inner shell 0.05; length of the spines 0.08, basal breadth 0.03.

_Habitat._--North Atlantic, Station 354, surface.

24. _Hexalonche sexaculeata_, Haeckel.

_Haliomma sexaculeatum_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 87, Taf. i. fig. 8.

Cortical shell thick walled, twice as broad as the medullary shell, and covered with short conical spines. Pores irregular polygonal (mostly hexagonal), twice to three times as broad as the bars; six to eight on the radius. Six spines triangular-pyramidal (not quadrangular), somewhat longer than the radius of the shell.

_Dimensions._--Diameter of the outer shell 0.11, pores 0.06 to 0.08, bars 0.03; inner shell 0.06; length of the spines 0.07, basal breadth 0.015.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte, Caltanisetta.

{187}25. _Hexalonche heracliti_, n. sp. (Pl. 22, fig. 7).

Cortical shell thick walled, covered with bunches of small spines, each bunch at the nodule point between every three pores composed of four to eight conical spinules. Pores irregular roundish, twice to four times as broad as the bars; four to six on the radius. Inner shell equal to one-third of the outer, connected with it by six thin radial beams, which are prolonged outside into six strong triangular spines about as long as the radius.

_Dimensions._--Diameter of the outer shell 0.15, pores 0.015 to 0.03, bars 0.08; inner shell 0.05; length of the spines 0.06, basal breadth 0.02.

_Habitat._--Indian Ocean, Madagascar, Rabbe, surface.

26. _Hexalonche xenophanis_, n. sp.

Cortical shell thin walled, covered with numerous short conical spines, four times as broad as the medullary shell. Pores irregular circular, twice to eight times as broad as the bars; five to seven on the radius. Six spines conical or more cylindrical, as long as the diameter of the shell or longer.

_Dimensions._--Diameter of the outer shell 0.16 to 0.24, pores 0.01 to 0.04, bars 0.005; inner shell 0.04 to 0.06; length of the spines 0.2 to 0.3, breadth 0.02.

_Habitat._--Central Pacific, Stations 266 to 272, surface.

27. _Hexalonche setosa_, n. sp.

Cortical shell thin walled, covered with numerous bristle-shaped spines, half as long as the six main spines. Pores irregular roundish, twice to five times as broad as the bars; ten to twelve on the radius. Inner shell equal to one-fifth of the outer. Six spines conical, as long as the radius.

_Dimensions._--Diameter of the outer shell 0.25, pores 0.008 to 0.02, bars 0.004; inner shell 0.05; length of the spines 0.12, basal breadth 0.03.

_Habitat._--South Pacific, Station 291, surface.

28. _Hexalonche hystricina_, n. sp. (Pl. 25, fig. 6).

Cortical shell thick walled, covered with numerous bristle-shaped spines, half as long as the six main spines. Pores irregular roundish, twice to four times as broad as the bars; five to seven on the radius. Medullary shell with very small circular pores, one-fourth of the cortical shell, connected with it by six thin prismatic radial beams, which are prolonged outside into six strong, short, three-sided pyramidal, cuspidated spines, only half as long as the radius of the outer shell.

_Dimensions._--Diameter of the outer shell 0.2, pores 0.015 to 0.03, bars 0.008; inner shell 0.05; length of the spines 0.05, basal breadth 0.02.

_Habitat._--Indian Ocean, Sunda Strait, surface, Rabbe.

{188}Genus 76. _Hexancistra_,[106] Haeckel, 1881, Prodromus, p. 451.

_Definition._--#Cubosphærida# with two concentric lattice-spheres and six branched spines of equal size.

The genus _Hexancistra_ differs from its ancestral form, _Hexalonche_, in the ramification of the six radial spines. These are very different in the two subgenera; in _Hexancora_ each spine bears only three simple lateral branches, while in _Hexapitys_ there are three rows of verticillate lateral branches on each spine.

Subgenus 1. _Hexancora_, Haeckel.

_Definition._--Each radial spine with three simple lateral branches only (one branch from each edge of the triangular spine).

1. _Hexancistra tricuspis_, n. sp. (Pl. 22, fig. 9).

Cortical shell thin walled, covered with short conical by-spines, three times as broad as the medullary shell; its pores regular circular, three times as broad as the bars; ten to twelve on the radius. Pores of the medullary shell half as large, also regular circular. The two shells connected by six thin prismatic radial beams, which are prolonged outside into six very stout main spines, three-sided prismatic, as long as the shell diameter, with three thin wing-like edges. Each edge at the distal end prolonged into a strong curved lateral branch.

_Dimensions._--Diameter of the outer shell 0.13, inner 0.4; cortical pores 0.01, bars 0.003; medullary pores 0.005, bars 0.003; length of the six spines 0.13, breadth 0.02.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

2. _Hexancistra ancorata_, n. sp.

Cortical shell thick walled, smooth, twice as broad as the medullary shell; its pores regular circular, twice as broad as the bars; six to eight on the radius. Six radial spines, three-sided prismatic, as long as the shell radius, with three recurved lateral branches at the distal end like the three teeth of an anchor.

_Dimensions._--Diameter of the outer shell 0.1, inner 0.05; cortical pores 0.006, bars 0.003; length of the six spines 0.05, breadth 0.02.

_Habitat._--South Pacific, Station 296, depth 1825 fathoms.

3. _Hexancistra triserrata_, n. sp. (Pl. 22, fig. 10).

Cortical shell thin walled, thorny, twice to three times as broad as the medullary shell; the two shells connected by six strong triangular beams. Inner shell spherical, with very small, regular, circular {189}pores; ten to twelve on the half meridian. Bars as broad as the pores. Outer shell regularly octahedral, with eight triangular perfectly regular even faces, separated by eight prominent edges; the meshes circular, regular, about twelve to fourteen on the half meridian, two to three times as broad as the bars between them. Six strong radial spines, about as long as the diameter of the outer shell, three-sided prismatic, cuspidate; their three edges prominent, serrate, spirally twisted. Each spine bears about its middle three strong flattened lateral branches, nearly perpendicular to it, not serrated, and slightly curved.

_Dimensions._--Diameter of the outer shell 0.13, inner 0.045; pores of the former 0.01, of the latter 0.004; length of the spine 0.12, breadth 0.014.

_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.

4. _Hexancistra quadricuspis_, n. sp. (Pl. 22, fig. 11).

Cortical shell thin walled, covered with short bristle-shaped by-spines, three and a half times as broad as the medullary shell. Pores of the latter regular circular, small; pores of the former three to six times as large, very irregular, roundish, double-edged. Six radial spines, three-sided prismatic, about as long as the shell diameter, with three wing-like, slightly twisted edges, which are prolonged towards the distal end into three curved horn-shaped branches.

_Dimensions._--Diameter of the outer shell 0.17, inner 0.05; cortical pores 0.01 to 0.03, bars 0.005; medullary pores 0.003, bars 0.001; length of the spines 0.15, breadth 0.013.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

Subgenus 2. _Hexapitys_, Haeckel, 1881, Prodromus, p. 451.

_Definition._--Each radial spine with three rows of verticillate lateral branches (a row arising from each edge of the spine).

5. _Hexancistra mirabilis_, n. sp. (Pl. 23, fig. 3).

_Hexapitys mirabilis_, Haeckel, 1881, Prodromus, p. 451.

Cortical shell very thin walled, three times as broad as the medullary shell. Inner shell spherical, with very delicate, subregular hexagonal meshes; seven to eight on the half diameter. Outer shell octahedral, with irregular polygonal meshes of very different size; on the surface numerous thin accessory radial spines, equal in length to its radius. Six main spines, extremely long and stout, many times longer than the diameter of the outer shell, nearly as broad as the radius of the inner shell, three-sided prismatic, with sharp, prominent, spirally twisted edges; on every edge a great number of thin lateral branches, arranged perpendicularly to it, as long as the diameter of the outer shell, and pinnated by ten to twenty pairs of delicate secondary spinules, biserial and perpendicular to the primary branches. (In the figured specimen the spherical central capsule, between both shells, was well preserved; its nucleus nearly filled the medullary shell. The thick jelly-veil around it was radially striped and octahedral.)

{190}_Dimensions._--Diameter of the outer shell 0.13, of the inner 0.05; length of the spines 0.5 to 0.8 or more, breadth 0.02.

_Habitat._--Central Pacific, Station 271, surface.

Genus 77. _Hexaloncharium_,[107] n. gen.

_Definition._--#Cubosphærida# with two concentric lattice-spheres and six simple spines of different sizes; one opposite pair larger than the two others.

The genus _Hexaloncharium_ exhibits the same relation to its ancestral form, _Hexalonche_, that _Hexastylarium_ bears to _Hexastylus_. Two opposite spines of one pair are larger than the four others, and correspond to the three axes of a quadratic crystal.

1. _Hexaloncharium octahedrum_, n. sp.

Cortical shell smooth, three to four times as broad as the spherical medullary shell, each having regular circular pores, twice to three times as broad as the bars. Form of the outer shell not a sphere, but a regular octahedron, with eight congruent, equilateral triangular even faces. Two opposite spines twice as long as the shell diameter, whilst the four others are scarcely equal to it. Basal breadth of all six the same (three times as large as one pore); form, three-sided prismatic, with cuspidate distal end. (Similar to _Hexalonche octahedra_, Pl. 22, fig. 8, but distinct in the unequal length of the spines.)

_Dimensions._--Diameter of the outer shell 0.16, inner 0.045; length of the major spine 0.3, minor 0.12, basal breadth 0.03.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

2. _Hexaloncharium philosophicum_, n. sp.

Cortical shell spherical, covered with short conical by-spines, twice as broad as the medullary shell; both with regular circular pores three to four times as broad as the bars. Two major spines cylindrical, with conical apex, three times as long as the four others, which are conical and about as long as the shell radius; basal breadth of all six the same (equal to one pore). Similar to _Hexalonche anaximenis_ (Pl. 25, fig. 5), but distinct in the enormous prolongation of two opposite spines.

_Dimensions._--Diameter of the outer shell 0.12, inner 0.06; length of the two major spines 0.2, of the four minor 0.06, basal breadth 0.02.

_Habitat._--Central Pacific, Station 267, depth 2700 fathoms.

{191}3. _Hexaloncharium hystricinum_, n. sp.

Cortical shell spherical, three times as broad as the medullary shell, and densely covered with oblique bristle-shaped by-spines. Pores irregular roundish. Two opposite major spines three-sided prismatic, longer than the shell diameter; four minor spines pyramidal, scarcely half as long as the shell radius. (Somewhat similar to _Hexalonche hystricina_, but distinct in the prolongation of two major spines.)

_Dimensions._--Diameter of the outer shell 0.15, inner 0.05; length of the two major spines 0.2, four minor 0.03, basal breadth 0.02.

_Habitat._--South Pacific, Station 288, surface.

Genus 78. _Hexalonchidium_,[108] Haeckel, 1881, Prodromus, p. 451.

_Definition._--#Cubosphærida# with two concentric lattice-spheres and six simple spines of different sizes in pairs; the two opposite spines of each pair equal, the three pairs unequal.

The genus _Hexalonchidium_ exhibits the same relation to _Hexalonche_ that _Hexastylidium_ bears to _Hexastylus_; the growth of the three spine-pairs is different, whilst both spines of each pair are equal; they correspond therefore to the three axes of a rhombic crystal.

1. _Hexalonchidium axonometrum_, n. sp.

Cortical shell thin walled, covered with short bristle-shaped by-spines, twice as broad as the medullary shell; both with regular hexagonal meshes, twice to three times as broad as the bars (inner meshes half as broad as the outer). All three spine-pairs three-sided prismatic, of very different length but of equal breadth (equal to three pores). Major spine-pair twice as long as the shell diameter; middle pair about equal to the latter, minor scarcely half as long. (Similar to _Hexalonche anaximandri_, Pl. 22, fig. 5, but distinct in the different length of the spines.)

_Dimensions._--Diameter of the outer shell 0.12, inner 0.06; length of the major spines 0.25, middle 0.1, minor 0.04.

_Habitat._--Indian Ocean, Madagascar, surface, Rabbe.

Subfamily HEXACONTIDA,[109] Haeckel, 1881, Prodromus, pp. 449, 452.

_Definition._--#Cubosphærida# with three concentric, spherical, or octahedral lattice-shells.

{192}Genus 79. _Hexacontium_, Haeckel,[110] 1881, Prodromus, p. 452.

_Definition._--Shell with three concentric lattice-spheres and six simple spines of equal size.

The genus _Hexacontium_, the ancestral form of the Hexacontida, is probably derived from _Hexalonche_ by duplication of the medullary shell. As in the latter, all six spines are of equal size, opposite in pairs in the three dimensive axes, and correspond therefore to the three equal axes of a tesseral crystal.

Subgenus 1. _Hexacontanna_, Haeckel.

_Definition._--Pores of the cortical shell regular or subregular, of nearly equal size and similar form; surface smooth, without radial spines or papillæ (other than the six main spines).

1. _Hexacontium phænaxonium_, n. sp.

Cortical shell thin walled, smooth; its pores regular hexagonal, six to nine times as broad as the bars; twelve to sixteen on the radius. Radial proportion of the three spheres = 1 : 2 : 4. Both medullary shells of the same structure as the cortical shell, only with smaller pores. The three spheres connected by six thin radial beams, which are prolonged on the outside into six strong triangular pyramidal spines, as long as the radius of the cortical shell, and, at the base, as broad as one of its pores. (Differs from _Hexastylus phænaxonius_ and from _Hexalonche phænaxonia_, Pl. 21, fig. 3, in the larger size and the triple shell.)

_Dimensions._--Diameter of the outer sphere 0.2, middle 0.1, inner 0.05; cortical pores 0.008, bars 0.0012; length of the spines 0.1.

_Habitat._--Central Pacific, Station 270, surface.

2. _Hexacontium axotrias_, n. sp. (Pl. 24, fig. 3).

Cortical shell thin walled, smooth; its pores regular circular, five to six times as broad as the bars; eleven to thirteen on the radius. Radial proportion of the three spheres = 1 : 3 : 8. Outer medullary shell with hexagonal frames around the regular circular pores (five to six on the radius). Inner medullary shell with simple small circular pores (three on the radius). The two outer shells connected by six triangular prismatic beams, which are prolonged outside to the length of the cortical radius or more.

_Dimensions._--Diameter of the outer sphere 0.2, middle 0.07, inner 0.025; cortical pores 0.016, bars 0.003; length of the spines 0.1 to 0.015, basal breadth 0.02.

_Habitat._--North Pacific, Station 253, surface.

3. _Hexacontium hexactis_, Haeckel.

_Actinomma hexactis_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 91, Taf. ii. fig. 7.

Cortical shell thick walled, smooth, or a little rough. Pores regular circular, of the same breadth as the bars; five to seven on the radius. Radial proportion of the three spheres {193}= 1 : 3 : 6. Both medullary shells of the same structure, but with smaller pores. Six spines triangular pyramidal, nearly as long as the diameter of the outer shell, three times as broad at the base as one pore.

_Dimensions._--Diameter of the outer sphere 0.1, middle 0.05, inner 0.016; cortical pores and bars 0.008; length of the spines 0.08, basal breadth 0.025.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

4. _Hexacontium lævigatum_, n. sp. (Pl. 24, fig. 6).

Cortical shell thick walled, quite smooth. Pores regular circular, with double margins, eight to ten on the radius, of the same breadth as the smooth bars. Radial proportion of the three spheres = 1 : 2 : 6. All three spheres connected by six very thin radial beams, which are prolonged outside into six short, stout, triangular, pyramidal spines, half as long as the radius of the outer shell.

_Dimensions._--Diameter of the outer shell 0.13, middle 0.04, inner 0.02; cortical pores and bars 0.008; length of the spines 0.04, basal breadth 0.02.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

5. _Hexacontium triplosphærium_, n. sp.

Cortical shell thick walled, smooth. Pores regular circular, three times as broad as the bars; ten to twelve on the radius. Radial proportion of the three spheres = 1 : 3 : 10. Six spines conical, about as long as the radius of the cortical shell.

_Dimensions._--Diameter of the outer shell 0.16, middle 0.05, inner 0.016; cortical pores 0.012, bars 0.004; length of the spines 0.07, basal breadth 0.02.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

6. _Hexacontium octahedrum_, n. sp.

Cortical shell a regular octahedron, thin walled, with twelve more or less rounded edges (between the spine-bases) and with smooth surface; its pores regular circular, five to seven on the radius, four times as broad as the bars. Radial proportion of the three shells = 1 : 3 : 9. Both medullary shells spherical, with very small circular pores. Six inner bars very thin; six outer spines (their prolongations) triangular pyramidal, as long as the radius of the outer shell. (Differs from _Hexalonche octahedra_, Pl. 22, fig. 8, almost solely in the duplication of the medullary shell.)

_Dimensions._--Diameter of the outer shell 0.12, middle 0.04, inner 0.013.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

7. _Hexacontium circumtextum_, n. sp. (Pl. 25, figs. 7, 7_a_).

Cortical shell double, enclosing a simple medullary shell. Radial proportion of the three spheres = 3 : 10 : 12. Inner cortical shell very thick walled, with regular circular, double-edged pores, four times as broad as the bars; seven to nine on the radius. From each nodal-point between {194}every six pores arises a small, bristle-shaped, radial spine, as long as the diameter of one pore. The distal ends of all these spines are connected by very delicate tangential threads, and consequently form by their attachment an outer cortical shell, with regular hexagonal meshes and smooth surface. Six main spines short, three-sided prismatic, scarcely as long as half the radius of the outer shell.

_Dimensions._--Diameter of the outer shell 0.12, middle 0.1, inner 0.03; pores of the middle shell 0.004, bars 0.001; length of the spines 0.025, basal breadth 0.01.

_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.

Subgenus 2. _Hexacontella_, Haeckel.

_Definition._--Pores of the cortical shell regular or subregular, of nearly equal size and similar form; surface covered with numerous conical or bristle-shaped, radial spines (other than the six main spines).

8. _Hexacontium hexagonale_, n. sp.

Cortical shell thin walled, bristly, with very delicate network; its pores regular hexagonal, twelve to sixteen on the radius, ten to twelve times as broad as the thin thread-like bars. At each nodal-point of the network (between every three meshes) arises a bristle-shaped, radial spine, as long as the diameter of one mesh. Six main spines hexagonal, as long as the radius of the outer shell, as broad at its base as one mesh. Radial proportion of the three spheres = 1 : 2 : 4. Pores of both medullary shells also regular hexagonal, but much smaller, in the middle shell eleven to twelve, in the inner, six to seven on the half meridian.

_Dimensions._--Diameter of the outer shell 0.12, of the middle 0.06, of the inner 0.03; meshes of the outer shell 0.008; length of the six spines 0.05, basal thickness 0.008.

_Habitat._--Indian Ocean, Ceylon, surface, Haeckel.

9. _Hexacontium favosum_, n. sp. (Pl. 24, figs. 2, 2_a_).

Cortical shell very thick walled, spiny, with regular, honeycomb-like network; its meshes funnel-shaped, with circular inner, hexagonal outer aperture, twice as broad as the bars; five to seven on the radius. Between every three meshes (at each corner of the hexagon) arises a short radial thorn, not so long as the thickness of the shell-wall. Six radial spines very short and stout, three-sided pyramidal, scarcely half so long as the radius of the outer shell. Radial proportion of the three spheres = 1 : 2 : 5. Pores of both medullary shells regular, circular, about as broad as the bars, six to eight on the half meridian.

_Dimensions._--Diameter of the outer shell 0.1 to 0.12, of the middle 0.04 to 0.05, of the inner 0.02; meshes of the outer shell 0.008; length of the six spines 0.2 to 0.3, basal breadth 0.015.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

10. _Hexacontium sceptrum_, n. sp. (Pl. 24, figs. 1, 1_a_).

Cortical shell thick walled, spiny, with regular, honeycomb-like network; its meshes funnel-shaped, with circular inner, hexagonal outer aperture, three to four times as broad as the bars; {195}five to six on the radius. Between every three meshes arises a short radial thorn, as long as the thickness of the shell-wall. Six radial spines sceptre-shaped, six-sided, somewhat constricted towards their middle part, strong, as long as the radius of the outer shell, as broad as one of its meshes. Radial proportion of the three spheres = 1 : 2 : 6. Pores of the two inner shells regular hexagonal, with thin bars, six to eight on the half meridian (fig. 1_a_).

_Dimensions._--Diameter of the outer shell 0.13, of the middle 0.04, of the inner 0.02; pores of the outer shell 0.01, of the middle 0.008, of the inner 0.004; length of the six spines 0.06, basal breadth 0.015.

_Habitat._--Equatorial Atlantic, Station 347, surface.

11. _Hexacontium prionacanthum_, n. sp. (Pl. 24, figs. 7, 7_a_).

Cortical shell thick walled, thorny; its pores regular circular, with elevated hexagonal frames six to nine on the radius, twice as broad as the crest-shaped bars. At each nodal-point of the hexagon arises one short conical papilla or thorn. Radial proportion of the three spheres = 1 : 3 : 10. Pores of both medullary shells much smaller, regular circular. Six main spines three-sided prismatic, longer than the radius of the outer shell, as broad as one of its meshes; their three edges serrated, with ten to twelve teeth.

_Dimensions._--Diameter of the outer shell 0.15, middle 0.045, inner 0.015; cortical pores 0.01, bars 0.005; length of the spines 0.1, breadth 0.012.

_Habitat._--West Tropical Pacific, Station 225, depth 4475 fathoms.

12. _Hexacontium clavigerum_, n. sp. (Pl. 23, fig. 5).

Cortical shell very thick walled, thorny; its pores regular circular, hexagonally framed, three times as broad as the bars, nine to twelve on the radius; between them short conical papillæ or thorns arising at the nodal-points. Radial proportion of the three spheres = 1 : 2 : 5. Outer medullary shell with regular circular, much smaller pores; connected with the cortical shell by numerous (twenty to thirty) thin radial beams. Six main spines very stout, club-shaped, scarcely as long as the radius of the outer shell, three times as broad as one of its pores, three-sided, with three to four teeth on each edge.

_Dimensions._--Diameter of the outer shell 0.2, of the middle 0.08, of the inner 0.04; cortical pores 0.012, bars 0.004; length of the six spines 0.08, breadth 0.03.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

13. _Hexacontium floridum_, n. sp. (Pl. 24, fig. 4).

Cortical shell papillose, thick walled. Pores regular, six-lobed, four times as broad as the bars, five to seven on the radius; each pore with six (sometimes also five or seven) concave indentations or lobules; between the pores at the nodal-points arise short conical papillæ or thorns. Radial proportion of the three spheres = 1 : 2 : 3. Radial main spines pommel-shaped, three-sided prismatic, longer than the radius of the outer shell, two to three times as broad as one pore.

{196}_Dimensions._--Diameter of the outer shell 0.12, middle 0.06, inner 0.03; cortical pores 0.012, bars 0.003; length of the six spines 0.08, breadth 0.03.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

14. _Hexacontium hexaconicum_, n. sp.

Cortical shell spiny, thick walled. Pores regular circular, of the same breadth as the bars, ten to twelve on the radius; between them long bristle-shaped by-spines, half as long as the six main spines. Radial proportion of the three spheres = 1 : 3 : 9. Six main spines conical, as long as the radius of the outer shell, four times as broad at the base as one pore.

_Dimensions._--Diameter of the outer shell 0.18, middle 0.06, inner 0.02; cortical pores and bars 0.005; length of the spines 0.1, basal breadth 0.02.

_Habitat._--Antarctic Sea, Station 157, depth 1950 fathoms.

15. _Hexacontium asteracanthion_, Haeckel.

_Haliomma asteracanthion_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 816.

_Actinomma asteracanthion, Haeckel_, 1862, Monogr. d. Radiol., p. 441, Taf. xxiii. figs. 5, 6.

Cortical shell thin walled, spiny; its pores circular, without hexagonal frame (as a rule very regular, but in other specimens more or less irregular), often very variable in size, three to six times as broad as the bars, commonly seven to eight on the radius. Radial proportion of the three spheres = 1 : 2 : 4, or sometimes 1 : 3 : 8. Pores of the two inner shells also circular, but much smaller; those of the middle shell about half as broad, those of the inner shell one-fourth to one-sixth as broad as the pores of the outer shell. Six radial spines strong, three-sided prismatic, about as long as (or somewhat longer than) the radius of the outer shell, as broad as one of its large meshes. Accessory spines very numerous and very thin, bristle-like, usually half as long as the six main spines. (For the variability of this common species compare my Monograph, p. 442.)

_Dimensions._--Diameter of the outer shell 0.1 to 0.12, of the middle 0.04 to 0.06, of the inner 0.02 to 0.03; cortical pores 0.005 to 0.01; length of the six spines 0.06 to 0.08.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

Subgenus 3. _Hexacontosa_, Haeckel.

_Definition._--Pores of the cortical shell irregular, of different size or form; surface smooth, without radial by-spines or papillæ (other than the six main spines).

16. _Hexacontium axophænum_, n. sp.

Cortical shell thin walled, smooth. Pores irregular polygonal, three to nine times as broad as the bars; seven to ten on the radius. Radial proportion of the three spheres = 1 : 3 : 8. Both {197}medullary shells with smaller, irregular roundish pores. Six spines three-sided pyramidal, longer than the radius of the outer shell, one to two times as broad as one larger pore.

_Dimensions._--Diameter of the outer shell 0.12, middle 0.045, inner 0.015; cortical pores 0.006 to 0.018, bars 0.002; length of the spines 0.06 to 0.12, basal breadth 0.02 to 0.03.

_Habitat._--Central Pacific, Stations 266 to 272, at various depths.

17. _Hexacontium polygonale_, n. sp.

Cortical shell thick walled, smooth. Pores irregular roundish, with polygonal frames, two to four times as broad as the bars; eight to twelve on the radius. Radial proportion of the three spheres = 1 : 3 : 10. Six spines pyramidal, nearly as long as the diameter of the outer shell, with six to nine prominent edges (along the corner number of the polygonal meshes).

_Dimensions._--Diameter of the outer shell 0.2, middle 0.06, inner 0.02; cortical pores 0.008 to 0.016, bars 0.004; length of the spines 0.16 to 0.18, basal breadth 0.02.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

18. _Hexacontium antarcticum_, n. sp.

Cortical shell thin walled, smooth, with irregular roundish pores, eight to ten on the radius, two to four times as broad as the bars. Radial proportion of the three spheres = 1 : 3 : 9. Both medullary shells with smaller roundish irregular pores. Six spines conical, pyramidal at their origin, about as long as the radius, as broad as one larger mesh.

_Dimensions._--Diameter of the outer shell 0.18, middle 0.06, inner 0.02; cortical pores 0.006 to 0.012, bars 0.003; length of the spines 0.1, basal breadth 0.12.

_Habitat._--Antarctic Ocean, Station 157, depth 1950 fathoms.

Subgenus 4. _Hexacontura_, Haeckel.

_Definition._--Pores of the cortical shell irregular, of different size or form; surface covered with numerous conical papillæ or bristle-shaped, radial by-spines (other than the six main spines).

19. _Hexacontium papillosum_, n. sp. (Pl. 24, fig. 5).

Cortical shell thick walled, papillose. Pores irregular roundish, often somewhat lobed, five to six on the radius, two to four times as broad as the bars. Radial proportion of the three spheres = 1 : 2.5 : 5. Both medullary shells with subregular circular pores (inner much smaller). Six radial spines short and stout, pommel or club shaped, with three prominent wings, about as long as the shell radius, and as broad as the medullary shell.

_Dimensions._--Diameter of the outer shell 0.1, middle 0.05, inner 0.02, cortical pores 0.006 to 0.012, bars 0.003; length of the spines 0.05, bars 0.02.

_Habitat._--Central Pacific, Stations 266 to 272, at various depths.

{198}20. _Hexacontium gladiatum_, n. sp. (Pl. 25, fig. 8).

Cortical shell very thick walled, spiny, with irregular network; its meshes roundish, two to five times as broad as the bars, of very different size, ten to fifteen on the half meridian. Bars between them very strong, three-sided prismatic, armed with a great number of small thorns, and with large spines at the nodal-points between every three meshes. Radial proportion of the three spheres = 1 : 3 : 12. Six strong radial main spines three-sided prismatic, with three prominent, somewhat contorted wings, acute, broader than the diameter of the inner shell and as long as the diameter of the outer shell. These six main spines are situated in the same three dimensive axes as the six thin radial beams connecting the two medullary shells. But the six radial beams which connect the middle with the outer shell alternate with the former and lie in three other dimensive axes,--a very rare and remarkable disposition.

_Dimensions._--Diameter of the outer shell 0.2, middle 0.05, inner 0.016; cortical pores 0.01 to 0.03, bars 0.006; length of the six spines 0.2, breadth 0.02 to 0.03.

_Habitat._--Tropical Atlantic, Station 342, depth 1445 fathoms.

21. _Hexacontium setosum_, n. sp.

Cortical shell thin walled, with numerous bristle-shaped, simple, radial by-spines of variable length. Pores irregular roundish, five to seven on the radius, two to eight times as broad as the bars. Radial proportion of the three spheres = 1 : 3 : 9. Main spines three-sided pyramidal, as long as the radius.

_Dimensions._--Diameter of the outer shell 0.1 to 0.015, middle 0.035 to 0.05, inner 0.013 to 0.016; cortical pores 0.01 to 0.03, bars 0.003 to 0.004; length of the six spines 0.05 to 0.08, basal breadth 0.012 to 0.015.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface; also fossil in Barbados.

22. _Hexacontium furcatum_, n. sp.

Cortical shell thin walled, covered with numerous thin, bristle-shaped by-spines, which are forked and nearly as long as the main spines. Pores irregular roundish, eight to ten on the radius, two to eight times as broad as the bars. Radial proportion of the three spheres = 1 : 2.5 : 10. Main spines triangular pyramidal, shorter then the radius.

_Dimensions._--Diameter of the outer shell 0.18, middle 0.045, inner 0.018; cortical pores 0.005 to 0.015, bars 0.002; length of the six spines 0.07, basal breadth 0.015.

_Habitat._--North Atlantic, Station 354, surface.

23. _Hexacontium drymodes_, Haeckel.

_Actinomma drymodes_, Haeckel, 1862, Monogr. d. Radiol., p. 442, Taf. xxiv. fig. 9.

Cortical shell thin walled, covered with numerous thin, bristle-shaped spines, which are double forked and half as long as the main spines. Pores irregular roundish, eight to ten on the radius, {199}two to eight times as broad as the bars. Radial proportion of the three spheres = 1 : 2 : 4. Main spines three-sided prismatic, with prominent, often somewhat contorted edges, at the distal end cuspidated; longer than the radius of the outer shell.

_Dimensions._--Diameter of the outer shell 0.15, middle 0.07, inner 0.035; cortical pores 0.01 to 0.03, bars 0.04; length of the six spines 0.11, basal breadth 0.03.

_Habitat._--Mediterranean (Messina), surface; Canary Islands (Lanzerote); Haeckel.

24. _Hexacontium periplectum_, n. sp.

Cortical shell double, enclosing a simple medullary shell. Radial proportion of the three shells = 1 : 4 : 5. Inner cortical shell thick walled, with irregular roundish pores, two to eight times as broad as the bars; five to seven on the radius. Numerous radial spines, arising from it, are connected below their distal ends (at equal distances from the centre) by delicate branched threads, and so form an outer, irregular, thin, cortical shell, with spiny surface. Six main spines three-sided pyramidal, about as long as the radius.

_Dimensions._--Diameter of the outer shell 0.22, middle 0.2, inner 0.045; cortical pores (of both outer shells) 0.01 to 0.03, bars 0.001 to 0.005; length of the spines 0.1, basal breadth 0.02.

_Habitat._--North Pacific, Station 241, surface.

Genus 80. _Hexadendron_,[111] Haeckel, 1881, Prodromus, p. 452.

_Definition._--#Cubosphærida# with three concentric lattice-spheres and six branched spines of equal size.

The genus _Hexadendron_ differs from _Hexacontium_ in the ramification of the six dimensive spines, and from the similar _Hexancistra_ in the duplication of the medullary shell. As in the latter instance, each spine can bear either three simple lateral branches or three rows of pinnate lateral branches.

1. _Hexadendron quadricuspis_, n. sp.

All three shells spherical, with radial proportion = 1 : 2 : 6. Pores of both medullary shells regular circular, twice as broad as the bars. Pores of the cortical shell irregular roundish, four to six times as broad as the bars; surface a little thorny. Six radial spines prismatic, with three prominent wing-like edges, which are prolonged below the distal end in three curved lateral branches. (Differs from _Hexalonche quadricuspis_, Pl. 22, fig. 11, mainly in the double medullary shell.)

_Dimensions._--Diameter of the outer shell 0.15, middle 0.05, inner 0.025; length of the spines 0.12, breadth 0.01.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

{200}2. _Hexadendron bipinnatum_, n. sp. (Pl. 23, fig. 1).

All three shells regular octahedral, with very delicate network of irregular polygonal meshes, and very thin, thread-like bars between them; their radial proportion = 1 : 2.5 : 7.5. Surface of the cortical shell covered with numerous bristle-shaped by-spines, as long as the radius. Six main spines very large, three-sided prismatic, with three rows of pinnate, lateral branches, on the three wing-like, spirally twisted edges (similar to those of _Hexancistra mirabilis_, p. 189, Pl. 23, fig. 3).

_Dimensions._--Diameter of the outer shell 0.12, middle 0.04, inner 0.016.

_Habitat._--Central Pacific, Station 272, surface.

Genus 81. _Hexacontarium_,[112] n. gen.

_Definition._--#Cubosphærida# with three concentric lattice-spheres and six simple spines of different size; one opposite pair larger than the two others.

The genus _Hexacontarium_ exhibits to its ancestral form _Hexacontium_ the same relation that _Hexaloncharium_ bears to _Hexalonche_; the former is developed from the latter by duplication of the medullary shell. As two opposite spines of one pair are larger than the four others, they correspond to the three axes of a quadratic crystal.

1. _Hexacontarium dentatum_, n. sp.

Cortical shell with regular circular, hexagonally framed pores, twice as broad as the bars, with smooth surface. Radial proportion of the three spheres = 1 : 2 : 5. Six radial spines three-sided prismatic, half as broad as the inner medullary shell, with three dentated edges. Two opposite major spines longer than the shell diameter; four other minor spines only half as long as the radius. (Similar to _Hexacontium clavigerum_, Pl. 23, fig. 5, but distinct by the prolongation of the spines of one axis.)

_Dimensions._--Diameter of the outer shell 0.15, middle 0.06, inner 0.03; length of the major spines 0.2, minor 0.04.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

2. _Hexacontarium clavatum_, n. sp.

Cortical shell covered with short conical by-spines and irregular roundish pores, three to four times as broad as the bars. Radial proportion of the three spheres = 1 : 3 : 8. Six radial spines three-sided prismatic, at the distal end club-shaped; two major spines three times as long as the four others, which are equal to the shell radius.

_Dimensions._--Diameter of the outer shell 0.16, middle 0.06, inner 0.02.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

{201}Subfamily HEXACROMYIDA,[113] Haeckel, 1881, Prodromus, pp. 449, 453.

_Definition._--#Cubosphærida# with four concentric spherical lattice-shells.

Genus 82. _Hexacromyum_,[114] Haeckel, 1881, Prodromus, p. 453.

_Definition._--#Cubosphærida# with four concentric lattice-spheres and six simple spines of equal size.

The genus _Hexacromyum_ possesses four concentric, spherical, or octahedral lattice-shells; two inner medullary shells within the central capsule, two outer cortical outside it. The four spheres are connected by six radial beams, which are prolonged outside into simple spines of equal size, opposite in pairs in the three dimensive axes. This genus can be derived from _Hexacontium_ by duplication of the cortical shell.

1. _Hexacromyum elegans_, n. sp. (Pl. 24, fig. 9).

Shell composed of four concentric shells, with radial proportion = 1 : 2.5 : 7.5 : 10. First (innermost) shell with very small circular pores, second shell with larger circular pores. Third shell (inner cortical shell) with large, subregular, circular, hexagonally framed pores (eight to nine on the radius), twice as broad as the bars; from the elevated nodal-points of the hexagonal frames (between every three pores) arise thin bristle-shaped radial beams, which are united at the distal end by vaulted branches forming the delicate fourth shell. Surface smooth. Radial spines three-sided pyramidal, as long as the radius, as broad at the base as the innermost shell.

_Dimensions._--Diameter of the four shells--(A) 0.02, (B) 0.05, (C) 0.15, (D) 0.2; length of the six radial spines 0.1, basal breadth 0.02.

_Habitat._--Central Pacific, Station 271, surface.

2. _Hexacromyum quadrigatum_, n. sp.

Shell composed of four concentric shells, with radial proportion = 1 : 3 : 8 : 10. Structure of all four shells the same, with regular, circular pores, twice to three times as broad as the bars; size of the pores gradually increasing from the innermost to the outermost shell; surface smooth. Radial spines three-sided pyramidal, as long as the radius, half as broad at the base as the innermost shell.

_Dimensions._--Diameter of the four shells--(A) 0.025, (B) 0.08, (C) 0.20, (D) 0.25; length of the spines 0.12, basal breadth 0.012.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

{202}3. _Hexacromyum arachnoides_, n. sp.

_Hexacromidium arachnoides_, Haeckel, 1881, Prodromus, p. 453.

Shell composed of four concentric shells, with radial proportion = 1 : 2 : 3 : 4. Innermost shell with regular, hexagonal meshes; the three other shells with irregular, polygonal meshes; bars between the large meshes in all four shells very thin, cobweb-like. Surface covered with thin bristle-shaped by-spines, as long as the radius. Six radial main spines three-sided prismatic, longer than the diameter of the whole shell.

_Dimensions._--Diameter of the four shells--(A) 0.08, (B) 0.16, (C) 0.24, (D) 0.32; length of the spines 0.4, breadth 0.01.

_Habitat._--South Pacific, Station 300, depth 1375 fathoms.

4. _Hexacromyum octahedrum_, n. sp. (Pl. 23, fig. 2).

Shell composed of four concentric shells which are not spherical (as in the three preceding species), but regular octahedral. Radial proportion = 1 : 2.5 : 6 : 9. Network in all four shells delicate, with irregular polygonal meshes and thin bars; the thickness of the bars and size of the meshes increasing from the innermost to the outermost shell. Six radial spines three-sided prismatic, increasing slowly in breadth towards the distal end, much longer than the shell diameter.

_Dimensions._--Diameter of the four shells--(A) 0.02, (B) 0.05, (C) 0.12, (D) 0.18; length of the radial spines 0.2 to 0.3 and more, breadth 0.01.

_Habitat._--Central Pacific, Station 263, depth 2650 fathoms.

Subfamily HEXACARYIDA,[115] Haeckel, 1881, Prodromus, p. 454.

_Definition._--#Cubosphærida# with five or more concentric lattice-shells.

Genus 83. _Cubosphæra_,[116] n. gen.

_Definition._--#Cubosphærida# with five to six or more concentric lattice-shells and six simple spines of equal size.

The genus _Cubosphæra_ is developed from the preceding _Hexacromyum_ by further addition of the concentric lattice-shells, their number amounting to five, six, or more. The innermost two of these are medullary shells, the others being cortical shells. All are connected by six radial beams, prolonged outside into six simple spines of equal size; these lie opposite in pairs in three dimensive axes, corresponding to the three axes of a cube.

{203}1. _Cubosphæra cubaxonia_, n. sp. (Pl. 24, fig. 8).

_Hexacromyon cubaxonium_, Haeckel, 1881, Prodrom. et Atlas.

Shell composed of five concentric spheres, with the radial proportion = 1 : 3 : 8 : 10 : 13. The two medullary shells with small regular, circular pores of the same breadth as the bars. Inner cortical shell (third shell) with large regular, circular pores, four times as broad as the bars, hexagonally framed. From each hexagon-corner arises a thin bristle-shaped radial by-spine, which at a fixed distance from the centre is united with the middle cortical shell (fourth shell), which has very small circular pores. The beginning of the fifth shell (outermost) is indicated by six small reticula, produced by the six main spines at equal distances from the centre. All five shells are united by six prismatic radial beams, ending outside in pyramidal furrowed spines.

_Dimensions._--Diameter of the five shells--(A) 0.2, (B) 0.15, (C) 0.12, (D) 0.045, (E) 0.015.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

2. _Cubosphæra concentrica_, n. sp.

Shell composed of six concentric spheres, with the radial proportion = 1 : 2 : 6 : 7.5 : 9 : 11. The two medullary shells with regular, circular pores, twice as broad as the bars. The four cortical shells of the same structure, with irregular, roundish pores, three to four times as broad as the bars. The size of these pores and the breadth of their bars gradually increase towards the smooth surface. All six shells are connected by six thin three-sided prismatic radial beams, which are prolonged outside in six stronger spines, angular pyramidal, with smooth edges, as long as the shell radius.

_Dimensions._--Diameter of the six shells--(A) 0.02 (B) 0.04, (C) 0.12, (D) 0.15, (E) 0.18, (F) 0.22.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

Genus 84. _Hexacaryum_,[117] Haeckel, 1881, Prodromus, p. 454.

_Definition._--#Cubosphærida# with five to six or more concentric lattice-shells and six branched spines of equal size.

The genus _Hexacaryum_ is distinguished from the foregoing _Cubosphæra_ by ramification of the six radial spines, and therefore exhibits the same relation to it that _Hexancistra_ bears to _Hexastylus_, &c.

1. _Hexacaryum arborescens_, n. sp. (Pl. 23, figs. 4, 4_a_).

Shell composed of five, six, or more concentric shells, which are united by six very large radial spines. The two medullary shells spherical, inner with regular, circular, outer with irregular polygonal pores. All cortical shells (third and following) not spherical, but regular octahedral, with irregular polygonal meshes and thin bars. Radial spines prismatic, with three wing-like, spirally twisted edges, which at equal distances send out thin forked lateral branches (six on each {204}verticil); by further ramification and communication of these branches the triangular net-plates arise, filling out the sides of the octahedral cortical shells. Diameter of all shells little different. The outer free parts of the six spines are arborescent, twice to three times as long as the enclosed inner parts, and bear six to eight verticils of free lateral branches, decreasing in size towards the distal end (similar to _Arachnosphæra_).

_Dimensions._--Diameter of the six shells--(A) 0.015, (B) 0.04, (C) 0.1, (D) 0.16, (E) 0.22, (F) &c.; average distance of the concentric octahedra = 0.06; length of the radial spines 0.3 to 0.4 and more, breadth 0.02.

_Habitat._--Central Pacific, Station 274, surface.

Subfamily HEXADORIDA,[118] Haeckel, 1881, Prodromus, pp. 449, 455.

_Definition._--#Cubosphærida# with spongy spherical or octahedral shell (with or without enclosed concentrical lattice-shells).

Genus 85. _Cubaxonium_,[119] n. gen.

_Definition._--#Cubosphærida# with solid spongy spherical or octahedral shell, without latticed medullary shell in the centre, and with six simple radial spines of equal size.

The genus _Cubosphæra_ may be regarded as a form of _Styptosphæra_, which develops six radial spines, opposite in pairs in the three dimensive axes. The solid spongy framework of the shell assumes the outer form either of a sphere, or of a regular octahedron.

1. _Cubaxonium spongiosum_, n. sp.

Spongy shell spherical, composed of a very dense spongy framework of nearly uniform structure; the meshes three to four times as broad as the bars; surface almost smooth. Six spines cylindrical, twice to three times as long as the diameter of the spongy sphere, about as broad as one half mesh.

_Dimensions._--Diameter of the sphere 0.2, meshes 0.006 to 0.008, bars 0.002; length of the spines 0.4 to 0.5, breadth 0.004.

_Habitat._--South Pacific, Station 288, surface.

2. _Cubaxonium octahedrum_, n. sp.

Spongy shell octahedral, composed of a loose spongy framework of nearly uniform structure; the meshes ten to twelve times as broad as the bars; surface thorny. Six spines three-sided {205}pyramidal, longer than the diameter of the octahedron, arising from its six corners, as broad at the base as one mesh.

_Dimensions._--Diameter of the shell 0.15, meshes 0.01 to 0.012, bars 0.001; length of the spines 0.2, basal breadth 0.01.

_Habitat._--South Pacific, Station 300, surface.

Genus 86. _Hexadoras_,[120] Haeckel, 1881, Prodromus, p. 455.

_Definition._--#Cubosphærida# with spongy spherical shell and one simple latticed medullary shell in its centre, having six simple spines of equal size.

The genus _Hexadoras_ exhibits the same structure of the spongy shell as _Spongoplegma_, but differs from it in the production of six dimensive spines. In the centre lies one simple, latticed, medullary shell, which is either spherical or octahedral. In the latter case the six spines arise from the six corners of the octahedron.

1. _Hexadoras axophæna_, n. sp.

Medullary shell spherical, with regular hexagonal meshes, twice as broad as the bars. Cortical shell entirely enclosing it, with loose irregular framework and thorny surface. Diameter of the outer shell three times as large as that of the inner. Six radial spines arising from the medullary shell, four to five times as long as the radius of the cortical shell, three-sided prismatic, with straight dentated edges.

_Dimensions._--Diameter of the outer shell 0.15, inner 0.05; length of the spines 0.3 to 0.4.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

2. _Hexadoras lychnosphæra_, n. sp.

Medullary shell spherical, with regular, circular, hexagonally framed pores, three times as broad as the bars. Cortical shell enveloping it, with loose irregular framework and spiny surface. Diameter of the outer shell eight times as large as that of the inner. Six radial spines arising from the inner shell, three-sided prismatic, with dentated, spirally contorted edges, seven times as long as the diameter of the medullary shell, with three lateral branches at the distal end (similar to _Lychnosphæra_, Pl. 11, fig. 1).

_Dimensions._--Diameter of the outer shell 0.5, inner 0.06; total length of the spines 0.4, breadth 0.01.

_Habitat._--Central Pacific, Station 270, depth 2925 fathoms.

3. _Hexadoras octahedrum_, n. sp.

Medullary shell regular octahedral, with irregular polygonal meshes, five times as broad as the bars. Cortical shell enveloping it, with dense spongy framework, also octahedral with rough surface. {206}Diameter of the outer shell five times as large as that of the inner. Six radial spines very long, arising from the six corners of the inner and piercing the spongy mass of the outer shell, considerably exceeding it at the free distal end, three-sided prismatic, with elegantly denticulate edges.

_Dimensions._--Diameter of the outer shell 0.2, inner 0.04; total length of the spines 0.3 or more, breadth 0.02.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

Genus 87. _Hexadoridium_,[121] Haeckel, 1881, Prodromus, p. 455.

_Definition_.--#Cubosphærida# with spongy spherical shell and two concentric latticed medullary shells in its centre, having six simple spines of equal size.

The genus _Hexadoridium_ differs from _Hexadoras_ in the duplication of the medullary shell, and exhibits therefore the same relation to it that _Spongodictyon_ bears to _Spongoplegma_. In the only known species the six spines are opposite, arranged quite regularly in pairs in the three dimensive axes, and consequently represent the three axes of a regular crystal or cube.

1. _Hexadoridium streptacanthum_, n. sp. (Pl. 25, figs. 1, 1_a_).

Both medullary shells spherical, with small regular, circular pores, twice as broad as the bars; outer twice as broad as the inner. Spongy cortical shell enclosing it with dense framework, five times as broad as the outer medullary shell, regular octahedral. Six radial spines, arising from the latter, are thinned at the inner end, three to five times as long as the diameter of the cortical shell, and nearly as broad as the inner medullary shell, with three dentated and spirally contorted edges. (Very similar to the common _Spongosphæra streptacantha_, with irregular and variable number and dispositions of spines; possibly its ancestral form?).

_Dimensions._--Diameter of the cortical shell 0.2, of the outer medullary shell 0.04, inner 0.02; length of the spines 1 mm. and more, breadth 0.02.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

Family X. #ASTROSPHÆRIDA# (Pls. 11, 18-20, 26-30).

_Astrosphærida_, Haeckel, 1881, Prodromus, p. 449.

_Definition._--#Sphæroidea# with numerous (eight to twelve or more, commonly between twenty and sixty) radial spines on the surface of the spherical shell; living solitary (not associated in colonies).

The family #Astrosphærida#, the largest and most varied of all #Sphæroidea#, is distinguished from the other members of this group by the possession of numerous {207}radial spines, which are either regularly or irregularly disposed on the surface of the spherical shell. The extreme variability and richness of form in this family is mainly due to the different size, shape, and disposition of these radial spines.

The simplest Astrosphærida are the Coscinommida, with a single spherical or polyhedral lattice-shell. To this ancestral group all other subfamilies can be opposed as "Astrosphærida composita," since their skeleton is composed of two or more concentric lattice-shells: two in the Haliommida, three in the Actinommida, four in the Cromyommida, five or more in the Caryommida. In these four subfamilies the concentric shells are all simple (not spongy) fenestrated spheres or endospherical polyhedra. In the sixth subfamily, the Spongiommida, the shell is wholly or partially composed of spongy irregular wicker-work, with or without a medullary shell in the centre.

_The Number of the Radial Spines_ in the Astrosphærida is extremely variable, and ranges from eight to forty or more; in many cases more than one hundred. Often each nodal-point of the network develops on the shell surface one spine. Still more frequently the number of the spines is less than that of the nodal-points. In all concentric Astrosphærida, having two or more concentrical shells, we can distinguish "primary spines," as outer prolongations of the inner radial beams connecting the shells, and "secondary spines," developed only on the outer surface of the shell. Naturally the former are of much greater importance than the latter. But we can also often distinguish among the latter larger "main spines" and smaller "by-spines," the latter commonly much more numerous than the former.

_The Disposition of the Radial Spines_, either regular or irregular, is a subject of great morphological interest, and remains to be exhausted by further observations. The following cases of regular disposition have been observed by me--(A) eight spines, opposite in pairs in four axes corresponding to the four diagonal axes of a cube; (B) nine spines, regularly disposed at equal distances (?) (not opposed in pairs); (C) ten spines, disposed at equal distances (?); (D) twelve spines, regularly disposed, corresponding to the twelve corners of the regular icosahedron; (E) fourteen spines, quite regularly disposed (six corresponding to the three axes of a regular octahedron, eight to the central points of its eight faces); (F) sixteen spines, regularly disposed (?); (G) twenty spines (very common!), either disposed in the same manner (after the law of Johannes Müller) as in the ACANTHARIA (?), or corresponding to the twenty corners of the regular or pentagonal dodecahedron, or disposed in the same manner as in many #Larcoidea# (Tholonida, &c., to be described afterwards); (H) twenty-four spines, regularly disposed (?); (I) thirty-two spines, quite regularly disposed (twenty corresponding to the twenty corners of the regular dodecahedron, twelve to the central points of its twelve faces); (K) forty spines, nearly regularly (or quite symmetrically?) disposed. If the number of the spines amounts to more than forty, it is as a rule impossible to determine their regular disposition in a satisfactory manner.

{208}_Synopsis of the Genera of Astrosphærida._

------------------------------------------------------------------------- I. Subfamily Coscinommida. (One single latticed shell.) ------------------------------------------------------------------------- { All spines of the same Spines all simple, not { kind, 88. _Acanthosphæra_. branched and not { tubulous. { Larger main spines and { smaller by-spines, 89. _Heliosphæra_.

Spines hollow conical tubes with porous walls, 90. _Conosphæra_.

Between simple spines the pores prolonged in hollow tubes, 91. _Coscinomma_.

{ Spines with lateral { branches, 92. _Cladococcus_. Spines branched or forked.{ { Spines forked or { dichotomous, 93. _Elaphococcus_. ------------------------------------------------------------------------- II. Subfamily Haliommida. (Two concentric latticed shells.) ------------------------------------------------------------------------- { All spines equal, { simple, 94. _Haliomma_. { A. Elatommida, one { All spines simple, of medullary and one cortical{ two different kinds, 95. _Heliosoma_. shell. { { Spines branched, 96. _Elatomma_.

{ No by-spines, 97. _Leptosphæra_. { B. Diplosphærida, both { Inner by-spines, 98. _Diplosphæra_. shells cortical. { { Outer by-spines, 99. _Drymosphæra_. { { Outer and inner { by-spines, 100. _Astrosphæra_. ------------------------------------------------------------------------- III. Subfamily Actinommida. (Three concentric latticed shells.) ------------------------------------------------------------------------- { All spines equal, 101. _Actinomma_. Radial spines not { branched. { Larger main spines and { smaller by-spines, 102. _Echinomma_.

Radial spines branched or forked, 103. _Pityomma_. ------------------------------------------------------------------------- IV. Subfamily Cromyommida. (Three concentric latticed shells.) ------------------------------------------------------------------------- { All spines equal, 104. _Cromyomma_. Radial spines not { branched. { Larger main spines and { smaller by-spines, 105. _Cromyechinus_.

Radial spines branched or forked, 106. _Cromyodrymus_. ------------------------------------------------------------------------- V. Subfamily Caryommida. (Numerous, five to ten or more, concentric latticed shells.) ------------------------------------------------------------------------- Two medullary shells and three or more cortical shells (lattice work ordinary), 107. _Caryomma_.

{ Triangular meshes, No medullary shells { simple bars, without (lattice work { diagonal bars, 108. _Arachnopila_. arachnoidal); three-sided { prismatic spines, { Triangular meshes, with verticils of three { simple bars; diagonal forked branches. { bars between the 109. _Arachnopegma_. (Arachnosphærida.) { shells, { { Polygonal meshes, bars { branched, 110. _Arachnosphæra_.

------------------------------------------------------------------------- VI. Subfamily Spongiommida. (Spherical shell whole or partly spongy, with or without enclosed latticed medullary shells in the centre.) ------------------------------------------------------------------------- I. Tribe {Spongy {Spines simple, 111. _Spongiomma_. Spongodrymida, { sphere { without { solid. {Spines branched, 112. _Spongodrymus_. latticed { medullary {Spongy {Spines simple, 113. _Spongechinus_. shell. { sphere { { hollow. {Spines branched, 114. _Spongothammus_.

{Framework arising { from the medullary { shell, 115. _Spongopila_. { {Medullary {Framework {No medullary by-spines, II. Tribe { shell { separate { 116. _Rhizoplegma_. Rhizoplegmida, { spherical. { from the { with { { medullary {Medullary by-spines, one single { { shell. { 117. _Lychnosphæra_. latticed { medullary {Medullary {Framework arising shell. { shell a { immediately from { simple { the medullary { cube. { shell, 118. _Centrocubus_. { { { {Framework separate { { from the medullary { { shell, 119. _Octodendron_.

{Framework arising III. Tribe Rhizosphærida, { from the medullary with two concentric { shell, 120. _Spongosphæra_. latticed medullary shells. { {Framework separate { from the medullary { shell, 121. _Rhizosphæra_.

Subfamily COSCINOMMIDA, Haeckel.

_Heliosphærida_, Haeckel, 1881, Prodromus, pp. 449, 450.

_Definition._--#Astrosphærida# with one single spherical lattice-shell.

Genus 88. _Acanthosphæra_,[122] Ehrenberg, 1858, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 12.

_Definition._--#Astrosphærida# with one simple lattice-sphere, covered with simple radial spines of the same kind.

The genus _Acanthosphæra_ exhibits the most simple form of all _Astrosphærida_; a simple spherical lattice-shell, the surface of which is covered by radial spines of one and the same kind. The number of the latter is very variable, often twelve to twenty, regularly disposed; in other cases forty to sixty or more; and sometimes at each nodal-point of the network a spine is developed.

{210}Subgenus 1. _Rhaphidococcus_, Haeckel, 1862, Monogr. d. Radiol., p. 365 (_sensu emendato_).

_Definition._--Pores of the spherical shell regular or subregular, all of nearly equal size and similar form. Radial spines arising from all the nodal-points of the network.

1. _Acanthosphæra tenuissima_, Haeckel.

_Heliosphæra tenuissima_, Haeckel, 1862, Monogr. d. Radiol., p. 351, Taf. ix. fig. 2.

Shell extremely thin walled, eight to ten times as broad as one pore. Meshes or pores regular, hexagonal, with thread-like bars; five to seven on the radius. At each nodal-point (between every three meshes) arises a bristle-shaped radial spine, as long as the diameter of one pore.

_Dimensions._--Diameter of the shell 0.2 to 0.25, of the meshes or pores 0.025 to 0.03, bars below 0.0001; length of the spines 0.03.

_Habitat._--Mediterranean (Messina), North Atlantic (Canary Islands).

2. _Acanthosphæra tenuis_, n. sp.

Shell very thin walled, about twenty times as broad as one pore. Meshes subregular, hexagonal, with thread-like bars; twelve to fourteen on the radius. At each nodal-point arises a bristle-shaped radial spine, about as long as the radius.

_Dimensions._--Diameter of the shell 0.3 to 0.35, pores 0.015 to 0.018, bars below 0.001; length of the spines 0.12 to 0.16.

_Habitat._--Central Pacific, Stations 266 to 274, depth 2350 to 2925 fathoms.

3. _Acanthosphæra macropora_, n. sp.

Shell thin walled, five to six times as broad as one mesh. Pores regular, circular, hexagonally framed, ten to twelve times as broad as the bars. Radial spines bristle-shaped, as long as the diameter of one pore, arising from all the nodal-points.

_Dimensions._--Diameter of the shell 0.07 to 0.08, pores 0.012, bars 0.001; length of the spines 0.012.

_Habitat._--Central Pacific, Station 271, surface.

4. _Acanthosphæra micropora_, n. sp.

Shell thick walled, forty to fifty times as broad as one pore. Pores regular, circular, hexagonally framed, half as broad as the bars. Radial spines bristle-shaped, as long as the radius of the shell, arising from all the nodal-points.

_Dimensions._--Diameter of the shell 0.22, pores 0.003, bars 0.006; length of the spines 0.1.

_Habitat._--South Pacific, Station 288, surface.

{211}5. _Acanthosphæra dentata_, Haeckel.

_Cladococcus dentatus_, Haeckel, 1862, Monogr. d. Radiol., p. 367, Taf. xiii. fig. 10.

Shell thin walled, eight to ten times as broad as one pore. Pores regular, circular, hexagonally framed, three times as broad as the bars. Radial spines arising from all the nodal-points of the network, three-sided prismatic, with dentated or serrated edges, longer than the shell diameter.

_Dimensions._--Diameter of the shell 0.08, pores 0.01, bars 0.003; length of the spines 0.1, breadth 0.003.

_Habitat._--Mediterranean (Messina), surface.

6. _Acanthosphæra acufera_, Haeckel.

_Rhaphidococcus acufer_, Haeckel, 1862, Monogr. d. Radiol., p. 366, Taf. xiv. fig. 1.

_Cladococcus acufer_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 800.

Shell thin walled, eight to ten times as broad as one mesh. Pores regular, circular, three times as broad as the bars. Radial spines bristle-shaped, arising with thicker conical bases from all the nodal-points, about as long as the diameter of the shell.

_Dimensions._--Diameter of the shell 0.08, pores 0.01, bars 0.003; length of the spines 0.08.

_Habitat._--Mediterranean (Messina); North Atlantic, Station 354, surface.

7. _Acanthosphæra castanea_, n. sp. (Pl. 26, fig. 3).

Shell thick walled, thirty times as broad as one mesh. Pores regular, circular, nearly of the same breadth as the bars. Radial spines bristle-shaped, arising with thicker conical bases from all the nodal-points, scarcely half as long as the radius of the shell.

_Dimensions._--Diameter of the shell 0.15, pores and bars 0.005; length of the spines 0.03.

_Habitat._--North Pacific, Station 244, surface.

8. _Acanthosphæra flosculenta_, n. sp.

Shell thick walled, thirteen times as broad as one mesh. Pores regular, circular, three times as broad as the bars, with an elegant six-lobed frame (Pl. 28, fig. 1_b_). In the intervals between the six lobes of each mesh arise six conical radial spines (half as long as the radius), six around each pore. (Differs from the similar _Haliomma flosculentum_, Pl. 28, fig. 1, in the absence of an enclosed medullary shell and the stronger development of the spines.)

_Dimensions._--Diameter of the shell 0.13, pores 0.01, bars 0.003; length of the spines 0.03.

_Habitat._--Indian Ocean, Cocos Islands, surface, Rabbe.

Subgenus 2. _Rhaphidocapsa_, Haeckel.

_Definition._--Pores of the spherical shell regular or subregular, all of nearly equal size and similar form. Radial spines scattered at some distance apart, not at all the nodal-points.

{212}9. _Acanthosphæra insignis_, Haeckel.

_Heliosphæra insignis_, R. Hertwig, 1879, Organismus der Radiol., p. 40, Taf. v. fig. 7.

Shell thin walled, about ten times as broad as one mesh. Pores regular, hexagonal, ten to twelve times as broad as the bars. Radial spines about one hundred and twenty, arising from certain nodal-points of the network, being as long as the diameter of the sphere, three-sided prismatic, with three thin denticulated edges.

_Dimensions._--Diameter of the shell 0.2, pores 0.02, bars 0.002; length of the spines 0.18, breadth 0.003.

_Habitat._--Cosmopolitan; Mediterranean (Messina), Atlantic (Stations 325, 347), Indian (Ceylon), Pacific (Stations 270 to 274), surface.

10. _Acanthosphæra fortispina_, n. sp.

Shell thin walled, about six times as broad as one mesh. Pores subregular, hexagonal, with thread-like bars; three to four on the radius. Radial spines about twenty, three-sided pyramidal, as long as the diameter, and one-third as broad at the base as one pore.

_Dimensions._--Diameter of the shell 0.06 to 0.09, pores 0.01 to 0.014, bars below 0.001; length of the spines 0.07 to 0.08, basal breadth 0.03 to 0.04.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

11. _Acanthosphæra mucronata_, n. sp. (Pl. 26, fig. 7).

Shell thick walled, fifteen times as broad as one pore. Pores regular, circular, hexagonally framed, funnel-shaped, three times as broad as the bars. Radial spines twenty to thirty, dagger-shaped or spindle-shaped, angular, twice as broad in the middle as one pore, about as long as the radius.

_Dimensions._--Diameter of the shell 0.11, pores 0.0075, bars 0.0025; length of the spines 0.06, breadth 0.015.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

12. _Acanthosphæra clavata_, n. sp. (Pl. 26, fig. 8).

Shell thick walled, ten to twelve times as broad as one mesh. Pores subregular, circular, three times as broad as the bars. Radial spines twenty, club-shaped, angular, with prominent edges, twice as broad at the distal end as one pore, about as long as the radius.

_Dimensions._--Diameter of the shell 0.11, pores 0.01, bars 0.003; length of the spines 0.06, breadth 0.02.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

13. _Acanthosphæra marginata_, n. sp.

Shell thick walled, twelve times as broad as one mesh. Pores regular, circular double-edged, four times as broad as the bars. Radial spines conical, fourteen in number, about as long as the {213}radius, and as broad at the base as one mesh. Six spines correspond to the six corners of a regular octahedron, eight to the centre of the eight faces.

_Dimensions._--Diameter of the shell 0.1, pores 0.008, bars 0.002; radial spines 0.06, basal breadth 0.01.

_Habitat._--Central Pacific, Station 274, surface.

14. _Acanthosphæra florida_, n. sp.

Shell thick walled, fifteen times as broad as one mesh. Pores regular, circular, hexagonally lobed, separated by prominent funnel-shaped crests of half the breadth. Twenty conical radial spines, half as long as the radius, as broad at the base as one funnel.

_Dimensions._--Diameter of the shell 0.15, pores 0.01, bars 0.005; length of the spines 0.04, basal breadth 0.02.

_Habitat._--South Atlantic, Station 325, depth 2650 fathoms.

15. _Acanthosphæra enneacantha_, n. sp.

Shell thin walled, fourteen times as broad as one mesh. Pores regular, circular, twice as broad as the bars. Nine radial spines, regularly disposed, as long as the shell diameter, three-sided prismatic, with pyramidal apex, as broad as one mesh.

_Dimensions._--Diameter of the shell 0.14, pores 0.01, bars 0.005; length of the spines 0.15, breadth 0.01.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

16. _Acanthosphæra octahedralis_, n. sp.

Shell thick walled, octahedral, fourteen times as broad as one mesh. Pores regular, circular, three times as broad as the bars. Fourteen radial spines, regularly disposed, conical, as long as the radius of the shell, twice as broad at the base as one mesh. Six spines correspond to the six corners of a regular octahedron, eight to the central points of its eight faces.

_Dimensions._--Diameter of the shell 0.14, pores 0.01, bars 0.003; length of the spines 0.08, basal breadth 0.02.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

17. _Acanthosphæra compacta_, n. sp.

Shell thick walled, about sixty times as broad as one mesh. Pores regular, circular, twice as broad as the bars. Thirty to forty radial spines, three-sided pyramidal, scarcely half as long as the radius, five to six times as broad at the base as one pore.

_Dimensions._--Diameter of the shell 0.24, pores 0.004, bars 0.002; length of the radial spines 0.05, basal breadth 0.02.

_Habitat._--Fossil in Barbados.

{214}Subgenus 3. _Raphidodrymus_, Haeckel.

_Definition._--Pores of the spherical shell irregular, of different size or form. Radial spines arising from all the nodal-points of the network.

18. _Acanthosphæra capillaris_, n. sp.

Shell thin walled, with irregular polygonal meshes, twelve to twenty times as broad as the bars; eight to ten on the radius. Radial spines bristle-shaped, arising from all the nodal-points of the network, about as long as the diameter of the largest meshes.

_Dimensions._--Diameter of the shell 0.15 to 0.2, pores 0.012 to 0.02, bars 0.001; length of the spines 0.02.

_Habitat._--Central Pacific, Stations 260 to 274, surface.

19. _Acanthosphæra arctica_, n. sp.

Shell thin walled, with irregular roundish, polygonally framed meshes, three to four times as broad as the bars. Radial spines arising from all the nodal-points of the network, pyramidal at the base; in the distal half bristle-shaped, as long as the radius.

_Dimensions._--Diameter of the shell 0.12, pores 0.006 to 0.008, bars 0.002; length of the spines 0.07.

_Habitat._--Arctic Ocean, Greenland (in the stomach of _Periphylla hyacinthina_).

20. _Acanthosphæra antarctica_, n. sp.

Shell thick walled, with irregular, roundish pores, about as broad as the bars. Radial spines arising from all nodal-points of the network, conical at the base, half as long as the radius.

_Dimensions._--Diameter of the shell 0.15, pores and bars 0.005 to 0.008; length of the spines 0.04.

_Habitat._--Antarctic Ocean, Station 157, depth 1950 fathoms.

Subgenus 4. _Rhaphidosphæra_, Haeckel, 1881, Prodromus, p. 450.

_Definition._--Pores of the spherical shell irregular, of different size or form. Radial spines scattered at intervals, not at all the nodal-points.

21. _Acanthosphæra echinoides_, Haeckel.

_Cyrtidosphæra echinoides_, Haeckel, 1865, Zeitschr. f. wiss. Zool., xv. p. 367, Taf. xxvi. fig. 5.

Shell thin walled, with irregular polygonal or more roundish pores of very different size. Forty to fifty very large meshes, separated by rows of much smaller meshes. Radial spines forty to sixty, half as long as the shell radius, bristle-shaped, with conical bases.

{215}_Dimensions._--Diameter of the shell 0.13, larger pores 0.03, smaller 0.003; length of the spines 0.03.

_Habitat._--Mediterranean (Nice), surface.

22. _Acanthosphæra longispina_, n. sp.

Shell thin walled, with irregular polygonal meshes, four to six times as broad as the bars; six to eight on the radius. Thirty to forty radial spines, three-sided prismatic, twice as broad as the bars, twice to three times as long as the diameter of the shell.

_Dimensions._--Diameter of the shell 0.12 to 0.15, pores 0.012 to 0.02, bars 0.003; length of the radial spines 0.2 to 0.4, breadth 0.006.

_Habitat._--North Pacific, Station 253, surface.

23. _Acanthosphæra brevispina_, n. sp.

Shell thick walled, with irregular polygonal meshes, twice to four times as broad as the bars; twelve to sixteen on the radius. Sixty to eighty radial spines, pyramidal, half as long as the radius of the shell, one-fourth as broad at the base.

_Dimensions._--Diameter of the shell 0.2 to 0.22, pores 0.006 to 0.012, bars 0.003; length of the spines 0.05, basal breadth 0.02.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

24. _Acanthosphæra acanthica_, Haeckel.

_Cenosphæra acanthica_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 86, Taf. i. fig. 3.

Shell thick walled, with irregular, roundish pores, twice to three times as broad as the bars; seven to nine on the radius. Ten to twenty radial spines pyramidal, shorter than the radius, twice as broad at the base as one mesh.

_Dimensions._--Diameter of the shell 0.12 to 0.16, pores 0.006 to 0.009, bars 0.003; length of the spines 0.04 to 0.06, basal breadth 0.01 to 0.015.

_Habitat._--Fossil in Tertiary rocks of Sicily and Barbados.

25. _Acanthosphæra haliphormis_, Ehrenberg.

_Acanthosphæra haliphormis_, Ehrenberg, 1861, Abhandl. d. k. Akad. d. Wiss. Berlin, 1872, Taf. ii. fig. 1.

Shell thick walled, with irregular, roundish pores, twice to four times as broad as the bars; four to five on the radius. Twelve to twenty radial spines pyramidal, longer than the radius, scarcely as broad as one mesh at the base.

_Dimensions._--Diameter of the shell 0.11, pores 0.01 to 0.02, bars 0.005; length of the spines 0.06 to 0.08, basal breadth 0.01.

_Habitat._--Arctic Ocean, near Greenland, depth 1000 fathoms.

{216}26. _Acanthosphæra angulata_, n. sp. (Pl. 26, fig. 4).

Shell thin walled; its pores irregular, roundish, with angular, double-edged margin, two to four times as broad as the bars; six to eight on the radius. Twenty to thirty radial spines pyramidal, angular, with prominent edges, shorter than the radius, as broad at the base as one small mesh.

_Dimensions._--Diameter of the shell 0.2, pores 0.02 to 0.04, bars 0.01; length of the spines 0.06, basal breadth 0.02.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

27. _Acanthosphæra conifera_, n. sp.

Shell thick walled, with irregular, roundish pores, twice to five times as broad as the bars; ten to twelve on the radius. Twenty radial spines conical, regularly disposed, half as long as the radius, as broad at the base as one of the largest meshes.

_Dimensions._--Diameter of the shell 0.2, pores 0.008 to 0.02, bars 0.004; length of the spines 0.05, basal breadth 0.02.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

28. _Acanthosphæra maxima_, n. sp.

Shell thick walled, with irregular, roundish pores, twice to eight times as broad as the bars; twelve to twenty on the radius. Radial spines very numerous (two to three hundred), short, conical, scarcely as long as the diameter of the largest meshes, and one-third as broad.

_Dimensions._--Diameter of the shell 0.3 to 0.4, pores 0.008 to 0.03, bars 0.004; length of the radial spines 0.03, basal breadth 0.01.

_Habitat._--Tropical Atlantic, Station 348, depth 2450 fathoms.

29. _Acanthosphæra simplex_, Haeckel.

_Rhaphidococcus simplex_, Haeckel, Monogr. d. Radiol., 1862, p. 366, figs. 5, 6.Taf. xiii.

_Cladococcus simplex_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 800.

Shell thick walled, with irregular, roundish pores, three to six times as broad as the bars; eight to nine on the radius. Forty to sixty radial spines, about as long as the diameter of the shell, three-sided prismatic, not straight, but more or less bent.

_Dimensions._--Diameter of the shell 0.12, pores 0.005 to 0.012, bars 0.0015 to 0.02; length of the spines 0.12, breadth 0.003.

_Habitat._--Mediterranean (Messina), surface, Haeckel.

30. _Acanthosphæra gibbosa_, n. sp.

Shell thin walled, rugged or tuberculate, covered by about twenty hill-shaped tubercles or protuberances with flat valleys between them. Network very delicate, with thread-like bars and {217}irregular, polygonal pores; twenty to thirty on the radius. Radial spines very numerous, bristle-shaped, twice to three times as long as the diameter of the pores.

_Dimensions._--Diameter of the shell 0.3, pores 0.01 to 0.02; length of the spines 0.02 to 0.05.

_Habitat._--Central Pacific, Station 274, surface.

31. _Acanthosphæra reticulata_, n. sp. (Pl. 26, fig. 5).

_Rhaphidosphæra reticulata_, Haeckel, 1881, Prodromus.

Shell thick walled, with irregular, roundish pores, twice to four times as broad as the bars; six to eight on the radius. Surface of the bars covered with a peculiar delicate network of very fine crests. Twenty to forty radial spines, angular, pyramidal, scarcely one-third as long as the radius of the shell, as broad at the base as the bars.

_Dimensions._--Diameter of the shell 0.22, pores 0.02 to 0.04, bars 0.01; length of the spines 0.04, basal breadth 0.01.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

Genus 89. _Heliosphæra_,[123] Haeckel, 1862, Monogr. d. Radiol., p. 350 (_sensu emendato_).

_Definition._--#Astrosphærida# with one simple lattice-sphere, covered with simple radial spines of two different kinds: larger main spines and smaller by-spines.

The genus _Heliosphæra_ (in the mended definition here employed) differs from the foregoing _Acanthosphæra_ in the possession of two different kinds of radial spines: larger main spines scattered on the surface or disposed regularly in limited numbers (twelve to twenty, sometimes forty to fifty or more), and smaller by-spines in much larger numbers, arising from all the nodal-points of the network (or sometimes also from its bars).

Subgenus 1. _Heliosphærella_, Haeckel.

_Definition._--Pores of the shell regular or subregular, all of nearly equal size and similar form.

1. _Heliosphæra hexagonaria_, n. sp. (Pl. 26, fig. 2).

Shell very thin walled, about twenty times as broad as one pore. Meshes or pores subregular, hexagonal, with thread-like bars; fifteen to seventeen on the radius. Radial spines at the nodal-points of the network; about forty main spines three-sided pyramidal, half as broad at the base as one pore, and twice as long as the bristle-shaped by-spines, which are very numerous, and as long as the diameter of one pore.

{218}_Dimensions._--Diameter of the shell 0.25 to 0.3, of the meshes or pores 0.012 to 0.015, bars below 0.001; length of the main spines 0.03, basal breadth 0.007.

_Habitat._--Central Pacific, Stations 272 to 274, depth 2350 to 2750 fathoms.

2. _Heliosphæra actinota_, Haeckel.

_Heliosphæra actinota_, Haeckel, 1862, Monogr. d. Radiol., p. 352, Taf. ix. fig. 3.

Shell very thin walled, about ten times as broad as one mesh. Pores regular, hexagonal, with thread-like bars; six to eight on the radius. Radial spines at the nodal-points of the network, bristle-shaped, scarcely broader than the bars; about twenty main spines as long as the diameter of the shell, and numerous by-spines, only one-third to one-half as long as the former.

_Dimensions._--Diameter of the shell 0.2 to 0.25, of the meshes 0.02 to 0.03, bars below 0.001; length of the main spines 0.2 to 0.3.

_Habitat._--Mediterranean (Messina), Atlantic (Canaries, Azores), surface.

3. _Heliosphæra echinoides_, Haeckel.

_Heliosphæra echinoides_, Haeckel, 1862, Monogr. d. Radiol., p. 352, Taf. ix. fig. 4.

Shell thin walled, about six times as broad as one mesh. Pores regular, hexagonal, eight times as broad as the bars. Radial spines arising, not from the nodal-points of the network, but from the midst of the bars (very rare disposition!); twenty main spines regularly disposed, as long as the radius, four times as long as the numerous by-spines; all spines bristle-shaped, of the same breadth as the bars.

_Dimensions._--Diameter of the shell 0.09, pores 0.015, bars 0.002; length of the main spines 0.04.

_Habitat._--Mediterranean (Messina), surface, Haeckel.

4. _Heliosphæra elegans_, Haeckel.

_Heliosphæra elegans_, Haeckel, 1862, Monogr. d. Radiol., p. 353, Taf. ix. fig. 5.

Shell very thin walled, about ten times as broad as one mesh. Pores regular, hexagonal, with thread-like bars, which are crossed by tangential bars, so that each side of a hexagon exhibits a regular rectangular cross (exactly the same as in Pl. 19, fig. 5). All radial spines bristle-shaped, as thin as the bars, and arising from the nodal-points; twenty main spines as long as the radius, numerous by-spines scarcely one-sixth as long.

_Dimensions._--Diameter of the shell 0.26, pores 0.026, bars below 0.001; length of the main spines 0.13.

_Habitat._--Mediterranean (Messina), surface, Haeckel.

5. _Heliosphæra pectinata_, n. sp. (Pl. 26, fig. 9).

_Acanthosphæra pectinata_, Haeckel, 1881, Atlas.

Shell thick walled, combed, about fourteen times as broad as one mesh. Pores subregular, circular, with elevated hexagonal frames, three times as broad as the bars. Radial spines very {219}numerous and stout; thirty to forty main spines, three-sided pyramidal, nearly as long as the radius, as broad as one mesh; by-spines small, conical, everywhere scattered at the nodal-points of the network and on the high combs of the bars.

_Dimensions._--Diameter of the shell 0.16, pores 0.012, bars 0.004; length of the main spines 0.07, basal breadth 0.016.

_Habitat._--West Tropical Pacific, Station 225, depth 4475 fathoms.

6. _Heliosphæra coronata_, n. sp. (Pl. 26, figs. 6, 6_a_).

_Acanthosphæra coronata_, Haeckel, 1881, Atlas.

Shell thick walled, about ten times as broad as one mesh. Pores regular, circular, five times as broad as the bars; each pore surrounded by a regular coronal of six short, conical by-spines (fig. 6_a_); twenty to thirty main spines, also conical, half as long as the radius, as broad as one pore.

_Dimensions._--Diameter of the shell 0.15, pores 0.015, bars 0.003; length of the main spines 0.04, basal breadth 0.015.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

7. _Heliosphæra floribunda_, n. sp.

Shell thick walled about ten times as broad as one mesh. Pores regular, six-lobed, twice as broad as the bars; each pore surrounded by six small conical by-spines (as in Pl. 28, figs. 1, 1_b_); twenty main spines regularly disposed cylindro-conical, as long as the diameter of the shell or longer.

_Dimensions._--Diameter of the shell 0.15, pores 0.015, bars 0.008; length of the main spines 0.16, breadth 0.008.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

8. _Heliosphæra cristata_, n. sp.

Shell thick walled, about twelve times as broad as one mesh. Pores subregular, circular, twice as broad as the bars; each pore surrounded by an elegant coronal of ten to twenty small, conical by-spines; twenty main spines regularly disposed, conical, only one-third as long as the radius, as broad at the base as one mesh.

_Dimensions._--Diameter of the shell 0.25, pores 0.02, bars 0.01; length of the main spines 0.04, basal breadth 0.02.

_Habitat._--South Pacific, Station 285, depth 2375 fathoms.

9. _Heliosphæra castanella_, n. sp.

Shell thick walled, about twenty times as broad as one mesh. Pores regular, circular, of the same breadth as the bars. Whole surface densely covered with innumerable bristle-shaped by-spines, half as long as the radius; fifty to eighty main spines, conical, nearly as long as the diameter, {220}twice as broad at the base as one pore. (Very similar to some species of Castanella, Pl. 113, but without the osculum characteristic of this Phæodarian; may be easily confounded with it.)

_Dimensions._--Diameter of the shell 0.3, pores 0.015, bars 0.015; length of the main spines 0.25, basal breadth 0.03.

_Habitat._--North Pacific (Japan), Station 234, surface.

Subgenus 2. _Heliosphæromma_, Haeckel.

_Definition._--Pores of the shell irregular, of different size or form.

10. _Heliosphæra polygonaria_, n. sp.

Shell very thin walled, with thread-like bars and irregular, polygonal pores (having four to eight angles, commonly five to seven); eight to ten on the radius. Radial spines at all the nodal-points of the network, bristle-shaped; forty to sixty main spines, as long as the radius, twice as thick as the numerous by-spines, which are not larger than one mesh.

_Dimensions._--Diameter of the shell 0.15 to 0.2, pores 0.012 to 0.02, bars 0.001; length of the main spines 0.08 to 0.1.

_Habitat._--Central Pacific, Stations 266 to 272, surface.

11. _Heliosphæra heteracantha_, n. sp.

Shell thin walled, with irregular, polygonal pores, twice to four times as broad as the bars; six to eight on the radius. Twenty radial main spines, three-sided pyramidal, nearly as long as the diameter of the shell, as broad as a larger mesh; innumerable bristle-shaped by-spines variously distributed on the bars and at the nodal-points of the net; half as long as the radius.

_Dimensions._--Diameter of the shell 0.12, pores 0.006 to 0.012, bars 0.003; length of the main spines 0.1, basal breadth 0.012.

_Habitat._--Equatorial Atlantic, Station 347, surface.

12. _Heliosphæra hyperionis_, n. sp.

Shell thick walled. Pores irregular, roundish, with polygonal frames, three to six times as broad as the bars; twelve to fourteen on the radius. Thirty to forty main spines, angular, pyramidal, scarcely as long as the radius and twice as long as the numerous bristle-shaped by-spines.

_Dimensions._--Diameter of the shell 0.24, pores 0.006 to 0.012, bars 0.002; length of the main spines 0.1, basal breadth 0.012.

_Habitat._--North Pacific, Station 256, surface.

13. _Heliosphæra elector_, n. sp.

Shell thick walled, with irregular, roundish pores, twice to three times as broad as the bars; eight to ten on the radius. Twenty main spines, three-sided pyramidal, somewhat longer than the radius and four times as long as the short bristle-shaped by-spines.

{221}_Dimensions._--Diameter of the shell 0.12, pores 0.005 to 0.01, bars 0.003; length of the main spines 0.08, basal breadth 0.01.

_Habitat._--South Atlantic, Station 325, surface.

14. _Heliosphæra solaris_, n. sp.

Shell thick walled, with irregular, roundish pores, about the same breadth as the bars; six to eight on the radius. Fifty to eighty main spines, conical, as long as the radius; by-spines very numerous, also conical, but only as large as one pore.

_Dimensions._--Diameter of the shell 0.15, pores and bars 0.006 to 0.008; length of the main spines 0.08, basal breadth 0.012.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

Genus 90. _Conosphæra_,[124] Haeckel, 1881, Prodromus, p. 451.

_Definition._--#Astrosphærida# with one simple latticed sphere, covered with radial spines having the form of hollow cones with porous walls.

The genus _Conosphæra_ differs from _Acanthosphæra_ in the peculiar formation of the radial spines, which are not simple solid sticks, but hollow cones with porous walls, as immediate elevations of the hollow sphere.

1. _Conosphæra platyconus_, n. sp.

Pores of the shell regular, circular, twice as broad as the bars; ten to twelve on the radius. Conical spines about sixty, regular, broader than they are high, with six to nine pores in the wall.

_Dimensions._--Diameter of the shell 0.16, pores 0.008, bars 0.004; length of the spines 0.012, basal breadth 0.024.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

2. _Conosphæra orthoconus_, n. sp. (Pl. 12, fig. 2).

Pores of the shell irregular, roundish, twice to three times as broad as the bars; fourteen to sixteen on the radius. Conical spines about forty, regular, higher than they are broad, as long as the radius, with sixteen to twenty pores in the wall.

_Dimensions._--Diameter of the shell 0.2, pores 0.008 to 0.012, bars 0.004; length of the spines 0.05, basal breadth 0.03.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

{222}3. _Conosphæra plagioconus_, n. sp. (Pl. 12, fig. 4).

Pores of the shell irregular, polygonal, twice to five times as broad as the bars; twenty to twenty-four on the radius. Conical spines about eighty, irregularly formed and scattered, with oblique (not radial) axes; about as high as broad, with eight to twelve pores in the wall.

_Dimensions._--Diameter of the shell 0.25, pores 0.005 to 0.015, bars 0.003; length of the spines 0.02, basal breadth 0.02.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

Genus 91. _Coscinomma_,[125] n. gen.

_Definition._--#Astrosphærida# with one simple lattice-sphere, covered with simple radial spines; the pores between them prolonged into hollow, conical, or cylindrical tubuli.

The genus _Coscinomma_ exhibits among the Astrosphærida the same peculiar formation that distinguishes _Ethmosphæra_ and _Sethosphæra_ among the Liosphærida; each pore of the simple shell is prolonged into a short conical or cylindrical tubulus, as a rule either on the outside or on the inside of the shell, but sometimes on both sides.

Subgenus 1. _Coscinommarium_, Haeckel.

_Definition._--Pores prolonged into short tubes both on the inside as well as the outside of the shell.

1. _Coscinomma amphisiphon_, Haeckel (Pl. 26, figs. 1, 1_a_, 1_b_).

Pores regular, circular, hexagonally framed, twice as broad as the bars, prolonged on the inside as well as on the outside of the shell into a short truncated conical tube; fifteen to eighteen pores on the radius. In each hexagon-corner arises a bristle-shaped radial spine, half as long as the radius.

_Dimensions._--Diameter of the shell 0.22, pores 0.01, bars 0.005; length of the spines 0.1.

_Habitat._--Central Pacific, Station 271, surface.

Subgenus 2. _Coscinommidium_, Haeckel.

_Definition._--Pores prolonged into external tubes on the outside of the shell.

2. _Coscinomma ectosiphon_, n. sp.

Pores regular, circular, hexagonally framed, twice as broad as the bars, prolonged on the outside of the shell into a short truncated conical tube; ten to twelve pores on the radius. In each {223}hexagon-corner arises a short bristle-shaped spine, twice as long as the tube, one-third as long as the radius. (Very similar to _Ethmosphæra conulosa_, Pl. 12, fig. 5, but differs in the possession of radial spines.)

_Dimensions._--Diameter of the shell 0.2, pores 0.012, bars 0.006; length of the spines 0.04, of the tubes 0.02.

_Habitat._--North Pacific, Station 253, surface.

3. _Coscinomma macrosiphon_, n. sp.

Pores regular, circular, without hexagonal frames, of the same breadth as the bars, prolonged on the outside of the shell into a long cylindrical tube, half as long as the radius (eight to nine pores on the radius); between them bristle-shaped, at the base conical, radial spines of double length.

_Dimensions._--Diameter of the shell 0.16, pores and bars 0.008; length of the spines 0.08, of the tubes 0.04.

_Habitat._--Central Pacific, Station 274, surface.

Subgenus 3. _Coscinommonium_, Haeckel.

_Definition._--Pores prolonged into internal tubes on the inside of the shell.

4. _Coscinomma endosiphon_, n. sp.

Pores regular, circular, hexagonally framed, twice as broad as the bars (fourteen to sixteen on the radius), prolonged on the inside of the shell into a short truncated cylindrical tube. In each hexagon-corner arises a thin, bristle-shaped, radial spine with pyramidal base, half as long as the radius, twice as long as the tube.

_Dimensions._--Diameter of the shell 0.25, pores 0.012, bars 0.006; length of the spines 0.066, of the tubes 0.03.

_Habitat._--South Pacific, Station 288, surface.

Genus 92. _Cladococcus_,[126] J. Müller, 1856, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 485.

_Definition._--#Astrosphærida# with one simple lattice-sphere, covered with branched radial spines (the stem of the spine never forked).

The genus _Cladococcus_, together with the following _Elaphococcus_, is distinguished from the other _Coscinommida_ by the ramification of the radial spines covering the surface of the simple hollow lattice-sphere. In _Cladococcus_ each spine sends out three or more lateral branches, which are either simple or again ramified; but the stem of the spine itself is not forked, as in _Elaphococcus_.

{224}Subgenus 1. _Cladococcalis_, Haeckel.

_Definition._--Branches of the spines simple, not ramified. Pores regular, all of nearly equal size and similar form.

1. _Cladococcus arborescens_, J. Müller.

_Cladococcus arborescens_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 31, Taf. i. fig. 2.

Pores of the spherical shell regular, hexagonal, three times as broad as the bars; three to four on the radius. Ten to twenty spines, three-sided prismatic, two to three times as long as the shell diameter; towards the distal end each spine with three branches (one lateral simple straight branch on each edge of the spine).

_Dimensions._--Diameter of the shell 0.1, pores 0.012, bars 0.004; length of the spines 0.2 to 0.3, breadth 0.02.

_Habitat._--Mediterranean (Nice); North Atlantic, Canary Islands, surface.

2. _Cladococcus spinifer_, Haeckel.

_Cladococcus spinifer_, Haeckel, 1862, Monogr. d. Radiol., p. 368, Taf. xiii. fig. 9.

Pores regular, circular, hexagonally framed, three times as broad as the bars; five to six on the radius. Radial spines, arising from all the nodal-points of the network, three-sided, longer than the shell diameter, with six to twelve simple verticillate branches (two to four branches on each edge).

_Dimensions._--Diameter of the shell 0.08, pores 0.01, bars 0.003; length of the spines 0.1, breadth 0.03.

_Habitat._--Mediterranean (Messina), surface.

3. _Cladococcus penicillus_, n. sp.

Pores subregular, hexagonal, twice as broad as the bars; eight to ten on the radius. Sixty to eighty radial spines, three-sided prismatic, pencil-shaped, longer than the shell diameter; each at the distal end with a brush or pencil composed of nine to twenty-one short, simple, curved branches (three to seven on each edge).

_Dimensions._--Diameter of the shell 0.1, pores 0.006, bars 0.003; length of the spines 0.12 to 0.16, breadth 0.006.

_Habitat._--Central Pacific, Station 271, surface.

Subgenus 2. _Cladococcinus_, Haeckel.

_Definition._--Branches of the spines simple, not ramified. Pores irregular, of different size or form.

{225}4. _Cladococcus antarcticus_, n. sp.

Pores irregular, polygonal, twice to four times as broad as the bars; five to six on the radius. Forty to fifty radial spines, angular, curved, of variable size and form, with three to nine irregular, simple, blunt curved branches.

_Dimensions._--Diameter of the shell 0.14, pores 0.01 to 0.02, bars 0.05; length of the spines 0.1 to 0.18, breadth 0.007.

_Habitat._--Antarctic Ocean, Station 157, depth 1950 fathoms.

5. _Cladococcus japonicus_, n. sp.

Pores irregular, roundish, of the same breadth as the bars; six to eight on the radius. Twenty to thirty radial spines, angular, longer than the shell diameter, with thirty to forty simple branches, decreasing in size from the middle part of the spine to the distal end (ten to thirteen branches on each edge).

_Dimensions._--Diameter of the shell 0.12, pores and bars 0.007; length of the spines 0.15 to 0.2, breadth 0.004.

_Habitat._--North Pacific (Japan), Station 240, surface.

6. _Cladococcus quadricuspis_, n. sp.

Pores irregular, roundish, twice to eight times as broad as the bars; eight to ten on the radius. About twenty radial spines, three-sided prismatic, as long as the shell diameter; in the proximal half simple, with smooth edges; in the distal half with three diverging simple branches, half the length of the spine, with dentated edges.

_Dimensions._--Diameter of the shell 0.15, pores 0.004 to 0.016, bars 0.002; length of the spines 0.17, breadth 0.01.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

Subgenus 3. _Cladococcodes_, Haeckel.

_Definition._--Branches of the spines again ramified. Pores regular, of nearly equal size and similar form.

7. _Cladococcus scoparius_, n. sp. (Pl. 27, fig. 2).

Pores regular, circular, three times as broad as the bars; five to six on the radius. Twenty radial spines, broom-shaped, three times as long as the shell diameter; in the proximal half simple, in the distal half branched, with three to nine branches, which are again ramified; spines and their branches with three smooth edges, not dentated.

_Dimensions._--Diameter of the shell 0.055, pores 0.0075, bars 0.0025; length of the spines 0.15, basal thickness 0.007.

_Habitat._--Central Pacific, Station 271, surface.

{226}8. _Cladococcus viminalis_, Haeckel.

_Cladococcus viminalis_, Haeckel, 1862, Monogr. d. Radiol., p. 369, Taf. xiv. figs. 2, 3.

Pores regular, circular, hexagonally framed, four times as broad as the bars; five to six on the radius. Radial spines, arising from all the nodal-points of the network, twice as long as the shell diameter; in the basal half simple, in the distal half with three to six long, thin, curved branches, which are partly forked; three edges of the spines dentated.

_Dimensions._--Diameter of the shell 0.08, pores 0.01, bars 0.003; length of the radial spines 0.16, basal breadth 0.003.

_Habitat._--Mediterranean (Messina).

9. _Cladococcus bifurcus_, Haeckel.

_Cladococcus bifurcus_, Haeckel, 1862, Monogr. d. Radiol., p. 368, Taf. xiii. figs. 7, 8.

Pores regular, circular, hexagonally framed, four times as broad as the bars; five to seven on the radius. Radial spines arising from all the nodal-points, three-sided prismatic, with dentated edges, longer than the shell diameter. On each spine six to nine branches, which are for the most part forked, the distal branches only being simple. (May be regarded as a further developmental stage of _Cladococcus spinifer_ and _Cladococcus viminalis_.)

_Dimensions._--Diameter of the shell 0.08, pores 0.01, bars 0.0025; length of the spines 0.1, basal breadth 0.003.

_Habitat._--Mediterranean (Messina), Canary Islands, Azores, surface.

10. _Cladococcus pinetum_, n. sp. (Pl. 27, fig. 1).

Pores regular, circular, polygonally framed, about the same breadth as the bars: two to three on the radius. About twenty radial spines, very large, three to four times as long as the shell diameter, branched like a pine tree, with straight, stout, three-sided prismatic stem; three prominent edges dentated. On each edge five to seven lateral branches, the distal ends of which are simple, the proximal again ramified, with numerous ramules. The figured specimen is a young one, with branches but little developed.

_Dimensions._--Diameter of the shell 0.06, pores and bars 0.008; length of the spines 0.2 to 0.25 breadth 0.01.

_Habitat._--Central Pacific, Station 266 to 274, surface.

Subgenus 4. _Cladococcurus_, Haeckel.

_Definition._--Branches of the spines again ramified. Pores irregular, of different size and form.

11. _Cladococcus abietinus_, n. sp. (Pl. 27, fig. 3).

Pores irregular, roundish, twice to four times as broad as the bars; six to ten on the radius. About twenty radial spines, two to three times as long as the shell diameter, branched like a pine {227}tree, with straight, stout, three-sided pyramidal stem. From the dentated edges arise numerous verticillate branches, the proximal ends of which are thickly ramified. (Differs from the preceding and similar species mainly in the large size and irregular lattice-work of the shell.)

_Dimensions._--Diameter of the shell 0.12 to 0.14, pores 0.006 to 0.012, bars 0.003; length of the spines 0.25 to 0.4, breadth 0.012.

_Habitat._--North Pacific, Station 256, surface.

12. _Cladococcus tricladus_, n. sp.

Pores irregular, polygonal, twice to eight times as broad as the bars; eight to ten on the radius. About twenty radial spines, three-sided prismatic, twice as long as the shell diameter; in the proximal half simple, with smooth edges; in the distal half with three diverging curved branches, which bifurcate two to three times or ramify irregularly. (Closely related to the simpler _Cladococcus quadricuspis_.)

_Dimensions._--Diameter of the shell 0.16, pores 0.04 to 0.016, bars 0.002; length of the spines 0.3, breadth 0.012.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

13. _Cladococcus stalactites_, n. sp. (Pl. 27, fig. 4).

Pores irregular, roundish, once to five times as broad as the bars; eight to ten on the radius. About twenty radial spines, very stout, longer than the shell diameter, with three wing-like, prominent smooth edges. At the middle, or in the distal half, each spine bears a verticil of three strong, irregularly formed ramified branches.

_Dimensions._--Diameter of the shell 0.14, pores 0.003 to 0.015, bars 0.003; length of the spines 0.16 to 0.2, breadth 0.02.

_Habitat._--West Tropical Pacific, Station 220, depth 1100 fathoms.

14. _Cladococcus dendrites_, n. sp. (Pl. 27, fig. 5).

Pores irregular, roundish, with denticulate margin, twice to four times as broad as the bars; eight to twelve on the radius. Fifty to eighty radial spines, three-sided prismatic, with elegantly denticulated edges; in the proximal two-thirds simple, in the distal third with a bunch of ten to twenty short simple spines (three to seven on each edge).

_Dimensions._--Diameter of the shell 0.16 to 0.2, pores 0.006 to 0.012, bars 0.003; length of the spines 0.2 to 0.3, breadth 0.01.

_Habitat._--Antarctic Ocean, Station 157, depth 1950 fathoms.

Genus 93. _Elaphococcus_,[127] Haeckel, 1881, Prodromus, p. 450.

_Definition._--#Astrosphærida# with one simple lattice-sphere, covered with forked or dichotomously branched radial spines (the stem of the spine always forked).

{228}The genus _Elaphococcus_ differs from the preceding _Cladococcus_ in the mode of ramification of the radial spines. These are forked; and the forked branches are either simple, again forked, or dichotomously ramified.

Subgenus 1. _Elaphococcinus_, Haeckel.

_Definition._--Pores of the shell regular, of nearly equal size and similar form.

1. _Elaphococcus furcatus_, n. sp.

Pores of the spherical shell regular, hexagonal, four times as broad as the bars; four to five on the radius. Radial spines, arising from all the nodal-points of the network, cylindrical, as long as the radius, simply forked at the distal end; both branches half as long as the undivided part.

_Dimensions._--Diameter of the shell 0.08, pores 0.01, bars 0.0025; length of the spines 0.04, breadth 0.004.

_Habitat._--Tropical Atlantic, Station 348, surface.

2. _Elaphococcus cervicornis_, Haeckel.

_Cladococcus cervicornis_, Haeckel, 1862, Monogr. d. Radiol., p. 370, Taf. xiv. figs. 4-6.

Pores regular, hexagonal, ten to twenty times as broad as the bars; five to seven on the radius. Fifty to ninety radial spines (or more), arising not only from the nodal-points of the network but also from the bars between them. Each spine is cylindrical, longer than the shell diameter, and repeatedly forked (three to six times), having, therefore, numerous (thirty to sixty or more) curved branches. The distal ends of all branches fall in one spherical face.

_Dimensions._--Diameter of the shell 0.07 to 0.09, pores 0.01 to 0.015, bars 0.001 to 0.015; length of the spines 0.1 to 0.15, breadth 0.005.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface.

3. _Elaphococcus elaphoceras_, n. sp.

Pores regular, circular, hexagonally framed, three to four times as broad as the bars; six to eight on the radius. At each nodal-point of the hexagon arises a short bristle-shaped, simple by-spine. In addition, there arise from the bars thirty to sixty large main spines, longer than the shell diameter, repeatedly forked in the same way as in the preceding species.

_Dimensions._--Diameter of the shell 0.1, pores 0.008, bars 0.002; length of the spines 0.12, breadth 0.002.

_Habitat._--Central Pacific, Station 272. depth 2600 fathoms.

4. _Elaphococcus umbellifer_, n. sp.

Pores regular, circular, three times as broad as the bars; ten to twelve on the radius. Twenty to forty straight cylindrical spines, as long as the shell diameter, having at the distal end a regular {229}umbel composed of nine to twelve curved branches of equal length, which are again ramified and resemble the inflorescence of an umbelliferous plant, the distal ends of all ramules falling in a spherical face.

_Dimensions._--Diameter of the shell 0.12, pores 0.006, bars 0.002; length of the spines 0.14, breadth 0.002.

_Habitat._--South Atlantic, Station 325, surface.

Subgenus 2. _Elaphococculus_, Haeckel.

_Definition._--Pores of the shell irregular, of different size or form.

5. _Elaphococcus dichotomus_, n. sp.

Pores irregular, polygonal, twice to four times as broad as the bars; six to eight on the radius. Thirty to sixty radial spines cylindrical, curved, as long as the shell diameter, simply forked at the distal end; both branches one-third as long as the undivided part.

_Dimensions._--Diameter of the shell 0.15, pores 0.007 to 0.015, bars 0.004; length of the spines 0.2, breadth 0.004.

_Habitat._--Arctic Ocean, Greenland, surface (Koch).

6. _Elaphococcus umbellatus_, n. sp.

Pores irregular, roundish, or polygonal, twice to five times as broad as the bars; six to eight on the radius. Forty to sixty radial spines cylindrical, curved, as long as the shell radius, having at the distal end an irregular umbel, composed of six to twelve short branches, which are irregularly ramified or forked. (Differs from the regular _Elaphococcus umbellifer_ mainly in the irregularity.)

_Dimensions._--Diameter of the shell 0.14, pores 0.007 to 0.015, bars 0.003; length of the spines 0.12, breadth 0.01.

_Habitat._--South-east Pacific (Juan Fernandez), Station 299, surface.

7. _Elaphococcus drymodes_, n. sp.

Pores irregular, roundish, little broader than the bars; ten to twelve on the radius. Eighty to one hundred and twenty (or more) radial spines, cylindrical, three to four times as long as the shell diameter, irregularly forked or repeatedly dichotomous (each spine with forty to sixty forked branches); the distal ends of all branches fall in a spherical plane. (Differs from the regular _Elaphococcus cervicornis_ mainly in the irregularity.)

_Dimensions._--Diameter of the shell 0.1, pores and bars 0.003 to 0.008; length of the spines 0.3 to 0.4, breadth 0.01.

_Habitat._--Arctic Ocean, Iceland (Steenstrup).

{230}Subfamily HALIOMMIDA,[128] Haeckel.

_Diplosphærida_, Haeckel, 1881, Prodromus, pp. 449, 451.

_Definition._--#Astrosphærida# with two concentric spherical lattice-shells, united by radial beams.

Genus 94. _Haliomma_,[129] Ehrenberg, 1838, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 128.

_Definition._--#Astrosphærida# with one medullary (intracapsular) and one cortical (extracapsular) shell, which are connected by radial beams, piercing the central capsule. Shell surface covered with simple radial spines of the same kind.

The genus _Haliomma_, one of the oldest known Radiolarian genera, contained in the catalogue of its discoverer, Ehrenberg, a large number of very different #Sphærellaria#, belonging to at least sixteen different genera. We limit here the conception of the genus to those Haliommida which bear simple radial spines of one kind on the surface of the cortical shell (the latter being separated from the medullary shell by the central capsule).

Subgenus 1. _Haliommantha_, Haeckel.

_Definition._--Pores of the cortical shell regular, of nearly equal size and similar form; spines on the whole surface (commonly one spine at each nodal-point).

1. _Haliomma hexagonium_, n. sp.

Cortical shell four times as broad as the medullary shell, both having very thin thread-like bars, and regular, hexagonal pores (eighteen to twenty on the radius of the outer, five to six on the radius of the inner shell). The two shells connected by twenty thin thread-like radial beams. At each nodal-point of the outer shell arises a bristle-shaped radial spine, half as long as the radius. (Similar to _Heliosoma radians_, Pl. 28, fig. 3, but with all the spines equal.)

_Dimensions._--Diameter of the outer shell 0.2, inner 0.05; pores of the outer 0.015, of the inner 0.01; length of the spines 0.05.

_Habitat._--Equatorial Atlantic, Station 347, surface.

2. _Haliomma arachnium_, n. sp.

Cortical shell three times as broad as the medullary shell; pores of the former regular, hexagonal, with very thin thread-like bars (fourteen to sixteen on the radius); pores of the latter regular, {231}circular, three times as broad as the bars (four to five on the radius). The two shells connected by about forty radial beams. At each nodal-point of the outer shell arises one bristle-shaped radial spine, twice as long as the diameter of one hexagonal mesh.

_Dimensions._--Diameter of the outer shell 0.15, inner 0.05; pores of the outer 0.012, of the inner 0.006; length of the spines 0.025.

_Habitat._--Central Pacific, Station 266, surface.

3. _Haliomma favosum_, n. sp.

Cortical shell thick walled, three times as broad as the medullary shell, with regular, circular, hexagonally framed pores, twice as broad as the bars; eight to ten on the radius. Medullary shell with simple, circular pores, of the same breadth as the bars. At each nodal-point of the outer shell arises a short triangular spine three times as long as one pore.

_Dimensions._--Diameter of the outer shell 0.12, inner 0.04; pores of the former 0.01, of the latter 0.005; bars 0.005; length of the spines 0.015.

_Habitat._--Central Pacific, Station 271 to 274, surface.

4. _Haliomma regulare_, n. sp.

Cortical shell thin walled, nearly twice as broad as the medullary shell, and connected with it by forty to sixty thin radial beams. Both shells of the same perfectly regular structure, with an identical number of regular, circular pores, which are hexagonally framed, four times as broad as the bars, nine to eleven on the radius. The outer pores are twice as broad as the inner, exactly corresponding pores. Between every three pores of the outer surface (in each corner of the cortical hexagon) arises one short three-sided pyramidal spine, twice as long as the diameter of one pore.

_Dimensions._--Diameter of the outer shell 0.2, of the inner 0.11; pores of the former 0.018, of the latter 0.009; length of the spines 0.04.

_Habitat._--South Atlantic (Tristan da Cunha), Station 332, depth 2200 fathoms.

5. _Haliomma melitomma_, n. sp. (Pl. 20, fig. 4).

_Melitomma formosum_, Haeckel, 1879, Atlas, _loc. cit._

Cortical shell thick walled, two and a half times as broad as the medullary shell, with regular pores of very elegant structure, twice as broad as the bars; eight to ten on the radius. The inner opening of each pore is simple, circular, the outer regular, six-lobed; corresponding to the six lobes are six short conical spines, which arise from the six corners of the regular hexagonal frames separating the pores. Pores of the medullary shell simple, circular, of the same breadth as the bars. The two shells connected only by six radial beams (in three dimensive axes).

_Dimensions._--Diameter of the outer shell 0.17, of the inner 0.07; pores of the former 0.012, of the latter 0.004; length of the spines 0.005 to 0.01.

_Habitat._--Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.

{232}6. _Haliomma lirianthus_, n. sp. (Pl. 28, figs. 1, 1_a_, 1_b_).

Cortical shell thick walled, three times as broad as the medullary shell, with regular, rosette-shaped pores, twice as broad as the bars; eight to ten on the radius. The regular structure of the elegant pores is the same as in the preceding species, but without prominent crested frames (fig. 1_b_). Also the medullary shell (fig. 1_a_) is different, much thinner and smaller, with simple, circular pores, which are three times as broad as the bars. The two shells are connected by numerous (twenty?) radial beams.

_Dimensions._--Diameter of the outer shell 0.15, of the inner 0.05; pores of the former 0.01, of the latter 0.005; length of the spines 0.005 to 0.02.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

7. _Haliomma castanea_, Haeckel.

_Haliomma castanea_, Haeckel, 1862, Monogr. d. Radiol., p. 428, Taf. xxiv. fig. 4.

Cortical shell thick walled, three times as broad as the medullary shell; pores of both regular, circular, twice as broad as the bars (seven to eight on the radius of the outer, four to five on the radius of the inner shell), the two connected by six to twelve (?) strong radial beams. Radial spines bristle-shaped, with conical bases, twice as long as the diameter of the cortical pores (one spine at the nodal-point between every three pores).

_Dimensions._--Diameter of the outer shell 0.1 to 0.15, inner 0.03 to 0.05; pores of the former 0.005, of the latter 0.003; length of the spines 0.005 to 0.01.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface.

8. _Haliomma horridum_, Stöhr.

_Haliomma horridum_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 87, Taf. i. fig. 10.

Cortical shell thick walled, two and a half times as broad as the medullary shell. Pores regular, circular, of the same breadth as the bars; eight to ten on the radius. Radial spines conical, stout, nearly half as long as the radius. (Differs from the closely allied _Haliomma castanea_ in the smaller pores and larger spines.)

_Dimensions._--Diameter of the outer shell 0.14, of the inner 0.06; pores of the former 0.004, of the latter 0.02.

_Habitat._--Fossil in Tertiary rocks of Barbados and Sicily; living in the Atlantic, Station 9, depth 3150 fathoms, and Station 353, depth 2965 fathoms.

9. _Haliomma datura_, n. sp.

Cortical shell thin walled, only one and a half times as broad as the medullary shell, both having regular, circular pores, four to six times as broad as the bars (five to six on the radius of the outer, three to four on the radius of the inner shell), the two connected by numerous (forty to sixty?) thin, short, radial beams. Radial spines conical, twice as long as the diameter of one cortical pore, arising from all the nodal-points between them.

{233}_Dimensions._--Diameter of the outer shell 0.08 to 0.12, inner 0.06 to 0.08; pores of the former 0.015 to 0.02, of the latter 0.007 to 0.012; length of the spines 0.02.

_Habitat._--Central Pacific, Stations 268 to 274, surface.

Subgenus 2. _Haliommetta_, Haeckel.

_Definition._--Pores of the cortical shell regular, of nearly equal size and similar form; the spines not covering the entire surface, but scattered at intervals (their number smaller than that of the nodal-points of the network).

10. _Haliomma circumtextum_, n. sp. (Pl. 28, figs. 7, 7_a_).

Cortical shell very delicate, with thin thread-like bars, and regular, hexagonal pores, little larger than the thick-walled medullary shell (= 7 : 6). Pores of the latter regular, circular, double-edged, with hexagonal frames, of the same breadth as the bars; from all the hexagon-corners arise thin bristle-shaped, radial spines, twice as long as the diameter of the pores, becoming connected at equal distances from the centre by tangential threads, regularly disposed, forming the cortical shell. Twelve strong, three-sided pyramidal, radial spines, as broad at the base as one mesh, and about half as long as the radius of the shell.

_Dimensions._--Diameter of the outer shell 0.14, of the inner 0.12; pores of the former 0.012, of the latter 0.005; length of the radial spines 0.04, basal breadth 0.012.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

11. _Haliomma duodecinum_, n. sp.

Cortical shell thick walled, three times as broad as the medullary shell. Both shells with regular, circular pores, twice as broad as the bars; eight to ten on the radius of the outer, five to six on the radius of the inner shell. Twelve conical, regularly disposed radial spines, as long as the radius, and as broad at the base as one mesh.

_Dimensions._--Diameter of the outer shell 0.12, of the inner 0.04; pores of the former 0.005, of the latter 0.002; length of the spines 0.05, basal breadth 0.005.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

12. _Haliomma megaporum_, Ehrenberg.

_Haliomma megaporum_, Ehrenberg, 1872, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 313.

Cortical shell thin walled, three times as broad as the medullary shell; the pores regular, circular, three to four on the radius, eight times as broad as the bars, quite as broad as the medullary shell, the pores of which are much smaller, twice as broad as the bars. Eight radial spines regularly disposed, conical, as long as the radius. (As the diagnosis of Ehrenberg is very {234}incomplete, and no figure is given with it, it remains doubtful whether his Mediterranean species be identical with my Atlantic variety.)

_Dimensions._--Diameter of the outer shell 0.12, of the inner 0.04; pores of the former 0.04, of the latter 0.008; length of the spines 0.06.

_Habitat._--Mediterranean (Grecian shore); North Atlantic, Station 354, surface.

13. _Haliomma oculatum_, Ehrenberg.

_Haliomma oculatum_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxviii. figs. 2, 3.

Cortical shell thick walled, four times as broad as the medullary shell; its pores regular, circular, four times as broad as the bars, six to eight on the radius. Pores of the medullary shell regular, hexagonal, with very thin bars, three to four on the radius. Nine radial spines, regularly disposed, conical, as long as the radius, as broad at the base as one cortical pore. (In the specimen figured by Ehrenberg, only two spines were preserved, seven being accidentally broken off.)

_Dimensions._--Diameter of the outer shell 0.16, of the inner 0.04; pores of the former 0.01, of the latter 0.005.

_Habitat._--Fossil in Barbados.

14. _Haliomma enneaxiphos_, n. sp.

Cortical shell thick walled, four times as broad as the dark medullary shell, with regular, circular, hexagonally framed pores, twice as broad as the bars; eight to ten on the radius. Nine radial spines regularly disposed, three sided pyramidal, as long as the radius, as broad at the base as one mesh.

_Dimensions._--Diameter of the outer shell 0.11, of the inner 0.03; cortical pores 0.008, bars 0.004; length of the radial spines 0.05, basal breadth 0.012.

_Habitat._--Central Pacific, Station 272, surface.

15. _Haliomma tenuispinum_, J. Müller.

_Haliomma tenuispinum_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 39, Taf. iv. fig. 9.

_Haliomma tenuispinum_, Haeckel, 1862, Monogr. d. Radiol., p. 431.

Cortical shell thin walled, three times as broad as the medullary shell. Both shells with very fine, thread-like bars, and regular, hexagonal pores; five to seven on the radius. Twenty radial spines, very thin, bristle-shaped, as long as the radius.

_Dimensions._--Diameter of the outer shell 0.12, of the inner 0.04; pores of the former 0.016, of the latter 0.006.

_Habitat._--Mediterranean (Nice); North Atlantic, Station 353, surface.

{235}16. _Haliomma longispinum_, J. Müller.

_Haliomma longispinum_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 39, Taf iv. fig. 8.

_Haliomma longispinum_, Haeckel, 1862, Monogr. d. Radiol., p. 431.

Cortical shell thick walled, three times as broad as the dark medullary shell. Pores regular, circular, hexagonally framed, twice as broad as the bars; four to six on the radius. Twenty radial spines, very long, regularly disposed, four to five times as long as the diameter of the shell, three-sided prismatic, with elegantly dentated edges, as broad as one cortical mesh.

_Dimensions._--Diameter of the outer shell 0.08, of the inner 0.03; pores of the former 0.01, bars 0.005; length of the spines 0.3 to 0.4.

_Habitat._--Mediterranean (Nice); Central Pacific, Station 272, surface.

17. _Haliomma capense_, n. sp.

Cortical shell thick walled, twice as broad as the medullary shell, both with regular, circular pores, twice as broad as the bars; eight to ten on the radius of the outer, four to six on the radius of the inner shell. Forty to sixty radial spines, conical, as long as the radius, as broad as one cortical pore.

_Dimensions._--Diameter of the outer shell 0.11, of the inner 0.05; pores of the former 0.01, bars 0.005; length of the spines 0.006, basal breadth 0.012.

_Habitat._--Cape of Good Hope, Station 142, surface.

18. _Haliomma denticulatum_, n. sp.

Cortical shell thick walled, three times as broad as the dark medullary shell, with regular, circular, double-edged pores, of the same breadth as the bars; eight to ten on the radius. Thirty to fifty radial spines, three-sided pyramidal, half as long as the radius, with three denticulated edges. (Very similar to _Actinomma denticulatum_, Pl. 29, fig. 3, but with simple medullary shell.)

_Dimensions._--Diameter of the outer shell 0.12, inner 0.04; pores and bars of the former 0.008; length of the spines 0.04, basal breadth 0.01.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

19. _Haliomma grande_, n. sp.

Cortical shell thick walled, five times as broad as the dark medullary shell, with small, regular, circular pores, half as broad as the bars; twenty to twenty-four on the radius. One hundred to one hundred and twenty conical radial spines, five times as long as broad, only half as long as the radius.

_Dimensions._--Diameter of the outer shell 0.4, inner 0.08; pores of the outer 0.006, bars 0.012; length of the spines 0.1, basal breadth 0.02.

_Habitat._--Equatorial Atlantic, Station 348, depth 2450 fathoms.

{236}Subgenus 3. _Haliommilla_, Haeckel.

_Definition._--Pores of the cortical shell irregular, of different size and form; spines covering the entire surface (commonly one spine at each nodal-point).

20. _Haliomma capillaceum_, Haeckel.

_Haliomma capillaceum_, Haeckel, 1862, Monogr. d. Radiol., p. 426, Taf. xxiii. fig. 2.

Cortical shell very thin walled, seven to eight times as broad as the medullary shell, both with irregular, polygonal pores, and very thin thread-like bars; outer pores twice to three times as broad as the inner. Radial spines very numerous, straight, bristle-shaped, about as long as the diameter of the medullary shell.

_Dimensions._--Diameter of the outer shell 0.2, inner 0.025 to 0.03; outer pores 0.02 to 0.04, inner 0.008 to 0.016, bars 0.001; length of the spines 0.02 to 0.03.

_Habitat._--Mediterranean (Messina), Atlantic (Canary Islands), surface.

21. _Haliomma erinaceum_, Haeckel.

_Haliomma erinaceum_, Haeckel, 1862, Monogr. d. Radiol., p. 427, Taf. xxiii. figs. 3, 4.

Cortical shell thin walled, seven to eight times as broad as the medullary shell, both with irregular, polygonal pores, two to ten times as broad as the bars, outer pores much larger than the inner. Radial spines very numerous, bristle-shaped, as long as the diameter of the medullary shell, the majority or all being either curved or obliquely depressed, the greater part neither straight nor radial.

_Dimensions._--Diameter of the outer shell 0.2, inner 0.025 to 0.03; outer pores 0.005 to 0.03, inner 0.008 to 0.016, bars 0.002 to 0.004; length of the spines 0.03.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

22. _Haliomma tenellum_, Haeckel.

_Haliomma tenellum_, Haeckel, 1862, Monogr. d. Radiol., p. 428.

_Haliomma spinuloso affine_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 40, Taf. iv. fig. 7.

Cortical shell thin walled, three times as broad as the medullary shell, with irregular, roundish pores, and very thin bars. Pores of the inner shell regular, circular. Radial spines very numerous, bristle-shaped, straight, as long as the radius of the outer shell.

_Dimensions._--Diameter of the outer shell 0.15, inner 0.05; outer pores 0.008 to 0.016, inner 0.005; length of the spines 0.07.

_Habitat._--Mediterranean (Nice); Atlantic, Stations 349 to 354, surface.

{237}23. _Haliomma spinulosum_, J. Müller.

_Haliomma spinulosum_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 39, Taf. iv. fig. 6.

Cortical shell thin walled, twice as broad as the medullary shell, with irregular, polygonal pores, and very thin bars. Pores of the inner shell subregular, hexagonal, ten to twelve times as broad as the bars. Radial spines very numerous, bristle-shaped, one-sixth to one-fourth as long as the radius of the outer shell.

_Dimensions._--Diameter of the outer shell 0.16, inner 0.08; outer pores 0.01 to 0.03, inner 0.02; length of the spines 0.02 to 0.03.

_Habitat._--Mediterranean (Nice); Central Pacific, Station 266, surface.

24. _Haliomma rhodococcus_, n. sp. (Pl. 19, fig. 6).

_Sethosphæra rhodococcus_, Haeckel, 1879, Atlas, pl. xix. fig. 6.

Cortical shell very thin walled, little larger than the thick walled medullary shell (= 10 : 9). Pores of the outer shell very irregular, roundish, twice to six times as broad as the bars, about twenty on the radius. Pores of the inner shell twice as broad as the bars, six to eight on the radius, very regular, circular on the inner, six-lobed on the outer opening, separated by prominent hexagonal crests; in the hexagon-corners arise short conical radial spines, which at equal distances from the centre are united by the outer shell, but are prominent over its surface. (A very peculiar form; the two shells may better be regarded as inner and outer cortical shell.)

_Dimensions._--Diameter of the outer shell 0.2, inner 0.18; outer pores 0.04 to 0.012, inner 0.01; length of the spines 0.01.

_Habitat._--Tropical Atlantic, Station 338, depth 1990 fathoms; also fossil in Barbados.

25. _Haliomma boreale_, n. sp.

Cortical shell thick walled, four times as broad as the medullary shell, with irregular, roundish pores, twice to four times as broad as the bars; eight to ten on the radius. Pores of the inner shell regular, circular, twice as broad as the bars, four to six on the radius. Radial spines very numerous, conical, nearly as long as the diameter of the shell.

_Dimensions._--Diameter of the outer shell 0.24, inner 0.06; outer pores 0.008 to 0.02, bars 0.005, inner pores 0.006, bars 0.003; length of the spines 0.2.

_Habitat._--Arctic Ocean, Greenland ("Alert" Expedition).

Subgenus 4. _Haliommura_, Haeckel.

_Definition._--Pores of the cortical shell irregular, of different size and form; spines not covering the entire surface, but scattered at intervals (their number smaller than that of the nodal-points in the network).

{238}26. _Haliomma macrodoras_, n. sp. (Pl. 28, figs. 6, 6_a_).

Cortical shell thin walled, twice as broad as the medullary shell, with irregular, polygonal meshes, three to six times as broad as the bars. Inner shell with regular, hexagonal meshes, ten times as broad as the bars. Twenty radial spines, very long, stout, three-sided prismatic, two to four times as long as the diameter of the shell, as broad as one medullary mesh, with three wing-like, denticulated edges. At the base of each spine three supporting curved beams.

_Dimensions._--Diameter of the outer shell 0.14 to 0.16, of the inner 0.07 to 0.08; outer pores 0.01 to 0.02, bars 0.003; inner pores 0.01, bars 0.001; length of the spines 0.3 to 0.6, breadth 0.01.

_Habitat._--Central Pacific, Station 271, surface.

27. _Haliomma antarcticum_, n. sp.

Cortical shell very thin walled, three times as broad as the medullary shell, with irregular, polygonal pores, and very thin thread-like bars. Inner shell with regular, hexagonal meshes, six times as broad as the bars. About forty radial spines, angular, pyramidal, half as long as the radius of the shell, as broad at the base as the largest mesh.

_Dimensions._--Diameter of the outer shell 0.2, of the inner 0.07; outer pores 0.006 to 0.015, inner 0.008; length of the spines 0.05, basal breadth 0.012.

_Habitat._--Antarctic Ocean, Station 154, surface.

28. _Haliomma wyvillei_, Haeckel.

_Haliomma wyvillei_, Haeckel, 1878, Protistenreich, p. 44, fig. 31.

_Haliomma species_, Wyville Thomson, 1877, Atlantic, vol. i. p. 236, fig. 54.

Cortical shell thin walled, three times as broad as the medullary shell. Both shells with irregular, large, polygonal pores, and very thin bars. From the inner shell arise very numerous (eighty to one hundred and twenty or more) radial spines, which pierce the outer shell, and are outside it, as long as the radius of the inner shell, straight, bristle-shaped, and as thick as the bars.

_Dimensions._--Diameter of the outer shell 0.18, of the inner 0.06; pores 0.01 to 0.02, bars 0.001 to 0.002; length of the free spines 0.06.

_Habitat._--Central Pacific, Stations 266 to 274, surface.

29. _Haliomma beroes_, Ehrenberg.

_Haliomma beroes_, Ehrenberg, 1854, Mikrogeol., Taf. xxxvB. B. iv. fig. 19.

_Haliomma beroes_, Haeckel, 1862, Monogr. d. Radiol., p. 434.

Cortical shell thin walled, three times as broad as the medullary shell, with irregular, roundish pores, twice to four times as broad as the bars. Inner shell with regular, circular pores, twice as broad as the bars. Both shells connected by four (or six ?) radial beams, perpendicularly crossed. Thirty to forty radial spines, conical, thin, shorter than the radius.

_Dimensions._--Diameter of the outer shell 0.11, inner 0.04; outer pores 0.007 to 0.012, inner 0.005; length of the spines 0.03, basal breadth 0.005.

_Habitat._--Atlantic, depth 2000 fathoms.

{239}30. _Haliomma compactum_, n. sp. (Pl. 28, figs. 5, 5_a_).

Cortical shell very thick walled, four times as broad as the thin walled medullary shell; pores of the former irregular, roundish, with high polygonal frames of very different size, twice to four times as broad as the bars. Inner shell with simple, small, polygonal pores, connected with the outer shell by eight (?) regularly disposed thin radial beams, opposite in pairs, prolonged outside into strong conical spines, longer than the radius.

_Dimensions._--Diameter of the outer shell 0.08, inner 0.02; outer pores 0.005 to 0.01, inner 0.005; length of the spines 0.06, basal breadth 0.012.

_Habitat._--Central Pacific, Stations 265 to 272, depth 2425 to 2925 fathoms.

31. _Haliomma permagnum_, n. sp.

Cortical shell thick walled, six times as broad as the medullary shell, with irregular, roundish, double-edged pores, three to six times as broad as the bars. Inner shell with regular, circular pores, twice as broad as the bars. One hundred and twenty to one hundred and fifty radial spines, conical, only one-fourth as long as the radius.

_Dimensions._--Diameter of the outer shell 0.42, inner 0.07; outer pores 0.012 to 0.025, bars 0.004; inner pores 0.008, bars 0.004; length of the spines 0.05, basal breadth 0.03.

_Habitat._--Central Pacific, Station 268, surface.

32. _Haliomma patagonicum_, n. sp.

Cortical shell thick walled, four times as broad as the medullary shell, with irregular, roundish pores, twice to three times as broad as the bars. Inner shell also with irregular, roundish pores, of half the size. Forty to fifty radial spines, cylindro-conical, about as long as the shell diameter.

_Dimensions._--Diameter of the outer shell 0.24, inner 0.06; outer pores 0.012 to 0.02, bars 0.006; inner pores 0.005 to 0.01, bars 0.004; length of the spines 0.3, breadth 0.02.

_Habitat._--South-east Pacific, west coast of Patagonia, Station 302, surface.

33. _Haliomma clavatum_, n. sp.

Cortical shell thick walled, three times as broad as the medullary shell, with irregular, roundish pores little larger than the bars; eight to twelve on the radius. Inner shell with similar but smaller pores. About twenty radial spines, club-shaped, as long as the radius, three-sided, with prominent edges, twice as broad at the distal end as at the base. (Similar to _Acanthosphæra clavata_, Pl. 26, fig. 8, but differs from it in the possession of a medullary shell.)

_Dimensions._--Diameter of the outer shell 0.2, inner 0.06; outer pores and bars 0.008 to 0.02, inner 0.006 to 0.01; length of the spines 0.1, distal breadth 0.03.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

{240}Genus 95. _Heliosoma_,[130] Haeckel, 1881, Prodromus, p. 452.

_Definition._--#Astrosphærida# with one medullary (intracapsular) and one cortical (extracapsular) shell, the two being connected by radial beams piercing the central capsule. Shell surface covered with simple radial spines of two different kinds; larger main spines and smaller by-spines.

The genus _Heliosoma_ differs from the preceding _Haliomma_ in the possession of two different kinds of radial spines, and exhibits therefore the same relation to it that _Heliosphæra_ bears to _Acanthosphæra_ among the Coscinommida. The smaller by-spines are much more numerous than the larger main spines.

Subgenus 1. _Heliosomantha_, Haeckel.

_Definition._--Pores of the cortical shell regular, of nearly equal size and similar form.

1. _Heliosoma radians_, n. sp. (Pl. 28, figs. 3, 3_a_).

Cortical shell very thin walled, with thread-like bars and regular, hexagonal meshes; twenty to twenty-two on the radius. Medullary shell only one-fifth as large, of the same structure. The two shells connected by twenty very thin radial beams, which are prolonged outside into twenty stout, three-sided pyramidal main spines, as long as the diameter of the inner shell. Between these, arising from the surface, numerous bristle-shaped by-spines.

_Dimensions._--Diameter of the outer shell 0.25, inner 0.05, pores 0.012; length of the main spines 0.05, basal breadth 0.012.

_Habitat._--Central Pacific, Stations 266 to 274, surface.

2. _Heliosoma elegans_, n. sp.

Cortical shell thick walled, with regular, circular, hexagonally framed pores, twice as broad as the bars; ten to twelve on the radius. Medullary shell half as large, with simple, regular, circular pores, twice as broad as the bars. The two shells connected by twenty very thin radial beams, which are prolonged outside into twenty slender, three-sided pyramidal main spines as long as the radius. In each corner of the surface hexagons a bristle-shaped by-spine one-fourth as long.

_Dimensions._--Diameter of the outer shell 0.12, inner 0.06; outer pores 0.006, bars 0.003; length of the main spines 0.05, basal breadth 0.01.

_Habitat._--Central Pacific, Station 271, surface.

3. _Heliosoma echinaster_, Haeckel.

_Haliomma echinaster_, Haeckel, 1862, Monogr. d. Radiol., p. 429, Taf. xxiv. figs. 1-3.

Cortical shell thin walled, with regular, circular, hexagonally framed pores, twice as broad as the bars; ten to twelve on the radius. Medullary shell one-fourth as large, with few irregular, large, {241}polygonal pores and very thin thread-like bars, connected with the former by nine similar thin radial beams, which are prolonged outside into nine pyramidal main spines, as long as the radius. From each corner of the surface hexagon arises a bristle-shaped by-spine, half as long as the main spine.

_Dimensions._--Diameter of the outer shell 0.16, inner 0.04; outer pores 0.008, bars 0.004; length of the main spines 0.08, basal breadth 0.01.

_Habitat._--Mediterranean (Messina), surface.

4. _Heliosoma duodecilla_, n. sp.

Cortical shell thick walled, with regular, circular pores, of the same breadth as the bars; sixteen to eighteen on the radius. Medullary shell one-third as large, of the same structure. Twelve radial main spines, regularly disposed, cylindro-conical, longer than the shell diameter, as broad as two pores. Whole surface covered with short conical by-spines.

_Dimensions._--Diameter of the outer shell 0.15, inner 0.05; outer pores and bars 0.007; length of the main spines 0.2, breadth 0.02.

_Habitat._--South Atlantic, Station 333, surface.

Subgenus 2. _Heliosomura_, Haeckel.

_Definition._--Pores of the cortical shell irregular, of different size and form.

5. _Heliosoma hastatum_, n. sp. (Pl. 28, fig. 4).

Cortical shell very thin walled, with large, irregular, polygonal meshes, three to six times as broad as the bars; four to six on the radius. Medullary shell one-third as large, with small, regular, circular pores. The two shells connected by twelve regularly disposed radial beams, which are prolonged outside into twelve very stout three-sided pyramidal main spines, somewhat longer than the radius, spear-shaped; each of the three wings in the middle part with one tooth. Scattered on the surface numerous by-spines of the same form, half as long and only one-fourth as broad.

_Dimensions._--Diameter of the outer shell 0.1, inner 0.033; outer pores 0.006 to 0.013, inner pores 0.002, bars 0.002; length of the main spines 0.06, breadth 0.015.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

6. _Heliosoma indicum_, n. sp.

Cortical shell thick walled, with irregular, roundish pores, twice to five times as broad as the bars. Medullary shell of the same structure, only one-fourth as large. Thirty to forty conical main spines, as long as the radius; between them numerous bristle-shaped by-spines, only half as long.

_Dimensions._--Diameter of the outer shell 0.2, inner 0.05; outer pores 0.004 to 0.01, bars 0.002; length of the main spines 0.1, breadth 0.01.

_Habitat._--Indian Ocean, between Aden and Socotora, surface, Haeckel.

{242}Genus 96. _Elatomma_,[131] n. gen.

The genus _Elatomma_ differs from _Haliomma_ in the ramification of the radial spines, and exhibits therefore the same relation to it that _Cladococcus_, among the Coscinommida, bears to _Acanthosphæra_.

Subgenus 1. _Elatommella_, Haeckel.

_Definition._--Pores of the cortical shell regular, of nearly equal size and similar form.

1. _Elatomma pinetum_, n. sp.

Cortical shell thick walled, with regular, circular, hexagonally framed pores, three times as broad as the bars. From its surface arise twenty to thirty large, three-sided prismatic, radial spines as long as the shell diameter, branched like a pine tree; on each edge of the spine five to six ramified branches, decreasing in size towards the distal end. Similar to _Cladococcus pinetum_ (Pl. 27, figs. 1, 3), but differing in the possession of a medullary shell (one-third as large as the outer), with regular, circular pores, as broad as the bars.

_Dimensions._--Diameter of the outer shell 0.2, inner 0.07; cortical pores 0.012, bars 0.004; length of the spines 0.2 to 0.24.

_Habitat._--Central Pacific, Stations 266 to 272, surface.

2. _Elatomma scoparium_, n. sp.

Cortical shell thick walled, with regular, circular pores, twice as broad as the bars, connected with the medullary shell by twenty thin radial beams, which are prolonged outside into twenty large cylindrical radial spines somewhat longer than the radius; in the proximal half simple, in the distal half with six to nine dichotomous, irregular branches. Similar to _Cladococcus scoparius_ (Pl. 27, fig. 2), but much larger, and with a large medullary shell (one-third as broad as the outer), and regular, circular pores.

_Dimensions._--Diameter of the outer shell 0.12, inner 0.04; cortical pores 0.01, bars 0.005; length of the spines 0.08.

_Habitat._--North Pacific, Station 240, surface.

Subgenus 2. _Elatommura_, Haeckel.

_Definition._--Pores of the cortical shell irregular, of different size or form.

{243}3. _Elatomma juniperinum_, n. sp. (Pl. 28, fig. 8).

Cortical shell thin walled, with regular, polygonal, or roundish pores, twice to four times as broad as the bars, connected with the small medullary shell by about twenty thin radial beams. Inner shell only one-eighth as broad as the outer, with few irregular, polygonal meshes. Surface covered with very numerous (one hundred to one hundred and fifty or more) branched conical radial spines, one-third as long as the shell radius, with six to twelve short lateral branches.

_Dimensions._--Diameter of the outer shell 0.2, inner 0.025; cortical pores 0.08 to 0.016, bars 0.004; length of the spines 0.04.

_Habitat._--Central Pacific, Station 271, surface.

4. _Elatomma penicillus_, n. sp.

Cortical shell thin walled, with irregular, polygonal pores, twice to four times as broad as the bars, connected with the medullary shell by twenty (or more?) very thin beams. These are prolonged outside into twenty straight, three-sided prismatic, radial spines as long as the radius, with a brush-like bunch of six to nine short, irregularly ramified branches at the end. Medullary shell very delicate (half as broad as the outer), with regular, hexagonal meshes and thread-like bars.

_Dimensions._--Diameter of the outer shell 0.15, inner 0.08; length of the spines 0.08.

_Habitat._--West coast of Norway, Bergen, Haeckel.

5. _Elatomma irregulare_, n. sp.

Cortical shell thin walled, with irregular, polygonal, or roundish meshes, twice to six times as broad as the bars; the medullary shell of the same structure, half as broad, with smaller irregular pores. Forty to sixty curved, three-sided, radial spines, as long as the shell, with a bunch of very irregular, curved, and partly ramified branches at the distal end.

_Dimensions._--Diameter of the outer shell 0.2, inner 0.1; length of the spines 0.2, breadth 0.01.

_Habitat._--North Atlantic, Gulf Stream, Færöe Channel, surface, John Murray.

Genus 97. _Leptosphæra_,[132] n. gen.

_Definition._--#Astrosphærida# with two extracapsular cortical shells without by-spines, connected by long prismatic radial spines.

The genus _Leptosphæra_, together with the three following genera, forms the very peculiar and typical small group of #Sphæroidea# which we call the Diplosphærida (with four genera and twenty-four species); their shell is composed of two concentric spheres as in the three foregoing genera; but whilst in these the inner shell is an intracapsular medullary shell and the outer an extracapsular cortical shell, in the Diplosphærida {244}both shells are extracapsular or cortical shells, therefore the inner shell of the latter corresponds to the outer of the former. The inner spherical shell of all Diplosphærida is composed of very delicate beams and large pores, which are either regular hexagonal or irregular polygonal (never roundish). From its surface arise a variable number (twenty to thirty) of stout long radial spines, which are invariably longer than the shell diameter (often two to three times as long or more), and of three-sided prismatic form, the three edges either smooth or serrate, often with three rows of lateral branches (commonly three to five branches in each row); the latter are invariably of the same form, concavely curved towards the spine, and decrease in size towards the distal end. From the three edges of each main spine in all Diplosphærida, at equal distances from the centre, arise six very thin, thread-like lateral branches (a pair from each edge) and connect the spine in a tangential direction with all neighbouring spines. In this manner the polyhedral outer shell is formed, the meshes of which therefore are always very large and triangular. Sometimes each of these primary triangular meshes becomes filled up with a secondary network, either of regular quadrangular or of irregular polygonal secondary meshes. Besides the constant twenty to thirty large main spines, in the majority of Diplosphærida bristle-shaped radial by-spines arise, either from the inner shell (_Diplosphæra_) or from the outer (_Drymosphæra_), or from both (_Astrosphæra_). They are absent only in _Leptosphæra_. Commonly the by-spines are simple, rarely forked or branched. The central capsule in the Diplosphærida is usually enclosed in the inner shell; often it completely fills up the latter, or drives out a cæcal protuberance through each mesh; but these processes rarely unite outside. The average size of the Diplosphærida, which are all pelagic organisms, is much larger than that of the other Haliommida.

Subgenus 1. _Leptosphærella_, Haeckel.

_Definition._--Radial spines simple, without lateral branches.

1. _Leptosphæra hexagonalis_, n. sp. (Pl. 19, fig. 2).

Inner shell with regular, hexagonal meshes, and very thin, thread-like bars; outer shell twice as broad, with simple triangular meshes. Radial spines with three smooth edges. (Fig. 2 represents the central capsule with numerous club-shaped saccules, prominent externally through the meshes; in the centre a large simple spherical nucleus, one-third as broad as the capsule. The skeleton of this species is identical with that of _Diplosphæra hexagonalis_, Pl. 19, fig. 3, but has no by-spines.)

_Dimensions._--Diameter of the outer shell 0.3, of the inner 0.15.

_Habitat._--Cosmopolitan; Mediterranean (Corfu), North Atlantic (Canary Islands), Tropical Pacific, surface.

{245}2. _Leptosphæra serrata_, n. sp.

Inner shell with regular, hexagonal meshes, five to six times as broad as the bars; outer shell three times as broad, with simple triangular meshes. Radial spines with three serrated edges (of the same form as the main spines of _Drymosphæra dendrophora_, Pl. 20, fig. 1).

_Dimensions._--Diameter of the outer shell 0.45, of the inner 0.15.

_Habitat._--Central Pacific, Station 271, surface.

3. _Leptosphæra polygonalis_, n. sp.

Inner shell with irregular, polygonal meshes and very thin thread-like bars; outer shell twice as broad, with simple triangular meshes. Radial spines with three smooth edges. (Resembles _Drymosphæra polygonalis_, Pl. 19, fig. 1, but has no by-spines.)

_Dimensions._--Diameter of the outer shell 0.35, inner 0.175.

_Habitat._--North Pacific, Station 256, surface.

Subgenus 2. _Leptosphæromma_, Haeckel.

_Definition._--Radial spines with three rows of lateral branches (one row on each edge).

4. _Leptosphæra ciliata_, n. sp.

Inner shell with regular, hexagonal meshes and very thin thread-like bars; outer shell three times as broad, with simple triangular meshes. Radial spines with smooth edges and three rows of simple, smooth, curved, lateral branches (six branches on each edge), similar to those of _Diplosphæra gracilis_.

_Dimensions._--Diameter of the outer shell 0.6, inner 0.2.

_Habitat._--South Atlantic, Station 325, surface.

5. _Leptosphæra spinosa_, Haeckel.

_Diplosphæra spinosa_, R. Hertwig, 1879, Organismus d. Radiol., p. 40, Taf. v. fig. 2.

Inner shell with regular, hexagonal meshes, five times as broad as the bars; outer shell three times as broad, with simple triangular meshes. Radial spines with three densely serrated edges, and with three rows of serrated, simple, curved, lateral branches (three branches on each edge). Differs from the preceding in the thicker bars and the elegantly denticulated spines and branches.

_Dimensions._--Diameter of the outer shell 0.66, inner 0.22.

_Habitat._--Mediterranean (Messina), R. Hertwig.

6. _Leptosphæra stellata_, n. sp.

Inner shell with regular, hexagonal meshes, six times as broad as the bars, each bar crossed by a transverse tangential rod, so that each mesh represents an elegant six-rayed star (as {246}in _Astrosphæra stellata_, Pl. 19, fig. 5, but without radial by-spines); outer shell twice as broad, with simple triangular meshes. Radial spines with serrated edges and three rows of simple lateral branches (four branches on each edge).

_Dimensions._--Diameter of the outer shell 0.44, inner 0.22.

_Habitat._--Tropical Atlantic (Ascension Island), Station 343, surface.

7. _Leptosphæra reticulum_, n. sp.

Inner shell with irregular, polygonal meshes and very thin thread-like bars; outer shell four times as broad, also with irregular, polygonal meshes, the sides of the triangular main meshes being connected by irregular lateral ramules, forming an extremely delicate reticulum.

_Dimensions._--Diameter of the outer shell 0.64, inner 0.16.

_Habitat._--South Pacific, Station 291, surface.

Genus 98. _Diplosphæra_,[133] Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 804.

_Definition._--#Astrosphærida# with two extracapsular cortical shells, connected by long, prismatic, radial spines; inner shell with thin radial by-spines.

The genus _Diplosphæra_ differs from its ancestral form _Leptosphæra_ in the development of radial by-spines on the surface of the inner shell, the outer shell being smooth.

Subgenus 1. _Diplosphærella_, Haeckel.

_Definition._--Radial main spines simple, without lateral branches.

1. _Diplosphæra hexagonalis_, n. sp. (Pl. 19, fig. 3).

Inner shell with regular, hexagonal meshes and very thin thread-like bars; at each nodal-point one bristle-shaped by-spine; outer shell twice as broad, with simple triangular meshes. Radial spines with three smooth edges. (The radially striped central capsule, enclosed in the inner shell, envelops a large central nucleus one-third its size, fig. 3.)

_Dimensions._--Diameter of the outer shell 0.36, inner 0.18.

_Habitat._--Central Pacific, Stations 265 to 274, surface.

2. _Diplosphæra ornata_, n. sp.

Inner shell with regular, hexagonal meshes, four times as broad as the bars; outer shell three times as broad, with simple triangular meshes. Radial main spines as well as the bars of both {247}shells very elegantly denticulated; radial by-spines (very numerous in the surface of the inner shell) smooth.

_Dimensions._--Diameter of the outer shell 0.7, inner 0.24.

_Habitat._--Indian Ocean, Madagascar, surface, Rabbe.

3. _Diplosphæra dictyota_, n. sp.

Inner shell with regular, hexagonal meshes, six times as broad as the bars; at each nodal-point one radial by-spine; outer shell two and a half times as broad, with very delicate square meshes, separated by thread-like bars which arise from the sides of the triangular main meshes. Radial main spines with three serrated edges. (Differs from the similar _Diplosphæra gracilis_ in the simple main spines, with delicate dentition of the edges.)

_Dimensions._--Diameter of the outer shell 0.5, inner 0.2.

_Habitat._--North Atlantic, Canary Islands, surface.

4. _Diplosphæra polygonalis_, n. sp.

Inner shell with irregular, polygonal meshes and very thin thread-like bars, covered with very numerous bristle-shaped by-spines; outer shell twice as broad, with simple triangular meshes. Radial main spines with three smooth edges.

_Dimensions._--Diameter of the outer shell 0.44, inner 0.22.

_Habitat._--South Pacific, Station 288, surface.

Subgenus 2. _Diplosphæromma_, Haeckel.

_Definition._--Radial main spines with three rows of lateral branches (one row on each edge).

5. _Diplosphæra gracilis_, Haeckel.

_Diplosphæra gracilis_, Haeckel, 1862, Monogr. d. Radiol., p. 354, Taf. x. fig. 1.

Inner shell with regular, hexagonal meshes and very thin bars; at each nodal-point one simple bristle-shaped radial by-spine; outer shell twice as broad, with very delicate square meshes, separated by thread-like bars which arise from the sides of the triangular main meshes. Radial spines with smooth edges and with three rows of simple curved lateral branches (four to six branches on each edge).

_Dimensions._--Diameter of the outer shell 0.54, inner 0.27.

_Habitat._--Mediterranean (Messina).

6. _Diplosphæra denticulata_, n. sp.

Inner shell with regular, hexagonal meshes, four times as broad as the bars; at each nodal-point is a simple bristle-shaped by-spine; outer shell three times as broad, with simple triangular meshes. {248}Radial spines very strong, with dentated edges and with three rows of lateral branches (six dentated curved branches on each edge).

_Dimensions._--Diameter of the outer shell 0.4, inner 0.13.

_Habitat._--North Atlantic, Azores, surface.

7. _Diplosphæra reticulata_, n. sp.

Inner shell with regular, hexagonal meshes, five times as broad as the bars, which are densely covered with very numerous, simple bristle-shaped by-spines; outer shell four times as broad, with very numerous small irregular polygonal meshes, forming a very delicate network, and filling out the large triangular main meshes. Radial spines with three serrated edges and three rows of short curved branches (four to five branches on each edge).

_Dimensions._--Diameter of the outer shell 0.6, inner 0.15.

_Habitat._--North Atlantic, Gulf Stream, Færöe Channel, surface, John Murray.

8. _Diplosphæra triglochin_, n. sp.

Inner shell with irregular, polygonal meshes and very thin thread-like bars; outer shell three times as broad, with similar irregular polygonal meshes, filling out the large triangular main meshes. Radial spines with three serrated edges, each of which bears one single large lateral branch, concavely curved towards the distal end. By-spines of the inner shell very numerous.

_Dimensions._--Diameter of the outer shell 0.5, inner 0.17.

_Habitat._--Central Pacific, Station 264, surface.

Genus 99. _Drymosphæra_,[134] Haeckel, 1881, Prodromus, p. 452.

_Definition._--#Astrosphærida# with two extracapsular cortical shells, connected by long prismatic, radial spines; outer shell with thin radial by-spines.

The genus _Drymosphæra_ differs from its ancestral form _Leptosphæra_ in the development of radial by-spines on the surface of the outer shell, the inner shell being smooth.

Subgenus 1. _Drymosphærella_, Haeckel.

_Definition._--Radial by-spines simple, not branched (main spines simple).

1. _Drymosphæra hexagonalis_, n. sp.

Inner shell with regular, hexagonal meshes and very thin thread-like bars; outer shell twice as broad, with simple triangular meshes and thin thread-like bars, which bear very numerous, {249}bristle-shaped radial by-spines. Radial main spines with three smooth edges. (Differs from the first species of the other three genera of Diplosphærida in the presence of by-spines on the outer, and their absence on the inner shell.)

_Dimensions._--Diameter of the outer shell 0.32, inner 0.16.

_Habitat._--Central Pacific, Station 274, surface.

2. _Drymosphæra polygonalis_, n. sp. (Pl. 19, fig. 1).

_Diplosphæra polygonalis_, Haeckel, 1879, Atlas.

Inner shell with irregular, polygonal meshes and very thin thread-like bars; outer shell one and a half times as broad, with simple triangular meshes and thicker bars, which bear numerous bristle-shaped radial by-spines (in the figure the majority of these are broken off). Radial main spines with three smooth edges. (Similar to _Leptosphæra polygonalis_ and _Diplosphæra polygonalis_, but differs from both in the presence of by-spines on the outer, and their absence on the inner shell.)

_Dimensions._--Diameter of the outer shell 0.33, inner 0.22.

_Habitat._--North Pacific, Station 236 south of Japan, surface.

Subgenus 2. _Drymosphæromma_, Haeckel.

_Definition._--Radial by-spines forked or branched (main spines simple).

3. _Drymosphæra furcata_, n. sp.

Inner shell with irregular, polygonal meshes and thin bars, the former five times as broad as the latter; outer shell two and a half times as broad, with simple triangular meshes and smooth bars, bearing numerous long smooth bristle-shaped by-spines, which in the distal half are forked. Radial main spines with three smooth edges.

_Dimensions._--Diameter of the outer shell 0.4, inner 0.16.

_Habitat._--Indian Ocean, Ceylon, surface, Haeckel.

4. _Drymosphæra cladophora_, n. sp.

Inner shell with irregular, polygonal meshes, three to six times as broad as the smooth bars; outer shell twice as broad, with simple triangular meshes and very thin smooth bars, bearing numerous curved, irregularly branched, smooth by-spines. Radial main spines with three serrated edges.

_Dimensions._--Diameter of the outer shell 0.4, inner 0.2.

_Habitat._--Central Pacific, Station 276, surface.

5. _Drymosphæra dendrophora_, n. sp. (Pl. 20, figs. 1, 1_a_, 1_b_).

Inner shell with irregular, polygonal meshes and very thin thread-like bars; outer shell one and a half times as broad, with simple triangular meshes and thicker bars, which bear a forest of {250}very numerous, repeatedly dichotomous or irregularly branched, curved by-spines, longer than the diameter of the outer shell. Radial main spines with three dentated edges. All parts of the skeleton, the net bars as well as the radial beams and spines, are very elegantly denticulated (fig. 1_b_). The central capsule (fig. 1_a_) completely distends the inner shell and forces out protuberances through all its pores; in its centre lies a nucleus one-third its size.

_Dimensions._--Diameter of the outer shell 0.25, inner 0.16.

_Habitat._--Central Pacific, Station 271, surface.

Genus 100. _Astrosphæra_,[135] n. gen.

_Definition._--#Astrosphærida# with two extracapsular cortical shells, connected by long, prismatic, radial spines; inner and outer shell with thin radial by-spines.

The genus _Astrosphæra_ differs from its ancestral form, _Leptosphæra_, in the development of radial by-spines on the surface of both shells.

Subgenus 1. _Astrosphærella_, Haeckel.

_Definition._--Radial main spines simple without lateral branches.

1. _Astrosphæra hexagonalis_, n. sp. (Pl. 19, fig. 4).

Inner shell with regular, hexagonal meshes and very thin bars, having a bristle-shaped, short radial by-spine in each hexagon-corner; outer shell twice as broad, with simple triangular meshes and thicker bars, bearing one row of simple bristle-shaped, curved, radial by-spines. Radial main spines with three smooth edges.

_Dimensions._--Diameter of the outer shell 0.32, inner 0.16.

_Habitat._--South Pacific (West Patagonia), Station 302, surface.

2. _Astrosphæra splendens_, n. sp.

Inner shell with regular, hexagonal meshes, four times as broad as the bars, and covered with numerous curved, long, bristle-shaped by-spines; outer shell three times as broad, with simple triangular meshes and thin bars, bearing a row of very long, curved, bristle-shaped by-spines. Radial main spines with three dentated edges. All parts of the skeleton elegantly denticulated, as in _Drymosphæra dendrophora_ (Pl. 20, fig. 1).

_Dimensions._--Diameter of outer shell 0.7, inner 0.24.

_Habitat._--Tropical Atlantic, Station 347, surface.

{251}Subgenus 2. _Astrosphæromma_.

_Definition._--Radial main spines with three rows of lateral branches (one row on each edge).

3. _Astrosphæra sideræa_, n. sp.

Inner shell with regular, hexagonal meshes, six times as broad as the bars, and covered with numerous short bristle-shaped by-spines; outer shell four times as broad, with simple triangular meshes, and rows of long bristle-shaped by-spines arising from the bars. Radial main spines with three serrated edges and three rows of lateral branches (four branches on each edge).

_Dimensions._--Diameter of the outer shell 0.6, inner 0.15.

_Habitat._--Central Pacific, Station 266, surface.

4. _Astrosphæra stellata_, n. sp. (Pl. 19, fig. 5).

_Diplosphæra stellata_, Haeckel, 1881, Prodrom. et Atlas.

Inner shell with regular, hexagonal, six-rayed meshes, each bar being crossed by a transverse tangential rod, at each nodal-point a long bristle-shaped by-spine; outer shell three times as broad, with simple triangular meshes and denticulated thin bars, bearing a row of bristle-shaped radial by-spines. Radial main spines in the proximal half with three serrated edges, in the distal half with three rows of curved lateral branches (five branches on each edge).

_Dimensions._--Diameter of the outer shell 0.6, inner 0.2.

_Habitat._--Central Pacific, Station 274, surface.

Subfamily ACTINOMMIDA,[136] Haeckel, 1862, Monogr. d. Radiol., p. 440 (_sensu emendato_).

_Definition._--#Astrosphærida# with three concentric, spherical, lattice-shells, united by radial beams.

Genus 101. _Actinomma_,[137] Haeckel, 1862, Monogr. d. Radiol., p. 440.

_Definition._--#Astrosphærida# with three concentric lattice-spheres and numerous simple radial spines of one kind.

The genus _Actinomma_ is here restricted to those #Sphæroidea# which combine the possession of three concentric lattice-shells with numerous radial spines on the surface; the spines are all simple, being of one and the same kind. Commonly two of the three shells are intracapsular medullary shells, connected by radial beams (piercing {252}the central capsule) with the outer, extracapsular, cortical shell. But in some species only one medullary shell is enclosed in the central capsule, whilst both other shells lie outside it. In such case the distance between these two cortical shells is much smaller than their distance from the simple internal medullary shell. These forms correspond more to aculeate _Rhodosphæræ_, whilst the others resemble aculeate _Thecosphæræ_.

Subgenus 1. _Actinommantha_, Haeckel.

_Definition._--Pores of the cortical shell regular, of nearly equal size and similar form; spines on the entire surface (commonly one spine at each nodal-point).

1. _Actinomma hexagonium_, n. sp.

Cortical shell, as well as both medullary shells, very thin walled, with regular, hexagonal pores and thread-like bars between them. Pores of the outer shell twice as broad as those of the middle, and three times as broad as those of the inner shells. Radial proportion of the three spheres = 1 : 3 : 9; about twenty thin radial beams between them. At each nodal-point of the surface arises one bristle-shaped radial spine, half as long as the radius.

_Dimensions._--Diameter of the outer shell 0.22, middle 0.07, inner 0.025; meshes of the cortical shell 0.01; length of the spines 0.05.

_Habitat._--Central Pacific, Stations 270 to 274, surface.

2. _Actinomma facetum_, n. sp.

Cortical shell thick walled, with regular, circular, hexagonally framed pores, three times as broad as the bars. Pores of both medullary shells regular, circular. Radial proportion of the three spheres = 1 : 2 : 4; about forty thin radial beams between them. At each nodal-point of the surface arises one short, three-sided pyramidal, radial spine, about one-third as long as the radius.

_Dimensions._--Diameter of the outer shell 0.16, middle 0.08, inner 0.04; cortical pores 0.012, bars 0.004; length of the spines 0.03, basal breadth 0.015.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

3. _Actinomma anthomma_, n. sp.

Cortical shell thick walled, with regular, six-lobed pores, twice as broad as the bars. At each nodal-point of the surface is one short conical radial spine, as long as the diameter of the pores; one corresponding to each lobe, and there is therefore around each pore a regular corona of six spines, as in _Haliomma lirianthus_ (Pl. 28, fig. 1_b_). Both medullary shells with simple, circular, regular pores. Radial proportion of the three spheres = 1 : 2.5 : 7; radial beams between them only six, opposite in pairs in the three dimensive axes.

{253}_Dimensions._--Diameter of the outer shell 0.2, middle 0.075, inner 0.003; cortical pores 0.01, bars 0.005; length of the spines 0.01.

_Habitat._--Central Pacific, Station 271, surface.

4. _Actinomma castanomma_, n. sp.

Cortical shell as well as both medullary shells thick walled, with regular, circular pores, twice as broad as the bars; between them at each nodal-point one bristle-shaped radial spine, one-third as long as the radius, with conical base. Radial proportion of the three spheres = 2 : 3 : 8; only six radial beams between them (opposed in pairs in the three dimensive axes).

_Dimensions._--Diameter of the outer shell 0.15, middle 0.06, inner 0.04; cortical pores 0.008, bars 0.004; length of the spines 0.025.

_Habitat._--South Atlantic, Station 333, surface.

5. _Actinomma entactinia_, Stöhr.

_Actinomma entactinia_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 93, Taf. ii. fig. 12.

Cortical shell as well as both medullary shells thick walled, with regular, circular pores, of the same breadth as the bars. Radial proportion of the three spheres = 1 : 3 : 8; radial beams between them very numerous (thirty to fifty or more?). Entire surface covered with short thick conical spines, only one-fifth as long as the radius.

_Dimensions._--Diameter of the outer shell 0.16, middle 0.06, inner 0.02; cortical pores and bars 0.007; length of the spines 0.015.

_Habitat._--Fossil in the Tertiary rocks of Sicily, Grotte, Caltanisetta.

Subgenus 2. _Actinommetta_, Haeckel.

_Definition._--Pores of the outer shell regular, of nearly equal size and similar form; spines not over the entire surface, but scattered at intervals (their number smaller than that of the nodal-points).

6. _Actinomma japonicum_, n. sp.

Cortical shell thick walled, with regular, circular, hexagonally framed pores, three times as broad as the bars. Both medullary shells with simple, circular, regular pores, of the same breadth as the bars. Radial proportion of the three spheres = 2 : 5 : 9; radial beams between them twenty, prolonged outside into twenty symmetrically disposed, three-sided pyramidal spines, as long as the radius.

_Dimensions._--Diameter of the outer shell 0.18, middle 0.1, inner 0.04; cortical pores 0.01, bars 0.003; length of the spines 0.1, basal breadth 0.012.

_Habitat._--North Pacific, Station 240, east of Japan, surface.

{254}7. _Actinomma denticulatum_, n. sp. (Pl. 29, fig. 3).

Cortical shell thick walled, with regular, circular, double-edged pores, twice as broad as the bars. Forty to fifty radial spines, three-sided pyramidal, half as long as the radius, with three elegantly denticulated edges. Radial proportion of the three spheres = 1 : 2 : 5. (Differs from _Haliomma denticulatum_ only in the double medullary shell and larger size.)

_Dimensions._--Diameter of the outer shell 0.14, middle 0.06, inner 0.03; cortical pores 0.01, bars 0.005; length of the spines 0.04, basal breadth 0.01.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

8. _Actinomma trinacrium_, Haeckel.

_Actinomma trinacrium_, Haeckel, 1862, Monogr. d. Radiol., p. 441, Taf. xxiv. figs. 6-8.

_Haliomma trinacrium_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 815.

Cortical shell as well as both medullary shells thin walled, with subregular, circular pores, twice as broad as the bars. Radial proportion of the three spheres = 1 : 3 : 9; radial beams between them twenty, prolonged outside into strong, three-sided pyramidal spines, as long as the radius; between them, on the surface, numerous similar spines. Sometimes the latter remain smaller, the pores more irregular, and then this species corresponds to _Echinomma trinacrium_.

_Dimensions._--Diameter of the outer shell 0.09, middle 0.03, inner 0.01; cortical pores 0.008, bars 0.004; length of the spines 0.04, basal breadth 0.01.

_Habitat._--Mediterranean (Messina, Corfu, Haeckel), surface.

9. _Actinomma pachyderma_, n. sp. (Pl. 29, figs. 4, 5).

Cortical shell very thick walled, with regular, circular, double-edged pores, twice as broad as the bars. Both medullary shells with simple, small, circular pores, of the same breadth as the bars. Radial proportion of the three spheres = 1 : 2 : 4; radial spines about twenty, conical, shorter than the radius, prolonged inside into twenty very thin connecting beams (fig. 4).

_Dimensions._--Diameter of the outer shell 0.08, middle 0.04, inner 0.02; cortical pores 0.01; bars 0.005; length of the spines 0.03, basal breadth 0.01.

_Habitat._--South Pacific, Station 297, depth 1775 fathoms.

Subgenus 3. _Actinommilla_, Haeckel.

_Definition._--Pores of the cortical shell irregular, of different size and form; spines over the entire surface (commonly one spine at each nodal-point).

10. _Actinomma spinigerum_, Stöhr.

_Actinomma spinigerum_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 92, Taf. ii. fig. 10.

Cortical shell thick walled, with irregular, roundish, or subcircular pores, twice to four times as broad as the bars. Radial proportion of the three spheres = 1 : 3 : 8; between them eight (?) {255}connecting radial beams. Entire surface densely covered with small conical spines, not larger than the pores.

_Dimensions._--Diameter of the outer shell 0.17, middle 0.07, inner 0.023; cortical pores 0.006 to 0.012, bars 0.003; length of the spines 0.01.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

11. _Actinomma hirsutum_, n. sp.

Cortical shell thick walled, with irregular, roundish pores, about the same breadth as the bars. Radial proportion of the three spheres = 1 : 2 : 8; between them numerous (twenty to thirty or more) cylindrical connecting beams. Entire surface densely covered with innumerable small bristle-shaped spines, as long as the diameter of the inner shell.

_Dimensions._--Diameter of the outer shell 0.25, middle 0.06, inner 0.03; cortical pores and bars 0.004 to 0.008; length of the spines 0.03.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

Subgenus 4. _Actinommura_, Haeckel.

_Definition._--Pores of the cortical shell irregular, of different size and form; spines not over the entire surface, but scattered at intervals (their number smaller than that of the nodal-points).

12. _Actinomma capillaceum_, n. sp. (Pl. 29, fig. 6).

Cortical shell very thin walled, with irregular, polygonal meshes (sixteen to eighteen on the radius), three to six times as broad as the bars. Both medullary shells with smaller pores of the same structure. Radial proportion of the three spheres = 1 : 2.5 : 7; radial connecting beams between them very thin and numerous (one hundred and twenty to one hundred and fifty or more), each prolonged outside into a short three-sided pyramidal spine, as long as the radius of the inner shell. (Similar to _Haliomma capillaceum_.)

_Dimensions._--Diameter of the outer shell 0.27, middle 0.1, inner 0.04; cortical pores 0.01 to 0.02, bars 0.003; length of the spines 0.02, basal breadth 0.005.

_Habitat._--Central Pacific, Stations 266 to 274, surface.

13. _Actinomma arcadophorum_, n. sp. (Pl. 29, figs. 7, 8).

Cortical shell very thin walled, with irregular, polygonal meshes, ten to twenty times as broad as the bars; twelve to sixteen on the radius. Both medullary shells with similar delicate network. Radial proportion of the three spheres = 1 : 2 : 6; numerous thin radial beams (forty to eighty or more) connect both medullary shells and alternate with other beams, which arise from arcade-shaped {256}protuberances of the outer medullary shell, and connect it with the cortical shell. Outer prolongations of these form the bristle-shaped spines of the surface.

_Dimensions._--Diameter of the outer shell 0.22, middle 0.09, inner 0.04; cortical pores 0.01 to 0.02, bars 0.001 to 0.002; length of the radial spines 0.2.

_Habitat._--Central Pacific, Station 266, surface.

14. _Actinomma schwageri_, Stöhr.

_Actinomma schwageri_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 92, Taf. ii. fig. 9_a_, _b_.

Cortical shell thick walled, with irregular, large, polygonal meshes, five to twelve times as broad as the bars; six to eight on the radius. Both medullary shells with very small, circular, regular pores. Radial proportion of the three spheres = 1 : 2 : 9; connecting radial beams between them nine, prolonged outside into nine short stout, three-sided pyramidal spines, as long as the diameter of the inner shell.

_Dimensions._--Diameter of the outer shell 0.17, middle 0.04, inner 0.02; cortical pores 0.01 to 0.03, bars 0.006 and less; length of the spines 0.02, basal breadth 0.01.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

15. _Actinomma dodecomma_, n. sp.

Cortical shell thin walled, with irregular, roundish pores, three to six times as broad as the bars. Both medullary shells with regular, circular pores, twice as broad as the bars. Radial proportion of the three shells = 1 : 2.5 : 7; connecting radial beams between them twelve, regularly disposed, prolonged outside into twelve strong, three-sided pyramidal spines, as long as the radius.

_Dimensions._--Diameter of the outer shell 0.14, middle 0.05, inner 0.02; cortical pores 0.008 to 0.018, bars 0.003; length of the spines 0.08, breadth 0.02.

_Habitat._--Tropical Atlantic, Station 348, depth 2450 fathoms.

16. _Actinomma pachycapsa_, n. sp.

Cortical shell very thick walled, with irregular, roundish pores, twice to four times as broad as the bars; twelve to sixteen on the radius. Radial proportion of the three spheres = 1 : 3 : 12. Both medullary shells of similar irregular structure, connected with the cortical shell by twelve regularly disposed radial beams, which are prolonged outside into twelve short stout conical spines, as long as the diameter of the middle shell.

_Dimensions._--Diameter of the outer shell 0.25, middle 0.06, inner 0.02; cortical pores 0.006 to 0.012, bars 0.003; length of the spines 0.05, breadth 0.02.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

17. _Actinomma giganteum_, n. sp.

Cortical shell thick walled, little larger than the outer medullary shell, whilst the inner is only one-tenth as large. Pores of all three shells irregular, roundish, or subcircular, twice to three times {257}as broad as the bars, on an average twice as large in the outer and middle as in the inner shell. Sixty to eighty short conical radial spines on the surface, about as long as the diameter of the inner shell, and one-fourth as broad at the base. Radial proportion of the three spheres = 1 : 9 : 10.

_Dimensions._--Diameter of the outer shell 0.4 to 0.5, middle 0.35 to 0.45, inner 0.05 to 0.06.

_Habitat._--Fossil in Barbados.

Genus 102. _Echinomma_,[138] Haeckel, 1881, Prodromus, p. 453.

_Definition._--#Astrosphærida# with three concentric lattice-spheres and numerous simple radial spines of two different kinds; larger main spines and smaller by-spines.

The genus _Echinomma_, differs from its ancestral form, _Actinomma_, in the differentiation of the radial spines. Whilst a large number of small by-spines cover the entire surface, a smaller number of large main spines are scattered over it, or limited to certain regularly distributed points. It represents _Heliosoma_ among the Haliommida.

Subgenus 1. _Echinommetta_, Haeckel.

_Definition._--Pores of the cortical shell regular, of nearly equal size and similar form.

1. _Echinomma echinidium_, n. sp.

Cortical shell thin walled, with regular, hexagonal pores, four times as broad as the bars; ten to twelve on the radius. Both medullary shells with regular, circular pores, twice as broad as the bars. Radial proportion of the three spheres = 1 : 2 : 5. Surface covered with short bristle-shaped by-spines (one in every hexagon-corner); twenty main spines regularly disposed, three-sided pyramidal, as long as the diameter of the inner shell.

_Dimensions._--Diameter of the outer shell 0.1, middle 0.045, inner 0.02; cortical pores 0.008, bars 0.002; length of the main spines 0.02, breadth 0.01.

_Habitat._--South Pacific, Station 295, surface.

2. _Echinomma cidaris_, n. sp.

Cortical shell thin walled, with regular, circular, hexagonally framed pores, twice as broad as the bars; six to eight on the radius. Both medullary shells with simple, circular pores. Radial proportion of the three spheres = 1 : 2 : 6. Surface covered with short bristle-shaped by-spines, half as long as the forty to fifty main spines, which are three-sided pyramidal, and reach the radius of the shell.

_Dimensions._--Diameter of the outer shell 0.18, middle 0.06, inner 0.03; cortical pores 0.01, bars 0.005; length of the main spines 0.08, basal breadth 0.015.

_Habitat._--Central Pacific, Station 272, surface.

{258}3. _Echinomma aculeatum_, Haeckel.

_Actinomma aculeatum_, Stöhr, 1880 Palæontogr., vol. xxvi. p. 92, Taf. ii. fig. 11.

Cortical shell thick walled with regular circular pores, of the same breadth as the bars; eight to ten on the radius. Radial proportion of the three spheres = 1 : 2 : 8. Surface covered with short conical by-spines about twenty strong main spines, three-sided pyramidal, one-third as long as the shell diameter.

_Dimensions._--Diameter of the outer shell 0.16, middle 0.04, inner 0.02; cortical pores and bars 0.003; length of the main spines 0.05, basal breadth 0.013.

_Habitat._--Fossil in the Tertiary rocks of Sicily and Barbados; living in the Atlantic, Station 332, depth 2200 fathoms.

4. _Echinomma diadema_, n. sp.

Cortical shell thick walled with regular circular pores, twice as broad as the bars; sixteen to eighteen on the radius. Radial proportion of the three spheres = 1 : 3 : 11. Surface covered with short bristle-shaped by-spines one third as long as the twelve stout conical main spines, which reach in length the radius, and lie opposite in pairs in six axes.

_Dimensions._--Diameter of the outer shell 0.22, middle 0.06, inner 0.02; cortical pores 0.006, bars 0.003 length of the main spines 0.12, basal breadth 0.02.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

Subgenus 2. _Echinommura_, Haeckel.

_Definition._--Pores of the cortical shell irregular, of different size or form.

5. _Echinomma sphærechinus_, n. sp. (Pl. 29, fig. 2).

_Actinomma sphærechinus_, Haeckel, 1879, Atlas (pl. xxix. fig. 2).

Cortical shell thin walled, with irregular, roundish pores, twice to five times as broad as the bars; five to seven on the radius. Both medullary shells with regular, circular pores, twice as broad as the bars. Radial proportion of the three spheres = 1 : 2 : 4. Surface covered with thirty to fifty pyramidal main spines, as long as the diameter of the inner shell, and with numerous small conical by-spines of half the length.

_Dimensions._--Diameter of the outer shell 0.11, middle 0.05, inner 0.025; cortical pores 0.01 to 0.02, bars 0.004; length of the main spines 0.03, basal breadth 0.005.

_Habitat._--North Atlantic, Station 353, surface.

6. _Echinomma trinacrium_, Haeckel.

_Actinomma trinacrium_, Haeckel, 1862, Monogr. d. Radiol., p. 441, Taf. xxiv. figs. 6-8.

Cortical shell thin walled, with irregular, roundish pores, twice to three times as broad as the bars. Both medullary shells with regular, circular pores. Radial proportion of the three spheres {259}= 1 : 3 : 9. On the surface about twenty three-sided pyramidal main spines, as long as the radius, and numerous (forty to sixty) by-spines of half the length. (Compare with this species _Actinomma trinacrium_, with which it is connected by transitional forms.)

_Dimensions._--Diameter of the outer shell 0.09, middle 0.03, inner 0.01; cortical pores 0.008 to 0.012, bars 0.004; length of the spines 0.02 to 0.05, basal breadth 0.01.

_Habitat._--Mediterranean (Messina).

7. _Echinomma toxopneustes_, n. sp. (Pl. 29, fig. 1).

Cortical shell thin walled, with large, irregular roundish, polygonally framed pores, twice to four times as broad as the crested bars. Both medullary shells of similar structure. Radial proportion of the three spheres = 1 : 2.5 : 6. Numerous (thirty to fifty or more) thin radial beams connecting them, prolonged outside into strong three-sided pyramidal spines, shorter than the radius; each of the three wings with two teeth. Between these, numerous smaller angular by-spines of one-quarter to one-half the length.

_Dimensions._--Diameter of the outer shell 0.12, middle 0.05, inner 0.02; cortical pores 0.01 to 0.03, bars 0.008; length of the main spines 0.05, basal breadth 0.01.

_Habitat._--South-east Pacific (South of Juan Fernandez), Station 300, surface.

Genus 103. _Pityomma_,[139] Haeckel, 1881, Prodromus, p. 453.

_Definition._--#Astrosphærida# with three concentric lattice-shells and numerous branched radial spines.

The genus _Pityomma_ differs from its ancestral form, _Actinomma_, in the ramification of its radial spines, and exhibits therefore the same relation to it that _Elatomma_, among the Haliommida, bears to _Haliomma_.

1. _Pityomma scoparium_, n. sp.

Cortical shell thick walled, connected with both concentric medullary shells by twenty thin radial beams, which are prolonged outside into twenty large cylindrical radial spines; these are somewhat shorter than the shell radius, simple in the proximal inner half, irregularly branched in the outer half. All three spheres with regular, circular pores, twice to three times as broad as the bars; radial proportion = 1 : 2 : 6. (Similar to _Cladococcus scoparius_, Pl. 27, fig. 2, and _Elatomma scoparium_, but differs from both in the double medullary shell.)

_Dimensions._--Diameter of the outer shell 0.15, middle 0.05, inner 0.025; length of the spines 0.1.

_Habitat._--Central Pacific, Station 273, surface.

{260}2. _Pityomma piniferum_, n. sp.

Cortical shell thin walled, with irregular, roundish pores, connected with both medullary shells by twenty stout radial beams, which are prolonged outside into twenty large three-sided prismatic spines. These are longer than the shell diameter and have three dentate edges, being branched like a pine tree (with four to six ramified branches on each edge, decreasing in size towards the distal end); similar to those of _Cladococcus abietinus_ (Pl. 27, fig. 3). Radial proportion of the three spheres = 1 : 2 : 8. Both medullary shells with regular, circular pores, twice as broad as the bars.

_Dimensions._--Diameter of the outer shell 0.2, middle 0.05, inner 0.025; length of the spines 0.25.

_Habitat._--South Pacific, Station 299 (Juan Fernandez), surface.

3. _Pityomma drymodes_, n. sp. (Pl. 29, fig. 9).

Cortical shell thin walled, connected with both medullary shells by very numerous (one hundred to two hundred or more) very thin radial beams, which are prolonged outside into thin branched radial spines, scarcely half as long as the shell radius, each spine bearing six to nine simple branches. Outer and middle shell uneven, with hill-shaped protuberances and valleys between them; the connecting radial beams, which arise from the top of the protuberances of the middle shell, are inserted into the deepest part of the valleys of the outer shell. Radial proportion of the three spheres = 1 : 3 : 8. Outer medullary shell with small, irregular, roundish, or polygonal pores, not much broader than the bars; innermost shell with polygonal pores and very thin bars.

_Dimensions._--Diameter of the outer shell 0.28, middle 0.1, inner 0.033; length of the spines 0.07, breadth 0.004.

_Habitat._--Central Pacific, Station 271, surface.

Subfamily CROMYOMMIDA,[140] Haeckel, 1881, Prodromus, pp. 449, 453.

_Definition._--#Astrosphærida# with four concentric spherical lattice-shells.

Genus 104. _Cromyomma_,[141] Haeckel, 1881, Prodromus, p. 454.

_Definition._--#Astrosphærida# with four concentric lattice-spheres and numerous simple radial spines of one kind.

The genus _Cromyomma_ is the common ancestral form of the Cromyommida, or of those Astrosphærida in which the shell is composed of four concentric spheres, connected by radial beams. Usually two of these are intracapsular or medullary {261}shells, two extracapsular or cortical shells; the distance between the former and the latter is greater than the distance between either the two inner or the two outer shells. In some cases, however (_e.g._, _Cromyomma zonaster_), the distance between all four shells is equal.

Subgenus 1. _Cromyommetta_, Haeckel.

_Definition._--Pores of the outer cortical shell regular, of nearly equal size and similar form.

1. _Cromyomma villosum_, n. sp. (Pl. 30, fig. 2).

Radial proportion of the four spheres = 1 : 2 : 4 : 5. Outer cortical shell thick walled, densely covered with innumerable bristle-shaped radial spines, half as long as the radius. Pores regular, circular, double-edged, of the same breadth as the bars; ten to twelve on the radius. The thick outer shell is so dark, that the outlines only of the other three shells can be seen.

_Dimensions._--Diameter of the four shells--(A) outer cortical shell 0.2, (B) inner cortical shell 0.16, (C) outer medullary shell 0.08, (D) inner medullary shell 0.04; pores and bars of the outer shell 0.008; length of the spines 0.04.

_Habitat._--Central Pacific, Station 267, depth 2700 fathoms.

2. _Cromyomma zonaster_, Haeckel.

_Acanthosphæra zonaster_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 285, Taf. ii. fig. 2.

Radial proportion of the four spheres = 2 : 3 : 4 : 5. Outer cortical shell thick walled, densely covered with numerous bristle-shaped radial spines, as long as the radius. Pores regular, circular, twice as broad as the bars; eight to ten on the radius. The thick outer shell is so dark, that the outlines only of the other three shells can be seen.

_Dimensions._--Diameter of the four shells--(A) 0.15, (B) 0.12, (C) 0.09, (D) 0.06; pores of the outer shell 0.01, bars 0.005; length of the spines 0.08.

_Habitat._--Arctic Ocean, Greenland (depth 1000 fathoms), "Alert" Expedition.

3. _Cromyomma perplexum_, Stöhr.

_Cromyomma perplexum_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 95, Taf. iii. fig. 5.

Radial proportion of the four spheres = 1 : 2 : 3 : 4. Outer cortical shell thick walled, densely covered with short conical spines, as long as the diameter of the pores. These are regular, circular, three times as broad as the bars; six to eight on the radius. The thick outer shell is so dark, that the outlines only of the three other shells can be seen.

_Dimensions._--Diameter of the four shells--(A) 0.17, (B) 0.13, (C) 0.087, (D) 0.043; pores of the outer shell 0.015, bars 0.005; length of the spines 0.02.

_Habitat._--Fossil in the Tertiary rocks of Sicily (Grotte) Stöhr.

{262}Subgenus 2. _Cromyommura_, Haeckel.

_Definition._--Pores of the outer cortical shell irregular, of different size and form.

4. _Cromyomma perspicuum_, n. sp. (Pl. 30, fig. 8).

_Cromyosphæra perspicua_, Haeckel, 1879, Atlas (pl. xxx. fig. 8).

Radial proportion of the four shells = 1 : 2.5 : 6 : 9. Outer cortical shell very thin walled, with thread-like bars, and irregular, polygonal pores; inner cortical shell with similar pores, but with thicker bars. Both medullary shells with regular, circular pores (the outer three times as broad as the inner). Numerous thin radial beams connect the latter with the former; other very thin and numerous beams connect the two cortical shells, and are prolonged outside into short bristle-shaped spines (often longer than in the figure).

_Dimensions._--Diameter of the four shells--(A) 0.18, (B) 0.12, (C) 0.05, (D) 0.02; pores of the outer shell 0.01 to 0.02; length of the spines 0.01 to 0.03.

_Habitat._--Central Pacific, Station 274, surface.

5. _Cromyomma quadruplex_, Haeckel.

_Cromyomma quadruplex_, Haeckel, 1862, Monogr. d. Radiol., p. 446.

_Haliomma quadruplex_, Ehrenberg, 1854, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 243.

Radial proportion of the four spheres = 1 : 3 : 7 : 10. Outer cortical shell thin walled, irregularly covered with numerous angular spines, as long as the radius. Pores of all four shells irregular, roundish, increasing in size from the first to the fourth.

_Dimensions._--Diameter of the four shells--(A) 0.15, (B) 0.1, (C) 0.045, (D) 0.015; pores of the outer shell 0.01 to 0.02; length of the spines 0.07.

_Habitat._--North Atlantic, Station 353, depth 2965 fathoms.

6. _Cromyomma macroporum_, Stöhr.

_Cromyomma macroporum_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 95, Taf. iii. fig. 4.

Radial proportion of the four spheres = 1 : 3 : 6 : 9. Outer cortical shell thick walled, densely covered with short conical spines, as long as the diameter of the pores; the latter are irregular, roundish, or polygonal, larger and smaller alternating.

_Dimensions._--Diameter of the four shells--(A) 0.1, (B) 0.066, (C) 0.033, (D) 0.011; pores of the outer shell 0.033 to 0.016, bars 0.003; length of the spines 0.01.

_Habitat._--Fossil in the Tertiary rocks of Sicily, Grotte, Stöhr.

7. _Cromyomma circumtextum_, n. sp. (Pl. 30, fig. 4).

Radial proportion of the four spheres = 1 : 2 : 5 : 7. Outer cortical shell very delicate and thin walled, with thread-like bars and large, irregular, polygonal meshes (larger than the innermost shell); {263}inner cortical shell also with irregular, polygonal pores, three to nine times as broad as the thick bars. Both medullary shells with subregular, circular pores (the outer three times as broad as the inner). Radial spines twelve to twenty, three-sided prismatic, stout, piercing the three outer shells, inserted on the innermost; their outer part pyramidal, half as long as the radius.

_Dimensions._--Diameter of the four shells--(A) 0.22, (B) 0.15, (C) 0.07, (D) 0.03; meshes of the outer shell 0.02 to 0.04; length of the outer spines 0.05.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

8. _Cromyomma mucronatum_, n. sp. (Pl. 30, figs. 5, 5_a_).

Radial proportion of the three spheres = 1 : 2 : 3 : 6. Outer cortical shell thin walled, with large, irregular, roundish pores and crested three-sided bars; inner cortical shell with regular, circular, hexagonally formed pores (four times as broad as the bars). Both medullary shells with simple, small, regular, circular pores (fig. 5_a_). Twelve radial spines three-sided prismatic, dagger-shaped, with three teeth, as long as the diameter of the innermost shell.

_Dimensions._--Diameter of the four shells--(A) 0.24, (B) 0.12, (C) 0.08, (D) 0.04; meshes of the outer shell 0.02 to 0.04; length of the spines 0.04.

_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.

Genus 105. _Cromyechinus_,[142] Haeckel, 1881, Prodromus, p. 454.

_Definition._--#Astrosphærida# with four concentric lattice-spheres and numerous simple spines of two different kinds; larger main spines and smaller by-spines.

The genus _Cromyechinus_ differs from _Cromyomma_ in the same way as _Echinomma_ from _Actinomma_; the radial spines being differentiated into two different kinds; a larger number of small by-spines, and a smaller number of large main spines.

1. _Cromyechinus icosacanthus_, n. sp. (Pl. 30, fig. 1).

Radial proportion of the three spheres = 1 : 2 : 6 : 8. Outer cortical shell very delicate, with very small, regular, circular pores, covered with very numerous bristle-shaped by-spines, half as long as the radius; inner cortical shell with very large, irregular, polygonal pores, three to eight times as broad as the bars. Both medullary shells with regular, circular pores, connected with the former by twenty regularly disposed, very thin bars; these are prolonged outside into twenty very stout, three-sided prismatic main spines, as long as the radius, which arise from the inner cortical shell, and at the distal end are cuspidate.

_Dimensions._--Diameter of the four shells--(A) 0.16, (B) 0.13, (C) 0.04, (D) 0.02; pores of the outer cortical shell 0.003, of the inner 0.03, bars 0.003; length of the spines 0.08.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

{264}2. _Cromyechinus dodecacanthus_, n. sp. (Pl. 30, figs. 3, 3_a_).

Radial proportion of the four spheres = 1 : 3 : 10 : 12. Outer cortical shell very delicate, with very small, regular, circular pores, covered with numerous short bristle-shaped by-spines, scarcely one-fourth as long as the radius; inner cortical shell with very large, irregular, polygonal pores, twice to six times as broad as the bars. Both medullary shells with very small, regular, circular pores, connected with the former by twelve regularly disposed, thin radial beams; these are prolonged outside into twelve strong, three-sided pyramidal main spines, one-third as long as the shell diameter. (Differs from the foregoing only in the number and form of the radial spines.)

_Dimensions._--Diameter of the four shells--(A) 0.12, (B) 0.1, (C) 0.03, (D) 0.01; pores of the outer cortical shell 0.002, of the inner 0.02, bars 0.002; length of the spines 0.04, basal breadth 0.01.

_Habitat._--South Atlantic, Station 325, surface.

3. _Cromyechinus polyacanthus_, n. sp.

Radial proportion of the four spheres = 1 : 2 : 8 : 10. Outer cortical shell of the same structure as the inner, with irregular, roundish pores, twice to six times as broad as the bars. Both medullary shells with small, regular, circular pores, twice as broad as the bars. Connecting radial beams forty to sixty, thin, cylindrical, prolonged outside into forty to sixty strong conical main spines, about as long as the radius. Between these, numerous thin bristle-shaped by-spines, nearly of the same length.

_Dimensions._--Diameter of the four shells--(A) 0.25, (B) 0.2, (C) 0.05, (D) 0.025; pores of both cortical shells 0.01 to 0.03; length of the spines 0.12.

_Habitat._--North Pacific, Station 237, surface.

Genus 106. _Cromyodrymus_,[143] Haeckel, 1881, Prodromus, p. 454.

_Definition._--#Astrosphærida# with four concentric lattice-spheres and numerous branched radial spines.

The genus _Cromyodrymus_ differs from its ancestral form, _Cromyomma_, in the ramification of the radial spines, and exhibits therefore the same relation to it that _Pityomma_ among the Actinommida bears to _Actinomma_.

1. _Cromyodrymus quadricuspis_, n. sp. (Pl. 30, figs. 7, 7_a_).

Radial proportion of the four shells = 1 : 3 : 6 : 12. All four shells with regular, circular pores, about twice as broad as the bars. Radial proportion of the pores in the four shells = 2 : 4 : 2 : 1. Radial spines fifty to sixty, three-sided prismatic, half as long as the radius, with three recurved teeth, each spine in this way bearing four points.

{265}_Dimensions._--Diameter of the four shells--(A) 0.16, (B) 0.08, (C) 0.04, (D) 0.013; length of the spines 0.03 to 0.04, breadth 0.007.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

2. _Cromyodrymus abietinus_, n. sp. (Pl. 30, fig. 6).

Radial proportion of the four shells = 1 : 2 : 5 : 11. All four shells with irregular, roundish pores, twice to four times as broad as the bars. Radial proportion of the pores in the four shells = 9 : 3 : 2 : 1. Radial spines eighty to one hundred and twenty, about as long as the radius, branched like a pine tree, with six to twelve ramified branches.

_Dimensions._--Diameter of the four shells--(A) 0.22, (B) 0.1, (C) 0.04, (D) 0.02; length of the spines 0.12, breadth 0.006.

_Habitat._--South-east Pacific (Juan Fernandez), Station 299, surface.

Subfamily CARYOMMIDA,[144] Haeckel.

_Arachnosphærida_, Haeckel, 1862, Monogr. d. Radiol., p. 354; Prodromus, 1881, p. 454.

_Definition._--#Astrosphærida# with five or more concentric spherical lattice-shells.

Genus 107. _Caryomma_,[145] n. gen.

_Definition._--#Arachnosphærida# with five to six or more concentric spherical lattice-shells; two inner (intracapsular) medullary and three or more outer (extracapsular) cortical shells, composed of ordinary lattice-work; distance between the former and the latter greater than between any other two shells.

The genus _Caryomma_ may be regarded as a _Cromyomma_, in which the number of the cortical shells is increased to three, four, or more. These lie outside the central capsule, whilst two medullary shells lie within it, and are connected with the former by numerous radial spines piercing the wall of the capsule. The ordinary lattice-work is not arachnoidal, as in the three following genera.

1. _Caryomma regulare_, n. sp.

Radial proportion of the five shells = 1 : 2 : 6 : 8 : 10. All five shells with regular, circular pores, twice to three times as broad as the bars, and gradually increasing in size from the innermost to the outermost shell. Radial beams connecting them twenty, prolonged on the surface into twenty stout, three-sided pyramidal, radial spines, half as long as the radius, regularly disposed.

_Dimensions._--Diameter of the five shells--(A) 0.25, (B) 0.2, (C) 0.15, (D) 0.05, (E) 0.025.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

{266}2. _Caryomma irregulare_, n. sp.

Radial proportion of the six shells = 1 : 2.5 : 8 : 10.5 : 13 : 15. Both inner (medullary) shells with regular, circular pores, the other four (cortical) shells with irregular, roundish pores, gradually increasing in size from the innermost to the outermost shell. Radial spines sixty to eighty, pyramidal, irregularly disposed.

_Dimensions._--Diameter of the six shells--(A) 0.3, (B) 0.26, (C) 0.21, (D) 0.16, (E) 0.05, (F) 0.02.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

Genus 108. _Arachnopila_,[146] n. gen.

_Definition._--#Astrosphærida# with five to ten or more cortical, concentric, polyhedral, or spherical lattice-shells, composed of a very thin cobweb-like network; innermost shell with hexagonal (regular) or polygonal (irregular) meshes; other shells with simple triangular meshes, without diagonal threads between them.

The genus _Arachnopila_, together with the two following genera, forms the peculiar small group of large Arachnosphærida, separated from the true Caryommida by the totally different structure and disposition of the numerous concentric shells; the former exhibits a similar relation to the latter that the Diplosphærida bears to the Elatommida among the dispherical Haliommida. The concentric shells (five to ten or more) lie outside the central capsule, and are composed of very delicate, cobweb-like threads. From the innermost shell arise numerous, three-sided prismatic, very long spines, from which at equal regular distances arise lateral branches (three pairs from each spine, and one pair from each corner). In _Arachnopila_ these threads pass directly from one spine to the other, and form simple, large, triangular meshes between them. The concentric shells are not connected by interwoven diagonal threads.

1. _Arachnopila hexagonella_, n. sp.

Innermost shell with regular hexagonal pores; its diameter twice as long as the equal distance between every two concentric shells. Radial spines twenty to forty, each with twenty to twenty-four verticils.

_Dimensions._--Diameter of the innermost shell 0.1; distance between the concentric shells 0.05.

_Habitat._--Central Pacific, Station 271, surface.

2. _Arachnopila polygonella_, n. sp.

Innermost shell with irregular, polygonal pores; its diameter fully as long as the equal distance between every two concentric shells. Radial spines sixty to eighty, each with twelve to sixteen verticils.

_Dimensions._--Diameter of the innermost shell 0.04; distance between the concentric shells 0.04.

_Habitat._--Central Pacific, Station 266, surface.

{267}Genus 109. _Arachnopegma_,[147] Haeckel, 1881, Prodromus, p. 454.

_Definition._--#Astrosphærida# with five to ten or more cortical, concentric, polyhedral, or spherical lattice-shells, composed of a very thin, cobweb-like network; innermost shell with hexagonal or polygonal meshes; other shells with simple triangular meshes, connected to one another by diagonal threads between them.

The genus _Arachnopegma_ differs from its ancestral form _Arachnopila_, in the possession of peculiar diagonal threads, which connect the verticils or nodal-points of every two neighbouring radial spines in two different neighbouring concentric shells. In this case, therefore, not only do triangular meshes lie in the spherical faces of the concentric spheres, but also between them, in numerous oblique diagonal planes; a very rare and remarkable structure, and forming a transition to spongy shells.

1. _Arachnopegma verticillatum_, n. sp.

Innermost shell with regular, hexagonal meshes; its diameter is the same as the equal distance between each of the two shells. Threads of the network smooth. Radial spines twenty to forty, each with fifteen to twenty verticils.

_Dimensions._--Diameter of the innermost shell 0.04, distance between the concentric shells 0.03 to 0.04.

_Habitat._--Central Pacific, Station 266, surface.

2. _Arachnopegma longispinum_, n. sp.

Innermost shell with regular, hexagonal meshes; its diameter half as large as the equal distance between every two shells. Threads of the network dentated or with small knots. Radial spines fifty to sixty, each with twenty to twenty-five verticils.

_Dimensions._--Diameter of the innermost shell 0.02; distance between the concentric shells 0.04 to 0.05.

_Habitat._--Central Pacific, Station 272, surface.

3. _Arachnopegma increscens_, n. sp.

Innermost shell with regular, hexagonal meshes; its diameter quite as large as the distance between it and the second shell; only half as large as the distance between the fourth and fifth shells. Forty to fifty radial spines, each with fifteen to twenty verticils.

_Dimensions._--Diameter of the innermost shell (A) 0.025; distance between the following shells--A, B = 0.025, B, C = 0.03, C, D = 0.04, D, E = 0.048, E, F = 0.056, F, G = 0.064, &c.

_Habitat._--Central Pacific, Station 274, surface.

{268}Genus 110. _Arachnosphæra_,[148] Haeckel, 1862, Monogr. d. Radiol., p. 355.

The genus _Arachnosphæra_ (accurately described by me in 1862, _loc. cit._) differs from the two preceding genera in the irregular form of the large meshes in all shells (except often the innermost). This is caused by the ramification of the thin threads, which on each shell connect the neighbouring spines. In _Arachnopila_ and _Arachnopegma_ the threads pass directly and undivided from each spine to the neighbouring spine (three pairs from the three edges), and therefore all meshes are triangular. In _Arachnosphæra_ they become polygonal by irregular ramification of the threads. There are here no diagonal threads.

Subgenus 1. _Arachnosphærella_, Haeckel.

_Definition._--Pores of the innermost shell regular, hexagonal.

1. _Arachnosphæra oligacantha_, Haeckel.

_Arachnosphæra oligacantha_, Haeckel, 1862, Monogr. d. Radiol., p. 356, Taf. x. fig. 2, Taf. xi. fig. 3.

Innermost shell with regular, hexagonal meshes; its diameter three times as long as the equal distances between every two concentric shells. Fifteen to twenty radial spines scattered at wide intervals, each with six to eight verticils.

_Dimensions._--Diameter of the innermost shell 0.12; distance between the concentric shells 0.04 to 0.05.

_Habitat._--Mediterranean (Messina), surface, Haeckel.

2. _Arachnosphæra myriacantha_, Haeckel.

_Arachnosphæra myriacantha_, Haeckel, 1862, Monogr. d. Radiol., p. 357, Taf. x. fig. 3, Taf. xi. fig. 4.

Innermost shell with regular, hexagonal meshes; its diameter twice as long as the equal distances between every two concentric shells. At each nodal-point occurs one radial spine with six to eight verticils (spines in all one hundred to one hundred and twenty or more).

_Dimensions._--Diameter of the innermost shell 0.1; distance between the concentric shells 0.04 to 0.05.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface.

{269}3. _Arachnosphæra dolichacantha_, n. sp.

Innermost shell with regular, hexagonal meshes, very small; its diameter only as long as the equal distances between every two concentric shells. At each nodal-point occurs one radial spine with twelve to sixteen verticils (altogether thirty to forty spines).

_Dimensions._--Diameter of the innermost shell 0.05; distance between the concentric shells 0.04 to 0.05.

_Habitat._--Central Pacific, Station 265 to 274, surface.

4. _Arachnosphæra increscens_, n. sp.

Innermost shell with regular, hexagonal meshes; its diameter three times as long as the distance between it and the second shell, quite as long as the distance between the fifth and sixth shells; the distances between the concentric shells gradually increasing from the centre. Radial spines about fifty to sixty, each with six to eight verticils.

_Dimensions._--Diameter of the innermost shell (A) 0.75; distances between the following shells--A, B = 0.025, B, C = 0.037, C, D = 0.05, D, E = 0.062, E, F = 0.075, &c.

_Habitat._--Central Pacific, Station 271, surface.

Subgenus 2. _Arachnosphæromma_, Haeckel.

_Definition._--Pores of the innermost shell irregular, polygonal.

5. _Arachnosphæra tenuissima_, n. sp.

Innermost shell with irregular, polygonal meshes; its diameter twice as long as the equal distance between every two concentric shells. Forty to fifty radial spines, each with twelve to sixteen verticils.

_Dimensions._--Diameter of the innermost shell 0.1, distance between the concentric shells 0.04 to 0.05.

_Habitat._--South Atlantic, Station 332, surface.

6. _Arachnosphæra velaris_, n. sp.

Innermost shell with irregular, polygonal meshes; its diameter twice as long as the distance between it and the second shell, quite as long as the distance between the third and fourth shells; the distance between the concentric shells gradually increasing from the centre. Radial spines twenty to thirty, each with ten to twelve verticils.

_Dimensions._--Diameter of the innermost shell (A) 0.5; distances of the following shells--A, B = 0.025, B, C = 0.037, C, D = 0.05, D, E = 0.062, E, F = 0.075.

_Habitat._--Tropical Atlantic, Station 347, surface.

{270}Subfamily SPONGIOMMIDA,[149] Haeckel.

_Definition._--#Astrosphærida# with spongy spherical or polyhedral shell (with or without enclosed concentric lattice-shells).

Genus 111. _Spongiomma_,[150] n. gen.

_Definition._--#Astrosphærida# with solid spongy sphere, with numerous simple radial spines, but without latticed medullary shells.

The genus _Spongiomma_ differs from its ancestral form, _Styptosphæra_, in the development of simple radial spines on the surface of the solid sphere, the entire mass of which is composed of an irregular, spongy wicker-work.

Subgenus 1. _Spongiommella_, Haeckel.

_Definition._--Radial spines on the surface of the spongy sphere all of the same shape.

1. _Spongiomma radiatum_, n. sp.

Spongy framework of the solid sphere of the same structure throughout, with small, irregular, polyhedral meshes and very thin thread-like bars. From the surface arise very numerous (one hundred and twenty to one hundred and sixty or more) straight, bristle-shaped radial spines, as long as the radius of the sphere (counting from the middle part of it).

_Dimensions._--Diameter of the spongy sphere 0.2; length of the radial spines 0.1.

_Habitat._--Central Pacific, Station 272, surface.

2. _Spongiomma denticulatum_, n. sp.

Spongy framework of the solid sphere of the same structure throughout, with small, almost equal meshes, four to eight times as broad as the thin, elegantly denticulated bars; from the surface arise very numerous (two hundred to three hundred or more) curved, radial spines, as long as the radius, and of the same form as the bars.

_Dimensions._--Diameter of the sphere 0.25; length of the spines 0.12.

_Habitat._--Central Pacific, Station 274, surface.

3. _Spongiomma spathillatum_, n. sp.

Spongy framework in the central part of the sphere much denser and darker, and with smaller meshes than in the peripheral part in which are very thin bars. Entire surface covered with {271}innumerable short, bristle-shaped radial spines, only one-eighth as long as the radius, of the same elegant form as in _Octodendron spathillatum_ (Pl. 18, figs. 2, 4); each spine developed in a zig-zag fashion, with very small beards, with a delicate spathillum (or coronal of beard spines) at the distal end.

_Dimensions._--Diameter of the spheres 0.16; length of the spines 0.01.

_Habitat._--South Pacific, Station 295, surface.

4. _Spongiomma clavatum_, n. sp.

Spongy framework in the central part of the sphere much denser and darker than in the peripheral part. On the surface are sixty to eighty stout, club-shaped radial spines, as long as the radius of the sphere, in the proximal half three-sided prismatic, with three dentated edges; they begin at the middle of the radius (where the denser inner framework changes into the looser outer) and are very thin at first but increase slowly in thickness towards the truncated distal end. (Similar to _Centrocubus rhopalophorus_, Pl. 18, fig. 1, but without the cubical medullary shell.)

_Dimensions._--Diameter of the sphere 0.4; length of the spines 0.2.

_Habitat._--North Pacific, Station 241, surface.

Subgenus 2. _Spongiommura_, Haeckel.

_Definition._--Radial spines on the surface of the spongy sphere of two different kinds; large main spines and small by-spines.

5. _Spongiomma helioides_, n. sp.

Spongy framework of the sphere everywhere of the same structure, with almost equal meshes, ten to twelve times as broad as the bars. Sixteen to twenty radial main spines, longer than the shell diameter, three-sided prismatic, with three serrated edges, beginning about the middle of the radius and increasing in thickness to the truncated distal end. Between them occur numerous thin, bent, bristle-shaped by-spines. (Very similar to _Spongosphæra helioides_, Monogr. d. Radiol., Taf. xii. figs. 11-13, but without medullary shells.)

_Dimensions._--Diameter of the sphere 0.3; length of the main spines 0.4, of the by-spines 0.01.

_Habitat._--Tropical Atlantic, Station 352, surface.

6. _Spongiomma multiaculeum_, Haeckel.

_Spongechinus multiaculeatus_, Dunikowski, 1882, Denkschr. d. k. Akad. d. Wiss. Wien, Bd. xlv. p. 29, Taf. v. figs. 60-63.

Spongy framework of the sphere very compact, with small meshes, scarcely broader than the bars; four to eight large main spines, three-sided pyramidal, longer than the shell radius; numerous (thirty to forty) thin by-spines, scarcely half as long.

{272}_Dimensions._--Diameter of the sphere 0.16; length of the main spines 0.11, of the by-spines 0.03.

_Habitat._--Fossil in the Alpine Jura, Schafberg near Salzburg (Dunikowski).

7. _Spongiomma asteroides_, n. sp.

Spongy framework in the central part of the sphere much denser and darker than in the peripheral part. Sixty to eighty cylindro-conical main spines, as long as the radius, between them are numerous straight, bristle-shaped by-spines half that length.

_Dimensions._--Diameter of the sphere 0.28; length of the main spines 0.16, of the by-spines 0.08.

_Habitat._--South Atlantic, Station 325, surface.

Genus 112. _Spongodrymus_,[151] Haeckel, 1881, Prodromus, p. 456.

_Definition._--#Astrosphærida# with solid spongy sphere, without latticed medullary shell, with numerous branched radial spines.

The genus _Spongodrymus_ differs from the preceding _Spongiomma_ in the ramification of the numerous radial spines, covering the surface of the solid spongy sphere.

1. _Spongodrymus elaphococcus_, n. sp. (Pl. 18, fig. 9).

Spongy framework of the solid sphere equal throughout, on the surface arising in the form of very numerous (sixty to eighty or more) spongy cones with rather rhomboidal meshes. Each cone is prolonged into a very thin, irregularly curved radial spine, which is twice as long as the shell diameter, simple in the proximal half, branched like a tree in the distal half; each arborescent spine has from sixteen to thirty-two terminal branches, which fall in one spherical face. The branches of neighbouring spines are partly connected by anastomoses, so that they begin to form an outer spherical shell (cortical shell) with a looser spongy framework.

_Dimensions._--Diameter of the whole spherical skeleton (sphere formed by the distal ends of the dichotomous branches) 0.9, of the inner solid spongy sphere 0.02.

_Habitat._--Tropical Atlantic, Station 349, surface.

2. _Spongodrymus abietinus_, n. sp.

Spongy framework denser and darker in the central part of the sphere than in the peripheral part, with rather coarse meshes and thick bars. From the surface arise very numerous (sixty to eighty) stout, radial branches, as long as the shell radius, branched like a pine tree (with six to twelve ramified branches). Similar in structure to _Cromyodrymus abietinus_ (Pl. 30, fig. 6), but with a quite irregular spongy texture in the central sphere.

_Dimensions._--Diameter of the sphere 0.3; length of the spines 0.015.

_Habitat._--Central Pacific, Station 272, surface.

{273}Genus 113. _Spongechinus_,[152] Haeckel, 1881, Prodromus, p. 456.

_Definition._--#Astrosphærida# with hollow, spongy sphere, without latticed medullary shell in the central cavity, and with numerous simple radial spines.

The genus _Spongechinus_ differs from its ancestral form, _Plegmosphæra_, in the development of numerous radial spines on the surface of the spongy sphere, within which is enclosed a large spherical central cavity.

1. _Spongechinus setosus_, n. sp.

Spongy sphere three times as broad as its inner cavity, with a very delicate, equal framework. Entire surface covered with short, straight, bristle-shaped radial spines, about half as long as the radius.

_Dimensions._--Diameter of the sphere 0.2, of its inner cavity 0.07; length of the spines 0.05.

_Habitat._--North Atlantic, Azores, surface.

2. _Spongechinus serrulatus_, n. sp.

Spongy sphere twice as broad as its inner cavity, with a delicate, equal framework. Entire surface covered with short, curved, radial spines, which are elegantly denticulated, and as long as the shell radius.

_Dimensions._--Diameter of the sphere 0.3, of its cavity 0.15; length of the spines 0.15.

_Habitat._--Central Pacific, Station 274, surface.

3. _Spongechinus cavus_, n. sp.

Spongy sphere only one-fourth broader than the large inner cavity, its spongy wall being only one-fourth as thick as the radius, composed of three to four strata of irregular, small meshes. Surface covered with short, bristle-shaped, curved spines, one-third as long as the radius.

_Dimensions._--Diameter of the sphere 0.5, of its inner cavity 0.4; length of the spines 0.08.

_Habitat._--North Atlantic, Station 354, surface.

Genus 114. _Spongothamnus_,[153] n. gen.

_Definition._--#Astrosphærida# with hollow, spongy sphere, without latticed medullary shell in the central cavity, and with numerous branched radial spines.

The genus _Spongothamnus_ differs from the preceding _Spongechinus_ in the ramification of the numerous radial spines, covering the surface of the hollow spongy sphere; {274}it therefore exhibits the same relation to the latter that _Spongodrymus_ bears to _Spongiomma._

1. _Spongothamnus furcatus_, n. sp.

Spongy sphere twice as broad as its inner cavity, with very delicate bars, and irregular, dense framework. From the surface arise one hundred and fifty to one hundred and eighty thin, forked, bristle-shaped spines, half as long as the radius; both fork branches one-third as long as the basal or simple part.

_Dimensions._--Diameter of the sphere 0.3, of its inner cavity 0.15; length of the spines 0.08.

_Habitat._--North Pacific, Station 241, surface.

2. _Spongothamnus scoparius_, n. sp.

Spongy sphere four times as broad as its inner cavity, with thick bars and rather loose framework. From the surface arise sixty to eighty broom-shaped radial spines, as long as the radius, each in the basal half simple, in the distal half with six to twelve irregularly ramified branches (similar to the spines of _Cromyodrymus abietinus_, Pl. 30, fig. 6).

_Dimensions._--Diameter of the sphere 0.4, of the inner cavity 0.1; length of the spines 0.2.

_Habitat._--Central Pacific, Station 271, surface.

Genus 115. _Spongopila_,[154] Haeckel, 1881, Prodromus, p. 456.

_Definition._--#Astrosphærida# with a single, spherical, latticed medullary shell, immediately enveloped by the spongy framework of the cortical shell; on the surface of the latter are numerous radial spines.

The genus _Spongopila_ is a _Spongoplegma_ with radial spines. On the other hand it may be derived either from _Elaphococcus_, by communication of the branched spines, or from _Arachnosphæra_, by development of spongy branches between the concentric spheres.

1. _Spongopila dichotoma_, n. sp.

Medullary shell with regular, hexagonal meshes, six times as broad as the bars. From each nodal-point (between every three meshes) arises a bristle-shaped radial spine, which is dichotomously branched. By communication of the neighbouring branches the loose spongy framework of the spherical cortical shell is formed, which is four times as broad as the medullary shell. On the surface occur very numerous bristle-shaped radial spines, as long as the diameter of the medullary shell. (May be derived from _Elaphococcus_.)

_Dimensions._--Diameter of the spongy cortical shell 0.3, of the medullary shell 0.08.

_Habitat._--Tropical Atlantic, Station 347, surface.

{275}2. _Spongopila verticillata_, n. sp.

Medullary shell with regular, hexagonal meshes, four times as broad as the bars. From its surface arise forty to sixty, three-sided prismatic radial spines, bearing eight to ten verticils of lateral branches, each verticil with six forked branches (two from each edge). By irregular ramification of these branches, and communication in all directions, the loose spongy framework of the cortical shell originates, which is six times as broad as the medullary shell. The free distal ends of the spines are as long as the shell radius. (May be derived from _Arachnosphæra_.)

_Dimensions._--Diameter of the spongy cortical shell 0.6, of the medullary shell 0.1.

_Habitat._--Tropical Pacific, Station 200, surface.

Genus 116. _Rhizoplegma_,[155] Haeckel, 1881, Prodromus, p. 456.

_Definition._--#Astrosphærida# with a single, spherical, latticed medullary shell, which is not armed with by-spines, but connected by stout radial main spines with the spongy cortical shell.

The genus _Rhizoplegma_ is immediately allied to the foregoing _Spongopila_, but differs from it in the large interval separating both shells. In this interval lies the wall of the central capsule, which is only pierced by the radial spines connecting both shells.

Subgenus 1. _Rhizoplegmarium_, Haeckel.

_Definition._--No free lateral branches of the radial spines between the two shells.

1. _Rhizoplegma polyacanthum_, n. sp.

Spongy cortical shell with a very fine dense framework and nearly smooth surface (without superficial by-spines). Its inner cavity is four times as broad as the medullary shell, which exhibits regular, hexagonal meshes. Radial spines sixty to eighty, three-sided prismatic, with three smooth edges, without lateral branches between both shells; their free outer part as long as the shell radius.

_Dimensions._--Diameter of the spongy cortical shell 0.3, of its inner cavity 0.2, of the medullary shell 0.05.

_Habitat._--Central Pacific, Station 274, surface.

2. _Rhizoplegma spirale_, n. sp.

Spongy cortical shell with a very delicate loose framework and bristly surface. Its inner cavity three times as broad as the medullary shell, which exhibits regular, hexagonal meshes. {276}Radial spines thirty to forty, prismatic, with three smooth, spirally contorted edges, without lateral branches between the two shells; their free outer part half as long as the shell radius.

_Dimensions._--Diameter of the spongy cortical shell 0.2, of its inner cavity 0.12, of the medullary shell 0.04.

_Habitat._--Central Pacific, Station 265, surface.

3. _Rhizoplegma trigonacantha_, n. sp.

Spongy cortical shell with a rather loose framework and coarse bars, with nearly smooth surface (without by-spines). Its inner cavity twice as broad as the medullary shell, which exhibits irregular, roundish pores. Radial spines forty to sixty, prismatic, with three smooth straight edges, without free branches between the two shells; their outer pyramidal part only one-third of the shell radius. (Very similar to the common _Rhizosphæra trigonacantha_, but with simple medullary shell.)

_Dimensions._--Diameter of the spongy shell 0.2, of its inner cavity 0.16, of the medullary shell 0.08.

_Habitat._--North Atlantic, Station 353, surface.

Subgenus 2. _Rhizoplegmidium_, Haeckel.

_Definition._--Between the two shells free lateral branches arise from the three edges of the radial spines.

4. _Rhizoplegma radicatum_, n. sp. (Pl. 15, figs. 9, 9_a_).

Spongy cortical shell with a very loose framework; on the surface are innumerable thin, forked, or repeatedly dichotomous by-spines. Its inner cavity three times as broad as the medullary shell, which exhibits regular, hexagonal meshes (fig. 9_a_). Radial spines twelve, prismatic, with straight dentated edges, their outer pointed part as long as the shell radius. Each spine between the two shells has a verticil of three forked lateral branches (fig. 9_a_). The central capsule completely distends the medullary shell, and forces out through each mesh a hernia-shaped process (fig. 9).

_Dimensions._--Diameter of the spongy shell 0.5, of its inner cavity 0.25, of the medullary shell 0.08.

_Habitat._--Central Pacific, Station 271, surface.

5. _Rhizoplegma lychnosphæra_, n. sp. (Pl. 11, fig. 5).

_Lychnosphæra rhizoplegma_, Haeckel, 1879, Atlas (pl. xi. fig. 5).

Spongy cortical shell with a very loose framework, composed of long thin beams as in _Lychnosphæra regina_ (Pl. 11, figs. 1-4). Surface covered with short bristles. Its inner cavity six times as broad as the medullary shell, which exhibits regular, hexagonal meshes. Radial spines twelve, prismatic, with three smooth edges; their outer pointed part half as long as the shell radius. Each spine has three verticils of three forked branches; the first verticil is free {277}between the two shells, while the two following verticils, by communication of their ramules, form the irregular framework. Central capsule with many herniæ, forced out through the meshes of the medullary shell (fig. 5).

_Dimensions._--Diameter of the spongy shell 0.7, of its inner cavity 0.45, of the medullary shell 0.07.

_Habitat._--South Pacific, Station 284, surface.

Genus 117. _Lychnosphæra_,[156] Haeckel, 1881, Prodromus, p. 453.

_Definition._--#Astrosphærida# with a single, spherical, latticed medullary shell, which is armed with free radial by-spines, and connected by stout radial main spines with the spongy cortical shell.

The genus _Lychnosphæra_, known only by one single, large, and very remarkable species, mainly differs from the foregoing in the development of free radial by-spines on the surface of the medullary shell, and in the free interval between it and the cortical shell; but beyond this the loose spongy framework of the latter exhibits a very remarkable structure, figured in Pl. 11.

1. _Lychnosphæra regina_ (Pl. 11, figs. 1-4).

Medullary shell (fig. 3) with regular, circular, hexagonally framed pores, twice as broad as the bars; from each hexagon-corner arises a radial, bristle-shaped by-spine, as long as the diameter. Twelve radial main spines each as broad as one of the meshes, three-sided prismatic, six to eight times as long as the medullary shell. From their three leaf-shaped (often somewhat denticulated or spirally contorted) edges arise four verticils of lateral branches, each composed of three forked, thin branches. The forked branches of the first verticil end free between the two shells (figs. 2, 3), while the two following verticils are ramified, and, by anastomosis of their branches, compose the loose spongy framework of the cortical shell. On the surface of the latter arise numerous radial (zig-zag-shaped) by-spines. The fourth verticil is terminal, with three shorter, thicker, dentated, simple branches, which constitute, together with the distal apex of the spine itself, a bunch of four terminal spines. The large central capsule completely distends the medullary shell, and forces out by its pores numerous club-shaped herniæ (fig. 1).

_Dimensions._--Diameter of the spongy cortical shell 0.6, of its inner cavity 0.4, of the central capsule 0.22, of the medullary shell 0.06; length of the radial spines 0.4, breadth 0.01.

_Habitat._--Central Pacific, Station 271, surface.

Genus 118. _Centrocubus_,[157] n. gen.

_Definition._--#Astrosphærida# with a single, cubical medullary shell, immediately surrounded by the spongy framework of the cortical shell; from the eight corners {278}of the central cube arise eight primary radial spines, and often others from the framework between them.

The genus _Centrocubus_ and the following closely allied _Octodendron_ may represent a peculiar small group of Spongiommida, remarkable for the regular, cubical form of the medullary shell, which is composed of twelve thin rods, corresponding to the twelve edges of a mathematical cube; from the eight corners invariably arise eight primary radial spines, the branches of which form the spongy cortical shell.

1. _Centrocubus octostylus_, n. sp.

Radial spines eight, arising from the eight corners of the cubiform, regular, medullary shell, gradually increasing in thickness towards the club-shaped distal end, which is five to six times as broad as the central end. From the three denticulate edges of each spine arise six to eight lateral branches, which ramify irregularly and form by their anastomosis the spongy framework which is of nearly similar structure throughout, and with large loose meshes. The free distal part of each spine is half as long as the enclosed part.

_Dimensions._--Diameter of the sphere 0.6, of the central cube 0.02; length of the spines 0.15, distal thickness 0.02.

_Habitat._--Central Pacific, Station 271, surface.

2. _Centrocubus cladostylus_, n. sp. (Pl. 18, fig. 1).

Radial spines thirty-two, club-shaped, at the distal end eight to ten times as broad as at the basal end. Eight primary spines arise from the eight corners of the regular, cubiform medullary shell, and from these, in the form of lateral branches, twenty-four secondary spines arise with concavely curved bases (three from the three denticulate edges of each spine, at nearly equal distances from the centre). The free distal end of each of the thirty-two spines is of the same shape, about half as long as the radius of the spongy sphere; framework much looser in the outer than in the inner part.

_Dimensions._--Diameter of the sphere 0.8, of the central cube 0.02; length of the spines 0.2, distal thickness 0.02.

_Habitat._--North Pacific, Station 256, surface.

3. _Centrocubus polystylus_, n. sp.

Radial spines sixty to eighty, club-shaped, four to six times as broad at the distal as at the basal end. Eight primary spines arise from the eight corners of the regular, cubiform medullary shell, the remainder either springing as lateral branches from the three denticulate corners of the former, or arising within the spongy framework, which is much denser and darker in the central than in the peripheral part. The free distal end of each spine is one-third as long as the radius.

{279}_Dimensions._--Diameter of the sphere 0.9, of the central cube 0.02; length of the spines 0.15, distal thickness 0.02.

_Habitat._--South Pacific, Station 295, surface.

Genus 119. _Octodendron_,[158] n. gen.

_Definition._--#Astrosphærida# with a single, cubical medullary shell, and eight primary radial spines arising from its eight corners; these are connected at equal distances by a latticed, spherical, cortical shell, from which the spongy framework directly springs; often from the latter secondary radial spines arise.

The genus _Octodendron_ has the same regular, cubical medullary shell as the preceding _Centrocubus_, but differs from it in the wide interval separating the medullary shell from the inner spherical face of the spongy cortical shell, the two being connected only by eight radial beams, arising from the eight corners of the cube.

Subgenus 1. _Octodendridium_, Haeckel.

_Definition._--Only eight primary radial spines, arising from the eight corners of the central cube.

1. _Octodendron cubocentron_, n. sp. (Pl. 18, fig. 3).

Radial spines eight, club-shaped, with three denticulate, straight edges, twice as long as the diameter of the central cavity of the cubical spongy shell; the inner face of the latter (or the "inner cortical shell") exhibits the form of a large cube, the spongy sides of which are parallel with the simple square sides of the central cube. The thin eight radial beams, connecting the corresponding corners of both cubes, are not thicker than the edge-bars of the central cube, whilst their outer prolongations are much thicker, with four to six verticils of lateral branches. Surface of the thin walled, loose, spongy shell armed with short simple thorns.

_Dimensions._--Diameter of the spongy shell 0.2, of its inner cavity 0.1, of the central cube 0.02; length of the spines 0.2 (from the centre 0.3).

_Habitat._--Central Pacific, Station 266, surface.

2. _Octodendron spirale_, n. sp.

Radial spines eight, three-sided prismatic, three times as long as the diameter of the inner shell-cavity; their three edges denticulated and spirally contorted around the spine axis. Thickness of the loose spongy shell-wall equal to the radius of the inner cavity, three times as large as the central cube. Surface covered, with numerous thin, bristle-shaped, bent spinules.

{280}_Dimensions._--Diameter of the spongy shell 0.24, of its inner cavity 0.12, of the central cube 0.02; length of the spines 0.4, breadth 0.01.

_Habitat._--North Pacific, Station 254, surface.

3. _Octodendron pinetum_, n. sp.

Radial spines eight, three-sided prismatic, three to four times as long as the diameter of the inner shell-cavity, with three spirally contorted edges. From each spine arise at equal distances (equal to the half radius of the cavity) fifteen to twenty verticils of branches which increase in size from the base of the spine. Each verticil is composed of six forked branches (two from each spine-edge); the inferior are richly branched, and form by their connection the loose network of the spongy cortical shell, the surface of which is covered with numerous bent threads. Each spine bears a resemblance to a pine tree.

_Dimensions._--Diameter of the spongy shell 0.3, of its inner cavity 0.15, of the central cube 0.02; length of the spines 0.5 to 0.6, breadth 0.01.

_Habitat._--Central Pacific, Station 272, surface.

4. _Octodendron araucaria_, n. sp.

Radial spines eight, three-sided prismatic, with three spirally contorted edges, eight to ten times as long as the diameter of the inner shell-cavity (the free distal portion twice to three times as long). From each spine arise at equal distances thirty to thirty-five verticils of branches, which decrease in size towards the distal end. Each verticil is composed of six forked branches (two from each spine-edge); the inferior are richly ramified and form by their connection the loose spongy framework; the distal branches bear on the free end elegant spathillæ (as in the following species). Surface covered with innumerable straight bristles, as long as the cavity radius, and ending with a spathilla. Diameter of the central capsule about equal to the radius of the spongy sphere, its membrane is double-edged.

_Dimensions._--Diameter of the spongy shell 1.4 mm., of its inner cavity 0.14, of the central cube 0.02, of the central capsule 0.5 to 0.6; length of the spines 0.9 to 1.2, breadth 0.02.

_Habitat._--South Pacific, Station 288, surface.

5. _Octodendron spathillatum_, n. sp. (Pl. 18, figs. 2, 4).

Radial spines eight, three-sided prismatic, with contorted edges, five to eight times as long as the diameter of the shell-cavity (the free part twice as long). From each spine arise ten to twelve verticils of lateral branches; each verticil composed of three forked branches. The proximal larger branches ramify richly, and form by their connection the loose spongy framework of the spherical shell; the distal smaller branches are simple or bifurcated, and the ramules are provided with an elegant spathillum at the end (fig. 4). Entire surface of the spongy sphere covered with innumerable bristle-shaped radial spines (half as long as the cavity radius), zig-zag, bent, with beards, and with a spathillum at the end.

{281}_Dimensions._--Diameter of the spongy sphere 1 mm., of its central cavity 0.15, of the central cube 0.02; length of the spines 1 to 1.2 mm., breadth 0.008.

_Habitat._--Central Pacific, Station 271, surface.

Subgenus 2. _Octodendronium_, Haeckel.

_Definition._--Radial spines thirty-two or more, eight primary (arising from the eight corners of the central cube) and twenty-four or more secondary (between them).

6. _Octodendron verticillatum_, n. sp.

Radial spines thirty-two, with three denticulate straight edges, six to eight times as long as the diameter of the shell-cavity; the distal parts half free. Eight primary spines arise from the eight corners of the central cube, twenty-four secondary from the edges of these (a verticil of every three from each primary spine). Distal free parts of all thirty-two spines equal. Each spine with eight to ten verticils of forked lateral branches, without spathillæ. Surface of the spongy sphere covered with short simple bristles.

_Dimensions._--Diameter of the spongy shell 0.3, of its cavity 0.12, of the central cube 0.02; length of the spines 0.7 to 1 mm., breadth 0.02.

_Habitat._--South Pacific, Station 291, surface.

7. _Octodendron contortum_, n. sp.

Radial spines thirty-two, disposed in a similar manner to those of the former species (eight primary and twenty-four secondary); also the spongy shell of the same shape. The difference arises in the form of the spines, the three edges of which are much broader and spirally contorted around the axis; and thus the corresponding branches of the verticil do not lie in the same meridian-plane, but alternate one with another.

_Dimensions._--Diameter of the spongy shell 0.4, of its cavity 0.1, of the central cube 0.02; length of the spines 0.8 to 1.2, breadth 0.04.

_Habitat._--Central Pacific, Station 274, surface.

8. _Octodendron arboretum_, n. sp.

Radial spines sixty to ninety, three-sided prismatic, with spirally contorted and denticulate edges, six to eight times as long as the diameter of the inner shell-cavity. Eight primary arise from the eight corners of the central cube, twenty-four others from their three edges (as in the two former species); the remaining thirty to sixty spines seem to arise between the former and immediately from the dense spongy framework, which is twice as thick as the diameter of the inner shell-cavity. The numerous verticils of the free distal part are of equal shape in all the spines, composed of three forked branches in the terminal, and of more ramified branches in the inferior parts. Entire surface of the spongy shell covered with simple radial bristles, without spathillæ.

{282}_Dimensions._--Diameter of the spongy shell 0.75, of its central cavity 0.15, of the central cube 0.02; length of the spines 0.9 to 1.2, breadth 0.02.

_Habitat._--Tropical Pacific, Station 225, surface.

Genus 120. _Spongosphæra_,[159] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

_Definition._--#Astrosphærida# with two concentric latticed medullary shells, connected by radial beams; the outer is immediately enveloped by the spongy framework, and bears numerous radial spines.

The genus _Spongosphæra_ (in the definition here restricted) differs from _Spongopila_ in the double medullary shell, which in the latter is simple; it exhibits to the latter the same relation that _Spongodictyon_ among the Liosphærida bears to _Spongoplegma_. The outer medullary shell of _Spongosphæra_ is immediately enveloped by the spongy wicker-work, which everywhere pierces the wall of the central capsule.

1. _Spongosphæra streptacantha_, Haeckel.

_Spongosphæra streptacantha_, Haeckel, 1862, Monogr. d. Radiol., p. 455, Taf. xxvi. figs. 1-3.

Spongy shell of polyhedric, irregular outline, the framework being prolonged sheath-like into the eight to twelve radial spines, which are quite irregularly distributed, very large, three-sided prismatic, with three serrated, spirally contorted edges; their length is twice to four times as great as the diameter of the spongy body; they arise with thinner bases from the outer medullary shell, which is three times as broad as the inner, both having roundish pores, twice to four times as broad as the bars; surface without radial by-spines.

_Dimensions._--Diameter of the spongy shell 0.2 to 0.6, outer medullary shell 0.04 to 0.06, inner 0.012 to 0.016.

_Habitat._--Cosmopolitan; common in all warmer seas, surface.

2. _Spongosphæra polyacantha_, J. Müller.

_Spongosphæra polyacantha_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 32, Taf. iv. figs. 1-4.

Spongy shell spherical, with ten to twenty large radial spines, which arise with thinner bases from the medullary shell, and are prominent on the surface at different lengths; they are three-sided prismatic (not four-sided), with three leaf-shaped straight edges. Whilst the spongy framework is much looser than in the preceding species, both medullary shells have nearly the same shape.

_Dimensions._--Diameter of the spongy shell 0.2 to 0.5, outer medullary shell 0.04 to 0.06, inner 0.012 to 0.016.

_Habitat._--Mediterranean (Nice); Atlantic, Station 353, surface.

{283}Subgenus _Spongosphæromma_, Haeckel.

_Definition._--Radial spines on the surface of the spongy shell of two different kinds; large piercing main spines and small superficial by-spines.

3. _Spongosphæra helioides_, Haeckel.

_Spongosphæra helioides_, Haeckel, 1862, Monogr. d. Radiol., p.456, Taf. xii. figs. 11-13.

Spongy shell spherical, with numerous curved, bristle-shaped by-spines on the surface, as long as the radius. Main spines ten to twenty, irregularly disposed, prismatic, with three dentated, spirally contorted edges, broader toward the distal end. Outer medullary shell three times as broad as the inner, with polygonal meshes (of the same size as those in the spongy framework) and fine bars.

_Dimensions._--Diameter of the spongy shell 0.2, outer medullary shell 0.02, inner 0.007.

_Habitat._--Mediterranean (Messina).

4. _Spongosphæra quadricuspis_, n. sp.

Spongy shell spherical, with numerous curved, bristle-shaped by-spines on the surface, half as long as the radius. Main spines twenty to thirty, irregularly disposed, prismatic, with three dentated, spirally contorted edges, and at the distal end four strong pyramidal divergent teeth (three as terminations of the edges, the fourth as end of the spine axis). Outer medullary shell twice as broad as the inner, both having circular, regular pores, twice to three times as broad as the bars.

_Dimensions._--Diameter of the spongy shell 0.3, outer medullary shell 0.04, inner 0.013.

_Habitat._--Central Pacific, Station 272, surface.

Genus 121. _Rhizosphæra_,[160] Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 840.

_Definition._--#Astrosphærida# with two concentric latticed medullary shells, connected by radial beams; from the outer arise numerous radial spines, which at equal distances are connected by a latticed spherical cortical shell, surrounded by a spongy framework.

The genus _Rhizosphæra_ exhibits the same relation to _Spongosphæra_ that _Rhizoplegma_ bears to _Spongopila_; but in the latter the latticed medullary shell is simple, in the two former double. The wall of the central capsule is pierced only by the radial spines connecting the medullary and the cortical shells.

1. _Rhizosphæra trigonacantha_, Haeckel.

_Rhizosphæra trigonacantha_, Haeckel, 1862, Monogr. d. Radiol., p. 452, Taf. xxv. figs. 1-7.

Central cavity of the spongy cortical shell twice as broad as the diameter of the outer medullary shell. Bars of all three shells of the same breadth as the thirty to fifty (or more) radial spines, {284}which are three-sided prismatic; their outer free distal end only as long as the diameter of the inner medullary shell.

_Dimensions._--Diameter of the spongy shell 0.25, of its inner cavity 0.2, outer medullary shell 0.1, inner 0.05.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface from many Stations.

2. _Rhizosphæra serrata_, n. sp. (Pl. 18, figs. 5-7).

Central cavity of the spongy shell five times as broad as the diameter of the outer medullary shell. Bars of all three shells of the same breadth as the forty to sixty (or more) thin radial beams between them. These are three-sided prismatic, with denticulate edges, scarcely half as broad as their outer prolongations, which are half as long as the shell radius, and possess three spirally contorted serrated edges. (The figured specimen is a young one; in the older specimens the spongy framework of the cortical shell is much more developed.)

_Dimensions._--Diameter of the spongy shell 0.3, of its central cavity 0.22, outer medullary shell 0.06, inner 0.02.

_Habitat._--Central Pacific, Stations 270 to 274, surface.

3. _Rhizosphæra leptomita_, Haeckel.

_Rhizosphæra leptomita_, Haeckel, 1862, Monogr. d. Radiol., p. 453, Taf. xxv. figs. 8-10.

Central cavity of the spongy cortical shell twice as broad as the diameter of the outer medullary shell; bars of both very thin, only one-third as broad as the bars of the inner medullary shell. Radial spines thirty to fifty (or more), curved, three-sided prismatic; inside the spongy shell as thin as their bars, outside three times as broad.

_Dimensions._--Diameter of the spongy shell 0.27, of its inner cavity 0.2, outer medullary shell 0.1, inner 0.05.

_Habitat._--Mediterranean (Messina); Atlantic, Stations 348 to 354, surface.

----

Suborder PRUNOIDEA, Haeckel, 1883 (Pls. 13-17, 39, 40).

_Definition._--SPUMELLARIA with an ellipsoidal or cylindrical central capsule, prolonged into one axis (sometimes articulate by annular transverse strictures); with an ellipsoidal or cylindrical, fenestrated siliceous shell (often articulate by annular strictures), invariably prolonged into one axis. Fundamental form monaxon, usually with the poles of the prolonged dimensive main axis equal.

The suborder #Prunoidea# comprises those SPUMELLARIA in which the fenestrated spherical shell appears prolonged into one axis. The geometric fundamental form of the shell, which in the #Sphæroidea# was a sphere, in this case therefore becomes an ellipsoid, and whilst in the former all axes originally have the same value (Homaxonia), {285}here one main axis is constantly larger than all other axes (Monaxonia). Usually both poles of this main axis are equal (Haplopola); but in some genera both poles become different (Diplopola).

In the #Sphæroidea# all planes going through the centre of the shell are circular, whereas in the #Prunoidea# only those planes are circular which are perpendicular to the main axis; all other planes going through the centre are elliptical; the largest of these are the meridian planes, in which is situated the main axis. Commonly all meridian planes are equal, as no transverse axes (or cross axes) are differentiated.

In my Monograph (1862) only very few forms of #Prunoidea#, such as _Didymocyrtis_ and _Spongurus_, are described, and the greater part of them are distributed under different genera of #Sphæroidea#, such as _Haliomma_ and _Actinomma_. In my Prodromus (1881) I separated them as the family Zygartida (p. 462). But it seems now much more convenient to restrict this term to a particular family and to give a wider extension to the whole suborder under the name #Prunoidea# (called after the characteristic ellipsoidal form of a plum, or _Prunus_, with its stone).

The suborder #Prunoidea# comprises seven different families, of which the Ellipsida constitutes the simplest and the probable common ancestral group. In all Ellipsida the fenestrated shell is simple, and never composed of concentric or twin shells. In their primitive genus _Cenellipsis_, the whole shell is geometrically nothing more than a simple ellipsoid (Pl. 39, figs. 1, 2). By development of radial spines it passes into _Ellipsidium_, by development of spongy framework into _Spongellipsis_. In the greater part of this family large spines are developed on both poles of the main axis of the shell, but sometimes instead of these solid spines, two opposite hollow fenestrated tubes are developed (_Pipettella_, Pl. 39, fig. 6).

The second family of #Prunoidea#, the Druppulida, is much richer in different forms than the simple Ellipsida. In this case the ellipsoidal shell is composed of two or three (rarely more) concentric shells. Constantly one or two of these fenestrated shells are enclosed in the central capsule, and may therefore be called "medullary shells"; and one or two (rarely more) lie outside the central capsule, "cortical shells." The inner medullary shells (one or two) are either spherical or ellipsoidal; the outer cortical shells (one or two, rarely more) are always ellipsoidal. All concentric shells are connected by radial beams. In the simplest form of the subfamily, _Druppula_ (Pl. 39, fig. 3), one medullary shell is connected with one cortical shell. By duplication of the medullary shell arises _Prunulum_ (Pl. 39, fig. 4), and by duplication or multiplication of the cortical shell _Cromyodruppa_ (Pl. 15, figs. 1-4) is formed. In by far the greater portion of this subfamily large spines are developed on both poles of the main axis of the cortical shell (Pls. 16, 17), but sometimes also instead of these solid spines two opposite hollow fenestrated tubes are developed (_Pipetta_, Pl. 39, figs. 7, 8).

{286}A third family of #Prunoidea#, closely allied to the two preceding families, is the Spongurida, in which we include all #Prunoidea# with an ellipsoidal or cylindrical, unjointed shell, in which the lattice-work of the cortical shell is transformed into an irregular, siliceous framework. In the simplest form, _Spongellipsis_, the simple lattice-shell of _Cenellipsis_ is substituted by an external spongy envelope. In other cases (_Spongurus_ and allied genera) the whole cavity of this external spongy shell is distended with a fine spongy framework. The subfamily of Spongodruppida is distinguished by the possession of a simple or double latticed medullary shell; this lies in the midst of the central capsule, and is connected by radial beams (perforating its membrane) with the enveloping spongy cortical shell. The surface of the latter may bear either radial spines, or two opposite strong polar spines, at the poles of the main axis (Pl. 17, fig. 12).

Closely allied to the Ellipsida and Druppulida are two other families of the #Prunoidea#, the Artiscida and Cyphinida, which differ from the former by a circular constriction in the equatorial plane of the ellipsoidal shell; and in this way assume a characteristic twin form, like a figure of eight. In the Artiscida the shell is simple (as in the Ellipsida), whereas in the Cyphinida it is composed of two or more concentric shells (as in the Druppulida). The simplest form of the Artiscida is _Artiscus_ (Pl. 39, fig. 9), differing from _Cenellipsis_ in the ring-shaped, equatorial constriction. In other Artiscida polar appendages are developed on both poles of the main axis, either in the form of solid, strong spines (_Stylartus_), or hollow fenestrated tubes (_Cannartus_, Pl. 39, fig. 10).

The family Cyphinida differs from the Druppulida in the equatorial constriction of the shell, and from the Artiscida in the presence of two or more concentric shells. One or two of these concentric fenestrated shells are enclosed in the central capsule (and therefore may be called "medullary shells"); the others (one or two, rarely more) lie outside of the central capsule (therefore "cortical shells"). The internal "medullary shells" are always spherical or somewhat lenticular, compressed from both sides; the external "cortical shells" have constantly a ring-like constriction in the equatorial plane, and "twin-shells" are therefore like a figure of eight. The simplest form of this subfamily is _Cyphanta_, composed of a simple medullary shell and a simple cortical shell, the two being connected in the equatorial plane by radial beams. In Cyphonium (Pl. 39, fig. 12) the medullary shell is doubled, and in _Cypassis_ (Pl. 39, fig. 13) the cortical shell likewise. On both poles of the main axis strong spines are often developed (_Cyphinus_, Pl. 39, fig. 14), or hollow fenestrated tubes (_Cannartidium_, Pl. 39, figs. 16-19).

The equatorial constriction of the ellipsoidal shell, which characterises the Artiscida and Cyphinida, is repeated or multiplied in the two following families, in the Panartida and Zygartida; in the former we find three ring-like strictures, in the latter five or more (lying in parallel transverse planes); therefore the fenestrated shell is composed in the one instance of four chambers, in the other of six or {287}more; all the chambers form a single series and have a common main axis. All constrictions lie in planes parallel to the equatorial plane of the original ellipsoid; in the centre of the latter constantly lies a double "medullary shell," composed of two concentric, either spherical or lenticular, compressed shells. In all Panartida we call the two inner chambers (on both sides of the equatorial constriction) "proximal chambers," the two outer chambers (on the poles of the main axis) "distal chambers." The four-chambered cortical shell of the Panartida is either simple (in _Panartus_, Pl. 40, figs. 1-4) or double, with an external mantle (as in _Peripanartus_, Pl. 40, figs. 5-7). The simplest form of the subfamily is _Panartus_ (_loc. cit._). In this case also on both poles of the main axis may be developed solid spines, or hollow fenestrated tubes (_Panarium_, Pl. 40, fig. 9).

The seventh and last family of the #Prunoidea#, the Zygartida is most nearly allied to the Panartida, and appears as a further developmental step from that family. Whilst in the Panartida the cortical shell is constantly four-chambered, with three parallel ring-like constrictions, in the Zygartida it is always prolonged and composed of six or more chambers, separated by five or more ring-shaped constrictions, in the middle of which is the equatorial stricture. In the centre of the latter (as also in the Panartida) always lies the double medullary shell, composed of two concentric, spherical, or lenticular shells. The number of the chambers of the cortical shells is commonly six or eight (with five to seven ring strictures), but it often mounts to ten and sometimes to twenty (with nineteen strictures), as in some species of _Zygartus_ (Pl. 40, fig. 13). All the chambers lie in one series, one behind another, with a common main axis. The cortical shell is usually simple (in _Ommatocampe_, Pl. 40, fig. 10), sometimes double (in _Desmocampe_, Pl. 40, fig. 12), rarely triple (in ZYGOCAMPE, Pl. 40, fig. 13). In all three cases hollow fenestrated tubes may be developed on the poles of the main axis.

The morphological references and the phylogenetic affinities of all #Prunoidea# are so complex, that they seem to represent a quite natural group; all forms of it may be derived from the common ancestral form _Cenellipsis_. But a far more difficult question is the manner in which its pedigree may be constructed. The oldest family is probably the simplest, namely, Ellipsida. From this the Druppulida may be derived by production of medullary shells, the Artiscida by equatorial constriction. The Cyphinida can be produced either from the Druppulida by equatorial constriction or from the Artiscida by development of medullary shells. The Panartida appear as further developmental steps of the Cyphinida, by duplication of the chamber number; and the Zygartida as further productions of the Panartida, by increasing the number of the chambers.

The seven subfamilies of the #Prunoidea# can be arranged in two sections according to the presence or absence of medullary shells. The Ellipsida, Spongellipsida, and Artiscida possess a simple cortical shell, without a medullary shell; they represent the {288}section Cenoprunida. All other families possess medullary shells, and so represent the section Coccoprunida.

Another character, which can be employed in the arrangement of the seven subfamilies in some larger groups, is the presence or absence of ring-like constrictions, by which the cortical shell is divided into chambers. I. The Monoprunida comprise all forms without any constriction, of which the Ellipsida are without a medullary shell, the Druppulida with one or two medullary shells, and the Spongurida with a spongy cortical shell. II. The Dyoprunida contain all forms with a cortical twin shell, or with two chambers separated by one equatorial constriction, of which the Artiscida are without a medullary shell and the Cyphinida have one or two medullary shells. III. The Polyprunida comprise all forms with several (three or more) constrictions, which separate four or more chambers, of which the Panartida have three constrictions and four chambers, and the Zygartida five or more constrictions and six or more chambers.

_The Central Capsule_ of the #Prunoidea# is originally ellipsoidal (monaxial), and preserves this form in the greater part of the genera. In some groups, where the axis of the ellipsoid is much prolonged, it passes over to the cylindrical form (with hemispherical vaultings on both poles), as in _Spongurus_ and _Spongocore_, in many Panartida and Zygartida. Very often the ellipsoidal or cylindrical capsule gets annular transverse constrictions, corresponding to those of the enveloping cortical shell (one single, equatorial stricture in the Artiscida and Cyphinida, three strictures in the Panartida, five or more in the Zygartida). In the Cenoprunida (Ellipsida and Artiscida, also in _Spongellipsis_) the central capsule lies freely in the cavity of the cortical shell, separated from its inner surface by the jelly-envelope; in all other groups it contains a part of the skeleton, the medullary shell and the beams which connect it with the enveloping cortical shell.

_Synopsis of the Families of_ #Prunoidea#.

{a. Shell simple, latticed (not { spongy), without enclosed internal { enclosed internal shells, 1. ELLIPSIDA. A. MONOPRUNIDA. { {b. Shell composed of two or more Shell without { concentric latticed shells transverse stricture { (not spongy), 2. DRUPPULIDA. { {c. Shell partially or wholly { composed of an irregular spongy { framework, 3. SPONGURIDA.

B. DYOPRUNIDA. { {d. Shell simple, without enclosed Shell bilocular, { internal shells, 4. ARTISCIDA. divided by an { equatorial stricture { into two communicating{e. Shell composed of two or more hemi-ellipsoidal { concentric shells, 5. CYPHINIDA. shells. {

C. POLYPRUNIDA. {f. Shell with three parallel { strictures and therefore four Shell multilocular, { cameræ, 6. PANARTIDA. divided by three { or more parallel {g. Shell with five or more parallel transverse strictures { strictures and therefore six into four or more { or more cameræ, 7. ZYGARTIDA. serial cameræ. {

{289}Family XI. #ELLIPSIDA#, Haeckel, 1882 (Pls. 13, 14, 39).

_Definition._--#Prunoidea# with simple ellipsoidal shell, without equatorial stricture (without enclosed medullary shell); network a simple lattice lamella, not spongy. Central capsule ellipsoidal or cylindrical, without annular equatorial constriction.

The family #Ellipsida# comprises the simplest forms of #Prunoidea#, and probably represents the ancestral forms of this whole suborder. The fenestrated shell, which encloses the ellipsoidal central capsule, is a perfectly simple "cortical shell" of the same form, without enclosed "medullary shell." Its form is commonly a regular monaxial ellipsoid; sometimes a little modified by unequal growth of the two poles of the main axis. Two opposite large spines are often developed at these poles, or it may be that instead of these, two hollow fenestrated tubes are present.

The ellipsoidal fenestrated shell exhibits in the regular Ellipsida all the characters of a geometric ellipsoid; one main axis surpasses in length all other possible axes. All sections going through this main axis are "meridian sections," with elliptical periphery; all sections perpendicular to the main axis are "transverse sections," with circular periphery. The largest of these is the equatorial section, which divides the main axis into halves. The diameter of this equatorial plane is the "minor axis" of the ellipsoid.

The proportion of the two axes of the ellipsoidal shell, of the major vertical or main axis and the minor horizontal or equatorial axis, is commonly between 6 : 5 and 3 : 2. In the former case it approaches the spherical shell, from which it is derived; in the latter case it becomes almost fusiform or cylindrical. The network of silex, constituting the shell, is constantly a simple latticed lamella, never composed of concentric shells (as in Druppulida) or spongy (as in Spongurida). The network is often very regular and elegant, in other cases irregular.

The simplest genus among the Ellipsida, and probably the common ancestral form of the whole subfamily, is the genus _Cenellipsis_, possessing a simple ellipsoidal shell without any appendages. It is derived from _Cenosphæra_ (the simplest spherical shell) by the prolongation of one axis. _Cenellipsis_ passes over into _Ellipsidium_ by the production of radial spines on the surface (corresponding to _Heliosphæra_). _Axellipsis_ is a peculiar genus differing from _Cenellipsis_ in an axial rod, which corresponds to the minor or equatorial axis. In all other genera of the subfamily both poles of the main axis are distinguished by peculiar polar prolongations, either hollow fenestrated tubes (as in _Pipettella_) or strong solid spines. Both polar spines are of equal size and similar form in _Ellipsoxiphus_, unequal in _Ellipsostylus_. From the latter is derived _Lithapium_, by reduction and loss of one spine (so that only one remains); _Lithomespilus_, by production of a bunch of several spines at one pole. In the three latter genera both poles of the main axis are unequal, in all others equal.

{290}The central capsule of the Ellipsida is in all cases ellipsoidal, and occupies the largest part of the shell, being separated from its inner surface by a thinner or thicker jelly-mantle.

_Synopsis of the Genera of Ellipsida._

------------------------------------------------------------------------- Ellipsoidal shell without polar appendages (neither solid spines nor hollow tubes at the poles of the axis). ------------------------------------------------------------------------- Surface without {Shell cavity radial spines. { simple, without { an axial rod, 122. _Cenellipsis_. { {Shell cavity { with a transverse { axial rod, 123. _Axellipsis_.

Surface covered with radial spines, 124. _Ellipsidium_. ------------------------------------------------------------------------- Ellipsoidal shell with polar appendages (either solid spines or hollow fenestrated tubes) at the poles of the main axis. ------------------------------------------------------------------------- Solid spines of {Shell cavity similar shape, { simple, without at both poles of { axial rods, 125. _Ellipsoxiphus_. the main axis. { {Shell cavity { with a cross of { axial rods, 126. _Axoprunum_.

Solid spines of {Two polar spines different shape, { of different at both poles { shape, 127. _Ellipsostylus_. of the main { axis. {A bunch of spines { at one pole { only, 128. _Lithomespilus_ { {Only a single { spine at one { one pole, 129. _Lithapium_.

Two hollow fenestrated tubes opposite, at the poles of the main axis, 130. _Pipettella_.

Genus 122. _Cenellipsis_,[161] n. gen.

_Definition_.--#Ellipsida# with simple ellipsoidal shell, without radial spines and without polar tubes.

The genus _Cenellipsis_ is the simplest and most primitive form, not only among the Ellipsida, but also among the #Prunoidea#, and it may therefore be regarded as the common ancestral form of the whole family. It corresponds to _Cenosphæra_ among the #Sphæroidea#, to _Cenodiscus_ among the #Discoidea#, to _Cenolarcus_ among the #Larcoidea#. Probably it is derived from _Cenosphæra_ by prolongation of one axis.

Subgenus 1. _Cenellipsium_, Haeckel.

_Definition._--Network of the shell regular, with meshes of equal size and similar form.

{291}1. _Cenellipsis primitiva_, n. sp.

Proportion of the longer axis of the ellipsoid to the shorter = 3 : 2. Network of the thin wall very delicate and regular, with hexagonal pores. All pores of nearly the same size and form, ten to twelve times as broad as the bars; nine to twelve on the half equator of the shell. Surface smooth.

_Dimensions._--Longer axis of the ellipsoid 0.09 to 0.11, shorter axis 0.06 to 0.08; pores 0.01, bars between them 0.001.

_Habitat._--Pacific, central area, Station 272, surface.

2. _Cenellipsis faceta_, n. sp. (Pl. 39, fig. 1).

Proportion of the longer axis of the ellipsoid to the shorter = 4 : 3. Network of the thin wall delicate and regular. All the pores of the same size and form, circular, with a hexagonal frame, twice to three times as broad as the bars; eight to ten on the half equator. Surface smooth or slightly spiny.

_Dimensions._--Longer axis of the ellipsoid 0.12 to 0.13, shorter axis 0.09 to 0.1; pores 0.013, bars 0.005.

_Habitat._--Pacific, central area. Station 274, surface.

3. _Cenellipsis ehrenbergii_, Haeckel.

_Haliomma (?) cenosphæra_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf xxvi. fig. 5.

Proportion of the longer axis to the shorter = 2 : 1. Network of the thin wall regular or subregular. All pores circular, nearly of the same size, without hexagonal frame, three to four times as broad as the bars; eight to nine on the half equator. Surface covered with small thorns.

_Dimensions._--Longer axis of the ellipsoid 0.16 to 0.2, shorter axis 0.08 to 0.1; pores 0.1, bars 0.003.

_Habitat._--Fossil in the Tertiary rocks of Barbados (Ehrenberg, Haeckel).

4. _Cenellipsis circopora_, n. sp.

Proportion of the longer axis to the shorter = 5 : 3. Network of the thin wall delicate and regular. All pores circular, nearly of the same size, without hexagonal frame, twice as broad as the bars; fifteen to twenty on the half equator. Surface quite smooth.

_Dimensions._--Longer axis of the ellipsoid 0.15 to 0.2, shorter axis 0.09 to 0.12; pores 0.08, bars 0.4.

_Habitat._--North Pacific, Station 236, surface.

5. _Cenellipsis micropora_, n. sp.

Proportion of the longer axis to the shorter = 5 : 4. Network of the thick wall quite regular. All pores circular, without hexagonal frame, very small, scarcely half as broad as the bars; six to eight on the half equator. Surface quite smooth.

{292}_Dimensions._--Longer axis of the ellipsoid 0.1, shorter axis 0.08; pores 0.004, bars 0.01.

_Habitat._--South Pacific, Station 289, surface.

Subgenus 2. _Cenellipsula_, Haeckel.

_Definition._--Network of the shell irregular, with meshes of different size or form.

6. _Cenellipsis heteropora_, n. sp.

Proportion of the longer axis to the shorter = 3 : 2 or = 5 : 3. Network of the thin wall very irregular, with polygonal meshes of different size and form (for the most part pentagonal or hexagonal, but also many tetragonal or heptagonal). The largest pores four to six times as broad as the smallest; ten to twenty pores on the half equator; bars between them thin. Surface smooth or somewhat spiny.

_Dimensions._--Longer axis of the ellipsoid 0.18 to 0.22, shorter axis 0.1 to 0.12; pores 0.004 to 0.008, bars 0.001.

_Habitat._--Indian Ocean, near the Cocos Islands, surface, Rabbe.

7. _Cenellipsis maxima_, n. sp.

Proportion of the longer axis to the shorter = 3 : 2. Network of the thin wall very irregular, with polygonal meshes of very different size and form, twice to eight times as broad as the bars; fifty to sixty on the half equator. Surface smooth.

_Dimensions._--Longer axis of the ellipsoid 0.36, shorter axis 0.25; pores 0.004 to 0.015, bars 0.002.

_Habitat._--Equatorial Atlantic, Station 347, surface.

8. _Cenellipsis ovulum_, n. sp.

Proportion of the longer axis to the shorter = 3 : 2. Network of the thin wall very irregular, with roundish or longish pores of very different size and form. Pores flat, with even margins, thirty to forty on the half equator, twice to six times as broad as the bars. Surface smooth. (This species being observed alive, showed a transparent central capsule of ellipsoidal form, two-thirds as large as the shell.)

_Dimensions._--Longer axis of the ellipsoid 0.3, shorter axis 0.2; pores 0.04 to 0.012, bars 0.002.

_Habitat._--Indian Ocean, Ceylon, Haeckel; Pacific, central area, Station 266, surface.

9. _Cenellipsis infundibulum_, n. sp. (Pl. 39, fig. 2).

Proportion of the longer axis to the shorter = 3 : 2. Network of the thick wall irregular, with roundish pores of different size and form. Pores funnel-like, with prominent, irregular, spiny {293}crests between them, their outer aperture three to four times as broad as the inner; twelve to fifteen pores on the half equator. Surface prickly.

_Dimensions._--Longer axis of the ellipsoid 0.14, shorter axis 0.11; outer aperture of the pores 0.01 to 0.012, inner aperture 0.003 to 0.004.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

10. _Cenellipsis oblonga_, n. sp.

Proportion of the longer axis to the shorter = 2 : 1. Network of the thick wall irregular, with roundish pores of different size and form. Pores with prominent conical edges, about as broad as the bars; twenty to twenty-five on the half equator. Sometimes each pore is prolonged into a short conical tubulus.

_Dimensions._--Longer axis of the ellipsoid 0.22, shorter axis 0.12; pores and bars 0.008 to 0.012.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

Genus 123. _Axellipsis_,[162] n. gen.

_Definition._--#Ellipsida# with simple ellipsoidal shell, without radial spines or polar tubes, but with an inner transverse axial rod, which corresponds to the shorter axis of the ellipsoid.

The genus _Axellipsis_ differs from the simple _Cenellipsis_ in a very peculiar character, namely, the presence of an inner siliceous bar marking the minor axis of the ellipsoidal shell. If in some forms of _Druppula_ (e.g., Pl. 39, fig. 3) we remove the central medullary shell and prolong both beams (connecting it with the cortical shell) till they unite in the centre, we shall arrive at _Axellipsis_. Therefore _Axellipsis_ may be derived in the same way from _Druppula_ as _Axoprunum_ is from _Lithatractus_, by phyletic loss of the medullary shell.

1. _Axellipsis perforata_, n. sp.

Proportion of the major axis of the ellipsoid to the minor = 3 : 2. Pores of the shell regular, circular, twice as broad as the bars; ten to twelve on the half equator. Surface smooth.

_Dimensions._--Longer axis of the shell 0.12, shorter axis 0.08; pores 0.006, bars 0.003.

_Habitat._--Central area of the Pacific, Station 266, depth 2750 fathoms.

2. _Axellipsis lobata_, n. sp.

Proportion of the major axis to the minor = 5 : 4. Meshes of the shell irregular, roundish, lobed, with three to six indentations (each mesh formed by the confluence of three to six, commonly {294}four or five, smaller pores); eight to nine meshes on the half equator, these being twice to four times as broad as the bars.

_Dimensions._--Longer axis of the shell 0.1, shorter axis 0.08; pores 0.007 to 0.01, bars 0.003.

_Habitat._--Tropical zone of the Western Pacific, Station 225, surface.

Genus 124. _Ellipsidium_,[163] n. gen.

_Definition._--#Ellipsida# with simple ellipsoidal shell, with numerous radial spines on the surface, without polar spines or tubes.

The genus _Ellipsidium_ differs from _Cenellipsis_ solely in the development of numerous radial spines on the surface, and exhibits the same phylogenetic relation to it that _Heliosphæra_ bears to _Cenosphæra_.

1. _Ellipsidium pandanidium_, n. sp.

Proportion of the longer axis of the ellipsoid to the shorter = 5 : 4. Shell thick walled, with regular and hexagonal meshes, twice as broad as the bars; eighteen to twenty on the half equator. In each hexagon-corner (between three pores) arises a short, three-sided pyramidal spine, half as long as the equatorial radius, and as thick at the base as a single mesh.

_Dimensions._--Major axis of the ellipsoid 0.15, minor 0.12; pores 0.006, bars 0.003; length of the radial spines 0.03, basal breadth 0.006.

_Habitat._--Fossil in the Tertiary rocks of Barbados (Haeckel).

2. _Ellipsidium datura_, n. sp.

Proportion of the longer axis of the ellipsoid to the shorter = 4 : 3. Shell thick walled, with regular, circular meshes, twice as broad as the thick bars between them eight to ten meshes on the half equator. Outer surface of the shell thorny, covered with short, conical, radial spines, which are regularly distributed (one spine between every three meshes), and about as long as the diameter of the meshes. (The shell is similar to the outer shell of _Haliomma castanea_, Haeckel, Monogr. d. Radiol., Taf. xxiv. fig. 4.)

_Dimensions._--Major axis of the ellipsoid 0.12, minor axis 0.09; meshes 0.012, bars 0.006.

_Habitat._--Western part of the Tropical Pacific, Station 225, depth 4475 fathoms.

3. _Ellipsidium artocarpus_, n. sp.

Proportion of the longer axis to the shorter = 3 : 2. Shell thick walled, with regular, circular meshes, separated by deep furrows, which represent a regular, hexagonal framework; on the half equator twelve to fifteen meshes, scarcely broader than the broad bars between them. Outer {295}surface spiny; between every three meshes arises a strong radial spine, twice to three times as long as the diameter of the meshes; the base of the spine is like a three-sided pyramid.

_Dimensions._--Major axis of the ellipsoid 0.12, minor axis 0.08; meshes 0.006, bars 0.005.

_Habitat._--Central area of the Pacific, Station 268, depth 2900 fathoms.

4. _Ellipsidium opuntia_, n. sp.

Proportion of the longer axis to the shorter = 5 : 4. Shell thin walled, with irregular, roundish meshes of different size and form, about twice to three times as broad as the irregular, thin bars between them; ten to fifteen meshes on the half equator. Between the meshes arise numerous thin, bristle-like, radial spines, about as long as the shorter radius of the shell. The number of the meshes may be three to four times as great as the number of the spines.

_Dimensions._--Major axis of the ellipsoid 0.15, minor axis 0.12; pores 0.006 to 0.01, bars 0.003 to 0.004.

_Habitat._--Southern Pacific, Station 284, surface.

5. _Ellipsidium echinidium_, n. sp.

Proportion of the longer axis to the shorter = 4 : 3. Shell thick walled, with irregular, roundish pores of different size and form, about as large or somewhat smaller than the broad bars; twelve to sixteen pores on the half equator. On the surface, irregularly scattered, twenty to thirty strong, three-sided pyramidal, radial spines, one-fourth to one-half as long as the main axis.

_Dimensions._--Major axis of the ellipsoid 0.16, minor 0.12; pores and bars 0.002 to 0.008; length of the radial spines 0.04 to 0.08, basal breadth 0.01.

_Habitat._--Equatorial Atlantic, Station 347, depth 2250 fathoms.

Genus 125. _Ellipsoxiphus_,[164] Dunikowski, 1882, Denkschr. d. k. Akad. d. Wiss. Wien, vol. xlv. p. 25.

_Definition._--#Ellipsida# with simple ellipsoidal shell, the main axis of which is prolonged at both poles into two strong opposite spines of equal size and similar form.

The genus _Ellipsoxiphus_ was established by Dunikowski (in 1882, _loc. cit._) for those simple amphistylous fenestrated shells, formerly united with _Xiphosphæra_, in which the mathematical form of the shell itself is not a true sphere, but an ellipsoid. It may therefore be derived from _Xiphosphæra_ by prolongation of the axis in which lie both polar spines; but it may also be derived from _Cenellipsis_ by the production of two equal spines at the poles of the main axis.

{296}Subgenus 1. _Ellipsoxiphetta_, Haeckel.

_Definition._--Network of the shell regular, with pores of equal size and similar form.

1. _Ellipsoxiphus elegans_, n. sp. (Pl. 14, fig. 7).

Proportion of the major axis of the ellipsoid to the minor = 5 : 4. Shell thick walled, with regular, circular meshes, separated by a regular, hexagonal elevated framework. From each hexagon-corner arises (between every three meshes) a short thin spine, about as long as the diameter of a mesh; twelve to fourteen meshes on the half equator, of the same breadth as the bars. Polar spines three-sided prismatic, cuspidate, about as long as the axis of the shell. (This elegant and not uncommon species is remarkable for its variations. By unequal development of both spines it passes over to _Ellipsostylus_.) In the figured variety (Pl. 14, fig. 7) the ends of the surface spines are connected by a very delicate network, so as to form an outer veil. This may further be separated as a peculiar genus _Ellipsoxiphium palliatum_.

_Dimensions._--Longer axis 0.08 to 0.13, shorter axis 0.06 to 0.11; pores and bars 0.008; length of the polar spines 0.06 to 0.12, basal breadth 0.01.

_Habitat._--Pacific, central area, Stations 270 to 274, from 2350 to 2925 fathoms.

2. _Ellipsoxiphus flosculus_, n. sp.

Proportion of the major axis to the minor = 6 : 5. Shell very thick walled, with regular, hexagonal meshes, eight to nine on the half equator, three to four times as broad as the bars. The inner contour of the meshes is circular, the outer six-lobed (similar to _Xiphostylus phasianus_, Pl. 13, fig. 9). Polar spines three-sided pyramidal, about as long as the major axis of the shell; their basal thickness equals one mesh.

_Dimensions._--Longer axis 0.12, shorter axis 0.1; pores 0.012 to 0.015, bars 0.004; length of the polar spines 0.12 to 0.15, basal breadth 0.015.

_Habitat._--Fossil in the Tertiary rocks of Barbados (Teuscher).

3. _Ellipsoxiphus fragilis_, n. sp.

Proportion of the major axis to the minor = 4 : 3. Shell thin walled, with regular, circular meshes, twice as broad as the bars; ten to twelve on the half equator. Surface smooth. Polar spines cylindrical, at the apex conical, half as long as the major axis.

_Dimensions._--Longer axis 0.16, shorter axis 0.12; pores 0.008, bars 0.004; length of the polar spines 0.09, basal breadth 0.008.

_Habitat._--South Atlantic, Station 325, surface.

Subgenus 2. _Ellipsoxiphilla_, Haeckel.

_Definition._--Network of the shell irregular, with pores of different size or form.

{297}4. _Ellipsoxiphus claviger_, n. sp. (Pl. 14, fig. 3).

_Xiphosphæra clavigera_, Haeckel, 1881, Prodromus et Atlas.

Proportion of the major axis to the minor = 5 : 4. Shell thick walled, with irregular network; meshes roundish or circular, double contoured, of unequal size, twice to four times as broad as the bars; eight to ten on the half equator. Polar spines club-shaped, with prominent edges, about as long as the minor axis; thicker in their middle part than at both ends (differs from _Xiphosphæra clavigera_ by the ellipsoidal form of the shell, and the double length of the spines).

_Dimensions._--Longer axis 0.15. shorter axis 0.12; pores 0.007 to 0.015, bars 0.004; length of the polar spines 0.12, thickness in the middle part 0.02.

_Habitat._--Central area of the Pacific, Station 272, depth 2600 fathoms.

5. _Ellipsoxiphus suessi_, Dunikowski.

_Ellipsoxiphus suessi_, Dunikowski, 1882, Denkschr. d. k. Akad. d. Wiss. Wien, Bd. xlv. p. 26, Taf. v. fig. 50.

Proportion of the major axis to the minor = 7 : 5. Shell thick walled, with irregular, roundish meshes, six to eight on the half equator, twice to three times as broad as the bars. Polar spines nearly cylindrical, blunt, as long as the major axis.

_Dimensions._--Longer axis 0.14; shorter axis 0.1; pores 0.018 to 0.023, bars 0.01; length of the polar spines 0.12; thickness of them 0.035.

_Habitat._--Fossil in the Alpine Lias, Schafberg near Salzburg, Dunikowski.

6. _Ellipsoxiphus parvoforaminus_, Dunikowski.

_Ellipsoxiphus parvoforaminus_, Dunikowski, 1882, Denkschr. d. k. Akad. d. Wiss. Wien, Bd. xlv. p. 26, Taf. v. fig. 51.

Proportion of the major axis to the minor = 7 : 6. Shell thick walled, with irregular, roundish or oval meshes, ten to twelve on the half equator, scarcely as broad as the bars. Polar spines conical, shorter than the minor axis.

_Dimensions._--Longer axis 0.14, shorter axis 0.12; pores 0.016 to 0.01, bars 0.01 to 0.02; length of the polar spines 0.1, basal thickness 0.045.

_Habitat._--Fossil in the Alpine Lias, Schafberg near Salzburg, Dunikowski.

7. _Ellipsoxiphus bipolaris_, n. sp. (Pl. 14, fig. 11).

_Xiphosphæra bipolaris_, 1881, Prodromus et Atlas.

Proportion of the major axis to the minor = 8 : 7. Shell thick walled, with irregular, roundish meshes, twice to three times as broad as the bars; sixteen to twenty on the half equator. Polar spines short and thick, three-sided pyramidal, scarcely half as long as the shorter radius of the shell; surrounding the base of every spine is a circle of eight to nine shorter spines.

_Dimensions._--Longer axis 0.08, shorter axis 0.07; pores 0.003 to 0.007, bars 0.002; length of the polar spines 0.02 to 0.03, basal thickness 0.02.

_Habitat._--Tropical part of the Western Pacific, Station 225, depth 4475 fathoms.

{298}8. _Ellipsoxiphus atractus_, n. sp. (Pl. 14, fig. 1).

Proportion of the major axis to the minor = 3 : 2. Shell spindle-shaped, very thick walled, with roundish, very irregular meshes, twice to five times as broad as the bars; eight to twelve on the half equator. The meshes are partly simple, oblong, partly lobed or composed of two to four (commonly three) confluent meshes. Surface smooth. Polar spines very short and thick, shorter than the minor radius of the shell, three-sided pyramidal, with prominent, somewhat contorted edges.

_Dimensions._--Longer axis 0.15, shorter axis 0.1; meshes 0.007 to 0.02, bars 0.004; length of the polar spines 0.04, basal thickness 0.03.

_Habitat._--Central area of the Pacific, Station 268, depth 2900 fathoms.

Genus 126. _Axoprunum_,[165] n. gen.

_Definition._--#Ellipsida# with simple ellipsoidal shell, the main axis of which is prolonged at both poles into two opposite spines of equal size and similar form. Within the cavity of the shell four radial rods arise from its inner surface, two in the main axis, two in the smallest axis, perpendicular to the former; their free inner ends are at the same distance from the centre.

The genus _Axoprunum_ possesses precisely the same shell as the foregoing _Ellipsoxiphus_, but differs from it in a very remarkable peculiarity. The two polar spines are centripetally prolonged into two internal beams, and perpendicular to these are two other, opposite, transverse beams, marking the minor axis of the ellipsoid. The free inner ends of all four radial rods bear little thickened knobs, and are at the same distance from the centre. It therefore appears as though a central, spherical, medullary shell had been lost, and this gives a strong support to the important hypothesis, that in many #Sphærellaria#, where the medullary shell is absent, it may have been lost by phylogenetic reduction or retrograde metamorphosis. In this case _Axoprunum_ (and _Ellipsoxiphus_) would arise from _Lithatractus_.

1. _Axoprunum stauraxonium_, n. sp. (Pl. 48, fig. 4).

Shell ellipsoidal, one and one-third times as long as broad, with smooth surface. Network regular, with circular meshes four times as broad as the bars. Two polar spines three-sided pyramidal, half as long as the shell, as thick at the base as a single mesh. Four inner radial beams (lying, two in the major and two in the minor axis of the ellipsoid) very thin, at the central free ends knob-like, thickened. The distance between two opposite beams equals one-third of the minor axis, and indicates probably the diameter of the lost spherical medullary shell. (Three perfect and complete specimens of the same size and shape were observed.)

{299}_Dimensions._--Major axis of the ellipsoid 0.14, minor axis 0.11; pores 0.012, bars 0.003; length of the polar spines 0.07, basal breadth 0.012. (Diameter of the lost medullary shell 0.03?)

_Habitat._--South Atlantic, Station 338, depth 1990 fathoms.

Genus 127. _Ellipsostylus_,[166] n. gen.

_Definition._--#Ellipsida# with simple ellipsoidal shell, the main axis of which is prolonged at both poles into two opposite spines of different size or form.

The genus _Ellipsostylus_ differs from _Ellipsoxiphus_ only in the unequal size or different form of the polar spines, which in the former are equal. This difference does not seem important at first, but in the further development it produces very singular and strange forms. Theoretically it is always important, because the fundamental haplopolar form of the monaxon body becomes diplopolar by this differentiation.

Subgenus 1. _Ellipsostyletta_, Haeckel.

_Definition._--Network of the shell regular, with pores of equal size and similar form.

1. _Ellipsostylus ornithoides_, n. sp.

Proportion of the major axis of the ellipsoid to the minor = 4 : 3. Shell thin walled, with regular, circular meshes and hexagonal framework between them, like that of _Xiphostylus favosus_ (Pl. 13, fig. 4). Circular pores about as broad as the bars; eight to nine on the half equator. Surface smooth. Polar spines three-sided pyramidal, as broad at the base as a single hexagon; the longer spine as long as the major axis, the shorter half as long.

_Dimensions._--Longer axis of the ellipsoidal shell 0.16, shorter axis 0.12; pores and bars 0.006; length of the longer polar spine 0.16, of the shorter 0.08.

_Habitat._--North Pacific, Station 241, depth 2300 fathoms.

2. _Ellipsostylus avicularis_, n. sp.

Proportion of the major axis to the minor = 3 : 2. Shell thick walled, with regular, rosette-shaped meshes, three times as broad as the bars; ten to twelve on the half equator. Every mesh on the outer margin with five to six rounded lobes, as in _Xiphostylus phasianus_ (Pl. 13, fig. 9). Surface smooth. Polar spines sharp edged, thick; the longer straight and equal to the longer axis, the shorter half as long, shaped like a bird's head.

_Dimensions._--Longer axis 0.18, shorter axis 0.12; pores 0.015, bars 0.005.

_Habitat._--South Pacific, Station 300, depth 1375 fathoms.

{300}3. _Ellipsostylus psittacus_, n. sp. (Pl. 13, fig. 6).

Proportion of the major axis to the minor = 4 : 3. Shell thin walled, with regular or subregular rosette-shaped meshes, twice as broad as the bars; eight to nine on the half equator; each mesh with three to four rounded lobes. Surface smooth. Polar spines sharp edged, very unequal; longer spine about twice as long as the major axis, somewhat curved; shorter spine scarcely longer than the radius, shaped like a bird's head.

_Dimensions._--Longer axis 0.08, shorter axis 0.06; pores 0.01, bars 0.005; length of the polar spines--longer 0.15, shorter 0.05.

_Habitat._--Central area of the Pacific, Station 266, depth 2750 fathoms.

4. _Ellipsostylus aquila_, n. sp. (Pl. 13, fig. 1).

Proportion of the major axis to the minor = 7 : 6. Shell thick walled, with subregular, circular meshes, five to six times as broad as the bars; ten to twelve on the half equator. Surface smooth. Polar spines sharp edged (six-sided?), very unequal; longer spine straight, about equal to the minor axis; shorter spine obliquely inserted, scarcely half as long, shaped like a bird's head.

_Dimensions._--Longer axis 0.15, shorter axis 0.13; pores 0.02, bars 0.004; length of the polar spines--longer 0.1, shorter 0.05.

_Habitat._--Central area of the Pacific, Station 272, depth 2600 fathoms.

5. _Ellipsostylus columba_, n. sp. (Pl. 13, fig. 3).

Proportion of the major axis to the minor = 4 : 3. Shell egg-shaped, thin walled, with regular, circular meshes, three times as broad as the bars; ten to twelve on the half equator. Surface somewhat thorny. Polar spines nearly of equal length (equal to the major axis), but of very different form; one straight, pyramidal, and obliquely inserted, the other like a bird's head.

_Dimensions._--Longer axis 0.08, shorter 0.06; pores 0.003, bars 0.01; length of the spines 0.09.

_Habitat._--South Atlantic, Station 332, surface.

6. _Ellipsostylus ciconia_, n. sp. (Pl. 13, fig. 8).

Proportion of the major axis to the minor = 7 : 5. Shell egg-shaped, thick walled; the meshes very small, regular, circular, three times as broad as the bars; sixteen to twenty on the half equator. Surface uneven. Polar spines nearly cylindrical, pointed; the smaller obliquely inserted, equal to the major axis; the larger more than twice as long and thick, furrowed at its base. (Compare with this and the allied species _Rhabdolithis pipa_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. i. fig. 27.)

_Dimensions._--Longer axis 0.07, shorter 0.05; pores 0.003, bars 0.001; length of the polar spines--longer 0.2, shorter 0.08.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

{301}Subgenus 2. _Ellipsostylissa_, Haeckel.

_Definition._--Network of the shell irregular, with pores of different size or form.

7. _Ellipsostylus megadictya_, Haeckel.

_Stylosphæra megadictya_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 299, Taf. viii. fig. 13.

Proportion of the major axis to the minor = 5 : 4. Shell thin walled, with irregular, roundish, large meshes, four to five times as broad as the bars; only four to five on the half equator. Surface smooth. Polar spines straight, thin, angular; the shorter equal to the minor axis, the longer four times as large.

_Dimensions._--Longer axis 0.05, shorter axis 0.04; meshes 0.01, bars 0.002; length of the polar spines--longer 0.12, shorter 0.03.

_Habitat._--Philippine Sea, 3300 fathoms, Ehrenberg.

8. _Ellipsostylus gallinula_, n. sp.

Proportion of the major axis to the minor = 3 : 2. Shell thick walled, with irregular, roundish meshes, twice to four times as broad as the bars; eight to ten on the half equator. Surface thorny. Polar spines conical, straight; the longer twice as long as the major axis, the minor scarcely half as long.

_Dimensions._--Longer axis 0.15, shorter 0.12; pores 0.01 to 0.02, bars 0.002 to 0.004.

_Habitat._--North Pacific, Station 253, surface.

9. _Ellipsostylus hirundo_, n. sp. (Pl. 13, fig. 2).

Proportion of the major axis to the minor = 4 : 3. Shell thick walled, with irregular, roundish meshes, three to five times as broad as the bars; eight to ten on the half equator. The inner aperture of every mesh is fenestrated by a delicate lamella of silex, perforated by six to eight very small circular pores. Polar spines sharp edged, more or less curved, the shorter equal to the minor axis, the longer twice as long.

_Dimensions._--Longer axis 0.16, shorter 0.12; pores 0.01 to 0.02, bars 0.003 to 0.006; length of the polar spines--longer 0.24, shorter 0.12.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms; the same form also fossil in the rocks of Barbados.

Genus 128. _Lithomespilus_,[167] Haeckel, 1881, Prodromus, p. 450.

_Definition._--#Ellipsida# with simple ellipsoidal or oviform shell, the main axis of which bears at one pole a single spine, at the other a bunch of several spines.

{302}The genus _Lithomespilus_ differs from the closely allied _Ellipsoxiphus_ in the further differentiation of both poles of the main axis. One pole exhibits only a single polar spine, the other pole a group of several spines, peculiarly grouped together. It differs from the similar _Sphæromespilus_ (Pl. 14, figs. 12, 13) in the ellipsoidal form of the shell.

1. _Lithomespilus phloginus_, n. sp. (Pl. 14, fig. 16).

Proportion of the major axis of the ellipsoid to the minor = 4 : 3. Shell thick walled, with circular pores of different size, the breadth of which equals that of the bars; twelve to fifteen pores on the half equator. Surface smooth, with the exception of a circumpolar region covered with numerous thick spines of unequal size, which surround the large single polar spine and are curved like a bow against its axis. This larger polar spine is straight, and equals in length the major axis of the shell. The other and opposite polar spine is scarcely one-fourth as long, perfectly simple, very stout, and of a three-sided pyramidal shape.

_Dimensions._--Longer axis of the ellipsoidal shell 0.08, shorter axis 0.06; pores 0.002 to 0.006, bars 0.003 to 0.005; length of the polar spines--longer 0.08, shorter 0.02.

_Habitat._--Indian Ocean, near Madagascar, depth 1200 fathoms, Smith.

2. _Lithomespilus phlogoides_, n. sp. (Pl. 14, fig. 17).

Proportion of the major axis to the minor = 5 : 4. Shell very thick walled, with roundish, double-contoured pores of different size and form, twice to three times as broad as the bars; sixteen to eighteen pores on the half equator. Surface smooth, with the exception of a circumpolar region covered with numerous thin spines of unequal size, which surround the large single polar spine and are curved like a bow against its axis. This larger polar spine is straight, and equals half the size of the major axis of the shell; the other polar spine (sometimes double, as in the figured specimen) is much shorter, being scarcely one-fourth as long.

_Dimensions._--Longer axis of the shell 0.08, shorter axis 0.065; pores 0.003 to 0.006, bars 0.002 to 0.004; length of the polar spines--longer 0.04, shorter 0.01.

_Habitat._--Central area of the Pacific, Stations 270 to 272, depth 2425 to 2925 fathoms.

3. _Lithomespilus flammeus_, n. sp.

_Stylosphæra species_, Bury, 1862, Polycystins of Barbados, pl. xi. fig. 3.

Proportion of the major axis to the minor = 4 : 3. Shell thick walled, with irregular, roundish pores, about as broad as the bars; ten to twelve pores on the half equator. Surface spiny. Length of the conical straight spines increasing towards the poles; each polar spine surrounded by a circumpolar group of larger, somewhat curved spines. The larger polar spine equals in length the major axis; the smaller is scarcely half as long. (The figure, given by Bury, is not quite exact; there the spines are situated in the pores, instead of between them. In my specimen the polar spines were not branched.)

{303}_Dimensions._--Longer axis of the shell 0.12, shorter axis 0.09; pores and bars 0.004 to 0.006; length of the polar spines--longer 0.12, shorter 0.06.

_Habitat._--Fossil in Barbados.

4. _Lithomespilus flammabundus_, n. sp. (Pl. 14, fig. 14).

Proportion of the major axis to the minor = 4 : 3. Shell thin walled, with irregular, roundish pores, partly simple, partly composed of three to six confluent pores; only six to eight pores on the half equator, twice to four times as broad as the bars. Surface spiny. Length of the conical irregular spines increasing towards the poles; each polar spine surrounded by a flame-shaped, circumpolar area of longer spines; all large spines (also the polar spines) curved or contorted at one pole and much stronger and more numerous than at the other; length variable, often equal to the longer axis.

_Dimensions._--Longer axis of the shell 0.12, shorter axis 0.09; pores 0.005 to 0.015, bars 0.003 to 0.005; length of the polar spines 0.1 to 0.15.

_Habitat._--Western part of the Tropical Atlantic, Station 347, depth 2250 fathoms.

Genus 129. _Lithapium_,[168] n. gen.

_Definition._--#Ellipsida# with simple ellipsoidal or pear-shaped shell; with a single spine only situated at one pole of the main axis.

The genus _Lithapium_ represents a peculiar modification of _Ellipsoxiphus_; one of the two opposite polar spines disappears by reduction, and in this way only a single spine remains, at one pole of the main axis. For this reason the shell assumes a characteristic pear-shape, and may easily be confounded with some similar Monocyrtida (_Halicapsa_).

1. _Lithapium pyriforme_, n. sp. (Pl. 14, fig. 9).

Proportion of the longer axis to the shorter = 6 : 5. Shell thin walled, with regular, circular pores, four times as broad as the bars; six to eight on the half equator. Surface a little thorny. The single polar spines three-sided pyramidal, as broad at the base as one mesh, about as long as the radius of the shell. (In the specimen figured, there was on the opposite pole a little rudiment of the other lost polar spine; it is missing in other specimens.)

_Dimensions._--Major axis of the ellipsoidal shell 0.12, minor axis 0.1; pores 0.02, bars 0.005; length of the single polar spine 0.05, basal thickness 0.02.

_Habitat._--Central area of the Pacific, Station 266, depth 2750 fathoms.

2. _Lithapium halicapsa_, n. sp. (Pl. 14, fig. 8).

Proportion of the longer axis to the shorter = 6 : 5. Shell thin walled, with irregular, lobed meshes, six to eight on the half equator, twice to five times as broad as the bars; each mesh {304}composed of two to five confluent roundish pores. Surface a little thorny. The single polar spine pyramidal, as broad at the base as one mesh, one-third as long as the axis.

_Dimensions._--Major axis 0.12, minor axis 0.1; pores 0.01 to 0.02, bars 0.002 to 0.006; length of the single polar spine 0.03, basal thickness 0.02.

_Habitat._--Central area of the Pacific, Station 270, depth 2925 fathoms.

3. _Lithapium monocyrtis_, n. sp. (Pl. 14, fig. 10).

Proportion of the longer axis to the shorter = 7 : 6. Shell thick walled, with irregular, lobed meshes, four to six on the half equator, three to six times as broad as the bars; each mesh composed of three to six confluent roundish pores. Surface quite smooth, without thorns. The single polar spine pyramidal, as broad at the base as the largest mesh, half as long as the radius. (This species is closely allied to the foregoing, but differs in the smooth surface and the larger meshes.)

_Dimensions._--Major axis 0.15, minor axis 0.13; pores 0.01 to 0.03, bars 0.003 to 0.01; length of the single spine 0.04, basal thickness 0.03.

_Habitat._--Central area of the Pacific, Station 268, depth 2900 fathoms.

Genus 130. _Pipettella_,[169] n. gen.

_Definition._--#Ellipsida# with simple ellipsoidal shell, the main axis of which is prolonged at the pole into two opposite hollow fenestrated tubes of equal size and similar form.

The genus _Pipettella_ is distinguished from the other Ellipsida by two hollow perforated tubes, which are directed in the longer axis of the ellipsoidal shell and arise from opposite poles of this axis. It may be derived from _Cenellipsis_ by prolongation of both poles of the main axis. As the same peculiar production of two opposite latticed tubuli at the poles of the main axis obtains in nearly all families of #Prunoidea# (_Pipetta_, _Cannartus_, _Panarium_, _Zygartus_, &c.), it may possess a peculiar value in this group.

1. _Pipettella fusiformis_, n. sp.

Shell spindle-shaped, thin walled, the two opposite tubes being conical and not longer than the short transverse axis of the ellipsoidal shell; no sharp demarcation between them. The two axes of the ellipsoid bear the proportion of 3 : 2. Network of the shell and of the tubes equal, delicate, regular, hexagonal, with circular apertures of equal size; fourteen to sixteen on the half equator of the shell. Bars very thin. The shell of this species is similar to that of _Cannartiscus amphiconiscus_ (Pl. 39, fig. 19), but possesses no equatorial stricture and no medullary shell.

_Dimensions._--Longer axis of the ellipsoid 0.18, shorter axis 0.12; length of the tubes 0.1, their basal breadth 0.05; pores of the network 0.01, bars 0.001.

_Habitat._--Northern Pacific, Station 244, depth 2900 fathoms.

{305}2. _Pipettella tubulosa_, n. sp.

Shell ellipsoidal, thin walled, distinctly separated from the two opposite tubes, which are cylindrical, longer than the main axis of the ellipsoid, and one-sixth as broad as the shorter axis. The longer axis of the ellipsoid bears to the shorter the proportion of 5 : 4. Network of the shell and of the tubes equal, regular, with very small circular pores, about as broad as the bars; sixteen to eighteen pores on the half equator of the shell.

_Dimensions._--Longer axis of the ellipsoid 0.15, shorter axis 0.12; length of the tubes 0.16 to 0.2, breadth of them 0.02; pores of the network 0.003, bars 0.003.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

3. _Pipettella elongata_, n. sp.

Shell ellipsoidal, thick walled, distinctly separated from both opposite tubes, which are cylindrical, much prolonged, twice to three times as long as the main axis of the ellipsoid, and one-fifth as broad as the shorter axis. Both axes of the ellipsoid bear the proportion of 3 : 2. Network of the shell and of the tubes irregular with small rounded pores of different size, separated by broader bars (often twice to three times as broad), four to six pores on the half equator of the shell. (This species somewhat recalls _Solenosphæra serpentina_, Pl. 7, fig. 7; but the tubes are straight, not contorted.)

_Dimensions._--Longer axis of the ellipsoid 0.2, shorter axis 0.14; length of the tubes 0.4 to 0.5, breadth 0.03; pores of the network 0.001 to 0.002, bars 0.003 to 0.004.

_Habitat._--Central area of the Pacific, Station 271, depth 2425 fathoms.

4. _Pipettella prismatica_, n. sp. (Pl. 39, fig. 6).

Shell ellipsoidal, thick walled, distinctly marked off from the two opposite tubes, which are longer than its main axis and as broad as one-fifth of it; they are nearly four-sided prismatic, with four strong ribs or edges; these are directed parallel to the main axis, in two meridian planes, perpendicular to one another. The wall of the shell is thickened in the equatorial plane, so as to form a slight stricture on the inside, separating its two halves. Both axes of the ellipsoid bear the proportion of 7 : 6. Network regular, with circular pores, somewhat broader than the bars. The meshes of the shell (fourteen to sixteen on the half equator) are twice as great as those of the tubes, which are arranged in two longitudinal rows between every two ribs (there being eight longitudinal rows on the whole tube). This species is very remarkable for the rudimentary internal equatorial stricture of the shell (transition to the genus _Cannartus_, Pl. 39, fig. 10), and by the four edges of the tubes, which indicate two of the dimensive axes, the third being represented by the main axis.

_Dimensions._--Longer axis of the ellipsoid 0.14, shorter axis 0.12; length of the tubes 0.15 to 0.16, breadth 0.03; pores of the shell 0.008 to 0.01, pores of the tubes 0.004.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

{306}Family XII. #DRUPPULIDA#, Haeckel, 1882 (Pls. 15, 16, 17, 39).

_Definition._--#Prunoidea# with ellipsoidal, latticed (not spongy) shell, composed of two or more concentric shells; a simple or double cortical shell enclosing one or two internal concentric shells (medullary shells), without equatorial stricture. Central capsule ellipsoidal or cylindrical, without annular equatorial constriction.

The family #Druppulida# differs from the Ellipsida only in the possession of a simple or double medullary shell, which is enclosed in the centre of the central capsule, and connected with the ellipsoidal cortical shell (lying outside it) by radial beams, perforating the membrane of the capsule. The Druppulida exhibit therefore the same relation to the Ellipsida that the Dyosphærida among the #Sphæroidea# bear to the Monosphærida. The cortical shell may be simple or multiple. The whole fenestrated shell is thus composed of a variable number (two at least) of concentric shells, which are connected by radial beams.

_The Medullary Shell_--enclosed in the centre of the central capsule--is either simple or double, and composed of two small concentric shells. Their form is either spherical, or ellipsoidal, or lenticular. If the medullary shell be ellipsoidal, the main axis of the ellipsoid is the same as in the cortical shell. Sometimes the inner medullary shell is spherical, the outer ellipsoidal or lenticular. If the medullary shell be lenticular (arising from both poles of the main axis) its vertical axis is also identical with that of the cortical shell (Pl. 39, fig. 5).

_The Radial Beams_, which connect the medullary and cortical shell, are either developed in all possible directions (Pls. 16, 17), or limited to the equatorial plane, more rarely to the meridional plane. Sometimes the connection is produced only by two opposite beams which lie in the minor or equatorial axis (Pl. 39, figs. 3, 7, 8); more rarely in the major or meridional axis (Pl. 17, figs. 7, 8).

_The Cortical Shell_ is constantly ellipsoidal, rarely with modifications, similar to those which appear in the simple shell of some Ellipsida. As a rule it is simple, rarely composed of two or more (sometimes six or more) concentric ellipsoidal shells (in _Cromyodruppa_ and _Cromyocarpus_). The outer surface is commonly smooth, more rarely covered with radial spines (in _Druppocarpus_, _Prunocarpus_, &c.). In the majority peculiar polar appendages are developed at both poles of the main axis, these being prolongations of them, either in the form of hollow fenestrated tubes (_Pipetta_, _Pipettaria_, Pl. 39, figs. 7, 8), or solid strong spines. The two polar spines are either equal in size and similar in form (as in _Lithatractus_, _Stylatractus_) or unequal (as in _Druppatractus_, _Xiphatractus_, Pls. 16, 17).

The most primitive of all Druppulida is _Druppula_, with simple medullary shell and simple cortical shell (Pl. 39, fig. 3); _Prunulum_ differs from it only in the possession {307}of a double medullary shell (Pl. 39, fig. 4). From these two genera all other forms of the subfamily may be derived.

_The Central Capsule_ of the Druppulida is constantly ellipsoidal, larger than the concentric enclosed medullary shells, smaller than the surrounding cortical shell; it is separated from the inner surface of the latter by a thinner or thicker jelly-mantle.

_Synopsis of the Genera of the Druppulida._

------------------------------------------------------------------------- Cortical shell without polar appendages (neither solid spines nor hollow tubes at the poles of the main axis). ------------------------------------------------------------------------- { {Surface {Medullary { smooth, 131. _Druppula_. { shell simple.{ { {Surface Cortical shell { { spiny, 132. _Druppocarpus_. simple, { ellipsoidal. { {Surface {Medullary { smooth, 133. _Prunulum_. { shell double.{ { {Surface { { spiny, 134. _Prunocarpus_.

Cortical shell }Medullary {Surface composed of } shell { smooth, 135. _Cromyodruppa_. two or more } double. { concentric } {Surface shells. } { spiny, 136. _Cromyocarpus_. ------------------------------------------------------------------------- Two opposite solid spines, arising from the poles of the main axis. ------------------------------------------------------------------------- { {Both polar {Medullary { spines equal, 137. _Lithatractus_. { shell { { simple. {Both polar Cortical { { spines shell { { unequal, 138. _Druppatractus_. simple, { ellipsoidal.{ {Both polar { { spines equal, 139. _Stylatractus_. {Medullary { { shell {Both polar { double. { spines { { unequal, 140. _Xiphatractus_.

Cortical shell composed of two or more concentric shells; medullary shell double; both polar spines equal, 141. _Cromyatractus_. ------------------------------------------------------------------------- Two opposite hollow fenestrated tubes, arising from the poles of the main axis. ------------------------------------------------------------------------- Medullary shell simple, 142. _Pipetta_.

Medullary shell double, 143. _Pipettaria_.

Genus 131. _Druppula_,[170] n. gen.

_Definition._--#Druppulida# with simple ellipsoidal, cortical shell, and simple medullary shell, without spines or polar tubes.

The genus _Druppula_, as the simplest form of the Druppulida, may be regarded as the common ancestral form of this subfamily. It may be derived phylogenetically either {308}from _Carposphæra_ by prolongation of one axis, or from _Cenellipsis_ by duplication of the fenestrated shell. The outer (or cortical) shell is always more or less ellipsoidal; the inner (or medullary) shell also is sometimes ellipsoidal, sometimes spherical. Both shells are concentric, connected by a variable number of radial beams. Compare _Haliomma oblongum_, Harting, 1863, L. N. 18, p. 15, pl. 2, fig. 42.

Subgenus 1. _Druppuletta_, Haeckel.

_Definition._--Pores of the cortical shell regular, hexagonal, or circular.

1. _Druppula drupa_, n. sp.

Cortical shell thin walled, with smooth surface and regular network; both its axes bear the proportion of 4 : 3. Pores regular, hexagonal, three times as broad as the bars; twelve to fifteen on the half equator. Medullary shell spherical, about one-third as broad as the cortical shell.

_Dimensions._--Major axis of the ellipsoidal cortical shell 0.1 to 0.12, minor axis 0.08 to 0.09; pores 0.06, bars 0.02; diameter of the medullary shell 0.03.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms; also fossil in Barbados.

2. _Druppula pandanus_, n. sp. (Pl. 39, fig. 3).

Cortical shell thin walled, somewhat rough, with regular network; both its axes bear the proportion of 3 : 2. Pores subregular, circular, hexagonally framed, one and a half times as broad as the elevated bars; ten to twelve on the half equator. Medullary shell spherical, one-fourth as broad as the cortical shell.

_Dimensions._--Major axis of the cortical shell 0.16 to 0.17, minor axis 0.11 to 0.12; pores 0.01, bars 0.007; diameter of the medullary shell 0.035.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

3. _Druppula cocos_, n. sp.

Cortical shell thick walled, somewhat rough, with regular network; proportion of both axes = 6 : 5. Pores regular, circular, hexagonally framed, quite as broad as the elevated bars; fourteen to sixteen on the half equator. Medullary shell ellipsoidal (with longitudinal main axis), nearly half as large as the cortical shell.

_Dimensions._--Major axis of the cortical shell 0.07 to 0.08, minor axis 0.6 to 0.65; pores and bars 0.003 to 0.004; diameter of the medullary shell 0.03 and 0.035.

_Habitat._--Western Tropical Pacific, Station 222, surface, Indian Ocean, Ceylon, Haeckel.

4. _Druppula phoenix_, n. sp.

Cortical shell thick walled, smooth, with regular network; proportion of both axes = 5 : 4. Pores regular, circular, hexagonally lobulate (in the same manner as in _Stauroxiphus gladius_, {309}Pl. 15, fig. 7), three times as broad as the bars; ten to twelve on the half equator. Medullary shell ellipsoidal (with longitudinal main axis), one-third as broad as the cortical shell.

_Dimensions._--Major axis of the cortical shell 0.1, minor axis 0.08; pores 0.009, bars 0.003; axis of the medullary shell 0.03 and 0.025.

_Habitat._--Mediterranean, Smyrna, Haeckel, surface.

5. _Druppula areca_, n. sp.

Cortical shell thin walled, with smooth surface and regular network; both its axes bear the proportion of 4 : 3. Pores regular, circular, four times as broad as the bars; fifteen to eighteen on the half equator. Medullary shell spherical, half as broad as the cortical shell.

_Dimensions._--Major axis of the ellipsoidal cortical shell 0.12 to 0.14, minor axis 0.1 to 0.11; pores 0.008, bars 0.002; diameter of the medullary shell 0.05 to 0.06.

_Habitat._--Indian Ocean, off Bombay, Haeckel.

6. _Druppula ovata_, Haeckel.

_Haliomma ovatum_, Ehrenberg, 1854, Mikrogeol., pl. xx. I. fig. 20.

_Haliomma ovatum_, Haeckel, 1862, Monogr. d. Radiol., p. 432.

Cortical shell thin walled, with smooth surface and regular network; proportion of both axes = 3 : 2. Pores regular, circular, three times as broad as the bars; nine to ten on the half equator. Medullary shell spherical, one-third as broad as the cortical shell.

_Dimensions._--Major axis 0.08 to 0.1, minor axis 0.05 to 0.06; pores 0.003, bars 0.001; diameter of the medullary shell 0.02.

_Habitat._--Fossil in the Tertiary rocks of the Mediterranean coast, Greece (Zante), Ehrenberg; Sicily (Caltanisetta), Haeckel.

7. _Druppula caryota_, n. sp.

Cortical shell thick walled, with rough surface and regular network; proportion of both axes = 5 : 4. Pores regular, circular, twice as broad as the bars; sixteen to twenty on the half equator. Medullary shell ellipsoidal, one-third as large as the cortical shell.

_Dimensions._--Major axis 0.2 to 0.22, minor 0.16 to 0.18, pores 0.008, bars 0.004; axes of the medullary shell 0.07 and 0.055.

_Habitat._--Pacific, central area, Stations 266 to 268, depth 2700 to 2900 fathoms.

Subgenus 2. _Druppulissa_, Haeckel.

_Definition._--Pores of the cortical shell irregular, of different form or size, usually subcircular or roundish, sometimes lobed or compound.

{310}8. _Druppula nucula_, n. sp.

Cortical shell thin walled, smooth, with irregular network; its two axes bear the proportion 3 : 2. Pores subcircular or irregular, roundish, twice to four times as broad as the bars; fifteen to twenty on the half equator. Medullary shell spherical, about one-third as broad as the cortical shell.

_Dimensions._--Major axis of the cortical shell 0.15 to 0.2, minor axis 0.1 to 0.14; pores 0.006 to 0.012, bars 0.03; diameter of the medullary shell 0.04.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

9. _Druppula elliptica_, Haeckel.

_Haliomma ellipticum_, Stöhr, 1880, Palæontogr., _loc. cit._, p. 88, Taf. i. fig. 11.

Cortical shell thin walled, rough, or thorny, with irregular network; proportion of the axes = 3 : 2. Pores subcircular or irregular, roundish, about as broad as the bars; ten to twelve on the half equator. Medullary shell half as broad as the cortical shell, irregularly polyhedral (with crooked beams in its interior).

_Dimensions._--Major axis 0.15, minor 0.06; pores and bars 0.006; diameter of the medullary shell 0.03.

_Habitat._--Fossil in the Tertiary rocks of Sicily: Grotte (Stöhr), Caltanisetta (Haeckel).

10. _Druppula prunum_, n. sp.

Cortical shell thick walled, smooth, with irregular network; proportion of the axes = 5 : 4. Pores subcircular or irregular, roundish, three to four times as broad as the bars; seven to eight on the half equator; every pore is closed at the bottom by a thin membrane, perforated by four to six irregular pores (like _Stylatractus sethoporus_, Pl. 17, fig. 3). Medullary shell spherical, one-third as broad as the cortical shell.

_Dimensions._--Major axis 0.2, minor axis 0.16; pores 0.03, bars 0.01; small enclosed porules 0.01; diameter of the medullary shell 0.05.

_Habitat._--Mediterranean, surface, Portofino near Genoa, Haeckel.

11. _Druppula oliva_, n. sp.

Cortical shell thick walled, rough, with irregular network; proportion of the axes = 5 : 4. Pores irregular, roundish, three to four times as broad as the bars; lobed or composed of several conjugated porules (as in _Lithapium halicapsa_, Pl. 14, fig. 8); five to six large pores on the half equator. Medullary shell ellipsoidal, about one-third as broad as the cortical shell.

_Dimensions._--Major axis of the cortical shell 0.15, minor 0.12; pores 0.02 to 0.03, bars 0.007; diameter of the medullary shell 0.04.

_Habitat._--Mediterranean (Corfu), Canary Islands (Lanzerote), Haeckel.

{311}Genus 132. _Druppocarpus_,[171] n. gen.

_Definition._--#Druppulida# with simple ellipsoidal cortical shell and simple medullary shell, with numerous radial spines, without polar tubes.

The genus _Druppocarpus_ differs from _Druppula_ only in the radial spines, which arise between the pores of the cortical shell, and therefore exhibits the same relation to it that _Ellipsidium_ bears to _Cenellipsis_, or _Prunocarpus_ to _Prunulum_.

Subgenus 1. _Druppocarpetta_, Haeckel.

_Definition._--Network of the cortical shell regular, with meshes of equal size and similar form.

1. _Druppocarpus ananassa_, n. sp.

Cortical shell thin walled, with regular, circular, hexagonally framed pores, of about the same breadth as the elevated bars; fourteen to sixteen on the half equator. From each hexagon-corner (between every three pores) arises a short thin radial spine, about as long as two pores, three-sided pyramidal at the base. Proportion of both cortical axes = 4 : 3. Medullary shell spherical, half as broad as the cortical shell. (Greatly resembles _Druppula pandanus_, Pl. 39, fig. 3, but differs in the larger medullary shell and the spines on the surface.)

_Dimensions._--Major axis of the ellipsoidal cortical shell 0.16, minor 0.12; pores and bars 0.006; length of the radial spines 0.02; diameter of the medullary shell 0.06.

_Habitat._--South Pacific, Station 289, surface.

2. _Druppocarpus castanea_, n. sp.

Cortical shell thin walled, with regular circular pores (without hexagonal frames), of about the same breadth as the bars; twelve to fourteen on the half equator. Between every three meshes arise a short conical spine with bristle-like apex, twice to four times as long as one pore. Proportion of both cortical axes = 3 : 2. Medullary shell spherical, one-third as broad as the cortical. (Resembles very closely the spherical _Haliomma castanea_, Haeckel, figured in my Monograph. pl. xxiv. fig. 4.)

_Dimensions._--Major axis 0.15, minor axis 0.1; pores and bars 0.005; length of the radial spines 0.01 to 0.02; medullary shell 0.035.

_Habitat._--North Atlantic, surface; Canary Islands, Lanzerote, Haeckel.

Subgenus 2. _Druppocarpissa_, Haeckel.

_Definition._--Network of the cortical shell irregular, with meshes of different size or form.

{312}3. _Druppocarpus chamaerops_, n. sp.

Cortical shell thin walled, with irregular, roundish, or subcircular pores of very different size, twice to six times as broad as the thin bars; eight to twelve on the half equator. Between them arise numerous thin, bristle-like radial spines, about half as long as the equatorial axis, and equal to the diameter of the spherical medullary shell; pores of the latter subregular, circular, very small. (Resembles _Prunocarpus artocarpus_, Pl. 39, fig. 5, but differs in the simple spherical medullary shell.)

_Dimensions._--Major axis 0.12, minor 0.09; meshes 0.005 to 0.02, bars 0.003; length of the radial spines 0.05; diameter of the medullary shell 0.04.

_Habitat._--Mediterranean, in the Strait of Gibraltar, Algesiras, Haeckel, surface.

4. _Druppocarpus borassus_, n. sp.

Cortical shell thick walled, with irregular, roundish, or subcircular pores, three to five times as broad as the bars; twelve to fifteen on the half equator. Irregularly scattered on the surface about twenty to thirty short conical spines; their length equals their basal breadth and the diameter of the largest pores. Medullary shell ellipsoidal, half as large as the cortical.

_Dimensions._--Major axis 0.1, minor 0.08; pores 0.006 to 0.01, bars 0.002; length and thickness of the radial spines 0.01; axes of the medullary shell 0.05 and 0.04.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

5. _Druppocarpus corypha_, n. sp.

Cortical shell thick walled, with irregular, funnel-like, roundish pores, scarcely as broad as the bars; sixteen to twenty on the half equator. Irregularly scattered on the surface about fifteen to twenty three-sided pyramidal radial spines, half as long as the equatorial axis, and as the diameter of the medullary shell.

_Dimensions._--Major axis 0.17, minor 0.14; pores and bars 0.003 to 0.009; length of the radial spines 0.08; diameter of the medullary shell 0.09.

_Habitat._--Fossil in the Tertiary rocks of the Nicobars, Haeckel.

Genus 133. _Prunulum_,[172] n. gen.

_Definition._--#Druppulida# with simple ellipsoidal cortical shell and double medullary shell; without spines or polar tubes.

The genus _Prunulum_ differs from _Druppula_ in the double (not simple) medullary shell, which is sometimes spherical, sometimes ellipsoidal; it may be derived either from _Druppula_ by duplication of the medullary shell, or from _Thecosphæra_ by prolongation of one axis.

{313}Subgenus 1. _Prunuletta_, Haeckel.

_Definition._--Network of the cortical shell regular, with meshes of equal size and similar form.

1. _Prunulum frugulum_, n. sp.

Cortical shell thin walled, smooth, with regular, hexagonal pores, three times as broad as the bars; ten to twelve on the half equator. Proportion of the major axis of the ellipsoid to the minor = 4 : 3. Both medullary shells spherical. (Differs from _Druppula drupa_ almost entirely in the double medullary shell.)

_Dimensions._--Major axis of the ellipsoidal cortical shell 0.12, minor 0.09; pores 0.006, bars 0.002; diameter of both medullary shells 0.05 and 0.03.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

2. _Prunulum cerasum_, n. sp.

Cortical shell thick walled, smooth, with circular, hexagonally framed pores, of the same breadth as the bars; sixteen to eighteen on the half equator. Proportion of the two axes of the ellipsoid = 5 : 4. Both medullary shells spherical. (The cortical shell resembles that of _Pipetta tuba_, Pl. 39, fig. 7, without the polar tubes.)

_Dimensions._--Major axis 0.15, minor 0.12; pores and bars 0.007; diameter of the medullary shells 0.08 and 0.04.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

3. _Prunulum amygdalum_, n. sp.

Cortical shell thick walled, smooth, with regular, circular, hexagonally lobulated pores, three times as broad as the bars; twelve to fourteen on the half equator (of the same form as in _Druppula phoenix_ and in _Stauroxiphos gladius_, Pl. 15, fig. 7). Proportion of the two axes = 6 : 5. Inner medullary shell spherical, outer ellipsoidal.

_Dimensions._--Major axis 0.12, minor 0.1; pores 0.009, bars 0.003; diameter of the medullary shells 0.07 and 0.04.

_Habitat._--Mediterranean (Corfu), surface.

4. _Prunulum coccymelium_ (Pl. 39, fig. 4).

Cortical shell thin walled, slightly rough, with regular, circular pores, twice as broad as the bars; twelve to fifteen on the half equator. Proportion of both axes = 4 : 3. Both medullary shells spherical.

_Dimensions._--Major axis 0.12, minor 0.09; pores 0.006, bars 0.003; diameter of the medullary shells 0.06 and 0.03.

_Habitat._--Pacific, central area, Station 273, depth 2350 fathoms.

{314}5. _Prunulum crenatum_, Haeckel.

? _Haliomma crenatum_, Ehrenberg, 1854, Mikrogeol., Taf. xxii. fig. 36.

_Actinomma crenatum_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 94, Taf. iii. fig. 3.

_Caryolithis crenata_, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 43.

Cortical shell thick walled, slightly rough or thorny, with small, regular, circular pores, of the same breadth as the bars; sixteen to eighteen on the half equator. Proportion of the two axes = 4 : 3. Both medullary shells ellipsoidal. (The figure of Stöhr represents exactly the fossil form, as I have observed it myself in the Caltanisetta rocks, whilst the figure of Ehrenberg is inaccurate and doubtful. The same form, somewhat variable in size and in the number of the pores, I have also observed in the Pacific ooze.)

_Dimensions._--Major axis 0.14 to 0.17, minor 0.1 to 0.13; pores and bars 0.006; main axes of the medullary shells 0.09 and 0.03.

_Habitat._--Fossil in the Tertiary rocks of Sicily (Grotte and Caltanisetta); living in the Central Pacific, Station 268, depth 2900 fathoms.

6. _Prunulum triplex_, Haeckel.

_Haliomma triplex_, Ehrenberg, 1854, Microgeol., Taf. xxxvB. fig. Biv., q.

_Actinomma triplex_, Haeckel, 1862, Monogr. d. Radiol., p. 444.

Cortical shell thin walled, covered with numerous very thin, short, bristle-like spines. Pores small, regular, circular, of the same breadth as the bars; fourteen to sixteen on the half equator. Proportion of the two axes = 3 : 2. Both medullary shells ellipsoidal. The description of Ehrenberg--as is very often the case--is quite incongruent with his figure. From a combination of both I give here the diagnosis of a deep-sea species, which is possibly identical with it. The velvet-like covering of very short and thin bristles is peculiarly characteristic of this species.

_Dimensions._--Major axis 0.1, minor 0.065; pores and bars 0.004; main axes of the medullary shells 0.04 and 0.02.

_Habitat._--North Atlantic, 1800 fathoms, Ehrenberg; Station 353, depth 2965 fathoms.

Subgenus 2. _Prunulissa_, Haeckel.

_Definition._--Network of the cortical shell irregular, with meshes of different form or size (usually roundish, but sometimes lobed or compound).

7. _Prunulum persicum_, n. sp.

Cortical shell thick walled, with smooth surface and irregular, roundish, double-contoured pores, twice to four times as broad as the bars; eight to ten on the half equator. Some of the pores are simple, often subcircular, others lobed, i.e., composed of from two to three confluent pores as in _Amphisphæra pluto_ (Pl. 17, fig. 7). Proportion of the two axes = 3 : 2. Both medullary shells ellipsoidal (or the inner spherical).

{315}_Dimensions._--Major axis 0.12, minor 0.08; pores 0.06 to 0.012, bars 0.003; main axes of the medullary shells 0.05 and 0.025.

_Habitat._--Indian Ocean, between Socotra and Ceylon, surface, Haeckel.

8. _Prunulum fenestratum_, Haeckel.

_Actinomma fenestratum_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 94, Taf. iii. fig. 2.

Cortical shell thick walled, rough, with irregular, roundish pores, once to three times as broad as the bars; twelve to fourteen on the half equator. Proportion of the two axes = 9 : 8. Both medullary shells ellipsoidal. (The pores in Stöhr's description are by mistake called "regular"; in the figure they are very irregular, as also in the fossil specimens observed by myself. Between the cortical pores arise very short irregular thorns.)

_Dimensions._--Major axis 0.12 to 0.15, minor 0.1 to 0.12; pores 0.003 to 0.01, bars 0.003; main axis of the outer medullary shell 0.07 to 0.09, of the inner 0.03 to 0.04.

_Habitat._--Fossil in the Tertiary rocks of Sicily; Grotte, Stöhr, Caltanisetta, Haeckel.

9. _Prunulum pyrenium_, n. sp.

Cortical shell very thick walled, smooth, with large irregular, roundish pores, three to four times as broad as the bars; six to eight on the half equator. The bottom of each funnel-like pore is closed by a thin siliceous membrane, perforated by three to five irregular roundish pores. Proportion of the two axes = 4 : 3. Both medullary shells ellipsoidal. (Closely resembles _Stylatractus sethoporus_, Pl. 17, figs. 2, 3, but is devoid of the polar spines.)

_Dimensions._--Major axis 0.16, minor 0.12; pores 0.015 to 0.02, bars 0.005; porules 0.01; main axes of the medullary shells 0.07 and 0.03.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

Genus 134. _Prunocarpus_,[173] n. gen.

_Definition._--#Druppulida# with simple ellipsoidal cortical shell and double medullary shell, with numerous radial spines, but without polar tubes.

The genus _Prunocarpus_ differs from _Prunulum_ only in the radial spines of the cortical shell, and exhibits therefore the same relation to it that _Druppocarpus_ bears to _Druppula_. While in the latter the medullary shell is simple, in the former it is double.

Subgenus 1. _Prunocarpetta_, Haeckel.

_Definition._--Network of the cortical shell regular, with meshes of equal size and similar form.

{316}1. _Prunocarpus datura_, n. sp.

Cortical shell thick walled, with regular, circular pores, twice as broad as the bars; ten to twelve on the half equator. Between every three meshes arises a short conical spine, twice to three times as long as one pore. Both medullary shells spherical. (Differs mainly from _Ellipsidium datura_ and from _Druppocarpus castanea_ in the double medullary shell. The outer network resembles _Haliomma castanea_, figured 1862 in my Monograph, Taf. xxiv. fig. 4.)

_Dimensions._--Major axis of the ellipsoid 0.16, minor 0.12; pores 0.012, bars 0.006; length of the radial spines 0.03; diameter of the medullary shells 0.06 and 0.04.

_Habitat._--North Atlantic, Færöe Channel, John Murray, surface.

2. _Prunocarpus sparganium_, n. sp.

Cortical shell thick walled, with very small, numerous, regular, circular pores, of the same size as the bars; forty to fifty on the half equator. Between them over the entire surface occur small conical spines. Irregularly scattered over the surface ten to twenty larger conical spines, three to six times as thick at the base as one pore, one-fourth to one-half as long as the main axis. Both medullary shells ellipsoidal.

_Dimensions._--Major axis of the cortical shell 0.16, of the outer medullary shell 0.11, of the inner 0.06; equatorial axis of the first shell 0.12, of the second 0.08, of the third 0.04; pores and bars on an average 0.005; length of the spines 0.05 to 0.1, basal breadth 0.02 to 0.03.

_Habitat._--Fossil in the Barbados deposits (Haeckel).

Subgenus 2. _Prunocarpilla_, Haeckel.

_Definition._--Network of the cortical shell irregular, with meshes of different size or form.

3. _Prunocarpus artocarpium_, n. sp. (Pl. 39, fig. 5).

Cortical shell thin walled with irregular, roundish pores of very different sizes, twice to nine times as broad as the thin bars; ten to fifteen on the half equator. Between them arise numerous bristle-shaped, radial spines, with conical base, on an average one-fourth to two-thirds as long as the equatorial axis. The outer medullary shell, with irregular, roundish pores, presents a transverse ellipsoid, its main axis lying in the equatorial axis of the cortical shell, whilst its equatorial axis corresponds to the main axis of the latter. Inner medullary shell very small, spherical, with very small pores.

_Dimensions._--Major axis of the cortical shell 0.14, of the outer medullary shell 0.05; minor axis of the former 0.1, of the latter 0.035; diameter of the inner medullary shell 0.014; pores of the cortical shell 0.005 to 0.02, bars 0.002; length of the radial spines 0.02 to 0.06.

_Habitat._--Indian Ocean, surface; Ceylon, Belligemma, Haeckel.

{317}4. _Prunocarpus melocactus_, n. sp.

Cortical shell thick walled, with irregular, roundish pores, twice to five times as broad as the bars; eighteen to twenty-four on the half equator. Between them arise over the entire surface small conical thorns, not longer than the largest pores. Irregularly scattered over the surface twenty to thirty strong, conical, radial spines, about half as long as the main axis, as broad at the base as a large pore. Both medullary shells ellipsoidal, their main axis identical with that of the cortical shell.

_Dimensions._--Major axis of the outer shell 0.18, of the middle 0.09, of the inner 0.05; minor axis of the first 0.14, of the second 0.07, of the third 0.04; pores of the cortical shell 0.006 to 0.02, bars 0.004; length of the spines 0.1, basal breadth 0.01.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms; also fossil in the Tertiary rocks of Sicily; Caltanisetta, Haeckel.

Genus 135. _Cromyodruppa_,[174] n. gen.

_Definition._--#Druppulida# with four or more concentric shells (two medullary and two or more cortical shells), without spines or polar tubes.

The genus _Cromyodruppa_ is characterised by the multiplication of the concentric fenestrated shell, which is composed of two medullary shells (enclosed in the central capsule) and two or more cortical shells (outside it). The former may be either spherical or ellipsoidal. The latter are always ellipsoidal, and in this it differs from _Cromyosphæra_. Probably _Cromyodruppa_ has arisen from _Prunulum_ by secondary apposition of more cortical envelopes.

Subgenus 1. _Cromyodruppium_, Haeckel.

_Definition._--Shell composed of four concentric shells, two medullary and two cortical.

1. _Cromyodruppa cepa_, n. sp.

Shell composed of two ellipsoidal, cortical, and two spherical medullary shells. Proportion of the main axes of the four shells = 1 : 2 : 4 : 5. Network of all four shells nearly of the same form, subregular, with circular pores of almost equal size in every shell. The absolute size of the pores increases from the innermost to the outermost shell, but the breadth of the bars does not increase in a similar degree. The bars of the outermost shell are only twice as broad as those of the innermost; but the pores are three to four times larger. Surface of all four shells smooth. (The shell greatly resembles that of _Cromyatractus tetraphractus_, Pl. 15, fig. 2, but is devoid of polar spines; it differs also in the spherical form of both medullary shells and their relative size.)

{318}_Dimensions._--Main axes of the four shells--(A) innermost 0.035, (B) second 0.08, (C) third 0.15, (D) outermost 0.2; their equatorial axes--(A) 0.03, (B) 0.08, (C) 0.12, (D) 0.16; pores 0.004 to 0.016, bars 0.002 to 0.004.

_Habitat._--Western Tropical Pacific, Station 198, depth 2150 fathoms.

Subgenus 2. _Caryodruppula_, Haeckel.

_Definition._--Shell composed of five or more concentric shells (two medullary and three or more cortical).

2. _Cromyodruppa mango_, n. sp.

Shell composed of six ellipsoidal, concentric shells, two medullary and four cortical. Proportion of their main axes = 2 : 3 : 8 : 11 : 14 : 18. Network of the two medullary shells and of the innermost cortical shell subregular, with subcircular pores, about the same breadth as the bars. Network of the three outer cortical shells more lax, with larger, irregular, roundish pores, twice to six times as broad as the bars. The size of the pores and bars increases gradually from the innermost to the outermost shell. Surface smooth.

_Dimensions._--Main axis of the six shells--(A) innermost 0.04, (B) 0.06, (C) 0.16, (D) 0.22, (E) 0.28, (F) 0.35; their equatorial axes--(A) innermost 0.03, (B) 0.05, (C) 0.12, (D) 0.16, (E) 0.2, (F) 0.25; pores 0.003 to 0.02, bars 0.003 to 0.005.

_Habitat._--Indian Ocean, surface; Matura, Ceylon, Haeckel.

Genus 136. _Cromyocarpus_,[175] n. gen.

_Definition._--#Druppulida# with four or more concentric shells (two medullary and two or more cortical shells), with numerous radial spines, but without polar tubes.

The genus _Cromyocarpus_ differs from _Cromyodruppa_ only in the development of numerous large radial spines which start from the outer surface of the shell. It exhibits therefore the same relation to the latter that _Prunocarpus_ bears to _Prunulum_, or _Druppocarpus_ to _Druppula_. It differs from both in the multiplication of the cortical shell.

1. _Cromyocarpus quadrifarius_, n. sp.

Shell composed of four concentric shells, two ellipsoidal cortical shells, and two spherical medullary shells. Proportion of their main axes = 10 : 8 : 3 : 2. Pores of the two cortical shells irregular, roundish, twice to four times as broad as the bars. Pores of the two medullary shells subregular, circular, about the same size as the bars. Outer surface covered with numerous conical radial spines, about half as long as the main axis, half as broad at the base as the innermost shell.

{319}_Dimensions._--Major axis of the outer cortical shell 0.2, of the inner 0.15; equatorial axis of the former 0.16, of the latter 0.12; diameter of the outer medullary shell 0.06, of the inner 0.04; pores of the cortical shells 0.01 to 0.02, of the medullary shells 0.004 to 0.008, bars 0.003 to 0.006; length of the radial spines 0.1, basal breadth 0.02.

_Habitat._--Indian Antarctic Ocean, Station 157, depth 1950 fathoms.

Genus 137. _Lithatractus_,[176] n. gen.

_Definition._--#Druppulida# with simple ellipsoidal cortical shell and simple medullary shell, with two large opposite polar spines in the main axis of equal size and similar form.

The genus _Lithatractus_, rich in common and widely distributed species, begins the series of those Druppulida which are characterised by peculiar polar spines at both poles of the main axis. It repeats the formation of _Stylosphæra_ and _Ellipsostylus_, and differs from the former in the ellipsoidal form of the cortical shell, from the latter in the possession of a medullary shell. Formerly all these forms were united in the one genus _Stylosphæra_ (see above, p. 121).

Subgenus 1. _Lithatractara_, Haeckel.

_Definition._--Network of the outer shell regular or subregular, with meshes of nearly equal size and similar form; surface smooth, without thorns or papillæ.

1. _Lithatractus hexagonalis_, n. sp.

Outer shell thin walled, smooth, without thorns or papillæ, with regular delicate network; the meshes hexagonal, three to four times as broad as the thin bars; ten to twelve on the half equator. Proportion of the major axis of the ellipsoid to the minor = 4 : 3. Minor axis three times as large as that of the inner spherical shell; pores of the latter, small, circular. Two spines three-sided pyramidal, as long as the radius of the outer shell, each as broad at its base as one mesh.

_Dimensions._--Longer axis of the ellipsoidal cortical shell 0.16, shorter axis 0.12; pores 0.011, bars 0.003; diameter of the spherical medullary shell 0.04; length of the polar spines 0.07; basal breadth 0.01.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

2. _Lithatractus fragilis_, n. sp. (Pl. 16, fig. 3).

_Stylosphæra fragilis_, Haeckel, 1881, Prodromus et Atlas, pl. xvi. fig. 3.

Outer shell thin walled, smooth, without thorns or papillæ, with regular network; the meshes circular, of equal size, eight to ten times as broad as the thin bars; six to eight on the half equator. {320}Proportion of the major axis of the ellipsoid to the minor = 5 : 4. Minor axis once and one-third as broad as that of the ellipsoidal inner shell, the pores of which are also circular, but of half the size. Two spines strong, three-sided pyramidal, acute, as broad as a large mesh, as long as the equatorial axis. The stout inner prolongations of these form the only connection between the two shells.

_Dimensions._--Longer axis of the ellipsoidal cortical shell 0.12, shorter axis 0.1; pores 0.02, bars 0.002; longer axes of the ellipsoidal medullary shell 0.09, shorter axis 0.07; pores 0.01, bars 0.002; length of the polar spines 0.1, basal breadth 0.002.

_Habitat._--Central area of the Pacific, Station 272, depth 2600 fathoms.

3. _Lithatractus leptostylus_, n. sp.

Outer shell thin walled, smooth, with regular, circular pores of equal size, three to four times as broad as the thin bars; ten to twelve on the half equator. Proportion of the major axis to the minor = 7 : 6. Minor axis three times as large as that of the inner spherical shell; pores of the latter half as large. Polar spines cylindrical, blunt, longer than the major axis, scarcely half as broad as one larger pore.

_Dimensions._--Longer axis of the cortical shell 0.14, shorter axis 0.12; pores 0.015 to 0.02, bars 0.004; diameter of the medullary shell 0.04; length of the polar spines 0.15 to 0.2, its thickness 0.01.

_Habitat._--Central area of the Pacific, Stations 270 to 272, depth 2425 to 2925 fathoms.

4. _Lithatractus pachystylus_, n. sp.

Outer shell thick walled, smooth, with regular, circular pores of equal size; twelve to fifteen on the half equator. Each pore is deep, funnel-shaped, its outer aperture double the size of the inner, its breadth about three times that of the high bars. Proportion of the major axis to the minor = 6 : 5. Major axis double as long as the diameter of the spherical medullary shell. Polar spines very thick and short, tetrahedral, one-fourth as long and broad as the major axis.

_Dimensions._--Longer axis of the cortical shell 0.17, shorter axis 0.14; pores 0.01, bars 0.003; diameter of the medullary shell 0.08; length and thickness of the polar spines 0.04.

_Habitat._--Central area of the Pacific, Station 271, depth 2425 fathoms.

5. _Lithatractus convallaria_, n. sp.

Outer shell thick walled, smooth, with elegant regular network; the meshes circular, six-lobed, rosette-like (of the same form as _Stauroxiphos gladius_, Pl. 15, fig. 7), twice to three times as broad as the bars; six to eight on the half equator. Proportion of the major axis of the ellipsoid to the minor = 4 : 3. Minor axis twice as long as the diameter of the inner spherical shell, which has regular, simple, circular pores of half the size. Polar spines short and thick, conical, only one-fourth to one-sixth as long as the minor axis, and quite as thick.

_Dimensions._--Longer axis of the cortical shell 0.16, shorter axis 0.12; pores 0.016, bars 0.006; diameter of the medullary shell 0.06; length of the polar spines 0.02 to 0.03, basal thickness the same.

_Habitat._--Central area of the Pacific, Station 268, depth 2900 fathoms.

{321}Subgenus 2. _Lithatractylis_, Haeckel.

_Definition._--Network of the outer shell regular, with meshes of equal size and similar form; surface thorny or papillose, covered with small conical spines or tubercles.

6. _Lithatractus echiniscus_, n. sp.

Outer shell thorny, thin walled, with regular network; meshes circular, with hexagonal frame, four to five times as broad as the thin bars; eighteen to twenty on the half equator. From every corner between the three meshes, where three hexagons unite, starts one short, straight, triangular thorn (as in _Ellipsoxiphus elegans_, Pl. 14, fig. 7). Proportion of the major axis of the ellipsoid to the minor = 4 : 3. Minor axis twice the diameter of the inner spherical shell, the pores of which are half as broad, circular. Polar spines three-sided pyramidal, about as long as the minor axis, as broad at the base as one hexagonal frame.

_Dimensions._--Longer axis of the cortical shell 0.08, shorter axis = 0.06; pores 0.004, bars 0.001; length of the polar spines 0.05, basal thickness 0.005; diameter of the inner shell 0.03.

_Habitat._--South Atlantic, off Tristan da Cunha, Station 334, surface.

7. _Lithatractus carduelis_, n. sp.

Outer shell thin walled, thorny, with regular network; meshes circular, simple, four to six times as broad as the thin bars; ten to twelve on the half equator. Between every three meshes is one short conical spine. Proportion of the major axis to the minor = 6 : 5. Minor axis equals three times the diameter of the inner spherical shell. Polar spines conical, thick, half as long as the major axis, thicker at the base than one pore. (This species differs from _Stylatractus carduus_ only by the simple medullary shell.)

_Dimensions._--Longer axis of the ellipsoid 0.12 to 0.16, shorter axis 0.1 to 0.14; pores 0.02 to 0.03, bars 0.005; length of the polar spines 0.05 to 0.10, basal breadth 0.04; diameter of the medullary shell 0.03 to 0.04.

_Habitat._--Central area of the Pacific, Stations 268 to 274, depth 2350 to 2900 fathoms; also fossil in the rocks of Barbados.

8. _Lithatractus cirsium_, n. sp.

Outer shell thin walled, thorny, with regular network; pores circular, simple, small, two to three times as broad as the thin bars; eighteen to twenty-four on the half equator. Proportion of the major axis to the minor = 4 : 3. Inner shell ellipsoidal, half as large as the outer. Polar spines cylindrical, blunt, thin, very variable in length (one-fourth to three-fourths of the major axis, not thicker than a mesh).

_Dimensions._--Longer axis of the ellipsoid 0.07 to 0.09, shorter axis 0.05 to 0.07; pores 0.005 to 0.006, bars 0.002; length of the polar spines 0.02 to 0.06, basal breadth 0.004; length of the inner shell 0.04, breadth 0.03.

_Habitat._--North Pacific, Station 244, surface.

{322}9. _Lithatractus rosetta_, n. sp.

Outer shell thick walled, thorny, with regular network; meshes circular, funnel-shaped, its outer aperture elegant, rosette-like, with eight to ten incisions (like _Stylosphæra calliope_, Pl. 16, fig. 6); eight to ten meshes on the half equator, three to four times as broad as the bars. Proportion of the longer axis to the shorter = 5 : 4. Shorter axis equals three times the diameter of the inner spherical shell. Polar spines three-sided pyramidal, about half as long as the shorter axis, as broad at the base as a mesh.

_Dimensions._--Longer axis of the cortical shell 0.15, shorter 0.12; pores 0.02, bars 0.005; length of the polar spines 0.05, basal breadth 0.02; diameter of the inner shell 0.04.

_Habitat._--South-eastern part of the Pacific, Station 302, depth 1450 fathoms.

Subgenus 3. _Lithatractona_, Haeckel.

_Definition._--Network of the outer shell irregular, with meshes of unequal size or dissimilar form; surface smooth, without thorns or papillæ.

10. _Lithatractus conifer_, n. sp.

Outer shell thin walled, smooth, with irregular, roundish pores, two to four times as broad as the thin bars; fifteen to twenty on the half equator. Margin of the pores simple. Proportion of the major axis to the minor = 3 : 2. Minor axis twice as large as the diameter of the inner spherical shell, the pores of which are also irregular, roundish, but of half the size. Polar spines conical, somewhat shorter than the main axis, on the base two to three times as thick as a large pore.

_Dimensions._--Longer axis of the outer shell 0.15, shorter axis 0.1; pores 0.002 to 0.004, bars 0.001; diameter of the inner shell 0.05; length of the polar spines 0.12, basal breadth 0.012.

_Habitat._--South Atlantic, Station 325, surface.

11. _Lithatractus lobatus_, n. sp.

Outer shell thick walled, smooth, with irregular, roundish pores, four to eight times as broad as the bars; six to eight on the half equator. Margin of the pores lobed, very irregular, bluntly dentate, by five to twenty slight incisions. Proportion of the major axis to the minor very variable, between 3 : 2 and 9 : 8. Diameter of the inner shell also variable, between one-third and one-half of the outer; pores of the former scarcely half the size of the latter, simple, roundish, or circular. The inner shell is at some parts quite spherical, at other parts more or less ellipsoidal. Polar spines conical, very variable in size and form, sometimes in the basal half triangular; they are sometimes somewhat longer than the main axis, at other times considerably shorter; their basal breadth is occasionally the same as that of the largest pores, sometimes, however, scarcely half as large. This deep-sea species is very common in the central area of the Tropical Pacific (Stations 266 to 272), and occurs also fossil in the Barbados deposits. It is interesting from its great variability, and sometimes constitutes a transitional form to _Stylosphæra_.

{323}_Dimensions._--Longer axis of the outer shell 0.1 to 0.15, shorter axis 0.05 to 0.12; pores 0.018 to 0.024, bars 0.002 to 0.004; diameter of the inner shell 0.04 to 0.08; length of the polar spines 0.08 to 0.2, basal thickness 0.01 to 0.02.

_Habitat._--Central area of the Pacific, common; Stations 266 to 272, depth 2425 to 2900 fathoms; also fossil in Barbados.

12. _Lithatractus jugatus_, n. sp. (Pl. 16, fig. 2).

_Stylosphæra jugata_, Haeckel, 1881, Prodromus et Atlas (pl. xvi. fig. 2).

Outer shell thick walled, smooth, or somewhat reticulated, with a peculiar, irregular, double network. The pores are roundish, of very different sizes, with double margin of the outer aperture, and so irregularly distributed in polygonal groups that every group contains two to six pores immediately touching each other; the groups are separated by broader bars. On the half equator of the shell are about six to eight groups and twelve to eighteen pores. Proportion of the longer axis of the ellipsoidal shell to the shorter = 6 : 5 or 5 : 4. Inner ellipsoidal shell about half the size; its pores are not easy to make out. Polar spines three-sided pyramidal, with prominent edges, about half as long as the major axis, as broad at the base as a group of pores. (Nearly allied to _Stylosphæra jugata_, p. 137.)

_Dimensions._--Longer axis of the cortical shell 0.12 to 0.16, shorter axis 0.1 to 0.13; pores 0.01 to 0.02; length of the polar spines 0.06 to 0.08, basal breadth 0.03 to 0.4.

_Habitat._--Central area of the Pacific, Stations 266 to 272, depth 2425 to 2900 fathoms.

Subgenus 4. _Lithatractium_, Haeckel.

_Definition._--Network of the outer shell irregular, with meshes of unequal size or dissimilar form; surface thorny or papillose, covered with small conical spines or tubercles.

13. _Lithatractus conostylus_, n. sp.

Outer shell thorny, thin walled, with irregular network; pores roundish, of unequal size, twice to four times as broad as the thin bars; sixteen to twenty on the half equator. Proportion of the longer axis to the shorter = 5 : 4. Shorter axis twice the diameter of the inner spherical shell. Polar spines conical, very stout, longer than the main axis, its base equals one-third of the minor axis.

_Dimensions._--Major axis of the cortical shell 0.1, shorter axis 0.08; pores 0.004 to 0.002, bars 0.001; diameter of the medullary shell 0.04; polar spines--length 0.12, thickness 0.03.

_Habitat._--Central area of the Pacific, Station 271, depth 2425 fathoms.

14. _Lithatractus gamoporus_, n. sp.

Outer shell thorny, thick walled, with irregular network; pores roundish, of unequal size, so irregularly distributed in polygonal groups that in every group two to six pores (commonly three to four) are near together; the groups are separated by broader bars. On the half equator {324}six to eight groups and eighteen to twenty-four pores. Proportion of the longer axis to the shorter = 6 : 5. Shorter axis equals twice the diameter of the inner ellipsoidal shell. Polar spines three-sided pyramidal, about as long as the equatorial axis, as broad at the base as a group of pores.

_Dimensions._--Major axis of the cortical shell 0.12, minor axis 0.1; pores 0.004 to 0.012, bars 0.003; length of the polar spines 0.1, basal breadth 0.03.

_Habitat._--Central area of the Pacific, Stations 271 to 274, depth 2350 to 2750 fathoms.

Genus 138. _Druppatractus_,[177] n. gen.

_Definition._--#Druppulida# with simple ellipsoidal cortical shell and simple medullary shell, with two large opposite polar spines in the main axis of different size or dissimilar form.

The genus _Druppatractus_ differs from its near relation _Lithatractus_ in the differentiation of the two polar spines, which are different in size or form, often to a very considerable degree. It has therefore the same relation to the latter that _Ellipsoxiphus_ bears to _Ellipsostylus_.

Subgenus 1. _Druppatractara_, Haeckel.

_Definition._--Network of the cortical shell regular or subregular, with meshes of nearly equal size and similar form; surface smooth, without thorns or papillæ.

1. _Druppatractus ichthydium_, n. sp.

Cortical shell thin walled, with smooth surface and regular network. Proportion of the major axis to the minor = 3 : 2. Pores circular, hexagonally framed, twice as broad as the bars; seven to eight on the half equator (as in _Xiphostylus alcedo_, Pl. 13, fig. 4). Medullary shell spherical, one-third as broad as the cortical shell. Polar spines straight, three-sided pyramidal, as broad at the base as one mesh; the longer equals the main axis of the cortical shell, the shorter only its half.

_Dimensions._--Major axis of the ellipsoidal cortical shell 0.18, minor axis 0.12; pores 0.01, bars 0.005; diameter of the medullary shell 0.04; length of the major polar spine 0.16 to 0.2, of the minor 0.01 to 0.12, basal breadth 0.01.

_Habitat._--Mediterranean (Corfu), surface, Haeckel.

2. _Druppatractus hippocampus_, n. sp. (Pl. 16, figs. 10, 11).

_Stylosphæra hippocampus_, Haeckel, 1881, Atlas, pl. xvi. figs. 10, 11.

Cortical shell thick walled, with smooth surface and regular network. Proportion of both axes = 7 : 6. Pores circular, hexagonally lobed, three times as broad as the bars; nine to ten on the half {325}equator. Medullary shell ellipsoidal, nearly half as large as the cortical. Larger polar spine horn-like curved, as long as the main axis, smaller scarcely half as long, pommel-shaped.

_Dimensions._--Major axis 0.09, minor 0.075; pores 0.01, bars 0.003; axes of the medullary shell 0.04 and 0.03; length of the larger polar spine 0.06 to 0.09, of the smaller 0.04, basal breadth 0.02.

_Habitat._--Pacific, central area, Stations 270 to 272, surface.

3. _Druppatractus belone_, n. sp.

Cortical shell thin walled, with smooth surface and regular network. Proportion of both axes = 4 : 3. Pores circular, twice as broad as the bars; ten to twelve on the half equator. Medullary shell spherical, one-third as broad as the cortical shell. Polar spines strong, straight, cylindrical, with conical apex, as broad at the base as two pores; the larger once and a half to twice as long as the main axis, the smaller only one-third to one-fourth as long.

_Dimensions._--Major axis 0.1 to 0.12, minor 0.08 to 0.09; pores 0.008, bars 0.004; diameter of the medullary shell 0.03; length of the larger polar spine 0.15 to 0.2, of the minor 0.04 to 0.05, basal thickness of them 0.02.

_Habitat._--Cosmopolitan; Atlantic, Indian, and Pacific, surface.

4. _Druppatractus testudo_, Haeckel.

_Stylosphæra testudo_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 299, Taf. viii. fig. 16.

Cortical shell thick walled, spindle-shaped, with smooth surface and regular network. Proportion of the two axes = 3 : 2. Pores circular, five times as broad as the bars; only six to seven on the half equator. Medullary shell ellipsoidal, about one-third as large as the cortical shell. Polar spines strong, short, three-sided pyramidal; the larger as long as half the transverse axis, the smaller only one-fourth as long.

_Dimensions._--Major axis 0.12, minor 0.8; pores 0.015, bars 0.003; axes of the medullary shell 0.04 and 0.03; length of the larger polar spine 0.04, of the smaller 0.02, basal thickness 0.01.

_Habitat._--Pacific, Philippine and Californian Sea (Ehrenberg), Stations 244, 266, 289, &c., depth 2550 to 2900 fathoms.

Subgenus 2. _Druppatractylis_, Haeckel.

_Definition._--Network of the cortical shell regular or subregular, with meshes of nearly equal size and similar form; surface thorny or papillose, covered with small conical spines or tubercles.

5. _Druppatractus accipenser_, n. sp.

Cortical shell thick walled, thorny, with regular network. Proportion of the two axes = 6 : 5. Pores circular, each with a six-lobed outer opening, funnel-shaped, twice as broad as the bars; nine {326}to ten on the half equator. Medullary shell spherical, one-third as broad as the cortical shell. Polar spines very strong, three-sided pyramidal, as broad at the base as three pores; the larger about as long as the main axis, the smaller only one-third as long.

_Dimensions._--Major axis 0.12, minor 0.1; pores 0.01, bars 0.005; medullary shell 0.035; length of the larger polar spine 0.11, of the smaller 0.04, basal breadth 0.03.

_Habitat._--Indian Ocean, Madagascar, surface, Rabbe.

6. _Druppatractus ostracion_, n. sp. (Pl. 16, figs. 8, 9).

Cortical shell thick walled, thorny, with regular network. Proportion of the two axes = 4 : 3. Pores circular, hexagonally framed, three to four times as broad as the crested bars; from every corner of the hexagon (between three meshes) arises a short papilla; the bottom of every funnel-like mesh is closed by a very thin plate with three regular, circular pores (occasionally four), sometimes confluent, at other times separate. Medullary shell (fig. 9) half as large as the cortical, ellipsoidal and papillate, with regular, circular pores. Polar spines very strong, three-sided prismatic, often somewhat irregular, with short apex; the larger once to twice as long as the main axis, the smaller scarcely half as long.

_Dimensions._--Major axis 0.16, minor 0.12; pores 0.02 (porules at their base 0.01), bars 0.006; axes of the medullary shell 0.07 and 0.06, its pores 0.01, bars 0.003; length of the larger polar spine 0.15 to 0.3, of the smaller 0.07 to 0.09, basal thickness 0.03.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

7. _Druppatractus coronatus_, Haeckel.

_Stylosphæra coronata_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxv. fig. 4.

Cortical shell thick walled, thorny, with regular network. Proportion of the two axes = 5 : 4. Pores circular, simple, twice as broad as the bars; eight to ten on the half equator. Medullary shell circular, one-third as broad as the cortical shell. Polar spines furrowed and angular; the longer and thinner pyramidal about as long as the main axis, the shorter and thicker scarcely half as long, thickened towards the short conical apex.

_Dimensions._--Major axis 0.08 to 0.1, minor 0.06 to 0.08; pores 0.01, bars 0.005; diameter of the medullary shell 0.03; length of the large polar spine 0.08 to 0.12, of the shorter 0.04 to 0.05.

_Habitat._--Fossil in the Tertiary rocks of Barbados; also living in the depths of the Pacific, central area, Stations 265 to 268, depth 2700 to 2900 fathoms.

Subgenus 3. _Druppatractona_, Haeckel.

_Definition._--Network of the cortical shell irregular, with meshes of unequal size or dissimilar form; surface smooth, without thorns or papillæ.

{327}8. _Druppatractus lævis_, Haeckel.

_Stylosphæra lævis_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxv. fig. 6.

Cortical shell thin walled, smooth, with irregular network. Proportion of the two axes = 3 : 2. Pores roundish or subcircular, of different size, one-half to twice as broad as the bars; eight to ten on the half equator. Medullary shell ellipsoidal, one-third as large as the cortical shell. Polar spines conical, the larger and thinner nearly as long as the main axis, the shorter and thicker scarcely one-third as long.

_Dimensions._--Major axis 0.07 to 0.1, minor 0.05 to 0.07; pores and bars 0.005 to 0.01; axes of the medullary shell 0.03 and 0.02; length of the major polar spine 0.06 to 0.09, of the shorter 0.03 to 0.04.

_Habitat._--Cosmopolitan; Atlantic, Indian, Pacific, surface.

9. _Druppatractus xiphias_, n. sp.

Cortical shell thick walled, smooth, with irregular network. Proportion of the two axes = 6 : 5. Pores funnel-shaped, composed of two to four confluent smaller porules, twice to four times as broad as the bars; ten to twelve on the half equator. Medullary shell spherical, half as broad. Polar spines three-sided pyramidal, the larger about as long as the main axis, the shorter one-third to one-half as long.

_Dimensions._--Major axis 0.12, minor 0.1; pores 0.012 to 0.018, bars 0.004; diameter of the medullary shell 0.05; length of the major polar spine 0.1, of the minor 0.03 to 0.05.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

Subgenus 4. _Druppatractium_, Haeckel.

_Definition._--Network of the cortical shell irregular, with meshes of unequal size or dissimilar form; surface thorny or papillose, covered with small spines or tubercles.

10. _Druppatractus diodon_, n. sp.

Cortical shell thin walled, thorny, with irregular network. Proportion of the two axes = 5 : 4. Pores simple, irregular, roundish, twice to four times as broad as the bars; eight to ten on the half equator. Medullary shell spherical, half as broad. Polar spines conical, more or less curved; the major longer than the main axis, the minor scarcely half as long. (Resembles _Sphærostylus ophidium_, Pl. 16, figs. 14, 15, but differs from it in the prolongation of the main axis.)

_Dimensions._--Major axis 0.15, minor 0.12; pores 0.01 to 0.02, bars 0.005; diameter of the medullary shell 0.06; length of the larger polar spine 0.12 to 0.18, of the shorter 0.06 to 0.08, basal thickness 0.003.

_Habitat._--Pacific, central area, Station 274, surface.

{328}11. _Druppatractus pisciculus_, n. sp.

Cortical shell thick walled, spiny, with irregular network. Proportion of the two axes = 3 : 2. Pores irregular, roundish, lobed, or composed of three to five confluent porules, twice to six times as broad as the bars; six to eight on the half equator. (Similar to _Ellipsoxiphus atractus_, Pl. 14, fig. 1.) Medullary shell ellipsoidal, nearly half as large as the cortical shell. Polar spines three-sided pyramidal, the major longer than the main axis, the minor scarcely one-third to one-fourth as long.

_Dimensions._--Major axis 0.18, minor 0.12; pores 0.01 to 0.03, bars 0.004; axes of the medullary shell 0.08 and 0.05; length of the major polar spine 0.2, of the minor 0.05, basal breadth 0.02.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

Genus 139. _Stylatractus_,[178] n. gen.

_Definition._--#Druppulida# with simple ellipsoidal cortical shell and double medullary shell, in the main axis with two large opposite polar spines of equal size and similar form.

The genus _Stylatractus_ differs from _Lithatractus_ in the double medullary shell, from _Amphisphæra_ in the ellipsoidal form of the cortical shell. As in these two genera, both opposite polar spines have the same shape and size.

Subgenus 1. _Stylatractara_, Haeckel.

_Definition._--Network of the cortical shell regular or subregular, with meshes of nearly equal size and similar form; surface smooth, without thorns or papillæ.

1. _Stylatractus neptunus_, n. sp. (Pl. 17, fig. 6).

_Amphistylus neptunus_, Haeckel, 1878, Atlas, pl. xvii. fig. 6.

Cortical shell thick walled, smooth, with subregular, circular, polygonally framed pores, quite as broad as the bars; ten to twelve on the half equator. Polar spines three-sided pyramidal, about as long as the half main axis, three times as broad at the base as the pores. (Much resembles _Amphisphæra neptunus_, p. 142, but differs from it by the prolongation of the main axis, which equals one and a half or one and a fourth the equatorial axis, and by the somewhat irregular formation of the cortical hexagonal network. Sometimes also, as in the figured specimen, the length of both polar spines is somewhat different.)

_Dimensions._--Major axis of the cortical shell 0.15, minor axis 0.12; pores and bars 0.007; main axes of both ellipsoidal medullary shells 0.08 and 0.05; length of the polar spines 0.08 to 0.1, basal breadth 0.02.

_Habitat._--Pacific, central area, Stations 266 to 268, depth 2700 to 2900 fathoms.

{329}2. _Stylatractus fusiformis_, n. sp.

Cortical shell thick walled, smooth, with regular, simple, circular pores, quite as broad as the bars; fourteen to sixteen on the half equator. Polar spines three-sided pyramidal, half as long as the main axis, as broad at the base as the inner medullary shell. (Resembles very nearly _Xiphatractus armadillo_, Pl. 17, fig. 11, but differs in the regular form and equal length of the polar spines.)

_Dimensions._--Major axis 0.17, minor axis 0.13; pores and bars 0.007; main axes of both ellipsoidal medullary shells 0.09 and 0.05; length of the polar spines 0.08, basal breadth 0.04.

_Habitat._--Cosmopolitan; Atlantic, Indian, Pacific, at various depths.

3. _Stylatractus compactus_, n. sp. (Pl. 17, fig. 4).

Cortical shell thick walled, smooth, with subregular, circular, double-contoured pores, smaller than the bars; sixteen to eighteen on the half equator. The thickness of the shell-wall equals the radius of the inner medullary shell. Polar spines short, three-sided pyramidal; their length and basal thickness variable, but commonly equal to the diameter of the inner medullary shell.

_Dimensions._--Major axis 0.16, minor axis 0.13; pores 0.007, bars 0.01; main axes of both ellipsoidal medullary shells 0.09 and 0.04; length and basal breadth of the polar spines 0.04 to 0.05.

_Habitat._--Pacific, central area, Stations 270 to 272, depth 2425 to 2925 fathoms.

Subgenus 2. _Stylatractylis_, Haeckel.

_Definition._--Network of the outer shell regular, with meshes of equal size and similar form; surface thorny or papillose, covered with small spinules or tubercles.

4. _Stylatractus giganteus_, n. sp. (Pl. 17, fig. 1).

_Amphistylus giganteus_, Haeckel, 1879, Atlas (pl. xvii. fig. 1).

Cortical shell papillose, very thick walled, with regular network; pores circular, with double margin, about twice as broad as the bars; ten to twelve on the half equator. The cortical shell is connected with the outer medullary shell by numerous strong beams, and the inner prolongations of both polar spines are much stronger. The circular pores of the outer medullary shell are three times as large as those of the inner, and equal to those of the cortical shell, but the bars are much thinner. Polar spines very strong, three-sided pyramidal, with spirally contorted edges, as long as the main axis, as broad at the base as the inner medullary shell.

_Dimensions._--Major axis of the cortical shell 0.3, minor axis 0.22; pores 0.02, bars 0.01; main axes of the ellipsoidal medullary shells 0.14 and 0.07; length of the polar spines 0.3, basal thickness 0.06.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

{330}5. _Stylatractus carduus_, Haeckel.

_Stylosphæra carduus_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxv. fig. 7.

Cortical shell thin walled, spiny, with regular, circular pores, five times as broad as the bars; ten to twelve on the half equator. Polar spines conical, half as long as the main axis, at the base broader than the pores. (The cortical shell is ellipsoidal as well as both medullary shells; the figure of Ehrenberg, as is generally the case, is more correct than his description. This interesting species occurs in the Barbados rocks, with double as well as with simple medullary shell, and may in the latter case be distinguished as _Lithatractus carduelis_.)

_Dimensions._--Major axis of the cortical shell 0.12 to 0.16, minor 0.1 to 0.14; pores 0.01 to 0.02, bars 0.002 to 0.005; main axes of the ellipsoidal medullary shells 0.05 and 0.03; length of the polar spines 0.06, basal breadth 0.02.

_Habitat._--Fossil in the Tertiary rocks of Barbados.

Subgenus 3. _Stylatractona_, Haeckel.

_Definition._--Network of the outer shell irregular, with meshes of different size or form; surface smooth, without thorns or papillæ.

6. _Stylatractus variabilis_, n. sp.

Cortical shell thin walled, smooth, with irregular, roundish pores, twice to six times as broad as the bars; twelve to sixteen on the half equator. Polar spines conical, about half as long as the main axis, and as broad at the base as the inner medullary shell. (The size and form of the pores and of the polar spines in this species are very variable, so that the proportions given are to be understood as averages.)

_Dimensions._--Major axis 0.13, minor axis 0.11; pores 0.004 to 0.012, bars 0.002; main axes of the ellipsoidal medullary shells 0.07 and 0.04; length of the polar spines 0.06, basal breadth 0.03.

_Habitat._--Pacific, central area. Stations 272 to 274, depth 2350 to 2750 fathoms.

7. _Stylatractus sethoporus_, n. sp. (Pl. 17, figs. 2, 3).

Cortical shell thick walled, smooth, with large irregular, roundish pores, twice to four times as broad as the bars; seven to eight on the half equator. At the bottom of each pore a thin lamella of silex, perforated by four to six irregular, roundish, double-contoured porules. Medullary shells resemble those of _Stylatractus giganteus_. Polar spines three-sided pyramidal; their length and basal thickness scarcely equal the diameter of the inner medullary shell.

_Dimensions._--Major axis 0.15, minor axis 0.13; pores 0.02, bars 0.005, porules 0.01; length of the polar spines 0.04.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

{331}Subgenus 4. _Stylatractium_, Haeckel.

_Definition._--Network of the outer shell irregular, with meshes of different size and form; surface thorny or papillose, covered with small spinules or tubercles.

8. _Stylatractus papillosus_, n. sp.

Cortical shell thin walled, with papillose surface, and irregular, simple, roundish pores, ten to sixteen on the half equator, twice to three times as broad as the bars. Conical papillæ of the surface irregularly scattered. Polar spines conical, about as long as the main axis, at the base half as broad as the inner medullary shell.

_Dimensions._--Major axis 0.12, minor 0.1; pores 0.006 to 0.01, bars 0.003; main axes of the medullary shells 0.09 and 0.06; length of the polar spines 0.13, basal breadth 0.04.

_Habitat._--Indian Ocean, surface (between Socotra and Ceylon), Haeckel.

9. _Stylatractus disetanius_, n. sp.

Cortical shell thin walled, with spiny surface, and irregular, roundish pores, eight to ten on the half equator, twice to three times as broad as the bars. Every pore is divided by thinner bars into four to six small roundish porules. Polar spines three-sided pyramidal, nearly as long as the main axis, as broad at the base as the inner medullary shell. (Resembles _Xiphatractus glyptodon_, Pl. 17, figs. 9, 10, but differs from it by the irregular network and the equal size of both polar spines.)

_Dimensions._--Major axis 0.14, minor 0.1; pores 0.02, bars 0.008, porules 0.007; main axes of the two medullary shells 0.08 and 0.05; length of the polar spines 0.13, basal breadth 0.04.

_Habitat._--South Pacific, near New Zealand, Station 169, surface.

Genus 140. _Xiphatractus_,[179] n. gen.

_Definition._--#Druppulida# with a simple ellipsoidal cortical shell and double medullary shell, in the main axis with two large opposite polar spines of different size or form.

The genus _Xiphatractus_ differs from the nearly related _Stylatractus_ in the differentiation of two polar spines (in the same manner as _Druppatractus_ differs from _Lithatractus_). From the spherical _Amphistylus_ it differs in the ellipsoidal form of the cortical shell.

Subgenus 1. _Xiphatractara_, Haeckel.

_Definition._--Network of the cortical shell regular or subregular, with meshes of nearly equal size and similar form; surface smooth, without thorns or papillæ.

{332}1. _Xiphatractus armadillo_, n. sp. (Pl. 17, fig. 11).

Cortical shell thick walled, smooth, with regular, circular pores, about as broad as the bars; fifteen to sixteen on the half equator. Polar spines three-sided pyramidal, with thick, prominent edges, of irregular form; the longer about as long as the main axis, the shorter scarcely one-third as long; their basal breadth equals the diameter of the inner medullary shell.

_Dimensions._--Major axis of the cortical shell 0.13, minor axis 0.1, thickness of its wall 0.01; pores and bars 0.005; main axes of the two medullary shells 0.07 and 0.03; length of the major polar spine 0.12, of the minor 0.04, basal thickness 0.04.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

2. _Xiphatractus euphractus_, n. sp.

Cortical shell thick walled, smooth, with regular, circular pores, twice as broad as the bars; eight to nine on the half equator. Each pore has six to nine excisions (commonly eight), elegantly lobed, flower-like (as in _Xiphostylus phasianus_, Pl. 13, fig. 9). Polar spines strong, angulate; the major pyramidal, longer than the main axis, the shorter elegantly pommel-like, scarcely one-third as long.

_Dimensions._--Major axis 0.15, minor 0.12; pores 0.014, bars 0.007; main axes of the two medullary shells 0.09 and 0.05; length of the larger polar spine 0.16, of the shorter 0.05, greatest thickness 0.03.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

Subgenus 2. _Xiphatractylis_, Haeckel.

_Definition._--Network of the cortical shell regular or subregular, with meshes of nearly equal size and similar form; surface thorny or papillose.

3. _Xiphatractus spinulosus_, Haeckel.

_Stylosphæra spinulosa_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxv. fig. 8.

Cortical shell thin walled, with spiny surface, and large, regular, circular pores, four times as broad as the bars; seven to eight on the half equator. Spines between the pores of the same size, conical. Polar spines also conical, but much larger; the major about as long as the main axis, the minor scarcely half as long; their basal thickness equals the largest pores.

_Dimensions._--Major axis 0.1, minor 0.08; pores 0.012, bars 0.003; diameter of the spherical medullary shells 0.06 and 0.03; length of the major polar spine 0.09, of the minor 0.04, basal thickness 0.02.

_Habitat._--Fossil in the Tertiary rocks of Barbados.

{333}4. _Xiphatractus sulcatus_, Haeckel.

_Stylosphæra sulcata_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxiv, fig. 6.

Cortical shell thick walled, with thorny surface, and regular, circular pores, quite as broad as the bars; nine to ten on the half equator. Polar spines cylindrical, with longitudinal basal furrows and conical apex, three times as broad as the pores; the larger about as long as the main axis, the shorter only one-half or two-thirds as long.

_Dimensions._--Major axis 0.01, minor 0.08; pores and bars 0.007; main axes of the two medullary shells 0.08 and 0.04; length of the major polar spine 0.1, of the minor 0.06, breadth of them 0.02.

_Habitat._--Fossil in the Barbados deposits.

5. _Xiphatractus dasypus_, n. sp.

Cortical shell thick walled, with spiny surface, and regular, elegant network; pores circular, hexagonally framed, about as broad as the bars; from every corner of the network (between three pores) arises a short bristle-like spine. Polar spines three-sided prismatic, as broad as one hexagon; the major once to twice as long as the main axis, the minor only one-half to one-fourth as long. (The cortical shell much resembles _Ellipsoxiphus elegans_, Pl. 14, fig. 7.)

_Dimensions._--Major axis 0.15, minor 0.13; pores and bars 0.01; main axes of the two medullary shells 0.1 and 0.06; length of the major polar spine 0.1 to 0.3, of the minor 0.05 to 0.1, thickness 0.01.

_Habitat._--Tropical Western Pacific, Station 222, surface.

Subgenus 3. _Xiphatractona_, Haeckel.

_Definition._--Network of the cortical shell irregular, with meshes of different size or form; surface smooth, without thorns or papillæ.

6. _Xiphatractus chlamydophorus_, n. sp.

Cortical shell thin walled, smooth, with irregular, roundish pores, twice to four times as broad as the bars; eight to twelve on the half equator. Polar spines angular, irregularly curved or contorted; the larger once to twice as long as the main axis, the shorter and thicker pommel-shaped, only one-third to one-half as long; their basal breadth equals two pores.

_Dimensions._--Major axis 0.14, minor 0.1; pores 0.006 to 0.012, bars 0.003; main axis of the two ellipsoidal medullary shells 0.09 and 0.04; length of the major polar spine 0.1 to 0.2, of the minor 0.05 to 0.08, breadth 0.02.

_Habitat._--Cosmopolitan; Atlantic, Pacific, many Stations, surface.

{334}Subgenus 4. _Xiphatractium_, Haeckel.

_Definition._--Network of the cortical shell irregular, with meshes of unequal size or dissimilar form; surface thorny or papillose.

7. _Xiphatractus radiosus_, Haeckel.

_Stylosphæra radiosa_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxiv. fig. 5.

Cortical shell very thick walled, with thorny surface, and irregular, roundish pores, once to three times as broad as the bars; nine and ten on the half equator. Polar spines conical, on the base about as broad as the largest pores; the larger as long as the main axis, the smaller scarcely one-fourth as long. (The radial striation, figured by Ehrenberg and applied to the name of this species, is produced by the contours of the funnel-shaped pores in the thick walls seen in optical section; the ellipsoidal cortical shell is double.)

_Dimensions._--Major axis 0.13, minor 0.09; pores 0.003 to 0.01, bars 0.003; main axes of the two medullary shells 0.05 and 0.03; length of the major polar spine 0.12, of the minor 0.03, basal breadth 0.01.

_Habitat._--Fossil in the Tertiary rocks of Barbados.

8. _Xiphatractus glyptodon_, n. sp. (Pl. 17, figs. 9, 10).

Cortical shell thick walled, covered with radial spines of the size of the pores; on the half equator eight to ten irregular or subregular roundish pores, twice to four times as broad as the bars. In the bottom of each pore a thin lamella of silex, perforated by four to six smaller roundish pores. Both medullary shells (fig. 10) spherical, with smaller, regular, circular pores. Larger polar spine three-sided pyramidal, in length equals the main axis; shorter spine only half as long, but twice as thick, of elegant pommel-form (fig. 9), with nine prominent edges.

_Dimensions._--Major axis 0.12, minor, 0.1; pores and spines 0.01 to 0.02, bars and porules 0.005; diameter of the two medullary shells 0.05 and 0.02; length of the major polar spine 0.1, of the minor 0.06, greatest thickness 0.04.

_Habitat._--Pacific, central area, Station 263, surface.

Genus 141. _Cromyatractus_,[180] n. gen.

_Definition._--#Druppulida# with four or more concentric shells (two medullary shells and two or more cortical shells), in the main axis with two large opposite polar spines of equal size and similar form.

The genus _Cromyatractus_ is very nearly allied to all the foregoing genera, which bear two equal spines opposite to one another on the poles of the main axis; it differs {335}from them in the multiplication of the cortical shell, and may be considered as the most highly developed form of this amphistylous series, which proceeds from _Ellipsoxiphus_ to _Lithatractus_ and _Stylatractus_.

Subgenus 1. _Cromyatractium_, Haeckel.

_Definition._--Shell composed of two medullary shells and two cortical shells.

1. _Cromyatractus tetraphractus_, n. sp. (Pl. 15, fig. 2).

_Stylocromium tetraphractum_, Haeckel, 1879, Atlas (pl. xv. fig. 2).

Proportion of the main axes of the four concentric shells about = 1 : 3 : 5 : 7. Network of all four shells nearly of the same structure, subregular, with circular pores of equal size (in one and the same shell). The absolute size of the pores increases gradually from the innermost to the outermost shell. The bars between the pores are smaller and quite smooth. Surface of the outermost shell smooth. Polar spines cylindrical, with conical apex, of variable length, nearly as broad as the innermost shell.

_Dimensions._--Main axes of the four shells--(A) inner medullary shell 0.03, (B) outer medullary shell 0.08, (C) inner cortical shell 0.15, (D) outer cortical shell 0.2; equatorial axes of them--(A) 0.025, (B) 0.06, (C) 0.12, (D) 0.15; pores of (A) 0.004, (B) 0.007, (C) 0.01, (D) 0.013, bars 0.002 to 0.004; length of the polar spines 0.1 to 0.3 (and more), breadth 0.015.

_Habitat._--Antarctic (Indian) Ocean, Station 157, depth 1950 fathoms.

2. _Cromyatractus tetralepas_, n. sp.

Proportion of the main axes of the four concentric shells about = 1 : 2 : 4 : 6. Network of the two medullary shells regular, with small circular pores, little larger than the bars. Network of the two cortical shells irregular, with much larger polygonal pores, three to nine times as broad as the thin bars. (Somewhat similar to _Cromyatractus ceparius_, Pl. 15, fig. 4.) Surface of the outermost shell smooth or a little thorny. Polar spines cylindrical, very large, twice to three times as long as the main axis of the outermost shell, about as broad as the innermost shell, with conical apex; smooth or a little thorny.

_Dimensions._--Main axes of the four shells--(A) 0.03, (B) 0.05, (C) 0.13, (D) 0.18; equatorial axes of them--(A) 0.2, (B) 0.45, (C) 0.11, (D) 0.14; pores of the two medullary shells 0.004 and 0.006, of both cortical shells 0.01 to 0.03, bars 0.003.

_Habitat._--Indian Ocean, Zanzibar, Pullen, 2200 fathoms.

3. _Cromyatractus tetracelyphus_, n. sp. (Pl. 15, figs. 1, 1_a_).

Proportion of the main axes of the four concentric shells about = 1 : 3 : 10 : 11. Network of the two spherical medullary shells (fig. 1_a_) regular, with small circular pores, twice as broad as {336}the bars. Network of the inner cortical shell regular with circular, hexagonally-framed pores, twice as broad as the bars. From every corner of the hexagons (between three pores) arises a very thin, hair-like, short radial spinule. These spinules communicate with one another by tangential branches (at equal distances from the inner cortical shell), and form thereby an outer, delicate cortical network, with large polygonal meshes and very thin bars. Polar spines very strong, pyramidal, with prominent edges, as long as the main radius of the cortical shell, and half as broad at the base.

_Dimensions._--Main axes of the four shells--(A) 0.02, (B) 0.06, (C) 0.2, (D) 0.22; equatorial axes of them--(A) 0.02, (B) 0.06, (C) 0.13, (D) 0.15; pores of the four shells--(A) 0.002, (B) 0.004, (C) 0.008, (D) 0.02; bars 0.001 to 0.003; length of the polar spines 0.1, basal breadth 0.05.

_Habitat._--South Atlantic, Station 335, depth 1425 fathoms.

Subgenus 2. _Caryatractus_, Haeckel.

_Definition._--Shell composed of two medullary shells and three or more cortical shells.

4. _Cromyatractus cepicius_, n. sp. (Pl. 15, fig. 3).

_Caryostylus cepicius_, Haeckel, 1879, Atlas (pl. xv. fig. 3).

_Caryodoras cepicius_, Haeckel, 1881, Prodromus, p. 454.

Proportion of the main axes of the five concentric shells about = 1 : 2 : 5 : 7 : 8. Network of both spherical medullary shells regular, with small circular pores, about as broad as the bars. Network of the three ellipsoidal cortical shells irregular, with large polygonal meshes, five to ten times as broad as the thin bars. Surface of the outermost shell smooth. Polar spines cylindrical, thorny, about as thick as the innermost shell and as long as the outermost shell, against the apex with a spindle-like intumescence, formed by delicate spongy framework (fig. 3).

_Dimensions._--Main axes of the five concentric shells--(A) 0.03, (B) 0.05, (C) 0.16, (D) 0.2, (E) 0.25; equatorial axes of them--(A) 0.03, (B) 0.05, (C) 0.12, (D) 0.16, (E) 0.2; pores of the two medullary shells 0.002 to 0.004, of the three cortical shells 0.02 to 0.04, bars 0.002; length of the polar spines 0.3, breadth 0.03.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

5. _Cromyatractus ceparius_, n. sp. (Pl. 15, fig. 4).

_Caryostylus ceparius_, Haeckel, 1881, Prodromus et Atlas (pl. xv. fig. 4).

Proportion of the main axes of the six concentric shells about = 1 : 2 : 7 : 10 : 13 : 18. Network of the three inner shells regular, with small, circular pores, which are about as broad as the bars and in the third shell hexagonally framed. Network of the three outer shells irregular, with large polygonal meshes, six to twelve times as broad as the bars. Surface smooth. Polar spines strong, spindle-shaped, thorny, outside of the sixth shell about as long as inside of it; broader than {337}the innermost shell; the thorns of their outer free part (arising at equal distances) represent perhaps the beginnings of three to four further shells.

_Dimensions._--Main axes of the six concentric shells--(A) 0.02, (B) 0.05, (C) 0.14, (D) 0.2, (E) 0.26, (F) 0.37; equatorial axes--(A) 0.02, (B) 0.05, (C) 0.09, (D) 0.15, (E) 0.21, (F) 0.3; pores of the three inner shells 0.003 to 0.006, of the three outer shells 0.02 to 0.04, bars 0.003 to 0.005; length of the polar spines, from the base of the innermost shell to the apex, 0.35, greatest breadth 0.03.

_Habitat._--South Pacific, Station 285, depth 2375 fathoms.

Genus 142. _Pipetta_,[181] n. gen.

_Definition._--#Druppulida# with simple ellipsoidal cortical shell and simple medullary shell, with two hollow fenestrated tubes opposite on both poles of the main axis.

The genus _Pipetta_ differs from _Pipettella_ (p. 304) in the possession of an inner (medullary) shell; it exhibits the same tubular prolongations of the cortical shell at both poles of the main axis.

1. _Pipetta fusus_, n. sp. (Pl. 39, figs. 8, 8_a_).

Cortical shell spindle-shaped, the middle ellipsoidal part gently passing over on both poles into the conical tubes, which attain about the same length. Network regular, with circular, hexagonally-framed pores, twice as broad as the bars, sixteen to eighteen on the half equator. In the middle part of the shell the pores arise from their hexagonal bases in the form of short conical funnels; on both tubes they are much smaller and simple, without frame. Medullary shell (fig. 8_a_) spherical, scarcely one-third as broad as the cortical, with regular, circular pores, twice as broad as the bars, eight to nine on the half equator. The two shells are connected only by two opposite beams, lying in the equatorial axis and ramified at the distal insertion (fig. 8_a_).

_Dimensions._--Middle ellipsoidal part of the cortical shell 0.13 to 0.15; polar tubes 0.15 long, 0.06 broad at the base; pores of the former 0.01, bars 0.005; pores of the tubes 0.06, bars 0.003. Medullary shell 0.04, pores 0.004, bars 0.002.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

2. _Pipetta tuba_, n. sp. (Pl. 39, fig. 7).

Cortical shell nearly spherical in the middle part, which is sharply separated at both poles from the long, nearly cylindrical tubes; these are longer than the main axis, at the distal end open (always broken off). Network regular, with circular, hexagonally-framed pores, of the same breadth as the bars, eighteen to twenty on the half equator. The pores of the polar tubes are of the same shape, only much smaller, and arranged in sixteen to eighteen longitudinal rows. Medullary shell {338}spherical, about one-third as broad as the cortical, with simple circular pores. The connection between the two shells is only made by two simple opposite beams, lying in the equatorial axis.

_Dimensions._--Middle spheroidal part of the cortical shell 0.14 to 0.16; polar tubes 0.15 to 0.2 or longer, 0.03 broad; pores and bars of the former 0.007, of the latter 0.003. Medullary shell 0.04, pores 0.006, bars 0.003.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

3. _Pipetta salpinx_, n. sp.

Cortical shell ellipsoidal, sharply separated from the cylindrical polar tubes, which reach about the same length (or more). Network regular, with circular pores, three times as broad as the bars, without hexagonal frames, fourteen to fifteen on the half equator. Pores of the polar tubes smaller, arranged in eight to ten longitudinal rows. Medullary shell spherical, one-fourth as broad as the cortical, connected with it by a circle of four to six radial beams, lying in the equatorial plane. Differs from _Pipettella prismatica_ (Pl. 39, fig. 6) in the possession of a medullary shell and the absence of the tube edges.

_Dimensions._--Main axis of the ellipsoid 0.14, equatorial axis 0.12, pores 0.01, bars 0.003; length of the tubes 0.15 or more, breadth 0.03. Medullary shell 0.03, pores 0.002, bars 0.001.

_Habitat._--Pacific, central area, Stations 265 to 268, depth 2700 to 2900 fathoms.

4. _Pipetta conus_, n. sp.

Cortical shell spindle-shaped, the middle ellipsoidal part gently passing over at both poles into the conical tubes, which attain only half its length. Network irregular, with roundish or subcircular pores, twice to three times as broad as the bars, twelve to sixteen on the half equator. Medullary shell spherical, one-fourth as broad as the cortical. (Differs from the foregoing species in the short conical tubes and the irregular reticulation.)

_Dimensions._--Middle part of the cortical shell 0.16 long, 0.13 broad; tubes 0.09 long, 0.05 on the base broad; pores 0.005 to 0.01, bars 0.003. Medullary shell 0.04.

_Habitat._--North Pacific, Station 241, depth 2300 fathoms.

Genus 143. _Pipettaria_,[182] n. gen.

_Definition._--#Druppulida# with simple ellipsoidal cortical shell and double medullary shell, with two hollow fenestrated tubes opposite on both poles of the main axis.

The genus _Pipettaria_ differs from the foregoing _Pipetta_ only in the duplication of the medullary shell; as in this, the tubular prolongations of the main axis of the cortical shell may be either conical (with closed apex) or cylindrical (with apical opening?).

{339}1. _Pipettaria fusaria_, n. sp.

Cortical shell spindle-shaped, the middle ellipsoidal part gently passing over on both poles into the conical tubes, which attain about half its length. Pores regular, circular, twice as broad as the bars, sixteen to eighteen on the half equator; pores of the tubes smaller. Both medullary shells spheroidal, compressed. (The appearance of the cortical shell resembles that of _Cannartiscus amphiconus_, Pl. 39, fig. 19, but without the equatorial constriction.)

_Dimensions._--Main axis of the ellipsoid 0.15, equatorial axis 0.13; length of the polar tubes 0.08, basal breadth 0.05; pores of the former 0.008, bars 0.004; diameter of the medullary shells 0.04 and 0.02.

_Habitat._--South Pacific, Station 300, depth 1375 fathoms.

2. _Pipettaria tubaria_, n. sp. (Pl. 39, fig. 15).

_Cannartidium tubarium_, Haeckel, 1882, Atlas (pl. xxxix. fig. 15).

Cortical shell ellipsoidal, on both poles distinctly separated from the short conical tubes, the length and breadth of which equal the outer medullary shell. In the equatorial plane arises a circle of four to six short conical protuberances, similar to the polar tubes. Pores subregular, circular, or roundish, scarcely broader than the bars, sixteen to twenty on the half equator. Both medullary shells spheroidal, somewhat compressed in the direction of the two poles (as in fig. 18_a_).

_Dimensions._--Main axis of the ellipsoid 0.12, equatorial axis 0.09; pores 0.005, bars 0.004; size of the equatorial protuberances and of the polar tubes 0.02.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

Family XIII. #SPONGURIDA#, Haeckel (Pl. 48, figs. 6, 7).

_Spongurida_, Haeckel, 1862, Monogr. d. Radiol., p. 447 (_sensu emendato_).

_Definition._--#Prunoidea# with spongy ellipsoidal or cylindrical shell, composed wholly or partially of a spongy framework, without equatorial stricture, with or without an enclosed medullary shell.

The family #Spongurida# comprises, in the sense here restricted, all those #Prunoidea# in which the ellipsoidal or cylindrical shell is composed wholly or partially of an irregular siliceous framework, not of simple lattice-work. It contains two subfamilies, differing in the absence or presence of a latticed medullary shell in the middle of the central capsule; in the Spongellipsida it is absent, in the Spongodruppida present; the former are most nearly related to the Ellipsida, the latter to the Druppulida, the difference consisting only in the spongy structure of the cortical shell.

In my Monograph (1862, p. 447) the family Spongurida had a much wider extent, comprising also a number of #Sphæroidea# and #Discoidea#, agreeing in the spongy {340}structure of the shell. Here we restrict the definition to those spongy #Sphærellaria# in which the central capsule and the enclosing spongy cortical shell are ellipsoidal or cylindrical, therefore each transverse section is a circle, and each meridional section an ellipse, as in all #Prunoidea#.

_The Cortical Shell_ in all Spongurida is composed of a delicate framework of irregularly branched and interwoven siliceous threads; commonly this spongy structure is rather dense or compact, but sometimes also very loose. In the simplest form, _Spongellipsis_, the spongy cortical shell contains a large cavity, in which lies freely the central capsule. In _Spongurus_ this cavity is completely distended by a spongy framework. In this case the solid spongy shell becomes often prolonged, and its original ellipsoidal form passes over into a cylindrical one (as in many Zygartida). Sometimes (particularly in _Spongocore_, Pl. 48, fig. 6) the cylinder becomes three-jointed by two more or less distinct annular constrictions. _Spongocore_ is distinguished by an outer veil, a thin lattice-lamella, which envelops the spongy shell and is connected with it by radial beams.

_The Medullary Shell_, absent in the Spongellipsida, is constant in the second subfamily Spongodruppida. It is either a simple latticed shell (_Spongodruppa_) or double, composed of two concentric latticed shells (_Spongoliva_); its form is either spherical or ellipsoidal. It lies in the middle of the central capsule, and is connected by radial beams (perforating the membrane of the latter) with the enveloping spongy cortical shell.

In many Spongurida the surface of the shell is armed with radial spines, and in some genera (_Spongoprunum_, _Spongatractus_, &c., Pl. 17, fig. 12), on both poles of the main axis, are developed two strong opposite polar spines, as in many other #Prunoidea#.

_The Central Capsule_ of the Spongurida is either ellipsoidal or cylindrical. Only in _Spongellipsis_ it lies freely in the internal cavity of the spongy shell. In all other genera it is perforated by a part of the skeleton; in the Spongodruppida it contains the simple or double medullary shell, and the radial beams which perforate its membrane and connect the latter with the external spongy cortical shell. In _Spongurus_ and the allied genera (_Spongocore_, _Spongoprunum_) the whole central capsule is filled with a spongy framework which also envelops its surface.

{341}_Synopsis of the Genera of Spongurida._

------------------------------------------------------------------------- I. Subfamily Spongellipsida. (Ellipsoidal shell composed only of a spongy framework without a latticed medullary shell in the centre.) ------------------------------------------------------------------------- Spongy shell }No polar spines, 144. _Spongellipsis_. with internal } cavity. }

{Without lattice Spongy shell { mantle. No polar solid, without { spines, 145. _Spongurus_. internal { cavity. {With lattice { mantle. { No polar spines, 146. _Spongocore_. { {Without lattice { mantle. Two { opposite spines { on the poles of { the axis, 147. _Spongoprunum_ ------------------------------------------------------------------------- II. Subfamily Spongodruppida. (Ellipsoidal shell composed of an outer spongy cortical shell and an inner latticed medullary shell.) ------------------------------------------------------------------------- Medullary shell {No polar spines, 148. _Spongodruppa_. simple. { {Two opposite spines { on the poles of { the axis, 149. _Spongatractus_.

Medullary shell {No polar spines, 150. _Spongoliva_. double. { { {Two opposite spines { on the poles of { the axis, 151. _Spongoxiphus_.

Subfamily 1. SPONGELLIPSIDA, Haeckel.

_Definition._--#Spongurida# with a spongy ellipsoidal or cylindrical shell, without an internal latticed medullary shell.

Genus 144. _Spongellipsis_,[183] n. gen.

_Definition._--#Spongurida# with an ellipsoidal or cylindrical spongy shell, containing an internal cavity, without a latticed medullary shell. Polar spines absent.

The genus _Spongellipsis_ embraces those very simple Spongurida in which the ellipsoidal central capsule is enclosed in a spongy cortical shell of the same form. It corresponds, therefore, to _Plegmosphæra_ among the #Sphæroidea#, to _Plegmodiscus_ among the #Discoidea#, and to _Spongolarcus_ among the #Larcoidea#. In some species the ellipsoidal form is prolonged and passes into a cylindrical one.

Subgenus 1. _Spongellipsarium_, Haeckel.

_Definition._--Surface of the shell smooth or rough, without radial spines.

{342}1. _Spongellipsis lævis_, n. sp.

Shell ellipsoidal, with smooth surface, its spongy wall scarcely one-tenth as thick as the minor axis of the inner cavity. Spongy framework very compact, with small meshes, three to six times as broad as the bars. Proportion of the major axis to the minor = 3 : 2.

_Dimensions._--Major axis (or length) of the shell 0.36, minor axis (or breadth) 0.24.

_Habitat._--Pacific, central area, Station 265, surface.

2. _Spongellipsis aspera_, n. sp.

Shell ellipsoidal, with rough surface, its spongy wall nearly half as thick as the minor axis of the inner cavity. Spongy framework very loose, with large meshes, ten to twenty times as broad as the bars. Proportion of the major axis to the minor = 4 : 3.

_Dimensions._--Length of the shell 0.24, breadth 0.18.

_Habitat._--North Pacific, Station 253, surface.

3. _Spongellipsis aplysina_, n. sp.

Shell nearly cylindrical, with rough surface, its spongy wall about one-fourth as thick as the minor axis of the internal cavity. Spongy framework loose, with large meshes, four to eight times as broad as the bars. Proportion of both axes = 6 : 1. (Similar to a spongy cylinder of Aplysina.)

_Dimensions._--Length of the shell 0.3, breadth 0.05.

_Habitat._--North Atlantic, Station 64, surface.

Subgenus 2. _Spongellipsidium_, Haeckel.

_Definition._--Surface of the shell covered with radial spines.

4. _Spongellipsis setosa_, n. sp.

Shell ellipsoidal, covered with numerous (sixty to eighty) thin, bristle-shaped, radial spines, about half as long as the major axis. Spongy framework loose, with large meshes, ten to twenty times as broad as the bars. Minor axis of the inner cavity twice as long as the thickness of the spongy wall. Proportion of both axes = 5 : 3.

_Dimensions._--Length of the shell 0.2, breadth 0.12.

_Habitat._--South Atlantic, Station 325, surface.

5. _Spongellipsis spinosa_, n. sp.

Shell nearly cylindrical, covered with numerous thorns and thirty to forty larger conical radial spines, somewhat longer than the major axis. Spongy framework compact, with small meshes, four {343}to eight times as broad as the bars. Minor axis of the inner cavity about six times as large as the thickness of the spongy wall. Proportion of both axes = 4 : 1.

_Dimensions._--Length of the shell 0.24, breadth 0.06.

_Habitat._--South Pacific, Station 300, surface.

Genus 145. _Spongurus_,[184] Haeckel, 1862, Monogr. d. Radiol., p. 465.

_Definition._--#Spongurida# with ellipsoidal or cylindrical (sometimes three-jointed) shell, of solid spongy framework, without internal cavity and without latticed medullary shell. Polar spines and outer lattice-mantle absent.

The genus _Spongurus_ was founded by me in 1862 for the common cosmopolitan _Spongurus cylindricus_, a massive spongy cylinder with radial spines. I enlarge here the conception of the genus, in receiving also ellipsoidal, massive spongy #Prunoidea#, with or without radial spines. Sometimes the cylindrical shell is more or less distinctly three-jointed, with two annular strictures, as also in the following and nearly allied genus.

Subgenus 1. _Spongurantha_, Haeckel.

_Definition._--Spongy framework everywhere of the same structure; surface smooth or rough, but without radial spines.

1. _Spongurus stuparius_, n. sp.

Shell ellipsoidal, one and a half times as long as broad, with nearly smooth surface. Spongy framework everywhere of equal structure, with small meshes, four to six times as broad as the bars.

_Dimensions._--Length of the shell (or major axis) 0.2, breadth of it (or minor axis) 0.14.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

2. _Spongurus stypticus_, n. sp.

Shell ellipsoidal, twice as long as broad, with thorny surface. Spongy framework everywhere of equal structure, with large meshes, ten to twenty times as broad as the bars.

_Dimensions._--Length of the shell 0.3, breadth 0.15.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

3. _Spongurus phalanga_, Haeckel.

_Spongurus cylindricus_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 119, Taf. vii. fig. 3.

Shell nearly cylindrical, five times as long as broad, with thorny surface. Spongy framework compact, everywhere of equal structure, with small meshes, scarcely broader than the bars.

{344}_Dimensions._--Length of the shell 0.24, breadth 0.05.

_Habitat._--Pacific, central area, Station 268, depth 2600 fathoms; fossil in the Tertiary rocks of Sicily, Stöhr.

Subgenus 2. _Spongurella_, Haeckel.

_Definition._--Spongy framework everywhere of the same structure; surface armed with radial spines.

4. _Spongurus asper_, Haeckel.

_Haliomma asperum_, Joh. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 40, Taf. ii. fig. 2.

_Haliomma asperum_, Haeckel, 1862, Monogr. d. Radiol., p. 431.

Shell ellipsoidal, one and a third times as long as broad, with thorny surface and twenty symmetrically disposed, thin, bristle-shaped, radial spines, about as long as the shell. Spongy framework everywhere of the same structure, very compact, with small meshes, three to four times as broad as the bars.

_Dimensions._--Length of the shell 0.11, breadth 0.08.

_Habitat._--Mediterranean, Ligurian coast (J. Müller), Portofino (Haeckel).

5. _Spongurus cylindricus_, Haeckel.

_Spongurus cylindricus_, Haeckel, 1862, Monogr. d. Radiol., p. 465, Taf. xxvii. fig. 1.

Shell cylindrical, four to five times as long as broad, with nearly smooth surface, and twenty to thirty thin, bristle-shaped, radial spines, about half as long as the shell. Spongy framework everywhere of the same structure, very compact, with small meshes, scarcely broader than the bars.

_Dimensions._--Length of the shell 0.2, breadth 0.04 to 0.05.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, and Pacific, surface.

6. _Spongurus tricolus_, n. sp.

Shell nearly cylindrical, with two slight annular transverse strictures; its middle part is somewhat broader. Surface thorny, with numerous (forty to sixty or more) short, thin, radial spines, not longer than the breadth of the shell. Spongy framework everywhere of the same structure, compact, with small meshes, twice to three times as broad as the bars.

_Dimensions._--Length of the shell 0.24, breadth 0.04 to 0.06.

_Habitat._--Pacific, central area, Station 272, 2600 fathoms.

Subgenus 3. _Sponguroma_, Haeckel.

_Definition._--Spongy framework in the inner part of the shell very compact, in the outer part very loose; surface armed with radial spines.

{345}7. _Spongurus radians_, n. sp.

Shell ellipsoidal, one and a half times as long as broad, with thorny surface, and eighty to one hundred and twenty (or more) thin, bristle-shaped, radial spines, somewhat longer than the shell. Spongy framework in the inner part very compact, in the outer part very loose, with a gradual transition between the two parts. Meshes in the central part not broader than the bars, in the superficial part ten to twenty times as broad.

_Dimensions._--Length of the shell 0.24, breadth 0.16.

_Habitat._--Mediterranean, Portofino, near Genoa, Haeckel, surface.

8. _Spongurus spongechinus_, n. sp.

Shell ellipsoidal, one and a third times as long as broad, with thorny surface, and thirty to forty thick, conical radial spines, about half as long as the shell. Spongy framework in the inner part of the shell compact, in the outer loose, with a gradual transition between the two parts. Meshes in the central part smaller than the bars, in the superficial part four to eight times as broad.

_Dimensions._--Length of the shell 0.18, breadth 0.14.

_Habitat._--North Atlantic, Station 353, surface.

Genus 146. _Spongocore_,[185] n. gen.

_Definition._--#Spongurida# with ellipsoidal or cylindrical (sometimes three-jointed) shell of solid spongy framework, without internal cavity and without latticed medullary shell. Polar spines absent. An outer lattice-mantle is connected with the spongy shell by radial beams.

The genus _Spongocore_ contains some widely distributed Spongurida, which are distinguished from the nearly related _Spongurus_ by the development of a peculiar veil or mantle of delicate lattice-work, which envelops either the whole shell or only the middle part of it, and is connected with it by numerous radial beams. The distance of the simple fine lattice-lamella from the spongy shell is everywhere the same. Often the cylindrical shell is three-jointed, with two annular strictures, as also in the foregoing _Spongurus._ It is derived from the latter by development of the veil connecting the points of the radial spines.

Subgenus 1. _Spongocorina_, Haeckel.

_Definition._--Shell without distinct annular strictures, not evidently three-jointed.

{346}1. _Spongocore velata_, n. sp.

Shell ellipsoidal, one and a half times as long as broad, without annular strictures. Spongy framework loose, with rather large meshes, four to six times as broad as the bars. The whole spongy shell enveloped by a delicate veil with smooth surface, connected with it by numerous thin radial beams. Breadth of the spongy ellipsoid (or minor axis) six times as large as its distance from the veil.

_Dimensions._--Length of the whole shell (with veil) 0.3, breadth 0.2; distance of the veil from the spongy ellipsoid 0.035.

_Habitat._--South Atlantic, Station 325, surface.

2. _Spongocore diplocylindrica_, n. sp.

Shell cylindrical, three times as long as broad, without annular strictures. Spongy framework compact, with small meshes, twice to three times as broad as the bars. The whole surface of the spongy cylinder, with exception of both rounded polar faces, enveloped by a delicate cylindrical veil with smooth surface, connected with it by numerous radial beams. Diameter of the spongy cylinder twice as large as its distance from the veil.

_Dimensions._--Length of the shell 0.3, breadth (with veil) 0.1; distance of the veil 0.025.

_Habitat._--South Pacific, Station 302, surface.

Subgenus 2. _Spongocorisca_, Haeckel.

_Definition._--Shell distinctly three-jointed, with two transverse annular strictures.

3. _Spongocore chrysalis_, n. sp.

Spongy shell cylindrical, without the veil six times as long as broad, three-jointed, with two annular strictures; all three joints of the same length. The whole spongy shell enveloped by a thin veil with thorny surface, connected with it by numerous radial beams. Breadth of the spongy cylinder three times as large as its distance from the veil.

_Dimensions._--Length of the shell (with veil) 0.4, breadth 0.1; distance of the veil from the spongy shell 0.02.

_Habitat._--South Atlantic (off Patagonia), Station 318, surface.

4. _Spongocore cincta_, n. sp.

Spongy shell cylindrical, without the veil four times as long as broad, three-jointed, with two annular strictures; all three joints of the same length. Only the middle joint enveloped by a thin veil with smooth surface, connected with it by radial beams. Both terminal joints with long, {347}bristle-shaped, radial spines. Breadth of the spongy cylinder twice as large as its distance from the veil.

_Dimensions._--Length of the shell 0.24, breadth (with veil) 0.12; distance of the veil 0.03.

_Habitat._--Indian Ocean, Madagascar, Rabbe, surface.

5. _Spongocore pupula_, n. sp.

Spongy shell cylindrical, without the veil six times as long as broad, three-jointed, with two annular strictures; the middle joint half as long as either terminal joint. Only the middle joint enveloped by a thin veil with spiny surface, connected with it by twenty to thirty radial beams, which are prolonged on the outside into short radial spines. Breadth of the spongy cylinder about equal to its distance from the veil.

_Dimensions._--Length of the shell 0.2, breadth (with veil) 0.1; distance of the veil 0.033.

_Habitat._--North Pacific, Station 244, surface.

6. _Spongocore puella_, n. sp. (Pl. 48, fig. 6).

Spongy shell cylindrical, without the veil five times as long as broad, three-jointed, with two annular strictures; the middle joint twice as long as either terminal joint. Only the middle joint enveloped by a thin veil with delicate lattice-work and smooth surface; both terminal joints armed with numerous thin, bristle-shaped, radial spines. Breadth of the spongy cylinder twice as large as the distance from the veil.

_Dimensions._--Length of the shell 0.25 to 0.3, breadth (with veil) 0.1 to 0.12; distance of the veil 0.028 to 0.032.

_Habitat._--South Pacific, Stations 295 to 304, surface.

Genus 147. _Spongoprunum_,[186] n. gen.

_Definition._--#Spongurida# with ellipsoidal or cylindrical shell of solid spongy framework, without internal cavity and without latticed medullary shell. On the poles of the axis occur two opposite strong spines.

The genus _Spongoprunum_ differs from the most nearly allied _Spongurus_ by the possession of two strong solid spines, lying in the axis of the ellipsoidal or cylindrical massive spongy shell, on its two opposite poles. _Spongoprunum_ bears therefore the same relation to _Spongurus_ that _Ellipsoxiphus_ does to _Cenellipsis_.

1. _Spongoprunum amphilonche_, n. sp. (Pl. 48, fig. 7).

Shell ellipsoidal, two and a third times as long as broad, with nearly smooth surface. Spongy framework very compact, in the whole solid shell of the same structure, with very small meshes, {348}scarcely broader than the bars. Two polar spines conical, very strong, about half as long as the main axis of the shell and three times as long as broad.

_Dimensions._--Length of the shell (without spines) 0.2, breadth 0.08.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms; fossil in the rocks of Barbados.

2. _Spongoprunum atractus_, n. sp.

Shell spindle-shaped, twice as long as broad, with thorny surface. Spongy framework loose, in the whole shell of the same structure, with large meshes, eight to twelve times as broad as the bars. Two polar spines angular, pyramidal, very strong, about one-third as long as the shell, and twice as long as broad.

_Dimensions._--Length of the shell 0.2, breadth 0.11.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

3. _Spongoprunum amphicylindrus_, n. sp.

Shell nearly cylindrical, four times as long as broad, with rough surface. Spongy framework compact, in the whole shell of equal structure, with small meshes, twice to three times as broad as the bars. Two polar spines cylindrical, very large, longer than the shell, and about one-fourth as thick as its diameter.

_Dimensions._--Length of the shell 0.2, breadth 0.05.

_Habitat._--South Atlantic, Station 333, surface.

Subfamily SPONGODRUPPIDA, Haeckel.

_Definition._--#Spongurida# with latticed medullary shell, enclosed by a spongy cortical shell.

Genus 148. _Spongodruppa_,[187] n. gen.

_Definition._--#Spongurida# with spongy ellipsoidal cortical shell, enclosing a simple, spherical or ellipsoidal, latticed medullary shell. Polar spines absent.

The genus _Spongodruppa_ opens the series of Spongodruppida, or of those Spongurida in which the ellipsoidal spongy cortical shell encloses a simple or double, latticed, medullary shell. In _Spongodruppa_, the simplest and probably the ancestral form of this subfamily, the medullary shell is simple and the polar spines absent. It may be derived from _Druppula_ by a spongy thickening of the simple latticed cortical shell.

{349}Subgenus 1. _Spongodruppula_, Haeckel.

_Definition._--Surface of the shell smooth or rough, without radial spines.

1. _Spongodruppa terebintha_, n. sp.

Cortical shell one and a third times as long as broad, with smooth surface, three times as broad as the spherical medullary shell. Spongy framework very compact, with small meshes of the same breadth as the bars. Thickness of the spongy wall equal to the radius of the medullary shell.

_Dimensions._--Length of the cortical shell (or major axis of the ellipsoid) 0.16, breadth (or minor axis) 0.12; thickness of its wall 0.02; medullary shell 0.04.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

2. _Spongodruppa pistacia_, n. sp.

Cortical shell one and a half times as long as broad, with thorny surface, nearly five times as broad as the spherical medullary shell. Spongy framework compact, its thickness equal to the diameter of the medullary shell.

_Dimensions._--Length of the cortical shell 0.2, breadth 0.14; thickness of its wall 0.03; medullary shell 0.03.

_Habitat._--Fossil in the rocks of Barbados.

3. _Spongodruppa lentisca_, n. sp.

Cortical shell twice as long as broad, with rough surface, four times as large as the ellipsoidal medullary shell. Spongy framework loose, with large meshes, its thickness equal to the length of the medullary shell.

_Dimensions._--Length of the cortical shell 0.25, breadth 0.13; thickness of its wall 0.06; length of the medullary shell 0.06, breadth 0.04.

_Habitat._--Pacific, central area, Station 266, surface.

Subgenus 2. _Spongodruppium_, Haeckel.

_Definition._--Surface of the shell armed with radial spines.

4. _Spongodruppa frangula_, n. sp.

Cortical shell one and a third times as long as broad, three times as broad as the spherical medullary shell. Spongy framework loose, with large meshes, its thickness half as large as the diameter of the medullary shell. Surface covered with numerous (forty to fifty) thin, bristle-shaped, radial spines, about as long as the cortical shell.

{350}_Dimensions._--Length of the cortical shell 0.24, breadth 0.18; thickness of its wall 0.035; diameter of the medullary shell 0.06.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

5. _Spongodruppa elliptica_, Haeckel.

_Acanthosphæra elliptica_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 285, Taf. vii. fig. 4.

Cortical shell nearly twice as long as broad, four times as broad as the ellipsoidal medullary shell. Spongy framework compact, with small meshes. Surface covered with very numerous short radial spines, about as long as the medullary shell.

_Dimensions._--Length of the cortical shell 0.2, breadth 0.11; length of the medullary shell 0.04, breadth 0.03.

_Habitat._--Philippine Sea, Ehrenberg, Station 206, depth 2100 fathoms.

6. _Spongodruppa polyacantha_, Haeckel.

_Haliomma polyacanthum_, J. Müller, 1858, Abhandl., p. 36, Taf. i. figs. 10, 11.

_Haliomma polyacanthum_, Haeckel, 1862, Monogr. d. Radiol., p. 430.

Cortical shell one and a third times as long as broad, twice as broad as the ellipsoidal medullary shell. Spongy framework loose on the surface, with large regular meshes. Surface covered with fifteen to twenty thick, conical spines, about as long as the radius of the shell.

_Dimensions._--Length of the cortical shell 0.12, of the medullary shell 0.09; diameter of the medullary shell 0.05 to 0.06.

_Habitat._--Mediterranean (south coast of France); Atlantic (Canary Islands), Station 354, surface.

Genus 149. _Spongatractus_,[188] n. gen.

_Definition._--#Spongurida# with spongy ellipsoidal cortical shell, enclosing a simple, spherical or ellipsoidal, latticed medullary shell. On the poles of the axis occur two opposite strong spines.

The genus _Spongatractus_ differs from _Spongodruppa_ by development of two strong spines in the axis of the shell, on its two opposite poles; therefore it bears the same relation to the latter that _Lithatractus_ does to _Druppula_, and can be derived from _Lithatractus_ by a spongy thickening of the cortical shell.

1. _Spongatractus pachystylus_, Haeckel.

_Spongosphæra pachystyla_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 82, Taf. xxvi. fig. 3.

Cortical shell one and a half times as long as broad, with rough surface. Spongy framework compact, with small meshes, about as thick as the spherical medullary shell. Polar spines very {351}stout, conical, slightly sulcated, about as long as the breadth of the cortical shell, as broad at the base as the medullary shell.

_Dimensions._--Length of the cortical shell 0.2, breadth 0.13; thickness of the spongy wall 0.045; diameter of the medullary shell 0.04.

_Habitat._--Fossil in the rocks of Barbados, Ehrenberg; living in the Equatorial Atlantic, Station 348, depth (2450) fathoms.

2. _Spongatractus fusiformis_, n. sp.

Cortical shell one and a third times as long as broad, with nearly smooth surface. Spongy framework very compact, with very small meshes, about as thick as the radius of the spherical medullary shell. Polar spines very strong, three-sided pyramidal, about as long as the breadth of the cortical shell, as broad at the base as the medullary shell.

_Dimensions._--Length of the cortical shell 0.16 to 0.18, breadth 0.12 to 0.14; thickness of the spongy wall 0.02; diameter of the medullary shell 0.04.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

3. _Spongatractus streptacanthus_, n. sp.

Cortical shell twice as long as broad, with thorny surface. Spongy framework loose, with large meshes, about as thick as the ellipsoidal medullary shell. Polar spines very long, three-sided prismatic, with three spirally contorted edges, much longer than the cortical shell, half as broad as the medullary shell.

_Dimensions._--Length of the cortical shell 0.25, breadth 0.13; thickness of the spongy wall 0.03; diameter of the medullary shell 0.03 to 0.04.

_Habitat._--North Atlantic, off Canary Islands, Haeckel.

Genus 150. _Spongoliva_,[189] n. gen.

_Definition._--#Spongurida# with spongy ellipsoidal cortical shell, enclosing a double, spherical or ellipsoidal, latticed medullary shell. Polar spines absent.

The genus _Spongoliva_ differs from the nearest _Spongodruppa_ by duplication of the medullary shell; it bears therefore the same relation to this that _Prunulum_ does to _Druppula_, and can be regarded as a _Prunulum_, in which the simple latticed cortical shell is replaced by a spongy framework.

Subgenus 1. _Spongolivetta_, Haeckel.

_Definition._--Surface of the shell smooth or rough, without radial spines.

{352}1. _Spongoliva cerasina_, n. sp.

Cortical shell one and a fourth times as long as broad, with smooth surface, four times as broad as the outer spherical medullary shell. Spongy framework very compact, with very small meshes, its thickness equal to the diameter of the outer medullary shell.

_Dimensions._--Length of the cortical shell 0.2, breadth 0.16; thickness of its wall 0.04; diameter of the outer medullary shell 0.04, of the inner 0.014.

_Habitat._--Fossil in the rocks of Barbados.

2. _Spongoliva prunulina_, n. sp.

Cortical shell one and a third times as long as broad, with smooth surface, three times as large as the outer ellipsoidal medullary shell. Spongy framework very compact, with small meshes, its thickness equal to the diameter of the inner medullary shell.

_Dimensions._--Length of the cortical shell 0.24, breadth 0.18; thickness of its wall 0.03; size of the outer medullary shell 0.08 to 0.06, of the inner 0.03.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

3. _Spongoliva persicina_, n. sp.

Cortical shell one and a half times as long as broad, with rough surface, five to six times as large as the ellipsoidal outer medullary shell. Spongy framework loose, with large meshes, its thickness about equal to the outer medullary shell.

_Dimensions._--Length of the cortical shell 0.26, breadth 0.18; thickness of its wall 0.04; size of the outer medullary shell 0.045 to 0.035, of the inner 0.015.

_Habitat._--Equatorial Atlantic, Station 348, depth (2450) fathoms.

4. _Spongoliva amygdalina_, n. sp.

Cortical shell twice as long as broad, with thorny surface, ten times as long as the small spherical outer medullary shell. Spongy framework loose, with large meshes, its thickness one and a half times as large as the outer medullary shell.

_Dimensions._--Length of the cortical shell 0.3, breadth 0.16; thickness of its wall 0.045; size of the outer medullary shell 0.03, of the inner 0.015.

_Habitat._--Fossil in the Tertiary rocks of Sicily (Caltanisetta).

Subgenus 2. _Spongolivina_, Haeckel.

_Definition._--Surface of the shell armed with radial spines.

5. _Spongoliva opuntina_, n. sp.

Cortical shell one and a third times as long as broad, armed with numerous thin, bristle-shaped, radial spines, nearly as long as the shell. Spongy framework loose, with large meshes, its thickness nearly equal to the diameter of the outer spherical medullary shell.

{353}_Dimensions._--Length of the cortical shell 0.18, breadth 0.14; thickness of its wall 0.035; diameter of the outer medullary shell 0.04, of the inner 0.02.

_Habitat._--South Atlantic, Station 325, surface.

6. _Spongoliva daturina_, n. sp.

Cortical shell one and a half times as long as broad, armed with numerous, thick and short, conical radial spines, about as long as the outer medullary shell. Spongy framework compact, with small meshes, its thickness equal to half the length of the outer ellipsoidal medullary shell.

_Dimensions._--Length of the cortical shell 0.24, breadth 0.16; thickness of its wall 0.025; diameter of the outer medullary shell 0.045 to 0.035, of the inner 0.025.

_Habitat._--Pacific, central area, Station 272, surface.

Genus 151. _Spongoxiphus_,[190] n. gen.

_Definition._--#Spongurida# with spongy ellipsoidal cortical shell, enclosing a double, spherical or ellipsoidal, latticed medullary shell. On the poles of the axis occur two opposite strong spines.

The genus _Spongoxiphus_ differs from _Spongoliva_ by the development of two strong spines in the axis of the shell, on its two opposite poles. From the similar _Spongatractus_ it differs in the duplication of the medullary shell. It may also be regarded as a _Stylatractus_, in which the simple latticed cortical shell is replaced by an irregular spongy framework.

1. _Spongoxiphus sphærococcus_, n. sp.

Cortical shell one and a half times as long as broad, with thorny surface. Spongy framework compact, with small meshes, its thickness equal to the radius of the outer medullary shell. Both medullary shells spherical, the outer three times as broad as the inner. Polar spines very stout, conical, slightly sulcated, about half as long as the cortical shell, as broad at the base as the outer medullary shell. (Differs from _Spongatractus pachystylus_ almost only in the double medullary shell.)

_Dimensions._--Length of the cortical shell 0.18, breadth 0.12; thickness of the spongy wall 0.025; diameter of the outer medullary shell 0.05, of the inner 0.016.

_Habitat._--Fossil in the rocks of Barbados (Haeckel); also living in the Pacific, central area, Station 265, depth 2900 fathoms.

{354}2. _Spongoxiphus prunococcus_, n. sp. (Pl. 17, figs. 12, 13).

_Spongostylus prunococcus_, Haeckel, 1881, Prodromus, p. 455, et Atlas, pl. xvii. figs. 12, 13.

Cortical shell one and a third times as long as broad, with smooth surface. Spongy framework very compact, with very small meshes, its thickness about equals the breadth of the outer medullary shell. Both medullary shells ellipsoidal, the outer three times as large as the inner. Polar spines very stout, three-sided pyramidal, about half as long as the cortical shell, on the base about as broad as the outer medullary shell. (Differs from the preceding in the ellipsoidal form of both medullary shells, and in the finer structure of the spongy framework.)

_Dimensions._--Length of the cortical shell 0.18 to 0.2, breadth 0.14 to 0.16; thickness of the spongy wall 0.035 to 0.04; length of the outer medullary shell 0.04 to 0.06, breadth 0.03 to 0.04.

_Habitat._--Pacific, central area, Stations 265 to 268, depths 2700 to 2900 fathoms.

Family XIV. #ARTISCIDA#, Haeckel (Pl. 39, figs. 9, 10; Pl. 48, fig. 5).

_Artiscida_, Haeckel, 1881, Prodromus, p. 462.

_Definition._--#Prunoidea# with an ellipsoidal twin-shell divided by an equatorial stricture into two communicating hemiellipsoidal or hemispherical chambers, without enclosed medullary shell. Central capsule ellipsoidal, with or without equatorial stricture.

The family #Artiscida# has a simple fenestrated outer shell, like that of the Ellipsida, but differs from these in the presence of an equatorial constriction, by which it assumes a characteristic twin form, somewhat similar to a violin (Pl. 39, figs. 9, 10). From the Cyphinida, which have the same form of the cortical shell, the Artiscida differ in the absence of the medullary shell. It is possible that the Artiscida are descended from the Cyphinida (by loss of the medullary shell), but it is more probable that they arise from the Ellipsida by an annular constriction in the equatorial plane (perhaps the formation of the shell originally took place while the central capsule was undergoing division). Both halves of the twin shell are always of the same size and form. Its outer surface is either smooth or covered with radial spines (_Artiscus_, Pl. 39, fig. 9). Sometimes on the opposite poles of the main axis are developed solid spines (_Stylartus_, Pl. 48, fig. 5) or hollow fenestrated tubes (_Cannartus_, Pl. 39, fig. 10).

_The Central Capsule_ is either simply ellipsoidal, or has also an equatorial constriction, which divides it into two equal halves. It is constantly smaller than the surrounding shell, and separated from its inner surface by a thicker or thinner jelly-mantle, the calymma.

_Synopsis of the Genera of Artiscida._

On the poles of the main axis neither solid spines nor hollow tubes, 152. _Artiscus_.

On the poles of the main axis two solid spines (or bunches of spines), 153. _Stylartus_.

On the poles of the main axis two hollow fenestrated tubes, 154. _Cannartus_.

{355}Genus 152. _Artiscus_,[191] Haeckel, 1881, Prodromus, p. 462.

_Definition._--#Artiscida# without peculiar polar appendages (without strong solid spines or hollow fenestrated tubes on the poles of the main axis).

The genus _Artiscus_ represents the most simple and primitive form of the Artiscida, and may therefore be regarded as the ancestral form of this subfamily. It resembles an ordinary double loaf, composed of two equal, nearly ellipsoidal fenestrated shells separated by the stricture in the equatorial plane. _Artiscus_ can be derived from _Cenellipsis_ simply by this equatorial constriction. But it can also be derived from _Cyphanta_ by loss of the medullary shell.

Subgenus 1. _Artiscium_, Haeckel.

_Definition._--Surface of the shell smooth or rough, without radial rods or spines.

1. _Artiscus paniscus_, n. sp.

Pores of the shell regular, hexagonal, four times as broad as the bars; ten to twelve pores on the half meridian, eight to nine on the half equator. Surface smooth. (The network of this species is quite the same as that of the proximal cameræ of _Panartus diploconus_, Pl. 40, fig. 1.)

_Dimensions._--Main axis of the shell 0.12, equatorial axis 0.07; meshes 0.013, bars 0.003.

_Habitat._--Pacific, central area, Station 271, depth 2425.

2. _Artiscus facetus_, n. sp.

Pores of the shell regular, circular, with prominent hexagonal frame, twice as broad as the bars; twenty-two to twenty-four pores on the half meridian, fourteen to fifteen on the half equator. Surface a little thorny. (The shell of this species exhibits nearly the same formation as that of _Cyphonium virgineum_, Pl. 39, fig. 12, but without enclosed medullary shells.)

_Dimensions._--Main axis of the shell 0.15, equatorial axis 0.09; meshes 0.01, bars 0.005.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

3. _Artiscus paniculus_, n. sp.

Pores of the shell regular, circular, without hexagonal frame, as broad as the bars; fourteen to sixteen pores on the half meridian, ten to eleven on the half equator. Surface quite smooth.

_Dimensions._--Main axis of the shell 0.13, equatorial axis 0.06; meshes 0.01, bars 0.01.

_Habitat._--Fossil in the Tertiary rocks of Barbados (Haeckel).

{356}4. _Artiscus panarius_, n. sp.

Pores of the shell irregular, roundish, twice to four times as broad as the bars; sixteen to eighteen pores on the half meridian, twelve to thirteen on the half equator. Surface smooth.

_Dimensions._--Main axis of the shell 0.11, equatorial axis 0.06; meshes 0.005 to 0.02, bars 0.001 to 0.004.

_Habitat._--Western Tropical Pacific, Station 224, depth 1850 fathoms.

Subgenus 2. _Artidium_, Haeckel, 1881, Prodromus, p. 462.

_Definition._--Surface of the shell covered with radial rods or spines.

5. _Artiscus elegans_, n. sp.

Pores of the shell regular, circular, with hexagonal frames, twice as broad as the bars; fourteen pores on the half meridian, eight to nine on the half equator. From every corner of the hexagonal frames (between every three pores) starts a thin, three-sided pyramidal spine, twice as large as a pore.

_Dimensions._--Main axis 0.13, equatorial axis 0.08; meshes 0.007, bars 0.004; spines 0.015 long.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

6. _Artiscus nodosus_, n. sp. (Pl. 39, fig. 9).

Pores of the shell subregular, circular, without hexagonal frame, three times as broad as the bars; sixteen to eighteen on the half meridian, ten to twelve on the half equator. Irregularly scattered on the whole surface a variable number (twenty-five to thirty in all) of stout short radial spines or rather blunt rods; the length and thickness of these is the same, and equals the size of two to three meshes; its form resembles a truncated six-sided pyramid.

_Dimensions._--Main axis 0.11, equatorial axis 0.08; meshes 0.01, bars 0.003; length and thickness of the radial sticks 0.02.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

7. _Artiscus hystrix_, n. sp.

Pores of the shell irregular, roundish, of very unequal size and dissimilar form, twice to eight times as broad as the bars; ten to fifteen on the half meridian, seven to nine on the half equator. Irregularly scattered on the whole surface a large number of thin conical spines, about as large as the meshes, partly directed radially, partly obliquely. (The shell of this species resembles very much that of _Cyphonium ceratospyris_ (p. 366) = _Didymocyrtis ceratospyris_, Monogr. d. Radiol., 1862, Taf. xxii. fig. 14, but is without the enclosed inner shells.)

{357}_Dimensions._--Main axis 0.12, equatorial axis 0.07; meshes 0.004 to 0.02, bars 0.002 to 0.005; spines 0.01 to 0.02.

_Habitat._--Atlantic, Eastern Tropical part, Station 346, surface.

Genus 153. _Stylartus_,[192] Haeckel, 1881, Prodromus, p. 462.

_Definition._--#Artiscida# with two strong, solid, polar spines, or two bunches of polar spines, opposite on the two poles of the main axis.

The genus _Stylartus_ differs from _Artiscus_ by the production of two large opposite spines in the main axis, starting from both poles of it; sometimes every spine is surrounded by a group of smaller radial spines. The genus is nearly allied to _Ellipsoxiphus_ (p. 295), and differs from it only in the equatorial stricture of the ellipsoidal shell. But it may also be derived from the similar _Cyphinus_ (Pl. 39, fig. 14) by loss of the medullary shell.

Subgenus 1. _Stylartella_, Haeckel.

_Definition._--On each pole of the main axis only one single large spine.

1. _Stylartus bipolaris_, n. sp. (Pl. 48, fig. 5).

Shell thick walled, rough; both its chambers nearly spherical, with irregular, roundish pores, twice to four times as broad as the bars; eight to ten on the half equator of each chamber. Polar spines very strong, conical, as long as the greatest breadth.

_Dimensions._--Length of the shell (without spines) 0.18, greatest breadth 0.13; length of the polar spines 0.13, basal breadth 0.03.

_Habitat._--Western Tropical Pacific, Station 224, depth 1850 fathoms.

2. _Stylartus bicuspis_, n. sp.

Shell thin walled, smooth, with regular, circular pores, twice as broad as the bars; twelve to fourteen on the half equator of each chamber. Polar spines very stout, straight, three-sided pyramidal, half as long as the shell.

_Dimensions._--Length of the shell 0.16, greatest breadth 0.12; length of the polar spines 0.08, basal thickness 0.025.

_Habitat._--Pacific, central area. Station 266, depth 2750 fathoms.

Subgenus 2. _Stylartura_, Haeckel.

_Definition._--On each pole of the main axis a bunch of several spines.

{358}3. _Stylartus palatus_, n. sp.

Shell thick walled, thorny, with irregular, roundish pores, twice to three times as broad as the bars; fifteen to eighteen on the half equator of each chamber. On each pole of the main axis a large conical spine, surrounded by a group of ten to fifteen smaller spines, one-third to two-thirds as long as the breadth of the deep equatorial stricture.

_Dimensions._--Length of the shell 0.14, greatest breadth 0.09; length of the polar spines 0.03 to 0.06, basal breadth 0.005 to 0.015.

_Habitat._--Indian Ocean, Madagascar, Rabbe, surface.

4. _Stylartus penicillus_, n. sp.

Shell thin walled, smooth, with irregular, roundish pores, three to four times as broad as the bars; ten to twelve on the half equator of each chamber. On each pole of the main axis a brush-like bunch of twenty to thirty thin conical radial spines, half as long as the shell.

_Dimensions._--Length of the shell 0.15, greatest breadth 0.1; length of the polar spines 0.08, basal breadth 0.005.

_Habitat._--Equatorial Atlantic, Station 347, surface.

Genus 154. _Cannartus_,[193] Haeckel, 1881, Prodromus, p. 462.

_Definition._--#Artiscida# with two hollow polar tubes (fenestrated cylindrical or conical tubuli, opposite on the two poles of the main axis).

The genus _Cannartus_ differs from _Artiscus_ by the production of two opposite hollow tubes on both poles of the main axis. The cavity of the conical or cylindrical fenestrated tubes communicates freely with that of the shell; the network in both is the same. The distal end of the tubes is nearly always broken off, sometimes closed, with a conical apex. _Cannartus_ can be derived either from _Pipettella_ by a transverse equatorial constriction, or from _Cannartiscus_ by the loss of the medullary shell, or from _Artiscus_ by the production of the polar tubes.

1. _Cannartus violina_, n. sp. (Pl. 39, fig. 10).

Pores of the shell subregular, circular, twice to three times as broad as the bars; eighteen to twenty on the half meridian, fourteen to sixteen on the half equator. Shell-wall in the "tropical zone" of both halves thickened. Polar tubes nearly cylindrical, about as long as the main axis, distal ends broken off.

_Dimensions._--Main axis 0.14, equatorial axis 0.09; meshes 0.008, bars 0.003; length of the polar tubes 0.12, breadth 0.02 to 0.03.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

{359}2. _Cannartus bitubulus_, n. sp.

Pores of the shell regular, circular, hexagonally framed, of the same breadth as the bars; fourteen to sixteen on the half meridian, ten to twelve on the half equator. Polar tubes cylindrical, longer than the main axis, sulcated, distal ends broken off. (Similar to _Pipetta tuba_, Pl. 39, fig. 7, but with equatorial stricture and without medullary shell.)

_Dimensions._--Main axis 0.16, equatorial axis 0.12; meshes and bars 0.006; length of the polar tubes 0.2, breadth 0.025.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

3. _Cannartus biscottus_, n. sp.

Pores of the shell irregular, roundish, twice to three times as broad as the bars; ten to twelve on the half meridian, six to eight on the half equator. Polar tubes conical, shorter than the main axis, with closed apex. (Similar to _Cannartidium bicinctum_, Pl. 39, fig. 18, but without enclosed medullary shell.)

_Dimensions._--Main axis 0.11, equatorial axis 0.07; meshes 0.005 to 0.01, bars 0.003; length of the polar tubes 0.08, breadth on the base 0.03.

_Habitat._--Equatorial Atlantic, Station 348, depth 2450 fathoms.

Family XV. #CYPHINIDA#, Haeckel (Pl. 39, figs. 11-19).

_Cyphinida_, Haeckel, 1881, Prodromus, p. 462.

_Definition._--#Prunoidea# with ellipsoidal twin-shell, divided by an equatorial stricture into two communicating hemiellipsoidal or hemispherical chambers; this external twin-shell (cortical shell) is either simple or double, and encloses one or more internal concentric shells (medullary shells). Central capsule ellipsoidal, commonly with an equatorial constriction.

The family #Cyphinida# have the same characteristic twin-form of the cortical shell as the Artiscida, but differ from them in the presence of a simple or double internal medullary shell, connected with the cortical shell by radial beams. The fenestrated shell is therefore composed of two or more concentric shells as in the Druppulida, but differs from these in the ring-like equatorial constriction.

_The Medullary Shell_, in the middle of the central capsule, is either single or double, composed of two concentric shells. As in the Druppulida, the form of the medullary shells is either spherical (Pl. 39, fig. 12_a_) or lenticular, compressed from both poles of the main axis (Pl. 39, fig. 18_a_); sometimes the inner medullary shell is spherical, the outer lenticular.

_The Radial Beams_, which connect the medullary shell with the equatorial constriction of the cortical shell, lie either all in the equatorial plane (Pl. 39, fig. 11) or near it on both sides (Pl. 39, figs. 12_a_, 18_a_).

{360}The _Cortical Shell_ is commonly simple (Pl. 39, figs. 12, 18), sometimes composed of two concentric shells (Pl. 39, fig. 13), rarely of three. As in the Artiscida, also in the Cyphinida, from both poles of the main axis solid spines or hollow fenestrated tubes are often developed (Pl. 39, figs. 14, 16-18).

_The Central Capsule_ of the Cyphinida (Pl. 39, fig. 13) is of the same form as in the Artiscida, generally ellipsoidal, but with an equatorial ring-like stricture, which divides it into two equal halves. It encloses the simple or double medullary shell, and is perforated by the radial beams starting from this. From the inner surface of the surrounding cortical shell it is separated by a thicker or thinner jelly-layer, the calymma. (Compare also Taf. xxii. fig. 14 of my Monograph, 1862.)

_Synopsis of the Genera of Cyphinida._

------------------------------------------------------------------------- Cortical shell without peculiar spines or hollow fenestrated tubes on both poles of the main axis. ------------------------------------------------------------------------- Cortical twin- {Medullary shell shell simple { simple, 155. _Cyphanta_. { {Medullary shell { double, 156. _Cyphonium_.

Cortical twin- {Cortical shell shell double { double, 157. _Cypassis_. or triple; { medullary {Cortical shell shell double. { triple, 158. _Cyphocolpus_. ------------------------------------------------------------------------- Cortical shell simple, with peculiar spines or hollow fenestrated tubes on both poles of the main axis. ------------------------------------------------------------------------- Two opposite {Medullary shell polar spines { simple, 159. _Cyphinus_. (or bunches { of spines). {Medullary shell { double, 160. _Cyphinidium_.

Two opposite {Medullary shell hollow { simple, 161. _Cannartiscus_. fenestrated { polar tubes. {Medullary shell { double, 162. _Cannartidium_.

Genus 155. _Cyphanta_,[194] n. gen.

_Definition._--#Cyphinida# with simple cortical shell and simple medullary shell, without polar spines or tubes.

The genus _Cyphanta_ is the most simple of all Cyphinida, and can be regarded as the common ancestral form of this family. It may be derived phylogenetically from _Druppula_ by a ring-like constriction in the equatorial plane of the ellipsoidal cortical shell, or from _Artiscus_ by secondary formation of a central (spherical or ellipsoidal) medullary shell.

Subgenus 1. _Cyphantella_, Haeckel.

_Definition._--Surface of the cortical shell smooth, without spines or thorns.

{361}1. _Cyphanta colpodes_, n. sp.

Cortical shell thin walled, with smooth surface; its pores regular, hexagonal, three to four times as broad as the bars; ten to twelve on the half meridian, seven to eight on the half equator. Medullary shell spherical, its diameter one-third of the equatorial axis of the cortical shell. (The cortical shell of this species is nearly identical with the central half of the cortical shell of _Panartus diploconus_, Pl. 40, fig. 1.)

_Dimensions._--Main axis of the cortical shell 0.12, equatorial axis 0.07; meshes 0.013; bars 0.003; diameter of the medullary shell 0.025.

_Habitat._--South Pacific, Station 285, depth 2375 fathoms.

2. _Cyphanta circopora_, n. sp.

Cortical shell thick walled, with smooth surface; pores subregular, circular, twice as broad as the bars; eighteen to twenty on the half meridian, twelve to fourteen on the half equator. Medullary shell spherical, its diameter one-half of the equatorial axis of the cortical shell. (The shell of this species is very similar to that of _Cannartiscus amphiconiscus_, Pl. 39, fig. 19, but without the polar tubes of that species.)

_Dimensions._--Main axis of the cortical shell 0.13, equatorial axis 0.08; meshes 0.007, bars 0.003; diameter of the medullary shell 0.04.

_Habitat._--Pacific, central area. Station 266, depth 2750 fathoms.

3. _Cyphanta lævis_, Haeckel.

_Ommatospyris lævis_, Ehrenberg, 1872, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 318.

Cortical shell thin walled, with smooth surface; pores of it irregular, roundish, of very different size (some very large in the tropical circles of both hemispheres). Pores twice to six times as broad as the bars; ten to twelve on the half meridian, six to eight on the half equator. Medullary shell spheroidal, compressed, its main axis somewhat shorter than its equatorial axis, which attains half the length of that of the cortical shell. (This species may be perhaps identical with _Ommatospyris lævis_ of Ehrenberg, the diagnosis of which is insufficient and figure not given.)

_Dimensions._--Main axis of the cortical shell 0.1, equatorial axis 0.06; meshes 0.005 to 0.02, bars 0.002 to 0.04; diameter of the medullary shell 0.03.

_Habitat._--Philippine Sea (Ehrenberg), Station 213, depths 2650 and 3300 fathoms.

4. _Cyphanta arachnoides_, n. sp.

Cortical shell very delicate and thin walled, cobweb-like, with smooth surface; pores irregular, polygonal (mostly pentagonal or hexagonal), eight to ten times as broad as the thread-like bars; ten to twelve on the half meridian, six to eight on the half equator. Medullary shell spheroidal, compressed, its main axis shorter than its equatorial axis, which is about one-third that of the cortical shell. (This species is very similar to the middle part of the shell of _Ommatocampe profundissima_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. viii. fig. 6.)

{362}_Dimensions._--Main axis of the cortical shell 0.11, equatorial axis 0.06; meshes 0.01 to 0.02, bars 0.002; diameter of the medullary shell 0.02.

_Habitat._--Atlantic, Canary Islands (Lanzerote), surface.

Subgenus 2. _Cyphantissa_, Haeckel.

_Definition._--Surface of the cortical shell spiny, everywhere scattered with numerous thorns or spines.

5. _Cyphanta hispida_, n. sp.

Cortical shell thick walled, with spiny surface; pores regular, circular, with hexagonal frame, twice as broad as the bars; twelve to fourteen on the half meridian, eight to ten on the half equator. From the corners of the hexagonal frames (between every three pores) arise short, straight, conical radial spines, somewhat longer than the breadth of the pores. Medullary shell subspherical, its diameter about one-third of the equatorial axis of the cortical shell. (The appearance of the cortical shell is the same as that of the middle part of _Peripanartus amphiconus_, Pl. 40, fig. 5.)

_Dimensions._--Main axis of the cortical shell 0.12, equatorial axis 0.07; meshes 0.01, bars 0.005; length of the spines 0.012; diameter of the medullary shell 0.02.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

6. _Cyphanta hystrix_, n. sp.

Cortical shell thin walled, with thorny surface; pores irregular, roundish, of very unequal size, twice to six times as broad as the bars; twelve to eighteen on the half meridian, eight to thirteen on the half equator. Between the pores irregularly scattered, bristle-like, thin spines about the same size, partly straight, partly oblique, rising from the surface. Medullary shell lenticular, compressed, its equatorial axis one and a half times the length of the main axis, and about half that of the cortical shell.

_Dimensions._--Main axis of the cortical shell 0.15, equatorial axis 0.09; meshes 0.004 to 0.02, bars 0.003 to 0.006; length of the spines 0.02; diameter of the medullary shell 0.04.

_Habitat._--South Atlantic, Station 318, surface.

Genus 156. _Cyphonium_,[195] n. gen.

_Definition._--#Cyphinida# with simple cortical shell and double medullary shell, without polar spines or tubes.

The genus _Cyphonium_ contains a number of very common species, among which are the earliest known forms of this family, partly described by Ehrenberg as Ommatospyris {363}(which genus contains also a number of other #Prunoidea#), partly by me (1862) as _Didymocyrtis_. Both names are inadequate, as allusions to quite different families of Nassellaria, but may be retained as significations of subgeneric divisions. _Cyphonium_ differs from _Cyphanta_ by the double medullary shell, which is either spherical or lenticular.

Subgenus 1. _Ommatospyris_, Ehrenberg (_partim_).

_Definition._--Surface of the cortical shell smooth, without thorns or spines.

1. _Cyphonium coscinoides_, n. sp.

_Ommatospyris coscinoides_, Haeckel, 1881, Prodromus, p. 462.

Cortical shell thin walled, with smooth surface; pores regular, hexagonal, three to four times as broad as the bars; five to six on the half meridian, eight to nine on the half equator of each chamber. Medullary shells both spherical. (The cortical shell of this species is nearly the same as that of _Cyphanta colpodes_, and as the middle part of the cortical shell of _Panartus diploconus_, Pl. 40, fig. 1.)

_Dimensions._--Main axis of the cortical shell 0.11, equatorial axis 0.06; greatest breadth of the chambers 0.08; pores 0.013, bars 0.003.

_Habitat._--North Pacific, Station 244, surface.

2. _Cyphonium virgineum_, n. sp. (Pl. 39, figs. 12, 12_a_).

_Ommatospyris virginea_, Haeckel, 1881, Prodromus et Atlas (pl. xxxix. fig. 12_a_).

Cortical shell thick walled, with smooth surface (sometimes a little rough with very small thorns); pores subregular, circular, with hexagonal elevated frames, about as broad as the bars; ten to twelve on the half meridian, sixteen to eighteen on the half equator of each chamber. Medullary shells (fig. 12_a_) both spherical. (Sometimes, as in the figured specimen, the shell is somewhat irregular, an individual abnormality.)

_Dimensions._--Main axis of the cortical shell 0.13 to 0.15; equatorial axis of the structure 0.08 to 0.09, of each chamber 0.1 to 0.12, pores and bars 0.005 to 0.007.

_Habitat._--Pacific, western tropical part, Station 225, depth 4475 fathoms.

3. _Cyphonium ethmarium_, n. sp.

_Ommatospyris ethmaria_, Haeckel, 1881, Prodromus, p. 462.

Cortical shell thin walled, with quite smooth surface; pores subregular, circular (without hexagonal frame), twice as broad as the bars; nine to ten on the half meridian of each chamber, sixteen to eighteen on its half equator. Medullary shells both spherical. (This species resembles the proximal internal chambers of _Peripanartus atractus_, Pl. 40, fig. 7.)

_Dimensions._--Main axis 0.13, equatorial axis 0.07; greatest breadth 0.09; pores 0.006, bars 0.003.

_Habitat._--Equatorial Atlantic, Station 347, surface.

{364}4. _Cyphonium trinacrium_, n. sp.

Cortical shell thick walled, with rough surface; pores subregular, circular (without hexagonal frame), not broader than the bars; five to six on the half meridian of each chamber, nine to ten on its half equator. Medullary shells both compressed, lenticular. This species resembles _Cypassis entomocora_ vel _Ommatocampe trinacria_, Stöhr, 1880, _loc. cit._, p. 90, Taf. ii. fig. 1, but has not its external mantle. It may be the ancestral form of it (both in an ontogenetic and phylogenetic sense).

_Dimensions._--Main axis 0.11, equatorial axis 0.07; greatest breadth 0.08; pores 0.005, bars 0.005.

_Habitat._--Fossil in Tertiary rocks of Sicily, Caltanisetta, Haeckel (Grotte, Stöhr?).

5. _Cyphonium diattus_, n. sp.

Cortical shell thin walled, with quite smooth surface; pores irregular, polygonal, mostly pentagonal or hexagonal, three to six times as broad as the bars; six to seven on the half meridian of the chamber, ten to twelve on its half equator. Medullary shells both spherical. (Resembles _Cyphonium profundum_, Ehrenberg, 1872, _loc. cit._, Taf. x. fig. 5, but does not possess the spines of the surface.)

_Dimensions._--Main axis 0.13, equatorial axis 0.06; greatest breadth 0.08; pores 0.005 to 0.012, bars 0.002 to 0.004.

_Habitat._--Indian Ocean, western part (Zanzibar), Pullen, depth 2200 fathoms.

6. _Cyphonium mammarium_, n. sp.

Cortical shell thick walled, with smooth surface (sometimes a little rough); pores irregular, roundish, twice to three times as broad as the bars; eleven to twelve on the half meridian of each chamber, sixteen to nineteen on its half equator. Internal medullary shell spherical, external lenticular compressed, sometimes both spherical or both compressed. (Resembles the internal cortical twin-shell of _Cyphocolpus virginis_, Pl. 40, fig. 11.)

_Dimensions._--Main axis 0.14, equatorial axis 0.08, greatest breadth 0.09; pores 0.004 to 0.006, bars 0.002.

_Habitat._--South Pacific, Station 285, depth 2375 fathoms.

Subgenus 2. _Ommatocyrtis_, Haeckel.

_Definition._--Surface of the cortical shell thorny or spiny.

7. _Cyphonium hexagonium_, n. sp.

_Didymocyrtis hexagonia_, Haeckel, 1881, Prodromus.

Cortical shell thin walled, with spiny surface; pores regular or subregular, hexagonal, twice to three times as broad as the bars; five to six on the half meridian, nine to ten on the half equator {365}of each chamber. Radial spines between them conical, about as long as the pores. Medullary shells both spherical.

_Dimensions._--Main axis 0.14, equatorial axis 0.08; greatest breadth of each chamber 0.1; pores 0.012, bars 0.004.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

8. _Cyphonium facettarium_, n. sp.

_Didymocyrtis facettaria_ Haeckel, 1881, Prodromus.

Cortical shell thick walled, with spiny surface; pores subregular, circular, with elevated hexagonal frames, twice as broad as the bars; eight to nine on the half meridian, fourteen to sixteen on the half equator of each chamber. In the corners of the hexagons (between every three meshes) arise radial spines, about twice as long as the pores. Both medullary shells spheroidal compressed. (This species is nearly identical with the internal cortical twin-shell of _Peripanartus amphiconiscus_, Pl. 40, fig. 5.)

_Dimensions._--Main axis 0.12, equatorial axis 0.07; greatest breadth of both chambers 0.09; pores 0.01, bars 0.005, spines 0.02.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

9. _Cyphonium cribellum_, n. sp. (Pl. 39, fig. 11).

Cortical shell thick walled, with spiny surface; pores regular, circular, about as broad as the bars; seven to eight on the half meridian of each chamber, thirteen to fifteen on its half equator. Radial spines between them conical, twice as long as the pores. Medullary shells both lenticular.

_Dimensions._--Main axis 0.11, equatorial axis 0.06; greatest breadth 0.08; pores and bars 0.004.

_Habitat._--North Atlantic, Station 353, surface.

10. _Cyphonium profundum_, Haeckel.

_Ommatospyris profunda_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 297, Taf. viii. fig. 5, Taf. x. fig. 5.

Cortical shell thin walled, with thorny surface; pores irregular, polygonal, three to six times as broad as the thin bars; five to six on the half meridian of each chamber, ten to twelve on its half equator. Thorns of the surface short. Medullary shells both spherical.

_Dimensions._--Main axis 0.1, equatorial axis 0.06; greatest breadth 0.07; pores 0.005 to 0.012, bars 0.002, spines 0.005.

_Habitat._--Pacific, tropical zone; Philippine Sea, depth 3300 fathoms, Ehrenberg; Stations 266 to 274, depth 2350 to 2925 fathoms.

{366}11. _Cyphonium ceratospyris_, Haeckel.

_Didymocyrtis ceratospyris_, Haeckel, 1862, Monogr. d. Radiol., p. 445, pl. xxii. figs. 14-16.

_Haliomma didymocyrtis_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 816.

Cortical shell thin walled, with spiny surface; pores irregular, roundish, three to nine times as broad as the bars; five to six on the half meridian of each chamber, eight to nine on its half equator. Spines of the surface partly very short, partly as long as the largest pores, either radially or obliquely inserted. Medullary shells both spherical. (Compare the detailed description and figures also of the soft body in my Monograph, _loc. cit._)

_Dimensions._--Main axis of the cortical shell 0.12, equatorial axis (in the stricture) 0.06; greatest breadth 0.08; pores 0.03 to 0.2, bars 0.002 to 0.006, spines 0.05 to 0.015.

_Habitat._--Mediterranean (Messina), Canary Islands (Lanzerote), Haeckel.

Genus 157. _Cypassis_,[196] n. gen.

_Definition._--#Cyphinida# with double cortical shell and double medullary shell, without polar spines or tubes.

The genus _Cypassis_ differs from _Cyphonium_ by duplication of the cortical twin-shell; from the outer surface of the simple twin-shell arise numerous radial spines, which become connected by anastomosing transverse branches, and in this manner form an outer envelope or mantle. _Cypassis_ may also be regarded as a _Cromyodruppa_, the double cortical shell of which is constricted in the equatorial plane.

Subgenus 1. _Didymospyris_, Haeckel (1881).

_Definition._--Surface of the shell smooth, without thorns or spines.

1. _Cypassis palliata_, n. sp.

Inner cortical shell thin walled, with regular, circular, hexagonally-framed pores, twice as broad as the bars; seven to eight on the half meridian of each chamber, ten to twelve on its half equator. Outer cortical shell very thin, with smooth surface, and very small, irregular, roundish pores, twice to five times smaller than those of the inner shell. Distance between the two cortical shells equals the diameter of the outer medullary shell, which, like the inner, is spherical. (The network of this species resembles that of _Peripanartus amphiconiscus_, Pl. 40, fig. 5.)

_Dimensions._--Main axis of the external cortical shell 0.18, of the internal 0.12; greatest breadth (in the equator of each chamber) of the former 0.13, of the latter 0.09; pores of the outer 0.002 to 0.005, of the inner shell 0.01, bars 0.002 to 0.005.

_Habitat._--South Pacific, Station 288, surface.

{367}2. _Cypassis eucolpos_, n. sp.

Inner cortical shell thick walled, with regular, circular pores, twice as broad as the bars (without hexagonal frames); nine to ten on the half meridian of each chamber, fifteen to seventeen on its half equator. Outer cortical shell very thin, with smooth surface, and very small, irregular, roundish pores, twice to three times smaller than those of the inner shell. Distance between the two cortical shells about one and a half times the diameter of the inner medullary shell, which, like the outer, is spherical. (The inner cortical shell resembles that of _Cannartiscus amphiconiscus_, Pl. 39, fig. 19, but without polar tubes.)

_Dimensions._--Main axis of the external cortical shell 0.2, of the internal 0.15; greatest breadth of the former 0.16, of the latter 0.12; pores of the outer 0.002, of the inner 0.006, bars 0.003.

_Habitat._--South Atlantic, Station 319, surface.

Subgenus 2. _Didymocyrtis_, Haeckel (1862).

_Definition._--Surface of the cortical shell thorny or spiny.

3. _Cypassis entomocora_, Haeckel.

_Astromma entomocora_, Ehrenberg, 1847, Mikrogeol., Taf. xxii. fig. 32.

_Haliomma didymum_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 83.

? _Haliomma amphisiphon_, Ehrenberg, 1844, Monatsber. d. k. Akad. d. Wiss. Berlin, p. 267.

_Ommatospyris entomocora_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, pp. 66, 74.

? _Ommatocampe trinacria_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 90, Taf. ii. fig. 1.

_Didymospyris entomocora_, Haeckel, 1881, Prodromus.

_Didymocyrtis entomocora_, Haeckel, 1862, Monogr. d. Radiol., p. 445.

Inner cortical shell thick walled, with regular, circular pores, twice as broad as the bars (without hexagonal frames); eight to nine on the half meridian of each chamber, ten to eleven on its half equator. Outer cortical shell thin walled, with regular, circular pores like those of the inner. Distance between the two cortical shells equals about twice the diameter of one pore (or the short axis of the lenticular double medullary shell). Surface covered with short conical spines (in the figure of Ehrenberg broken off).

_Dimensions._--Main axis of the external cortical shell 0.2, of the internal 0.15; greatest breadth of the former 0.13, of the latter 0.1; pores of the outer 0.005 to 0.01, of the inner 0.01, bars 0.004; length of the surface spines 0.005 to 0.01.

_Habitat._--Fossil in the Tertiary rocks of Barbados, Bermuda, and Sicily (Caltanisetta); also living in the greatest depth of the Pacific, Stations 268, 225, depth 2900 to 4475.

4. _Cypassis puella_, n. sp. (Pl. 39, fig. 13).

_Didymospyris colpodes_, Haeckel, 1881, Prodromus et Atlas (pl. xxxix., fig. 13).

Internal cortical shell thin walled, with irregular, circular pores of very different size, once to four times as broad as the bars; fourteen to fifteen on the half meridian of each chamber, eighteen {368}to twenty on its half equator. Outer cortical shell thin walled, with irregular, circular pores, only one-third to one-half as large as those of the inner. Distance between the two shells equals the largest diameter of the double lenticular medullary shell. Surface of both cortical shells covered with short conical spines (not longer than the largest pores).

_Dimensions._--Main axis of the external cortical shell 0.2, of the internal 0.15, of the central capsule 0.1; greatest breadth of the first 0.14, of the second 0.1, of the third 0.07; pores of the outer shell 0.001 to 0.005, of the inner 0.002 to 0.01, bars 0.002 to 0.003; length of the surface spines 0.005 to 0.01.

_Habitat._--Pacific, central area; Stations 266 to 274, surface; Atlantic, Canary Islands (Haeckel), Station 354, surface.

5. _Cypassis halicora_, n. sp.

Internal cortical shell thin walled, with irregular, roundish pores, once to three times as broad as the bars; ten to eleven on half meridian of each chamber, fourteen to sixteen on its half equator. Outer cortical shell thin walled, with very delicate network, spindle-like, with conical prolongations at both poles. Distance between the two shells larger than the greatest diameter of the double lenticular medullary shell. Surface of both cortical shells covered with innumerable small thorns. (Resembles closely _Cyphocolpus virginis_, Pl. 40, fig. 11, but without the third shell.)

_Dimensions._--Main axis of the external cortical shell 0.21, of the internal 0.14, greatest breadth of the former 0.13, of the later 0.09; pores 0.003 to 0.009; bars of the outer shell 0.001, of the inner 0.004.

_Habitat._--Indian Ocean, Ceylon (Haeckel), surface.

Genus 158. _Cyphocolpus_,[197] n. gen.

_Definition._--#Cyphinida# with triple cortical shell and double medullary shell, without polar spines or tubes.

The genus _Cyphocolpus_ differs from both foregoing genera by the increased number of the cortical twin-shells. Whilst these are simple in _Cyphonium_, double in _Cypassis_, they are triple in _Cyphocolpus_, composed of three concentric envelopes. The three genera named represent a phylogenetic series, which is repeated in the ontogenetic development of _Cyphocolpus_.

1. _Cyphocolpus didymus_, n. sp.

Inner cortical shell with circular, subregular pores, twice as broad as the bars; five to six on the half meridian of each chamber, eight to ten on its half equator. Middle cortical shell also with subregular, circular pores of the same size. Outer cortical shell with smooth surface, with more irregular, roundish pores of very different size. The distance between every two shells equals the diameter of the inner medullary shell, which, like the outer, is spheroidal.

{369}_Dimensions._--Main axis of the outer cortical shell 0.3, of the middle 0.22, of the inner 0.15; greatest breadth of the inner cortical shell 0.1, its pores 0.01, bars 0.005.

_Habitat._--Indian Ocean, Madagascar, Rabbe, surface.

2. _Cyphocolpus virginis_, n. sp. (Pl. 40, fig. 11).

_Zygartus virginis_, Haeckel, 1881, Prodromus et Atlas (pl. xl. fig. 11).

Inner cortical shell with irregular, roundish pores, twice to three times as broad as the bars; eleven to twelve on the half meridian of each chamber, sixteen to eighteen on its half equator. Middle cortical shell with very delicate network, its irregular, polygonal pores of the same size as those of the inner, but separated by extremely thin bars. Outer cortical shell with spiny surface, and with more irregular, roundish pores of different size. The distance between each two shells is variable, and attains more than the diameter of the outer medullary shell, which, like the inner, is spheroidal, slightly compressed.

_Dimensions._--Main axis of the outer cortical shell 0.26, of the middle 0.22, of the inner 0.14; greatest breadth of the inner cortical shell 0.09, its pores 0.004 to 0.006, bars 0.002.

_Habitat._--Pacific, central area, Station 271, surface.

Genus 159. _Cyphinus_,[198] Haeckel, 1881, Prodromus, p. 463.

_Definition._--#Cyphinida# with simple cortical shell and simple medullary shell, with two opposite polar spines (or bunches of polar spines) on the poles of the main axis.

The genus _Cyphinus_ differs from _Cyphanta_ by the development of two opposite spines (or bunches of spines) on both poles of the main axis. It simulates therefore the bipolar formation of _Stylartus_, and differs from this in the possession of a medullary shell.

Subgenus 1. _Cyphinoma_, Haeckel.

_Definition._--On both poles of the main axis only one single large spine.

1. _Cyphinus amphacanthus_, n. sp.

Cortical shell with smooth surface, and circular, regular pores, twice as broad as the bars; five to six pores on the half meridian of each chamber, ten to twelve on its half equator. On both poles of the main axis, one single, very strong, conical spine, about half as long as this axis, and half as broad at the base as the spherical medullary shell.

_Dimensions._--Main axis of the cortical shell (without spines) 0.2, greatest breadth (in the equator of each chamber) 0.1; pores 0.006, bars 0.003; length of the polar spines 0.1, basal thickness of them 0.02.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

{370}2. _Cyphinus dixiphus_, n. sp.

Cortical shell with rough surface, and irregular, roundish pores, twice to four times as broad as the bars; eight to nine pores on the half meridian of each chamber, twelve to fourteen on its half equator. On both poles of the main axis, one single, strong, conical spine, with prominent edges at the base, and nearly as broad as the spherical medullary shell, nearly as long as the main axis.

_Dimensions._--Main axis (without spines) 0.18, greatest breadth 0.13; pores 0.003 to 0.008, bars 0.002; length of the polar spines 0.16, basal thickness 0.03.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

Subgenus 2. _Cyphinura_, Haeckel.

_Definition._--On both poles of the main axis a bunch or circle of several spines.

3. _Cyphinus amphilophus_, n. sp. (Pl. 39, fig. 14).

_Cyphinidium amphilophus_, Haeckel, 1882, Atlas (pl. xxxix. fig. 14).

Cortical shell thick walled, with rough surface, and subregular, circular pores of different size, twice to five times as broad as the bars; nine to ten pores on the half meridian of each chamber, twelve to fourteen on its half equator. On both poles of the main axis a bunch of six to eight strong conical spines, the largest of which are about as long as the greatest breadth of the shell; their basal part is furrowed, and nearly half as thick as the spherical medullary shell.

_Dimensions._--Main axis of the cortical shell (without spines) 0.18 to 0.2, greatest breadth 0.1 to 0.12; pores 0.004 to 0.01, bars 0.002; length of the polar spines 0.04 to 0.12, basal thickness 0.02 to 0.04.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

4. _Cyphinus penicillatus_, Haeckel.

_Ommatospyris penicillata_, Ehrenberg, 1872, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 318; Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. viii. fig. 4.

Cortical shell thin walled, with rough surface, and irregular, polygonal pores, six to eight times as broad as the bars; five to six pores on the half meridian of each chamber, nine to ten on its half equator. Around both poles of the main axis a polar circle of eight to ten divergent radial spines, scarcely thicker than the bars, and about as long as the diameter of the spherical medullary shell. (In the figure of Ehrenberg the network is too thin and the spines too short.)

_Dimensions._--Main axis (without spines) 0.1, greatest breadth 0.09; pores 0.008 to 0.014, bars 0.001 to 0.002; length of the spines 0.02 to 0.04.

_Habitat._--Pacific, Philippine Sea, 3300 fathoms, Ehrenberg; Station 206, depth 2100 fathoms.

{371}Genus 160. _Cyphinidium_,[199] n. gen.

_Definition._--#Cyphinida# with simple cortical shell and double medullary shell, with two opposite polar spines (or bunches of polar spines) on the poles of the main axis.

The genus _Cyphinidium_ differs from _Cyphinus_ only in the duplication of the medullary shell, which is composed of two concentric spheres or somewhat compressed lenticular spheroids. It exhibits therefore the same relation to _Cyphinus_ that _Stylatractus_ in the Druppulida bears to _Lithatractus_. Possibly the two former genera are derived from the two latter by an annular constriction in the equatorial plane.

Subgenus 1. _Cyphinidoma_, Haeckel.

_Definition._--On both poles of the cortical shell one single polar spine or a bunch of polar spines.

1. _Cyphinidium amphistylium_, n. sp.

Cortical shell thick walled, with smooth surface, and subregular, circular pores, twice to three times as broad as the bars; eight to ten on the half meridian, sixteen to eighteen on the half equator of each chamber. Both medullary shells spherical. The cortical shell resembles very much that of _Cannartiscus amphiconiscus_ (Pl. 39, fig. 19), but exhibits instead of the hollow polar tubes two strong solid polar spines of conical form, half as long as the main axis, and as broad at the base as the inner medullary shell.

_Dimensions._--Main axis of the cortical shell (without polar spines) 0.14, greatest breadth 0.1; pores 0.008, bars 0.004; length of the polar spines 0.08, basal thickness 0.02.

_Habitat._--North Pacific, off Japan, Station 241, depth 2300 fathoms.

2. _Cyphinidium apicatum_, Haeckel.

_Ommatospyris apicata_, Ehrenberg, 1872, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 317.

Cortical shell thin walled, with thorny surface, and irregular, polygonal pores, three to five times as broad as the thin bars; eight to nine on the half meridian, thirteen to fifteen on the half equator of each chamber. On both poles a bunch of four to eight strong conical spines, the central of which (in the main axis) is much larger than the others, and twice as long as the diameter of the outer spheroidal medullary shell; size and number of the polar spines is very variable (commonly five to six).

{372}_Dimensions._--Main axis (without spines) 0.12, greatest breadth 0.08; pores 0.005 to 0.01, bars 0.002; length of the polar spines 0.02 to 0.06, basal thickness 0.01.

_Habitat._--Northern Pacific, Californian Sea, depth 2500 fathoms, Ehrenberg; Station 253, depth 3125 fathoms.

Subgenus 2. _Cyphinidura_, Haeckel.

_Definition._--On both poles of the cortical shell, a circle of divergent polar spines.

3. _Cyphinidium coronatum_, n. sp.

Cortical shell with thorny surface, and irregular, roundish pores, twice to four times as broad as the bars; seven to eight on the half meridian, eleven to thirteen on the half equator of each chamber. Around both poles of the main axis occurs a circle of ten to twelve strong, radially divergent spines, about as long as the diameter of the outer medullary shell, which, like the inner, is spheroidal. (This species is identical with the younger developmental stage of _Panicium coronatum_, Pl. 40, fig. 4, before the formation of two distal chambers.)

_Dimensions._--Main axis 0.12, greatest breadth 0.1; pores 0.008 to 0.016, bars 0.004; length of the polar spines 0.02, thickness 0.005.

_Habitat._--Pacific, central area, Stations 270 to 274, depth 2350 to 2925 fathoms.

Genus 161. _Cannartiscus_,[200] n. gen.

_Definition._--#Cyphinida# with simple cortical shell and simple medullary shell, with two hollow fenestrated polar tubes, opposite on both poles of the main axis.

The genus _Cannartiscus_ differs from _Cyphanta_ in the development of two hollow fenestrated tubes, opposite on both poles of the main axis. It simulates therefore the characteristic formation of _Cannartus_, and differs from this Artiscid in the possession of a medullary shell.

1. _Cannartiscus amphiconiscus_, n. sp. (Pl. 39, fig. 19).

_Cannartidium amphiconiscus_, Haeckel, 1882, Atlas (pl. xxxix. fig. 19).

Cortical shell thick walled, smooth, with regular, circular pores, twice as broad as the bars; nine to ten on the half meridian, sixteen to eighteen on the half equator of each chamber. Polar tubes conical, about as long as one single chamber, on the base somewhat broader than the simple spherical medullary shell. Pores of the tubes only one-third as great as those of the chambers.

_Dimensions._--Main axis of the cortical shell (without tubes) 0.14, greatest breadth 0.1; {373}pores 0.008, bars 0.004. Length of the polar tubes 0.07, basal breadth 0.04; pores 0.003, bars 0.002.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

2. _Cannartiscus amphicylindrus_, n. sp.

Cortical shell thick walled, rough, with subregular, circular pores, twice to four times as broad as the bars; six to seven on the half meridian, ten to twelve on the half equator of each chamber. Polar tubes cylindrical, on the distal end open (broken off?) nearly as long as the main axis, somewhat narrower than the spherical medullary shell. Pores of the tubes much smaller than those of the chambers.

_Dimensions._--Main axis (without tubes) 0.17, greatest breadth 0.12; pores 0.006 to 0.012, bars 0.003. Length of the polar tubes 0.15, breadth of them 0.03; pores 0.003, bars 0.002.

_Habitat._--Pacific, central area, Station 268, 2900 fathoms; the same form occurs fossil in the rocks of Barbados.

Genus 162. _Cannartidium_,[201] n. gen.

_Definition._--#Cyphinida# with simple cortical shell and double medullary shell, with two hollow fenestrated polar tubes, opposite on both poles of the main axis.

The genus _Cannartidium_ differs from _Cannartiscus_ and _Cannartus_ in the duplication of the medullary shell, which is composed of two concentric spheres or compressed lenticular spheroids. The three genera named form therefore one morphological series, with identical cortical shell, and only differing in the absence or presence of a simple or double medullary shell.

Subgenus 1. _Cannartidella_, Haeckel.

_Definition._--Surface of the cortical shell smooth or a little rough, but without spines or fenestrated protuberances.

1. _Cannartidium amphiconicum_, n. sp.

Cortical shell thick walled, smooth with regular circular pores twice as broad as the bars; eight to nine on the half meridian, fifteen to sixteen on the half equator of each chamber. Polar tubes conical, with smaller pores, tapering towards the closed apex, about as long as one single chamber, at the base one-third as broad as the equatorial constriction. Both concentric medullary shells spherical. (Nearly identical with _Cannartiscus amphiconiscus_, Pl. 39, fig. 19, but differs in the possession of the double medullary shell.)

{374}_Dimensions._--Main axis of the cortical shell (without tubes) 0.15, greatest breadth 0.11; pores 0.009, bars 0.004; length of the polar tubes 0.08, basal breadth 0.04.

_Habitat._--Pacific, western tropical part, Station 225, depth 4475 fathoms.

2. _Cannartidium amphicanna_, Haeckel.

"Curious twin Polycystin," Bury, 1862, Polycystins of Barbados, pl. xx. fig. 4.

Cortical shell thick walled, rough, with regular, circular pores, not broader than the bars; six to seven on the half meridian, ten to twelve on the half equator of each chamber. Polar tubes cylindrical, at the distal end open (broken off?), nearly as long as the main axis, about one-third as broad as the equatorial constriction. Both concentric medullary shells spherical.

_Dimensions._--Main axis 0.14, greatest breadth 0.11; pores and bars 0.005; length of the polar tubes 0.13, breadth of them 0.03.

_Habitat._--Fossil in the Barbados deposits.

3. _Cannartidium amphisiphon_, Haeckel.

? _Haliomma amphisiphon_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 267.

Cortical shell thick walled, rough, with irregular, roundish pores, twice to five times as broad as the bars; five to six on the half meridian, nine to ten on the half equator of each chamber. Polar tubes conical, with smaller pores, about as long as one single chamber, half as broad at the base as the equatorial constriction. (This deep-sea form is probably identical with that fossil species which Ehrenberg, in 1844, described as _Haliomma amphisiphon_, and which he afterwards, in 1875, erroneously identified with his _Astromma entomocora_ (= _Cypassis entomocora_). But the figure given of the latter is quite different from the given diagnosis of the former.)

_Dimensions._--Main axis of the cortical shell (without tubes) 0.13, greatest breadth 0.1; pores 0.006 to 0.12, bars 0.003; length of the polar tubes 0.07, basal breadth of them 0.04.

_Habitat._--Tropical Atlantic, Antilles, Station 24, depth 390 fathoms; fossil in the Tertiary rocks of Bermuda.

4. _Cannartidium bicinctum_, n. sp. (Pl. 39, fig. 18).

Cortical shell thick walled, with a thickened ring-shaped protuberance in the greatest breadth of both chambers. Pores subregular, circular, twice to three times as broad as the bars; seven to eight on the half meridian, thirteen to fifteen on the half equator of each chamber. Polar tubes conical, with smaller pores, somewhat shorter than the greatest breath, nearly as thick at the base as the outer spheroidal medullary shell (fig. 18_a_).

_Dimensions._--Main axis (without tubes) 0.12, greatest breadth 0.08; pores 0.003 to 0.006, bars 0.002; length of the polar tubes 0.08, basal thickness 0.03.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

{375}Subgenus 2. _Cannartidissa_, Haeckel.

_Definition._--Surface of the cortical shell with conical fenestrated protuberances in the greatest breadth of both chambers.

5. _Cannartidium mammiferum_, n. sp. (Pl. 39, fig. 16).

Cortical shell-thin walled, having a circle of six to eight conical protuberances in the greatest breadth of both chambers, each of which exhibits a central apical pore, surrounded by a circle of six to eight oblique larger pores. Between the protuberances occur nine to ten pores on the half meridian of each chamber, circular, subregular, twice to three times as broad as the bars. Polar tubes cylindrical, conical at the closed end, with smaller pores, about as long as the greatest breadth of the chambers, as broad as the spherical outer medullary shell.

_Dimensions._--Main axis (without tubes) 0.13, greatest breadth (including the protuberances) 0.1; pores 0.005 to 0.008, bars 0.003; length of the polar tubes 0.09, basal thickness 0.02.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

6. _Cannartidium mastophorum_, n. sp. (Pl. 39, fig. 17).

Cortical shell thin walled, of the same form and structure as in the foregoing species, differs from this mainly in the form of the polar tubes, which are not cylindrical but conical, tapering gradually from the base towards the closed apex. Besides this, the conical protuberances (six in the greatest periphery of each chamber) are more regular and acute, with smaller and more numerous pores. Both medullary shells are here also spherical.

_Dimensions._--Main axis (without tubes) 0.14, greatest breadth (including the protuberances) 0.13; pores 0.006 to 0.009, bars 0.004; length of the polar tubes 0.07, basal thickness 0.03.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

Family XVI. #PANARTIDA#, Haeckel (Pl. 40, figs. 1-9).

_Definition._--#Prunoidea# with a four-jointed cortical shell, the external shell being divided by three parallel transverse constrictions into four chambers, in the centre enclosing two internal concentric shells (medullary shells). Central capsule cylindrical, commonly four-jointed (with three transverse annular constrictions).

The family #Panartida# (Pl. 40, figs. 1-9) is characterised by its four-jointed cortical shell, constantly composed of four chambers, lying one behind another in the elongated main axis. They are separated by three ring-like constrictions lying in three parallel transverse planes; the middle of these is the equatorial plane. In the centre of this latter lies constantly a double medullary shell.

The Panartida must be derived from the Cyphinida by further increase in the longitudinal or main axis, and by repetition of the equatorial constriction in two transverse planes parallel to it and at an equal distance from it.

{376}_The Medullary Shell_ is always double in this family, composed of two small concentric shells lying in the middle of the central capsule. They are either spherical or lenticular, compressed towards both poles of the main axis; sometimes the inner is spherical, the outer lenticular. From the equatorial circumference of the latter starts a number of radial beams, which perforate the central capsule, and are inserted into the equatorial constriction of the cortical shell. Commonly all radial beams lie in the equatorial plane, sometimes also a part of them on both sides of it.

_The Cortical Shell_ is constantly composed of four completely latticed chambers, which are only separated by the three annular constrictions. In many species all four chambers have the same form and size (Pl. 40, fig. 3), but in the greater number of species both proximal (or central) chambers are different in size, shape, or structure from both distal (or polar) chambers. The cortical shell is either simple or double, composed of two concentric four-jointed shells; rarely it is triple or multiple, composed of three or more shells fitting one inside the other. Very often the outer cortical shell is incomplete, and only developed around the two proximal chambers of the complete inner cortical shell, both distal chambers of the latter remaining simple.

On both poles of the main axis often are developed solid spines (_Panicium_, Pl. 40, fig. 4) or hollow fenestrated tubes (_Panarium_, Pl. 40, fig. 9), as in the foregoing families. Besides this, the surface of the cortical shell may be armed with spines.

_The Central Capsule_ of the Panartida is always cylindrical, on both poles hemispherical; commonly it is more or less distinctly four-jointed, with three ring-like constrictions corresponding to those of the enclosing cortical shell. From the inner surface of the latter it is separated by a thinner or thicker jelly-mantle.

_Synopsis of the Genera of Panartida._

On both poles of the main { Cortical shell simple, 163. _Panartus_. axis neither peculiar { polar spines nor { Cortical shell double or fenestrated tubes. { triple, 164. _Peripanartus_.

On both poles of the main { Cortical shell simple, 165. _Panicium_. axis a large apical { spine or a group of { Cortical shell double or polar spines. { triple, 166. _Peripanicium_.

On both poles of the main { Cortical shell simple, 167. _Panarium_. axis a conical or { cylindrical fenestrated { Cortical shell double or tube. { triple, 168. _Peripanarium_.

Genus 163. _Panartus_,[202] n. gen.

_Definition._--#Panartida# with simple cortical shell and double medullary shell, without polar spines or tubes on both poles of the main axis.

{377}The genus _Panartus_ represents the common ancestral form of all Panartida, as all other genera of this subfamily must be derived from it and are only further developmental stages, from an ontogenetic as well as from a phylogenetic point of view. The cortical shell of _Panartus_ is constantly composed of four fenestrated chambers jointed to one another in the main axis; both proximal chambers are separated from one another by the equatorial ring-like constriction, in the centre of which lies the double medullary shell; both distal chambers are separated from the former by two other annular constrictions (in planes parallel to the equatorial plane). All four chambers may exhibit the same (kidney-shaped) form and structure (in the subgenera _Panartella_ and _Panartoma_); or the proximal chamber may differ more or less in shape and size from the distal (in the subgenera _Panartissa_ and _Panartura_). The outer surface of the cortical shell is sometimes smooth (as in _Panartella_ and _Panartissa_), at other times spiny or thorny (as in _Panartoma_ and _Panartura_). The double medullary shell is sometimes spherical, or commonly compressed at both poles and spheroidal or lenticular.

Subgenus 1. _Panartella_, Haeckel.

_Definition._--Surface of the cortical shell smooth, without spines or thorns. All its four chambers exhibit nearly the same form and structure.

1. _Panartus tetraplus_, n. sp.

All four chambers of the cortical shell of the same form, size, and structure, kidney-shaped, twice as broad as long. Pores rather regular, hexagonal, all nearly of the same size and form, four times as broad as the thin bars; five to six pores on the half meridian, nine to ten on the half equator of each chamber. Surface of the cortical shell smooth, its main axis three times as long as its equatorial axis (in the median constriction). Both concentric medullary shells spherical; the equatorial axis of the outer half as long as that of the cortical shell. (All four chambers of this species have the same appearance as the two proximal chambers of _Panartus diploconus_, Pl. 40, fig. 1.)

_Dimensions._--Main axis of the cortical shell 0.21, equatorial axis 0.07; breadth of every chamber 0.09; meshes 0.013, bars 0.03.

_Habitat._--Central area of the Pacific, Stations 270 to 274, depth 2350 to 2925 fathoms.

2. _Panartus tetracolus_, n. sp.

All four chambers of the cortical shell of the same form, size, and structure, kidney-shaped, twice as broad as long. Pores regular, circular, with hexagonal frame, twice as broad as the bars; six to seven pores on the half meridian, ten to twelve on the half equator of each chamber. Surface of the cortical shell smooth; its main axis three times as long as the equatorial axis. Both concentric medullary shells spheroidal, somewhat compressed at both poles; the equatorial axis {378}of the outer almost equals half that of the cortical shell. (All four chambers of this species exhibit the structure of the two proximal chambers of _Peripanartus amphiconus_, Pl. 40, fig. 5.)

_Dimensions._--Main axis of the cortical shell 0.24, equatorial axis 0.08; breadth of every chamber 0.01; meshes 0.01, bars 0.005.

_Habitat._--Equatorial Atlantic, Station 348, depth 2450 fathoms.

3. _Panartus tetrameres_, n. sp.

All four chambers of the cortical shell of the same form, size, and structure, kidney-shaped, twice as broad as long. Pores rather regular, circular, without hexagonal frame, about as broad as the bars; five to six pores on the half meridian, ten to twelve on the half equator of each chamber. Surface of the cortical shell smooth, its main axis three times as long as the equatorial axis. Both concentric medullary shells spheroidal, compressed; the outer half as broad as the constriction. (This species is very much like _Ommatocampe increscens_, Stöhr, 1880, _loc. cit._, Taf. ii. fig. 2, and may be considered as the ancestral form of it.)

_Dimensions._--Main axis of the cortical shell 0.2, equatorial axis 0.065; breadth of every chamber 0.08; meshes and bars 0.005.

_Habitat._--Fossil in the Tertiary rocks of Sicily, Caltanisetta, Haeckel.

4. _Panartus tetraphalangus_, n. sp.

All four chambers of the cortical shell of the same form, size, and structure, kidney-shaped, twice as broad as long. Pores irregular, polygonal (mostly pentagonal or hexagonal), four to eight times as broad as the thin bars; four to seven on the half meridian, eight to fifteen on the half equator of each chamber. Surface of the cortical shell smooth, its main axis three times as long as its equatorial axis. Both concentric medullary shells compressed, the outer, half as broad as the constriction.

_Dimensions._--Main axis of the cortical shell 0.26, equatorial axis 0.09; breadth of every chamber 0.12; meshes 0.003 to 0.02, bars 0.001 to 0.003.

_Habitat._--Fossil in the rocks of Barbados, Haeckel.

5. _Panartus tetrathalamus_, n. sp. (Pl. 40, fig. 3).

All four chambers of the cortical shell of the same form, size, and structure, kidney-shaped, twice as broad as long. Pores irregular, roundish, twice to three times as broad as the bars; a circle of larger pores at the base of both distal chambers; five to six pores on the half meridian, ten to twelve on the half equator of each chamber. Surface of the cortical shell smooth; its main axis two and a half times as long as the equatorial axis. Both medullary shells spheroidal, compressed, the outer one-third as broad as the constriction. (In the specimen figured spines begin to arise from both distal chambers; this forms a transition to _Panartus quadrijugus_.)

_Dimensions._--Main axis of the cortical shell 0.18, equatorial axis 0.07; breadth of every chamber 0.09; meshes 0.003 to 0.01, bars 0.002 to 0.004.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, in various depths.

{379}Subgenus 2. _Panartissa_.

_Definition._--Surface of the cortical shell smooth, without spines or thorns. Both its proximal chambers differ in form and structure from the two distal chambers.

6. _Panartus diploconus_, n. sp. (Pl. 40, fig. 1).

Both proximal chambers nearly ellipsoidal, one and a half times as broad as long, with regular hexagonal pores, four times as broad as the bars; five to six pores on the half meridian, nine to ten on the half equator of each chamber. Both distal chambers conical, with a circle of ten to twelve large square pores at the base; the other pores very small and numerous, roundish, sixteen to twenty in the height of each cone, and the same number on the half periphery of its base. Both concentric medullary shells compressed, the outer, half as broad as the constriction of the cortical shell, the surface of which is quite smooth.

_Dimensions._--Total length of the shell (or main axis) 0.34; greatest breadth of each chamber 0.09; pores of the proximal chambers 0.013, bars 0.003; pores and bars of the distal chambers 0.003; large basal square pores 0.02.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

7. _Panartus amphiconus_, n. sp.

Both proximal chambers nearly kidney-shaped, one and a half times as broad as long, with regular, circular pores, with hexagonal frames, twice as broad as the bars; six to seven pores on the half meridian, ten to twelve on the half equator of each chamber. Both distal chambers conical, with a circle of ten to twelve very large pores at the base; the other pores very small, roundish, ten to fifteen in the height of each cone, twenty to thirty on the half basal periphery. Both concentric medullary shells compressed, the outer one-third as broad as the constriction of the cortical shell, whose surface is smooth. (This species resembles _Peripanartus amphiconus_, Pl. 40, fig. 5, but is without the surface spines and the outer envelope.)

_Dimensions._--Total length of the shell 0.28; greatest breadth of the proximal chambers 0.1, of the distal chambers 0.14; pores of the former 0.008, of the latter 0.004; bars of both 0.003 to 0.005.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

8. _Panartus fusiformis_, n. sp.

Both proximal chambers nearly ellipsoidal, one and a half times as long as broad, with irregular, roundish pores, twice to three times as broad as the bars; eight to ten pores on the half meridian, twelve to fifteen on the half equator of each chamber. Both distal chambers hemiellipsoidal or egg-shaped, somewhat higher and narrower than the proximal chambers, with a circle of larger square pores at their base; the other pores roundish and very irregular. Both medullary shells spheroidal, one-third as broad as the constriction of the cortical shell, whose surface is quite smooth. (This {380}species is similar to _Peripanartus atractus_, Pl. 40, fig. 7, but is without the superficial spines and the equatorial girdle-like envelope of the latter.)

_Dimensions._--Total length of the shell 0.25 to 0.3; greatest breadth (in the equator of the proximal chambers) 0.08 to 0.1; pores of the proximal chambers 0.008 to 0.012, pores of the distal chambers half their size, bars 0.002 to 0.006.

_Habitat._--North Pacific, Station 237, surface.

9. _Panartus profundissimus_, Haeckel.

_Ommatocampe profundissima_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 297, Taf. viii. fig. 6.

Both proximal chambers nearly ellipsoidal, with irregular, polygonal pores, six to eight times as broad as the bars; four to five pores on the half meridian, eight to nine on the half equator of each chamber. Both distal chambers hemispherical, with a very delicate irregular network. Medullary shells spherical; surface of the shell smooth.

_Dimensions._--Total length of the shell 0.15; greatest breadth in the equator of the proximal chambers 0.08; pores of the proximal chambers 0.015, bars 0.002.

_Habitat._--Philippine Sea, depth 3300 fathoms, Ehrenberg; Station 213, depth 2050 fathoms.

Subgenus 3. _Panartoma_, Haeckel.

_Definition._--Surface of the cortical shell thorny, covered with scattered spines. All its four chambers exhibit the same form and structure.

10. _Panartus quadriceps_, n. sp.

All four chambers of the cortical shell of the same form, size, and structure, kidney-shaped, twice as broad as long. Pores rather regular, circular, with hexagonal frames, twice to three times as broad as the bars; six to seven pores on the half meridian, ten to twelve on the half equator of each chamber. Surface spiny; from the corners of the hexagonal frames (between every three pores) arise short radial spines. Both medullary shells spherical, the outer one-third as broad as the constriction of the cortical shell. (All the four chambers of this species have the same form as the two proximal chambers of _Peripanartus amphiconus_, Pl. 40, fig. 5.)

_Dimensions._--Main axis of the cortical shell 0.24, equatorial axis 0.08; meshes 0.01, bars 0.003 to 0.005; length of the spines 0.01 to 0.02.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

11. _Panartus quadrijugus_, n. sp.

All four chambers of the cortical shell of the same form and size, kidney-shaped, twice as broad as long. Pores irregular, roundish, twice to three times as broad as the bars; a circle of larger pores at the base of both distal chambers; six to eight pores on the half meridian, twelve to {381}fourteen on the half equator of each chamber. Surface spiny, everywhere covered with small irregular thorns. (This species differs from the smooth _Panartus tetrathalamus_, Pl. 40, fig. 3, almost entirely by the thorny surface.)

_Dimensions._--Main axis 0.2, equatorial axis 0.08; breadth of every chamber 0.1; meshes 0.005 to 0.01, bars 0.003, spines 0.01 to 0.02.

_Habitat._--Cosmopolitan; on the surface of the Atlantic, Indian, and Pacific Oceans.

12. _Panartus quadrigeminus_, n. sp.

All four chambers of the cortical shell nearly of the same size and form, kidney-shaped, twice as broad as long. Pores irregular, polygonal (mostly pentagonal or hexagonal), six to eight times as broad as the thin bars; five to seven on the half meridian, twelve to sixteen on the half equator of each chamber. Surface of the cortical shell spiny, covered with numerous irregularly scattered, often oblique, bristle-like thorns.

_Dimensions._--Main axis 0.27, equatorial axis 0.1; breadth of each chamber 0.13; meshes 0.01 to 0.02, bars 0.001 to 0.005.

_Habitat._--Cosmopolitan; surface of the Atlantic and Pacific, many Stations.

Subgenus 4. _Panartura_, Haeckel.

_Definition._--Surface of the cortical shell thorny, covered with scattered spines. Both its proximal chambers differ in form or structure from the two distal chambers.

13. _Panartus spinosus_, n. sp.

Both proximal chambers nearly ellipsoidal, with regular, circular pores enclosed by hexagonal frames. Both distal chambers conical, with a circle of ten to twelve large square pores at the base; the other pores small, roundish. The cortical shell of this species is quite the same as that of _Panartus amphiconus_ (Pl. 40, fig. 5), but differs in the absence of the external envelope (or the second cortical shell), and is covered with short, conical spines on the whole surface.

_Dimensions._--Total length of the cortical shell 0.25, greatest breadth (on the base of the distal chambers) 0.12; meshes of the proximal chambers 0.008, of the distal chambers 0.004; bars 0.002 to 0.04, spines 0.01 to 0.02.

_Habitat._--North Pacific, Station 240, surface.

14. _Panartus setosus_, Haeckel.

_Ommatocampe setosa_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 297, Taf. viii. fig. 7.

Both proximal chambers kidney-shaped, broader than the two hemispherical distal chambers. Meshes of the cortical shell irregular, polygonal, or subregular hexagonal; at the base of each {382}distal chamber a circle of large square meshes. The breadth of the pores is eight to twelve times that of the bars between them. The whole surface is covered with small bristle-like spines.

_Dimensions._--Total length of the cortical shell 0.14, greatest breadth (in the equator of each proximal chamber) 0.07; meshes 0.008 to 0.015, bars 0.002, spines 0.01.

_Habitat._--Pacific (Philippine and Californian Sea) 3300 and 2300 fathoms, Ehrenberg; Station 200, depth 250 fathoms; Station 253, depth 3125 fathoms.

15. _Panartus pluteus_, n. sp. (Pl. 40, fig. 2).

Both proximal chambers kidney-shaped, with irregular, roundish pores, twice to four times as broad as the bars; their surface everywhere covered with short conical thorns. From both polar circles arise ten to twelve radial rods, which bear a fenestrated cap, and form thus either the beginning of a second, external, cortical shell, or (if remaining thus) two imperfect distal chambers. The spherical segment, which forms their surface, is concentric with the proximal chambers, is perforated by the same irregular, roundish pores, and covered with numerous bristle-like spines.

_Dimensions._--Main axis of the cortical shell 0.17, equatorial axis (in the constriction) 0.06; distance between the proximal and distal chambers 0.03; pores 0.003 to 0.01, bars 0.003 to 0.005.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

Genus 164. _Peripanartus_,[203] n. gen.

_Definition._--#Panartida# with double cortical shell and double medullary shell, without polar spines or tubes on both poles of the main axis.

The genus _Peripanartus_ differs from _Panartus_ only in the development of an outer reticulated envelop, which mantle-like surrounds the shell and represents a second or external cortical shell. This mantle or veil envelops either the whole internal cortical shell or only both proximal chambers. _Peripanartus_ exhibits the same relation to _Panartus_ as in the foregoing ancestral family _Cypassis_ bears to _Cyphonium_.

Subgenus 1. _Peripanartula_, Haeckel.

_Definition._--Surface of the outer cortical shell smooth, without spines or thorns.

1. _Peripanartus palliatus_, n. sp.

Internal cortical shell with four kidney-shaped chambers of equal size and similar form, identical with the cortical shell of _Panartus tetrathalamus_ and _Panartus quadrijugus_ (Pl. 40, fig. 3), with irregular, roundish pores, twice to three times as broad as the bars. It differs from these two species {383}only by the external cortical shell enveloping the whole internal one, in the same manner as in _Peripanartus cylindrus_ (Pl. 40, fig. 6). The two shells are connected by numerous radial rods. The surface of the outer cortical shell is quite smooth, its irregular, roundish pores about half as large as those of the inner cortical shell.

_Dimensions._--Main axis of the external cortical shell 0.27, of the internal 0.2; greatest breadth of the former (in the equator of each chamber) 0.13, of the latter 0.09; pores of the external cortical shell 0.002 to 0.004, of the internal 0.004 to 0.008; bars of the former 0.002, of the latter 0.003.

_Habitat._--Pacific, central area, Stations 271, 272, depth 2425 to 2600 fathoms.

2. _Peripanartus lævigatus_, n. sp.

Internal cortical shell with four unequal chambers, both proximal kidney-shaped (with subregular polygonal pores, twice to three times as broad as the bars), both distal nearly hemispherical, with subregular, roundish pores of half that size. External cortical shell envelops only the proximal chambers, and appears as the direct continuation of the internal shell of the distal chambers, with the same small roundish pores. The outer surface is quite smooth. This species has nearly the same structure as _Peripanicium amphicorona_ (Pl. 40, fig. 8), but differs from it by the absence of the polar spine-circles, and by the perfect smoothness of the surface.

_Dimensions._--Main axis of the shell 0.25, greatest breadth (in the equator of the proximal chambers) 0.15; equatorial stricture of the external shell 0.10, of the internal 0.07; pores of the internal shell of the proximal chambers 0.013, of the external 0.006; bars 0.003.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

3. _Peripanartus amphiconus_, n. sp. (Pl. 40, fig. 5).

Inner cortical shell with four very unequal chambers; both proximal chambers kidney-shaped (with regular, circular, hexagonally framed pores, twice as broad as the bars); both distal chambers conical, with a circle of large square pores at the base, the other pores very small, roundish. Outer cortical shell very thin, quite smooth, with irregular, roundish pores, envelops in younger specimens only the distal chambers. But the radial spines on the surface of the internal cortical shell of the proximal chambers indicate that these will also be afterwards enclosed by the growing of the external shell. This species exhibits the progressive (ontogenetic as well as phylogenetic) development of _Panartus amphiconus_.

_Dimensions._--Main axis of the outer cortical shell 0.3, its greatest breadth (at the prominent distal ends of the radial rods between the large square pores) 0.15; pores 0.003 to 0.001, bars 0.005; main axis of the inner cortical shell 0.26, its greatest breadth 0.13; pores of its distal chambers 0.003, of its proximal chambers 0.01; large square pores 0.03; bars 0.004.

_Habitat._--Pacific, central area, Station 270, depth 2925 fathoms.

{384}Subgenus 2. _Peripanartium_, Haeckel.

_Definition._--Surface of the outer cortical shell covered with spines or thorns.

4. _Peripanartus atractus_, n. sp. (Pl. 40, fig. 7).

Inner cortical shell with four very unequal chambers; both proximal chambers spheroidal (with subregular, roundish pores, twice to three times as broad as the bars), both distal chambers nearly conical, with a circle of eight to ten very large square pores at the base; the other pores very small, roundish. Outer cortical shell envelops only the proximal chambers and the basal half of the distal chambers, appearing as the direct continuation of the microporous covering of their apical half. The whole external cortical shell is inflated in the equatorial zone, and hence assumes an irregular, spindle-like appearance. Its whole surface is rough with innumerable very short thorns.

_Dimensions._--Main axis 0.28, equatorial axis 0.17; pores of the external cortical shell 0.002 to 0.004, bars 0.002; main axis of the proximal chambers of the internal cortical shell 0.07, equatorial axis 0.09; pores 0.007, bars 0.004.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

5. _Peripanartus cylindrus_, n. sp. (Pl. 40, fig. 6).

Internal cortical shell with four unequal chambers; both proximal chambers kidney-shaped (with regular, circular, hexagonally framed pores of the same breadth as the bars), both distal chambers nearly hemispherical, with a circle of eight to ten very large square pores at their base; the other pores very small, roundish. External cortical shell envelops the whole internal like a perfect hollow cylinder, which is closed at both poles by a hemispherical cap. The whole surface of this cylindrical mantle is perforated by innumerable very small roundish pores, and covered with small bristle-like spines.

_Dimensions._--Main axis of the cylinder 0.3, equatorial axis 0.12; pores and bars 0.006; spines of its surface 0.012 to 0.15; main axis of the internal cortical shell 0.2; equatorial axis (in the constriction) 0.06; pores and bars of its proximal chambers 0.007, of its distal chambers 0.003; large square pores at their base 0.02.

_Habitat._--Pacific, central area, Stations 270 to 274, depth 2350 to 2925 fathoms.

Genus 165. _Panicium_,[204] n. gen.

_Definition._--#Panartida# with simple cortical shell and double medullary shell, with two opposite apical spines on both poles of the main axis, or with a group of polar spines.

The genus _Panicium_ comprises those forms of _Panartus_ which develop a peculiar armature on both poles of the cortical shell. This may be only a single strong spine {385}on each pole, lying in the main axis (subgenus _Panicidium_); or a bunch or a circle of polar spines diverging radially (subgenus _Panartidium_); in the latter case the polar spines can either form a bunch on the pole itself, or a crown of thorns around it.

Subgenus 1. _Panicidium_, Haeckel.

_Definition._--On both poles of the main axis only a single large spine.

1. _Panicium amphacanthum_, n. sp.

All four chambers of the cortical shell nearly of the same size and form, kidney-shaped, with subregular, circular pores, twice as broad as the bars; five to six pores on the half meridian, ten to eleven on the half equator of each chamber. Surface covered with small spines. On both poles of the main axis is a very strong, conical, apical spine, half as long as the main axis, on the base one-fourth as broad as the equatorial axis.

_Dimensions._--Main axis (without polar spines) 0.22, equatorial axis 0.06; pores 0.01, bars 0.005; length of the polar spines 0.12, basal thickness 0.015.

_Habitat._--Antarctic, Station 152, depth 1260 fathoms.

2. _Panicium amphistylus_, n. sp.

Both proximal chambers kidney-shaped, both distal chambers nearly hemispherical, somewhat smaller. Pores irregular, roundish, twice to three times as broad as the bars; four to six on the half meridian, eight to ten on the half equator of each chamber; a circle of larger square pores on the base of each distal chamber. Surface thorny. On both poles of the main axis one strong, pyramidal, apical spine, one-third as long as the main axis, on the base one-fourth as broad as the equatorial constriction. (Similar to _Panarium tubularium_, Pl. 40, fig. 9, but without tubes.)

_Dimensions._--Main axis (without polar spines) 0.2, equatorial axis 0.05; pores 0.005 to 0.01, bars 0.003; length of the polar spines 0.07, basal thickness 0.012.

_Habitat._--Antarctic, Station 156, depth 1975 fathoms.

Subgenus 2. _Panartidium_, Haeckel.

_Definition._--On both poles of the main axis a bunch or a circle of aggregated spines.

3. _Panicium scoparium_, n. sp.

Both proximal chambers kidney-shaped, both distal chambers nearly hemispherical, somewhat smaller. Pores irregular, polygonal, twice to five times as broad as the bars; six to eight on the half meridian, twelve to fourteen on the half equator of each chamber. Surface spiny, covered with thin, {386}bristle-like spines. On both poles of the main axis a bunch of six to eight aggregated larger conical spines, about as high as a single chamber.

_Dimensions._--Main axis (without polar spines) 0.2, equatorial axis 0.06; pores 0.005 to 0.015, bars 0.003; length of the polar spines 0.05, basal thickness 0.005.

_Habitat._--Pacific, central area, Stations 270 to 274, depth 2350 to 2925 fathoms.

4. _Panicium coronatum_, n. sp. (Pl. 40, fig. 4).

Both proximal chambers kidney-shaped, covered with short stout spines. Pores irregular, roundish, twice to four times as broad as the bars; seven to eight on the half meridian, eleven to thirteen on the half equator of each chamber. Both distal chambers cap-like, separated from the former by a circle of ten to twelve very large square pores; the other pores very small, roundish. The circumpolar area is smooth, surrounded by a circle of ten to twelve very stout, conical, radial spines, which arise from the distal ends of the bars separating the large square meshes.

_Dimensions._--Main axis (without spines) 0.22, equatorial axis 0.08; greatest breadth in the equator of the chambers 0.1; pores of the proximal chambers 0.007 to 0.015, bars 0.004; square pores of the distal chambers 0.02 to 0.03, small pores 0.005, bars 0.004; length of the radial spines of the polar circles 0.07, basal thickness 0.007.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

Genus 166. _Peripanicium_,[205] n. gen.

_Definition._--#Panartida# with double cortical shell and double medullary shell, on both poles of the main axis with two opposite apical spines, or with a bunch or circle of polar spines.

The genus _Peripanicium_ differs from _Panicium_ only in the development of an outer reticulated envelope, which mantle-like surrounds the shell, and represents a second or external cortical shell. As in _Panicium_, its ancestral form, so also in _Peripanicium_, there can be distinguished two subgenera:--_Peripanicea_, where only a single large spine arises from each pole (lying in the main axis), and _Peripanicula_, where a variable number of spines is to be found, either diverging bunch-like from the pole itself, or surrounding it as a crown-like polar circle.

Subgenus 1. _Peripanicea_, Haeckel.

_Definition._--On both poles of the main axis only a single large spine.

1. _Peripanicium amphixiphus_, n. sp.

Internal cortical shell with four unequal chambers, with thorny surface. Both proximal chambers kidney-shaped (with subregular hexagonal pores, three times as broad as the bars). {387}Both distal chambers nearly hemispherical (with a circle of ten to twelve very large square pores at their base, the other pores very small). From both poles arises a single, strong, conical spine, half as long as the main axis. The internal cortical shell is very much like that of _Panarium tubularium_ (Pl. 40, fig. 9), but differs by the solid polar spines (instead of the hollow tubules) and by the formation of an external, cylindrical, very thin, cortical shell, which envelops the whole internal, and is connected with it by numerous beams. The surface of the external shell is quite smooth, and perforated by innumerable very small roundish pores.

_Dimensions._--Main axis of the external cortical shell 0.25, of the internal 0.19; transverse axis of the former 0.13, of the latter 0.08; pores of the proximal chambers of the internal shell 0.01, bars 0.003; pores of external cortical shell 0.002, bars 0.001; length of both polar spines 0.12, basal thickness of them 0.02.

_Habitat._--South Atlantic, near Tristan da Cunha, Station 333, depth 2025 fathoms.

Subgenus 2. _Peripanicula_, Haeckel.

_Definition._--On both poles of the main axis a bunch or a circle of aggregated polar spines.

2. _Peripanicium amphicorona_, n. sp. (Pl. 40, fig. 8).

_Peripanartus amphicorona_, Haeckel, 1881, Prodromus et Atlas (pl. xl. fig. 8).

Internal cortical shell with four very unequal chambers. Both proximal chambers kidney-shaped, with subregular, polygonal pores, three times as broad as the bars. Both distal chambers double cone-shaped; the proximal cone of these formed by a circle of ten to twelve radial beams, which separate the same number of large square meshes; the distal cone with five to six circles of very small roundish, irregular pores. The continuation of the thin porous lamella of this distal cone forms the external cortical shell, whose surface is a little rough with innumerable very small thorns. On both poles is a large circular opening (nearly as broad as the equatorial constriction of the inner shell), surrounded by a delicate crown of thorns. The spines of this crown equal the diameter of the polar opening; they are very thin and bristle-like, connected by a few bridges and diverge outwards.

_Dimensions._--Main axis (without the crowns of polar thorns) 0.26, greatest breadth (in the equator of the proximal chambers) 0.15; equatorial constriction of the external shell 0.12, of the internal 0.07; pores of the proximal chambers of the internal cortical shell 0.01, of the external 0.005, bars 0.003; diameter of the circular polar opening 0.05; length of the polar spines 0.05.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

3. _Peripanicium coronarium_, n. sp.

Internal cortical shell with four unequal chambers. Both proximal chambers kidney-shaped, with irregular, roundish pores, twice to four times as broad as the bars. Both distal chambers cap-like, with a basal circle of ten to twelve large square meshes, the other pores very small. External {388}cortical shell very thin, with smooth surface, and very small, irregular, roundish pores; it envelops the whole internal shell at a constant distance, which equals the breadth of the square meshes. From the distal ends of the radial beams between the square meshes arise on every polar circle ten to twelve strong spines, as direct prolongations of those beams. These form two regular, polar crowns of thorns. The inner part of the thorns (between both shells) has only one-third to one-fourth the length of the outer free part. (This species represents a further development of _Panicium coronatum_, Pl. 40, fig. 4, by secondary formation of an external mantle, like that of _Peripanartus atractus_, Pl. 40, fig. 7.)

_Dimensions._--Main axis 0.27, greatest breadth 0.15; pores of the internal proximal chambers 0.008 to 0.016, bars 0.004; square meshes of the distal chambers 0.03; pores of the outer cortical shell 0.003; length of the spines of the polar circles 0.1 to 0.15.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

Genus 167. _Panarium_,[206] Haeckel, 1881, Prodromus, p. 463.

_Definition._--#Panartida# with simple cortical shell and double medullary shell, with two hollow fenestrated tubes, opposite on the poles of the main axis.

The genus _Panarium_ differs from _Panartus_ by two hollow latticed tubes, which start from both poles of the main axis and lie in it. It repeats therefore in this family the same peculiar and remarkable formation, which we find in _Pipettella_ among the Ellipsida, in _Pipetta_ among the Druppulida, in _Cannartidium_ among the Cyphinida, in _Cannartus_ among the Artiscida, &c.

Subgenus 1. _Panarelium_, Haeckel.

_Definition._--Surface of the shell smooth, without spines or thorns.

1. _Panarium facettarium_, n. sp.

Surface of the cortical shell smooth. All the four chambers nearly of the same size and form, kidney-shaped, about twice as broad as long. Pores of these subregular, circular, with hexagonal frames, about as broad as the bars; nine to ten on the half meridian, twelve to fourteen on the half equator of each chamber. Polar tubuli nearly cylindrical, longer than half the main axis of the cortical shell, about one-fourth as broad as the equatorial constriction. Pores of the tubuli of the same shape as those of the chambers, but only half as large. (This species is like _Pipetta tuba_, Pl. 39, fig. 7, but distinguished by three parallel transverse constrictions.)

_Dimensions._--Total length of the shell (without tubuli) 0.26; breadth of each chamber 0.12; pores 0.01, bars 0.01; length of the tubuli 0.15, breadth of them 0.03.

_Habitat._--Pacific central area, Station 268, depth 2900 fathoms.

{389}2. _Panarium pipettarium_, n. sp.

Surface of the cortical shell smooth. Both proximal chambers nearly kidney-shaped; both distal chambers somewhat smaller, hemispherical. Pores of all four chambers subregular, circular, without hexagonal frames, twice as broad as the bars; six to seven pores on the half meridian, ten to eleven on the half equator of each chamber. Polar tubuli slender, conical, nearly half as long as the main axis of the shell, one-third as broad at the base as the equatorial constriction. Pores of the tubuli of the same shape as those of the chambers, but only half as large. (This species resembles somewhat _Cannartiscus amphiconiscus_, Pl. 39, fig. 19, but with double the number of chambers.)

_Dimensions._--Total length of the shell (without tubuli) 0.25, greatest breadth 0.1; pores 0.008, bars 0.004; length of the polar tubuli 0.11, basal breadth 0.03.

_Habitat._--Pacific, western tropical part, Station 225, depth 4475 fathoms.

Subgenus 2. _Panaromium_, Haeckel.

_Definition._--Surface of the shell spiny, covered with short thorns.

3. _Panarium annularium_, n. sp.

Surface of the cortical shell thorny, everywhere covered with small bristle-like spines. All four chambers nearly of the same size and form, kidney-shaped. Their pores subregular, circular, three to four times as broad as the bars; seven to eight on the half meridian, ten to eleven on the half equator of each chamber. Polar tubuli conical, nearly half as long as the main axis, half as broad at the base as the equatorial constriction. Pores of the tubuli like those of the chambers, but only half as broad.

_Dimensions._--Total length of the shell (without tubuli) 0.16; breadth of each chamber 0.07; pores 0.006 to 0.008, bars 0.002; length of the polar tubuli 0.07, basal breadth 0.03.

_Habitat._--Northern Pacific, Station 253, depth 3125 fathoms.

4. _Panarium artophorum_, n. sp.

Surface of the shell thorny, with scattered small spines. Both proximal chambers nearly kidney-shaped; both distal hemispherical, somewhat smaller. Pores of all chambers irregular, roundish, little broader than the bars; four to five on the half meridian, six to eight on the half equator of each chamber. Polar tubuli cylindrical, longer than the half main axis, only one-fourth as broad the equatorial constriction. Pores of the tubuli only one-third to one-fourth as broad as those of the chambers.

_Dimensions._--Total length of the shell (without tubuli) 0.22, greatest breadth (in the equator of the proximal chambers) 0.09; pores and bars 0.008 to 0.012; length of the polar tubuli 0.14, breadth of them 0.02.

_Habitat._--Southern Pacific, Station 289, depth 2550 fathoms.

{390}5. _Panarium tubularium_, n. sp. (Pl. 40, fig. 9).

Surface of the cortical shell thorny, covered with small spines. Both proximal chambers nearly kidney-shaped, with irregular, polygonal pores, three to four times as broad as the bars; five to six pores on the half meridian, nine to ten on the half equator of each chamber. Both distal chambers nearly hemispherical, with a circle of ten to twelve large square pores at their base; the other pores much smaller, irregular, roundish. Polar tubuli prismatic, with prominent edges, nearly half as long as the main axis, only one-fourth as broad as the equatorial constriction. Pores of the tubuli very small, in longitudinal series between the edges.

_Dimensions._--Total length of the shell (without tubuli) 0.18 to 0.2, greatest breadth (in the equator of the proximal chambers) 0.07 to 0.09; pores 0.003 to 0.01, bars 0.002 to 0.004; length of the polar tubuli 0.06 to 0.09, breadth of them 0.015 to 0.02.

_Habitat._--Pacific, central area, Stations 270 to 272, depth 2425 to 2925 fathoms.

Genus 168. _Peripanarium_,[207] n. gen.

_Definition._--#Panartida# with double cortical shell and double medullary shell, with two hollow fenestrated tubes, opposite on the poles of the main axis.

The genus _Peripanarium_ differs from _Panarium_ only in the development of an outer reticulated envelop, which mantle-like surrounds the shell and represents a second or external cortical shell. It bears therefore to _Panarium_ the same relation as _Peripanartus_ to _Panartus_, &c.

1. _Peripanarium cenoconicum_, n. sp.

Internal cortical shell with four kidney-shaped chambers of nearly the same form and size; their pores irregular, roundish, twice to four times as broad as the bars. External cortical shell cylindrical, hemispherical at both poles, with irregular, very small, roundish pores, only one-third to one-half as large as those of the internal. From both poles of the internal cortical shell arises a hollow conical fenestrated tube, which perforates the external. The outer free part of this slender cone equals in length the inner part or the distance between the two cortical shells, which is about equal to the length of one chamber. External surface covered with small thorns. (This species has the same appearance as _Desmartus larvalis_, Pl. 40, fig. 12, but has only four chambers instead of six.)

_Dimensions._--Main axis (without cones) 0.23, greatest breadth 0.11; pores of the inner cortical shell 0.004 to 0.009, of the outer 0.002 to 0.003; bars of the former 0.002, of the latter 0.001; total length of the polar cones 0.05, basal thickness of them 0.03.

_Habitat._--West Tropical Pacific, Station 225, depth 4475 fathoms.

{391}2. _Peripanarium cenocylindricum_, n. sp.

Internal cortical shell with four unequal chambers, the two proximal kidney-shaped, the two distal conical, and somewhat smaller; pores irregular, polygonal-roundish, twice to five times as broad as the bars. External cortical shell nearly spindle-shaped, in the equatorial zone inflated, conical, tapering towards both poles, its pores very small, roundish, its surface covered with small thorns. The shell of this species resembles very much _Peripanartus atractus_ (Pl. 40, fig. 7), but differs by the hollow cylindrical polar tubes, which arise from both poles of the inner cortical shell and attain more than half the length of the main axis. They are open at their ends (broken away), about as broad as the outer medullary shell, and perforated by irregular, roundish pores.

_Dimensions._--Main axis (without polar tubes) 0.28, greatest breadth (in the equator) 0.16; pores of the inner cortical shell 0.004 to 0.01, of the outer 0.002 to 0.005; bars of the former 0.004, of the latter 0.002; total length of the polar tubes 0.16, breadth of them 0.03.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

Family XVII. #ZYGARTIDA#, Haeckel (Pl. 40, figs. 10-13).

_Zygartida_, Haeckel, 1881, Prodromus, p.462 (_sensu restricto_).

_Definition._--#Prunoidea# with annulated cortical shell, the external shell being divided by five or more parallel transverse constrictions into six or more chambers, enclosing in the centre two internal concentric shells (medullary shells). Central capsule cylindrical, commonly annulated (corresponding to the transverse annular constrictions of the cortical shell).

The family #Zygartida#, the seventh and last of the #Prunoidea#, comprises, in the sense here restricted, all those #Prunoidea# in which the cortical shell is annulated and composed of six to twenty or more (at least six) cameræ, lying one behind another in the elongated main axis, and separated by five or more annular constrictions. When I constituted this family in 1881 (_loc. cit._), I had given to it a much wider extent, embracing all those #Prunoidea# which exhibit annular constrictions of the cortical shell; as the number of these, in consequence of further researches, is much increased, it seems now more convenient to restrict the family to the extent here given.

No doubt the Zygartida must be derived from the Panartida by progressive growth of the cortical shell in the main axis and accompanying increase of the number of its chambers. Whilst this number in the Panartida is constantly restricted to four, in the Zygartida it amounts to ten, twenty, or more, and is in the lowest case six (Pl. 40, fig. 10). The maximum number is variable in the different species, but of course also different in the various degrees of individual development. Each Zygartid is at the beginning of its growth a Cyphinid, later a Panartid. The number of the annular constrictions separating the chambers and lying in parallel transverse planes is at least {392}five, but may amount to nineteen, to twenty-one or more; they lie constantly in pairs on both sides of the equatorial constriction (Pl. 40, figs. 12, 13).

The cortical shell may either remain simple (_Ommatocampe_, Pl. 40, fig. 10), or become double (_Desmocampe_, Pl. 40, fig. 12), or sometimes triple (_Zygocampe_, Pl. 40, fig. 13). In the latter cases the outer (secondary and tertiary) cortical shells are commonly incomplete, and only developed around the proximal chambers of the complete first (primary) cortical shell, its distal chambers remaining simple.

_The Medullary Shell_ is constantly double, as in the Panartida; its form is either spherical or lenticular, compressed in the direction of the main axis. It is always connected with the equatorial constriction of the cortical shell by a number of radial beams, lying either in the equatorial plane or on each side of it (Pl. 40, figs. 10-13).

_The Central Capsule_ of the Zygartida is constantly cylindrical; its increasing growth on both poles of the axis corresponds to that of the including cortical shell. Commonly (but not always) its cylindrical surface is annulated, with five or more transverse strictures, corresponding to those of the cortical shell. From the inner surface of the latter it is separated by a jelly-mantle, the calymma.

_Synopsis of the Genera of Zygartida._

I. Ommacampida. { Without polar tubes, 169. _Ommatocampe_. 1. Cortical shell { simple. { With two hollow fenestrated (Medullary shell { tubes, on the poles of double.) { the axis, 170. _Ommatartus_.

II. Desmocampida. { Without polar tubes, 171. _Desmocampe_. 2. Cortical shell { double. { With two hollow fenestrated (Medullary shell { tubes, on the poles of double.) { the axis, 172. _Desmartus_.

III. Zygocampida. { Without polar tubes, 173. _Zygocampe_. 3. Cortical shell { triple. { With two hollow fenestrated (Medullary shell { tubes, on the poles of double.) { the axis, 174. _Zygartus_.

Genus 169. _Ommatocampe_,[208] Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 832.

_Definition._--#Zygartida# with simple cortical shell and double medullary shell, without polar tubes.

The genus _Ommatocampe_ was founded by Ehrenberg in 1860 for one of his "_Haliommatina_," with the following diagnosis:--"Shell rod-like, long, articulate, with nucleus, without spines, with four or more joints." The species figured by him, _Ommatocampe {393}polyarthra_, exhibits five pairs of chambers on both sides of the meridian plane of the cortical shell, the centre of which includes a double medullary shell. It represents the most simple form of all Zygartida, and may be derived phylogenetically from _Cyphonium_ simply by multiplication of the chambers of the cortical shell, growing on both poles of the main axis.

Subgenus 1. _Ommatocampium_.

_Definition._--Surface of the cortical shell smooth or rough, without thorns or spines, also without polar spines.

1. _Ommatocampe polyarthra_, Ehrenberg.

_Ommatocampe polyarthra_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 279, Taf. vi. fig. 9.

Cortical shell with smooth surface, composed of six to ten chambers of the same size and form. Every chamber kidney-shaped, about twice as broad as long, with three transverse rows of circular, subregular pores, twice to three times as broad as the bars. Both medullary shells spherical.

_Dimensions._--Length of the six-chambered cortical shell 0.15; greatest breadth of each chamber 0.04; pores 0.005 to 0.007, bars 0.002 to 0.003.

_Habitat._--Californian Sea, depth 2600 fathoms, Ehrenberg; Pacific, central area, Station 268, depth 2900 fathoms; fossil in the Tertiary rocks of Barbados, Haeckel.

2. _Ommatocampe increscens_, Stöhr.

_Ommatocampe increscens_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 90, Taf. ii. fig. 2, _a_, _b_.

Cortical shell with rough surface, composed of six to ten chambers of nearly the same size and form; the breadth of the chambers a little increasing towards both poles. Every chamber kidney-shaped, the proximal chambers twice as broad as long, with four or five transverse rows of pores; the distal chambers three to four times as broad as long, with two or three transverse rows of pores. Form of the pores irregular, roundish, bars between them in the distal part smaller, in the proximal part larger than the pores. Both medullary shells compressed lenticular.

_Dimensions._--Length of the six-chambered cortical shell 0.22; greatest breadth of the chambers 0.09 to 0.1; pores and bars 0.003 to 0.006.

_Habitat._--Fossil in the Tertiary rocks of Sicily, Grotte, Stöhr.

3. _Ommatocampe annulata_, n. sp.

Cortical shell with smooth surface, composed of six to twelve chambers of nearly the same size and form. Each chamber kidney-shaped, twice as broad as long, with four to five transverse rows of {394}irregular, roundish pores, once to five times as broad as the bars. On the base of each distal chamber (beginning in the second or third pair) a circle of twelve to sixteen larger square pores. Both medullary shells compressed lenticular. (Resembles the inner cortical shell of _Desmartus larvalis_, Pl. 40, fig. 12, but is without the polar tubes and the outer envelope of this species.)

_Dimensions._--Length of the six-chambered cortical shell 0.23; greatest breadth of each chamber 0.07; pores 0.002 to 0.01, bars 0.002.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, in various depths.

Subgenus 2. _Ommatocampula_, Haeckel.

_Definition._--Surface of the cortical shell thorny or spiny, but without peculiar polar spines and without regular coronals of spines.

4. _Ommatocampe erucæformis_, n. sp.

Cortical shell with spiny surface, composed of six to twelve chambers of nearly the same size and form, the distal chambers a little smaller. The form and structure of the cortical shell is nearly the same as in the foregoing species, only the pores are somewhat larger, and the whole surface is covered with bristle-like radial spines, about half as long as the breadth of one chamber. Both medullary shells compressed and lenticular.

_Dimensions._--Length of the six-chambered cortical shell 0.24; greatest breadth of each chamber 0.08; pores 0.005 to 0.012, bars 0.002.

_Habitat._--North Atlantic, Canary Islands, Station 353, depth 2965 fathoms.

5. _Ommatocampe nereis_, n. sp. (Pl. 40, fig. 10).

Cortical shell with spiny surface, composed of six (or more) chambers of different size and structure. Both proximal chambers kidney-shaped, with subregular, circular, hexagonally framed pores, twice as broad as the bars. All following chambers cap-like, with much smaller, irregular, roundish pores, at the base of every chamber a circle of ten to twelve large square pores. Spines of the surface short, irregularly scattered. Both medullary shells spherical. (All the observed specimens possessed only six chambers.)

_Dimensions._--Length of the six-chambered cortical shell 0.25; greatest breadth of each chamber 0.08; pores of both proximal chambers 0.01, bars 0.005; basal pores of the other chambers 0.02; pores of their distal caps 0.003 to 0.006, bars 0.003.

_Habitat._--Pacific, central area, Stations 271 to 274, depth 2350 to 2750 fathoms.

Subgenus 3. _Ommatocorona_, Haeckel.

_Definition._--Surface of the cortical shell spiny, on every chamber a regular circle or coronal of radial spines.

{395}6. _Ommatocampe chætopodum_, n. sp.

Cortical shell with spiny surface, composed of six (or more) kidney-shaped chambers of different size and form. Both proximal chambers kidney-shaped, with subregular, circular, hexagonally framed pores, about as broad as the bars. All the following chambers hemispherical, with irregular, roundish pores; at the base of every chamber a circle of ten to twelve larger square pores. The beams between these latter are prolonged into free radial spines, twice as thick as the bars. Therefore every chamber is surrounded by a circle of radial spines, like those of _Panicium coronatum_ (Pl. 40, fig. 4). Both medullary shells lenticular.

_Dimensions._--Length of the six-chambered cortical shell 0.3, greatest breadth 0.08, pores and bars of both proximal chambers 0.01; pores of the other chambers 0.002 to 0.008; square pores 0.02, bars 0.005; length of the coronal spines 0.03, thickness 0.01.

_Habitat._--Indian Ocean, Madagascar, Rabbe.

Subgenus 4. _Ommatacantha_, Haeckel.

_Definition._--Surface of the shell smooth or spiny, on the poles of the main axis occur two strong opposite polar spines.

7. _Ommatocampe amphilonche_, n. sp.

Cortical shell composed of six kidney-shaped chambers of nearly the same size and structure; every chamber twice as broad as long, with four to five transverse rows of irregular, roundish pores, once to four times as broad as the bars. Both medullary shells lenticular. Surface of the cortical shell covered with bristle-like spines. On both poles of the main axis one larger, strong, conical spine, about half as long as this axis, and on the base as broad as the inner medullary shell. (Resembles on the whole _Desmartus larvalis_, Pl. 40, fig. 12, but without external mantle, and with two solid polar spines instead of the polar tubes.)

_Dimensions._--Length of the six-chambered cortical shell 0.24; greatest breadth of each chamber 0.08; pores 0.002 to 0.08, bars 0.002; length of the polar spines 0.12, basal thickness 0.02.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

Genus 170. _Ommatartus_,[209] Haeckel, 1881, Prodromus, p. 463.

_Definition._--#Zygartida# with simple cortical shell and double medullary shell, with two hollow fenestrated tubes, opposite on both poles of the main axis.

The genus _Ommatartus_ differs from _Ommatocampe_ by the development of two hollow fenestrated tubes on both poles of the main axis, and bears therefore the same relation to it as _Cannartidium_ to _Cyphonium_. The former two genera differ from the two latter by the augmentation of the chambers of the cortical shell.

{396}1. _Ommatartus amphicanna_, n. sp.

Cortical shell with spiny surface, composed of six chambers of equal size and kidney-shaped; every chamber with four to five transverse rows of irregular, roundish pores, twice to three times as broad as the bars. Both medullary shells lenticular. Polar tubes conical, about as long as one chamber, with smaller pores. Both medullary shells spheroidal, more or less compressed. (Resembles _Desmartus larvalis_, Pl. 40, fig. 12, but is without the external shell.)

_Dimensions._--Length of the six-chambered cortical shell 0.24; greatest breadth of each chamber 0.07; pores 0.008 to 0.012, bars 0.004; length of the polar tubes 0.04 to 0.05, basal thickness 0.02.

_Habitat._--Pacific, central area, Stations 270 to 274, depth 2350 to 2925 fathoms.

2. _Ommatartus amphisiphon_, n. sp.

Cortical shell with spiny surface, composed of six or eight chambers of different size and form. Both proximal chambers kidney-shaped, each with five to six transverse rows of irregular, polygonal pores, three to four times as broad as the bars. The other (four to six) chambers somewhat smaller, more hemispherical, with smaller, irregular pores, but on the base of each a circle of ten to twelve larger square pores. Polar tubuli prismatic, about half as long as the main axis, with prominent edges and longitudinal rows of smaller pores between them. Both medullary shells lenticular. (Resembles closely _Panarium tubularium_, Pl. 40, fig. 9, but with six to eight chambers instead of four, and with longer tubuli.)

_Dimensions._--Length of the six-chambered cortical shell 0.26; greatest breadth of the proximal chambers 0.09, of the distal chambers 0.07; pores of the former 0.01, of the latter 0.004; large square pores 0.013, bars 0.003; length of the polar tubes 0.1 to 0.12, thickness 0.02.

_Habitat._--South Pacific, Station 297, depth 1775 fathoms.

3. _Ommatartus amphobolus_, n. sp.

Cortical shell with spiny surface, composed of six chambers of different size and form. Both proximal chambers kidney-shaped, with four to five transverse rows of subregular, circular pores, twice as broad as the bars. Both middle chambers cap-like, with a basal circle of ten to twelve larger square pores, and small roundish pores on the cap. Both distal chambers smaller, conical, with very small roundish pores. Polar tubuli conical, nearly half as long as the main axis, also with very small pores. Both medullary shells lenticular.

_Dimensions._--Length of the six-chambered shell 0.28, greatest breadth 0.08; pores of the proximal chambers 0.01, bars 0.005; pores of the distal chambers and the polar tubes 0.002 to 0.004, bars 0.002; length of the polar tubes 0.13, basal thickness 0.03.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

Genus 171. _Desmocampe_,[210] n. gen.

_Definition._--#Zygartida# with double cortical shell and double medullary shell, without polar tubes.

{397}The genus _Desmocampe_ differs from _Ommatocampe_ in the duplication of the jointed cortical shell; the radial spines, which start from the surface of the inner cortical shell, are connected one with another by transverse communicating branches which form an outer envelop around it; but this reticulated mantle is commonly not quite perfect and more or less irregular.

1. _Desmocampe catenula_, n. sp.

Inner cortical shell with six to eight chambers of the same size and form. Every chamber kidney-shaped, with three to four transverse rows of circular, subregular pores, twice as broad as the bars. Outer cortical shell cylindrical, hemispherical at both poles, with smooth surface and irregular, roundish pores of very different size. Distance between the two cortical shells equals the diameter of the outer medullary shell, which, like the inner, is spherical. (Resembles Ommatocampe polyarthra, Ehrenberg, 1872, _loc. cit._, Taf. vi, fig. 9, but differs in the external mantle.)

_Dimensions._--Length of the six-chambered inner cortical shell 0.16, of the outer 0.21; greatest breadth of each chamber of the former 0.05, of the latter 0.09; pores of the inner 0.006, bars 0.003; pores of the outer 0.002 to 0.008, bars 0.002.

_Habitat._--North Pacific, Station 237, off Japan, surface.

2. _Desmocampe tænioides_, n. sp.

Inner cortical shell with six to ten chambers of nearly the same size and form; the distal chambers somewhat smaller. Every chamber kidney-shaped, with four to five transverse rows of irregular roundish pores, twice to three times as broad as the bars. Outer cortical shell cylindrical, hemispherical at both poles, with spiny surface; its pores like those of the inner, but the bars between them much thinner. Distance between the two cortical shells equals the diameter of the outer medullary shell. Both medullary shells lenticular. (Resembles _Desmartus larvalis_, Pl. 40, fig. 12, but is without polar tubes.)

_Dimensions._--Length of the six-chambered inner cortical shell 0.25, of the outer 0.3; greatest breadth of the former 0.07, of the latter 0.11; pores 0.005 to 0.012; bars of the inner shell 0.004, of the outer 0.001.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

3. _Desmocampe aphrodite_, n. sp.

Inner cortical shell with six to ten chambers of different size and structure. Both proximal chambers kidney-shaped, with five to six transverse rows of subregular, circular, hexagonally-framed pores, twice as broad as the bars. All following chambers cap-like, with much smaller, irregular, roundish pores, on the base of each a circle of ten to twelve large square pores. Outer cortical shell cylindrical, on both poles hemispherical, with spiny surface and very delicate network of small polygonal pores. Both medullary shells spherical. (The inner cortical shell of this species resembles that of _Ommatocampe nereis_, Pl. 40, fig. 10; the outer that of _Cyphocolpus virginis_, Pl. 40, fig. 11.)

{398}_Dimensions._--Length of the six-chambered internal cortical shell 0.25, of the outer 0.3; greatest breadth of the former 0.08, of the latter 0.12; pores of the proximal chambers of the inner shell 0.01, bars 0.005; pores of the distal chambers 0.003 to 0.005, square pores 0.02, bars 0.003; pores of the external cortical shell 0.002 to 0.006, bars 0.001.

_Habitat._--North Atlantic, Station 353, depth 2965 fathoms.

4. _Desmocampe atractus_, n. sp.

Inner cortical shell with six chambers of very different size and structure. Both proximal chambers kidney-shaped, with seven to eight transverse rows of subregular, roundish pores, twice to three times as broad as the bars. Both middle chambers cap-like, on the base with a circle of eight to ten very large square pores, on the distal cap with small irregular, roundish pores. Both distal chambers conical, also with small irregular, roundish pores. Outer cortical shell spindle-shaped, inflated in the equatorial zone, tapering conically towards both poles, with very delicate network of small roundish pores and thin bars. Surface covered with innumerable very small spines. Both medullary shells lenticular. (Resembles very much _Peripanartus atractus_, Pl. 40, fig. 7, but differs in the number of the chambers and their proportion to the outer mantle, which envelops spindle-like all six chambers.)

_Dimensions._--Length of the six-chambered internal cortical shell 0.27, of the outer 0.32; greatest breadth of the former 0.09, of the latter 0.15; pores of the inner cortical shell (on an average)--proximal chambers 0.008, middle chambers 0.02, distal chambers 0.004, bars 0.004; pores of the outer cortical shell 0.002 to 0.004, bars 0.002.

_Habitat._--North Pacific, Station 241, depth 2300 fathoms.

Genus 172. _Desmartus_,[211] n. gen.

_Definition._--#Zygartida# with double cortical shell and double medullary shell, with two hollow fenestrated tubes, opposite on both poles of the main axis.

The genus _Desmartus_ differs from _Desmocampe_ by the development of two hollow fenestrated tubes, opposite on both poles of the main axis, and bears therefore the same relation to it as _Ommatartus_ to _Ommatocampe_. Both the former genera can be produced from the two latter by duplication of the cortical shell.

1. _Desmartus larvalis_, n. sp. (Pl. 40, fig. 12).

_Zygartus larvalis_, Haeckel, 1881, Prodromus et Atlas (pl. xl, fig. 12).

Inner cortical shell composed of six kidney-shaped chambers of nearly the same size and structure; every chamber twice as broad as long, with four to five transverse rows of irregular, roundish pores, twice to five times as broad as the bars; the basal pores of the distal chambers {399}somewhat larger and more square. Outer cortical shell cylindrical, hemispherical at both poles, with irregular, polygonal pores, on an average twice as large as those of the inner, but the bars between them much thinner. Outer surface spiny. Both medullary shells lenticular. Polar tubes conical, a little longer than one internal chamber, as broad at the base as the inner medullary shell. Sometimes the tubes exhibit prominent edges (as in the lower spine of fig. 12); the pores of these are very small, and roundish.

_Dimensions._--Length of the six-chambered internal cortical shell 0.23, of the external 0.3; greatest breadth of the former 0.07, of the latter 0.11; pores of the inner shell 0.004 to 0.01, of the outer 0.01 to 0.02; bars of the former 0.002, of the latter 0.001; length of the polar tubes 0.05, basal thickness 0.02.

_Habitat._--North Pacific, Station 241, depth 2300 fathoms.

2. _Desmartus tubulatus_, n. sp.

Inner cortical shell composed of six to ten kidney-shaped chambers, tapering in size towards both poles, every chamber with six to seven transverse rows of irregular, roundish pores, twice to six times broader than the bars. Outer cortical shell spindle-shaped, in the equatorial zone inflated, tapering towards both poles, its network similar to the inner, only more delicate. Polar tubes conical, twice as long as an inner chamber, as broad at the base as the outer medullary shell. Both medullary shells lenticular.

_Dimensions._--Length of the six-chambered internal cortical shell 0.25, of the external 0.32; greatest breadth of the former 0.08, of the latter 0.12; pores of the inner shell 0.002 to 0.012, of the outer 0.003 to 0.01; bars of the former 0.002, of the latter 0.001; length of the polar tubes 0.07, basal thickness 0.03.

_Habitat._--North Pacific, Station 256, depth 2950 fathoms.

Genus 173. _Zygocampe_,[212] n. gen.

_Definition._--#Zygartida# with triple (or multiple) cortical shell and double medullary shell, without polar tubes.

The genus _Zygocampe_ differs from _Desmocampe_ and _Ommatocampe_ by the multiplication of the cortical shell, which is composed of three or more concentric envelopes. The three mentioned genera form therefore a phylogenetic series, produced by the concentric increase on the outside of the jointed cortical shell. Commonly the second cortical shell is not as complete as the first (or innermost), and the third (or outermost) is yet more incomplete. Rarely the number of the concentric cortical shells surpasses three.

1. _Zygocampe pupula_, n. sp.

Inner cortical shell with six to twelve chambers of nearly the same size and form. Every chamber kidney-shaped, with four to five transverse rows of circular, subregular pores, twice as {400}broad as the bars. Middle cortical shell cylindrical, hemispherical at both poles, with subregular circular pores somewhat smaller than those of the inner; the bars also thinner. Outer cortical shell of the same form as the middle, but with very delicate network, and quite irregular, roundish pores and very thin bars. Surface quite smooth. Both medullary shells lenticular. (May be regarded in a phylogenetic as well as an ontogenetic sense, as the further developmental form of _Desmocampe catenula_ and _Ommatocampe polyarthra_.)

_Dimensions._--Length of the six-chambered inner cortical shell 0.17, of the middle 0.22, of the outer 0.27; greatest breadth of the first 0.05, of the second 0.09, of the third 0.12; pores of the inner cortical shell 0.005, of the middle 0.004, of the outer 0.003 to 0.012; bars of the first 0.003, of the second 0.002, of the third 0.001.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

2. _Zygocampe corasium_, n. sp.

Inner cortical shell with six to eight chambers of different size and form. Both proximal chambers kidney-shaped, with five to six transverse rows of subregular, circular, hexagonally framed pores, twice as broad as the bars. All following chambers cap-like, the distal somewhat smaller; their pores much smaller, irregular, roundish; only at the base of each chamber a circle of ten to twelve large square pores. Middle cortical shell cylindrical, in the equatorial zone a little constricted, hemispherical at both poles, with irregular delicate network of roundish, polygonal meshes. Outer cortical shell of the same form as the middle, but with a very delicate and quite irregular network of polygonal meshes. Commonly this outer mantle is incomplete, and sometimes interwoven in a spongy manner with the middle (or also with the inner). Surface covered with many irregular, thin, bristle-like spines. Both medullary shells lenticular. (May be considered in a phylogenetic and ontogenetic sense as a further developmental stage of _Desmocampe aphrodite_ and _Ommatocampe nereis_, Pl. 40, fig. 10.)

_Dimensions._--Length of the six-chambered inner cortical shell 0.24, of the middle 0.3, of the outer 0.36; greatest breadth of the first 0.08, of the second 0.12, of the third 0.16, pores of the first (on an average) 0.005 to 0.02, of the second 0.003 to 0.015, of the third 0.01 to 0.05; bars corresponding 0.005 or 0.003 or 0.001.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

3. _Zygocampe chrysalidium_, n. sp. (Pl. 40, fig. 13).

Inner cortical shell with six to eighteen chambers of different size and form. Both proximal chambers kidney-shaped, with six to seven transverse rows of subregular, circular pores, three to four times as broad as the bars. All following chambers with more irregular pores, with a circle of ten to twelve larger square pores at the base. Middle cortical shell with smaller, irregular, roundish pores. Outer cortical shell with larger polygonal, quite irregular pores. Both outer shells appear commonly incomplete or somewhat irregularly developed, and sometimes in a spongy manner interwoven with one another. Surface covered with irregular, bristle-like spines. Both medullary shells spherical. The breadth of the chambers decreases gradually towards both poles, so that the whole shell assumes a spindle form. Sometimes on both poles is developed a short conical {401}polar tube (in fig. 13 only on the upper pole), and so this species is transformed into _Zygartus chrysalis_.

_Habitat._--Pacific, central area, Stations 272 to 274, depth 2350 to 2750 fathoms.

Genus 174. _Zygartus_,[213] Haeckel, 1881, Prodromus, p. 463.

_Definition._--#Zygartida# with triple (or multiple) cortical shell and double medullary shell, with two hollow fenestrated tubes, opposite on both poles of the main axis.

The genus _Zygartus_ differs from Zygocampe by the development of two hollow fenestrated tubes, on the two opposite poles of the main axis. It exhibits therefore to the latter the same relation that _Desmartus_ does to _Desmocampe_ and _Ommatartus_ to _Ommatocampe_; it differs from these by the multiplication of the cortical shell, which is composed of at least three concentric envelopes.

1. _Zygartus doliolum_, n. sp.

Inner cortical shell composed of six (or more) kidney-shaped chambers, all nearly of the same size and structure, every chamber with four to five transverse rows of irregular, roundish pores, twice to four times as broad as the bars; the basal pores scarcely larger than the apical pores. Middle cortical shell nearly of the same structure as the inner, only the pores larger and the bars thinner. Outer cortical shell cylindrical, hemispherical at both poles, its network very delicate, with large irregular, polygonal pores, and very thin bars between them; its surface covered with thin bristle-like spines. Both medullary shells lenticular. Polar tube cylindrical, with conical apex, and with very small pores; its length equals the breadth of two internal chambers, its breadth that of the inner medullary shell. (This species appears to be a further developed form of _Ommatocampe annulata_ and _Desmartus larvalis_, Pl. 40, fig. 12.)

_Dimensions._--Length of the six-chambered inner cortical shell 0.25, of the middle 0.3, of the outer 0.35; greatest breadth of the first 0.07, of the second 0.11, of the third 0.15; pores of the inner shell 0.005 to 0.01, of the middle 0.003 to 0.007, of the outer 0.008 to 0.02; bars of the first 0.002, of the second and third 0.001; length of the polar tubes 0.15, basal thickness 0.02.

_Habitat._--Pacific, central area, Station 270, depth 2925 fathoms.

2. _Zygartus chrysalis_, n. sp. (Pl. 40, fig. 13).

Inner cortical shell composed of six to twenty (commonly eight to twelve) chambers of different size and form. Both proximal chambers nearly hemispherical, with spiny surface and subregular, {402}circular pores, three to four times as broad as the bars. All following chambers cap-like, tapering towards both poles, with more irregular, roundish pores, with a circle of ten to twelve larger square pores at the base. Middle cortical shell with smaller roundish pores. Outer cortical shell with larger polygonal, quite irregular pores. Both medullary shells lenticular. Polar tubes conical or cylindrical with conical apex, of very variable length, sometimes not longer than one internal chamber, at other times twice to four times as long (in the figured specimen not fully developed, as also a part of the shells). Differs from _Zygocampe chrysalis_ only by the production of polar tubes.

_Dimensions._--Length of the six-chambered inner cortical shell 0.25, of the middle 0.3, of the outer 0.35; greatest breadth of the first 0.07, of the second 0.11, of the third 0.14; other measures the same as in _Zygocampe chrysalis_; length of the tubes 0.05 to 0.12 or more.

_Habitat._--Pacific, central area, Stations 270 to 274, depth 2350 to 2925 fathoms.

----

Suborder V. DISCOIDEA, Haeckel (Pls. 31-38, 41-48).

_Discida_ vel _Discoidea_, Haeckel, 1862, Monogr. d. Radiol., pp. 56, 476. _Discoida_, _Discoidea_, _Discida_, Haeckel, 1878, Protistenreich, p. 103.

_Definition._--SPUMELLARIA with discoidal or lenticular central capsule (often with radial prolongations, rarely allomorphic); with discoidal or lenticular fenestrated siliceous shell (often with radial spines or fenestrated arms, rarely allomorphic). Growth reduced or diminished in the direction of one dimensive axis.

The section #Discoidea# comprises those SPUMELLARIA in which the fenestrated shell is more or less discoidal or lenticular, flattened or compressed in the direction of one axis. The geometric fundamental form of the latticed shell, which in the #Sphæroidea# is a sphere, here becomes a flat disk, like a medal, or a biconvex lens, sometimes also a biconcave lens. The #Discoidea# can be derived from the #Sphæroidea# by shortening of one axis. This shortened vertical axis is the main axis of the disk; both its poles are constantly equal. Perpendicular to this axis is the equatorial plane of the disk by which it becomes divided into equal halves. In the simplest forms of #Discoidea# all axes of this horizontal equatorial plane (all "equatorial axes" or "cross axes") are equal; in the most of the genera and species these cross axes are different, so that rays of stronger growth ("perradii") alternate with rays of weaker growth ("interradii"). The number of these cross axes distinguishable is commonly two to four, rarely more. In the direction of these are developed either radial marginal spines or spongy arms.

The order #Discoidea# was founded in my Monograph (1862, p. 476) as the family "Discida" (Radiolaria with flat discoidal or biconvex lenticular shell), comprising the {403}"_Calodictya_ and _Lithocyclidina_" of Ehrenberg and a great part of his "_Haliommatina_." As three different subfamilies of that family I separated the Coccodiscida (with five genera), the Trematodiscida (with seven genera), and the Discospirida (with two genera; Monogr. d. Radiol., p. 485). A fourth group of #Discoidea# was constituted by the Spongodiscida (with eight genera, including the _Spongocyclida_), which at that time I united with the Spongurida, because of their spongy structure (_loc. cit._, p. 452).

As the number of fossil #Discoidea# found in the Tertiary rocks of Barbados and of the Mediterranean shores (Sicily and Greece) is comparatively very large, we find even in the first system of Polycystina of Ehrenberg (1847), not less than twelve genera distinguished, viz., six _Calodictya_, two _Haliommatina_, and four _Lithocyclidina_ (Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, 1847, p. 53). The whole number of Radiolarian genera distinguished in that first system was forty-four. The diagnoses of them given by Ehrenberg were as usual very insufficient. The characters of the three families given by him were the following:--_Calodictya_--"Testarum intus spongiosarum et nucleo destitutarum orbes; _Haliommatina_--Testæ subglobosæ nucleus radiatus; _Lithocyclidina_--Testarum disci in media parte nucleati margine celluloso." In the latest work of Ehrenberg (1875, p. 157) the same system was repeated, but some new genera added; and thirty-eight different species, appertaining to the #Discoidea#, were figured in the same work (Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Tafs. xx.-xxx.).

Richard Hertwig, 1879, in his excellent work, Der Organismus der Radiolarien (pp. 57-68), gave a detailed description of the skeleton of some #Discoidea#, and arrived at the conclusion that this whole family had a spirally constructed skeleton, and should therefore be derived from the Lithelida. But this conclusion is certainly erroneous, and in my opinion the whole explanation of that spiral structure, and of its signification in the development of #Discoidea#, is the weakest part of that otherwise very important work.

In my Prodromus (1881, p. 456) I gave a provisional system of the #Discida# or #Discoidea# from the immense quantity of new material collected by the Challenger, and could distinguish not less than eighty-four genera. This number is from subsequent research only augmented by seven, so that in the following pages ninety-one genera with five hundred and one species are described. In the Prodromus I had disposed them in four different families, which number is now increased to six. These six families can be again disposed in two main groups or sections, the #Phacodiscaria# and the #Cyclodiscaria#, each section with three families.

The #Phacodiscaria# are characterised by the possession of a typical "phacoid shell," and contain the three families Cenodiscida, Phacodiscida, and Coccodiscida. On the other hand, the #Cyclodiscaria# are distinguished by the absence of such a "phacoid shell," and contain the three families Porodiscida, Pylodiscida, and Spongodiscida. Both sections exhibit an analogous development.

{404}The #Cenodiscida# (Pl. 48, figs. 1-3) open the series of the #Discoidea# as their simplest forms; a discoidal or lenticular simple lattice-shell encloses a central capsule of the same form, and is separated from it by the calymma or jelly-veil. The common ancestral form of this family is _Cenodiscus_, without radial marginal spines; it can be derived from _Cenosphæra_ in the most simple way, by flattening in one axis. If on the equatorial margin of the lens a peculiar solid girdle be developed, we obtain _Zonodiscus_; in all other genera of the Cenodiscida radial spines are developed on the margin. As the simple lenticular cortical shell of _Cenodiscus_, in which the central capsule is enclosed, is most characteristic not only of this family, but also of the two following families, we call it the phacoid shell (that is, a lenticular extracapsular or cortical lattice-shell).

The #Phacodiscida# (Pls. 31-35), the second family, have the same extracapsular "phacoid shell" as the Cenodiscida, but differ from these by the possession of one or two intracapsular concentric medullary shells, which are connected with the former by radial beams, perforating the lenticular central capsule. The radial beams are commonly numerous, and arranged in two opposite bunches around the shortened main axis. But often also besides these occur other longer radial beams, situated in the equatorial plane; the number of these is commonly four, and they form a regular rectangular cross, lying opposite in pairs in two equatorial diameters, perpendicular one to another. In the simplest genera of this family (the _Sethodiscida_) the equatorial margin of the phacoid shell is simple or surrounded by a solid smooth girdle; in all other genera are developed on the margin solid radial spines lying in the equatorial plane, either regularly disposed in a somewhat constant number (two to eight, _Heliosestrida_), or irregularly disposed, in a larger and more variable number (ten to twenty or more, _Heliodiscida_).

The #Coccodiscida# (Pls. 36-38) form a third family of the #Discoidea#, directly associated with the Phacodiscida; both have the same characteristic extracapsular "phacoid shell," which is connected by radial beams with a simple or double, intracapsular medullary shell. But whilst in the foregoing family the equatorial margin of the phacoid shell is simple or only armed with radial spines, in the Coccodiscida it is surrounded by peculiar concentric chambered girdles, or rings, which resemble those of the following family, the Porodiscida. Each of these "chambered girdles" is composed of a circular ring in the equatorial plane, a variable number of radial beams dividing it into incomplete chambers, and two porous cover-plates or "sieve-plates," covering the upper and lower face of the disk. These sieve-plates may be regarded as incomplete lenticular cortical shells, which are only developed in the peripheral part of the disk, whilst their central part is represented by the only complete cortical shell, the "phacoid shell." The number of these concentric chamber-girdles amounts to from one to ten or more. The margin of the disk is either simple (Lithocyclida) or armed with radial spines (Stylocyclida), or provided with two to five chambered radial arms (Astracturida); the structure of the arms is the same as that of the girdles.

{405}The #Porodiscida# (Pls. 41-47), the largest family of all #Discoidea#, begins the series of #Cyclodiscaria#, or those #Discoidea# in which there is no "phacoid shell," but a small simple central chamber surrounded by a number of small latticed chambers of nearly the same size and form. In the Porodiscida these chambers are arranged in complete circular concentric rings or spiral convolutions; in the small family of Pylodiscida the central chamber is surrounded by three radial arm-chambers separated by three open spaces; in the third family of #Cyclodiscaria#, the Spongodiscida, all the chambers are arranged more or less irregularly, and the whole disk becomes spongy; also the surface of the disk is spongy, whilst in both former families it is covered by two regular even porous plates or "sieve-plates." Probably all #Cyclodiscaria# can be derived phylogenetically from _Archidiscus_, a very small and simple lenticular disk, which is composed of a small spherical latticed central chamber and of a single concentric chambered ring or girdle; the margin of this ring is connected with the central chamber by a variable number of radial beams. This _Archidiscus_ can be derived either from _Saturnalis_ (Pl. 13, fig. 16.) by the development of lattice-work between the equatorial ring and both polar faces of the concentric central chamber, or from _Sethodiscus_ (Pl. 33, figs. 1-3) by flattening of the lenticular shell, so that the enclosed inner medullary shell (the central chamber) meets the outer phacoid shell at both poles.

The Porodiscida are commonly flat or biconvex (rarely biconcave) disks, the central chamber of which is surrounded not by a single, but by a variable number (commonly three to six) of concentric chambered girdles or rings; they arise from _Archidiscus_ by apposition of new concentric chambered rings around the first ring, all lying in the equatorial plane. Afterwards the disk often becomes thickened by apposition of concentric chamber-rings on both flat sides also, so that two to four or more layers are stratified one over the other. The circular concentric rings often become interrupted, or spirally convoluted (wholly or partially); also the chambers sometimes become irregularly crowded. But in all cases both surfaces of the disk (upper and lower) continue to be porous plates or sieve-plates, at least in the centre, but they never become spongy.

The margin of the disk exhibits in the Porodiscida a great variety of different forms, serving for distinction of subfamilies and of genera. In the Trematodiscida the margin remains quite simple, as in the Archidiscida, or is only surrounded by a hyaline equatorial girdle. In the Ommatodiscida it is distinguished by one or two peculiar oscula, surrounded by a corona of spines. The Stylodictyida are distinguished by a number of solid radial spines, and the Euchitonida by a number of chambered, or spongy, radial arms, arising from the margin of the disk and lying in the equatorial plane. The variety of these radial marginal appendages is in the Porodiscida much greater than in the Coccodiscida.

The #Pylodiscida# (Pl. 48, figs. 12-20) represent a new, small, but very remarkable family of #Discoidea#, all triradial, and distinguished by the peculiar formation of {406}large open spaces in the latticed discoidal shell, which reappear in a similar shape among the #Larcoidea# in the Pylonida (_Tetrapyle_, &c.). We get the best understanding of this peculiar formation if we return to _Archidiscus_, probably the common ancestral form of all #Cyclodiscaria#, of the Porodiscida as well as of the Pylodiscida and Spongodiscida. In some species of _Archidiscus_ (_Archidiscus hexoniscus_, _Archidiscus pyloniscus_, &c.) the small lenticular shell is composed of a spherical latticed central chamber and of a concentric equatorial girdle composed of six such chambers, either all six equal, or alternately larger and smaller. This latter form is nearly identical with _Triodiscus_, and if we imagine the lattice-work of only three ring-chambers complete, whilst that of the three alternating chambers is reduced to the marginal ring, we get _Triopyle_, by loss of this ring _Triolene_ (a disk composed of four simple lattice-chambers, lying in one plane, three radial around one central spherule). The genera mentioned form together the subfamily of Triopylida. In the second subfamily, Hexapylida, the same formation is doubled; here three double arm-chambers are separated by three double spaces (two in each radius). Also here the three distal spaces may be either quite open (_Pylolena_), or half closed by the marginal girdle (_Hexapyle_), or quite loosely latticed (_Pylodiscus_). If the margin of this latter form become surrounded by a perfect chambered equatorial girdle, we get _Discozonium_, and if this acquire a peculiar marginal ostium (surrounded by a corona of spines) we arrive at _Discopyle_. These two latter genera form the third subfamily, the Discopylida. The eight genera of Pylodiscida represent therefore a continuous phylogenetic series.

The #Spongodiscida# are the sixth and last family of the #Discoidea#, differing from the five other families in the irregular, spongy structure of the discoidal skeleton; both surfaces of the flat disk (upper and lower) are here principally covered with a rough, spongy framework, whilst in the five other families they are covered by the flat and smooth porous plates or sieve-plates. Nevertheless there is no sharp boundary between the Spongodiscida and the closely allied Porodiscida. In these latter also the discoidal shell becomes often more or less spongy (mainly in the peripheral part, _e.g._, in _Myelastrum_, Pl. 47); but at least the central part of the disk here remains constantly covered by sieve-plates. The massive skeleton of the Spongodiscida is either of perfectly irregular structure, only composed of innumerable fine branched siliceous threads, interwoven in all possible directions; or only the outer part of the disk is composed of such spongy framework, whilst the central part is more or less distinctly composed of concentric chambered rings, as in the Porodiscida. These latter forms indeed exhibit an immediate transition to this family, and were formerly (in 1862) separated by me as Spongocyclida. Also the polymorphous shape of the disk margin in the Spongodiscida is quite analogous to that of the Porodiscida. Whilst in the first subfamily, the Spongophacida, the margin is quite simple; in the second, the Spongotrochida, it is armed with solid radial spines; and in the third, the Spongobrachida, it is provided with two, three, {407}or four spongy, radial arms--the former as well as the latter lying in the equatorial plane of the disk, either regularly or irregularly disposed.

_The Equatorial Margin_ of the lenticular disk exhibits in all six families of #Discoidea# similar characters, mainly serving for the distinction of subfamilies and genera. In the most primitive genera of all six families the margin is simple, without radial prolongations (spines or arms); it is quite simple in _Cenodiscus_, _Sethodiscus_, _Phacodiscus_, _Lithocyclia_, _Coccodiscus_, _Archidiscus_, _Porodiscus_, _Pylodiscus_, and _Spongodiscus_. In some genera the simple margin of the lenticular disk is bordered and surrounded by a thin, hyaline, equatorial girdle of silex, either quite solid or slightly porous (_Zonodiscus_, _Periphæna_, _Perizona_, _Perichlamydium_, and _Spongophacus_).

A quite peculiar and remarkable character of few genera is the development of one or two oscula, larger marginal openings, which are surrounded by a corona of spines, and probable are fit for the issue a peculiar bunch of pseudopodia or of a "sarcode flagellum." Such oscula occur only in two families of #Cyclodiscaria#; in the Porodiscida and Pylodiscida; in the former _Ommatodiscus_, in the latter _Discopyle_ (Pl. 48, figs. 19, 20) is distinguished by a single marginal osculum; besides this, in the former occurs _Stomatodiscus_, with two such oscula, opposite on the poles of one axis (Pl. 48, fig. 8). These oscula may be compared with the similar polar formations in some Ellipsida (_Lithomespilus_) and in many Cyrtoidea; but they do not prove a nearer affinity with the latter, and are only analogous, not homologous.

_Radial Spines_ occur on the margin in the equatorial plane of the #Discoidea# in the greatest variety of number, form, size, and disposition. If the number be low (between two and eight) they are commonly regularly disposed; if the number be larger (ten to twenty or more) their disposition becomes commonly more or less irregular. The regular disposition is of great promorphological importance, as indicating the axes in which the growth is preponderant, and introduces other peculiar radial formations. Regarding these axes we can generally distinguish two groups, _Artiacantha_ with a paired number (two, four, eight), and _Perissacantha_ with odd numbers (usually three). The section of _Artiacantha_ could be divided into three following groups:--A. Stylodiscida, with two radial spines only, lying opposite on both poles of one equatorial axis (the "first cross axis")--_Stylodiscus_, _Sethostylus_, _Stylocyclia_, _Xiphodictya_, _Spongolonche_ (Pl. 31, figs. 9-12; Pl. 38, fig. 1; Pl. 42, figs. 10-12, &c.); B. Staurodiscida, with four radial spines, lying opposite in pairs on the poles of two crossed equatorial axes, perpendicular to one another (first and second cross axes)--_Crucidiscus_, _Sethostaurus_, _Staurocyclia_, _Staurodictya_, _Spongostaurus_ (Pl. 31, figs. 1-8; Pl. 37, figs. 1-4; Pl. 42, figs. 1-6; Pl. 48, fig. 2, &c.); C. Octostylida, with eight radial spines, opposite in pairs in four axes, which are crossed at angles of 45°--_Heliosestrum_, _Astrosestrum_, &c. (Pl. 32, figs. 4, 5; Pl. 34, figs. 3, 6); in this latter case sometimes the radial symmetry is the same as in many Medusæ, four larger (perradial) {408}spines alternating with four smaller (interradial), indicating radii of first and second order. The section of _Perissacantha_ is much smaller, and commonly represented only by triradial forms, with three spines at equal distances (120°)--_Triactis_, _Tripocyclia_, _Tripodictya_, _Spongotripus_, &c. (Pl. 33, fig. 6; Pl. 37, fig. 5; Pl. 42, figs. 7-9).

_Radial Arms_ on the margin of the disk appear in similar variety of number, form, and disposition as the radial spines; but the number is here commonly limited to from two to four, rarely five to six. The arms are absent in the families Cenodiscida and Phacodiscida; in the four other families they return under similar forms. These arms are direct prolongations of the disk, and exhibit the same structure, so that they may be regarded both as centrifugal productions of certain radii, and also inversely as peripheral parts of a disk, the interjacent radii of which are reduced. The regular disposition and shape of the arms, an important character for the distinction of genera and species, is repeated in a quite analogous manner in the four above mentioned families, so that we can distinguish the following groups--A. Amphibrachida, with two radial arms, opposite on the poles of one equatorial axis (the first cross axis)--_Diplactura_, _Amphibrachium_, _Spongobrachium_ (Pl. 38, figs. 3-5; Pl. 44, figs. 6-11); B. Triobrachida, with three radial arms; the most important group (with all Pylodiscida); either all three arms are equal and disposed at equal distances (_Trigonactura_, _Dictyastrum_, _Rhopalodictyum_, Pl. 38, figs. 6-9; Pl. 43, figs. 5, 13, 16; Pl. 48, figs. 12-19), or a single odd arm differs in size and position, and is often larger than both the opposite paired arms (_Rhopalastrum_, _Euchitonia_, Pl. 43, figs. 6, 10, 15, &c.); C. Tetrabrachida, with four radial arms, opposite in pairs in two crossed axes, commonly perpendicular one to another, _Stauractura_, _Stauralastrum_, _Spongaster_, &c. (Pls. 46, 47).

The arms are commonly simple, undivided, but sometimes also forked or branched (Pl. 43, figs. 15, 16; Pl. 47). Their basal parts are either free, separately inserted into the margin of the circular central disk, or they are connected by a "patagium," a peculiar connecticulum, like a web-membrane, which is composed of a chambered, commonly more or less spongy framework, different in texture from the lattice-work of the arms (Pl. 38, figs. 8, 9; Pl. 43, figs. 9-16; Pl. 46). Sometimes the patagium overgrows the whole shell. A peculiar modification of it appears in _Stephanastrum_ (Pl. 44, fig. 1), where only the distal parts of the arms are connected by the ring-shaped patagium, whilst the basal parts are free; therefore open gates rest between them, like those of the Pylodiscida (Pl. 48, figs. 12-20).

The _Central Capsule_ of the #Discoidea# is constantly discoidal, more or less lenticular; in some cases more biconvex, with vaulted faces and thin margin; in others more medal-shaped, with flat faces and thick margin. In the Cenodiscida alone the capsule lies freely inside the simple phacoid shell, and is separated from it by the jelly-veil. In the other five families the capsule encloses the central parts of the skeleton, and is enveloped by the superficial parts of it, whilst its membrane is perforated by radial beams {409}connecting the latter with the former. In the Phacodiscida and Coccodiscida the capsule encloses the simple or double medullary shell, but is itself enclosed by the cortical phacoid shell. In all #Cyclodiscaria# (in the Porodiscida, Pylodiscida, and Spongodiscida) the capsule fills out the greatest part of the chambered or spongy skeleton, and is only protected by the superficial parts of it, in the Porodiscida and Pylodiscida by the covering sieve-plates, in the Spongodiscida by the spongy cortical substance of the shell. The growth of the capsule corresponds to that of the including shell, gradually increasing on the margin in the equatorial plane. Whilst in the greater number of #Discoidea# its form continues circular, in many forms provided with radial arms it enters into the arms and assumes their form. The protoplasm of the capsule is commonly coloured by brown or red pigment, and often contains many oil-globules. The nucleus is originally enclosed by the medullary shell or the central chamber, and with increasing size enters into the surrounding parts; in the #Cyclodiscaria# it often fills out the internal concentric rings. The extracapsular jelly or the calymma is commonly thick, and envelops the greater part or the whole body.

_Synopsis of the Families of the_ #Discoidea#.

------------------------------------------------------------------------- I. Section #Phacodiscaria#. Discoidea with external phacoid shell (or lenticular latticed cortical shell). ------------------------------------------------------------------------- Phacoid shell simple, without enclosed 1. CENODISCIDA. medullary shell

Phacoid shell with { Margin without simple or { chambered girdles, 2. PHACODISCIDA. double { enclosed { Margin surrounded by medullary shell. { by chambered { girdles. 3. COCCODISCIDA. ------------------------------------------------------------------------- II. Section #Cyclodiscaria#. Discoidea without external phacoid shell (no lenticular latticed cortical shell). ------------------------------------------------------------------------- Surface of the { Concentric rings around shell covered { the central chamber by convex or { complete (without even porous { open spaces), 4. PORODISCIDA. sieve-plates { (not spongy). { Concentric rings around { the central chamber { interrupted by three { open spaces, 5. PYLODISCIDA.

Surface of the shell spongy, not covered by peculiar porous sieve-plates, 6. SPONGODISCIDA.

Family XVIII. #CENODISCIDA#, n. fam. (Pl. 31, fig. 11; Pl. 48, figs. 1-3).

_Definition._--#Discoidea# with simple extracapsular phacoid shell (or lenticular latticed cortical shell), without medullary shell and without chambered equatorial girdles.

The new family #Cenodiscida# opens the long series #Discoidea#, as their most simple and primitive form. The circular lenticular central capsule is enclosed by a {410}simple latticed shell of the same form, only separated from it by a thinner or thicker jelly-veil. The lenticular or discoidal fenestrated shell is therefore an extracapsular or "cortical shell," without an enclosed medullary shell.

The few genera of the Cenodiscida differ only in the shape of the equatorial margin of the lenticular disk. In the first subfamily, Zonodiscida, the margin is either quite simple (_Cenodiscus_) or surrounded by a smooth, solid equatorial girdle (_Zonodiscus_). In the second subfamily, Trochodiscida, the margin is armed with solid radial spines, lying in the equatorial plane. According to the number and disposition of these marginal spines, we distinguish _Stylodiscus_ (with two spines, opposite in one equatorial axis), _Crucidiscus_ (with four spines, opposite in pairs in two equatorial axes, perpendicular one to another), _Theodiscus_ (with three marginal spines), and _Trochodiscus_ (with numerous, commonly twenty to thirty, irregularly disposed spines). The spines are constantly simple, not branched; sometimes more conical or cylindrical, at other times more angular or pyramidal.

The two convex faces of the lenticular shell are constantly of similar shape, commonly smooth, sometimes more or less thorny, or armed with bristle-shaped radial spines. The pores are commonly more or less regular, circular, and disposed in series, which are occasionally more radial, at other times more concentric. If the wall of the hollow lens be rather thick, the difference in the shape of the central and peripheral pores is often striking. The central pores perforating the thick wall perpendicularly are short cylindrical tubes; the marginal pores perforating it in an oblique direction are longer conical tubes. The bars between the central pores are often somewhat smaller.

_The Central Capsule_ of the Cenodiscida is in all cases a perfect, circular, biconvex lens, the equatorial diameter of which is commonly between two-thirds and three-fourths of the enclosing lattice-shell. The interval between the two is filled up by the jelly-veil, or the hyaline "calymma," which is perforated by the numerous pseudopodia that pass through the shell-pores.

As the Cenodiscida possess the most simple shell-form of all #Discoidea#, we may regard _Cenodiscus_ as the common ancestral form of this large section, in the same manner as _Cenosphæra_ is the ancestral form of #Sphæroidea#, _Cenellipsis_ of the Prunoidea, Cenolarcus of the Larcoidea. But it is also possible that a part of Cenodiscida (or all?) arises from the Phacodiscida by reduction and loss of the medullary shell. For in some cases we find arising from the inside of the shell centripetal radial beams, which end at a certain equal distance from the hollow centre (Pl. 31, fig. 11; Pl. 38, fig. 2). Cenodiscus itself can be derived either from _Cenosphæra_ by compression of the spheroidal shell in one axis, or from _Sethodiscus_ by loss of the intracapsular medullary shell, or from _Actidiscus_ (the lenticular Actissa) by formation of a cortical shell around the lenticular central capsule.

{411}_Synopsis of the Genera of the Cenodiscida._

I. Subfamily {Margin quite simple, Zonodiscida. { without equatorial girdle, 175. _Cenodiscus_. Margin of the disk { without radial {Margin surrounded by a solid spines. { siliceous equatorial girdle, 176. _Zonodiscus_.

II. Subfamily {Two spines opposite in one Trochodiscida. { equatorial axis, 177. _Stylodiscus_. Margin of the disk { armed with radial {Three spines on the margin of spines (lying in { the disk, 178. _Theodiscus_. the equatorial { plane). {Four spines opposite in pairs { in two perpendicularly { crossed equatorial axes, 179. _Crucidiscus_. { {Ten to twenty or more radial { spines (variable in number { and commonly irregular { in disposition), 180. _Trochodiscus_.

Subfamily 1. ZONODISCIDA, Haeckel.

_Definition._--#Cenodiscida# without radial spines on the margin of the disk.

Genus 175. _Cenodiscus_,[214] n. gen.

_Definition._--#Cenodiscida# with simple margin of the circular disk, without surrounding equatorial girdle and without radial spines.

The genus _Cenodiscus_ is the most simple and primitive form of all #Discoidea#, and represents possibly the common ancestral form of this order. The latticed shell is a simple biconvex lens, and encloses a smaller central capsule of the same form, separated from it by the jelly-veil. _Cenodiscus_ can be derived phylogenetically either from _Cenosphæra_ by lenticular flattening of a simple latticed sphere, or directly from _Actissa_ by formation of a lenticular fenestrated shell around the lentiform central capsule. Possibly also some forms of _Cenodiscus_ can be derived from _Sethodiscus_ by reduction and loss of the medullary shell.

1. _Cenodiscus phacoides_, n. sp. (Pl. 48, figs. 1, 1_a_).

Disk with smooth surface, without radial ribs or spines. Margin of the lenticular biconvex disk thin, simple. Pores regular, circular; fifteen to sixteen on the radius of the disk. (Very similar to _Sethodiscus phacoides_, but without medullary shell.)

_Dimensions._--Diameter of the disk 0.2, of the pores 0.005.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

{412}2. _Cenodiscus rotula_, n. sp.

Disk with smooth surface, without medial ribs or spines. Margin of the disk blunt, very thick, rounded; both faces little convex. Pores regular, circular; thirteen to fourteen on the radius of the disk. (Similar to _Phacodiscus rotula_, Pl. 35, fig. 7, but without medullary shell.)

_Dimensions._--Diameter of the disk 0.16, of the pores 0.006.

_Habitat._--North Pacific, Station 241, depth 2300 fathoms.

3. _Cenodiscus lenticula_, n. sp.

Disk with thorny surface, scattered with small, conical spines. Margin of the lenticular biconvex disk thin. Pores irregular, roundish; ten to eleven on the radius of the disk.

_Dimensions._--Diameter of the disk 0.15, of the pores 0.008.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

Genus 176. _Zonodiscus_,[215] n. gen.

_Definition._--#Cenodiscida# with surrounding solid equatorial girdle on the margin of the lenticular disk, without radial spines.

The genus _Zonodiscus_ differs from the preceding _Cenodiscus_ only in the development of a solid siliceous girdle around the keen margin of the lenticular disk. This form can also be derived from _Periphæna_ or _Perizona_ by reduction and loss of the medullary shell. The same girdle formation returns not only in both these Phacodiscida (Pl. 32, fig. 7; Pl. 33, fig. 4), but also in the Porodiscid _Perichlamydium_.

1. _Zonodiscus saturnalis_, n. sp.

Disk with smooth surface, without radial spines. Pores regular, circular, fifteen to sixteen on the radius of the disk, in its distal half arranged in fifty to sixty radial series, which are separated by prominent radial crests or ribs. The crests are prolonged into the proximal half of the thin solid equatorial girdle, which is one-third as broad as the radius of the disk.

_Dimensions._--Diameter of the disk 0.25, of the pores 0.05.

_Habitat._--South Atlantic, Station 335, depth 1425 fathoms.

Subfamily 2. TROCHODISCIDA, Haeckel.

_Definition._--#Cenodiscida# with radial spines on the margin of the disk, disposed in the equatorial plane.

Genus 177. _Stylodiscus_,[216] n. gen.

_Definition._--#Cenodiscida# with two radial spines on the margin of the disk, opposite in one equatorial axis.

{413}The genus _Stylodiscus_ opens the series of the Trochodiscida or of those Cenodiscida in which the thin margin of the hollow lenticular disk is armed with a number of solid radial spines, situated in its equatorial plane. _Stylodiscus_ is at the same time the most simple form of the Stylodiscida, or of the numerous #Discoidea# (belonging to different families) in which the disk bears only two spines, opposite in one equatorial axis. Hitherto only two species of this genus have been observed, but they seem to represent two different subgenera.

Subgenus 1. _Stylentodiscus_, Haeckel.

_Definition._--Internal cavity of the shell with centripetal axial rods.

1. _Stylodiscus endostylus_, n. sp. (Pl. 31, fig. 11).

_Sethostylus endostylus_, Haeckel, 1881, Prodromus et Atlas (pl. xxxi, fig. 11).

Disk with smooth surface and dentated margin. Pores irregular, roundish; ten to twelve on the radius of the disk. Marginal teeth conical, short, irregular. Both opposite polar spines cylindrical, longer than the diameter of the disk, and as broad as one larger pore. On the inside of the hollow disk both spines are prolonged into two strong centripetal axial rods, which do not reach the centre. Also a number of smaller centripetal axial rods surrounds the central cavity, so that an original medullary shell (_Sethostylus_) seems to have been lost (comp. above, p. 410).

_Dimensions._--Diameter of the disk 0.25, of the pores 0.005 to 0.02; length of the polar spines 0.3 and more, thickness 0.012.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

Subgenus 2. _Stylexodiscus_, Haeckel.

_Definition._--Internal cavity of the shell without axial rods.

2. _Stylodiscus amphistylus_, n. sp.

Disk with smooth surface and smooth margin. Pores regular, circular; eight to nine on the radius of the disk. Both opposite polar spines pyramidal, sulcated, about as long as the radius of the disk, and three times as long as broad at the base. Inner cavity of the disk simple, without centripetal rods.

_Dimensions._--Diameter of the disk 0.15, of the pores 0.007; length of the polar spines 0.08, basal breadth 0.03.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

{414}Genus 178. _Theodiscus_,[217] n. gen.

_Definition._--#Cenodiscida# with three radial spines on the margin of the disk, placed in its equatorial plane.

The genus _Theodiscus_ is the most simple form of those very numerous #Discoidea# in which three rays are developed on the margin of the disk; a symbol of the Christian dogma of the Trinity. Commonly the three angles between the three spines are equal, more rarely one angle is larger than the two others which are equal. The shell of some species is nearly spherical (formerly separated by me as _Theosphæra_), whilst in others it is a flattened biconvex lens.

Subgenus 1. _Theodiscoma_, Haeckel.

_Definition._--Angles between the three radial spines equal (triangle equilateral).

1. _Theodiscus divinus_, n. sp.

Disk nearly spherical, with smooth surface. Pores regular, circular, hexagonally framed; seven to eight on the radius. Three angles between the spines equal. Spines prismatic, straight, twice as broad as one pore, eight to eleven times as long as the shell diameter.

_Dimensions._--Diameter of the disk 0.1, of the pores 0.006; length of the spines 0.8 to 1.1, breadth 0.01.

_Habitat._--Central Pacific, Station 265, surface.

2. _Theodiscus christianus_, n. sp.

Disk nearly spherical, with smooth surface. Pores regular, circular, prolonged into short cylindrical, prominent tubuli, half as high as broad; eight to nine on the radius. Three angles between the spines equal. Spines prismatic, straight, twice as broad as one pore, twelve to fifteen times as long as the shell diameter.

_Dimensions._--Diameter of the disk 0.08, of the pores 0.005; length of the spines 1.1 to 1.2, breadth 0.01.

_Habitat._--Central Pacific, Station 271, surface.

3. _Theodiscus trinitatis_, n. sp.

Disk a rather flattened, biconvex lens, about twice as broad as thick. Pores regular, circular, not prolonged into tubuli; five to six on the radius. Three angles between the spines equal. Spines pyramidal, three times as broad as one pore, about twice as long as the shell diameter.

{415}_Dimensions._--Diameter of the disk 0.06, of the pores 0.007; length of the spine 0.12, basal breadth 0.02.

_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.

Subgenus 2. _Theodiscura_, Haeckel.

_Definition._--Angles between the three radial spines unequal, two paired angles equal, larger or smaller than the odd angle (triangle isosceles).

4. _Theodiscus vanitatis_, n. sp.

Disk nearly spherical, with smooth surface. Pores irregular, roundish; eight to ten on the radius. Three angles between the spines unequal; one odd angle larger than both others. Spines pyramidal, of unequal size; one odd spine larger, both others smaller than the shell diameter.

_Dimensions._--Diameter of the disk 0.12, pores 0.004 to 0.006; length of the odd spine 0.2, of the paired spines 0.1.

_Habitat._--South Atlantic, Station 335, depth 1425 fathoms.

5. _Theodiscus nirvana_, n. sp.

Disk a flat biconvex lens, about twice as broad as thick. Pores regular, circular; ten to twelve on the radius. Three angles between the spines unequal; one odd angle smaller than both others. Spines prismatic, very long and thin, twice as broad as one pore, ten to twelve times as long as the shell diameter.

_Dimensions._--Diameter of the disk 0.1, pores 0.005; length of the spines 1 to 1.2 or more, breadth 0.01.

_Habitat._--Indian Ocean, Ceylon, surface, Haeckel.

Genus 179. _Crucidiscus_,[218] n. gen.

_Definition._--#Cenodiscida# with four radial spines on the margin of the disk, crossed in the equatorial plane.

The genus _Crucidiscus_ is the most simple form of the Staurodiscida, or of the numerous #Discoidea# (belonging to different families) in which the margin of the disk bears four radial spines, lying in the equatorial plane, and crossed at right angles. Whilst commonly the internal shell-cavity of _Crucidiscus_ is quite simple, in one case it bears four centripetal axial rods, as inner prolongations of the outer radial cross-spines, perhaps indications of a lost medullary shell (comp. p. 410).

{416}Subgenus 1. _Staurentodiscus_, Haeckel.

_Definition._--Internal cavity of the shell with centripetal axial rods.

1. _Crucidiscus endostaurus_, n. sp. (Pl. 48, fig. 2).

Disk with smooth surface and smooth simple margin. Pores regular, circular; thirteen to fourteen on the radius of the disk. Four crossed spines conical, strong, longer than the radius of the disk, on the inside prolonged into four thinner centripetal axial rods, which do not reach the centre. In the middle part of the disk also some other short axial rods arise from the inside, not reaching the centre (as in _Stylodiscus endostylus_, Pl. 31, fig. 11).

_Dimensions._--Diameter of the disk 0.16, of the pores 0.004; length of the spines 0.2, breadth 0.014.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

Subgenus 2. _Staurexodiscus_, Haeckel.

_Definition._--Internal cavity of the shell without centripetal axial rods.

2. _Crucidiscus cuspidatus_, n. sp.

Disk with smooth surface and simple smooth margin. Pores regular, circular; seven to eight on the radius of the disk. Four crossed spines pyramidal, with prominent edges, somewhat shorter than the radius of the disk, twice as broad at their thick base as one pore. No internal axial rods in the shell cavity.

_Dimensions._--Diameter of the disk 0.12, of the pores 0.005; length of the spines 0.05, basal breadth 0.025.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

3. _Crucidiscus echinatus_, n. sp.

Disk with thorny surface and thorny margin. Pores regular, circular, six to seven on the radius. Four crossed spines pyramidal (four sided?), about as long as the radius of the disk, as broad at their base as one pore. No internal axial rods. Spines of the surface short, conical.

_Dimensions._--Diameter of the disk 0.14, of the pores 0.008; length of the spines 0.08, basal breadth 0.02.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

4. _Crucidiscus cruciatus_, n. sp.

Disk with smooth surface and broad dentated margin. Pores regular, circular; eleven to twelve on the radius. Four crossed spines pyramidal, sulcated, about as long as the radius of the disk, as {417}broad at their base as the radiated margin, which bears fifty to sixty triangular pointed teeth of irregular size. (Similar to _Sethostaurus cruciatus_, Pl. 31, fig. 5, but without internal axial rods and medullary shell.)

_Dimensions._--Diameter of the disk 0.2, of the pores 0.007; length of the spines 0.1, basal breadth 0.02.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

Genus 180. _Trochodiscus_,[219] n. gen.

_Definition._--#Cenodiscida# with numerous (ten to twenty or more) radial spines on the margin of the disk, situated in its equatorial plane.

The genus _Trochodiscus_ bears on the thin margin of the latticed disk a variable number of radial spines (commonly ten to twenty, sometimes fifty to eighty or more). Their size and disposition are commonly more or less irregular. For the most part all the marginal spines lie in the equatorial plane; but sometimes part of them are crowded into two or four parallel girdles. Several species of this genus are very similar to some species of _Heliodiscus_, and only differ in the absence of the medullary shell, perhaps in consequence of the phylogenetic loss of it; if this be the case, the former are to be derived from the latter (compare p. 410).

Subgenus 1. _Trochodisculus_, Haeckel.

_Definition._--Bases of the marginal spines free, not connected by a solid equatorial girdle.

1. _Trochodiscus cenophacus_, n. sp.

Disk with smooth surface. Pores regular, circular; eleven to twelve on the radius. Marginal spines sixteen to twenty, conical, of irregular size and disposition, about three times as long as broad, and as long as the radius of the disk.

_Dimensions._--Diameter of the disk 0.15, of the pores 0.006; length of the spines 0.06 to 0.09, basal breadth 0.02 to 0.03.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

2. _Trochodiscus medusinus_, n. sp.

Disk with smooth surface. Pores regular, circular; nine to ten on the radius. Marginal spines ten to twelve, equilateral triangular, deeply sulcated, about half as long and broad as the radius of the disk. (Very similar to _Heliosestrum medusinum_, Pl. 34, fig. 6, but without enclosed medullary shell. Compare p. 410.)

_Dimensions._--Diameter of the disk 0.2, of the pores 0.01; length of the spines 0.05, basal breadth 0.05.

_Habitat._--North Pacific, Station 241, depth 2300 fathoms.

{418}3. _Trochodiscus odontotrochus_, n. sp.

Disk with smooth surface, in the distal part radially sulcated. Pores irregular, roundish; twelve to fourteen on the radius. Marginal spines very short and numerous (thirty to forty), conical, scarcely one-fourth as long as the radius of the disk, which resembles a wheel with marginal teeth.

_Dimensions._--Diameter of the disk 0.18, of the pores 0.004; length of the spines 0.02, basal breadth 0.01.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

4. _Trochodiscus solaris_, n. sp.

Disk with smooth surface. Pores subregular, circular; eight to nine on the radius. Marginal spines very numerous (sixty to eighty), in two to four girdles densely crowded together, the largest as long as the diameter of the disk, bent and conical. (Similar to _Heliodiscus solaster_, Pl. 34, fig. 4, but without medullary shell.)

_Dimensions._--Diameter of the disk 0.15, of the pores 0.008; length of the spines 0.05 to 0.15, basal breadth 0.01.

_Habitat._--South Pacific, Station 300, depth 1375 fathoms.

5. _Trochodiscus echiniscus_, n. sp.

Disk with spiny surface. Pores irregular, roundish; ten to eleven on the radius. Marginal spines conical, very numerous (forty to fifty), irregular in size and disposition, the largest half as long as the radius of the disk. (Similar to _Heliodiscus echiniscus_, Pl. 34, fig. 5, but without medullary shell.)

_Dimensions._--Diameter of the disk 0.18, of the pores 0.005 to 0.015; length of the spines 0.02 to 0.04, basal breadth 0.01.

_Habitat._--North Atlantic, Færöe Channel, John Murray.

Subgenus 2. _Pristodiscus_, Haeckel.

_Definition._--Bases of the marginal spines connected by a solid siliceous equatorial girdle.

6. _Trochodiscus stellaris_, n. sp. (Pl. 48, fig. 3).

Disk with smooth surface. Pores subregular, circular; seven to eight on the radius. Marginal spines twelve to sixteen, triangular, of subregular size and disposition, about half as long as the radius of the disk, connected at their broad base by a solid equatorial girdle of half the breadth; girdle and spines radially striped.

_Dimensions._--Diameter of the disk 0.25, of the pores 0.015; length of the spines 0.04 to 0.06, basal breadth 0.02 to 0.04.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

{419}7. _Trochodiscus cingillum_, n. sp.

Disk with smooth surface, in the distal part radially sulcated. Pores regular, circular; twelve to thirteen on the radius. Marginal spines twenty to twenty-four, triangular, of equal size and at regular distances, only one-fourth as long as the radius of the disk, connected at their broad base by a solid equatorial girdle of the double breadth. (Similar to _Heliodiscus cingillum_, Pl. 33, fig. 7, but without medullary shell.)

_Dimensions._--Diameter of the disk 0.22, of the pores 0.004; length of the spines 0.02, basal breadth 0.02

_Habitat._--South Pacific, Station 285, depth 2375 fathoms.

Family XIX. #PHACODISCIDA#, Haeckel (Pls. 31-35).

_Phacodiscida_, Haeckel, 1881, Prodromus, p. 456.

_Definition._--#Discoidea# with simple extracapsular phacoid shell (or lenticular latticed cortical shell), connected by radial beams with an intracapsular, simple or double, concentric medullary shell, without chambered equatorial girdles.

The family #Phacodiscida# comprises a large number of splendid forms (about a hundred species), which agree with the preceding Cenodiscida in the possession of the characteristic extracapsular "phacoid shell," but differ from them in having one or two intracapsular "medullary shells"; these concentric spherical medullary shells are connected with the lenticular cortical shell or phacoid shell by means of radial beams perforating the central capsule. The Phacodiscida bear therefore the same relation to the Cenodiscida that the Disphærida and Trisphærida do to the Monosphærida.

Formerly several species belonging to the family were described by Ehrenberg and Johannes Müller, but not distinguished from the Sphæroidea, genus _Haliomma_ (_e.g._, _Haliomma sol_ et _Haliomma humboldtii_ of the former, _Haliomma amphidiscus_ of the latter). For these oldest known species I constituted in 1862 my genus _Heliodiscus_ (Monogr. d. Radiol., p. 436). Some other genera were afterwards (1875) figured by Ehrenberg as _Periphæna_ and _Chilomma_. The rich material of the Challenger revealed this family as very polymorphic and widely distributed, so that in my Prodromus (1881, p. 457) I could enumerate eighteen different genera of Phacodiscida. This number is here reduced to fifteen, uniting several of them into one genus as "subgenera."

_The Medullary Shell_ of the Phacodiscida, or the intracapsular latticed shell, is either simple and spherical, or double, composed of two concentric spheres, which are united by a variable number of radial beams. We could distinguish therefore as two subfamilies the Carpodiscida (with simple medullary shell) and the Thecodiscida (with double concentric medullary shell); the former corresponding to the Carposphærida (or _Dyosphæria_), the latter to the Thecosphærida (or _Triosphæria_). But as this difference seems not to be so important as the different shape of the disk margin, we prefer this latter as a character {420}for the separation of subfamilies. The form of the medullary shells is commonly quite spherical (as also in the above mentioned #Sphæroidea#); sometimes it is a little compressed in the same direction as the enclosing lenticular phacoid shell. The diameter of the latter is commonly three to four times as large as the diameter of the medullary shell; if this be double (in the Thecodiscida) then the diameter of the outer medullary shell is commonly three to four times as large as that of the inner. The radial beams connecting the two seem to be very variable in number and disposition (compare Pl. 31, fig. 8; Pl. 32, figs. 3, 4_a_, 7, 8_a_; Pl. 33, figs. 2, 3; Pl. 35, figs. 4, 8, 9, &c.).

_The Radial Beams_, which connect the medullary shell with the cortical or "phacoid shell," and which pierce the membrane of the lenticular central capsule, are commonly aggregated into two polar bunches around the shortened axis of the disk (compare Pl. 31, fig. 8; Pl. 32, figs. 3, 8; Pl. 33, figs. 2, 3, &c.). Their number seems to be usually between ten and thirty. More rarely piercing radial beams lie also in the equatorial plane, and then commonly as inner prolongations of the outer marginal spines; so we find two opposite in one axis, in _Heliostylus_ (Pl. 34, figs. 1, 2), or four opposite in pairs in two crossed axes, in _Phacostaurus_ (Pl. 31, figs. 1, 2, 7). Often the thickness of the beams increases from the centre towards the periphery.

_The Phacoid Shell_, or the lenticular extracapsular cortical shell, exhibits in the Phacodiscida quite the same general character as in the Cenodiscida, above described (p. 410). Commonly the equatorial diameter of the lens is twice to three times as large as the vertical diameter or the shortened "main axis." The convexity of both opposite faces is either quite even to the sharp margin (Pl. 31, fig. 2; Pl. 33, figs. 2, 5), or the central part of the lens is more strongly vaulted, and often the margin is thickened or truncated (Pl. 31, fig. 10; Pl. 35, fig. 7). The surface of the lens is commonly smooth, but sometimes also covered with bristle-shaped radial spines (Pl. 34, figs. 3, 5; Pl. 32, figs. 2, 3); rarely these spines are prolonged and branched (Pl. 35, figs. 3, 5). The pores of the phacoid shell are usually quite regular, circular, and regularly arranged, either in more concentric or in more radial rows; the latter are sometimes separated by radial crests arising towards the margin (Pl. 35, fig. 6). If the wall of the phacoid shell be much thickened, the pores in its central part are shorter and cylindrical, in its marginal part longer and conical (Pl. 31, fig. 7; Pl. 32, fig. 1).

_The Margin of the Lens_ of the Phacodiscida is very polymorphic, and serves mainly for the separation of genera. In the first subfamily, Sethodiscida, it is either quite simple (Pl. 35, figs. 6-8) or surrounded by a thin solid equatorial girdle, the basal part of which is often radially striped (Pl. 32, figs. 7, 8). In the second subfamily, Heliosestrida, we find on the margin a small number of radial spines in the equatorial plane regularly disposed, either two opposite in one axis (Pl. 31, figs. 9-12) or four opposite in pairs in two crossed axes (Pl. 31, figs. 1-8), or eight opposite in pairs in four axes, crossed at angles of 45° (Pl. 34, figs. 3, 6); in the latter case we can sometimes distinguish {421}(as in many Medusæ) four larger perradial spines alternating with four smaller interradial spines. Often in one and the same species occur abnormalities in number and disposition of the radial spines, three or five spines instead of four, or also seven or nine spines instead of eight; often both halves of the disk become asymmetrical. If the number of the marginal spines exceed eight to ten, they commonly become very variable in size and irregular in disposition; these variations characterise the third subfamily, Heliodiscida. Commonly also here all spines lie in the equatorial plane; but sometimes they become crowded in several parallel circles on both sides of the margin (Pl. 32, fig. 1). The form of the marginal spines is commonly conical or flattened triangular, often also pyramidal or deeply furrowed (Pl. 31, figs. 6-9). Very rarely the spines are fenestrated (Pl. 35, fig. 1); only in one genus (_Heliodrymus_) they are all or partly branched (Pl. 33, fig. 9; Pl. 35, figs. 3, 5).

The peculiar development of the phacoid shell has been already described by J. Müller (compare my Monograph, 1862, pp. 156, 438).

_The Central Capsule_ of the Phacodiscida is everywhere circular, lenticular, envelops the medullary shell, and is enclosed by the phacoid shell, perforated by the radial beams, which connect the latter to the former.

_Synopsis of the Genera of the Phacodiscida._

------------------------------------------------------------------------- I. Subfamily Sethodiscida. Margin of the disk without radial spines. ------------------------------------------------------------------------- Margin simple, without {Medullary shell simple, 181. _Sethodiscus_. equatorial girdle. { {Medullary shell double, 182. _Phacodiscus_.

Margin surrounded by a {Medullary shell simple, 183. _Periphæna_. hyaline equatorial girdle. { {Medullary shell double, 184. _Perizona_. ------------------------------------------------------------------------- II. Subfamily Heliosestrida. Margin of the disk with two to eight solid radial spines, usually quite regularly disposed. (Number usually constant.) ------------------------------------------------------------------------- Two radial spines {Medullary shell simple, 185. _Sethostylus_. (opposite in one axis). { {Medullary shell double, 186. _Phacostylus_.

Three radial spines. Medullary shell simple, 187. _Triactiscus_.

Four radial spines (in {Medullary shell simple, 188. _Sethostaurus_. cross form). { {Medullary shell double, 189. _Phacostaurus_.

Six radial spines. Medullary shell simple, 190. _Distriactis_.

Eight radial spines. {Medullary shell simple, 191. _Heliosestrum_. { {Medullary shell double, 192. _Astrosestrum_. ------------------------------------------------------------------------- III. Subfamily Heliodiscida. Margin of the disk with numerous (ten to twenty or more) radial spines, usually irregularly disposed. (Number variable.) ------------------------------------------------------------------------- Radial spines all simple, {Medullary shell simple, 193. _Heliodiscus_. not branched. { {Medullary shell double, 194. _Astrophacus_.

Radial spines all or }Medullary shell simple, 195. _Heliodrymus_. partly branched. }

{422}Subfamily 1. SETHODISCIDA, Haeckel, 1881, Prodromus, p. 457.

_Definition._--#Phacodiscida# without radial spines on the margin of the disk.

Genus 181. _Sethodiscus_,[220] Haeckel, 1881, Prodromus, p. 457.

_Definition._--#Phacodiscida# with simple medullary shell and simple margin of the circular disk, without surrounding equatorial girdle and without radial spines.

The genus _Sethodiscus_ is the most simple and primitive form of all Phacodiscida, and may be regarded as the common ancestral form of this family. The simple spherical medullary shell is connected by a variable number of radial beams with the lenticular or discoidal cortical shell (or "phacoid shell"). The margin of this latter is quite simple, circular, without solid equatorial girdle or radial spines. From the nearly allied genus _Carposphæra_ of the #Sphæroidea#, its probable ancestral form, _Sethodiscus_ can be derived simply by lenticular compression of the spheroidal cortical shell.

Subgenus 1. _Sethodiscinus_, Haeckel.

_Definition._--Surface of the disk smooth, without radial ribs or spines.

1. _Sethodiscus phacoides_, n. sp.

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; fourteen to fifteen on the radius of the disk. (Very similar to _Periphæna cincta_, Pl. 33, fig. 4, but without the girdle of the margin.)

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.07, of the pores 0.005.

_Habitat._--Pacific, central area, Stations 270 to 274, in various depths.

2. _Sethodiscus macroporus_, n. sp.

Disk with smooth surface, twice as broad as the medullary shell. Pores regular, circular, very large; five to six on the radius of the disk. (Remarkable for the extraordinary size of the pores, which reaches half the radius of the medullary shell.)

_Dimensions._--Diameter of the disk 0.1, of the medullary shell 0.05, of the pores 0.012.

_Habitat._--North Atlantic, Gulf Stream, Færöe Channel, John Murray.

3. _Sethodiscus microporus_, n. sp.

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular, very small; twenty-two to twenty-four on the radius of the disk. (The small pores are scarcely half as broad as the thick bars between them.)

{423}_Dimensions._--Diameter of the disk 0.25, of the medullary shell 0.06, of the pores 0.002.

_Habitat._--South Pacific, Station 288, surface.

4. _Sethodiscus lenticula_, n. sp. (Pl. 33, figs. 1, 2).

Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, polygonal; eight to nine on the radius of the disk. (The pores of the medullary shell, fig. 2, are also irregular, polygonal, or roundish.)

_Dimensions._--Diameter of the disk 0.17, of the medullary shell 0.04, of the pores 0.01.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

5. _Sethodiscus macrococcus_, n. sp. (Pl. 33, fig. 3).

Disk with smooth surface, two and a half times as broad as the medullary shell. Pores irregular, polygonal; eleven to twelve on the radius of the disk. (The pores of the medullary shell, fig. 3, are regular, circular, with elevated hexagonal frames between them. The figured specimen is a young one, both halves of the biconvex disk being not yet united in the equatorial plane.)

_Dimensions._--Diameter of the disk 0.16, of the medullary shell 0.065, of the pores 0.01.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

6. _Sethodiscus micrococcus_, n. sp.

Disk with smooth surface, five times as broad as the medullary shell. Pores irregular, roundish, very small; twenty-six to twenty-eight on the radius of the disk. (The pores of the small medullary shell are regularly circular, of the same size as those of the disk.)

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.04, of the pores 0.002.

_Habitat._--South Atlantic, Station 335, depth 1425 fathoms.

Subgenus 2. _Sethodisculus_, Haeckel.

_Definition._--Surface of the disk with elevated radial ribs or spines.

7. _Sethodiscus radiatus_, Haeckel.

_Haliomma radians_, Ehrenberg, 1854, Mikrogeol., Taf. xix. fig. 50.

_Haliomma radiatum_, Ehrenberg, 1854, Mikrogeol., Taf. xxi. fig. 54.

Disk with radiated surface, four times as broad as the medullary shell. Pores regularly circular; nine to ten on the radius of the disk, arranged in radial series (about forty), which are separated by smooth crests, not prominent on the smooth margin.

_Dimensions._--Diameter of the disk 0.12, of the medullary shell 0.03, of the pores 0.003.

_Habitat._--Fossil in Tertiary deposits of the Mediterranean, Greece, Sicily, Oran, &c.

{424}8. _Sethodiscus echinatus_, Haeckel.

_Haliomma echinatum_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxvii. fig. 2.

Disk with radiated thorny surface, three times as broad as the medullary shell. Pores regular, circular; eleven to twelve on the radius of the disk, arranged in radial series (about sixty), which are separated by thorny crests, prominent a little on the dentated margin.

_Dimensions._--Diameter of the disk 0.18, of the medullary shell 0.06, of the pores 0.01.

_Habitat._--Fossil in the rocks of Barbados.

9. _Sethodiscus cristatus_, n. sp.

Disk with radiated surface, four times as broad as the medullary shell. Pores regularly circular; sixteen to seventeen on the radius of the disk, arranged in radial series (about eighty), which are separated in the distal half by smooth elevated crests, strongly prominent on the dentated margin. (Very similar to _Phacodiscus cristatus_, Pl. 35, fig. 6, but with simple medullary shell.)

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05, of the pores 0.005.

_Habitat._--South Pacific, Station 285, depth 2375 fathoms.

Genus 182. _Phacodiscus_,[221] Haeckel, 1881, Prodromus, p. 457.

_Definition._--#Phacodiscida# with double medullary shell and simple margin of the circular disk, without surrounding equatorial girdle and without radial spines.

The genus _Phacodiscus_ differs from the ancestral genus _Sethodiscus_ only in the duplication of the medullary shell, and has therefore the same relation to it that _Thecosphæra_ in the #Sphæroidea# exhibits to _Carposphæra_. Both former discoidal genera differ from the two latter spheroidal by the lenticular flattening of the cortical shell.

Subgenus 1. _Phacodiscinus_, Haeckel.

_Definition._--Surface of the disk smooth, without radial ribs or spines.

1. _Phacodiscus rotula_, n. sp. (Pl. 35, fig. 7).

Disk with smooth surface, four and a half times as broad as the outer and fourteen times as broad as the inner medullary shell. Pores regularly circular; sixteen to eighteen on the radius of the disk. Margin of the lens very thick, truncated, nearly as broad as the outer medullary shell.

_Dimensions._--Diameter of the disk 0.21, of the outer medullary shell 0.045, of the inner 0.015; pores 0.008.

_Habitat._--North Pacific, Station 224, depth 1850 fathoms.

{425}2. _Phacodiscus lentiformis_, n. sp. (Pl. 35, fig. 8).

Disk with smooth surface, three and a half times as broad as the outer, and ten times as broad as the inner medullary shell. Pores regularly circular; twelve to thirteen on the radius of the disk. Margin of the disk sharp, as in a biconvex lens.

_Dimensions._--Diameter of the disk 0.25, of the outer medullary shell 0.07, of the inner 0.025; pores 0.01.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms; fossil in Barbados.

3. _Phacodiscus grandis_, n. sp.

Disk with thorny surface, five times as broad as the outer, and fifteen times as broad as the inner medullary shell. Pores regularly circular; twenty-two to twenty-four on the radius of the disk. Margin of the disk thick, rounded.

_Dimensions._--Diameter of the disk 0.45, of the outer medullary shell 0.09, of the inner 0.03; pores 0.01.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

Subgenus 2. _Phacodisculus_, Haeckel.

_Definition._--Surface of the disk with elevated radial ribs or spines.

4. _Phacodiscus echiniscus_, n. sp.

Disk with spiny surface, four times as broad as the outer, and ten times as broad as the inner medullary shell. Pores irregularly roundish; fourteen to fifteen on the radius of the disk. Margin of the disk sharp, as in a biconvex lens.

_Dimensions._--Diameter of the disk 0.3, of the outer medullary shell 0.75, of the inner 0.03; pores 0.007.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

5. _Phacodiscus clypeus_, n. sp. (Pl. 35, figs. 6, 9).

Disk with radiated surface, four times as broad as the outer, and twelve times as broad as the inner medullary shell. Pores regularly circular; sixteen to eighteen on the radius of the disk; in the distal half disposed in sixty to seventy radial series, which are separated by prominent crests; the sharp margin therefore a little jagged.

_Dimensions._--Diameter of the disk 0.2, of the outer medullary shell 0.05, of the inner 0.017; pores 0.006.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

{426}Genus 183. _Periphæna_,[222] Ehrenberg, 1873 Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 246.

_Definition._--#Phacodiscida# with simple medullary shell, without radial spines, but with a solid equatorial girdle around the margin of the lenticular disk.

The genus _Periphæna_, founded by Ehrenberg in 1873 for the fossil _Periphæna decora_ of Barbados, differs from its ancestral form _Sethodiscus_ in the development of a very thin siliceous solid girdle around the margin of the lenticular disk; this girdle lies in the equatorial plane of the shell, and reappears in similar form in _Perichlamydium_ among the Porodiscida, in _Spongophacus_ among the Spongodiscida, and in _Zonodiscus_ among the Cenodiscida.

1. _Periphæna cincta_, n. sp. (Pl. 33, fig. 4).

Disk with smooth surface, four times as broad as the medullary shell. Pores regularly circular; fourteen to sixteen on the radius of the disk. Girdle of the margin about half as broad as the radius of the medullary shell, in the distal half structureless, in the proximal half with seventy to eighty short radial ribs.

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05, of the pores 0.005.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

2. _Periphæna decora_, Ehrenberg.

_Periphæna decora_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 80, Taf. xxviii. fig. 6.

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; twenty to twenty-two on the radius of the disk, disposed in radial series. Girdle of the margin nearly as broad as the radius of the medullary shell, in the distal half structureless, in the proximal half with eighty to ninety short radial ribs.

_Dimensions._--Diameter of the disk 0.25, of the medullary shell 0.08, of the pores 0.06.

_Habitat._--Fossil in Barbados.

3. _Periphæna statoblastus_, n. sp.

Disk with smooth surface, five times as broad as the medullary shell. Pores regularly circular; twenty-four to twenty-six on the radius of the disk, disposed in radial series, those in the distal half of the disk being separated by piercing radial beams. Girdle of the margin twice as broad as the radius of the medullary shell, in the whole breadth with one hundred and twenty to one hundred and thirty piercing radial ribs, the prolongations of the beams.

_Dimensions._--Diameter of the disk 0.3, of the medullary shell 0.06, of the pores 0.04.

_Habitat._--South Pacific, Station 300, depth 1375 fathoms.

{427}Genus 184. _Perizona_,[223] Haeckel, 1881, Prodromus, p. 457.

_Definition._--#Phacodiscida# with double medullary shell, without radial spines, but with a solid equatorial girdle around the margin of the lenticular disk.

The genus _Perizona_ differs from its ancestral form _Phacodiscus_ in the development of a thin solid siliceous girdle, lying in the equatorial plane around the margin of the disk. The two genera bear the same relation to each other that _Periphæna_ bears to _Sethodiscus_. But in the two latter genera the spherical medullary shell is simple, in the two former double.

1. _Perizona scutella_, n. sp. (Pl. 32, fig. 7).

Disk with smooth surface, in the distal third radiated, four times as broad as the outer, and ten times is broad as the inner medullary shell. Pores subregular, circular; thirteen to fourteen on the radius of the disk, in the marginal part separated by eighty to ninety prominent radial crests, which are prolonged into the proximal half of the solid girdle. Breadth of the girdle equal to that of the inner medullary shell.

_Dimensions._--Diameter of the disk 0.25, of the outer medullary shell 0.06, of the inner 0.025; pores 0.007.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

2. _Perizona pterygota_, n. sp. (Pl. 32, figs. 8, 8_a_).

Disk with smooth surface, six times as broad as the outer, and fifteen times as broad as the inner medullary shell. Pores regularly circular; eighteen to twenty on the radius of the disk. Margin much thickened and truncated, abruptly separated in the equatorial circumference from the peripheral sharp margin of the solid girdle; breadth of the girdle equal to that of the outer medullary shell.

_Dimensions._--Diameter of the disk 0.25, of the outer medullary shell 0.04, of the inner 0.015; pores 0.006.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

Subfamily 2. HELIOSESTRIDA, Haeckel.

_Definition._--#Phacodiscida# with a constant number of radial spines on the margin of the disk (two, three, four, six, or eight), which are commonly regularly disposed (sometimes more or less irregularly).

{428}Genus 185. _Sethostylus_,[224] Haeckel, 1881, Prodromus, p. 457.

_Definition._--#Phacodiscida# with simple medullary shell and with two radial spines on the margin of the disk, opposite in the equatorial axis.

The genus _Sethostylus_ opens the series of the Heliosestrida or of those Phacodiscida in which a constant number of radial spines (two to eight) is more or less regularly disposed on the margin of the disk. All these marginal spines lie in the equatorial plane of the lens, and have in the same species a rather constant number and similar size, a certain form and disposition. Sometimes they incline more or less to irregular variations. In _Sethostylus_ there are only two spines, opposite in the equatorial diameter of the lens; it corresponds to _Stylocyclia_ among the Coccodiscida, and to _Xiphodictya_ among the Porodiscida.

Subgenus 1. _Sethostylium_, Haeckel.

_Definition._--Margin of the disk simple, smooth, without equatorial girdle and without a corona of marginal spines.

1. _Sethostylus distyliscus_, n. sp. (Pl. 31, fig. 9).

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; nine to ten on the radius of the disk, in the outer rows cylindrical. Margin of the disk simple, smooth, thin, without peculiar equatorial girdle, radially striped by the prominent beams of the peripheral series of pores. Both marginal spines of equal size, pyramidal, sulcated, about as long as the radius of the disk and as broad at the base as the medullary shell.

_Dimensions._--Diameter of the disk 0.13 to 0.16, of the medullary shell 0.04 to 0.05; length of both opposite spines 0.06 to 0.08, basal breadth 0.03 to 0.04.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

2. _Sethostylus dicylindrus_, n. sp. (Pl. 31, fig. 10).

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; sixteen to eighteen on the radius of the disk. Margin of the disk simple, smooth, thick, without peculiar equatorial girdle. Both marginal spines cylindrical, about as long as the diameter of the disk, about twice as broad as a single pore. (Walls of the disk in the central part twice to three times as thick as in the peripheral part.)

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05; length of both spines 0.2 to 0.3, breadth 0.008.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

{429}Subgenus 2. _Heliostylus_, Haeckel, 1881, Prodromus, p. 457.

_Definition._--Margin of the disk with a solid equatorial girdle or a corona of radial spines.

3. _Sethostylus dentatus_, n. sp. (Pl. 34, fig. 1).

_Heliostylus dentatus_, Haeckel, 1881, Prodromus et Atlas (pl. xxxiv. fig. 1).

Disk with smooth surface, six times as broad as the medullary shell. Pores regular, circular; eighteen to twenty on the radius of the disk. Margin of the disk with a broad solid equatorial girdle, which bears fifty to sixty strong conical teeth on the periphery; teeth about as long as the diameter of the medullary shell. Both opposite marginal spines cylindro-conical, about as long as the diameter of the disk, and as broad as the girdle.

_Dimensions._--Diameter of the disk 0.3, of the medullary shell 0.05; length of both main spines 0.2 to 0.3, breadth 0.02.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

4. _Sethostylus serratus_, n. sp. (Pl. 34, fig. 2).

_Heliostylus serratus_, Haeckel, 1881, Prodromus et Atlas (pl. xxxiv. fig. 2).

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; fourteen to sixteen on the radius of the disk. Margin with a broad solid equatorial girdle, which bears forty to fifty strong conical teeth on the periphery; teeth about as long as the radius of the medullary shell. Both opposite marginal spines spindle-shaped, about as long as the diameter of the disk, and as broad as the girdle.

_Dimensions._--Diameter of the disk 0.3, of the medullary shell 0.075; length of both main spines 0.2 to 0.3, breadth 0.03.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

5. _Sethostylus hastatus_, n. sp.

Disk with smooth surface, two and a half times as broad as the medullary shell. Pores irregular, roundish; ten to twelve on the radius of the disk. Margin with a broad solid equatorial girdle, which bears on the periphery six conical teeth, three on each half between the two main spines, which are cylindrical, longer than the diameter of the disk, and half as broad as the girdle. (This species can be derived from _Heliosestrum_, two opposite spines of the eight marginal spines being much stronger developed than the other six.)

_Dimensions._--Diameter of the disk 0.15, of the medullary shell 0.06; length of both main spines 0.2, breadth 0.01.

_Habitat._--North Atlantic, Station 354, surface.

{430}6. _Sethostylus spicatus_, n. sp.

Disk with spiny surface, four times as broad as the medullary shell. Pores irregular roundish, with many unequal conical spines between them. Margin with an equatorial girdle, composed of three to four concentric series of conical radial spines, about as long as the radius of the medullary shell. Both main spines very large, cylindrical, longer than the diameter of the disk, and as broad as the radius of the medullary shell.

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05; length of the main spines 0.3 or more, breadth 0.025.

_Habitat._--Fossil in the rocks of Barbados, Haeckel; living in the depths of the Equatorial Atlantic, Station 348, depth (2450) fathoms.

Genus 186. _Phacostylus_,[225] Haeckel, 1881, Prodromus, p. 457.

_Definition._--#Phacodiscida# with double medullary shell and with two radial spines on the margin of the disk, opposite in the equatorial axis.

The genus _Phacostylus_ differs from the foregoing _Sethostylus_ by the duplication of the medullary shell, and bears the same relation to it as _Phacodiscus_ does to _Sethodiscus_, or as _Amphicyclia_ in the Coccodiscida does to _Stylocyclia_.

Subgenus 1. _Phacostylium_, Haeckel.

_Definition._--Margin of the disk simple, smooth, without equatorial girdle, and without a corona of marginal spines.

1. _Phacostylus amphistylus_, n. sp. (Pl. 31, fig. 12).

Disk with smooth surface, four times as broad as the outer, and twelve times as broad as the inner medullary shell. Pores regular, circular; twelve to fourteen on the radius of the disk. Margin of the disk simple, smooth, without spines and equatorial girdle. Both polar spines conical, longer than the diameter of the disk, furrowed at the base, and twice as broad as the inner medullary shell.

_Dimensions._--Diameter of the disk 0.16 to 0.18, of the outer medullary shell 0.045, of the inner 0.015; length of the polar spines 0.2, basal breadth 0.03.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

2. _Phacostylus amphixiphus_, n. sp.

Disk with smooth surface, three times as broad as the outer, and eight times as broad as the inner medullary shell. Pores irregular, roundish; ten to eleven on the radius. Margin of the disk {431}simple, smooth, without spines and equatorial girdle. Both polar spines sword-shaped triangular, two-edged, about as long as the radius of the disk, and as broad at the base as the inner medullary shell.

_Dimensions._--Diameter of the disk 0.15, of the outer medullary shell 0.05, of the inner 0.02; length of the polar spines 0.08, basal breadth 0.02.

_Habitat._--Indian Ocean, Madagascar, Rabbe, surface.

Subgenus 2. _Astrostylus_, Haeckel.

_Definition._--Margin of the disk with a solid equatorial girdle or a corona of radial spines.

3. _Phacostylus amphipyramis_, n. sp.

Disk with spiny surface, four and a half times as broad as the outer, and fourteen times as broad as the inner medullary shell. Pores irregular, roundish; eight to ten on the radius. Margin of the disk with a corona of irregular, radial spines. Both opposite polar spines pyramidal, twice as long as broad, and nearly as long as the radius of the disk.

_Dimensions._--Diameter of the disk 0.22, of the outer medullary shell 0.05, of the inner 0.016; length of the polar spines 0.1, basal breadth 0.05.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

4. _Phacostylus caudatus_, n. sp. (Pl. 32, fig. 6).

_Astrosestrum caudatum_, Haeckel, 1881, Prodromus et Atlas (pl. xxxii. fig. 6).

Disk with smooth surface, two and a half times as broad as the outer, and six times as broad as the inner medullary shell. Pores regular, circular; six to seven on the radius of the disk. Margin with a solid equatorial girdle, and irregularly bordered with eight to ten conical spines; two opposite of these are much longer than the others. (This species can be derived from _Astrosestrum_, two opposite marginal spines being much more strongly developed than the six to eight others.)

_Dimensions._--Diameter of disk 0.12, of the outer medullary shell 0.05, of the inner 0.02; length of the polar spines 0.1 to 0.25, basal breadth 0.025.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

5. _Phacostylus maximus_, n. sp.

Disk with smooth surface, five times as broad as the outer, and ten times as broad as the inner medullary shell. Pores regular, circular; twenty to twenty-two on the radius. Margin with a solid equatorial girdle, bearing on the periphery one hundred to one hundred and twenty plain teeth, and two very large polar spines, which are cylindrical, longer than the diameter of the disk, and as broad at the furrowed base as the radius of the outer medullary shell. (Similar to _Sethostylus dentatus_, Pl. 34, fig. 1, but much larger, and with a double medullary shell.) {432}_Dimensions._--Diameter of the disk 0.4, of the outer medullary shell 0.08, of the inner 0.04; length of the polar spines 0.5, basal breadth 0.04.

_Habitat._--Fossil in the rocks of Barbados.

Genus 187. _Triactiscus_,[226] Haeckel, 1881, Prodromus, p. 457.

_Definition._--#Phacodiscida# with simple medullary shell, and with three radial spines on the margin of the disk, placed in the equatorial plane.

The genus _Triactiscus_ exhibits on the margin of the lenticular phacoid shell three radial solid spines, the distance between which is sometimes equal, at other times unequal. Either all the three spines are of equal size and similar form, or one odd arm is smaller than the two paired arms. The triradial form of this genus is repeated in _Tripodocyclia_ among the Coccodiscida, and in _Tripodictya_ among the Porodiscida. The medullary shell of _Triactiscus_ is simple.

1. _Triactiscus tripyramis_, n. sp. (Pl. 33, fig. 6).

Disk with smooth surface and smooth margin, three times as broad as the medullary shell. Pores regular, circular; twelve to thirteen on the radius of the disk. Three radial spines of nearly equal size and equidistant, or one odd spine a little smaller, and the opposite angle (between the paired spines) also smaller. Spines pyramidal, with broad prominent edges, one to one and a half times as long as the radius of the disk, as broad at the base as the radius of the medullary shell.

_Dimensions._--Diameter of the disk 0.15; of the medullary shell 0.05, pores 0.006.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

2. _Triactiscus tricuspis_, n. sp. (Pl. 33, fig. 5).

Disk with smooth surface and smooth margin, five times as broad as the medullary shell. Pores irregular, roundish; ten to eleven on the radius of the disk. Three radial spines of unequal size and at unequal distances, very short, conical, not longer than the radius of the medullary shell.

_Dimensions._--Diameter of the disk 0.15, of the medullary shell 0.03; pores 0.004 to 0.008.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

3. _Triactiscus tripodiscus_, Haeckel.

_Haliomma triactis_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 236, Taf. xxviii. fig, 4.

Disk with thorny surface and spiny margin, three times as broad as the medullary shell. Pores regular, circular; eight to nine on the radius of the disk. Three radial spines of different {433}size and at unequal distances, one odd spine as long as the radius, both paired spines as long as the diameter of the disk; the odd angle between the latter is smaller. Spines pyramidal, with broad edges.

_Dimensions._--Diameter of the disk 0.16, of the medullary shell 0.05, pores 0.008.

_Habitat._--Fossil in the rocks of Barbados.

Genus 188. _Sethostaurus_,[227] Haeckel, 1881, Prodromus, p. 457.

_Definition._--#Phacodiscida# with simple medullary shell and with four radial spines on the margin of the disk, crossed in the equatorial plane.

The genus _Sethostaurus_ exhibits four marginal spines, which form commonly a more or less regular cross in the equatorial plane. Sometimes the size and disposition of the four spines become more or less different, and also the angles between them vary; the regular rectangular cross passes over into a bilateral or irregular form. The medullary shell is simple. The same cross-form of the disk is seen in _Staurocyclia_ among the Coccodiscida, and in _Staurodictya_ among the Porodiscida.

Subgenus 1. _Sethostaurium_, Haeckel.

_Definition._--Margin of the disk without a solid equatorial girdle or a corona of spines.

1. _Sethostaurus orthostaurus_, n. sp. (Pl. 31, figs. 1, 2).

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; thirteen to fourteen on the radius of the disk. Margin simple, smooth, without girdle. Four crossed spines equal, pommel-shaped, angular, contracted at the base, scarcely as long as the diameter of the medullary shell.

_Dimensions._--Diameter of the disk 0.16, of the medullary shell 0.05; length of the crossed spines 0.04, breadth 0.02.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

2. _Sethostaurus conostaurus_, n. sp. (Pl. 34, figs. 7, 8).

Disk with spiny surface, three times as broad as the medullary shell. Pores irregular, roundish; seven to eight on the radius. Margin simple, smooth, without girdle. Four crossed spines subregular, equal, conical, about as long as the diameter and as broad at the base as the radius of the medullary shell. (Fig. 7 exhibits the normal form, fig. 8 an abnormality with five spines.)

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.06; length of the crossed spines 0.05, basal breadth 0.03.

_Habitat._--South Atlantic, Station 333, surface.

{434}3. _Sethostaurus rhombostaurus_, n. sp. (Pl. 31, fig. 4).

Disk with smooth surface, two and a half times as broad as the medullary shell. Pores regular, circular; ten to eleven on the radius. Margin simple, smooth, without girdle. Two opposite spines longer than the diameter of the disk, four times as long as the two others, which only equal its radius. Spines sword-shaped, angular.

_Dimensions._--Diameter of the disk 0.14, of the medullary shell 0.06; length of the major spines 0.2, of the minor 0.05, breadth 0.025.

_Habitat._--North Atlantic, Station 353, depth 2965 fathoms.

4. _Sethostaurus recurvatus_, n. sp. (Pl. 31, fig. 3).

Disk with smooth surface, three times as broad as the medullary shell. Pores irregular, roundish; eight to nine on the radius. Margin simple, smooth, without girdle. Four spines cylindrical, irregularly curved, of different sizes; one single very large, much longer than the three others; two opposite lateral spines recurved, hook-shaped.

_Dimensions._--Diameter of the disk 0.15, of the medullary shell 0.05; length of the major spine 0.32, of the opposite spine 0.16, of both lateral spines 0.08.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

Subgenus 2. _Heliostaurus_, Haeckel 1881, Prodromus, p. 457.

_Definition._--Margin of the disk with a solid equatorial girdle or a corona of spines.

5. _Sethostaurus cruciatus_, n. sp. (Pl. 31, fig. 5).

_Heliostaurus cruciatus_, Haeckel, 1881, Prodromus et Atlas (pl. xxxi. fig. 5).

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; eleven to twelve on the radius. Margin with a solid, radially striped girdle, which bears on the periphery forty to fifty triangular pointed teeth of unequal length. Four crossed spines of equal size and similar form, pyramidal, sulcated, about as long as the radius of the disk, as broad at the base as the girdle.

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.06; length of the crossed spines 0.1, basal breadth 0.02.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

6. _Sethostaurus coronatus_, n. sp.

Disk with spiny surface, twice as broad as the medullary shell. Pores irregular, roundish; nine to ten on the radius. Margin of the disk with a solid broad girdle, bearing on the periphery a corona of thirty to forty flat tongue-shaped teeth of different length. Four crossed spines {435}prismatic with prominent edges, about as long as the diameter of the disk, and as broad as the girdle.

_Dimensions._--Diameter of the disk 0.16, of the medullary shell 0.08, length of the crossed spines 0.18, breadth 0.02.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

7. _Sethostaurus gigas_, n. sp.

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; twenty to twenty-two on the radius. Margin of the disk with a narrow solid girdle, bearing on the periphery one hundred to one hundred and twenty slender flat pointed teeth. Four crossed spines equal, conical, about as long as the radius of the disk, as broad at their furrowed base as the radius of the medullary shell.

_Dimensions._--Diameter of the disk 0.4, of the medullary shell 0.1; length of the crossed spines 0.5, basal breadth 0.05.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

Genus 189. _Phacostaurus_,[228] Haeckel, 1881, Prodromus, p. 457.

_Definition._--#Phacodiscida# with double medullary shell and with four radial spines on the margin of the disk, crossed in the equatorial plane.

The genus _Phacostaurus_ differs from the foregoing _Sethostaurus_ by the duplication of the medullary shell, and bears to it the same relation as _Phacodiscus_ does to _Sethodiscus_. Also in this genus the cross of the shell is commonly regular, rectangular, sometimes more or less irregular.

Subgenus 1. _Phacostaurium_, Haeckel.

_Definition._--Margin of the disk without a solid equatorial girdle or a corona of spines.

1. _Phacostaurus oceanidum_, n. sp. (Pl. 31, fig. 6).

Disk with smooth surface, three times as broad as the outer and eight times as broad as the inner medullary shell. Pores regular, circular; eleven to twelve on the diameter of the disk. Margin smooth. Four crossed spines pyramidal, deeply sulcate, about as long as the diameter of the outer medullary shell, and two-thirds as broad at the base.

_Dimensions._--Diameter of the disk 0.15, of the outer medullary shell 0.05, of the inner 0.02; length of the spines 0.05, basal breadth 0.03.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

{436}Subgenus 2. _Astrostaurus_, Haeckel, 1881, Prodromus, p. 457.

_Definition._--Margin of the disk with a solid equatorial girdle, or a corona of spines.

2. _Phacostaurus quadrigatus_, n. sp.

Disk with smooth surface, four times as broad as the outer and ten times as broad as the inner medullary shell. Pores irregular, roundish; fifteen to sixteen on the diameter of the disk. Margin with a broad solid equatorial girdle, from which arise four crossed spines, conical, as long as the radius of the disk.

_Dimensions._--Diameter of the disk 0.2, of the outer medullary shell 0.05, of the inner 0.02; length of the spines 0.1, basal breadth 0.03.

_Habitat._--South Pacific, Station 300, depth 1375 fathoms.

3. _Phacostaurus magnificus_, n. sp. (Pl. 31, figs. 7, 8).

_Astrostaurus magnificus_, Haeckel, 1881, Prodromus et Atlas (pl. xxxi. figs.7, 8).

Disk with smooth surface, three times as broad as the outer and nine times as broad as the inner medullary shell. Pores regular, circular; thirteen to fourteen on the diameter of the disk. Margin with a corona of fifty to sixty conical spines of unequal length. Four spines of the cross very large pyramidal, deeply sulcated, longer than the radius of the disk, and as broad at the base as the radius of the medullary shell.

_Dimensions._--Diameter of the disk 0.22, of the outer medullary shell 0.07, of the inner 0.025; length of the four spines 0.16, basal breadth 0.04.

_Habitat._--Indian Ocean, Madagascar, Rabbe, surface.

Genus 190. _Distriactis_,[229] n. gen.

_Definition._--#Phacodiscida# with simple medullary shell and with six radial spines on the margin of the disk placed in the equatorial plane.

The genus _Distriactis_ exhibits on the margin of the lenticular phacoid shell six radial solid spines. Their distance is commonly equal, rarely unequal. Either all six spines are of equal size and similar form, or three larger (perradial) alternating with three smaller (interradial), so that _Distriactis_ appears to be derived from _Triactiscus_ by development of three secondary between three primary spines.

1. _Distriactis liriantha_, n. sp.

Disk smooth, four times as broad as the medullary shell, with regular, circular pores (about ten on the radius). Six marginal spines of equal size and at equal distances, triangular, sulcate, half as long as the radius. (Similar to _Heliosestrum medusinum_, Pl. 34, fig. 6.)

{437}_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05; length of the spines 0.05, basal breadth 0.04.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

2. _Distriactis corallantha_, n. sp.

Disk thorny, three times as broad as the medullary shell, with regular, circular pores, about eight on the radius. Six marginal spines of equal size and equidistant, conical, nearly as long as the diameter of the disk, half as broad at the base as the medullary shell.

_Dimensions._--Diameter of the disk 0.12, of the medullary shell 0.04; length of the spines 0.1, breadth 0.02.

_Habitat._--South Pacific, Station 300, surface.

3. _Distriactis alterna_, n. sp.

Disk smooth, five times as broad as the medullary shell, about twelve pores on the radius. Six marginal spines pyramidal, at equal distances, but unequal alternating size; three larger (perradial) spines as long as the shell radius, three smaller between them (interradial) half as long and broad.

_Dimensions._--Diameter of the disk 0.15, of the medullary shell 0.03; length of the three major spines 0.08, of the three minor 0.05.

_Habitat._--North Atlantic, Station 353, surface.

4. _Distriactis palmantha_, n. sp.

Disk rough, four times as broad as the medullary shell, about ten pores on the radius. Six marginal spines conical, at equal distances, but unequal alternating size; three larger (perradial) spines as long as the shell diameter, three smaller between them (interradial) as long as the radius.

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05; length of the three major spines 0.2, of the three minor 0.1,

_Habitat._--South Atlantic, Station 325, surface.

5. _Distriactis amphithecta_, n. sp.

Disk thorny, three times as broad as the medullary shell. Six marginal spines conical, of very different size; one single (anterior) much larger than the five others, the opposite (posterior) much smaller. The other four spines are paired, the anterior pair larger than the posterior.

_Dimensions._--Diameter of the disk 0.15, of the medullary shell 0.05; length of the longest spine 0.2, of the shortest 0.04, of the anterior pair 0.1, of the posterior 0.07.

_Habitat._--Indian Ocean, Cocos Islands, surface, Rabbe.

{438}Genus 191. _Heliosestrum_,[230] Haeckel, 1881, Prodromus, p. 457.

_Definition._--#Phacodiscida# with simple medullary shell and with eight radial spines on the margin of the disk (more or less regularly disposed, sometimes seven or nine).

The genus _Heliosestrum_ (with simple medullary shell) and the following _Astrosestrum_ (with double medullary shell) contain those Phacodiscida in which the margin of the lenticular disk bears eight radial spines, commonly more or less regularly disposed in the equatorial plane, so that the equal angles between them amount to 45°. There are, however, many exceptions to this regular eight-rayed form, either the angles between the eight spines becoming unequal or the number of the spines amounting to seven or nine (sometimes also six or ten) in one and the same species. But the regular form is as prevalent, and also in the abnormal forms indicated by the position of the spines, that we separate the genus _Heliosestrum_ from _Heliodiscus_. Both genera are rich in common species, and in some of the former four perradial (larger) spines alternate regularly with four interradial (smaller) spines.

Subgenus 1. _Heliosestantha_, Haeckel.

_Definition._--Surface of the disk smooth, without radial spines. Bases of the marginal spines free, not connected by an equatorial girdle.

1. _Heliosestrum medusinum_, n. sp. (Pl. 34, fig. 6).

_Heliodiscus medusinus_, Haeckel, 1881, Atlas (pl. xxxiv. fig. 6).

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; about ten on the radius of the disk. Eight marginal spines regularly distributed (sometimes seven or nine, more or less irregular), angular, nearly pyramidal (with equilateral triangular outline), about as long and broad as the diameter of the medullary shell, without connecting equatorial girdle. From the broad base of each spine run eight to ten deep furrows convergent to its apex.

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05; length of the radial spines 0.05, basal breadth 0.05.

_Habitat._--North Pacific, Station 266, surface.

2. _Heliosestrum octastrum_, n. sp.

Disk with smooth surface, three times as broad as the medullary shell. Pores irregular, roundish; eight to nine on the radius. Eight marginal spines regularly distributed (sometimes {439}seven or nine, more or less irregular), conical, about as long as the diameter of the disk, without a connecting equatorial girdle.

_Dimensions._--Diameter of the disk 0.15, of the medullary shell 0.05; length of the radial spines 0.16, basal breadth 0.01.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

3. _Heliosestrum solarium_, Haeckel.

_Haliomma sol_ (_partim_), Ehrenberg, 1875 (_non_ 1844), Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxviii. fig. 1.

Surface of the disk smooth; its diameter six times as large as that of the medullary shell. Pores regular, circular; nine to ten on the radius. Eight marginal spines regularly distributed (sometimes seven or nine, more or less irregular), conical, about as long as the diameter of the medullary shell, without a connecting equatorial girdle.

_Dimensions._--Diameter of the disk 0.18, of the medullary shell 0.03; length of the radial spines 0.03, basal breadth 0.01.

_Habitat._--Fossil in the Tertiary rocks of Barbados.

4. _Heliosestrum liriope_, n. sp.

Surface of the disk smooth; its diameter four times as large as that of the medullary shell. Pores subregular, circular; seven to eight on the radius. Eight marginal spines regularly distributed, conical, compressed, alternating longer and shorter; the longer equal to the diameter of the disk, the shorter to the radius.

_Dimensions._--Diameter of the disk 0.16, of the medullary shell 0.4; length of the major radial spines 0.15, of the minor 0.09.

_Habitat._--North Pacific, Station 236, surface.

5. _Heliosestrum quadrigeminum_, n. sp.

Surface of the disk smooth; its diameter four times as large as that of the medullary shell. Pores irregular, roundish; six to seven on the radius. Eight marginal spines triangular, flat, regularly disposed, alternating longer and shorter, the major as long as the radius of the shell, and half as broad at the base, with three to four deep furrows on both sides, without a connecting equatorial girdle.

_Dimensions._--Diameter of the disk 0.16, of the medullary shell 0.04; length of the larger radial spines 0.08, of the smaller 0.04, basal breadth 0.04.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

6. _Heliosestrum contiguum_, Haeckel.

_Haliomma contiguum_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxvii. fig. 5.

Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, roundish, touching, with very thin bars; nine to ten on the radius. Eight marginal spines (often {440}seven or nine) conical, half as long as the radius, twice as long as broad, without a connecting equatorial girdle.

_Dimensions._--Diameter of the disk 0.17, of the medullary shell 0.04; length of the radial spines 0.04, basal breadth 0.02.

_Habitat._--Fossil in Barbados.

7. _Heliosestrum irregulare_, n. sp.

Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, roundish; nine to eleven on the radius. Eight conical radial spines of irregular size and distribution, often seven or nine, about as long as the radius of the disk (in some cases longer, in others shorter). No connecting equatorial girdle.

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05; length of the radial spines 0.1, basal breadth 0.02.

_Habitat._--Central Pacific, Stations 270 to 272, depth 2425 to 2925 fathoms.

Subgenus 2. _Heliosestilla_, Haeckel.

_Definition._--Surface of the disk armed with radial spines. Bases of the marginal spines free, without a connecting equatorial girdle.

8. _Heliosestrum octonum_, n. sp. (Pl. 34, fig. 3).

Disk with spiny surface, three times as broad as the medullary shell. Pores circular, of very different sizes; eight to ten on the radius. Eight conical marginal spines of equal size and equidistant, as long as the radius of the disk, and one-third as broad at the base as the medullary shell. Numerous spines on the surface bristle-shaped, on the margin half as long as the eight main spines, in the central part shorter.

_Dimensions._--Diameter of the disk 0.18, of the medullary shell 0.06; length of the marginal spines 0.1, basal breadth 0.02.

_Habitat._--Central Pacific, Station 271, surface.

9. _Heliosestrum ægineta_, n. sp.

Disk with spiny surface, four times as broad as the medullary shell. Pores irregular, roundish, of different sizes; twelve to fourteen on the radius. Eight pyramidal marginal spines regularly disposed, four larger (perradial) alternating with four smaller (interradial); the former as long as the radius of the disk, the latter half as long.

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05; length of the marginal spines 0.05 to 0.1, basal breadth 0.03.

_Habitat._--South Atlantic, Station 330, surface.

{441}Subgenus 3. _Heliosestomma_, Haeckel.

_Definition._--Surface of the disk smooth, without radial spines. Bases of the marginal spines connected by a solid equatorial girdle.

10. _Heliosestrum octangulum_, n. sp.

Disk with smooth surface, octagonal, twice as broad as the medullary shell. Pores regular, circular; nine to ten on the radius. Equatorial girdle narrow, radially striped, connecting the points of the eight short, regularly disposed, marginal spines in such a manner that the whole shell forms a regular octagon with rectilinear sides.

_Dimensions._--Diameter of the disk 0.11 to 0.12, of the medullary shell 0.05 to 0.06; length of the sides of the octagon 0.06.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

11. _Heliosestrum octogonium_, n. sp.

Disk with smooth surface, octagonal, four times as broad as the medullary shell. Pores irregular, roundish; eight to nine on the radius. Equatorial girdle broad, smooth, connecting the points of the eight short, triangular, flat marginal spines in such a manner that the whole shell forms a subregular octagon with concave, nearly equal sides. (Sometimes seven or nine spines instead of eight are developed.)

_Dimensions._--Diameter of the disk 0.16 to 0.18, of the medullary shell 0.04 to 0.05; length of the radial spines 0.02 to 0.04, basal breadth 0.03.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

12. _Heliosestrum craspedotum_, n. sp.

_Haliomma humboldti_, var., Bury, 1862, Polycystins of Barbados, pl. viii. fig. 4 (below).

Disk with smooth surface, three times as broad as the medullary shell. Pores subregular, circular; ten to twelve on the radius. Eight marginal spines (sometimes seven or nine) triangular, deeply sulcated, half as long and one-third as broad as the radius of the disk, connected by a narrow, radially striped equatorial girdle.

_Dimensions._--Diameter of the disk 0.18, of the medullary shell 0.06; length of the radial spines 0.05, basal breadth 0.03.

_Habitat._--Central Pacific, Stations 271 to 274, at various depths, also fossil in Barbados.

Genus 192. _Astrosestrum_,[231] Haeckel, 1881, Prodromus, p. 457.

_Definition._--#Phacodiscida# with double medullary shell and with eight radial spines on the margin of the disk (more or less regularly disposed, sometimes seven or nine).

{442}The genus _Astrosestrum_ differs from the foregoing _Heliosestrum_ by the duplication of the medullary shell. The eight marginal spines in the majority of individuals are regularly formed and disposed, of equal size and equidistant. But there are frequent exceptions to this rule, either the angles between the eight spines being more or less different, or the number amounting to seven or nine, instead of eight. Here also in some species four larger (perradial) spines alternate regularly with four smaller (interradial spines), after the same law of symmetry, which is common in the Medusæ.

Subgenus 1. _Astrosestantha_, Haeckel.

_Definition._--Surface of the disk smooth, without radial spines. Bases of the marginal spines free, not connected by an equatorial girdle.

1. _Astrosestrum ephyra_, n. sp. (Pl. 32, figs. 4, 4_a_).

Disk with smooth surface, three times as broad as the outer and nine times as broad as the inner medullary shell. Pores subregular, circular; seven to eight on the radius of the disk. Eight marginal spines (sometimes seven or nine) more or less irregularly disposed, of variable size, commonly as long as the radius of the disk, twice as long as broad, pyramidal, sulcate, without a connecting equatorial girdle.

_Dimensions._--Diameter of the disk 0.12, of outer medullary shell 0.04, of the inner 0.014; length of the marginal spines 0.05 to 0.07, basal breadth 0.03.

_Habitat._--Central Pacific, Stations 270 to 274, depths 2350 to 2925 fathoms.

2. _Astrosestrum nauphanta_, n. sp. (Pl. 32, fig. 5).

Disk with smooth surface, two and a half times as broad as the outer and five times as broad as the inner medullary shell. Pores regular, circular; eight to nine on the radius of the disk. Eight marginal spines (often seven or nine) more or less regularly disposed, of equal size, half as long as the radius of the disk, and quite as broad at the base, compressed triangular, sulcate, without a connecting equatorial girdle.

_Dimensions._--Diameter of the disk 0.15, of the outer medullary shell 0.06, of the inner 0.03; length of the marginal spines 0.04, basal breadth 0.04.

_Habitat._--Pacific, central area, Stations 266 to 268, depth 2700 to 2900 fathoms.

3. _Astrosestrum octacanthum_, Haeckel.

_Haliomma octacanthum_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 295, Taf. viii. fig. 11.

Disk with smooth surface, twice as broad as the outer and six times as broad as the inner medullary shell. Pores regular, circular; six to seven on the radius of the disk. Eight marginal spines {443}regularly disposed, of variable size, the longest as long as the radius, pyramidal, not broader at the base than one pore, without a connecting equatorial girdle.

_Dimensions._--Diameter of the disk 0.12, of the outer medullary shell 0.06, inner 0.02; length of the marginal spines 0.03 to 0.06, basal breadth 0.01.

_Habitat._--Western Pacific, Philippine Sea, 3300 fathoms, Ehrenberg; Station 225, depth 4475 fathoms.

4. _Astrosestrum acraspedum_, n. sp.

Disk with smooth surface, three times as broad as the outer and six times as broad as the inner medullary shell. Pores regular, circular; nine to ten on the radius of the disk. Eight marginal spines regularly disposed, of alternating size; four major (perradial) spines as long as the diameter of the disk, four minor (interradial) half as long; spines cylindrical, not broader at the base than one pore, without a connecting equatorial girdle.

_Dimensions._--Diameter of the disk 0.2, of the outer medullary shell 0.07, of the inner 0.035; length of the larger spines 0.2, of the smaller 0.1, basal breadth 0.01.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

Subgenus 2. _Astrosestilla_, Haeckel.

_Definition._--Surface of the disk covered with radial spines. Bases of the marginal spines free, not connected by an equatorial girdle.

5. _Astrosestrum acanthastrum_, n. sp.

Disk with spiny surface, three times as broad as the outer and nine times as broad as the inner medullary shell. Pores subregular, circular; ten to eleven on the radius. Eight marginal spines (sometimes seven or nine) regularly disposed, triangular, about half as long as the radius of the disk, and one-third as broad at the base, without a connecting equatorial girdle.

_Dimensions._--Diameter of the disk 0.18, of the outer medullary shell 0.06, of the inner 0.02; length of the radial spines 0.05, basal breadth 0.03.

_Habitat._--North Atlantic, Gulf Stream, Færöe Channel, surface, John Murray.

6. _Astrosestrum echinastrum_, n. sp.

Disk with spiny surface, twice as broad as the outer and four times as broad as the inner medullary shell. Pores irregular, roundish; eight to nine on the radius. Eight marginal spines more or less regularly disposed, pyramidal, nearly as long as the radius of the disk, and not broader at the base than one large pore, without a connecting equatorial girdle.

_Dimensions._--Diameter of the disk 0.15, of the outer medullary shell 0.07, of the inner 0.04; length of the radial spines 0.07, basal breadth 0.01.

_Habitat._--Fossil in the Tertiary rocks of Sicily, Caltanisetta, Teuscher.

{444}Subgenus 3. _Astrosestomma_, Haeckel.

_Definition._--Surface of the disk smooth, without radial spines. Bases of the marginal spines connected by a solid equatorial girdle.

7. _Astrosestrum pelagia_, n. sp.

Disk with smooth surface, three times as broad as the outer and eight times as broad as the inner medullary shell. Pores regular, circular; eight to nine on the radius. Eight marginal spines conical, about as long as the radius of the disk, of nearly equal length, one-third as broad at the base, connected by a radially striped equatorial girdle.

_Dimensions._--Diameter of the disk 0.18, of the outer medullary shell 0.06, of the inner 0.023; length of the radial spines 0.09, basal breadth 0.03.

_Habitat._--Indian Ocean, Ceylon, Haeckel, surface.

8. _Astrosestrum floscula_, n. sp.

Disk with smooth surface, two and a half times as broad as the outer and five times as broad as the inner medullary shell. Pores irregular, roundish; ten to eleven on the radius. Eight marginal spines triangular, plain, scarcely half as long as the radius of the disk, nearly as broad at the base, connected by an even equatorial girdle.

_Dimensions._--Diameter of the disk 0.2, of the outer medullary shell 0.08, of the inner 0.04; length of the radial spines 0.09, basal breadth 0.07.

_Habitat._--South Atlantic, Station 325, surface.

Subfamily 3. HELIODISCIDA, Haeckel, 1881, Prodromus, p. 457.

_Definition._--#Phacodiscida# with a variable number of radial spines on the margin of the disk (ten to twenty or more), which are commonly more or less irregular (sometimes regularly formed and disposed).

Genus 193. _Heliodiscus_,[232] Haeckel, 1862, Monogr. d. Radiol., p. 436.

_Definition._--#Phacodiscida# with simple medullary shell and with numerous (ten to twenty or more) simple radial spines on the margin of the disk (commonly with a variable number and an irregular disposition of the undivided spines).

The genus _Heliodiscus_, the most common and polymorphic of all #Phacodiscida#, was founded by me in 1862 as the first known type of this family (_loc. cit._). I use {445}here the diagnosis of this genus in a restricted sense, including only the species, in which the number of marginal spines amounts to ten, twenty, or more (sometimes fifty to eighty, rarely more than one hundred). The number of spines is in the different species variable, and their disposition commonly more or less irregular, whilst in the preceding genera (with two, three, four, six, or eight marginal spines) their distance and form are commonly regular.

Subgenus 1. _Heliodiscetta_, Haeckel.

_Definition._--Surface of the disk smooth, without radial spines. Bases of the marginal spines free, without a connecting equatorial girdle.

1. _Heliodiscus asteriscus_, n. sp. (Pl. 33, fig. 8).

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; ten to twelve on the radius of the disk. Marginal spines fifteen to twenty, conical, often double contoured, of variable size and disposition, the largest as long as the radius of the disk, as broad at the base as one pore.

_Dimensions._--Diameter of the disk 0.15, of the medullary shell 0.05; length of the radial spines 0.04 to 0.07, basal breadth 0.01.

_Habitat._--Cosmopolitan; Mediterranean (Corfu), Indian Ocean (Madagascar), Atlantic and Pacific, many Stations, surface and various depths.

2. _Heliodiscus trochiscus_, n. sp. (Pl. 34, figs. 10, 13).

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; fourteen to sixteen on the radius. Marginal spines twelve to sixteen, conical, of variable size and disposition, the largest as long as the diameter of the medullary shell, twice as broad as one pore.

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05; length of the radial spines 0.01 to 0.025, basal breadth 0.005.

_Habitat._--Central Pacific, Stations 272 to 274, surface.

3. _Heliodiscus trigonodon_, n. sp.

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; eighteen to twenty on the radius. Marginal spines sixteen to twenty, equilateral triangular, flat, smooth, about as long and broad as the radius of the medullary shell.

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05; length of the radial spines 0.03, basal breadth 0.03.

_Habitat._--Central Pacific, Stations 266 to 274, depths 2350 to 2925 fathoms.

{446}4. _Heliodiscus glyphodon_, n. sp. (Pl. 35, fig. 2).

_Heliosestrum glyphodon_, Haeckel, 1881, Prodromus et Atlas (pl. xxxv. fig. 2).

Disk with smooth surface, four times as broad as the medullary shell. Pores subregular, circular; seven to eight on the radius. Marginal spines ten to twelve, equilateral triangular, flat, deeply furrowed, twice as long as broad, and as long as the radius of the disk.

_Dimensions._--Diameter of the disk 0.14, of the medullary shell 0.035; length of the radial spines 0.07, basal breadth 0.035.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

5. _Heliodiscus helianthus_, Haeckel.

_Haliomma helianthus_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxvii. fig. 1.

Disk with smooth surface, five times as broad as the medullary shell. Pores regular, oblong, disposed regularly in sixty to eighty radial series; fourteen to sixteen on the radius. Marginal spines sixty to eighty, conical, about as long as the diameter of the medullary shell, twice as broad as one pore.

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.04; length of the radial spines 0.04, basal breadth 0.005.

_Habitat._--Fossil in Barbados.

6. _Heliodiscus sol_, Haeckel.

_Haliomma sol_, Ehrenberg, 1854, Mikrogeol., Taf. xix. fig. 52.

_Heliodiscus sol_, Haeckel, 1862, Monogr. d. Radiol., p. 438.

Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, roundish; eight to ten on the radius. Marginal spines twenty to thirty, conical, the largest as long as the radius of the medullary shell, their bases widely distant. (The species from Barbados figured by Ehrenberg, 1875, as _Haliomma sol_, appertains to _Heliosestrum solare_.)

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05; length of the radial spines 0.02 to 0.025, basal breadth 0.01.

_Habitat._--Fossil in Tertiary rocks of Greece (Ægina), Ehrenberg.

7 _Heliodiscus siculus_, Stöhr.

_Heliodiscus siculus_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 89, Taf. i. fig. 14.

Disk with smooth surface, three times as broad as the medullary shell. Pores irregular roundish; seven to eight on the radius. Marginal spines forty to fifty, conical, very irregular, the largest as long as the radius of the medullary shell, their bases coming in contact.

_Dimensions._--Diameter of the disk 0.13 to 0.15, of the medullary shell 0.04 to 0.05; length of the radial spines 0.02 to 0.03, basal breadth 0.002 to 0.006.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte (Stöhr), Caltanisetta (Teuscher).

{447}8. _Heliodiscus polymorphus_, n. sp. (Pl. 34, figs. 11, 12).

Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, roundish; ten to twelve on the radius. Marginal spines ten to fifteen, pyramidal, angular, very irregular and variable in size and distribution, the largest nearly as long as the diameter of the disk, as broad at the base as the radius of the medullary shell.

_Dimensions._--Diameter of the disk 0.15 to 0.2, of the medullary shell 0.04 to 0.05; length of the radial spines 0.06 to 0.18, basal breadth 0.02 to 0.03.

_Habitat._--Central Pacific, Stations 265 to 268, depths 2700 to 2900 fathoms.

9. _Heliodiscus solaster_, n. sp. (Pl. 34, fig. 4).

Disk with smooth surface, three times as broad as the medullary shell. Pores subregular, roundish; nine to ten on the radius. Marginal spines fifty to sixty, cylindro-conical, flexuose, very variable in size, the largest nearly as long as the diameter of the disk. The spines lie not only in the equatorial plane (as usual), but also in two to four crowded girdles on both sides of it.

_Dimensions._--Diameter of the disk 0.15, of the medullary shell 0.05; length of the radial spines 0.05 to 0.15, basal breadth 0.008.

_Habitat._--Indian Ocean, Madagascar, Rabbe, surface.

Subgenus 2. _Heliodiscilla_, Haeckel.

_Definition._--Surface of the disk covered with radial spines. Bases of the marginal spines free, without a connecting equatorial girdle.

10. _Heliodiscus phacodiscus_, Haeckel.

_Heliodiscus phacodiscus_, Haeckel, 1862, Monogr. d. Radiol., p. 437, Taf. xvii. figs. 5-7.

_Haliomma phacodiscus_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 815.

Disk with spiny surface, three times as broad as the medullary shell. Pores regular, circular; six to eight on the radius. Marginal spines twelve to sixteen, conical, as long as the radius of the disk, and one-third as broad as the diameter of the medullary shell.

_Dimensions._--Diameter of the disk 0.12 to 0.16, of the medullary shell 0.04 to 0.05; length of the marginal spines 0.06 to 0.08, basal breadth 0.01 to 0.02.

_Habitat._--Mediterranean (Messina), Canary Islands (Lanzerote).

11. _Heliodiscus amphidiscus_, Haeckel.

_Heliodiscus amphidiscus_, Haeckel, 1862, Monogr. d. Radiol., p. 437.

_Haliomma amphidiscus_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 154, Taf. ii. figs. 3-7.

Disk with spiny surface, three times as broad as the medullary shell. Pores regular, circular; eight to ten on the radius. Marginal spines twelve to fifteen, bristle-shaped, not larger than the surface spines, about as long as the radius of the medullary shell.

{448}_Dimensions._--Diameter of the disk 0.16, of the medullary shell 0.05; length of the marginal spines 0.03, basal breadth 0.002.

_Habitat._--Mediterranean (south shore of France), J. Müller.

12. _Heliodiscus echiniscus_, n. sp. (Pl. 34, fig. 5).

Disk with spiny surface, three times as broad as the medullary shell. Pores irregular, roundish or polygonal; eight to ten on the radius. Marginal spines thirty to fifty, pyramidal, angular, of very variable size, number, and disposition, gradually passing into the surface-spines; the largest nearly as long as the diameter of the medullary shell.

_Dimensions._--Diameter of the disk 0.14, of the medullary shell 0.045; length of the radial spines 0.02 to 0.04, basal breadth 0.006.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

13. _Heliodiscus pertusus_, n. sp. (Pl. 35, fig. 1).

_Heliosestrum pertusum_, Haeckel, 1881, Prodromus et Atlas (pl. xxxv. fig. 1).

Disk with spiny surface, three times as broad as the medullary shell. Pores irregular, circular, hexagonally framed; eight to ten on the radius. Marginal spines ten to thirty, very variable in size and disposition; commonly eight to twelve larger spines, which are pyramidal, about as long as the radius of the disk and perforated by two to four irregular, longish pores. Between these fenestrated large spines are commonly ten to twenty smaller conical spines, gradually passing into those of the surface.

_Dimensions._--Diameter of the disk 0.13 to 0.16, of the medullary shell 0.04 to 0.05; length of the marginal spines 0.04 to 0.08, basal breadth 0.01 to 0.015.

_Habitat._--North Pacific, Stations 241 to 244, depths 2300 to 2900 fathoms.

Subgenus 3. _Heliodiscomma_, Haeckel.

_Definition._--Surface of the disk smooth, without radial spines. Bases of the marginal spines connected by a solid equatorial girdle.

14. _Heliodiscus cingillum_, n. sp. (Pl. 33, fig. 7).

Disk with smooth surface, five times as broad as the medullary shell. Pores regular, circular; twelve to fourteen on the radius. Equatorial girdle about as broad as the medullary shell, in the proximal half radially striped, on the margin with twenty to twenty-four short, flat, triangular spines, which are shorter than the breadth of the girdle.

_Dimensions._--Diameter of the disk 0.25, of the medullary shell 0.05; length of the marginal spines 0.02, basal breadth 0.02.

_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.

{449}15. _Heliodiscus humboldti_, Haeckel.

_Heliodiscus humboldti_, Haeckel, 1862, Monogr. d. Radiol., p. 438.

_Haliomma humboldti_, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 27; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Taf. xxvii. fig. 3.

_Haliomma humboldti_, Bury, 1862, Polycystins of Barbados, pl. viii. fig. 3 (at left).

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; eighteen to twenty on the radius. Equatorial girdle half as broad as the medullary shell, in the proximal half radially striped, on the margin with sixteen to twenty short, flat, triangular teeth, which are longer than the breadth of the girdle.

_Dimensions._--Diameter of the disk 0.12 to 0.2, of the medullary shell 0.03 to 0.05; length of the marginal spines 0.02 to 0.04, basal breadth 0.02.

_Habitat._--Fossil in Barbados (common and very variable).

16. _Heliodiscus marginatus_, n. sp. (Pl. 34, fig. 9).

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; nine to ten on the radius. Equatorial girdle one-fourth to one-half as broad as the medullary shell, in the whole breadth radially striped, on the margin with twelve to eighteen very short and broad, triangular, marginal spines.

_Dimensions._--Diameter of the disk 0.15 to 0.2, of the medullary shell 0.05 to 0.06; length of the marginal spines 0.01 to 0.02, basal breadth 0.02.

_Habitat._--Central Pacific, Stations 265 to 268, depth 2900 fathoms.

17. _Heliodiscus sulcatus_, n. sp.

Disk with smooth surface, four times as broad as the medullary shell. Pores subregular, circular; twelve to fifteen on the radius. Equatorial girdle as broad as the medullary shell, in the whole breadth radially striped on the margin with ten to fifteen triangular, deeply sulcated teeth, about as long and broad as the medullary shell. (Similar to _Heliodiscus glyphodon_, Pl. 35, fig. 2, but with broad sulcated girdle and shorter, more numerous spines.)

_Dimensions._--Diameter of the disk 0.15 to 0.2, of the medullary shell 0.04 to 0.05; length of the radial spines 0.05 to 0.06, basal breadth 0.04 to 0.05.

_Habitat._--Atlantic and Pacific, tropical part, many Stations, surface.

18. _Heliodiscus umbonatus_, Haeckel.

_Haliomma umbonatum_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxvii. fig. 4.

Disk with smooth surface, three times as broad as the medullary shell. Pores irregular, roundish; eight to ten on the radius. Equatorial girdle half as broad as the medullary shell, hyaline, not radially striped, on the margin with ten to twenty triangular, irregular, smooth teeth, very variable in size and disposition.

{450}_Dimensions._--Diameter of the disk 0.15 to 0.2, of the medullary shell 0.05 to 0.06; length of the marginal spines 0.02 to 0.08, basal breadth 0.01 to 0.03.

_Habitat._--Cosmopolitan; Atlantic, Pacific, in various depths; also fossil in Barbados and Sicily.

Subgenus 4. _Heliodiscura_, Haeckel.

_Definition._--Surface of the disk covered with radial spines. Bases of the marginal spines connected by a solid equatorial girdle.

19. _Heliodiscus apollinis_, n. sp.

Disk with spiny or bristly surface, three times as broad as the medullary shell. Pores regular, circular; eleven to twelve on the radius. Equatorial girdle narrow, on the margin with sixteen to twenty broad, flat, triangular teeth, which are half as long and one-fourth as broad as the medullary shell. (Very similar to _Astrophacus apollinis_, Pl. 32, fig. 2, but with simple medullary shell.)

_Dimensions._--Diameter of the disk 0.18, of the medullary shell 0.06; length of the marginal spines 0.03, basal breadth 0.015.

_Habitat._--Mediterranean (Corfu), Haeckel, surface.

20. _Heliodiscus zoroaster_, n. sp.

Disk with spiny surface, four times as broad as the medullary shell. Pores subregular, circular; fourteen to sixteen on the radius. Equatorial girdle broad, radially striped, on the margin with ten to twelve pyramidal, deeply sulcated radial spines, which are nearly as long as the radius of the disk, and one-fourth as broad at the base.

_Dimensions._--Diameter of the disk 0.24, of the medullary shell 0.06; length of the marginal spines 0.11, basal breadth 0.03.

_Habitat._--Indian Ocean, between Aden and Ceylon, Haeckel, surface.

Genus 194. _Heliodrymus_,[233] Haeckel, 1881, Prodromus, p. 457.

_Definition._--#Phacodiscida# with simple medullary shell and with numerous (ten to twenty or more) branched radial spines on the margin of the disk (commonly with a variable number and an irregular disposition of the ramified spines).

The genus _Heliodrymus_ differs from the nearly allied _Heliodiscus_ by the ramification of the marginal spines, a character hitherto observed in no other genus of Phacodiscida. The branching is more or less irregular, either a simple bifurcation or a repeated fissure; the spines and their branches are commonly more or less flexuose. {451}We can distinguish two subgenera: in _Heliocladus_ the surface of the disk is smooth, in _Heliodendrum_ covered with bristle-shaped radial spines, which are either simple or also branched, sometimes longer than the thick marginal spines.

Subgenus 1. _Heliocladus_, Haeckel, 1881, Prodromus, p. 457.

_Definition._--Surface of the disk smooth, without radial spines.

1. _Heliodrymus dendrocyclus_, n. sp. (Pl. 33, fig. 9).

_Heliocladus dendrocyclus_, Haeckel, 1881, Prodromus et Atlas (pl. xxxiii. fig. 9).

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular, hexagonally framed; eight to nine on the radius. Marginal spines sixteen to twenty, cylindrical, very strong, flexuose, irregularly branched, nearly as long as the diameter of the disk. Between these main spines, each of which bears two to six irregular branches, are scattered on the margin numerous smaller simple spines.

_Dimensions._--Diameter of the disk 0.16, of the medullary shell 0.05; length of the main spines 0.1 to 0.14, breadth 0.01 to 0.02.

_Habitat._--Central Pacific, Station 271, surface.

2. _Heliodrymus furcatus_, n. sp.

Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, roundish; ten to twelve on the radius. Marginal spines twenty to twenty-five, cylindrical, flexuose, forked, about as long as the radius of the disk; fork-branches irregular, of unequal size. Some smaller simple spines are scattered between the forked ones.

_Dimensions._--Diameter of the disk 0.15, of the medullary shell 0.04; length of the radial spines 0.07 to 0.09, breadth 0.01.

_Habitat._--Central Pacific, Station 265, surface.

3. _Heliodrymus grottensis_, Haeckel.

_Heliodiscus grottensis_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 89, Taf. i. fig. 13.

Disk with smooth surface, two and a half times as broad as the medullary shell. Pores irregular, roundish; eight to nine on the radius. Marginal spines twenty to thirty, conical, very irregular in form, size, and disposition; the smaller simple, the larger irregularly branched and half as long as the radius of the disk.

_Dimensions._--Diameter of the disk 0.17, of the medullary shell 0.07; length of the marginal spines 0.02 to 0.04, basal breadth 0.01 to 0.02.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

{452}Subgenus 2. _Heliodendrum_, Haeckel.

_Definition._--Surface of the disk armed with simple or branched radial spines.

4. _Heliodrymus setosus_, n. sp.

Disk with spiny surface, four times as broad as the medullary shell. Pores regular, circular; twelve to thirteen on the radius. Marginal spines ten to twelve, cylindrical, irregularly branched, each with two to eight flexuose branches of different sizes; the largest as long as the diameter of the disk. Spines of the surface bristle-shaped, half as long, not branched.

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05; length of the marginal spines 0.12 to 0.18, breadth 0.025.

_Habitat._--North Pacific, Station 254, surface.

5. _Heliodrymus ramosus_, n. sp. (Pl. 35, figs. 3, 4).

Disk with spiny surface, three times as broad as the medullary shell. Pores regular, circular, hexagonally framed; eleven to twelve on the radius. Marginal spines sixteen to twenty, cylindrical, about as long as the radius, irregularly forked or branched, with unequal flexuose branches. Spines of the surface nearly as long, bristle-shaped, also irregularly branched.

_Dimensions._--Diameter of the disk 0.15, of the medullary shell 0.05; length of the spines 0.06 to 0.08, basal breadth 0.01 to 0.015.

_Habitat._--South Pacific, Station 288, surface.

6. _Heliodrymus viminalis_, n. sp. (Pl. 35, fig. 5).

Disk with spiny surface, two and a half times as broad as the medullary shell. Pores irregular, roundish; ten to twelve on the radius. Marginal spines fifteen to twenty, cylindro-conical, strong, partly simple, partly forked, about as long as the diameter of the disk. Spines of the surface very numerous, bristle-shaped, longer than the marginal spines, and more branched.

_Dimensions._--Diameter of the disk 0.15, of the medullary shell 0.06; length of the marginal spines 0.11 to 0.14, basal breadth 0.01 to 0.015; length of the surface spines 0.2 to 0.03.

_Habitat._--Central Pacific, Station 271, surface.

Genus 195. _Astrophacus_,[234] Haeckel, 1881, Prodromus, p. 457.

_Definition._--#Phacodiscida# with double medullary shell and with numerous (ten to twenty or more) simple radial spines on the margin of the disk (commonly with a variable number and an irregular disposition of the undivided spines).

The genus _Astrophacus_ differs from the similar _Heliodiscus_ in the duplication of the medullary shell. The number and disposition of the radial spines of the margin {453}(commonly between ten and twenty) is also here variable in one and the same species. The greater number of observed species of _Astrophacus_ resemble in a very remarkable manner the corresponding species of _Heliodiscus_, and differ only in the double medullary shell.

Subgenus 1. _Astrophacetta_, Haeckel.

_Definition._--Surface of the disk smooth, without radial spines. Bases of the marginal spines free, without a connecting equatorial girdle.

1. _Astrophacus asteriscus_, n. sp.

Disk with smooth surface, three times as broad as the outer and eight times as broad as the inner medullary shell. Pores regular, circular; twelve to fourteen on the radius. Marginal spines fifteen to twenty, of variable size and disposition; the largest as long as the radius of the disk, as broad at the base as one pore. (Very similar to _Heliodiscus asteriscus_, Pl. 33, fig. 8, but differing in the double medullary shell.)

_Dimensions._--Diameter of the disk 0.2, of the outer medullary shell 0.07, of the inner 0.025; length of the marginal spines 0.05 to 0.1, basal breadth 0.01.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

2. _Astrophacus trochiscus_, n. sp. (Pl. 34, fig. 14).

Disk with smooth surface, three times as broad as the outer and seven times as broad as the inner medullary shell. Pores irregular, roundish; twelve to thirteen on the radius. Marginal spines sixteen to twenty, conical, of irregular variable size and disposition; the largest as long as the inner medullary shell. (Differs from _Heliodiscus trochiscus_ in the double medullary shell.)

_Dimensions._--Diameter of the disk 0.22, of the outer medullary shell 0.08, of the inner 0.03.

_Habitat._--North Atlantic, Station 354, surface.

3. _Astrophacus solaris_, n. sp. (Pl. 32, fig. 1).

Disk with smooth surface, three times as broad as the outer and seven times as broad as the inner medullary shell. Pores subregular, roundish; twelve to fourteen on the radius. Marginal spines one hundred to one hundred and twenty, conical, flexuose, of irregular size and form; the largest one-third as long as the diameter of the disk. The spines lie not only in the equatorial plane (as is usual) but also in two to four crowded girdles on both sides of it. (Very similar to _Heliodiscus solaster_, Pl. 34, fig. 4, but of double the size, with double the number of spines and with a double medullary shell.)

_Dimensions._--Diameter of the disk 0.3, of the outer medullary shell 0.11, of the inner 0.045; length of the spines 0.03 to 0.1, basal breadth 0.01 to 0.02.

_Habitat._--Indian Ocean, Sunda Strait, Rabbe, surface.

{454}Subgenus 2. _Astrophacilla_, Haeckel.

_Definition._--Surface of the disk covered with radial spines. Bases of the marginal spines free, without a connecting equatorial girdle.

4. _Astrophacus phacodiscus_, n. sp. (Pl. 32, fig. 3).

Disk with spiny surface, two and a half times as broad as the outer and seven times as broad as the inner medullary shell. Pores subregular, circular; ten to twelve on the radius. Marginal spines twelve to sixteen, conical, stout, nearly as long as the radius of the disk, and as broad at the base as the inner medullary shell. The numerous bristle-shaped spines of the surface are scarcely half as long. (Similar to _Heliodiscus phacodiscus_, Haeckel, Monogr. d. Radiol., Taf. xvii. figs. 5-7, but differing in the double medullary shell.)

_Dimensions._--Diameter of the disk 0.18, of the outer medullary shell 0.07, of the inner 0.025; length of the marginal spines 0.08 to 0.09, basal breadth 0.03.

_Habitat._--South Pacific, Station 300, surface.

Subgenus 3. _Astrophacomma_, Haeckel.

_Definition._--Surface of the disk smooth, without radial spines. Bases of the marginal spines connected by a solid equatorial girdle. (Perhaps = _Chilomma_(?) Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.)

5. _Astrophacus cingillum_, n. sp.

_Haliomma humboldti_, var., Bury, 1862, Polycystins of Barbados, pl. viii. fig. 3 (at right).

Disk with smooth surface, three times as broad as the outer and eight times as broad as the inner medullary shell. Pores regular, circular; eleven to thirteen on the radius. Equatorial girdle about as broad as the inner medullary shell, in the proximal half radially striped, on the margin with eighteen to twenty-four short, flat, triangular spines, about as long as the breadth of the girdle. (Similar to _Heliodiscus cingillum_, but with double medullary shell.)

_Dimensions._--Diameter of the disk 0.2, of the outer medullary shell 0.07, of the inner 0.025; length of the spines 0.02, basal breadth 0.02.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms; also fossil in Barbados.

6. _Astrophacus saturnus_, Haeckel.

? _Chilomma saturnus_, Ehrenberg, 1861, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 297; 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 286, Taf. ii. fig. 5.

? _Chilomma saturnus_, Haeckel, 1862, Monogr. d. Radiol., p. 447.

Disk with smooth surface, two and a half times as broad as the outer, six times as broad as the inner medullary shell. Pores large, irregular, roundish; five to seven on the radius (?). Equatorial girdle very broad, radially striped, nearly as broad as the outer medullary shell, perforated by {455}twenty to thirty (or more?) radial spines. (The position of this species, and the identity of _Chilomma_ with _Astrophacomma_, remains doubtful, as the imperfect figure given by Ehrenberg of _Chilomma saturnus_, the only species of the genus, is in contradiction with his vague description, as is very often the case.)

_Dimensions._--Diameter of the disk 0.12 (with girdle 0.22) of the outer medullary shell 0.05, of the inner 0.02.

_Habitat._--Arctic Ocean (Greenland, depth 1000 fathoms), Ehrenberg.

Subgenus 4. _Astrophacura_, Haeckel.

_Definition._--Surface of the disk covered with radial spines. Bases of the marginal spines connected by a solid equatorial girdle.

7. _Astrophacus apollinis_, n. sp. (Pl. 32, fig. 2).

Disk with spiny surface, three times as broad as the outer, eight times as broad as the inner medullary shell. Pores regular, circular; eleven to twelve on the radius of the disk. Equatorial girdle narrow, smooth, on the margin with twelve to sixteen broad, flat, triangular spines, of the same length as the numerous bristle-shaped spines of the surface, which reach half the radius of the disk. (Very similar to _Heliodiscus apollinis_, but differing in the double medullary shell.)

_Dimensions._--Diameter of the disk 0.24, of the outer medullary shell 0.08, of the inner 0.03; length of the radial spines 0.06, basal breadth 0.03.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

Family XX. #COCCODISCIDA#, Haeckel (Pls. 36-38).

_Coccodiscida_, Haeckel, 1862, Monogr. d. Radiol., p. 485. _Coccodiscida_, Haeckel, 1881, Prodromus, p. 458. _Lithocyclidina_, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 214 (_partim_).

_Definition._--#Discoidea# with extracapsular phacoid shell (or lenticular latticed cortical shell), connected by radial beams with an intracapsular, simple or double, concentric medullary shell, and surrounded by one or more concentric chambered equatorial girdles on the margin.

The family #Coccodiscida# was founded by me in 1862 for those #Discoidea# which agree with the Phacodiscida in the formation of the lenticular "phacoid shell" (including a simple or double medullary shell), but differ from them in the development of peculiar concentric chambered rings or girdles around the equatorial margin of the disk, similar to those of the Porodiscida.

The Coccodiscida represent a polymorphic family, in which we here distinguish sixteen genera with fifty-seven species; it comprises the greater part of those {456}#Discoidea# which Ehrenberg united in his group Lithocyclidina (1875, represented by four genera and eight species); several of these, however, appertain to quite different families, as his _Astromma entomocora_, _Lithocyclia amphitrites_, &c. His knowledge of the structure was very imperfect. The peculiar differentiation of the genera and species exhibits the greatest analogy to that of the following family, Porodiscida, though the structure of the central disk in both families is quite different.

_The Phacoid Shell_, or the circular, lenticular cortical shell exhibits in the Coccodiscida quite the same structure and composition as in the Phacodiscida, described above (p. 420), so that there can be no doubt as to the phylogenetic origin of the former from the latter. Quite in the same way in both families, the lenticular "phacoid shell" is connected by numerous, short, radial beams with the intracapsular, simple or double, medullary shell; and also here these beams are commonly disposed in two groups around the poles of the shortened main axis of the lens, so that their distal ends are implanted in both circumpolar areas (Pl. 36, figs. 2-6; Pl. 37, figs. 3, 7; Pl. 38, figs. 2, 7). The medullary shell is commonly simple, spherical, sometimes a little lenticularly compressed; more rarely it is double, composed of two concentric lattice-shells, which are connected by radial beams; in this case either both concentric medullary shells are spherical, or the inner is spherical, and the outer lenticular, very rarely the inner is lenticular also. In average size and structure they agree perfectly with those of the Phacodiscida.

_The Chamber Girdles_ or "chambered rings" around the equatorial margin of the disk, which constitute the only difference between the Coccodiscida and the Phacodiscida, seem to exhibit a considerable degree of difference of structure in the numerous species of this family; but I regret that I cannot explain them here satisfactorily. The study of these structures is extremely difficult because of the thickness and darkness of the massive opaque shells; to get a perfect knowledge of them, it is indispensable to compare slides made in different directions (horizontal slides through the equatorial and parallel planes, vertical slides through radial and parallel planes, oblique slides in different directions). But this requires a long time and a most careful study of the slides, which are very difficult to get in satisfactory condition. Therefore the following remarks can have only a provisional value.

In all Coccodiscida we can distinguish on the equatorial chamber-girdle of the lens-margin (even on superficial inspection) three different elements of structure, viz.:--(A) concentric circular rings in the equatorial plane; (B) numerous radial beams piercing the former and dividing them into imperfect chambers; (C) porous plates or sieve-plates on both convex faces of the disk. The probable morphological significance of these three elements is the following:--Each ring or girdle corresponds to an outer lenticular cortical shell, which is only developed on the marginal part, whilst its central part is represented by the phacoid shell. Therefore the radial beams (separating the imperfect chambers) are the same as in the concentric Polysphærida, and the {457}sieve-plates of the surface are the porous walls of the cortical shell itself. The correctness of this explanation seems to be proved by such forms as figured in Pl. 38, figs. 2, 4, where the whole surface of the phacoid shell is covered by a concentric chamber-work, as a central continuation of the marginal concentric rings. If we imagine a system of perfect concentric lenticular phacoid shells, compressed strongly from both poles of the shortened main axis, we get the same figure.

Rarely one single girdle only is developed on the equatorial margin of the lenticular disk (Pl. 37, figs. 2, 3, 5). Commonly the number of concentric girdles amounts to three to six, often to ten to twelve or more. Some of these largest Coccodiscida reach a considerable size. Commonly all girdles are of the same breadth, which is about equal to the radius or to the diameter of the inner medullary shell. Rarely the first (or innermost) girdle differs by its greater breadth from the succeeding ones (Pl. 36, fig. 8).

Only in few Coccodiscida the girdle-building remains restricted to the equatorial planes, so that all the chambers lie in it. Commonly on both sides of this plane become developed several layers, and often the number of these (three to six or more) increases towards the periphery; in other cases not their number, but their height increases. Therefore very often the margin of the discoidal shell is much thickened, as thick as the centre of the lenticular phacoid shell (or even more); whilst between the latter and the former (on the proximal girdles) the disk is considerably thinner (Pl. 36, figs. 2, 4; Pl. 37, figs. 7, 8; Pl. 38, figs. 2, 4). The stratified layers communicate by large openings between their chambers. The radial beams are commonly more or less regular and piercing, but also frequently irregular and interrupted; often their number increases towards the margin by intercalation of new beams.

_The Pores_ of the sieve-plates, which cover both sides of the chambered disk, appear on the margin of the phacoid shell as direct continuations of the pores of the latter, and sometimes they are so regularly disposed that one single circular pore is situated on the surface of each chamber (Pl. 36, fig. 7; Pl. 37, fig. 1). But commonly the pores are of variable size and number, two to three on each chamber, and often quite irregularly scattered.

_The Margin_ of the chambered disk exhibits many differences, which afford characters for the distinction of genera. In the first subfamily, the Lithocyclida, the margin is quite simple without radial appendages. In the second subfamily, the Stylocyclida, it is armed with solid radial spines lying in the equatorial plane, and often regularly disposed in the same manner as in the Phacodiscida (compare above, p. 421). In the third subfamily, the Astracturida, the margin bears two or more (commonly three or four) chambered arms, also situated in the plane of the disk, and of the same structure as the circular chambered girdles (Pl. 38). In some cases even the whole system of chamber-girdles is represented only by the radial arms, which are inserted immediately on the margin of the phacoid shell. We may regard therefore these formations as imperfect chambered disks, which are developed only in the direction of certain rays {458}(perradii), and reduced in the direction of the alternating rays (interradii). In some Astracturida the chambered arms exhibit a structure different from the more irregular chamber-work between them, so that we can distinguish the latter, connecting the arms like a web-membrane, as a peculiar "patagium" (as in many Porodiscida) (Pl. 38, figs. 8, 9). Often the distal ends of the chambered arms are armed with a radial spine (Pl. 38, figs. 5, 6, 9).

_The Central Capsule_ of the Coccodiscida is originally always of the same form and shape as in their ancestral group, the Phacodiscida; a circular lenticular disk, which envelops the simple or double medullary shell and is enclosed by the cortical phacoid shell. But whilst in the Phacodiscida the phacoid shell envelops the central capsule perfectly, in the Coccodiscida it envelops only the capsule from the two flat sides (by the upper and lower sieve-plates); the marginal part of the lenticular capsule overgrows the margin of the phacoid shell by peripheral extension, and fills out the chambered cavity of the concentric girdles. In the Lithocyclida and the Stylocyclida, where there are no chambered arms, the central capsule remains a simple circular lens or disk; in the Astracturida, where chambered radial arms surround the margin of the circular central disk, the capsule enters also into these arms and fills out the greatest part of their chambered cavities.

_Synopsis of the Genera of Coccodiscida_.

------------------------------------------------------------------------- I. Subfamily Lithocyclida. Margin of the disk simple, circular, without radial appendages. ------------------------------------------------------------------------- Neither radial spines nor {Medullary shell simple, 196. _Lithocyclia_. chambered arms on the { circular margin. {Medullary shell double, 197. _Coccodiscus_. ------------------------------------------------------------------------- II. Subfamily Stylocyclida. Margin of the disk armed with solid radial spines. ------------------------------------------------------------------------- Two opposite spines. {Medullary shell simple, 198. _Stylocyclia_. { {Medullary shell double, 199. _Amphicyclia_.

Three radial spines. Medullary shell simple, 200. _Trigonocyclia_.

Four crossed spines. Medullary shell simple, 201. _Staurocyclia_.

Five to ten or more {Medullary shell simple, 202. _Astrocyclia_. radial spines. { {Medullary shell double, 203. _Coccocyclia_. ------------------------------------------------------------------------- III. Subfamily Astracturida. Margin of the disk with two to five or more (commonly three or four) hollow radial chambered arms (with or without a connecting patagium). (Medullary shell commonly simple.) ------------------------------------------------------------------------- Two arms, opposite in {Without patagium, 204. _Diplactura_. one axis. { {With patagium, 205. _Amphiactura_.

Three radial arms (at {Without patagium, 206. _Trigonactura_. equal distances). { {With patagium, 207. _Hymenactura_.

Four arms (in two {Without patagium, 208. _Astractura_. crossed diameters). { {With patagium, 209. _Stauractura_.

Five radial arms (at {Without patagium, 210. _Pentactura_. variable distances). { {With patagium, 211. _Echinactura_.

{459}Subfamily 1. LITHOCYCLIDA, Haeckel, 1881, Prodromus, p. 458.

_Definition._--#Coccodiscida# with simple circular disk, without any radial appendages of the margin (either solid radial spines or chambered arms).

Genus 196. _Lithocyclia_,[235] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

_Definition._--#Coccodiscida# with simple circular margin of the disk, without radial appendages. Medullary shell simple.

The genus _Lithocyclia_ is the most simple form of Coccodiscida, and represents the common ancestral form of this family, from which all other genera of it can be derived. The lenticular, biconvex disk is quite simple, composed of a variable number of concentric, circular, chambered rings, which are pierced by radial beams, and which surround the circular lenticular cortical shell or "phacoid shell." The latter contains a simple spherical medullary shell in its centre, and is connected with it by radial beams. The margin of the disk is circular, quite simple, without radial spines or chambered arms.

1. _Lithocyclia cingulata_, n. sp.

Phacoid shell (or lenticular porous cortical shell) three times as broad as the spherical enclosed medullary shell, surrounded by one single chambered girdle or ring (with about forty chambers of equal size, separated by radial beams). Margin of the disk circular, smooth. Pores of the convex covering plates regular, circular; eight on the radius of the phacoid shell, two on the breadth of the ring.

_Dimensions._--Diameter of the disk (with one ring) 0.13, of the phacoid shell 0.1, of the medullary shell 0.033.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

2. _Lithocyclia lenticula_, n. sp. (Pl. 36, figs. 3, 4).

Phacoid shell two and a half times as broad as the enclosed medullary shell, surrounded by three chambered girdles of equal size, which are divided by piercing radial beams each into about fifty chambers. Margin of the disk thorny. Pores irregular, roundish; seven on the radius of the phacoid shell, two on the breadth of each girdle.

_Dimensions._--Diameter of the disk (with three girdles) 0.2, of the phacoid shell 0.11, of the medullary shell 0.045.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

{460}3. _Lithocyclia ocellus_, Ehrenberg.

_Lithocyclia ocellus_, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 30; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Taf. xxix. fig. 3.

Phacoid shell three times as broad as the medullary shell, surrounded by numerous (seven to eleven) chambered rings, which are divided by piercing radial beams each into sixty to ninety chambers. Margin of the disk smooth. Pores regular, circular; nine on the radius of the phacoid shell, one single pore on each chamber.

_Dimensions._--Diameter of the disk (with eleven rings) 0.22, of the phacoid shell 0.1, of the medullary shell 0.035.

_Habitat._--Fossil in the rocks of Barbados.

4. _Lithocyclia monococcus_, n. sp.

_Stephanopyxis dubiosa_ (?), Bury, 1862, Polycystins of Barbados, pl. xiii. figs. 1, 2.

Phacoid shell four times as broad as the medullary shell, surrounded by numerous (five to eight) chambered rings, which are divided by piercing radial beams each into fifty to seventy chambers. Margin of the disk thickened, thorny. Pores regular, circular; seven on the radius of the phacoid shell, one single pore on each chamber.

_Dimensions._--Diameter of the disk (with eight rings) 0.18, of the phacoid shell 0.12, of the medullary shell 0.03.

_Habitat._--Pacific, central area, Station 267, depth 2700 fathoms; also fossil in the rocks of Barbados.

5. _Lithocyclia heteropora_, n. sp.

Phacoid shell two and a third times as broad as the medullary shell, surrounded by five to nine chambered rings, which are divided by piercing radial beams each into fifty to seventy chambers. Margin of the disk smooth. Pores very different in the inner and outer part of the surface; in the phacoid shell larger, regular, circular, eight on its radius, in the chambered periphery very small and irregular, somewhat spongy.

_Dimensions._--Diameter of the disk (with nine rings) 0.2, of the phacoid shell 0.13, of the medullary shell 0.055.

_Habitat._--Pacific, central area, Station 263, depth 2650 fathoms.

Genus 197. _Coccodiscus_,[236] Haeckel, 1862, Monogr. d. Radiol., p. 485.

_Definition._--#Coccodiscida# with simple circular margin of the disk, without radial appendages. Medullary shell double.

The genus _Coccodiscus_ has quite the same form and structure as the preceding _Lithocyclia_, and differs from it only in the double medullary shell, composed of two concentric latticed spheres; sometimes the inner medullary shell is spherical, the outer {461}lenticular; the latter is connected with the lenticular phacoid shell (or cortical shell) by radial beams.

1. _Coccodiscus lamarckii_, n. sp. (Pl. 36, fig. 1).

Phacoid shell (or lenticular porous cortical shell) very thick walled (as thick as one ring), three times as broad as the outer and seven times as broad as the inner medullary shell, surrounded by two to three chambered rings of equal breadth, each of which is divided by piercing radial beams into thirty-six to forty square chambers. Margin of the disk circular, smooth. Pores regular, circular, of equal size; ten on the radius of the phacoid shell, two on the breadth of each chamber.

_Dimensions._--Diameter of the disk (with two rings) 0.2, of the phacoid shell 0.14, outer medullary shell 0.05, inner 0.02.

_Habitat._--Western Tropical Pacific, Station 220, depth 1100 fathoms.

2. _Coccodiscus darwinii_, Haeckel.

_Coccodiscus darwinii_, Haeckel, 1862, Monogr. d. Radiol., p. 486, Taf. xxviii. figs. 11, 12.

Phacoid shell three times as broad as the outer and nine times as broad as the inner medullary shell, surrounded by five to eight chambered rings of equal breadth, each of which is divided by forty piercing radial beams into forty square chambers of equal size. Margin of the disk smooth, circular. Pores irregular, roundish, of unequal size; eleven on the radius of the phacoid shell, one to two on each chamber.

_Dimensions._--Diameter of the disk (with eight rings) 0.32, of the phacoid shell 0.11, outer medullary shell 0.036, inner 0.012.

_Habitat._--Mediterranean, Messina, surface.

3. _Coccodiscus goethei_, n. sp. (Pl. 36, fig. 2).

Phacoid shell two and a half times as broad as the outer and five times as broad as the inner medullary shell, surrounded by three to seven chambered rings of equal breadth, each of which is divided by piercing radial beams into sixty to eighty chambers. Margin of the disk thorny. Pores regular, circular; eight on the radius of the phacoid shell, a single one on the breadth of each chamber.

_Dimensions._--Diameter of the disk (with seven rings) 0.25, of the phacoid shell 0.1, of the medullary shell 0.04, inner 0.02.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

Subfamily 2. STYLOCYCLIDA, Haeckel, 1881, Prodromus, p. 458.

_Definition._--#Coccodiscida# with solid radial spines on the margin of the circular disk, situated in its equatorial plane (without chambered arms).

{462}Genus 198. _Stylocyclia_,[237] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

_Definition._--#Coccodiscida# with two opposite solid radial spines on the margin of the circular disk. Medullary shell simple.

The genus _Stylocyclia_ opens the series of the Stylocyclida or of those Coccodiscida in which the margin of the chambered disk is armed with solid radial spines, situated in its equatorial plane, but without chambered arms. _Stylocyclia_ is the most simple form of this subfamily, and bears only two marginal spines, opposite in one equatorial axis of the disk. The medullary shell is simple. This genus corresponds to _Xiphodictya_ in the family Porodiscida. The genus was previously known only by one single species described by Ehrenberg.

1. _Stylocyclia dimidiata_, Ehrenberg.

_Stylocyclia dimidiata_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxix. fig. 4.

Phacoid shell three times as broad as the medullary shell, surrounded by five to eight chambered rings of equal breadth, divided by eighty to ninety piercing radial beams into square chambers. Pores subregular, circular; six to seven on the radius of the phacoid shell, a single one on each chamber. Both opposite marginal spines strong, club-shaped, their thickness decreasing from the margin towards the centre of the disk. (The figure of Ehrenberg is very incomplete.)

_Dimensions._--Diameter of the disk (with eight rings) 0.25, of the phacoid shell 0.11, of the medullary shell 0.035.

_Habitat._--Fossil in the Tertiary rocks of Barbados; living in the depths of the Equatorial Atlantic, Station 348, depth (2450) fathoms.

2. _Stylocyclia prionacantha_, n. sp. (Pl. 37, fig. 6).

Phacoid shell two and a half times as broad as the medullary shell, surrounded by five to six chambered rings, which are divided by fifty to sixty piercing radial beams into square chambers. Pores in the thick-walled phacoid shell regularly circular, increasing in size from the centre; eight to nine on its radius. Pores on the surface of the chambered girdle smaller, very irregular, two to three on each ring. Both marginal spines longer than the diameter of the disk, with broad serrated edges.

_Dimensions._--Diameter of the disk (with five rings) 0.23, of the phacoid shell 0.12, of the medullary 0.05.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

{463}3. _Stylocyclia excavata_, n. sp. (Pl. 37, fig. 8).

Phacoid shell four times as broad as the medullary shell, surrounded by four chambered rings, which are divided by twenty to thirty radial beams into broad chambers. The height of the rings increases strongly from the centre, so that the fourth ring is two and a half times as high as the first. Pores irregular, roundish; five to six on the radius of the phacoid shell, one to two on the breadth of each ring. Margin of the disk smooth. Both marginal spines thin and long, cylindrical, arising from the medullary shell, longer than the diameter of the disk.

_Dimensions._--Diameter of the disk (with four rings) 0.25, of the phacoid shell 0.1, of the medullary shell 0.025.

_Habitat._--Fossil in the rocks of Barbados. Indian Ocean, Cocos Islands, Rabbe.

4. _Stylocyclia amphacantha_, n. sp.

Phacoid shell twice as broad as the medullary shell, surrounded by five chambered rings, divided by piercing beams each into forty to fifty chambers. Pores regular, circular; eight to nine on the radius of the phacoid shell, one on each chamber. Margin of the disk thorny. Both marginal spines strong, conical, as long as its radius.

_Dimensions._--Diameter of the disk (with five rings) 0.24, of the phacoid shell 0.1, of the medullary shell 0.05.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

Genus 199. _Amphicyclia_,[238] Haeckel, 1881, Prodromus, p. 458.

_Definition._--#Coccodiscida# with two opposite solid radial spines on the margin of the circular disk. Medullary shell double.

The genus _Amphicyclia_ has the same form and structure as _Stylocyclia_, and differs from it only in the double concentric medullary shell. It bears therefore to the latter the same relation that _Coccodiscus_ does to _Lithocyclia_.

1. _Amphicyclia chronometra_, n. sp. (Pl. 38, fig. 1).

Phacoid shell three times as broad as the outer and nine times as broad as the inner medullary shell, surrounded by two broad chambered rings, which are divided into irregular chambers by fifty to sixty radial beams of different distance. Margin of the disk thorny, lacerated. Pores irregular, roundish; twelve to sixteen on the radius of the phacoid shell, two to three on the breadth of each ring. The two opposite marginal spines strong, prismatic, with prominent edges, about as long as the diameter of the disk.

_Dimensions._--Diameter of the disk (with two rings) 0.24, of the phacoid shell 0.15, outer medullary shell 0.05, inner 0.017.

_Habitat._--Pacific, central area, Stations 265 to 268, depths 2700 to 2900 fathoms.

{464}2. _Amphicyclia amphistyla_, n. sp. (Pl. 37, fig. 7).

_Stylocyclia amphistyla_, Haeckel, 1879, MS. et Atlas (pl. xxxvii. fig. 7).

Phacoid shell thin walled, two and a half times as broad as the outer and seven times as broad as the inner medullary shell, divided by eighty to ninety radial beams into irregular chambers, which are stratified in four to five floors. Pores regular, circular; eight to nine on the radius of the phacoid shell, two on the breadth of each chamber. Both marginal spines cylindrical.

_Dimensions._--Diameter of the disk (with seven rings) 0.27, of the phacoid shell 0.1, outer medullary shell 0.04, inner 0.014.

_Habitat._--North Atlantic, Canary Islands, Station 354, surface.

3. _Amphicyclia pachydiscus_, n. sp. (Pl. 38, fig. 2).

Phacoid shell very thick, spongy, twice as broad as the outer and five times as broad as the inner medullary shell, divided by fifty to seventy radial beams into subregular chambers, which are stratified in five to six floors. Pores irregular, roundish; ten to twelve on the radius of the phacoid shell, two to three on the breadth of each chamber. The two opposite marginal spines quadrangular prismatic, very long, as broad as the radius of the inner medullary shell. Fig. 2 exhibits a vertical section (slide) through the centre.

_Dimensions._--Diameter of the disk (with five rings) 0.22, of the phacoid shell 0.1, outer medullary shell 0.05, inner 0.02.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms; fossil in Barbados.

Genus 200. _Trigonocyclia_,[239] Haeckel, 1881, Prodromus, p. 458.

_Definition._--#Coccodiscida# with three solid radial spines on the margin of the circular disk. Medullary shell simple.

The genus _Trigonocyclia_ (only known by one single species, once observed) bears on the margin of the chambered disk three solid radial spines, at equal distances one from another. It corresponds to the genus _Tripodictya_ amongst the Porodiscida.

1. _Trigonocyclia triangularis_, n. sp. (Pl. 37, fig. 5).

Phacoid shell three times as broad as the medullary shell, connected with it by six equidistant radial beams, three of which are prolonged into marginal spines. In the equatorial plane only one single chambered ring, divided by forty-four radial beams into narrow chambers. Pores large, irregular, roundish; five on the radius of the phacoid shell, two on each chamber. Surface and margin of the disk spiny. Three strong conical marginal spines, divergent at equal angles, as long as the radius of the disk.

_Dimensions._--Diameter of the disk 0.16, of the phacoid shell 0.12, of the medullary shell 0.04.

_Habitat._--Indian Ocean, Zanzibar, depth 2200 fathoms, Pullen.

{465}Genus 201. _Staurocyclia_,[240] Haeckel, 1881, Prodromus, p. 458.

_Definition._--#Coccodiscida# with four solid radial spines on the margin of the disk, crossed in two equatorial diameters perpendicular one to another. Medullary shell simple.

The genus _Staurocyclia_ is characterised by four radial spines on the margin of the disk, which are opposite in pairs and situated in two equatorial diameters, commonly perpendicular one to another. They form therefore a rectangular cross (rarely more or less irregular). The genus corresponds exactly to _Staurodictya_ in the family Porodiscida. The medullary shell is simple.

1. _Staurocyclia cruciata_, n. sp. (Pl. 37, fig. 1).

Phacoid shell two and a half times as broad as the medullary shell, surrounded by six to eight regular rings, which are divided by fifty to seventy piercing beams into square chambers. Pores regular, circular; six on the radius of the phacoid shell, one single pore on each chamber. Four crossed radial spines, arising from the medullary shell by thin bases, prolonged over the dentated margin as four strong quadrangular swords, as long as the radius of the disk.

_Dimensions._--Diameter of the disk (with eight rings) 0.23, of the phacoid shell 0.09, of the medullary shell 0.035.

_Habitat_--Pacific, central area, Station 267, depth 2700 fathoms.

2. _Staurocyclia serrata_, n. sp.

? _Haliomma_ sp., Bury, 1862, Polycystins of Barbados, pl. xxii. fig. 2.

Phacoid shell twice as broad as the medullary shell, surrounded by three to four spongy rings, which are divided by thirty to forty radial beams into irregular chambers. Pores in the phacoid shell regular, circular, five on its radius; in the chambered spongy girdle much smaller and irregular. Margin dentated, with four crossed, very large, quadrangular spines, as long as the radius of the disk, with wing-shaped, serrated edges.

_Dimensions._--Diameter of the disk (with four rings) 0.2, of the phacoid shell 0.1, of the medullary shell 0.05.

_Habitat._--Fossil in the rocks of Barbados.

3. _Staurocyclia phacostaurus_, n. sp. (Pl. 37, figs. 2, 3).

_Phacostaurus pyramidalis_, Haeckel, 1879, MS. (as a separate genus).

Phacoid shell two and a quarter times as broad as the medullary shell, connected with it by twelve radial beams (four equatorial and eight divergent) and surrounded by one single ring, which is divided by forty radial beams into regular chambers. Pores regular, honeycomb-like in the {466}phacoid shell, seven on its radius; smaller on the equatorial ring, three on its breadth. Four marginal spines pyramidal four-sided, as long and as broad at the base as the ring.

_Dimensions._--Diameter of the disk (with one ring) 0.14, of the phacoid shell 0.11, of the medullary shell 0.048.

_Habitat._--South Atlantic, Station 335, depth 1425 fathoms.

4. _Staurocyclia magniducis_, n. sp. (Pl. 37, fig. 4).

_Coccostaurus magniducis_, Haeckel, 1881, MS. et Atlas (pl. xxxvii. fig. 4).

Phacoid shell twice as broad as the medullary shell, connected with it by numerous radial beams and surrounded by eight chambered rings, which are divided by one hundred to one hundred and twenty piercing radial beams into small chambers. Pores subregular, circular; ten on the radius of the phacoid shell, two on the breadth of each chamber. Margin of the disk armed with numerous bristle-shaped radial spines, as long as the breadth of the chambered girdle. Four very large crossed spines, nearly as long as the diameter of the disk, quadrangular, with four dentated edges; at the club-shaped distal end thorny, as broad as the medullary shell and three times as broad as at the narrow base. I name this splendid species in the honour of H.R.H. the Grand Duke of Saxe-Weimar, Carl Alexander, the magnanimous protector of arts and sciences, the rector magnificentissimus of the University of Jena.

_Dimensions._--Diameter of the disk (with eight rings) 0.27, of the phacoid shell 0.11, of the medullary shell 0.05; length of the four crossed club-spines 0.2, basal breadth 0.02, distal breadth 0.06.

_Habitat._--Indian Ocean, Ceylon, Belligemma, surface (Haeckel).

Genus 202. _Astrocyclia_,[241] Haeckel, 1881, Prodromus, p. 458.

_Definition._--#Coccodiscida# with numerous (five or more, commonly thirty to sixty) solid radial spines on the margin of the circular disk. Medullary shell simple.

The genus _Astrocyclia_ exhibits on the margin of the circular chambered disk a large but variable number of solid radial spines, commonly between thirty and sixty. They are the external prolongations of the inner piercing radial beams, which divide the concentric rings of the disk into chambers. All the spines lie in the equatorial plane of the disk. The genus corresponds to _Stylodictya_ in the family Porodiscida.

1. _Astrocyclia solaster_, n. sp. (Pl. 36, fig. 7).

Phacoid shell two and a half times as broad as the medullary shell, surrounded by four to six regular rings of equal breadth, which are divided by thirty to forty piercing radial beams into broad {467}chambers. Pores regular, circular; seven on the radius of the phacoid shell, one single pore on each chamber (the size increasing from the centre). Margin with thirty to forty angular, broad, dentate spines, the prolongations of the inner radial beams.

_Dimensions._--Diameter of the disk (with six rings) 0.22, of the phacoid shell 0.1, of the medullary shell 0.04.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

2. _Astrocyclia stella_, Haeckel.

_Lithocyclia stella_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 78, Taf. xxix. fig. 2.

Phacoid shell three times as broad as the medullary shell, surrounded by four to eight rings of increasing breadth from the centre, the outer of which are more or less spongy. Each ring is divided by forty to fifty piercing radial beams into chambers of increasing size. Pores regular, circular; a single one on each chamber, ten on the radius of the phacoid shell. On the margin are scattered ten to twenty thick and short spines, four-sided pyramidal, about as long and as broad at the base as the diameter of the medullary shell.

_Dimensions._--Diameter of the disk (with eight rings) 0.25, of the phacoid shell 0.09, of the medullary shell 0.03.

_Habitat._--Fossil in the rocks of Barbados.

3. _Astrocyclia rotula_, n. sp.

Phacoid shell four times as broad as the medullary shell, surrounded by one single ring, which is divided by forty radial beams into equal chambers. Pores regular, circular; two on the breadth of the ring, six on the radius of the phacoid shell. Margin with forty short, conical spines, the prolongations of the inner radial beams, twice as long as the breadth of the ring.

_Dimensions._--Diameter of the disk 0.13, of the phacoid shell 0.1, of the medullary shell 0.025.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

4. _Astrocyclia arachnia_, n. sp.

Phacoid shell twice as broad as the medullary shell, surrounded by four to six rings of equal breadth, which are divided by twelve to twenty radial beams into broad chambers. Pores regular, circular; two on the breadth of each ring, eight on the radius of the phacoid shell. Margin with twelve to twenty very long and thin, bristle-shaped, radial spines, the prolongations of the inner beams, longer than the diameter of the disk. (Resembles _Stylodictya arachnia_, but differs in the possession of a phacoid shell.)

_Dimensions._--Diameter of the disk (with six rings) 0.22, of the phacoid shell 0.09, of the medullary shell 0.045.

_Habitat._--North Atlantic, Canary Islands.

{468}5. _Astrocyclia heterocycla_, n. sp. (Pl. 36, fig. 8). Phacoid shell two and a half times as broad as the medullary shell, surrounded by three rings of unequal breadth, the first ring as broad as the second and third together. They are divided by fifty to sixty piercing radial beams into chambers, which are square in the second and third rings, and half as large as in the first. The radial beams are alternately thicker and thinner, prolonged into short marginal spines. Pores subregular, circular; eight on the radius of the phacoid shell, two on the breadth of the first ring, a single one on each chamber of the second and third rings.

_Dimensions._--Diameter of the disk (with three rings) 0.2, of the phacoid shell 0.12, of the medullary shell 0.05.

_Habitat._--Equatorial Atlantic, Station 348, depth (2450) fathoms; also fossil in Barbados.

Genus 203. _Coccocyclia_,[242] Haeckel, 1881, Prodromus, p. 458.

_Definition._--#Coccodiscida# with numerous (five or more) solid radial spines on the margin of the circular disk. Medullary shell double.

The genus _Coccocyclia_ has the same form and structure as the foregoing _Astrocyclia_, and differs from it only in the double concentric medullary shell. It bears therefore to the latter the same relation as _Coccodiscus_ to _Lithocyclia_.

1. _Coccocyclia liriantha_, n. sp.

Phacoid shell three times as broad as the outer and ten times as broad as the inner medullary shell, connected with both by six equidistant piercing radial beams. The margin of the phacoid shell is surrounded by one or two equatorial rings, each as broad as the outer medullary shell, and divided by thirty to forty radial beams into narrow chambers. Pores subregular, circular, about nine to ten on the radius of the phacoid shell, three to four on the breadth of each ring. Margin of the disk ciliated, with six regularly disposed radial spines as prolongations of the inner six piercing beams. Each spine cylindrical, delicately crenulated, about as broad as the inner medullary shell, and once to twice as long as the diameter of the whole disk, elegantly undulated, with a conical terminal point.

_Dimensions._--Diameter of the disk (with two rings) 0.32, of the phacoid shell 0.2, of the outer medullary shell 0.06, of the inner 0.02.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

2. _Coccocyclia heliantha_, n. sp. (Pl. 36, figs. 5, 6).

Phacoid shell two and a half times as broad as the outer and six times as broad as the inner medullary shell, surrounded by six to eight rings of nearly equal breadth, the outer somewhat smaller. They are divided by fifty to sixty piercing radial beams into irregular chambers. Pores {469}irregular, roundish; ten on the radius of the phacoid shell, a single one on each chamber of the equatorial girdle. Margin of the disk with numerous strong conical radial spines of different breadths, arranged in several circles, the strongest in the equatorial plane, about as broad as one ring and twice as long. Surface thorny.

_Dimensions._--Diameter of the disk (with seven rings) 0.3, of the phacoid shell 0.12, of the outer medullary shell 0.05, of the inner 0.02.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms; also fossil in Barbados.

Subfamily 3. ASTRACTURIDA, Haeckel, 1881, Prodromus, p. 458.

_Definition._--#Coccodiscida# with two or more (commonly three or four) chambered radial arms on the margin of the disk, situated in its equatorial plane (with or without a connecting patagium between the arms).

Genus 204. _Diplactura_,[243] Haeckel, 1881, Prodromus, p. 458.

_Definition._--#Coccodiscida# with two opposite chambered arms on the margin of the circular disk, without a connecting patagium.

The genus _Diplactura_ is the simplest form of the Astracturida, or of those Coccodiscida in which the margin of the disk bears chambered arms, situated in its equatorial plane. This subfamily corresponds to the Euchitonida among the Porodiscida, to the Spongobrachida among the Spongodiscida. In _Diplactura_ there are only two free arms, opposite in one equatorial diameter (corresponding to _Amphibrachium_ among the former, to _Spongolena_ among the latter).

Subgenus 1. _Diplacturium_, Haeckel.

_Definition._--Arms blunt at the distal end, without radial spines.

1. _Diplactura diplobrachia_, n. sp.

Phacoid shell twice as broad as the medullary shell, with six pores on its radius, without a perfect chambered ring around it. Arms club-shaped, one and a half times as long as the diameter of the phacoid shell, at the distal end rounded, blunt, as broad as the latter, at the base only half as broad.

_Dimensions._--Diameter of the phacoid shell 0.08, of the medullary shell 0.04; length of the arms 0.12, basal breadth 0.04, distal breadth 0.08.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

{470}Subgenus 2. _Diplactinium_, Haeckel.

_Definition._--Arms on the distal end armed with a radial terminal spine.

2. _Diplactura diploconus_, n. sp. (Pl. 38, fig. 5).

_Amphiactura diploconus_, Haeckel, 1877, MS. et Atlas (pl. xxxviii. fig. 5).

Phacoid shell three times as broad as the medullary shell, with eight pores on its radius, surrounded by a single chambered ring. Arms club-shaped, twice as long as the diameter of the phacoid shell, at the distal end as broad as the latter, at the base only half as broad. Both poles of the common axis of the arms are armed with a strong spindle-shaped terminal spine.

_Dimensions._--Diameter of the phacoid shell 0.09, of the medullary shell 0.03; length of the arms (without terminal spines) 0.17, basal breadth 0.05, distal breadth 0.09.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

Genus 205. _Amphiactura_,[244] Haeckel, 1881, Prodromus, p. 458.

_Definition._--#Coccodiscida# with two opposite chambered arms on the margin of the circular disk, connected by a spongy patagium.

The genus _Amphiactura_ differs from the foregoing _Diplactura_ in the development of a patagium between the arms, and therefore bears the same relation to it as _Amphymenium_ in the Porodiscida does to _Amphibrachium_, or _Spongobrachium_ in the Spongodiscida does to _Spongolene_. In this and in the following #Discoidea# provided with a patagium, this connecting web constantly exhibits a different texture of its framework, which is sometimes more regularly chambered, at other times more irregularly spongy.

1. _Amphiactura amphibrachia_, n. sp. (Pl. 38, figs. 3, 4).

Phacoid shell three times as broad as the medullary shell, with eight pores on its radius. Arms nearly equilateral triangular, twice as long as the diameter of the phacoid shell, at the truncated distal end as broad as the latter, at the base only one-third as broad. Patagium a circular lenticular disk, enveloping only the basal third of the arms, with three to four concentric circular rings, divided into chambers by about forty radial beams, which are prolonged beyond the margin of the patagium into radial spines. The vertical section (fig. 4) shows that the chambers of each arm (eleven to twelve transverse rows in the radius) are disposed in two layers.

_Dimensions._--Diameter of the phacoid shell 0.09, of the medullary shell 0.03; length of the arms 0.18, basal breadth 0.03, distal breadth 0.09.

_Habitat._--Pacific, central area, Station 263, depth 2650 fathoms.

{471}Genus 206. _Trigonactura_,[245] Haeckel, 1881, Prodromus, p. 459.

_Definition._--#Coccodiscida# with three chambered arms on the margin of the circular or triangular disk, without a connecting patagium.

The genus _Trigonactura_ exhibits three radial arms, which in all known species are separated by three equal angles. The terminal points of the arm-axes are the corners of an equilateral triangle. It corresponds therefore to _Dictyastrum_ among the Porodiscida.

Subgenus 1. _Trigonacturium_, Haeckel.

_Definition._--Distal end of the arms blunt or truncated, without a terminal spine.

1. _Trigonactura pythagoræ_, Haeckel.

_Astromma pythagoræ_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xxx. fig. 2.

Phacoid shell circular, twice as broad as the medullary shell, with five pores on its radius, without a completely surrounding chambered girdle. Arms nearly square, at the truncated distal end as broad as long, and scarcely broader than at the base, two-thirds as long as the diameter of the central disk.

_Dimensions._--Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.07, distal breadth 0.07.

_Habitat._--Cosmopolitan; Atlantic, Indian, Pacific, in various depths; also fossil in Tertiary rocks of Barbados and Nicobar.

2. _Trigonactura rhopalastrella_, n. sp.

_Stephanastrum_ sp., Bury, 1862, Polycystins of Barbados, pl. xv. fig. 7.

Phacoid shell twice as broad as the medullary shell, with five pores on its radius, without a perfect chambered ring around it. Arms club-shaped, at the blunt distal end rounded, as long as the diameter of the phacoid shell; their basal breadth is one-fourth, their distal breadth one-half of its length.

_Dimensions._--Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.1, basal breadth 0.025, distal breadth 0.05.

_Habitat._--Pacific, central area, Stations 270 to 274, depths 2400 to 2800 fathoms; also fossil in Tertiary rocks of Barbados.

{472}3. _Trigonactura trigonobrachia_, n. sp.

Phacoid shell two and a half times as broad as the medullary shell, with six pores on its radius, without a perfect chambered girdle. Arms nearly equilateral triangular, twice as long as the diameter of the phacoid shell, at the truncated distal end as broad as its diameter and three times as broad as at the narrow base. (Resembles _Hymenactura hexagona_, but without a patagium.)

_Dimensions._--Diameter of the phacoid shell 0.11, of the medullary shell 0.045; length of the arms 0.2, basal breadth 0.035, distal breadth 0.1.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

4. _Trigonactura lanceolata_, n. sp.

Phacoid shell three times as broad as the medullary shell, with eight pores on its radius, surrounded by one perfect chambered ring. Arms lanceolate, three times as long as the diameter of the phacoid shell, and four times as long as broad in the middle part, at both ends very narrow, blunt.

_Dimensions._--Diameter of the phacoid shell 0.09, of the medullary shell 0.03; length of the arms 0.25, breadth in the midst 0.06.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

Subgenus 2. _Trigonactinium_, Haeckel.

_Definition._--Distal end of the arms armed with a radial spine.

5. _Trigonactura triacantha_, n. sp. (Pl. 38, figs. 6, 7).

Phacoid shell two and a half times as broad as the medullary shell, with eight pores on its radius, surrounded by one perfect chambered ring. Arms nearly lanceolate, in the middle part one and a half times as broad as at both ends, twice as long as the phacoid shell, at the distal end with a strong pyramidal terminal spine. Through the spongy framework of each arm shine sixteen to eighteen transverse bars (as septa of the joints) and six to eight longitudinal piercing beams.

_Dimensions._--Diameter of the phacoid shell 0.09, of the medullary shell 0.038; length of the arms 0.2, greatest breadth 0.08.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

6. _Trigonactura trigonodiscus_, n. sp.

? _Astromma_ sp., Bury, 1862, Polycystins of Barbados, Taf. xv. fig. 2.

Phacoid shell triangular, twice as broad as the spherical medullary shell, with six to seven pores on its radius, surrounded by one chambered ring. Arms equilateral triangular, as long as {473}the diameter of the central disk and at the base half as broad, slowly decreasing in breadth towards the distal end, which is armed with a strong pyramidal spine.

_Dimensions._--Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.12, basal breadth 0.07.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms; also fossil in Barbados.

7. _Trigonactura trixiphos_, n. sp.

Phacoid shell circular, twice as broad as the medullary shell, without a completely surrounding chambered ring, with four pores on its radius. Arms club-shaped, about as long as the diameter of the central disk, at the base half as broad as long, at the rounded distal end broader, and armed with a strong pyramidal terminal spine, nearly as long as the arm itself.

_Dimensions._--Diameter of the phacoid shell 0.08, of the medullary shell 0.04; length of the arms (without terminal spine) 0.08, basal breadth 0.04, distal breadth 0.06.

_Habitat._--Fossil in the rocks of Barbados.

Genus 207. _Hymenactura_,[246] Haeckel, 1881, Prodromus, p. 459.

_Definition._--#Coccodiscida# with three chambered arms on the margin of the circular or triangular disk, connected by a spongy patagium.

The genus _Hymenactura_ differs from the foregoing _Trigonactura_ in the spongy patagium between the arms, and bears therefore to it the same relation that among the Porodiscida _Hymeniastrum_ does to the simpler _Dictyastrum_. The oldest known species of this genus is _Hymenactura pythagoræ_, described by Ehrenberg as _Hymeniastrum pythagoræ_, but differing from this in the structure of the central disk.

Subgenus 1. _Hymenacturium_, Haeckel.

_Definition._--Distal end of the arms blunt or truncated, without terminal spines.

1. _Hymenactura archimedis_, n. sp. (Pl. 38, fig. 8).

Phacoid shell three times as broad as the medullary shell, with eight pores on its radius. Arms nearly trapezoidal, somewhat longer than the diameter of the central disk, at the truncated distal end nearly as broad, at the base only half as broad. In each arm eleven to twelve transverse rows of square chambers, each of which exhibits on the surface one large pore. Patagium enveloping the basal half of the arms, with four to five convex rows of chambers, forming together a circular concentric disk.

_Dimensions._--Diameter of the phacoid shell 0.11, of the medullary shell 0.035; length of the arms 0.12, basal breadth 0.05, distal breadth 0.1.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

{474}2. _Hymenactura pythagoræ_, Haeckel.

_Hymeniastrum pythagoræ_, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 31; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, p. 76, Taf. xxx. fig. 5.

Phacoid shell three times as broad as the medullary shell, with six pores on its radius. Arms nearly trapezoidal, somewhat longer than the diameter of the central disk, at the truncated distal end nearly as broad, at the base two-thirds as broad. In each arm eight to nine transverse rows of square chambers, each chamber with one pore on the surface. Patagium enveloping the basal half of the arms, with four to five rectilinear parallel rows of chambers, forming together a regular triangle. Differs from the preceding species mainly in the quite different structure of the patagium, from the true _Hymeniastrum pythagoræ_ in the phacoid shell of the central disk, which encloses only one simple medullary shell.

_Dimensions._--Diameter of the phacoid shell 0.11, of the medullary shell 0.04; length of the arms 0.13, basal breadth 0.07, distal breadth 0.12.

_Habitat._--Fossil in the rocks of Barbados.

3. _Hymenactura trigona_, n. sp.

_Astromma_ sp., Bury, 1862, Polycystins of Barbados, pl. xv. fig. 1.

Phacoid shell twice as broad as the medullary shell, with four to five pores on its radius. Arms slender, lanceolate, three times as long as the diameter of the phacoid shell and five times as long as broad in the middle part; distal ends blunt. Patagium enveloping only the basal half of the arms, forming a regular triangle with concave sides.

_Dimensions._--Diameter of the phacoid shell 0.08, of the medullary shell 0.035; length of the arms 0.2, greatest breadth 0.04.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms; fossil in the rocks of Barbados.

4. _Hymenactura hexagona_.

_Hymeniastrum_ sp., Bury, 1862, Polycystins of Barbados, pl. xv. fig. 3.

Phacoid shell twice as broad as the medullary shell, with four to five pores on its radius. Arms nearly equilateral triangular, three times as long as the diameter of the phacoid shell, at the truncated distal end nearly three-fourths as broad as long, at the narrow base only one-fourth as broad. Patagium complete, enveloping the arms completely, so that the whole body represents a regular hexagonal disk.

_Dimensions._--Diameter of the phacoid shell 0.08, of the medullary shell 0.04; length of the arms 0.18, basal breadth 0.04, distal breadth 0.16.

_Habitat._--Fossil in the rocks of Barbados and Nicobar.

{475}Subgenus 2. _Hymenactinium_, Haeckel.

_Definition._--Distal ends of the arms armed with terminal spines.

5. _Hymenactura ptolemæi_, n. sp.

_Astromma_ sp., Bury, 1862, Polycystins of Barbados, pl. xv. figs. 5, 6.

Phacoid shell twice as broad as the medullary shell, with six to seven pores on its radius. Arms nearly square, about as large as the phacoid shell, at the truncated distal end little broader than at the base, and armed with a strong pyramidal terminal spine. Patagium incomplete, enveloping the basal half of the arms.

_Dimensions._--Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length and greatest breadth of the arms 0.08.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms; fossil in the rocks of Barbados.

6. _Hymenactura copernici_, n. sp. (Pl. 38, fig. 9).

Phacoid shell three times as broad as the medullary shell, with six pores on its radius. Arms lanceolate, nearly twice as long as the phacoid shell, in the middle part twice as broad as the medullary shell, with a strong conical terminal spine at the distal end. In each arm about ten transverse rows of chambers. Patagium enveloping the basal half of the arms, with four convex parallel rows of chambers.

_Dimensions._--Diameter of the phacoid shell 0.1, of the medullary shell 0.035; length of the arms 0.17, greatest breadth 0.07.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

Genus 208. _Astractura_,[247] Haeckel, 1881, Prodromus, p. 459.

_Definition._--#Coccodiscida# with four chambered arms on the margin of the circular or quadrangular disk, crossed in two equatorial diameters, without a connecting patagium.

The genus _Astractura_ has the form of a regular cross, four radial arms being opposite in two equatorial diameters perpendicular one to another. In the Porodiscida the same form is repeated by _Stauralastrum_, in the Spongodiscida by _Spongasteriscus_. The oldest known species of the genus is _Astromma aristotelis_ of Ehrenberg, in which genus this author confounded triradial and four-radial forms.

{476}Subgenus 1. _Astracturium_, Haeckel.

_Definition._--Distal end of the arms blunt or truncated, without terminal spines.

1. _Astractura ordinata_, n. sp.

? _Astromma_ sp., Bury, 1862, Polycystins of Barbados, pl. xiv. fig. 3.

Phacoid shell three times as broad as the medullary shell, with six pores on its radius, without a completely developed chambered ring. Arms trapezoidal, somewhat longer than the radius of the disk, at the truncated distal end as broad as long, at the base one-third smaller.

_Dimensions._--Diameter of the phacoid shell 0.08, of the medullary shell 0.03; length of the arms 0.05, distal breadth 0.05, basal breadth 0.035.

_Habitat._--Tropical Atlantic, Station 348, depth 2450 fathoms; also fossil in Barbados.

2. _Astractura clavigera_, n. sp.

_Astromma aristotelis_, Bury, 1862, Polycystins of Barbados, pl. iv. fig. 2.

Phacoid shell twice as broad as the medullary shell, with ten pores on its radius, surrounded by one perfect chambered ring. Arms club-shaped, about as long as the radius of the central disk, at the rounded distal end two-thirds, at the base one-third as broad as long.

_Dimensions._--Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.06, basal breadth 0.02, distal breadth 0.04.

_Habitat._--Pacific, central area, Stations 270 to 274, depths 2350 to 2925 fathoms; fossil in the rocks of Barbados.

Subgenus 2. _Astractinium_, Haeckel.

_Definition._--Distal end of the arms furnished with a radial spine.

3. _Astractura aristotelis_, Haeckel.

_Astromma aristotelis_, Ehrenberg, 1856, Microgeol., Taf. xxxvi. fig. 32; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, p. 66, Taf. xxx. fig. 4.

_Astromma aristotelis_, Haeckel, 1862, Monogr. d. Radiol., p. 489.

? _Astromma aristotelis_, Bury, 1862, Polycystins of Barbados, pl. xiv. fig. 4.

Phacoid shell three times as broad as the medullary shell, with six to eight pores on its radius, surrounded by one perfect chambered ring. Arms nearly trapezoidal, about as long as the diameter of the central disk, at the base half as broad, at the truncated distal end nearly as broad as long, and armed with a large pyramidal terminal spine. Each arm with about eight transverse and longitudinal rows of chambers.

{477}_Dimensions._--Diameter of the phacoid shell 0.11, of the medullary shell 0.04; length of the arms 0.1, basal breadth 0.05, distal breadth 0.09.

_Habitat._--Cosmopolitan; Atlantic, Indian, Pacific, at various depths; fossil in the Tertiary rocks of Barbados and Nicobar.

4. _Astractura democriti_, n. sp.

_Astromma aristotelis_, var., Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf, xxx. fig. 3.

? _Astromma aristotelis_, var., Bury, 1862, Polycystins of Barbados, pl. xiv. fig. 4.

Phacoid shell twice as broad as the medullary shell, with five to seven pores on its radius, without perfect chambered ring. Arms about twice as long as broad, longer than the diameter of the central disk, at the truncated distal end a little broader than at the base, and armed with a strong, pyramidal, terminal spine.

_Dimensions._--Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.15, basal breadth 0.04, distal breadth 0.08.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms; fossil in Barbados.

5. _Astractura hippocratis_, n. sp.

Phacoid shell three times as broad as the medullary shell, with seven pores on its radius, surrounded by two to three perfect chambered rings. Arms nearly square, scarcely as long and nearly as broad as the diameter of the central disk, at the rounded distal end armed with a very strong, pyramidal, terminal spine, longer than the arm itself, and at the base as broad as the medullary shell.

_Dimensions._--Diameter of the phacoid shell 0.09, of the medullary shell 0.03; length of the arms 0.08, breadth 0.1.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

Genus 209. _Stauractura_,[248] Haeckel, 1881, Prodromus, p. 459.

_Definition._--#Coccodiscida# with four chambered arms on the margin of the circular or quadrangular disk, crossed in two equatorial diameters, connected by a spongy patagium.

The genus _Stauractura_ differs from the foregoing in the patagium between the arms, and bears therefore the same relation to it as _Histiastrum_ in the Porodiscida does to _Stauralastrum_. All known species of this genus form a regular square, if we connect the end points of the arm axes by lines.

Subgenus 1. _Stauracturium_, Haeckel.

_Definition._--Distal end of the arms blunt or truncated, without terminal spines.

{478}1. _Stauractura octogona_, n. sp.

Phacoid shell twice as broad as the medullary shell, with eight pores in its radius. Arms nearly square, little larger than the phacoid shell, with broad truncated distal ends. The corners of the latter are so connected by the complete patagium, that the whole shell forms a regular octagon.

_Dimensions._--Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.12, distal breadth 0.11.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

2. _Stauractura tetragona_, n. sp.

Phacoid shell three times as broad as the medullary shell, with eleven pores on its radius. Arms club-shaped, nearly as long as the diameter of the phacoid shell, and one and a half times as long as broad at the distal part; at the distal end rounded, blunt, without terminal spine. The terminal points of the arms are so connected by a thin, complete patagium, that the whole shell becomes a regular square.

_Dimensions._--Diameter of the phacoid shell 0.13, of the medullary shell 0.045; length of the arms 0.12, greatest breadth 0.08.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

Subgenus 2. _Stauractinium_, Haeckel.

_Definition._--Distal end of the arms furnished with a radial spine.

3. _Stauractura medusina_, n. sp.

Phacoid shell two and a half times as broad as the medullary shell, with nine pores on its radius. Arms club-shaped, one and a half times as long as the diameter of the phacoid shell, and in the outer third nearly as broad as the latter, at the base scarcely one-third as broad; their truncated distal end armed with a strong pyramidal terminal spine. Patagium incomplete, enveloping only the basal half of the arms, with three rectilinear parallel rows of chambers, forming a square.

_Dimensions._--Diameter of the phacoid shell 0.1, of the medullary shell 0.04; length of the arms 0.14, greatest breadth 0.08.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

4. _Stauractura quadrata_, n. sp.

Phacoid shell twice as broad as the medullary shell, with seven pores on the radius. Arms nearly square, about as large as the phacoid shell, with a strong pyramidal terminal spine at the distal end. Patagium complete, between every two arms triangular, with rectilinear parallel {479}rows of chambers; it connects the end points of the arm radius in such a manner that the whole shell becomes a regular square.

_Dimensions._--Diameter of the phacoid shell 0.09, of the medullary shell 0.045; length of the arms 0.1, greatest breadth 0.08.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

Genus 210. _Pentactura_,[249] Haeckel, 1881, Prodromus, p. 459.

_Definition._--#Coccodiscida# with five chambered arms on the margin of the circular or pentagonal disk, without a connecting patagium.

The genus _Pentactura_ possesses five free radial arms, and resembles _Pentalastrum_ among the Porodiscida. The distance of the five arms seems to be sometimes equal, at other times different in one and the same species.

1. _Pentactura pentactis_, Haeckel.

_Astromma pentactis_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xxx. fig. 1.

Phacoid shell two and a half times as broad as the medullary shell, with eight pores on its radius. Arms regularly or irregularly disposed, nearly square, about half as large as the phacoid shell, at the truncated distal end little broader than at the base. In the specimen figured, and very imperfectly described by Ehrenberg, (_loc. cit._), the arms were asymmetrically disposed, two opposite in one axis of the disk, two others on one side of this axis, the fifth opposite to these on the other side. Another specimen which I found in the Barbados rocks had five arms of equal size, regularly disposed, at equal intervals.

_Dimensions._--Diameter of the phacoid shell 0.1, of the medullary shell 0.04; length and breadth of the arms 0.05 to 0.06.

_Habitat._--Fossil in the rocks of Barbados.

2. _Pentactura astropecten_, n. sp.

Phacoid shell three times as broad as the medullary shell, with ten pores on its radius. Arms regularly disposed, club-shaped, nearly twice as long as the diameter of the phacoid shell, and equal to it in breadth at the rounded distal end. The latter is armed with a short conical spine, and is twice as broad as the base.

_Dimensions._--Diameter of the phacoid shell 0.09, of the medullary shell 0.03; length of the arms 0.17, basal breadth 0.05, distal breadth 0.08.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

{480}Genus 211. _Echinactura_,[250] n. gen.

_Definition._--#Coccodiscida# with five chambered arms on the margin of the circular or pentagonal disk, connected by a spongy patagium.

The genus _Echinactura_ differs from the foregoing _Pentactura_ in the patagium between the arms, and bears therefore the same relation to it as _Pentinastrum_ in the Porodiscida does to _Pentalastrum_.

1. _Echinactura culcita_, n. sp.

Phacoid shell pentagonal, three times as broad as the medullary shell, with nine pores on its radius. Arms egg-shaped, about as long as the diameter of the phacoid shell, and in the distal part half as broad. The blunt ends of the arms are so connected by the complete patagium that the whole shell becomes a regular pentagonal disk.

_Dimensions._--Diameter of the phacoid shell 0.1, of the medullary shell 0.035; length of the arms 0.11, basal breadth 0.04, distal breadth 0.06.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

2. _Echinactura asteriscus_, n. sp.

Phacoid shell twice as broad as the medullary shell, with seven pores on its radius. Arms lanceolate, twice as long as the diameter of the phacoid shell, in the middle part nearly as broad as the latter, at the distal end with a strong conical terminal spine. Patagium incomplete, enveloping only the basal half of the arms.

_Dimensions._--Diameter of the phacoid shell 0.09, of the medullary shell 0.045; length of the arms 0.2, greatest breadth 0.08.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

3. _Echinactura goniaster_, n. sp.

Phacoid shell three times as broad as the medullary shell, with nine pores on its radius. Arms club-shaped, one and a half times as long as the diameter of the phacoid shell, in the distal part nearly as broad as the latter, in the basal part one-third as broad; at the end a strong pyramidal spine. Patagium nearly complete, with concave dentated margin between each pair of arms, therefore the pentagonal disk of the whole shell with concave sides.

_Dimensions._--Diameter of the phacoid shell 0.12, of the medullary shell 0.04; length of the arms (without terminal spine) 0.18, basal breadth 0.04, distal breadth 0.1.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

{481}Family XXI. #PORODISCIDA#, Haeckel (Pls. 41-47).

_Porodiscida_, Haeckel, 1881, Prodromus, p. 459. _Trematodiscida_ et _Discospirida_, Haeckel, 1862, Monogr. d. Radiol., pp. 485, 491, 513. _Calodictya_, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 53 (_partim_).

_Definition._--#Discoidea# without phacoid shell, with flat discoidal shell, in which a simple spherical central chamber is surrounded by concentric chambered rings (each ring divided by radial beams into imperfect chambers). Surface of the disk on the two flat sides covered by a porous sieve-plate.

The family #Porodiscida# is by far the largest and richest in different and common forms among all #Discoidea#; already in my Monograph (1862) nine genera and twenty-eight species have been enumerated. Their number is here increased to more than thirty genera and two hundred species. Many of these species appertain to the most common and widely distributed SPUMELLARIA, both living and fossil. But the study of their structure is not easy, and requires (as in the foregoing Coccodiscida) not only careful examination of the facial views of the disk, but also of the marginal view and of slides and sections through different planes.

In my Monograph (1862, pp. 485, 491, 513) I had constituted for these #Discoidea# two different families, the Trematodiscida and Discospirida; but the comparative study of a far greater number of different types in the Challenger collection has since convinced me that those two families are but little different, and united by transitional forms within one and the same genus, so that they must be united as Porodiscida. Of the group, which Ehrenberg formerly had called "Calodictya," many genera appertain to the Porodiscida, whilst many others are true Spongodiscida.

The Porodiscida represent the first and the most important family of the #Cyclodiscaria#, or of those #Discoidea# which are devoid of the peculiar extracapsular lenticular "phacoid shell," characteristic of the three preceding families (united therefore as #Phacodiscaria#). Probably all #Cyclodiscaria# can be derived from _Archidiscus_, from a morphological as well as a phylogenetic point of view. _Archidiscus_ seems to be the common ancestral form not only of the Porodiscida, but also of the nearly allied Pylodiscida and Spongodiscida. This important _Archidiscus_ (Pl. 48, figs. 9-11) is a small lenticular circular disk, in which a simple latticed spherical central chamber is surrounded by one single concentric ring, connected with it by a variable number of radial beams in the equatorial plane. From this typical _Archidiscus_, as from their "architype," all other #Cyclodiscaria# may be derived; the Porodiscida by regular apposition of new concentric chambered rings on the margin, the Spongodiscida by irregular apposition of a spongy framework, the Pylodiscida by a peculiar interrupted, concentric, triradial growth, three radial arm-chambers alternating with three open gates or holes, so that already the first chambered ring is not complete.

{482}_Archidiscus_ (Pl. 48, figs. 9-11) is not only the common phylogenetic ancestral form of all #Cyclodiscaria#, but also the common ontogenetic original form of all Porodiscida, or at least of the greater part of them. The numerous species of _Archidiscus_, which are distinguished in the sequel, are at the same time the embryonic forms of different Porodiscida, corresponding to the "biogenetic main law of development." The small shell of _Archidiscus_ is sometimes completely lenticular, circular, at other times more or less polygonal; commonly on the biconvex centre much thicker than on the margin, but sometimes also of nearly equal thickness (like a medal or a short cylinder). The latticed central chamber of it is probably in the majority of species spherical, but in some more or less compressed, lenticular; the number of small pores on its surface is probably commonly between ten and twenty (four to eight usually being visible on each hemisphere). The number of radial beams, which connect it with the equatorial ring, varies commonly from four to eight; but sometimes only two or three are to be found, in other cases nine to ten or more. The regular disposition of these beams (in certain equatorial axes of the disk) is probably of great importance, as determining the later development of characteristic radial appendages of the margin in the more highly developed Porodiscida. The equatorial ring itself, forming the margin of the lenticular disk, is either a simple solid ring or a broader latticed girdle; in the latter case it merges slowly into the opposite sieve-plates of the two flat disk sides, or the porous "cover-plates," covering its parallel or convex surfaces. These latter can be regarded as direct peripheral continuations of the polar regions of the spherical central chamber. The ring-chambers, surrounding the latter in a single circle, are commonly of nearly the same breadth, but often also of different irregular size. Their number varies between two and ten or more, but commonly between four and eight; each ring-chamber is covered on the upper and lower side by the sieve-plate, bounded on the inner (proximal) side by the wall of the central chamber, on the outer (distal) side by the marginal ring, on both lateral sides by the contiguous neighbouring ring-chambers.

The important question as to the phylogenetic origin of _Archidiscus_ can be answered in a twofold way. The most simple form of _Archidiscus_ (_Archidiscus dioniscus_) can be derived immediately from the Stylosphærida, _Saturnalis_ (Pl. 13, fig. 16), only by the development of lattice-work between the equatorial ring and the two polar faces of the concentric central chamber (on the surface of the biconvex jelly-mantle). But on the other hand _Archidiscus_ may also be derived from the simplest Phacodiscida, _Sethodiscus_ (Pl. 33, figs. 1-3), by the stronger compression of the biconvex lenticular shell, so that the enclosed medullary shell on the two poles runs together with the lenticular phacoid shell, of which only the peripheral part remains free, and thus forms the chambered ring; this latter explanation seems the more natural in many cases, as often in the Porodiscida the central chamber is enclosed in one or two concentric spherical or lenticular lattice-shells.

{483}The second subfamily of the Porodiscida are the Trematodiscida, which are derived from the preceding Archidiscida by concentric growth in the equatorial plane. In the same way in which the simple chambered ring of _Archidiscus_ is connected by radial beams with the central chamber, so in _Porodiscus_ a variable number of concentric rings is connected with that first ring. The number of these concentric rings varies between two and ten or more, but commonly amounts to between three and five. The radial beams connecting them are either piercing or interrupted; their number increases gradually from the centre towards the periphery. The chambers between them are sometimes more regular, at other times more irregular in size and form. Their upper and lower wall is formed by the two covering "sieve-plates," or the porous cover-plates, which are continued from the central disk to the margin. If these two sieve-plates continue being parallel, the disk becomes medal-shaped or a short cylinder; if the two plates become more or less concavely vaulted one against the other, the disk becomes biconvex lenticular, the middle part thicker than the marginal part. Rarely the contrary is the case, the margin thicker than the centre, and then the disk biconcave.

In my Monograph I had separated as two different subfamilies the true Trematodiscida (with circular concentric rings) from the Discospirida (with spirally convoluted rings). But the enormous mass of specimens, which I afterwards examined in the Challenger collection, has convinced me that this separation was not natural. For in one and the same genus of most nearly allied forms we find on one hand quite regular concentric circular forms (_Trematodiscus_), on the other hand spirally convoluted forms (_Discospira_), and connecting between them such forms as are in the central part concentric, in the marginal part spiral (_Perispira_)--or conversely, these in the centre spiral, on the margin concentric (_Centrospira_)--and frequently also more or less irregular forms with interrupted rings (_Atactodiscus_); therefore, all those genera (Prodromus, 1881, Nos. 448-452) have only the value of subgenera of _Porodiscus_. But a distinct genus is _Perichlamydium_, in which the two sieve-plates run on the margin of the lens and form a broad hyaline porous or solid girdle. More important is the distinction of the Ommatodiscida, in which the margin of the disk exhibits one larger osculum, armed with a corona of spines (_Ommatodiscus_), or two oscula, opposite on the poles of one axis (_Stomatodiscus_). Whilst in many Porodiscida all chambers of the concentric rings lie in one and the same (equatorial) plane, in many others with further growth they become stratified in floors, and the whole disk is therefore composed of two to four or more parallel disks, each with a system of concentric chambered rings or girdles, quite as in the majority of the Coccodiscida (p. 457). Often the central part of the lenticular disk becomes thickened by apposition of such floors or strata, whilst the marginal part remains simple, with one single stratum. The communication between the chambers of the different strata seems to be the same as in the similar Coccodiscida.

Also the margin of the disk exhibits in the Porodiscida the same characteristic {484}differences as in the foregoing family. In the subfamily of Stylodictyida it bears a certain number of solid radial spines, often regularly disposed (as in the Stylocyclida). In the subfamily of Euchitonida the margin is distinguished by the possession of two to six or more (commonly three or four) chambered arms, also situated in the plane of the disk, and of the same structure (sometimes more or less irregular, spongy). These arms are very variable in size, form, and structure, exhibit the same peculiarities as in the Astracturida, and are sometimes free, at other times connected by a "patagium" or an interbrachial spongy skeleton of different structure, like a web membrane (compare above, p. 458). In some genera the arms become forked or branched on the distal end. Sometimes their distal end bears a terminal radial spine.

_The Central Capsule_ of the Porodiscida assumes generally the form of the including shell, with or without arms, but is constantly somewhat smaller, as it remains enclosed by the sieve-plates of the disk surface. Often the capsule is filled with many coloured oil-globules, disposed regularly in the chamber rows. The nucleus of it is enclosed by the central chamber, and in many cases by this and the innermost concentric rings.

_Synopsis of the Genera of the Porodiscida._

------------------------------------------------------------------------- I. Section of the Porodiscida--Archidiscaria. Central chamber of the disk surrounded only by one single chambered ring. -------------------- 1. Subfamily Archidiscida. Only one single chambered girdle surrounds the central chamber; margin smooth or spiny. ------------------------------------------------------------------------- Margin smooth, without spines, 212. _Archidiscus_.

Margin armed with radial spines, 213. _Axodiscus_.

II. Section of the Porodiscida--Astrodiscaria.

Central chamber of the disk surrounded by two or more (commonly three to six) concentric chambered rings or radiated girdles. ------------------------------------------------------------------------- II. Section of the Porodiscida--Astrodiscaria. Central chamber of the disk surrounded by two or more (commonly three to six) concentric chambered rings or radiated girdles. -------------------- 2. Subfamily Trematodiscida. Margin of the disk quite simple, without radial appendages (spines or chambered arms), without peculiar oscula. ------------------------------------------------------------------------- Margin simple, without an equatorial girdle, 214. _Porodiscus_.

Margin with a thin porous equatorial girdle, 215. _Perichlamydium_. ------------------------------------------------------------------------- 3. Subfamily Ommatodiscida. Margin of the disk without chambered arms but distinguished by one or two large oscula, or wide openings armed with a crown of spines. ------------------------------------------------------------------------- Disk with a single marginal osculum, 216. _Ommatodiscus_.

Disk with two opposite marginal oscula, 217. _Stomatodiscus_. ------------------------------------------------------------------------- 4. Subfamily Stylodictyida. Margin of the disk without peculiar oscular openings and without chambered arms, but armed with solid radial spines. ------------------------------------------------------------------------- Radial spines of the { Two opposite spines, 218. _Xiphodictya_. margin two, three, or{ four, usually quite { Three equidistant regularly disposed. { spines, 219. _Tripodictya_. { { Four crossed spines, 220. _Staurodictya_.

Radial spines of the { Margin simple, without margin five or more, { an equatorial girdle, 221. _Stylodictya_. commonly irregularly { disposed (generally {Margin with a thin porous ten to twelve). { equatorial girdle, 222. _Stylochlamydium_. ------------------------------------------------------------------------- 5. Subfamily Euchitonida.{485} Margin of the disk with radial chambered arms (or hollow chambered appendages), on the distal end of the arms with or without solid radial spines. ------------------------------------------------------------------------- { Two arms { Without a patagium, 223. _Amphibrachium_. { simple, { Two arms, { undivided. { With a patagium, 224. _Amphymenium_. opposite { in one { Two arms { Without a patagium, 225. _Amphirrhopalum_. main axis.{ forked (or { { one simple, { { other { With a patagium, 226. _Amphicraspedum_. { forked). {

{ { Regular, 227. _Dictyastrum_. { { Without a { Three { Three arms { patagium. { Bilateral, 228. _Rhopalastrum_. arms { simple, { (either { undivided. { regular, { { { Regular, 229. _Hymeniastrum_. equal, or { { With a { bilateral,{ { patagium. { Bilateral, 230. _Euchitonia_. with { { { unequal { arms). { { Without a { { Either { patagium, 231. _Chitonastrum_. { Three arms {regular or { { forked. {bilateral. { With a { { { patagium, 232. _Trigonastrum_.

Four arms { { { Regular, 233. _Stauralastrum_. (either { { Without a { regular, { Four arms { patagium. { Bilateral, 234. _Hagiastrum_. with four { simple, { equal { undivided. { { Regular, 235. _Histiastrum_. crossed { { With a { arms, or { { patagium. { Bilateral, 236. _Tessarastrum_. bilateral,{ { with { { With a terminal paired { { patagial girdle, 237. _Stephanastrum_ arms). { { { Regular, 238. _Dicranastrum_. { Four arms { Without a { { forked. { patagium. { Bilateral, 239. _Myelastrum_.

{ Five arms { Without a patagium, 240. _Pentalastrum_. { simple, { Five arms { undivided. { With a patagium, 241. _Pentinastrum_. (equal or { unequal). { Five arms { Without a patagium, 242. _Pentophiastrum_. { forked. {

Six arms { Six arms { Without a patagium, 243. _Hexalastrum_. (equal or { simple, { unequal). { undivided. { With a patagium, 244. _Hexinastrum_.

Subfamily 1. ARCHIDISCIDA, Haeckel.

_Definition._--#Porodiscida# with a simple spherical or lenticular latticed central chamber, surrounded by a single concentric latticed ring, which is divided by radial beams into two to six or more radial chambers.

{486}Genus 212. _Archidiscus_,[251] n. gen.

_Definition._--#Porodiscida# with a simple central chamber, surrounded by a single concentric ring, which is divided by radial beams into two to six or more radial chambers, without radial spines on the margin.

The genus _Archidiscus_ begins the long and polymorphous series of the #Cyclodiscaria# or of those #Discoidea# which do not possess the peculiar "phacoid shell" characteristic of the three preceding families, united as "#Phacodiscaria#." As already mentioned above, both these groups are probably of independent origin, derived from the #Sphæroidea# in different ways (compare pp. 402, 405, &c.). Among all #Cyclodiscaria# _Archidiscus_ is the most simple, and probably the common ancestral form, from which the other genera may be derived.

Subgenus 1. _Dioniscus_, Haeckel.

_Definition._--Ring with two chambers, separated by two radial beams.

1. _Archidiscus dioniscus_, n. sp.

Ring circular, connected with the central chamber by two radial beams, opposite in one axis, therefore two equal semicircular ring chambers. (This primitive form has an interesting reference to _Saturnalis_, Pl. 13, fig. 16, and differs from it only in the lattice-work covering both faces of the lenticular disk, the margin of which forms the ring.)

_Dimensions._--Diameter of the ring 0.05, of the central chamber 0.016.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

2. _Archidiscus dithalamus_, n. sp.

Ring roundish, connected with the central chamber by two radial beams, not opposite in one axis; both semicircular ring chambers more or less unequal, one of them larger than the other, and sometimes much more prominent. (If this prominence increase, we can regard it as the beginning of spiral convolutions, _Discospira_.)

_Dimensions._--Diameter of the ring 0.06, of the central chamber 0.014.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

Subgenus 2. _Trioniscus_, Haeckel.

_Definition._--Ring with three chambers, separated by three radial beams.

{487}3. _Archidiscus trioniscus_, n. sp.

Ring triangular, roundish, equilateral, connected with the central chamber by three radial beams at equal distances (120°); therefore three equal ring chambers. (Resembles the central part of the disk of _Tripodictya trigonaria_, Pl. 42, fig. 8, and may be the ancestral form of it.)

_Dimensions._--Diameter of the ring 0.04, of the central chamber 0.014.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

4. _Archidiscus trithalamus_, n. sp.

Ring irregular, roundish, connected with the central chamber by three radial beams at unequal distances; therefore three ring chambers of different size. (If these differences be important, they introduce a spiral convolution in the further development of the _Porodiscus_ arising from it.)

_Dimensions._--Diameter of the ring 0.06, of the central chamber 0.016.

_Habitat._--South Pacific, Station 288, surface.

Subgenus 3. _Tetroniscus_, Haeckel.

_Definition._--Ring with four chambers, separated by four radial beams.

5. _Archidiscus stauroniscus_, n. sp. (Pl. 48, figs. 9, 9_a_).

Ring regular, square, connected with the central chamber by four radial beams at equal distances, opposite in pairs in two axes perpendicular one to another; therefore four equal ring chambers (or congruent quadrants of the ring). Resembles the central part of the disk of _Staurodictya medusa_, &c. (Pl. 42, figs. 1-3); also of _Staurodictya gracilis_, Ehrenberg, 1875 (Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. xxiii. fig. 3).

_Dimensions._--Diameter of the ring 0.05, of the central chamber 0.016.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

6. _Archidiscus tetroniscus_, n. sp.

Ring elliptical, of rhomboidal fundamental form, connected with the central chamber by four radial beams, halving the sides of the rhombus and opposite in pairs in two axes which are not perpendicular one to another; therefore four ring chambers in pairs different, two opposite equal and larger than the two others.

_Dimensions._--Diameter of the ring 0.05 to 0.07, of the central chamber 0.016.

_Habitat._--Central Pacific, Station 263, depth 2650 fathoms.

7. _Archidiscus tetrathalamus_, n. sp.

Ring irregular, quadrangular, connected with the central chamber by four radial beams of increasing unequal length; therefore all four ring chambers of different size, gradually increasing {488}in the following quadrants of the ring. Important as an ancestral type of such spiral and semi-spiral forms as _Staurodictya cruciata_ (Pl. 42, figs. 4, 12, &c.) and _Stylodictya clavata_, _Stylodictya stellata_, &c., of Ehrenberg, 1875 (Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. xxiii. figs. 2, 7, 8, 9).

_Dimensions._--Diameter of the ring 0.05 to 0.08, of the central chamber 0.06.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

Subgenus 4. _Pentoniscus_, Haeckel.

_Definition._--Ring with five chambers, separated by five radial beams.

8. _Archidiscus pentoniscus_, n. sp.

Ring pentagonal or nearly circular, regular, connected with the central chamber by five radial beams of equal length and at equal distances (72°); therefore all five chambers of the ring of equal size and similar form. (Resembles the central part of the disk of _Pentinastrum asteriscus_, Pl. 44, fig. 2.)

_Dimensions._--Diameter of the ring 0.05, of the central chamber 0.015.

_Habitat._--North Pacific, Station 244, surface.

Subgenus 5. _Hexoniscus_, Haeckel.

_Definition._--Ring with six chambers, separated by six radial beams.

9. _Archidiscus hexoniscus_, n. sp. (Pl. 48, figs. 10, 10_a_).

Ring regular, hexagonal, or nearly circular, connected with the central chamber by six radial beams of equal length and at equal distances (60°); therefore all six chambers of the same size and form. (Resembles the central part of the disk of _Hexinastrum geryonidum_, Pl. 44, fig. 4.)

_Dimensions._--Diameter of the ring 0.06, of the central chamber 0.018.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

10. _Archidiscus pyloniscus_, n. sp. (Pl. 48, figs. 11, 11_a_).

Ring triangular, connected with the central chamber by six radial beams at alternating distances; therefore three larger chambers (of looser network) alternate with three smaller chambers (of denser network); pores of the former twice to three times as large as those of the latter. This species is of peculiar importance, as an immediate transitional form to the Pylodiscida. If these three larger ring chambers lose their few lattice-beams and so became open gates, we get _Triolene_ or _Triopyle_, the original forms of the Pylodiscida.

_Dimensions._--Diameter of the ring 0.05, of the central chamber 0.015.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

{489}11. _Archidiscus hexathalamus_, n. sp.

Ring irregular, roundish, or hexagonal, connected with the central chamber by six radial beams of unequal increasing length; therefore all six ring chambers of gradually increasing size (beginning a spiral convolution, original form of some _Discospira_).

_Dimensions._--Diameter of the ring 0.05 to 0.07, of the central chamber 0.014.

_Habitat._--South Pacific, Station 300, depth 1375 fathoms.

Subgenus 6. _Circoniscus_, Haeckel.

_Definition._--Ring with seven or more chambers, separated by seven or more radial beams.

12. _Archidiscus octoniscus_, n. sp.

Ring circular or regular octagonal, connected with the central chamber by eight equidistant radial beams; therefore eight ring chambers of equal size. (Compare the central part of the disk of _Porodiscus quadrigatus_, Pl. 41, fig. 3.)

_Dimensions._--Diameter of the ring 0.04, of the central chamber 0.014.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

13. _Archidiscus polythalamus_, n. sp.

Ring circular, connected with the central chamber by nine to ten or more radial beams at nearly equal distances. Ring chambers nine to ten, more or less equal, sometimes also eleven to twelve, more different. (This species is very variable, and may perhaps be divided into a number of different "transformistic species.")

_Dimensions._--Diameter of the ring 0.04 to 0.06, of the central chamber 0.015.

_Habitat._--Central Pacific, Stations 265 to 274, depths 2350 to 2925 fathoms.

Genus 213. _Axodiscus_,[252] n. sp.

_Definition._--#Porodiscida# with a simple central chamber, surrounded by one single concentric ring, which is divided by radial beams into two to six or more radial chambers; margin of the disk armed with radial spines.

The genus _Axodiscus_ differs from the preceding _Archidiscus_ only in the shape of the margin of the small lenticular disk, which is armed with a variable number of radial spines, indicating certain axes or radii of the shell. If these marginal spines at certain equal distances from the margin branch and their distal ends become united by these branches forming a concentric second ring, the genus passes into _Porodiscus_. The different number and disposition of the marginal spines are probably very important, {490}as determining the later development of two to four or more radii in the different genera of Porodiscida.

1. _Axodiscus stylophorus_, n. sp.

Ring circular, with two equal semicircular chambers, connected with the central chamber by two opposite radial beams, which are prolonged outside into two strong conical spines.

_Dimensions._--Diameter of the ring 0.05, of the central chamber 0.016.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

2. _Axodiscus triradiatus_, n. sp.

Ring regular, triangular, equilateral, connected with the central chamber by three equidistant radial beams, which are prolonged outside into three short conical spines. (Differs from _Archidiscus trioniscus_ in the possession of marginal spines.)

_Dimensions._--Diameter of the ring 0.04, of the central chamber 0.013.

_Habitat._--Central Pacific, Station 267, depth 2700 fathoms.

3. _Axodiscus staurophorus_, n. sp.

Ring regular, square, connected with the central chamber by four radial beams, which lie opposite in pairs in two perpendicularly crossed axes, and are prolonged outside into four delicate cylindrical spines.

_Dimensions._--Diameter of the ring 0.045, of the central chamber 0.015.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

4. _Axodiscus hexagonus_, n. sp.

Ring regular, hexagonal, connected with the central chamber by six radial beams at equal distances, which are prolonged outside into six strong pyramidal spines.

_Dimensions._--Diameter of the ring 0.06, of the central chamber 0.018.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

5. _Axodiscus trigonus_, n. sp.

Ring regular, triangular, equilateral, connected with the central chamber by six radial beams of alternating length and distance; therefore three smaller (perradial) chambers (with denser and darker network) alternating with three larger (interradial) chambers (with looser and finer network). On the margin three strong conical radial spines, arising in the radius of the larger chambers. (Differs from _Archidiscus pyloniscus_, Pl. 48, fig. 11, mainly in the strong angular spines on the three corners of the triangular shell.)

_Dimensions._--Diameter of the ring 0.05, of the central chamber 0.014.

_Habitat._--South Pacific, Station 296, depth 1825 fathoms.

{491}6. _Axodiscus octogonus_, n. sp.

Ring circular or nearly octagonal, connected with the central chamber by eight radial beams at nearly equal distances, which are prolonged outside into eight short conical spines. (Differs from _Archidiscus octoniscus_ in the marginal prolongation of the eight beams.)

_Dimensions._--Diameter of the ring 0.04, of the central chamber 0.013.

_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.

7. _Axodiscus spinosus_, n. sp.

Ring circular, connected with the central chamber by ten to twelve radial beams at nearly equal distances, which are prolonged outside into short conical spines of variable length. (May be regarded as an aculeate variety of _Archidiscus polythalamus_.)

_Dimensions._--Diameter of the ring 0.04 to 0.05, of the central chamber 0.014.

_Habitat._--Central Pacific, Stations 265 to 274, depths 2350 to 2950 fathoms.

Subfamily 2. TREMATODISCIDA, Haeckel, 1862, Monogr. d. Radiol., p. 491 (_sensu emendato et restricto_).

_Definition._--#Porodiscida# without radial appendages of the disk (solid spines or chambered arms on the margin), and without peculiar oscula on the margin of the disk, which is composed of two to four or more concentric rings.

Genus 214. _Porodiscus_,[253] Haeckel, 1881, Prodromus, p. 459.

_Definition._--#Porodiscida# with simple circular disk, composed of several rings (without radial appendages or peculiar oscula on the margin of the disk).

The genus _Porodiscus_ is, next to its ancestral form, _Archidiscus_, the simplest and most primitive form of the Porodiscida, from which all other genera of this family can be derived. The disk is quite simple, without any marginal appendages, composed of a variable number of rings, commonly of circular form, sometimes more or less polygonal, elliptical, or irregular. In my Monograph (1862, pp. 491, 513) I had separated the species, here united in _Porodiscus_, into two different genera: _Trematodiscus_ with concentric rings, and _Discospira_ with spiral rings. But the extended study of these very common forms in a great number of specimens in the Challenger collection has convinced me that the separation of those two genera cannot be maintained. In one and the same locality, where one single characteristic disk-form is very common, we find intermingled quite regular disks with only concentric, circular rings (_Trematodiscus_), and other disks with one single perfect spiral ring (_Discospira_); and between {492}these a smaller number of specimens, in which the rings of the disk are partly concentric, partly spiral; either the rings of the central part of the disk are concentric, the outer spiral (_Perispira_), or the proportion is inverse (_Centrospira_); and sometimes the whole disposition of the concentric and spiral rings is irregular, and the rings often interrupted (_Atactodiscus_). Therefore it appears more natural to give to all these different forms only the value of subgenera of _Porodiscus_, as I have already proposed in my Prodromus (1881, p. 459). Even the numerous species of _Porodiscus_ (mainly characterised by the equal or different breadth of the rings, and by the number, form, and size of the connecting radial beams and of the superficial pores) are for the most part very variable and hard to distinguish, as all those characters are not constant. _Porodiscus_ is a quite "transformistic genus."

Subgenus 1. _Trematodiscus_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 841.

_Definition._--All rings of the disk concentric (commonly circular, rarely a little elliptical or polygonal).

1. _Porodiscus orbiculatus_, Haeckel.

_Trematodiscus orbiculatus_, Haeckel, 1862, Monogr. d. Radiol., p. 492, Taf. xxix. fig. 1.

_Trematodiscus orbiculatus_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 108.

All rings of the disk circular, concentric, of equal breadth, connected by numerous alternating radial beams. Chambers differing little in size, about as large as the central chamber. Pores regular, circular, two to two and a half on the breadth of each ring.

_Dimensions._--Diameter of the disk (with nine rings) 0.18; breadth of each ring 0.01; pores 0.003.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface; also fossil in Tertiary rocks of Barbados, Sicily, and Nicobar.

2. _Porodiscus concentricus_, Haeckel.

_Trematodiscus concentricus_, Haeckel, 1862, Monogr. d. Radiol., p. 493.

_Trematodiscus concentricus_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 108.

_Flustrella concentrica_, Ehrenberg, 1838, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 132; _Ibid._, 1875, p. 72, Taf. xxii. fig. 13.

? _Flustrella concentrica_, Ehrenberg, 1854, Mikrogeol., Taf. xix. fig. 61, Taf. xx. fig. 42, Taf. xxi. fig. 51, Taf. xxxvi. fig. 29.

All rings of the disk circular, concentric, of equal breadth, connected by numerous piercing radial beams. Chambers different in size, increasing from the centre towards the periphery. Pores regular, circular, one and half to two on the breadth of each ring.

_Dimensions._--Diameter of the disk (with eight rings) 0.16; breadth of each ring 0.01; pores 0.003.

_Habitat._--Fossil in many Tertiary rocks--Barbados, Sicily, Greece, &c.

_Porodiscus haeckelii_ = _Trematodiscus haeckelii_, Bütschli, 1882, L. N. 41, Taf. xxiv. figs. 5_a_, 5_b_.

{493}3. _Porodiscus flustrella_, n. sp. (Pl. 41, fig. 1).

_Trematodiscus flustrella_, Haeckel, 1866, MS. Canar. Ins.

All rings of the disk circular, concentric, of equal breadth, connected by numerous piercing radial beams. Chambers different in size, increasing from the centre towards the periphery. Pores very irregular, polygonal, or roundish, one to three on the breadth of each ring.

_Dimensions._--Diameter of the disk (with six rings) 0.12; breadth of each ring 0.01; pores 0.002 to 0.006.

_Habitat._--Cosmopolitan; Atlantic, Pacific, &c., many Stations, surface.

4. _Porodiscus sorites_, Haeckel.

_Trematodiscus sorites_, Haeckel, 1862, Monogr. d. Radiol., p. 492, Taf. xxix. fig. 2.

All rings of the disk circular, concentric, of equal breadth, connected by numerous alternating radial beams. Chambers different in size, increasing from the centre. Pores regular, circular, one to one and a half on the breadth of each ring.

_Dimensions._--Diameter of the disk (with six rings) 0.12; breadth of each ring 0.01; pores 0.006.

_Habitat._--Mediterranean (Messina), surface.

5. _Porodiscus macroporus_, Haeckel.

_Trematodiscus macroporus_, Haeckel, 1879, MS.

_Flustrella macropora_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 160.

All rings of the disk circular, concentric, of equal breadth, connected by numerous piercing radial beams. Chambers of different breadth, increasing from the centre. Pores regular, very large, nearly square, one single pore on the breadth of each ring.

_Dimensions._--Diameter of the disk (with five rings) 0.11; breadth of each ring 0.01; pores 0.005.

_Habitat._--Fossil in the Tertiary rocks of Barbados.

6. _Porodiscus microporus_, Haeckel.

_Trematodiscus microporus_, Stöhr, 1880, Palæontogr., vol xxvi. p. 108, Taf. iv. fig. 17.

All rings of the disk concentric, either circular or a little elliptical; the innermost rings of the same breadth as the central chamber, the third ring much broader. Radial beams between them alternating; chambers of different size. Pores very small, subregular, everywhere of the same size, four to five pores on the breadth of each ring.

_Dimensions._--Diameter of the disk (with three rings) 0.15; breadth of the inner rings 0.02, of the outer 0.03; pores 0.0016.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

{494}7. _Porodiscus ellipticus_, Haeckel.

_Trematodiscus ellipticus_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 108, Taf. iv. fig. 16.

All rings of the disk concentric, either circular or a little elliptical, connected by eight piercing radial beams; central chamber elliptical, of the same breadth as the first ring, broader than the following rings, the breadth of which decreases towards the periphery. Pores irregular, in the inner rings twice as broad as in the outer (third) ring, four to five on the breadth of each ring.

_Dimensions._--Diameter of the disk (with three rings) 0.18; breadth of the inner rings 0.03, of the outer 0.02; pores 0.003 to 0.006.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

8. _Porodiscus heterocyclus_, Haeckel.

_Trematodiscus heterocyclus_, Haeckel, 1862, Monogr. d. Radiol., p. 493, Taf. xxix. fig. 3.

? _Flustrella cyclia_, Harting, 1863, Fauna Banda-Zee, p. 11, pl. i. fig. 19.

_Trematodiscus heterocyclus_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 108.

All rings of the disk concentric, circular, connected by numerous radial beams, which are partly piercing, partly alternating. The breadth of the rings increases gradually from the centre towards the periphery, corresponding also to the size of the pores; two to three circular pores on the breadth of each ring.

_Dimensions._--Diameter of the disk (with six rings) 0.17; breadth of the second ring 0.007, of the sixth 0.02; pores 0.002 to 0.006.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface; also fossil in Tertiary rocks of Barbados and the Mediterranean.

9. _Porodiscus quadrigatus_, n. sp. (Pl. 41, fig. 3).

All rings of the disk concentric, of nearly equal breadth, connected by four interradial beams, perpendicular one to another. The first ring (surrounding the central chamber) with eight chambers, the second only with four (alternating with the four radial beams). Size of the four chambers of each ring increases much towards the periphery. Pores regular, circular, about two on the breadth of each ring.

_Dimensions._--Diameter of the disk (with six rings) 0.18; breadth of each ring 0.05; pores 0.004.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

Subgenus 2. _Perispira_, Haeckel, 1881, Prodromus, p. 459.

_Definition._--The inner rings of the disk concentric (commonly circular); the outer rings spirally convoluted.

{495}10. _Porodiscus perispira_, n. sp. (Pl. 41, fig. 2).

_Perispira perforata_, Haeckel, 1881, Prodromus.

Inner rings of the disk (two or three) concentric, outer rings (three or four) spirally convoluted, spiral line simple. All rings nearly of the same breadth, connected by alternating irregular radial beams. Pores irregular, two to three on the breadth of each ring.

_Dimensions._--Diameter of the disk (with six rings) 0.17; breadth of each ring 0.016; pores 0.003 to 0.005.

_Habitat._--Pacific, central area, Stations 272 to 274, surface.

11. _Porodiscus radiatus_, n. sp.

_Perispira radiata_, Haeckel, 1881, Prodromus.

Inner rings of the disk (four or five) concentric, outer rings (three or four) spirally convoluted, spiral line simple. All rings connected by piercing radial beams (eight in the inner half, sixteen in the outer half). Breadth of the rings and of the pores increasing from the centre towards the periphery, three to four pores on the breadth of each ring.

_Dimensions._--Diameter of the disk (with eight rings) 0.18; breadth of the second ring 0.006, of the eighth ring 0.02; pores 0.002 to 0.006.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

Subgenus 3. _Centrospira_, Haeckel, 1881, Prodromus, p. 459.

_Definition._--The inner rings of the disk spirally convoluted, the outer rings concentric (commonly circular).

12. _Porodiscus centrospira_, n. sp. (Pl. 41, fig. 6).

_Centrospira perispongidium_, Haeckel, 1881, Prodromus.

Inner rings of the disk (two or three) spirally convoluted (with simple or double spiral line), outer rings (three or four) concentric, subcircular. All rings nearly of the same breadth, connected by alternating radial beams. Pores subregular, two to three on the breadth of each ring. Lattice-work in the periphery of the disk a little spongy (as in Pl. 41, fig. 11).

_Dimensions._--Diameter of the disk (with five rings) 0.15; breadth of each ring 0.015; pores 0.003.

_Habitat._--Pacific, central area, Station 267, depth 2700 fathoms.

Subgenus 4. _Discospira_, Haeckel, 1862, Monogr. d. Radiol., p. 513.

_Definition._--All rings of the disk spirally convoluted, forming parts of a simple or double spiral turning.

{496}13. _Porodiscus helicoides_, Haeckel.

_Discospira helicoides_, Haeckel, 1862, Monogr. d. Radiol., p. 514, Taf. xxix. fig. 7.

_Trematodiscus helicoides_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 841.

All rings of the disk spirally convoluted around the central chamber; spiral line regular, simple. All rings nearly of the same breadth, connected by numerous alternating radial beams. Chambers little different in size, little longer than broad. Pores of equal size, regular, two on the breadth of each ring.

_Dimensions._--Diameter of the disk (with ten rings) 0.2; breadth of each ring 0.01; pores 0.0025.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific; also fossil in the Tertiary rocks of the Mediterranean, Sicily, Oran, &c.

14. _Porodiscus spiralis_, Haeckel.

_Flustrella spiralis_, Ehrenberg, 1840, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 210; Mikrogeol., 1854, Taf. xix. fig. 62.

_Discospira spiralis_, Haeckel, 1862, Monogr. d. Radiol., p. 513.

All rings of the disk spirally convoluted around the central chamber; spiral line regular, simple. All rings nearly of the same breadth, connected by numerous (twelve to sixteen) piercing radial beams. Chambers increasing in size from the centre towards the periphery. Pores irregular, of different size, one and a half to two on the breadth of each ring.

_Dimensions._--Diameter of the disk (with eight rings) 0.16; breadth of each ring 0.01; pores 0.004.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific; also fossil in the Tertiary rocks of Barbados, Sicily, Greece, &c.

15. _Porodiscus operculina_, Haeckel.

_Discospira operculina_, Haeckel, 1862, Monogr. d. Radiol., p. 514, Taf. xxix. fig. 8.

All rings of the disk spirally convoluted around the central chamber, spiral line regular, simple. Breadth of the rings and length of the chambers increasing in size from the centre towards the periphery. Most part of chambers twice as long as broad. Pores irregular, of very different sizes, two to three on the breadth of each ring.

_Dimensions._--Diameter of the disk (with six rings) 0.16; breadth of the rings 0.012 to 0.016; pores 0.002 to 0.006.

_Habitat._--Mediterranean (Messina), surface.

16. _Porodiscus bilix_, Haeckel.

_Discospira bilix_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 113, Taf. vi. fig. 3.

All rings of the disk spirally convoluted around the large elliptical central chamber. Spiral convolutions of the inner rings simple, of the outer rings double; the latter twice as broad as the {497}former. Pores regular, circular, in the inner rings one pore on the breadth, in the outer rings two to three pores. Radial beams piercing, numerous, on the margin prominent.

_Dimensions._--Diameter of the disk (with six rings) 0.14; breadth of the inner rings 0.007, of the outer 0.013; pores 0.0017.

_Habitat._--Fossil in the Tertiary rocks of Sicily, Grotte, Stöhr.

17. _Porodiscus bispiralis_, Haeckel.

_Stylodictya bispiralis_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 160. Taf. xxiv. fig. 1.

All rings of the disk spirally convoluted, in a perfect double spiral, with increasing breadth of the rings; the fourth ring twice as broad as the first. Pores regular, circular; in the inner rings one pore on the breadth, in the outer rings two to three pores. Radial beams piercing, numerous, prominent on the margin.

_Dimensions._--Diameter of the disk (with four rings) 0.1; breadth of the inner rings 0.006, of the outer 0.012; pores 0.0015.

_Habitat._--Fossil in the rocks of Barbados; living in the depths of the Central Pacific, Station 268, depth 2900 fathoms.

18. _Porodiscus duplex_, Haeckel.

_Discospira duplex_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 114, Taf. vi. fig. 4.

All rings of the disk spirally convoluted, in a perfect double spiral, with increasing breadth of the broad rings. Pores regular, circular; in the inner rings two to three, in the outer four to five on the breadth. Radial beams interrupted. Margin of the rings thorny.

_Dimensions._--Diameter of the disk (with three rings) 0.15; breadth of the rings 0.02 to 0.04; pores 0.007.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

19. _Porodiscus semispiralis_, n. sp. (Pl. 41, fig. 4).

All rings of the disk spirally convoluted, divided by four radial, perpendicularly crossed and zigzag shaped beams into four quadrants; the quarter rings of each quadrant halving the rings of each adjacent quarter. Half spiral line often irregular or partly interrupted. Breadth of all rings nearly equal. Pores irregular, roundish, two on the breadth of each ring. Margin of the disk dentated.

_Dimensions._--Diameter of the disk (with nine rings) 0.22; breadth of each ring 0.012; pores 0.002 to 0.006.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

Subgenus 5. _Atactodiscus_, Haeckel, 1881, Prodromus, p. 459.

_Definition._--Rings of the disk more or less irregular, partly concentric, partly spirally convoluted, often interrupted.

{498}20. _Porodiscus deformis_, Haeckel.

_Discospira deformis_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 114, Taf. vi. fig. 6.

Rings of the disk irregular, partly concentric, partly spiral, often interrupted, increasing in breadth from the centre. Radial beams not piercing; pores regular, circular, two to six on the breadth of the different rings. (Very variable and irregular, sometimes more spiral, at other times more concentric, but always with equal pores.)

_Dimensions._--Diameter of the disk (with four rings) 0.18; breadth of the first ring 0.014, of the second 0.03, of the fourth 0.06; pores 0.005.

_Habitat._--Fossil in the Tertiary rocks of Barbados and Sicily; living in the Central Pacific, Stations 266 to 268, depths 2700 to 2900 fathoms.

21. _Porodiscus irregularis_, n. sp. (Pl. 41, fig. 7).

_Atactodiscus irregularis_, Haeckel, 1881, Prodromus, p. 459.

_Perispongidium irregulare_, Haeckel, 1878, MS. et Atlas (pl. xli. fig. 7).

Rings of the disk irregular, partly concentric, partly spiral, often interrupted, with nearly equal breadth. Radial beams not piercing; pores irregular, roundish, two to four on the breadth of each ring; network in the periphery of the disk spongy. (Very variable and irregular, sometimes more spiral, at other times more concentric; disk in the peripheral part often more or less spongy. Differs from the preceding by the equal breadth of the rings and the different size of the pores.)

_Dimensions._--Diameter of the disk (with six rings) 0.15; breadth of each ring 0.011; pores 0.002 to 0.004.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface; also fossil in Barbados.

Genus 215. _Perichlamydium_,[254] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

_Definition._--#Porodiscida# with a simple circular disk (without radial spines and chambered arms), surrounded on the margin by a thin porous (but not chambered) equatorial girdle.

The genus _Perichlamydium_ differs from _Porodiscus_ only in the development of a thin, porous, equatorial girdle, which surrounds the circular margin of the chambered disk. This girdle lies in the equatorial plane of the lenticular disk, and represents a very delicate siliceous plate, perforated by numerous small pores. Sometimes the proximal part of the girdle is ribbed by thin radial beams, the distal prolongations of the radial rods of the central disk. If these ribs reach the margin of the girdle and are prominent over it, _Perichlamydium_ passes over into _Stylochlamydium_.

{499}1. _Perichlamydium praetextum_, Ehrenberg.

_Perichlamydium praetextum_, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 43; Mikrogeol., 1854, Taf. xxii. fig. 21 (non 20).

_Perichlamydium praetextum_, Haeckel, 1862, Monogr. d. Radiol., p. 495.

All rings of the disk (three to four) concentric, circular, of equal breadth, with interrupted (not piercing) radial beams. Equatorial girdle without radial beams, nearly as broad as the disk; its circular pores of the same size as those of the disk; about two pores on the breadth of each ring.

_Dimensions._--Diameter of the disk (without the girdle, with four rings) 0.11; breadth of each ring 0.012; breadth of the girdle 0.06 to 0.1; pores 0.004.

_Habitat._--Cosmopolitan; Atlantic, Indian, Pacific, surface; also fossil in the Tertiary rocks of Barbados and Sicily.

2. _Perichlamydium saturnus_, n. sp. (Pl. 41, fig. 5).

All rings of the disk (three to four) concentric, circular (sometimes partly concentric, circular, partly spiral, or irregular), with interrupted (not piercing) radial beams. Equatorial girdle without radial beams, about half as broad as the disk; its circular pores very small, scarcely half as large as those of the disk; about three pores on the breadth of each ring. (Very variable in the ring-form, differs from the preceding in the small pores of the girdle.)

_Dimensions._--Diameter of the disk (without the girdle, with three rings) 0.11; breadth of each ring 0.02, pores 0.004, breadth of the girdle 0.05, pores 0.002.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

3. _Perichlamydium accrescens_, Haeckel.

_Discospira accrescens_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 114, Taf. vi. fig. 5.

All rings of the disk (six to seven) not concentric, convoluted in a simple spiral, of nearly equal breadth, with interrupted (not piercing) radial beams. Equatorial girdle in the proximal part with numerous radial beams, which do not reach its margin; its pores half as large as those of the disk, where one to two pores arise on the breadth of each ring. (The girdle becomes twice to three times as broad as in the figure of Stöhr.)

_Dimensions._--Diameter of the disk (with seven rings, without the girdle) 0.13; breadth of each ring 0.007 to 0.01; pores 0.0036; breadth of the girdle 0.05, pores of it 0.0017.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte (Stöhr), Caltanisetta (Haeckel); living in the Central Pacific, Station 266, depth 2750 fathoms.

4. _Perichlamydium spirale_, Ehrenberg.

_Perichlamydium spirale_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 80, Taf. xxii. fig. 12.

All rings of the disk (three to four) not concentric, convoluted in a simple spiral, of increasing breadth from the centre; connected by numerous piercing radial beams. Equatorial girdle about {500}half as broad as the disk, without radial beams; its pores of the same size as those of the disk, regular, circular; three pores on the breadth of the first ring, six pores of the fourth ring.

_Dimensions._--Diameter of the disk (with four rings, without the girdle) 0.12; breadth of the first ring 0.01, of the fourth 0.02; breadth of the girdle 0.05; pores 0.003.

_Habitat._--Fossil in the rocks of Barbados.

Subfamily 3. OMMATODISCIDA, Stöhr, 1880, Palæontographica, vol. xxvi. p. 115.

_Definition._--#Porodiscida# without radial appendages of the concentrically annulated disk, but distinguished by one single or two opposite large marginal oscula, or wide openings on the margin of the disk, armed with a coronet of spines.

Genus 216. _Ommatodiscus_,[255] Stöhr, 1880, Palæontographica, vol. xxvi. p. 115.

_Definition._--Porodiscida without chambered arms and radial spines on the margin of the circular or elliptical disk, but with one large marginal osculum or opening surrounded by a coronet of spines.

The genus _Ommatodiscus_, together with the following _Stomatodiscus_, form the peculiar small subfamily of Ommatodiscida, founded by Stöhr in 1880 (_loc. cit._). These remarkable Porodiscida, very nearly allied to _Porodiscus_, are distinguished by one or two large openings on the margin of the disk, and these "marginal oscula" are constantly armed with a coronet of spines (comparable to the osculum coronatum of _Sycon_ in the Calcispongiæ). Probably in the living Ommatodiscida the osculum is the door from which a "sarcode-flagellum" issues (comp. above, p. 407). Perhaps this osculum is comparable to the peculiar coronet of spines which is developed on one pole of the shell axis in some Ellipsida (_Lithomespilus_, _Lithapium_). The internal structure of the disk is commonly more or less obscure, as the lenticular disk is much thickened, sometimes nearly ellipsoidal. It is possible that the Ommatodiscida are more nearly related to the Lithelida than to the Porodiscida; but there is no indication of an internal trizonal medullary shell. Also the apparent resemblance to the Cyrtida is of no morphological value; both groups are of quite independent phylogenetic origin.

Subgenus 1. _Ommatodiscinus_, Haeckel.

_Definition._--Disk circular.

1. _Ommatodiscus decipiens_, Stöhr.

_Ommatodiscus decipiens_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 115, Taf. vi. figs. 8, 8_a._

Disk circular, with two chambered rings around the spherical central chamber, of equal breadth. Chambers twice as high as broad. Pores very small, one-third as broad as the bars {501}between them, two on the breadth of each ring. Osculum of the same breadth as the central chamber, surrounded by numerous very short teeth.

_Dimensions._--Diameter of the disk 0.12; breadth of the central chamber and of each ring 0.03; pores 0.0015.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

2. _Ommatodiscus stöhrii_, n. sp.

Disk circular with three chambered rings around the spherical central chamber, of equal breadth. Chambers broader than high. Pores of the same breadth as the bars between them, four on the breadth of each ring. Osculum of the same breadth as the central chamber, surrounded by a corona of ten to twenty thin, bristle-shaped teeth, as long as its diameter.

_Dimensions._--Diameter of the disk 0.2; breadth of the central chamber and of each ring 0.03; pores 0.004.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

3. _Ommatodiscus circularis_, n. sp.

Disk circular, with four circular chambered rings around the spherical central chamber, of increasing breadth; the fourth ring twice as broad as the second. Chambers about as broad as high. Pores large, twice as broad as the bars, one to two on the breadth of each ring. Osculum twice as broad as the central chamber, surrounded by a coronal of strong conical teeth, twice as long as its diameter.

_Dimensions._--Diameter of the disk 0.18; breadth of the central chamber and inner rings 0.015, of the outer rings 0.03; pores 0.01.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

Subgenus 2. _Ommatodisculus_, Haeckel.

_Definition._--Disk elliptical.

4. _Ommatodiscus haeckelii_, Stöhr.

_Ommatodiscus haeckelii_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 115, Taf. vi. figs. 7, 7_a._

Disk elliptical (6 : 7), with four chambered rings around the elliptical central chamber, of equal breadth. Chambers about as high as broad. Pores small, half as broad as the bars, two on the breadth of each ring. Osculum three times as broad as the central chamber, surrounded by a crown of strong conical teeth.

_Dimensions._--Length of the disk 0.18, breadth 0.16; breadth of each ring and of the central chamber 0.02; pores 0.003.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte (Stöhr), Caltanisetta (Haeckel).

{502}5. _Ommatodiscus lævigatus_, Stöhr.

_Ommatodiscus lævigatus_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 116, Taf. vi. figs. 9, 9_a._

Disk elliptical (3 : 4), with three chambered rings around the circular central chamber, the third ring half as broad as the second. Chambers twice as high as broad. Pores very small, one-third as broad as the bars. Osculum twice as broad as the central chamber, armed with a crown of short conical teeth.

_Dimensions._--Length of the disk 0.15, breadth 0.11; breadth of inner rings 0.02, of the outer 0.01; pores 0.0017.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

6. _Ommatodiscus fragilis_, Stöhr.

_Ommatodiscus fragilis_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 116, Taf. vi. figs. 10, 10_a._

Disk elliptical (4 : 5), with five chambered rings around the elliptical central chamber, the fifth ring twice as broad as each of the others. Chambers about as high as broad. Pores very small, one-fifth as broad as the bars. Osculum three times as broad as the central chamber, surrounded by a coronet of short teeth.

_Dimensions._--Length of the disk 0.17, breadth 0.13; breadth of the inner rings 0.01, of the outer 0.02; pores 0.001.

_Habitat._--Fossil in Tertiary rocks of Sicily and Barbados; living in depths of the Tropical Atlantic and Pacific, Station 353, depth 2965 fathoms, Station 265, depth 2900 fathoms, &c.

Genus 217. _Stomatodiscus_,[256] n. gen.

_Definition._--#Porodiscida# without chambered arms and radial spines on the margin of the circular or elliptical disk, but with two large, opposite, marginal oscula, or openings surrounded by a coronet of spines.

The genus _Stomatodiscus_ has the same characteristic structure as the foregoing _Ommatodiscus_, and differs from it only in the duplication of the large marginal openings. Whilst in the latter there is only one such marginal osculum, here we find on the margin of the disk two oscula, opposite on the poles of one equatorial axis.

1. _Stomatodiscus amphistomus_, n. sp.

Disk circular, with three concentric rings of equal breadth around the central chamber. Pores irregular, roundish, about two on the breadth of each ring. Surface of the lenticular shell spiny. On two opposite points of the margin a large osculum, three to four times as broad as the central chamber, armed with a coronet of strong pyramidal spines of different length, the longest equal to the radius of the disk.

{503}_Dimensions._--Diameter of the disk (with three rings) 0.12; breadth of each ring 0.016; pores 0.004.

_Habitat._--South Pacific, Station 302, depth 1450 fathoms.

2. _Stomatodiscus osculatus_, n. sp. (Pl. 48, fig. 8).

Disk elliptical, nearly twice as long as broad, with three concentric rings around the elliptical central chamber, one piercing radial beam in the main axis, the other beams interrupted. Surface of the shell with small scattered thorns. Pores very irregular, roundish, partly aggregated in groups of four to eight smaller porules. On both poles of the main axis a large elliptical marginal osculum, about as large as the central chamber, armed with a coronet of short conical spines.

_Dimensions._--Length of the disk (with three rings) 0.18, breadth 0.1; pores 0.001 to 0.006.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

Subfamily 4. STYLODICTYIDA, Haeckel, 1881, Prodromus, p. 459.

_Definition._--#Porodiscida# with solid radial spines on the margin of the concentrically annulated disk, situated in the equatorial plane of the disk (without chambered arms and marginal oscula).

Genus 218. _Xiphodictya_,[257] Haeckel, 1881, Prodromus, p. 460.

_Definition._--#Porodiscida# with two opposite, solid, radial spines on the margin of the circular or elliptical disk.

The genus _Xiphodictya_ opens the series of the Stylodictyida or of those Porodiscida in which the margin of the chambered disk is armed with solid radial spines, all situated in the equatorial plane of the disk. _Xiphodictya_ exhibits the minimum number of spines, two being opposite on the poles of one equatorial axis of the disk. It repeats, therefore, in this family the same amphistylic formation as _Sethostylus_ in the Phacodiscida and _Stylocyclia_ in the Coccodiscida.

Subgenus 1. _Xiphodictyon_, Haeckel.

_Definition._--All rings of the disk concentric, circular.

1. _Xiphodictya amphibelonia_, n. sp. (Pl. 42, fig. 10).

All rings of the disk concentric, circular, of equal breadth. Pores irregular, roundish, one and a half to two on the breadth of each ring. Margin of the disk thorny, of the same thickness as {504}the central part of the medal-shaped or cylindrical disk. Two opposite radial spines very long and thin, cylindrical, twice to three times as long as the diameter of the disk, only half as thick as the breadth of one ring.

_Dimensions._--Diameter of the disk (with five rings) 0.17; breadth of each ring 0.014; pores 0.003 to 0.012.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

2. _Xiphodictya amphirrhopalia_, n. sp. (Pl. 42, fig. 11).

All rings of the disk concentric, circular, with increasing breadth from the centre; the fifth ring twice as broad as the second. Central chamber very large. Margin of the lenticular disk thorny, much thinner than the central part. Pores irregular, roundish, two to three on the breadth of each ring. Two opposite radial spines club-shaped, about as long as the diameter of the disk, in the outer spindle-shaped part three to four times as broad as at the base.

_Dimensions._--Diameter of the disk (with six rings) 0.17; breadth of the second ring 0.008, of the fifth ring 0.016.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms; also fossil in the Tertiary rocks of Sicily (Caltanisetta).

Subgenus 2. _Xiphospira_, Haeckel.

_Definition._--All rings of the disk or a part of them not concentric, spirally convoluted; sometimes irregular or interrupted.

3. _Xiphodictya staurospira_, n. sp. (Pl. 42, fig. 12).

All rings of the disk not concentric, half spiral. Four radial beams, crossed perpendicularly and zigzag-shaped, divide each ring into four quadrants; the quarter-ring of each quadrant halves the two adjacent rings. All rings of equal breadth. Pores irregular, roundish, two on the breadth of each ring. Two opposite radial spines pyramidal, somewhat shorter than the diameter of the disk.

_Dimensions._--Diameter of the disk (with six rings) 0.16; breadth of each ring: 0.014; pores 0.003 to 0.007.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

4. _Xiphodictya heliospira_, n. sp.

All rings of the disk not concentric, convoluted in a simple, regular, spiral line; all nearly of equal breadth. Pores subregular, circular, two on the breadth of each ring. Two opposite radial spines conical, about as long as the radius of the disk. Margin of the disk thorny. (Differs from _Stylodictya heliospira_, Pl. 41, fig. 8, mainly by the two strong, opposite, radial spines.)

{505}_Dimensions._--Diameter of the disk (with six rings) 0.14; breadth of each ring 0.01 to 0.012; pores 0.002 to 0.006.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

Genus 219. _Tripodictya_,[258] Haeckel, 1881, Prodromus, p. 460.

_Definition._--#Porodiscida# with three solid, equidistant, radial spines on the margin of the circular or triangular disk.

The genus _Tripodictya_ exhibits three radial spines on the margin of the disk, divergent at equal angles; rarely in some specimens the angles differ more or less. Perhaps this genus bears a near relation to the Dictyastrida (or to the Euchitonida with three chambered arms--_Dictyastrum_, _Euchitonia_, &c.).

1. _Tripodictya trigonaria_, n. sp. (Pl. 42, fig. 8).

All rings of the disk concentric, triangular, with three equal convex sides, all of the same breadth; first and second rings with three simple chambers, third and fourth rings with six chambers, fifth ring with twelve chambers. Central chamber also equilateral triangular, from its three corners arise three piercing perradial beams; from the second ring arise three interradial beams, alternate with the latter; from the fourth ring between these and the former arise six adradial beams. Pores subregular, two on the breadth of each ring. Three marginal spines pyramidal, as long as the radius of the disk and as broad as one ring.

_Dimensions._--Diameter of the disk (with five rings) 0.11; breadth of each ring 0.011; pores 0.004.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

2. _Tripodictya triacantha_, n. sp. (Pl. 42, fig. 7).

All rings of the disk concentric, circular, of the some breadth, connected by very numerous irregular radial beams, the number of which increases towards the periphery. Pores irregular, roundish, two on the breadth of each ring. Three marginal spines spindle-shaped, as long as the radius of the disk, and in the middle part as broad as one ring.

_Dimensions._--Diameter of the disk (with eight rings) 0.2; breadth of each ring 0.012; pores 0.004.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

3. _Tripodictya tribelonia_, n. sp. (Pl. 42, fig. 9).

All rings of the disk, or a part of them, not concentric, spirally convoluted, of equal breadth, connected by numerous irregular, interrupted radial beams, the number of which increases from the centre. (In one marginal view of the disk, Pl. 42, fig. 9, the disk seemed to be composed of seven {506}parallel chambered plates in the central part, and five similar plates in the peripheral part.) Pores irregular, roundish, three on the breadth of each ring. Three marginal spines long and thin, cylindrical (as in _Staurodictya cruciata_, Pl. 42, fig, 4), longer than the diameter of the disk, and half as thick as one ring.

_Dimensions._--Diameter of the disk (with nine rings) 0.18; breadth of each ring 0.01; pores 0.002 to 0.004.

_Habitat._--Pacific, central area, Station 263, depth 2650 fathoms.

Genus 220. _Staurodictya_,[259] Haeckel, 1881, Prodromus, p. 460.

_Definition._--#Porodiscida# with four solid radial spines (commonly crossed at right angles) on the margin of the circular or quadrangular disk.

The genus _Staurodictya_ is characterised by four marginal spines, lying opposite in pairs in two crossed equatorial diameters of the disk, perpendicular one to another. Sometimes the regular rectangular position of the spines becomes more or less irregular. Commonly the marginal spines are the extreme prolongations of four internal crossed radial beams, which are either rectilinear or zigzag-shaped. In the latter case the concentric disposition of the circular rings becomes more or less spiral. Perhaps _Staurodictya_ has a near relation to the Stauralastrida (or to the Euchitonida with four crossed chambered arms--_Stauralastrum_, _Histiastrum_, &c.).

Subgenus 1. _Staurodictyon_, Haeckel.

_Definition._--All rings of the disk concentric (commonly circular, sometimes with four incisions, produced by two crossed constrictions, or nearly square).

1. _Staurodictya medusa_, n. sp. (Pl. 42, fig. 3).

All rings of the disk concentric, of nearly equal breadth, divided into four quadrants by two perradial constrictions (perpendicular one to another). Pores irregular, roundish, two to three on the breadth of each ring. Four marginal spines strong, pyramidal, nearly as long as the radius of the disk. Margin between them denticulated.

_Dimensions._--Diameter of the disk (with four rings) 0.13; breadth of each ring 0.015; pores 0.002 to 0.01.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

2. _Staurodictya ciliata_, n. sp. (Pl. 42, fig. 2).

All rings of the disk concentric, of nearly equal breadth, circular or roundish, without perradial constrictions. Pores subregular, circular, three to four on the breadth of each ring. Four marginal {507}spines short, pyramidal, about as long as the breadth of one ring. Margin between them ciliated, with thin radial bristles.

_Dimensions._--Diameter of the disk (with four rings) 0.13; breadth of each ring 0.015; pores 0.0025.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

3. _Staurodictya elegans_, n. sp. (Pl. 42, fig. 1).

All rings of the disk concentric, circular, or roundish, of increasing breadth towards the margin; the fifth ring twice as broad as the first. Pores irregular, roundish, two to three on the breadth of each ring. Four marginal spines very large, conical, with a thin pedicle at the base, cancellated by ten to twelve deep furrows, about as long as the radius of the disk and three times as long as broad at the base (above the pedicle). Margin between them ciliated, with numerous short radial spines.

_Dimensions._--Diameter of the disk (with six rings) 0.14; breadth of the inner rings 0.006, of the outer 0.012; pores 0.002 to 0.008.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

4. _Staurodictya quadrispina_, Haeckel.

_Stylodictya quadrispina_, Haeckel, 1862, Monogr. d. Radiol., p. 496, Taf. xxix. fig. 4.

All rings of the disk concentric, circular, of increasing breadth towards the margin; the fourth ring twice as broad as the second. Pores irregular, roundish, two to three on the breadth of each ring. Four marginal spines short and thin, conical, about as long as the breadth of one ring. Margin between them smooth.

_Dimensions._--Diameter of the disk (with six rings) 0.12; breadth of the inner rings 0.006, of the outer rings 0.012; pores 0.001 to 0.006.

_Habitat._--Mediterranean, Atlantic (Canary Islands), surface.

Subgenus 2. _Staurospira_, Haeckel.

_Definition._--All rings of the disk or a part of them not concentric, spirally convoluted; spiral line simple or double, sometimes half or irregular, interrupted.

5. _Staurodictya cruciata_, n. sp. (Pl. 42, figs. 4, 5).

All rings of the disk nearly of the same breadth, not concentric, half-spiral, interrupted by four zigzag-shaped radial beams crossed in two diameters perpendicular one to another. The quarter ring of each quadrant halving both neighbouring quarters. Pores irregular, roundish, two on the breadth of each ring. Pores of the outermost (eighth) ring much smaller than the others. Four marginal spines cylindrical or nearly spindle-shaped, thick, about as long as the radius of the disk. Margin between them smooth.

_Dimensions._--Diameter of the disk (with eight rings) 0.2; breadth of each ring 0.011; pores 0.004.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

{508}6. _Staurodictya splendens_, Haeckel.

_Stylodictya splendens_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxiii. fig. 9.

All rings of the disk nearly of the same breadth, not concentric, half-spiral, interrupted by four zigzag-shaped perradial beams, crossed in two diameters. The quarter ring of each quadrant halving both neighbouring quarters. Pores regular, circular, only one single on the breadth of each ring. Four marginal spines conical or spear-shaped, about half as long as the radius of the disk. Margin between them ciliated, with short bristle-shaped radial spines.

_Dimensions._--Diameter of the disk (with eight rings) 0.2; breadth of each ring 0.012; pores 0.004.

_Habitat._--Fossil in the rocks of Barbados.

7. _Staurodictya grandis_, n. sp.

All rings of the disk (twelve to sixteen) of the same breadth, not concentric, irregular, partly spiral, interrupted by irregular turnings, and by ramified radial beams, which divide each ring into numerous square chambers. Pores subregular, circular, only one single on the breadth of each ring (and on each chamber). Four marginal spines short and stout, conical, twice as long as broad at the base, four to five times as long as the breadth of one ring. Margin between them dentated.

_Dimensions._--Diameter of the disk (with sixteen rings) 0.3; breadth of each ring 0.01; pores 0.005.

_Habitat._--Pacific, central area, Stations 265 to 268, depth 2900 fathoms; also fossil in the Tertiary rocks of Barbados.

8. _Staurodictya ocellata_, Haeckel.

_Stylodictya ocellata_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxiii. fig. 7.

All rings of the disk irregular, not concentric, half-spiral, interrupted by four zigzag-shaped, crossed, radial beams; the quarter ring of each quadrant halving both neighbouring quarters. Breadth of the rings increasing towards the periphery; the fourth ring twice as broad as the second. Pores irregular, with increasing size from the centre, three on the breadth of each ring. Four marginal spines thick and long, cylindrical; margin between them smooth.

_Dimensions._--Diameter of the disk (with four rings) 0.1; breadth of the inner rings 0.01, of the outer 0.02; pores 0.002 to 0.006.

_Habitat._--Fossil in the rocks of Barbados.

_Stylodictya haeckelii_, Zittel, 1876, L. N. 29, p. 85, Taf. ii. fig. 9, is a fossil Cretaceous species, related to _Stylodictya multispina_.

{509}Genus 221. _Stylodictya_,[260] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

_Definition._--#Porodiscida# with numerous (five or more, commonly eight to twelve) solid radial spines, regularly or irregularly disposed on the margin of the circular or polygonal disk; margin simple, without a porous equatorial girdle.

The genus _Stylodictya_ comprises the majority of this subfamily, in which the number of the marginal spines exceeds four. Commonly we find eight to twelve spines, more or less regularly disposed (four perradial and four interradial, or four perradial and eight adradial); but often also the number and disposition become irregular (sometimes very large). In my Monograph (1862 pp. 495, 515) I had separated the concentric disks with closed circular rings (as true _Stylodictya_, s. str.) from the spiral disks with convoluted rings (_Stylospira_). But I retain these two groups here only as two subgenera, as intermediate forms between them are very common, and often a part of the disk concentric, a part spiral (compare above, p. 492).

Subgenus 1. _Stylodictyon_, Haeckel, 1862, Monogr. d. Radiol., p. 495.

_Definition._--All rings of the disk concentric, commonly circular (rarely a little elliptical or polygonal).

1. _Stylodictya gracilis_, Ehrenberg.

_Stylodictya gracilis_, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 28.

_Stylodictya gracilis_, Ehrenberg, 1873, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 257; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Taf. xxiii. fig. 3.

_Stylodictya gracilis_, Haeckel, 1862, Monogr. d. Radiol., p. 499.

All rings of the disk concentric, circular, of equal breadth (the first ring sometimes, but not constantly, four-lobed). Pores regular, circular, small, three on the breadth of each ring. Four perradial beams (crossed in two perpendicular diameters) beginning from the circular central chamber, four interradial beams from the first or second ring (sometimes others between them). Beams prolonged into eight to twelve (or more) marginal spines, bristle-shaped, as long as the radius of the shell.

_Dimensions._--Diameter of the disk (with four rings) 0.12; breadth of each ring 0.013; pores 0.0025.

_Habitat._--Fossil in Tertiary rocks of Barbados and Nicobar; living in the depths of the Pacific and Atlantic.

{510}2. _Stylodictya multispina_, Haeckel.

_Stylodictya multispina_, Haeckel, 1862, Monogr. d. Radiol., p. 496, Taf. xxix. fig. 5.

_Stylodictya forbesii_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 160, Taf. xxiii. fig. 6.

All rings of the disk concentric, circular, of equal breadth. Pores regular, circular, two and a half to three on the breadth of each ring. Eight to twelve radial beams beginning from the central chamber, others from the inner rings. Commonly from the third or fourth ring arise twenty-four to thirty (sometimes forty or more) piercing beams, which are prolonged at the margin into bristle-shaped radial spines, as long as the breadth of two to four rings.

_Dimensions._--Diameter of the disk (with seven rings) 0.2; breadth of each ring 0.013; pores 0.004.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface and various depths.

3. _Stylodictya hastata_, Ehrenberg.

_Stylodictya hastata_, Ehrenberg, 1873, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 257; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Taf. xxiii. fig. 5.

_Stylodictya gracilis_, Bury, 1862, Polycystins of Barbados, pl. ii. fig. 1.

All rings of the disk concentric, circular, of equal breadth. Pores regular, circular, very small, two on the breadth of each ring. Eight to twelve marginal spines very large, spear-shaped, sulcated, pyramidal, nearly as long as the diameter of the disk, with a thin pedicle at the base, above this as thick as the breadth of one ring.

_Dimensions._--Diameter of the disk (with five rings) 0.13; breadth of each ring 0.012; pores 0.003.

_Habitat._--Fossil in the rocks of Barbados.

4. _Stylodictya stellata_, Bailey.

_Stylodictya stellata_, Bailey, 1856, Amer. Journ., vol. xxii. p. 6, pl. i. fig. 20.

_Stylodictya stellata_, Haeckel, 1862, Monogr. d. Radiol., p. 499.

All rings of the disk concentric, circular, of equal breadth. Pores regular, circular, very small, two on the breadth of each ring. Marginal spines fourteen (probably variable in number, twelve to sixteen), very thick and short, conical; their length seems to be equal to their basal breadth and to the breadth of one ring. Related to _Stylochlamydium_?

_Dimensions._--Diameter of the disk (with five rings) 0.11; breadth of each ring 0.01; pores 0.003.

_Habitat._--North Pacific, depths of the Kamtschatka Sea, Bailey; Station 241, depth 2300 fathoms.

5. _Stylodictya arachnia_, Haeckel.

_Stylodictya arachnia_, Haeckel, 1862, Monogr. d. Radiol., p. 497.

_Stylocyclia arachnia_, J. Müller, 1856, p. 492; Abhandl. d. k. Akad. d. Wiss. Berlin, 1858, p. 41, Taf. i. figs. 8, 9.

All rings of the disk concentric, circular, or polygonal; their breadth increases from the centre towards the periphery, so that the fourth or fifth ring is twice as broad as the second. Pores {511}subregular, circular, two on the breadth of each ring. Radial beams partly piercing. Marginal spines eight to sixteen (commonly twelve), bristle-shaped, very thin, once to three times as long as the diameter of the disk. (On the numerous varieties of this common species compare my Monograph, 1862, p. 498.)

_Dimensions._--Diameter of the disk (with ten rings) 0.22; breadth of the inner rings 0.004 to 0.008, of the outer 0.012 to 0.015; pores 0.003 to 0.005.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface.

6. _Stylodictya solmaris_, n. sp.

All rings of the disk concentric, polygonal, with eight to sixteen rounded corners; their breadth increases from the centre; eighth ring twice as broad as the second. Pores subregular circular, large, only one pore on the breadth of each ring. Twenty to thirty marginal spines, bristle-shaped, undulating, about as long as (or longer than) the diameter of the disk.

_Dimensions._--Diameter of the disk (with eight rings) 0.2; breadth of the inner rings 0.005, of the outer 0.012; pores 0.004 to 0.008.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

7. _Stylodictya octogonia_, n. sp.

All rings of the disk concentric, increasing in breadth from the centre. The outer rings (five to eight) regular, octogonal, twice as broad as the circular inner rings. Pores subregular, circular, two to three on the breadth of each ring. Eight piercing perradial spines (alternating with the eight corners of the octogonal rings) bristle-shaped, longer than the diameter of the disk.

_Dimensions._--Diameter of the disk (with eight rings) 0.24; breadth of the inner rings 0.006, of the outer 0.014; pores 0.005 to 0.01.

_Habitat._--North Atlantic, Station 353, depth 2965 fathoms.

Subgenus 2. _Stylodictula_, Haeckel.

_Definition._--Rings of the disk partly concentric, completely annular; partly spiral or interrupted, often irregular.

8. _Stylodictya perispira_, n. sp.

Inner rings of the disk (two to four) concentric, circular, or roundish, outer rings forming a simple spiral, breadth a little increasing from the centre. Pores subregular, circular, about two on the breadth of each ring. Marginal spines bristle-shaped, ten to fifteen, about as long as the diameter of the disk.

_Dimensions._--Diameter of the disk (with eight rings) 0.2; breadth of each ring 0.013; pores 0.004.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

{512}9. _Stylodictya centrospira_, n. sp. (Pl. 41, fig. 9).

Inner rings of the disk (three or four) convoluted in a simple or double spiral, often interrupted or irregular; outer rings (two to three) concentric, circular, or roundish. Breadth of the rings variable, irregular. Pores irregular, of very different sizes, in the outer concentric part twice to four times as large as in the inner spiral part. Radial beams partly interrupted, partly piercing. Marginal spines fifty to eighty, very variable in size and number, commonly fifteen to twenty strong conical spines, twice to three times as long as the ring-breadth, and numerous (thirty to sixty) smaller spines. Very variable.

_Dimensions._--Diameter of the disk (with seven rings) 0.2; breadth of the rings 0.01 to 0.02; pores 0.002 to 0.01.

_Habitat._--Pacific, central area, Stations 263 to 274, depth 2350 to 2925 fathoms.

10. _Stylodictya setigera_, Ehrenberg.

_Stylodictya setigera_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxiii. fig. 4.

Inner rings of the disk (two to three) convoluted in a simple or double spiral, outer rings (two to three) concentric, circular, or roundish. Breadth of the rings nearly equal. Pores regular, circular, three on the breadth of each ring. Marginal spines twenty to forty, bristle-shaped, about twice as long as the ring-breadth. (The specimen figured by Ehrenberg was a young one; in older specimens I found the inner spiral disk surrounded by two to three concentric circular rings.)

_Dimensions._--Diameter of the disk (with six rings) 0.16; breadth of the rings 0.12; pores 0.003.

_Habitat._--Fossil in the rocks of Barbados; also living in the depths of the Central Pacific, Station 266, depth 2750 fathoms.

Subgenus 3. _Stylospira_, Haeckel, 1862, Monogr. d. Radiol., p. 515.

_Definition._--All rings of the disk convoluted in a simple or double spiral (sometimes also in quartered half-spirals).

11. _Stylodictya heliospira_, n. sp. (Pl. 41, fig. 8).

_Stylospira heliospira_, Haeckel, 1879, MS.

All rings of the disk convoluted in a simple regular spiral, increasing in breadth from the centre towards the periphery; the sixth ring twice as broad as the second. Pores irregular, roundish, two on the breadth of each ring. Marginal spines numerous, thirty to forty, bristle-shaped, nearly half as long as the radius of the disk.

_Dimensions._--Diameter of the disk (with seven rings) 0.16; breadth of the inner rings 0.008, of the outer 0.016; pores 0.002 to 0.006.

_Habitat._--Mediterranean, Portofino near Genoa, surface; also fossil in the Tertiary rocks of Sicily; Caltanisetta, Haeckel.

{513}12. _Stylodictya hertwigii_, Haeckel.

_Stylospira arachnia_, R. Hertwig, 1879, Organismus d. Radiol., p. 59, Taf. vi. fig. 8.

All rings of the disk convoluted in a simple regular spiral, with increasing breadth from the centre; the fifth ring twice as broad as the second. Pores regular, circular, two on the breadth of each ring. Twelve piercing radial beams and some others interrupted, prolonged into twelve to twenty radial marginal spines, bristle-shaped, about as long as the diameter of the disk.

_Dimensions._--Diameter of the disk (with five rings) 0.15; breadth of the second ring 0.01, of the fifth 0.02; pores 0.006.

_Habitat._--Mediterranean (Messina), R. Hertwig.

13. _Stylodictya dujardinii_, Haeckel.

_Stylospira dujardinii_, Haeckel, 1862, Monogr. d. Radiol., p. 515, Taf. xxix. figs. 9, 10.

All rings of the disk convoluted in a simple regular spiral, of nearly equal breadth. Pores regular, circular, two on the breadth of each ring. Very numerous (twenty to thirty or more) piercing radial beams, prolonged into bristle-shaped marginal spines, about as long as the diameter of the disk.

_Dimensions._--Diameter of the disk (with six rings) 0.12; breadth of each ring 0.01; pores 0.004.

_Habitat._--Mediterranean (Messina), Haeckel.

14. _Stylodictya echinastrum_, Ehrenberg.

_Stylodictya echinastrum_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxiii. fig. 1.

All rings of the disk convoluted in a double spiral, of nearly equal breadth. Pores irregular, roundish, two to three on the breadth of each ring. Marginal spines numerous, twenty to thirty, of very different size, the largest conical, strong, about as long as the diameter of the disk, and on the base as broad as one ring.

_Dimensions._--Diameter of the disk (with five rings) 0.12; breadth of each ring 0.01; pores 0.002 to 0.006.

_Habitat._--Fossil in the rocks of Barbados.

15. _Stylodictya clavata_, Ehrenberg.

_Stylodictya clavata_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxiii. fig. 2.

All rings of the disk convoluted in a half spiral, of nearly equal breadth; each ring by four zigzag beams (crossed in two perpendicular diameters) divided into four equal quarters; the spiral line of each quarter ring halving both neighbouring quarters. Pores regular, circular, two on the breadth of each ring. Eight marginal spines short, conical, with thin pedicle; four perradial (as {514}prolongations of the four internal beams) alternating with four interradial spines arising from the margin of the disk.

_Dimensions._--Diameter of the disk (with five rings) 0.13; breadth of each ring 0.014; pores 0.003.

_Habitat._--Fossil in the rocks of Barbados.

Genus 222. _Stylochlamydium_,[261] Haeckel, 1881, Prodromus, p. 460.

The genus _Stylochlamydium_ is intermediate between _Perichlamydium_ (with which it was formerly united) and _Stylodictya_. It deals with the former in the peculiar equatorial girdle, with the latter in the radial spines of the disk margin, which pierce the girdle. To both these genera it shows slow transitions, and can hardly be subjected to a sharp definition.

Subgenus 1. _Stylochlamys_, Haeckel.

_Definition._--All rings of the disk concentric, circular (or somewhat polygonal).

1. _Stylochlamydium asteriscus_, n. sp. (Pl. 41, fig. 10).

_Perichlamydium asteriscus_, Haeckel, 1879, MS.

All rings of the disk concentric, circular, or polygonal, with increasing breadth from the centre; the fifth ring twice as broad as the second. Pores irregular, roundish, three to four on the breadth of each ring; in the rings two to six times as large as in the equatorial girdle, which is half as broad or two-thirds as broad as the radius of the disk. Twelve bristle-shaped radial spines are connected by the girdle near to the points; four crossed spines arising from the central chamber; two others between these in each quadrant arising from the first ring.

_Dimensions._--Diameter of the disk (with five rings) 0.15, with the girdle 0.25; breadth of the second ring 0.01, of the fifth ring 0.02; pores 0.001 to 0.005.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

2. _Stylochlamydium limbatum_, Haeckel.

_Perichlamydium limbatum_, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 43; Mikrogeol., 1854, Taf. xxii. fig. 20.

_Perichlamydium limbatum_, Haeckel, 1862, Monogr. d. Radiol., p. 494.

All rings of the disk concentric, circular, of equal breadth. Pores regular, circular, two on the breadth of each ring; twice to three times as large as the fine pores of the equatorial girdle, which is {515}about half as broad as the radius of the disk. Twelve (or eleven) bristle-shaped radial spines are connected by the girdle near to the points, irregularly disposed.

_Dimensions._--Diameter of the disk (with five rings) 0.12, with the girdle 0.2, breadth of each ring 0.01; pores 0.001 to 0.003.

_Habitat._--Fossil in the Tertiary rocks of Sicily, Caltanisetta, Grotte.

3. _Stylochlamydium venustum_, Haeckel.

_Perichlamydium venustum_, Bailey, 1856, Amer. Journ., vol. xxii. p. 5, pl. i. figs. 16, 17.

_Perichlamydium venustum_, Haeckel, 1862, Monogr. d. Radiol., p. 495.

All rings of the disk concentric, circular, of equal breadth. Pores regular, circular, everywhere of nearly equal size, three on the breadth of each ring, a little smaller in the equatorial girdle, which is about as broad as the radius of the disk. Twenty to twenty-four bristle-shaped radial spines, irregularly disposed, proceed with their free points over the margin.

_Dimensions._--Diameter of the disk (with four rings) 0.1, with the girdle 0.3; breadth of each ring 0.011; pores 0.002.

_Habitat._--North Pacific, Kamtschatka, Bailey.

4. _Stylochlamydium æquale_, Haeckel.

_Perichlamydium æquale_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 109, pl. v. fig. 2.

All rings of the disk concentric, circular, with increasing breadth from the centre; the sixth ring twice as broad as the second. Pores regular, circular, everywhere of equal size; on the breadth of the inner rings one, of the outer two, of the girdle three pores. Girdle only one-fourth as broad as the radius of the disk. About twenty bristle-shaped radial spines, irregularly disposed, are connected by the girdle near to the points.

_Dimensions._--Diameter of the disk (with six rings) 0.11, with the girdle 0.17; breadth of the second ring 0.006, of the sixth 0.013; pores 0.006.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

Subgenus 2. _Stylochlamyum_, Haeckel.

_Definition._--Rings of the disk all (or in part) not concentric, spirally convoluted or irregular.

5. _Stylochlamydium perispirale_, Haeckel.

_Perichlamydium limbatum_, var. Stöhr, 1880, Palæontogr., vol. xxvi. p. 109, Taf. v. fig. 1.

Inner rings of the disk concentric, circular, outer rings convoluted spirally, all rings of equal breadth. Pores regular, circular, two on the breadth of each ring, twice as large as in the equatorial {516}girdle, which is about half as broad as the radius of the disk. Twelve to sixteen bristle-shaped radial spines, irregularly disposed, are connected by the girdle near to the points.

_Dimensions._--Diameter of the disk (with six rings) 0.12, with the girdle 0.2; breadth of each ring 0.011; pores in the central disk 0.004, in the girdle 0.002.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

6. _Stylochlamydium spongiosum_, Haeckel.

_Perichlamydium spongiosum_, Stöhr, 1880, Palæontogr., vol. xxvi, p. 109, Taf. v. fig. 3.

Rings of the disk partly concentric, partly spiral, more or less irregular and often interrupted, with increasing breadth from the centre. Central part of the disk more or less spongy and obscure. Equatorial girdle half as broad as the radius of the chambered disk, with smaller pores than the latter, pierced by twenty to thirty thin, bristle-shaped radial beams, which proceed over the margin of the disk.

_Dimensions._--Diameter of the disk (with ten rings) 0.2, with the girdle 0.3; breadth of the rings 0.005 to 0.015; pores 0.001 to 0.005.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms; also fossil in the Tertiary rocks of Barbados and Sicily.

Subfamily 5. EUCHITONIDA, Haeckel.

_Definition._--#Porodiscida# with two or more (commonly three or four) radial chambered or spongy arms on the margin of the concentrically annulated disk, situated in its equatorial plane (with or without a connecting patagium between the arms).

Genus 223. _Amphibrachium_,[262] Haeckel, 1881, Prodromus, p. 460.

_Definition._--#Porodiscida# with two simple, undivided, chambered arms, opposite in one axis, without a patagium.

The genus _Amphibrachium_ opens the long series of the Euchitonida, or of those Porodiscida which bear on the margin of the circular central disk a certain number of chambered arms, composed of a series of chambers which are separated by transverse septa. The first group or tribe of this subfamily is formed by the Amphibrachida, in which the disk bears only two arms opposite on the poles of one axis. The simplest form of these is _Amphibrachium_, in which both arms are simple, equal, and without a patagium or spongy connecticulum.

{517}Subgenus 1. _Amphibrachella_, Haeckel.

_Definition._--Both arms equal, of the same form and size, blunt at the distal end, without a terminal spine.

1. _Amphibrachium sponguroides_, n. sp.

Both opposite arms of the same form and size, nearly cylindrical, three times as long as broad, with six to eight transverse septa or joints, at the distal end rounded, blunt, without a terminal spine.

_Dimensions._--Radius of each arm 0.22, breadth 0.065.

_Habitat._--Antarctic Ocean, Station 154, surface.

2. _Amphibrachium lanceolatum_, n. sp.

Both arms equal, lanceolate, in the middle part three times as broad as at the two ends, two and a half times as long as broad, with eight to nine transverse septa, at the distal end blunt, without a terminal spine.

_Dimensions._--Radius of each arm 0.3, greatest breadth 0.09.

_Habitat._--Pacific, central area, Station 267, depth 2700 fathoms.

3. _Amphibrachium dilatatum_, n. sp. (Pl. 44, fig. 6).

Both arms equal, trapezoidal, somewhat broader than long, on the convex distal end three times as broad as on the narrow base, with five to six transverse septa, without a terminal spine. Central disk large, somewhat irregular, with three to four rings, twice as broad as the base of the arms.

_Dimensions._--Radius of each arm 0.32, basal breadth 0.15, terminal breadth 0.44.

_Habitat._--South Atlantic, off Patagonia, Station 319, surface.

Subgenus 2. _Amphibrachidium_, Haeckel.

_Definition._--Both arms equal, of the same size and form, with terminal spines.

4. _Amphibrachium amphilonche_, n. sp.

Both arms equal, lanceolate, in the middle part four times as broad as at the two ends, twice as long as broad; on the distal end of each arm is a long conical spine.

_Dimensions._--Radius of each arm (without terminal spine) 0.2, breadth 0.08.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

{518}5. _Amphibrachium capitatum_, n. sp.

Both arms equal, club-shaped, three times as long as broad, in the outer distal half thickened, three times as broad as at the narrow base; on the distal end of each arm a strong, angular, terminal spine. (The form of the arms like that of _Stephanastrum capitatum_, Pl. 44, fig. 1.)

_Dimensions._--Radius of each arm 0.22, basal breadth 0.02, terminal breadth 0.06.

_Habitat._--Equatorial Atlantic, Station 347, surface.

6. _Amphibrachium armatum_, n. sp.

Both arms equal, four times as long as broad, in the thickened distal part twice as broad as at the base, thorny, with twenty to thirty larger spines on the distal end, and a very large pyramidal spine in the longitudinal axis. (The form of the arms like that of the odd arm in _Euchitonia carcinus_, Pl. 43, fig. 10.)

_Dimensions._--Radius of each arm 0.24, basal breadth 0.03, distal breadth 0.06.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

Subgenus 3. _Amphibrachoma_, Haeckel.

_Definition._--Both arms of different size or form, without terminal spines.

7. _Amphibrachium indicum_, n. sp.

Both arms club-shaped, but very different in size and form; larger arm three times as long and twice as broad as the smaller arm; the larger with nine joints slowly increasing in size, the smaller with four joints, rapidly increasing; the terminal joint three times as broad as the basal. Distal end blunt, rounded, without spines.

_Dimensions._--Radius of the larger arm 0.24, of the smaller 0.08; distal breadth of the former 0.06, of the latter 0.03; basal breadth 0.015.

_Habitat._--Indian Ocean, Ceylon, Haeckel, surface.

Subgenus 4. _Amphibrachura_, Haeckel.

_Definition._--Both arms of different size or form, with terminal spines.

8. _Amphibrachium clavula_, n. sp.

Both arms different in size and form; larger arm club-shaped, four times as long as broad, at the distal end three times as broad as at the base, and twice as long as the smaller arm, which resembles a stalked knob, with thin basal peduncle and spherical distal part. Ends of the two arms {519}thorny (with numerous smaller, and three to five larger spines); one very large conical terminal spine on each pole of the main axis.

_Dimensions._--Radius of the larger arm 0.3, of the smaller 0.15; distal breadth of the former 0.06, of the latter 0.04; basal breath 0.02.

_Habitat._--South Atlantic, Station 333, surface.

Genus 224. _Amphymenium_,[263] Haeckel, 1881, Prodromus, p. 460.

_Definition._--#Porodiscida# with two simple, undivided, chambered arms, opposite in one axis, connected by a patagium.

The genus _Amphymenium_ differs from the preceding _Amphibrachium_, its ancestral form, by development of a patagium or connecticulum between both arms. This forms a latticed or more spongy envelop, which surrounds either the middle part of the shell, or the whole shell with exception of the distal ends of both arms. If the envelop become very spongy, the shell may be confounded with the cylindrical Ellipside _Spongocore_ (nearly allied to _Spongurus_); possibly also _Ommatogramma_ of Ehrenberg belongs to this genus.

Subgenus 1. _Ommatogramma_, Ehrenberg (?).

_Definition._--Both opposite arms of the same size and form, blunt, without terminal spines.

1. _Amphymenium pupula_, n. sp. (Pl. 44, fig. 8).

Both arms equal, twice as long as broad, three-jointed; the terminal joint egg-shaped, as large as both other joints together; distal end rounded, blunt. Patagium nearly complete, enveloping the arms with exception of the distal end. Perimeter nearly spindle-shaped.

_Dimensions._--Radius of each arm 0.17, greatest breadth 0.06; transverse breadth of the patagium 0.13.

_Habitat._--Pacific, central area, Station 273, depth 2350 fathoms.

2. _Amphymenium naviculare_, Haeckel.

? _Ommatogramma navicularis_, Ehrenberg, 1872, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 317; Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. vi. fig. 7.

Both arms equal, three times as long as broad, spongy, not jointed; distal end a little club-shaped, blunt. Patagium nearly complete, enveloping the arms with exception of the distal end. Perimeter nearly lanceolate. The imperfect diagnosis and figure of Ehrenberg make it doubtful {520}whether this species belongs to the Porodiscida (_Amphymenium_) or to the Spongodiscida (_Spongobrachium_) or perhaps to the Spongurida (_Spongocore_).

_Dimensions._--Radius of each arm 0.1, greatest breadth 0.03; transverse breadth of the patagium 0.05.

_Habitat._--North Pacific, Californian Sea, depth 2600 fathoms, Ehrenberg.

3. _Amphymenium zygartus_, n. sp. (Pl. 44, fig. 7).

Both arms equal, four times as long as broad, with seven to eight joints, slowly decreasing in size towards the blunt end. Patagium incomplete, protecting only the middle part of the shell on both sides; on each side two parallel lattice-plates, connected by transverse radial beams, perpendicular to the surface. Perimeter nearly rectilinear. (Resembles much certain forms of _Zygartus_, Pl. 40, but is a true Discoid, no Prunoid.) Compare also Pl. 45, fig. 8.

_Dimensions._--Radius of each arm 0.2, greatest breadth 0.05; transverse breadth of the patagium 0.11.

_Habitat._--Pacific, central area, Station 271, surface.

4. _Amphymenium monstrosum_, n. sp. (Pl. 44, fig. 11).

Both arms equal, little longer than broad, with six to seven convex joints. The axis of both arms is not common and straight, as in all other species of this genus, but broken, therefore the incomplete patagium, which envelops only two to three joints of the arms, is on one side convex, on the other side concave; it is formed by a simple lattice-plate, connected with the arms by numerous radial beams. This anomalous form, seen only once, may perhaps be a monstrosity of _Euchitonia_.

_Dimensions._--Radius of each arm 0.12, greatest breadth 0.06; transverse breadth of the patagium 0.13.

_Habitat._--South Pacific, Station 290, surface.

Subgenus 2. _Ommathymenium_, Haeckel.

_Definition._--Both opposite arms of the same size and form, armed at the distal end with terminal spines.

5. _Amphymenium amphistylium_, n. sp. (Pl. 44, fig. 9).

Both arms equal, three times as long as broad, thickened towards the truncated distal end, and armed with a strong pyramidal terminal spine. Each arm with seven joints, separated by convex, transverse septa, and halved by a radial beam lying in the longitudinal axis. Patagium incomplete, cylindrical, enveloping only the middle part of the shell.

_Dimensions._--Radius of each arm 0.18, greatest breadth 0.06; transverse breadth of the patagium 0.08.

_Habitat._--North Atlantic, Station 354, surface.

{521}6. _Amphymenium fusiforme_, n. sp.

Both arms equal, lanceolate, three times as long as broad in the width, with seven to eight joints. Distal end pointed, armed with a strong conical terminal spine. Patagium complete, enveloping the whole shell with exception of the terminal spines. Whole form spindle-shaped.

_Dimensions._--Radius of each arm 0.2, greatest breadth 0.07; transverse breadth of the patagium 0.15.

_Habitat._--South Atlantic, Station 330, surface.

Genus 225. _Amphirrhopalum_,[264] Haeckel, 1881, Prodromus, p. 460.

_Definition._--#Porodiscida# with two chambered arms, opposite in one axis, without a patagium; one arm or both forked at the distal end.

The genus _Amphirrhopalum_ differs from _Amphibrachium_, its ancestral form, by bifurcation of the distal ends of the arms, which may affect either both arms, or only one of them.

Subgenus 1. _Amphirrhopalium_, Haeckel.

_Definition._--Both opposite arms of similar size and form, with blunt branches, without terminal spines.

1. _Amphirrhopalum ximorphum_, n. sp.

Both arms equal, in the proximal half simple, in the distal half forked, with six to seven transverse septa; distal end of each branch blunt, without terminal spine, somewhat broader than the base of the whole arm. Axis of the branches concavely curved. (Resembles _Amphicraspedum maclaganium_, Pl. 45, fig. 11, but wants the patagium.)

_Dimensions._--Radius of the arms 0.18, basal breadth 0.065; terminal breadth of each branch 0.075.

_Habitat._--North Pacific, off Japan, Station 240, surface.

2. _Amphirrhopalum amphidicranum_, n. sp.

Both arms equal, in the proximal half simple, in the distal half forked, with irregular septa; distal end of each arm blunt, without a terminal spine, smaller than the basal breadth of the arm. Axis of the branches straight. (Resembles _Dicranastrum furcatum_, Pl. 47, fig. 2, but without lateral arms.)

_Dimensions._--Radius of each arm 0.15, basal breadth 0.03; terminal breadth of each branch 0.02.

_Habitat._--Pacific, central area, Station 263, depth 2650 fathoms.

{522}Subgenus 2. _Amphirrhopella_, Haeckel.

_Definition._--Both opposite arms of similar size and form, with terminal spines.

3. _Amphirrhopalum bigeminum_, n. sp.

Both arms equal, in the proximal larger half simple, in the distal smaller half forked; each branch triangular, with a strong conical terminal spine. Axis of the branches straight. (Resembles _Dicranastrum cornutum_, Pl. 45, fig. 2, but without lateral arms.)

_Dimensions._--Radius of the arms (without spines) 0.15, basal breadth 0.03; breadth of the bifurcation 0.08.

_Habitat._--South Pacific, Station 284, surface.

4. _Amphirrhopalum echinatum_, n. sp. (Pl. 45, fig. 10).

Both arms equal, in the proximal smaller half simple, nearly square, in the distal larger half forked; the branches thorny, armed at the end with numerous spines, one larger on the terminal pole of the concavely curved arm-axis.

_Dimensions._--Radius of the arms (without spines) 0.15, basal breadth 0.05; breadth of branches 0.03.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

Subgenus 3. _Amphirrhopoma_, Haeckel.

_Definition._--Both opposite arms of different size or form, without terminal spines.

5. _Amphirrhopalum ypsilon_, n. sp.

Both arms very different. Larger arm simple, egg-shaped, twice as long as broad; smaller arm in the basal half simple, nearly square, in the distal half forked; both branches egg-shaped, blunt. (Resembles _Amphicraspedum wyvilleanum_, Pl. 45, fig. 12, but wants the patagium.)

_Dimensions._--Radius of the larger simple arm 0.18, breadth 0.09; radius of the smaller forked arm 0.15, breadth of its branches 0.05.

_Habitat._--Indian Ocean, Madagascar, Rabbe, surface.

Genus 226. _Amphicraspedum_,[265] Haeckel, 1881, Prodromus, p. 460.

_Definition._--#Porodiscida# with two chambered arms, opposite in one axis, connected by a lateral patagium; one arm or both forked at the distal end.

The genus _Amphicraspedum_ exhibits the same bifurcation of the arms as does _Amphirrhopalum_, but differs from this ancestral form in the development of a patagium, an external connecticulum between the arms, which envelops the disk totally or partially.

{523}Subgenus 1. _Amphicraspedon_, Haeckel.

_Definition._--Both arms of equal size and form, without terminal spines of the branches.

1. _Amphicraspedum maclaganium_, n. sp. (Pl. 45, fig. 11).

Both arms equal, in the proximal half simple, in the distal half forked, with six to seven transverse septa; distal end of each branch rounded, blunt, somewhat broader than the base of the whole arm. Divergent axes of both branches concavely curved. Patagium incomplete, with elliptical perimeter, enveloping only the middle part of the shell. I call this interesting species in honour of Miss Nellie Maclagan, the learned translator of several zoological papers from German into English.

_Dimensions._--Radius of each arm 0.25, basal breadth 0.07; distal breadth of each branch 0.08; equatorial breadth of the patagium 0.25.

_Habitat._--North Atlantic, off Halifax, Station 50, surface.

Subgenus 2. _Amphicraspedina_, Haeckel.

_Definition._--Both arms of different size or form, without terminal spines on the branches.

2. _Amphicraspedum wyvilleanum_, n. sp. (Pl. 45, fig. 12).

Both arms different. Larger arm simple, egg-shaped, with eleven convex joints, one and a half times as long as broad; smaller arm in the basal half simple, triangular, with six cap-like joints, in the distal half forked; both branches egg-shaped, with five joints and blunt ends. Patagium nearly complete with four to five concave chamber-rows. Called in honour of Sir C. Wyville Thomson.

_Dimensions._--Radius of the larger simple arm 0.18, breadth 0.08; radius of the smaller forked arm 0.16; breadth of the branches 0.05; transverse breadth of the patagium 0.2.

_Habitat._--South Atlantic, Station 333, surface.

Subgenus 3. _Amphicraspedula_, Haeckel.

_Definition._--Both arms of different size or form, with terminal spines of the branches.

3. _Amphicraspedum murrayanum_, n. sp. (Pl. 44, fig. 10).

_Amphymenium murrayanum_, Haeckel, 1879, MS. et Atlas (pl. xliv. fig. 10).

Both arms different in size; the larger one and a half times as long and broad as the smaller. Both arms triangular, forked at the broader distal end, with two very strong, conical, divergent, {524}straight terminal spines. Patagium broad, incomplete, with circular perimeter. Called in honour of my friend Dr. John Murray.

_Dimensions._--Radius of the larger arm (including the spines) 0.24, of the smaller 0.16; distance of the terminal points of the former 0.18, of the latter 0.09; diameter of the patagium 0.2.

_Habitat._--North Atlantic, Færöe Channel, Gulf Stream, surface, John Murray.

Genus 227. _Dictyastrum_,[266] Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 830.

_Definition._--#Porodiscida# with three simple, undivided, chambered arms, without a patagium; triangular shell regular, with three equal arms and three equal angles.

The genus _Dictyastrum_ is the simplest form of the Trigonastrida, or of the Porodiscida, in which the margin of the central disk is furnished with three chambered arms. In _Dictyastrum_ these are quite simple and regular, without a patagium, separated by equal angles, so that the whole shell represents a regular, equilateral triangle, if we connect the distal points of the arms by lines. The genus _Dictyastrum_, founded by Ehrenberg in 1860, differs from his _Rhopalodictyum_--after his own diagnosis--only by an insignificant difference in the form of the simple arms, which is scarcely a specific character. I therefore apply this name here in the above amended sense, seeing that the only figured species of Ehrenberg (_Dictyastrum angulatum_) occurs in two different, but externally very similar forms: one of these is a true Porodiscid (_Dictyastrum_) with two porous covering-plates and concentric rings; the other is a true Spongodiscid (_Rhopalodictyum_) with quite spongy, irregular network, and is probably identical with the _Rhopalodictyum truncatum_ of Ehrenberg.

Subgenus 1. _Dictyastrella_, Haeckel.

_Definition._--Arms with blunt ends, without terminal spines.

1. _Dictyastrum angulatum_, Ehrenberg.

_Dictyastrum angulatum_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 289, Taf. viii. fig. 18.

Arms nearly square with straight edges, towards the truncated end a little broader, about the same diameter as the triangular central disk. The figure of Ehrenberg seems to represent a Spongodiscid (_Rhopalodictyum angulatum_), but in the same locality (Philippine Sea) occurs also a true _Dictyastrum_ of quite the same form, but with three to four concentric rings of the central disk, and with jointed arms.

{525}_Dimensions._--Radius of each arm (length from the centre to the distal end) 0.13; breadth of the truncated end 0.1.

_Habitat._--Tropical Pacific, Philippine Sea, Station 200, depth 250 fathoms.

2. _Dictyastrum bandaicum_, Haeckel.

_Rhopalastrum bandaicum_, Harting, 1863, Mikr. Fauna Banda-Zee, p. 16, Taf. iii. fig. 45.

Arms nearly square, with convex edges, in the middle a little broader than at both ends, about half the diameter of the central disk. Differs from the nearly allied preceding species by the half size of the arms and the convex edges.

_Dimensions._--Radius of each arm 0.12, its greatest breadth 0.07.

_Habitat._--Tropical Pacific, Banda Sea, Harting.

3. _Dictyastrum hexagonum_, n. sp. (Pl. 43, fig. 7).

_Rhopalastrum hexagonum_, Haeckel, 1880, Atlas (pl. xliii. fig. 1).

Arms nearly triangular, one and a third times as broad at the distal end as long, and three times as broad as at the base. Central disk about the same diameter. In each arm six simple broad chambers. If we connect the six corners of the truncated distal ends by straight lines, we get a regular hexagon.

_Dimensions._--Radius of each arm 0.17, basal breadth 0.06, terminal breadth 0.17.

_Habitat._--Equatorial Atlantic, Station 347, surface.

4. _Dictyastrum trirrhopalum_, n. sp.

Arms club-shaped, five times as long as broad at the base, at the thickened end three times as broad as at the base. Diameter of the central disk equals half the length of the arms. (Similar to _Rhopalastrum malleus_, Pl. 43, fig. 1, but with three equal angles and much smaller disk.)

_Dimensions._--Radius of each arm 0.25, basal breadth 0.04, distal breadth 0.12.

_Habitat._--Pacific, central area, Station 273, surface.

Subgenus 2. _Dictyastromma_, Haeckel.

_Definition._--Arms on the distal end provided with terminal spines.

5. _Dictyastrum trispinosum_, n. sp. (Pl. 43, fig. 5).

_Rhopalastrum trispinosum_, Haeckel, 1881, Prodromus et Atlas (pl. xliii. fig. 5).

Arms trapezoid, at the rounded distal end twice as broad as at the base, with a strong and short, conical, terminal spine. Diameter of the circular central disk about equal to the length and the greatest breadth of the arms.

_Dimensions._--Radius of each arm 0.15, basal breadth 0.06, distal breadth 0.11.

_Habitat._--Equatorial Atlantic, Station 347, surface.

{526}6. _Dictyastrum triactis_, Ehrenberg.

_Dictyastrum triactis_, Ehrenberg, 1872, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 306.

Arms rectilinear, four times as long as broad, with parallel edges, pointed at the distal end, with a short terminal spine. Diameter of the circular central disk equal to double the breadth of the arms.

_Dimensions._--Radius of each arm 0.2, breadth 0.04.

_Habitat._--Pacific, Philippine Sea, Station 206, depth 2100 fathoms.

7. _Dictyastrum aculeatum_, n. sp.

Arms lanceolate, three times as long as broad, twice as broad in the middle as at either end, with thorny surface and numerous conical terminal spines, one very large in the radius. Central disk triangular, about as broad as the arms. (Resembles _Rhopalastrum arcticum_, Pl. 43, fig. 6, but differs by the equal angles and the triangular disk.)

_Dimensions._--Radius of each arm 0.2, breadth 0.06.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

Genus 228. _Rhopalastrum_,[267] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

_Definition._--#Porodiscida# with three simple undivided, chambered arms, without a patagium; triangular shell bilateral, one odd arm opposite to the odd angle between two paired arms.

The genus _Rhopalastrum_, founded by Ehrenberg (1847) with a very insufficient diagnosis, is here retained for those Trigonastrida that agree in the generic characters with the only species figured by him, viz., _Rhopalastrum lagenosum_ (compare my Monograph, 1862, p. 500). It comprises, therefore, such Euchitonida as agree with the preceding _Dictyastrum_ in the simple form of the three arms and the absence of a patagium, but differ from it in the different size of the three angles, and often also in the divergent form and size of the three arms; one odd arm is opposite to the odd angle between the two paired arms.

Subgenus 1. _Rhopalastrella_, Haeckel.

_Definition._--Arms with blunt ends, without terminal spines.

1. _Rhopalastrum truncatum_, Haeckel.

_Rhopalastrum truncatum_, Haeckel, 1862, Monogr. d. Radiol., p. 500, Taf. xxix. fig. 6.

Distance of both paired arms about half as large as their distance from the odd arm. All three arms nearly of the same form and size, very short and broad; their breadth nearly equals that of {527}the roundish central disk, whilst their length reaches only one-fourth of it. End of the arms convex rounded, without spines.

_Dimensions._--Radius of each arm 0.1, breadth 0.15.

_Habitat._--Mediterranean (Messina), Atlantic (Canary Islands), surface, Haeckel.

2. _Rhopalastrum pistillum_, Stöhr.

_Rhopalastrum pistillum_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 110, Taf. v. fig. 4.

Distance between the paired arms about two-thirds as large as their distance from the odd arm. All three arms nearly of the same form and size, about three times as long as the diameter of the central disk, at the base one-third as broad as at the convex rounded end, without spines. Stöhr has only observed a fragment with one arm; some perfect specimens, which I found in the Caltanisetta-rock, exhibited nearly the same form as _Rhopalastrum malleus_ (Pl. 43, fig. 1), but differ from this by the smaller disk, the broader arms, and the smaller angle between the paired arms.

_Dimensions._--Radius of all three arms 0.2; basal breadth of each arm 0.045, terminal breadth 0.13.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte (Stöhr), Caltanisetta (Haeckel).

3. _Rhopalastrum malleus_, n. sp. (Pl. 43, fig. 1).

Distance between the paired arms one and a third times as large as their distance from the odd arm. All three arms nearly of the same form and size, hammer-shaped, three times as broad at the truncated distal end as at the base. Central disk broader than the arms.

_Dimensions._--Radius of each arm 0.25, basal breadth 0.05, distal breadth 0.15.

_Habitat._--South Atlantic, Station 325, surface.

4. _Rhopalastrum lagenosum_, Ehrenberg.

_Rhopalastrum lagenosum_, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 43; Mikrogeol., 1854, Taf. xxii. fig. 22.

_Rhopalastrum lagenosum_, Haeckel, 1862, Monogr. d. Radiol., p. 501.

_Flustrella bilobata_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 81.

_Haliomma lagena_, Ehrenberg, 1840, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 200.

Distance between the paired arms one and a half times as great as their distance from the odd arm. All three arms nearly of the same form and size, about one and a half times as long as the diameter of the central disk, at the base half as broad as at the convex rounded end, without spines. Ehrenberg has only observed a fragment with two paired arms; some perfect specimens with three arms, observed by me, differed from the nearly allied _Rhopalastrum pistillum_ (from the same locality) by the larger disk, the broader arms, and the larger unpaired angle.

_Dimensions._--Radius of all three arms 0.2, basal breadth 0.05, terminal breadth 0.09.

_Habitat._--Fossil in Tertiary rocks of Sicily, Caltanisetta.

{528}5. _Rhopalastrum ypsilinum_, n. sp. (Pl. 43, fig. 2).

Distance between the paired arms half as large as their distance from the odd arm. All three arms at the concavely curved distal end three times as broad as at the narrow base. Odd arm twice as long and broad as the paired arms. Central disk smaller than the latter. No terminal spines.

_Dimensions._--Radius of the odd arm 0.32, of the paired arms 0.2; terminal breadth of the former 0.2, of the latter 0.12.

_Habitat._--Indian Ocean, Cocos Islands, Rabbe, surface.

6. _Rhopalastrum clavatum_, n. sp.

Distance between the paired arms half as large as their distance from the odd arm. All three arms club-shaped, at the thickened, nearly spherical, distal end three times as broad as at the narrow base. Odd arm nearly twice as long and broad as the paired arms. Central disk equal to the distal knob of the latter. No terminal spines.

_Dimensions._--Radius of the odd arm 0.3, of the paired arms 0.18; distal breadth of the former 0.16, of the latter 0.08.

_Habitat._--South Atlantic, Station 332, surface.

7. _Rhopalastrum irregulare_, n. sp. (Pl. 43, fig. 8).

Distance between all three arm-points different. All three arms cylindrical, nearly of the same length, but of different form, irregularly curved, about four times as long as broad, with blunt ends.

_Dimensions._--Length of each arm about 0.2, breadth 0.05.

_Habitat._--Antarctic Sea, Station 157, depth 1950 fathoms.

Subgenus 2. _Rhopalastromma_, Haeckel.

_Definition._--Arms on the distal end provided with one or more terminal spines.

8. _Rhopalastrum martellum_, n. sp.

Distance between all three arm-points nearly the same; but the odd arm is one and a half times as large as both paired arms, and is perpendicular to the common axis of the latter, therefore the shell has the form of a hammer. Each arm is twice as broad at the distal end as at the base, and armed with a conical terminal spine; the latter is vertical in the odd arm, horizontal in the paired arms.

_Dimensions._--Radius of the odd arm 0.3, of the paired arms 0.15; distal breadth of the former 0.12, of the latter 0.06.

_Habitat._--North Atlantic, Station 354, surface.

{529}9. _Rhopalastrum triceros_, n. sp. (Pl. 43, fig. 4).

Distance between the paired arms about two-thirds as large as their distance from the odd arm. All three arms club-shaped, three times as broad at the thickened distal part as at the base, and armed with one single, conical, terminal spine. Odd arm of the same breadth, but twice as long as the paired arms.

_Dimensions._--Radius of the odd arm 0.35, of the paired arms 0.2; basal breadth 0.04, distal breadth 0.12.

_Habitat._--Pacific, central area, Station 274, surface.

10. _Rhopalastrum hexaceros_, n. sp. (Pl. 43, fig. 3).

Distance between the paired arms equals four-fifths of their distance from the odd arm. All three arms nearly of the same size, about square, a little broader at the truncated distal end, which is armed at both corners with a strong, conical, radial spine.

_Dimensions._--Radius of each arm 0.2, basal breadth 0.1, distal breadth 0.12.

_Habitat._--Indian Ocean, Ceylon, Belligemma, Haeckel, surface.

11. _Rhopalastrum arcticum_, n. sp. (Pl. 43, fig. 6).

Distance between the paired arms half as large as their distance from the odd arm, which is a little larger. All three arms of the same form, lanceolate, twice to three times as long as broad, twice as broad in the middle as at either end. Each arm with twelve to fourteen transverse septa, at the distal end with a bunch of conical spines, and one single, very large, pyramidal, terminal spine.

_Dimensions._--Radius of each arm (without spine) 0.17, greatest breadth of it 0.05 to 0.06.

_Habitat._--Arctic Ocean, lat. 83° 19' N., North Polar expedition of the "Alert."

Genus 229. _Hymeniastrum_,[268] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

_Definition._--#Porodiscida# with three simple, undivided, chambered arms, connected by a patagium; triangular shell regular, with three equal arms and three equal angles.

The genus _Hymeniastrum_ was founded by Ehrenberg (1847) with a very incomplete diagnosis, and hitherto known only by one single species, figured by him as _Hymeniastrum pythagoræ_ (Mikrogeol., 1854, Taf. xxxvi. fig. 31). This form occurs in two different states, externally quite identical; in one state the central disk (as figured, _loc. cit._), is a simple lens or hollow disk, containing a medullary shell or "central chamber"; in the other state the central disk is composed of two concentric rings surrounding the "central chamber." We retain here the name _Hymeniastrum_ for this latter state, {530}expressed in the diagnosis given above, and call the former state (the Coccodiscid) _Hymenactura_ (compare above, p. 473). One practical advantage, obtained in this way, is that all genera of #Discoidea# ending with "_-astrum_" belong to the Porodiscida. _Hymeniastrum_ differs from _Dictyastrum_ by the possession of a patagium, and from _Euchitonia_ by the equal size of the angles and the arms.

Subgenus 1. _Hymenastrella_, Haeckel.

_Definition._--Arms with blunt ends, without terminal spines.

1. _Hymeniastrum leydigii_, Haeckel.

_Euchitonia leydigii_, Haeckel, 1862, Monogr. d. Radiol., p. 510, Taf. xxxi. figs. 4, 5.

_Hymeniastrum leydigii_, Haeckel, 1881, Prodromus, p. 460.

_Histiastrum trinacrium_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 843.

Arms twice as long as broad, two-thirds as broad at the base as at the blunt, nearly truncated distal end. Patagium nearly complete, perfectly filling out the interbrachial spaces, with six to seven regular, concave chamber-rows; only the truncate terminal faces of the arms free.

_Dimensions._--Radius of the arms 0.15 to 0.18, breadth on their base 0.04 to 0.05, on their broadest distal end 0.06 to 0.07.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface. Very common and variable.

2. _Hymeniastrum köllikeri_, Haeckel.

_Euchitonia köllikeri_, Haeckel, 1862, Monogr. d. Radiol., p. 511, Taf. xxxi. figs. 6, 7.

_Hymeniastrum köllikeri_, Haeckel, 1881, Prodromus, p. 460.

Arms nearly lanceolate, twice as long as broad, half as broad at the base as at the broadest middle part, pointed at the distal end. Patagium complete, enveloping the whole triangular disk, with irregular chamber-rows.

_Dimensions._--Radius of the arms 0.2, breadth on their base 0.04, on the broadest part 0.08.

_Habitat._--Mediterranean (Messina), surface.

3. _Hymeniastrum gümbelii_, Haeckel.

_Stylactis gümbelii_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 112, Taf. vi. fig. 1.

Arms twice as long as broad, nearly twice as broad in the circular distal half as in the square proximal half. Patagium incomplete, circular, with eight to nine convex chamber-rows, enveloping only the proximal square halves of the arms; the lenticular distal halves remain free.

_Dimensions._--Radius of the arms 0.14; breadth at the base 0.04, at the distal lenticular part 0.07.

_Habitat._--Fossil in the Tertiary rocks of Sicily, Grotte, Stöhr.

{531}4. _Hymeniastrum euclidis_, n. sp. (Pl. 43, fig. 13).

_Euchitonia euclidis_, Haeckel, 1881, Prodromus, p. 460 et Atlas (pl. xliii. fig. 13).

Arms one and a half times as long as broad, club-shaped, three times as broad in the oval distal part as in the narrow square proximal part. Patagium complete, enveloping the whole triangular disk, and also the convex ends of the arms, with eight to nine convex chamber-rows.

_Dimensions._--Radius of the arms 0.18; breadth at the base 0.025, at the broadest distal part 0.07.

_Habitat._--Pacific, central area, Stations 270 to 274, surface.

5. _Hymeniastrum pythagoræ_, Ehrenberg.

_Hymeniastrum pythagoræ_, Ehrenberg, 1854 (_partim_), Mikrogeol., Taf. xxxvi. fig. 31.

Arms nearly as broad as long, two-thirds as broad at the base as at the truncated distal end. Patagium incomplete, enveloping only the basal half of the arms, with four to five rectilinear parallel chamber-rows. (This form has the greatest resemblance to the figure given by Ehrenberg, _loc. cit._, but differs by the central disk, which is composed of two concentric rings surrounding the small central chamber; compare above _Hymenactura pythagoræ_, p. 474.)

_Dimensions._--Radius of the arms 0.18; breadth at the base 0.08, at the truncated end 0.12.

_Habitat._--Equatorial Atlantic, Station 347, depth 2250 fathoms.

6. _Hymeniastrum archimedis_, n. sp.

Arms nearly triangular, at the truncated, slightly convex end three times as broad as at the narrow base and one and a third times as broad as long; each arm with six simple chambers. Patagium incomplete, enveloping only the basal half of the arms with three to four convex chamber-rows. (Differs from _Rhopalastrum hexagonum_, Pl. 43, fig. 7, only by the patagium.)

_Dimensions._--Radius of the arms 0.2; breadth at the base 0.07, at the truncated end 0.2.

_Habitat._--Pacific, central area, Station 274, surface.

Subgenus 2. _Hymenastromma_, Haeckel.

_Definition._--Arms at the distal end provided with radial spines.

7. _Hymeniastrum ternarium_, Haeckel.

_Histiastrum ternarium_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 76, Taf. xxiv. fig. 2.

Arms two and a half times as long as broad, three times as broad at the truncated end as at the narrow base, with a strong, conical, radial spine at the end. Patagium incomplete, enveloping only the basal half of the arms, with three to four convex chamber-rows.

_Dimensions._--Radius of the arms (without terminal spine) 0.02; breadth at the base 0.025, at the broadest terminal part 0.08.

_Habitat._--Fossil in the rocks of Barbados.

{532}8. _Hymeniastrum trigonarium_, n. sp.

Arms one and a half times as long as broad, a little broader at the rounded end than at the base, with three strong conical radial spines, one larger (in the radius of each arm) and two smaller on both sides of this. Patagium complete, with four to five rectilinear parallel chamber-rows, enveloping the whole arms (with exception of the terminal spines) and forming a perfect equilateral triangle.

_Dimensions._--Radius of the arms (without terminal spines) 0.18; breadth at the base 0.1, at the distal part 0.12.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

Genus 230. _Euchitonia_,[269] Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 831 (_sensu emendato_).

_Definition._--#Porodiscida# with three simple, undivided, chambered arms, connected by a patagium; triangular shell bilateral, one odd arm opposite to the odd angle between the two paired arms.

The genus _Euchitonia_, quite insufficiently characterised by Ehrenberg, was founded by him (1860) for one single species, afterwards (1872) described and figured as _Euchitonia furcata_. Retaining this species correctly as the type of this genus, I give to it here the above diagnosis. In my Monograph (1862, p. 503) I described seven Mediterranean species of _Euchitonia_. Three of these have in common the characters according to the present diagnosis: _Euchitonia mülleri_, _Euchitonia virchowii_, _Euchitonia beckmanni_; two others appertain (on account of the regular, not bilateral form) to _Hymeniastrum_, and two others (on account of the forked, not simple arms) to _Trigonastrum_. Afterwards (1880) three true fossil species of _Euchitonia_ were described by Stöhr (_Euchitonia cruciata_, _Euchitonia zittelii_, and _Euchitonia acuta_). Some species of this genus are cosmopolitan, and appertain to the most common and everywhere represented #Discoidea#.

Subgenus 1. _Stylactis_, Ehrenberg, 1872 (_loc. cit._).

_Definition._--Arms with blunt ends, without terminal spines.

1. _Euchitonia furcata_, Ehrenberg.

_Euchitonia furcata_, Ehrenberg, 1872, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 308; Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. vi. iii. fig. 6.

Distance between the paired arms about half as large as their distance from the odd arm. All three arms nearly of the same size and form, about twice as long as broad, one and a half times at the {533}blunt convex end as broad as at the base. Patagium incomplete, with concave chamber-rows and irregular network, only enveloping the basal half of the arms.

_Dimensions._--Radius of all three arms 0.15, basal breadth of each arm 0.04, terminal breadth 0.06.

_Habitat._--North Pacific, Californian Sea, depth 2600 fathoms, Ehrenberg.

2. _Euchitonia mülleri_, Haeckel.

_Euchitonia mülleri_, Haeckel, 1862, Monogr. d. Radiol., p. 508, Taf. xxx. figs. 5-10.

_Euchitonia mülleri_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 110, Taf. v. fig. 5.

Distance between the paired arms about two-thirds as large as their distance from the odd arm, which is somewhat larger. Length of the arms equals two and a half times the breadth of the blunt convex end or five times the breadth of the base. Patagium with concave chamber-rows, nearly complete, enveloping the arms with exception of the terminal face. (This common species is very variable; compare my Monograph.)

_Dimensions._--Radius of all three arms 0.16 to 0.22, basal breadth 0.03 to 0.05, terminal breadth 0.06 to 0.08.

_Habitat._--Cosmopolitan; one of the most common #Discoidea# in all seas, on the surface as well as at different depths; also fossil in the Tertiary rocks of Barbados and Sicily.

3. _Euchitonia triangulum_, Haeckel.

_Stylactis triangulum_, Ehrenberg, 1872, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 320; Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. viii. fig. 9.

_Stylactis triangulum_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 113, Taf. vi. fig. 2.

Distance between the paired arms about two-thirds as large as their distance from the odd arm. All three arms nearly of the same size and form, about one and a half times as long as broad, nearly as broad at the base as at the blunt rounded end. Patagium incomplete, with convex chamber-rows, enveloping about two-thirds of the arms.

_Dimensions._--Radius of all three arms 0.15, basal breadth 0.05, terminal breadth 0.06.

_Habitat._--Pacific and Atlantic, Stations 253, 272, 354, surface; also fossil in the Tertiary rocks of Barbados and Sicily.

4. _Euchitonia cruciata_, Stöhr.

_Euchitonia cruciata_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 111, Taf. v. fig. 7.

Distance between the paired arms about one and a half times as large as their distance from the odd arm, which is a little larger. Length of the arm nearly equals twice the breadth, which is the same at the base and at the rounded blunt ends. Patagium incomplete, with concave chamber-rows, enveloping only the base of the arms, and forms between them three other smaller arms; therefore the whole shell forms six angles with six alternating arms.

_Dimensions._--Radius of all three arms 0.15, basal breadth 0.05.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

{534}5. _Euchitonia lanceolata_, n. sp. (Pl. 43, fig. 9).

Distance between the paired arms about one and a third times as large as their distance from the odd arm. All three arms nearly of the same size and form, three times as long as broad, lanceolate, much broader in the middle part than at both ends; distal end cuspidate, but not spiny. Patagium incomplete, with convex chamber-rows, envelops about two-thirds of the arms.

_Dimensions._--Radius of all three arms 0.18, greatest breadth (in the width) 0.06.

_Habitat._--North Atlantic, Station 353, depth 2965 fathoms.

6. _Euchitonia zittelii_, Haeckel.

_Stylactis zittelii_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 112, Taf. v. fig. 8.

Distance between the paired arms about one-fifth as large as their distance from the odd arm. All three arms nearly of the same size and form, in the proximal half thinner and nearly square, in the distal half thicker and circular; the latter half twice to three times as broad as the former. Patagium incomplete, with convex chamber-rows, envelops only the proximal square half of the arms.

_Dimensions._--Radius of all three arms 0.15, basal breadth 0.03, terminal breadth 0.08.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.

7. _Euchitonia stöhrii_, n. sp. (Pl. 43, fig. 12).

Distance between the paired arms about four-fifths as large as their distance from the odd arm, which is one and a half times as long as the former. Arms about three times as long as broad, twice as broad in the distal half as in the proximal half, with rounded blunt ends. Patagium complete, with concave chamber-rows, enveloping the whole shell, also the ends of the arms.

_Dimensions._--Radius of the paired arms 0.2, of the odd arm 0.25; basal breadth 0.03, distal breadth 0.06.

_Habitat._--Fossil in the rocks of Barbados and of Nicobar Islands, Haeckel. Indian Ocean, Cocos Islands (Rabbe). Also in the Central Pacific, Station 267.

8. _Euchitonia beckmannii_, Haeckel.

_Euchitonia beckmannii_, Haeckel, 1862, Monogr. d. Radiol., p. 505, Taf. xxxi. fig. 1.

Distance between the paired arms scarcely half as large as their distance from the odd arm, which is somewhat larger. Each arm with six simple broad chambers (without radial septa), the terminal chambers semilunar, convex, blunt, four times as broad as the first (basal) chamber. Patagium incomplete, with convex chamber-rows, enveloping the arms with exception of the broad blunt terminal face.

_Dimensions._--Radius of the paired arms 0.15, of the odd arm 0.18; basal breadth 0.02 to 0.03, terminal breadth 0.1 to 0.15.

_Habitat._--Mediterranean (Messina), Haeckel, surface.

{535}9. _Euchitonia virchowii_, Haeckel.

_Euchitonia virchowii_, Haeckel, 1862, Monogr. d. Radiol., p. 503, Taf. xxx. figs. 1-4.

_Histiastrum fasciatum_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 842.

Distance between the paired arms about half as large as their distance from the odd arm, which is somewhat larger. Each arm with six broad chambers, bisected by a radial septum; the terminal chamber convex, blunt, twice as broad as the basal chamber. Patagium incomplete, with concave chamber-rows, enveloping the arms with exception of the broad blunt terminal face.

_Dimensions._--Radius of the paired arms 0.15, of the odd arm 0.16; basal breadth 0.05, terminal breadth 0.1 to 0.12.

_Habitat._--Mediterranean (Messina), Atlantic (Canary Islands).

Subgenus 2. _Pteractis_, Ehrenberg, 1872 (_loc. cit._).

_Definition._--Arms provided with radial spines at the distal end.

10. _Euchitonia elegans_, Haeckel.

_Pteractis elegans_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 299, Taf. viii. fig. 3.

Distance between the paired arms half as large as their distance from the odd arm. This latter is straight, while both the former are concavely curved towards the middle line. Arms five times as long as broad, at the distal end pointed and armed with a short conical terminal spine. Patagium nearly complete, enveloping four-fifths of the arms, with four to five concave chamber-rows.

_Dimensions._--Radius of the arms 0.2, breadth of them 0.03.

_Habitat._--Tropical Pacific, Philippine Sea, depth 3300 fathoms (Ehrenberg).

11. _Euchitonia carcinus_, n. sp. (Pl. 43, fig. 10).

Distance between the paired arms scarcely one-fourth as great as their distance from the odd arm. This latter is straight, twice as long as the former, which are concavely curved towards the middle line. The odd arm is three times as broad at the distal end as at the narrow base. The end of each arm is furnished with a strong triangular radial spine and a group of smaller spines. Patagium incomplete, with two to three concave chamber-rows, enveloping only the basal half of the arms.

_Dimensions._--Radius of the paired arms 0.15, breadth 0.03; radius of the odd arm 0.3, breadth on its base 0.02, on its distal end 0.07.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

{536}12. _Euchitonia acuta_, Stöhr.

_Euchitonia acuta_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 111, Taf. v. fig. 6.

Distance between the paired arms two-thirds as great as their distance from the odd arm. All three arms nearly of the same size and form, two and a half times as long as broad, nearly lanceolate, at their broadest part one and a half times as broad as at their base. Patagium complete, enveloping the whole triangular disk, with five to six concave chamber-rows. In the figure of Stöhr the ends of the arms are simply pointed, while I find in the same fossil form a short terminal conical spine.

_Dimensions._--Radius of all three arms 0.14; breadth at the base 0.04, at the broadest part 0.06.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte (Stöhr), Caltanisetta (Haeckel).

13. _Euchitonia ypsiloides_, Haeckel.

_Histiastrum ypsiloides_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 843.

Distance between the paired arms two-thirds as great as their distance from the odd arm, which is somewhat larger. Length of the arms equals five times the breadth of the narrow base, which is half that of the distal end; this latter is armed with three to five short conical spines. Patagium complete, with six to seven concave chamber-rows, enveloping the whole arms with the exception of the terminal spines. (Differs from _Euchitonia mülleri_ almost solely by the possession of terminal spines.)

_Dimensions._--Radius of the arms 0.18 to 0.2; breadth at the base 0.04, at the distal end 0.08.

_Habitat._--Mediterranean (Messina), Atlantic (Canary Islands), surface.

14. _Euchitonia echinata_, n. sp. (Pl. 43, fig. 11).

Distance between paired arms three-fourths as great as their distance from the odd arm, which is somewhat larger. Arms one and a half times as long as broad, somewhat constricted in the middle part, armed at the rounded ends with numerous (thirty to forty) strong, conical spines. Patagium complete, with four or five rectilinear parallel chamber-rows, enveloping the whole of the arms with the exception of the spiny ends.

_Dimensions._--Radius of the arms (without spines) 0.2, breadth 0.06 to 0.09.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

Genus 231. _Chitonastrum_,[270] Haeckel, 1881, Prodromus, p. 460.

_Definition._--#Porodiscida# with three forked, chambered arms, without a patagium. (Arms and angles between them either equal or unequal.)

The genus _Chitonastrum_ differs from its ancestral form, _Dictyastrum_, by the bifurcation of the distal ends of the arms. The few species of this genus are partly {537}regular (like _Dictyastrum_), partly bilateral (like _Rhopalastrum_). If the number of species increases much, these two subgenera may be separated into two genera: _Chitonastrella_ corresponding to the former, _Chitonastromma_ to the latter.

Subgenus 1. _Chitonastrella_, Haeckel.

_Definition._--All three arms of the same size and form, equidistant; fundamental form of the shell therefore an equilateral triangle.

1. _Chitonastrum triglochin_, n. sp.

All three arms equal and equidistant. Each arm has the form of an isosceles triangle, twice as high as broad; the truncated apex of the triangle is inserted into the large central disk, whilst its distal base (four times as broad) is divided by a deep incision (half as long as the arm). Each arm with ten to twelve joints, simple in its basal half, double in its distal half. Axes of the six branches straight. (Resembles _Trigonastrum regulare_, Pl. 43, fig. 16, but differs in the absence of a patagium.)

_Dimensions._--Radius of each arm 0.24, greatest breadth 0.11, basal breadth 0.03.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

2. _Chitonastrum bathybium_, n. sp.

All three arms equal and equidistant, in the basal two-thirds simple, rectilinear, three times as long as broad, in the distal third forked, both branches equal, straight, blunt, half as broad as the basal part.

_Dimensions._--Radius of each arm 0.18, basal breadth 0.04, breadth of the branches 0.02.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

Subgenus 2. _Chitonastromma_, Haeckel.

_Definition._--One odd arm different in size or form from the two other arms, which are paired; distance between them different; fundamental form of the shell therefore a bilateral, isosceles triangle.

3. _Chitonastrum jugatum_, n. sp. (Pl. 43, fig. 14).

_Dictyastrum jugatum_, Haeckel, 1881, Prodromus et Atlas (pl. xliii. fig. 14).

Arms very different; odd arm club-shaped, twice as long as broad, at the blunt distal end twice as broad as at the base; its axis is perpendicular to the common axis of both paired arms, which are only two-thirds as long, not so broad, and in the distal half divided into two branches; the anterior branch is straight, nearly horizontal, the posterior shorter and curved backwards.

{538}_Dimensions._--Radius of the odd arm 0.2, of the paired arms 0.15; distal breadth of the former 0.08, basal breadth 0.04; breadth of the paired arms 0.04.

_Habitat._--South Atlantic, Station 325, surface.

4. _Chitonastrum dicranoides_, n. sp.

All three arms in the basal half simple, nearly square, in the distal half forked; branches straight, blunt. Odd arm twice as large as the paired arms; angle between the latter larger than the angles between them and the odd arm. (The form of the arms resembles _Dicranastrum furcatum_, Pl. 47, fig. 2.)

_Dimensions._--Radius of the odd arm 0.24, of the paired arms 0.12; basal breadth 0.06.

_Habitat._--North Atlantic, Station 353, surface.

5. _Chitonastrum lyra_, n. sp. (Pl. 43, fig. 15).

_Dictyastrum lyra_, Haeckel, 1881, Prodromus et Atlas (pl. xliii. fig. 15).

All three arms forked and nearly of the same size, but different in form and position. The distance between the branches of the two paired arms is only one-fourth of the distance between them and the odd arm. Each arm in the basal two-thirds is simple, with eleven to twelve transverse septa, in the distal third forked, each branch with four to five transverse septa. The branches of each arm are curved convexly one to another, ending obtusely. The axis of the simple proximal part is straight in the odd arm, in the paired arms curved concavely towards the middle line. In the figured specimen, which I observed living in Portofino (in September 1880), the central chamber of the central disk and the first surrounding ring were filled with the nucleus of the cell; both external rings were filled (like all chambers of the arms) with pink oil-globules of the red central capsule. From the mantle, enveloping the shell, radiated innumerable fine pseudopodia (much too short in the figure), and between the two paired arms a long "sarcode-flagellum."

_Dimensions._--Radius of each arm 0.16; greatest breadth of the odd arm 0.04; basal breadth of the paired arms 0.02; distance of both branches of each arm 0.08.

_Habitat._--Mediterranean, Portofino, near Genoa, Haeckel.

Genus 232. _Trigonastrum_,[271] n. gen.

_Definition._--#Porodiscida# with three forked, chambered arms, connected by a patagium. (Arms and angles between them either equal or unequal.)

The genus _Trigonastrum_ differs from the preceding _Chitonastrum_, its ancestral form, in the development of a patagium between the arms. It bears therefore to the latter the same relation that _Euchitonia_ does to _Rhopalastrum_.

{539}Subgenus 1. _Trigonastrella_, Haeckel.

_Definition._--All three arms of the same size and form, equidistant; fundamental form of the shell therefore a regular, equilateral triangle.

1. _Trigonastrum regulare_, n. sp. (Pl. 43, fig. 16).

_Chitonastrum regulare_, Haeckel, 1881, Prodromus et Atlas (pl. xliii. fig. 16).

All three arms equal and equidistant. Each arm has the form of an isosceles triangle, twice as high as broad, the truncated apex of which is inserted into the large circular central disk, whilst its distal base (four times as broad) is divided by a deep incision (half as long as the arm). Each arm with ten to twelve joints. Patagium between the arms nearly complete, spongy. (Differs from _Chitonastrum triglochin_ mainly in the possession of a patagium.)

_Dimensions._--Radius of each arm 0.24, greatest breadth 0.11, basal breadth 0.03; length of the sides of the regular triangle 0.45.

_Habitat._--Pacific, central area, Station 274, surface.

Subgenus 2. _Trigonastromma_, Haeckel.

_Definition._--One odd arm different in form or size from the other two arms, which are paired; distance between them different; fundamental form of the shell therefore an isosceles triangle.

2. _Trigonastrum krohnii_, Haeckel.

_Euchitonia krohnii_, Haeckel, 1862, Monogr. d. Radiol., p. 507.

All three arms different; distance between the two paired arms smaller than their distance from the odd arm. Odd arm with six joints. Each paired arm with seven joints, increasing in breadth towards the distal end. Odd arm and one paired arm forked at the end, the other paired arm simple. Patagium nearly complete. (The asymmetry in this form may perhaps be an individual anomaly, as also in _Myelastrum anomalum_, Pl. 47, fig. 9.)

_Dimensions._--Radius of the arms about 0.13 to 0.16, breadth 0.05 to 0.08.

_Habitat._--North Atlantic, Funchal, Madeira, Krohn, surface.

3. _Trigonastrum gegenbauri_, Haeckel.

_Euchitonia gegenbauri_, Haeckel, 1862, Monogr. d. Radiol., p. 506, Taf. xxxi. figs. 2, 3.

Arms different; distance between the paired arms larger than their distance from the odd arm, which is one-third shorter. Odd arm egg-shaped, simple, with seven joints, undivided. Both paired arms equal, with ten joints, in the distal third forked. Patagium nearly complete.

_Dimensions._--Radius of the odd arm 0.14, greatest breadth 0.08; radius of the paired arms 0.2.

_Habitat._--Mediterranean (Messina), Haeckel, surface.

{540}Genus 233. _Stauralastrum_,[272] n. gen.

_Definition._--#Porodiscida# with four simple, undivided, chambered arms, without a patagium; quadrangular shell a regular cross, with four equal arms placed at right angles.

The genus _Stauralastrum_ is the most simple form of the Tessarastrida, or of those Porodiscida in which the margin of the central disk is armed with four chambered arms. In _Stauralastrum_ these four arms are quite simple and equal, without a patagium, separated by four right angles, so that the whole shell represents a regular rectangular cross. If we connect the distal points of the arms by lines, we get a complete square. (In my Prodromus, 1881, the species of this genus were united with _Hagiastrum_, which genus I now retain for the simple bilateral Tessarastrida.)

Subgenus 1. _Stauralastrella_, Haeckel.

_Definition._--Ends of the arms blunt, without terminal spines.

1. _Stauralastrum cruciforme_, n. sp. (Pl. 45, fig. 6).

Arms very thin, nearly linear, four to five times as long as broad, of equal breadth at the base and at the truncated distal end; their breadth equals one-third of the radius of the central disk. Edges of the arms parallel.

_Dimensions._--Radius of each arm 0.8, breadth 0.016.

_Habitat._--South Pacific, Station 293, surface.

2. _Stauralastrum lanceolatum_, n. sp.

Arms lanceolate, three times as long as broad, in their middle part three times as broad as at both ends; their greatest breadth nearly equals the diameter of the central disk. (The arms have the same form as in _Euchitonia lanceolata_, Pl. 43, fig. 9.) Edges of the arms convex.

_Dimensions._--Radius of each arm 0.3, greatest breadth (in the middle part) 0.08.

_Habitat._--Pacific, central area, Station 273, depth 2350 fathoms.

3. _Stauralastrum ordo_, n. sp.

Arms trapezoid, about as long as broad, twice as broad at their truncated distal end as at the base; their basal breadth equals the radius of the central disk, which exhibits two to three rings. (The arms have nearly the same form as those in _Hagiastrum mosis_, Pl. 45, fig. 3.) Edges of the arms rectilinear, divergent towards the ends.

_Dimensions._--Radius of each arm 0.12, basal breadth 0.04, distal breadth 0.08.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

{541}4. _Stauralastrum clavigerum_, n. sp.

Arms twice as long as broad, in their distal half lenticular, nearly circular, twice as broad as in their square proximal half; their distal breadth equals the diameter of the central disk, which exhibits three to four rings. Edges of the arms concave.

_Dimensions._--Radius of each arm 0.2, basal breadth 0.04, distal breadth 0.08.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

5. _Stauralastrum dilatatum_, n. sp.

Arms of nearly equal length and breadth, at their convex distal end three times as broad as at their narrow base; their distal breadth three times as large as the radius of the central disk, which exhibits three to four rings. (Resembles _Histiastrum quadrigatum_, Pl. 46, fig. 3, but has no patagium.) Edges of the arms concave.

_Dimensions._--Radius of each arm 0.15, basal breadth 0.04, terminal breadth 0.12.

_Habitat._--South Pacific, Station 300, depth 1375 fathoms.

Subgenus 2. _Stauralastromma_, Haeckel.

_Definition._--Ends of the arms with one or more terminal spines.

6. _Stauralastrum rhopalophorum_, n. sp. (Pl. 45, fig. 1).

_Hagiastrum rhopalophorum_, Haeckel, 1881, Prodromus, p. 460.

Arms cylindrical, eight times as long as broad at their base, at their distal end club-shaped, three times as broad as at their base; their distal breadth twice as large as the diameter of the central disk, which exhibits two to three rings. Surface thorny, with larger spines towards the end, and one radial, very strong, angular terminal spine. Edges of the arms parallel.

_Dimensions._--Radius of each arm (without terminal spine) 0.32, basal breadth 0.03, terminal breadth 0.1.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

7. _Stauralastrum antiquum_, n. sp.

_Rhopalastrum_ sp. Bury, 1862, Polycystins of Barbados, pl. xiv. fig. 5.

Arms six times as long as broad at their base, in their distal half nearly spherical, three times as broad as in their cylindrical basal half; their distal breadth nearly equals the diameter of the central disk which exhibits three to four rings. On the end of each arm one strong, angular, terminal spine. (Differs from the preceding species by larger central disk and stouter arms, also by less developed spines.) Edges of the arms parallel.

_Dimensions._--Radius of each arm 0.25, basal breadth 0.04, terminal breadth 0.12.

_Habitat._--Fossil in the Barbados rocks; and living in the depths of the Central Pacific, Station 266, depth 2750 fathoms.

{542}8. _Stauralastrum staurolonche_, n. sp.

Arms four times as long as broad at their base, gradually increasing towards their truncated end, which is one and a half times as broad as their base; their distal breadth equals the radius of the central disk, which exhibits four to five rings. At the end of each arm is a very strong conical terminal spine. (Resembles _Histiastrum quaternarium_, _Abhandl. k. Akad. Wiss. Berlin_, 1875, Taf. xxiv. fig. 3, but has no patagium.) Edges of the arms rectilinear, divergent.

_Dimensions._--Radius of each arm 0.25, basal breadth 0.045, distal breadth 0.07.

_Habitat._--Fossil in the Barbados rocks; and living in the depth of the Equatorial Atlantic, Station 348, depth (2450) fathoms.

9. _Stauralastrum horridum_, n. sp.

Arms three times as long as broad at their base, gradually increasing towards their rounded end, which is twice as broad as their base, their distal breadth equals the diameter of the central disk, which exhibits four to five rings. Surface thorny, at the distal end of each arm is a group of twenty to twenty-five smaller and five to six larger, straight, conical spines. Edges of the arms rectilinear, divergent.

_Dimensions._--Radius of each arm 0.15, basal breadth 0.05, distal breadth 0.1.

_Habitat._--Pacific, central area, Station 270, depth 2925 fathoms.

Genus 234. _Hagiastrum_,[273] Haeckel, 1881, Prodromus, p. 460.

_Definition._--#Porodiscida# with four simple, undivided, chambered arms, without a patagium; quadrangular shell bilateral, two opposite arms of the main axis (or principal arms) different from the two others (or lateral arms).

The genus _Hagiastrum_, as here defined, was formerly united by me with the foregoing _Stauralastrum_, but differs from it by the bilateral or symmetrical form. Whilst in the latter all four arms and the four angles between them are equal, they are here differentiated into pairs.

Subgenus 1. _Hagiastrella_, Haeckel.

_Definition._--Both longitudinal arms of equal size and form.

1. _Hagiastrum buddhae_, n. sp. (Pl. 45, fig. 5).

Cross rectangular. Both longitudinal arms of equal size, twice as long as the transverse arms; all arms smooth, club-shaped, twice as broad at their globose distal part as at their base, each with three large conical terminal spines.

{543}_Dimensions._--Radius of the principal arms 0.4, of the lateral arms 0.2; basal breadth 0.06, distal breadth 0.12.

_Habitat._--Indian Ocean, Belligemma, Ceylon, surface, Haeckel.

2. _Hagiastrum bramae_, n. sp.

Cross rectangular. Both longitudinal arms of equal size, one and a half times as long as the transverse arms; all arms thorny, club-shaped, at their pear-shaped distal part three times as broad as at their base, provided with numerous conical spines, one larger terminal spine at their distal point. (Resembles _Stauralastrum rhopalophorum_, Pl. 45, fig. 1, but is distinguished by the different size of the arm-pairs, and by the stronger spines.)

_Dimensions._--Radius of the principal arms 0.3, of the lateral arms 0.2; basal breadth 0.04, distal breadth 0.12.

_Habitat._--Indian Ocean, off Maldive Islands, surface, Haeckel.

Subgenus 2. _Hagiastromma_, Haeckel.

_Definition._--The two longitudinal arms different in size or form.

3. _Hagiastrum mosis_, n. sp. (Pl. 45, fig. 3).

Cross rectangular. All four arms nearly isosceles, triangular, at their narrow base half as broad as at their truncated, concavely fluted, distal end. The posterior principal arm with twelve to thirteen joints, twice as long as the anterior arm, which has six to seven joints and is one and a half times as long as the two lateral arms (with four to five joints).

_Dimensions._--Radius of the posterior arm 0.3, of the anterior 0.15, of the lateral arms 0.1; basal breadth 0.05, terminal breadth 0.1.

_Habitat._--Mediterranean (Smyrna), surface, Haeckel.

4. _Hagiastrum mohammedis_, n. sp.

Cross with unequal angles, the anterior little smaller than the posterior. All four arms club-shaped, thorny, three times as broad at their globose distal end as at their narrow base, and furnished with ten to twelve conical spines. Posterior principal arm twice as long as the anterior, and four times as long as the rudimentary lateral arms.

_Dimensions._--Radius of the posterior arm 0.4, of the anterior 0.2, of the lateral arms 0.1; basal breadth 0.02 to 0.03, distal breadth 0.06 to 0.1.

_Habitat._--Philippine Sea, Samboangan, Station 200, surface.

5. _Hagiastrum christi_, n. sp.

Cross with unequal angles, the anterior somewhat smaller than the posterior. All four arms of similar form, lanceolate, in their middle twice as broad as at either obtuse end. The posterior {544}principal arm with twelve joints, one and a half times as long as the anterior (with nine joints) and twice as long as the two lateral arms (each with six joints). The form and structure of the arms in this species are nearly the same as in _Tessarastrum straussi_ (Pl. 45, fig. 8); but the arms are broader in the middle, and are not connected by a patagium.

_Dimensions._--Radius of the principal posterior arm 0.2, of the anterior 0.15, of each lateral arm 0.1; greatest breadth (in the width) 0.01, basal breadth 0.03.

_Habitat._--North Atlantic, Færöe Channel, Gulf Stream, surface, John Murray.

Genus 235. _Histiastrum_,[274] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

_Definition._--#Porodiscida# with four simple, undivided, chambered arms, connected by a patagium; square shell a regular cross, with four equal arms and four right angles between them.

The genus _Histiastrum_, quite insufficiently characterised by Ehrenberg (1847), was afterwards (1875) illustrated by the figures of two different fossil species. One of these, _Histiastrum ternarium_, with three arms, belongs to _Hymeniastrum_; the other, _Histiastrum quaternarium_, is here retained as the true, typical representative species of the genus. It differs from its ancestral form _Stauralastrum_, by the possession of a patagium, from _Tessarastrum_ by the regular square form of the shell.

Subgenus 1. _Histiastrella_, Haeckel.

_Definition._--Distal ends of the arms blunt, without terminal spines.

1. _Histiastrum quadrigatum_, n. sp. (Pl. 46, fig. 3).

Arms at their distal end nearly as broad as long, and four times as broad as at their narrow base; their lateral edges concave, their terminal edge convex, without spines. Each arm is divided by seven to eight convex transverse septa into eight to nine simple, broad chambers. Central disk with three to four rings, about as broad as the fifth chamber. Patagium complete, connecting all the lateral edges of the arms.

_Dimensions._--Radius of each arm 0.15, basal breadth 0.03, terminal breadth 0.12.

_Habitat._--Equatorial Atlantic, Station 347, surface.

2. _Histiastrum excisum_, n. sp.

Arms four times as long as broad at their base, and twice as broad at their rounded blunt distal end as at their base; their lateral edges rectilinear, divergent. Central disk with three to four rings, {545}somewhat broader than their distal end. Patagium incomplete, connecting only the basal half of the arms, with three to four concave chamber-rows, on the margin concave. (May be regarded as _Euchitonia mülleri_, with four arms.)

_Dimensions._--Radius of each arm 0.2, basal breadth 0.05, distal breadth 0.1.

_Habitat._--Atlantic, surface, Canary Islands.

3. _Histiastrum velatum_, n. sp. (Pl. 46, fig. 4).

_Dictyastrum velatum_, Haeckel, 1879, Atlas (pl. xlvi. fig. 4).

Arms pear-shaped, rapidly increasing from their narrow base, nearly circular, little longer than broad; each with eight to nine transverse chamber-rows; their lateral edges at their base concave, at their end circular. Central disk with three to four rings, somewhat smaller than one arm. Patagium complete, with six to seven radial beams, filling out perfectly the intervals between the arms. A peculiar girdle of finer network and equal breadth surrounds the whole equatorial periphery of the disk, and gives it the appearance of a square with rounded corners.

_Dimensions._--Radius of each arm 0.2, basal breadth 0.03, distal breadth 0.12.

_Habitat._--South Atlantic, Station 330, surface.

Subgenus 2. _Histiastromma_, Haeckel.

_Definition._--Distal ends of the arms spiny, furnished with one or more terminal spines.

4. _Histiastrum quaternarium_, Ehrenberg.

_Histiastrum quaternarium_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxiv. figs. 3, 4.

Arms six times as long as broad at their base, with rectilinear, little divergent edges; at their truncated distal end a little broader, with one single, very strong, conical, terminal spine. Central disk with four to five rings, somewhat broader than the arm. Patagium incomplete, enveloping only the basal half of the arms.

_Dimensions._--Radius of each arm 0.18, basal breadth 0.03, distal breadth 0.05.

_Habitat._--Fossil in the rocks of Barbados.

5. _Histiastrum gladiatum_, n. sp.

_Astromma_ sp., Bury, 1862, Polycystins of Barbados, pl. v. fig. 1.

Arms triangular, eight times as long as broad at their base; at their distal end three times as broad as at their base, with rectilinear, divergent edges; their truncated end with a large conical, terminal spine. Central disk with four to five rings, broader than the arms. Patagium incomplete, enveloping only the basal half of the arms.

{546}_Dimensions._--Radius of each arm 0.12, basal breadth 0.013, distal breadth 0.04.

_Habitat._--Fossil in the rocks of Barbados; and living in the depth of the Central Pacific, Station 268, depth 2900 fathoms.

6. _Histiastrum boseanum_, n. sp. (Pl. 46, fig. 1).

Arms linear, twelve times as long as broad at their base (at their distal end twice as broad as at their base), with rectilinear, parallel edges. The club-shaped end thickened, dentate, with two lateral rows of strong teeth in the equatorial plane, and with one very stout, angular, terminal spine. Central disk with two to three rings, broader than the arms. Patagium incomplete, with four to five concave chamber-rows, enveloping only the basal half of the arms. I call this splendid species in honour of Dr. Graf Bose, the great friend of nature and patron of the University of Jena.

_Dimensions._--Radius of each arm 0.25, basal breadth 0.02, distal breadth 0.05.

_Habitat._--Indian Ocean, Madagascar, Rabbe.

7. _Histiastrum coronatum_, n. sp.

_Stephanastrum_ sp., Bury, 1862, Polycystins of Barbados, pl. iv. fig. 1.

Arms linear, eight times as long as broad, with rectilinear parallel edges; the thickened, nearly spherical, distal end three times as broad, with five strong conical spines, one middle (perradial) larger and two smaller on each side of it. Central disk with two to three rings, of the same breadth as the terminal knot of the arms. Patagium incomplete, square, enveloping the arms, with the exception of the knot.

_Dimensions._--Radius of each arm 0.16, basal breadth 0.02, terminal breadth 0.06.

_Habitat._--Fossil in the rocks of Barbados.

8. _Histiastrum circulare_, n. sp.

_Stephanastrum_ sp., Bury, 1862, Polycystins of Barbados, pl. xxiii. fig. 1.

Arms linear in their inner half, egg-shaped and three times as broad in their outer half, with ten to twelve strong terminal spines, the middle (perradial) larger, in all three times as long as broad. Central disk with three to four rings, broader than their distal knobs. Patagium nearly complete, circular, enveloping the whole arms, with exception of the outermost end.

_Dimensions._--Radius of each arm 0.22, basal breadth 0.02, terminal breadth 0.06.

_Habitat._--Fossil in the rocks of Barbados; and living in the depths of the Central Pacific, Station 268, depth 2900 fathoms.

9. _Histiastrum pentadiscus_, n. sp. (Pl. 46, fig. 2).

Arms in their inner half linear, twice as long as broad, in their outer half circular, three times as broad, with the same structure as the central disk, exhibiting three concentric rings around one {547}central chamber. Patagium complete, spongy, with radiating beams, enveloping the whole disk, with the exception of the outermost end of the arms, which is armed with twelve to sixteen strong conical spines, the middle (perradial) spine much larger.

_Dimensions._--Radius of each arm (without terminal spine) 0.18, basal breadth 0.025, terminal breadth 0.08.

_Habitat._--South Atlantic, Station 333, surface.

Genus 236. _Tessarastrum_,[275] n. gen.

_Definition._--#Porodiscida# with four simple, undivided, chambered arms, connected by a patagium; quadrangular shell bilateral, two opposite arms of the main axis (or principal arms) different from the two others (or lateral arms).

The genus _Tessarastrum_, formerly united by me with _Histiastrum_, differs from the latter in its bilateral or symmetrical form, and bears therefore the same relation to it that _Hagiastrum_ does to _Stauralastrum_.

Subgenus 1. _Tessarastrella_, Haeckel.

_Definition._--Both longitudinal arms of equal size and form.

1. _Tessarastrum straussii_, n. sp. (Pl. 45, fig. 8).

_Histiastrum straussii_, Haeckel, 1881, Prodromus et Atlas (pl. xlv. fig. 8).

Cross not rectangular. Both principal arms of equal size and form, four times as long as broad, and twice as long as the broader lateral arms; the former with ten to eleven, the latter with five to six joints, separated by convex transverse septa. Distal ends of the arms blunt. Axes of the smaller arms not perpendicular to that of the larger arms; therefore the anterior angles between them smaller than the posterior angles. Patagium between the arms incomplete. I call this remarkable species after the great German philosopher David Strauss.

_Dimensions._--Radius of the principal arms 0.24, of the lateral arms 0.12; greatest breadth (in the middle) of the former 0.05, of the latter 0.06.

_Habitat._--North Pacific, _Hyalonema_-ground, March 5, 1875.

2. _Tessarastrum spinozæ_, n. sp.

Cross rectangular. Both principal arms of equal size and form, ten times as long as broad, and twice as long as the lateral arms, which are only five times as long as broad. All arms linear, at their distal end club-shaped, and armed with twenty to thirty very strong angular spines. Patagium incomplete, enveloping only the basal half of the arms. (Resembles _Histiastrum boseanum_, {548}Pl. 46, fig. 1, but differs in the broader arms and the unequal size of both pairs.) I call this species after the great monistic philosopher Benedictus Spinoza.

_Dimensions._--Radius of the principal arms 0.3, of the lateral arms 0.16; basal breadth 0.025, distal breadth 0.05.

_Habitat._--South Atlantic, Station 333, surface.

3. _Tessarastrum brunonis_, n. sp. (Pl. 45, fig. 9).

_Histiastrum brunonis_, Haeckel, 1881, Prodromus et Atlas (pl. xlv. fig. 9).

Cross rectangular. Both principal arms of equal size and form, three times as long as broad, each with ten joints, three times as long as the lateral arms, which are nearly square, with four joints. All arms rounded, at their truncated end little broader than at their base. No spines. Patagium complete, envelops the whole shell, and is composed of two parallel lattice-lamellæ on each side of the flat disk, which are connected by very fine perpendicular bars. This is shown clearly in fig. 9, Pl. 45, where the disk is seen from the edge. I call this species after the great Italian philosopher Giordano Bruno.

_Dimensions._--Radius of the principal arms 0.22, of the lateral arms 0.12; basal breadth 0.04, distal breadth 0.05.

_Habitat._--South Pacific, Station 285, depth 2375 fathoms.

Subgenus 2. _Tessarastromma_, Haeckel.

_Definition._--The two principal arms of different size or form.

4. _Tessarastrum democriti_, n. sp. (Pl. 45, fig. 7).

_Histiastrum democriti_, Haeckel, 1881, Prodromus et Atlas (pl. xlv. fig. 7).

Cross not rectangular; the two anterior angles smaller than the two posterior. All four arms club-shaped, twice as broad at their rounded obtuse distal end as at their base, of unequal length. Posterior principal arm one and a fourth times as long as the posterior, and one and two-thirds as long as the lateral arms. Patagium incomplete, enveloping only the basal half of the arms. I call this species after the great Greek philosopher Democritus.

_Dimensions._--Radius of the posterior arm 0.3, of the anterior 0.25, of each lateral arm 0.22; basal breadth 0.05, distal breadth 0.1.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

Genus 237. _Stephanastrum_,[276] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

_Definition._--#Porodiscida# with four simple, undivided, chambered arms, connected on the distal ends by a spongy, square or rhomboidal, patagial girdle (or a patagium with four large, interbrachial openings). Shell either regular or bilateral (with equal or unequal arms).

{549}The genus _Stephanastrum_, founded (1847) by Ehrenberg for the very peculiar _Stephanastrum rhombus_, differs from the nearly allied foregoing genera in the imperfect development of the peculiar patagium, connecting only the distal ends of the four arms, while it is absent at their base. Two new species, different from _Stephanastrum rhombus_ by the regular square form, were found in the Challenger collection.

Subgenus 1. _Stephanastrella_, Haeckel.

_Definition._--All four arms of the cross have the same size.

1. _Stephanastrum quadratum_, n. sp. (Pl. 46, fig. 5).

All four arms of the same size, six times as long as broad at their base, ending with a strong, short, four-sided pyramidal spine. In the outer half of each arm are two opposite lateral spongy wings, which form an equilateral triangle, and from union of the bases of the four triangles arises the peculiar patagium, which forms a square with four large interbrachial openings.

_Dimensions._--Radius of each arm 0.25, basal breadth 0.035; length of the sides of the square patagium 0.3.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

2. _Stephanastrum capitatum,_ n. sp. (Pl. 44, fig. 1).

All four arms of the same size, five times as long as broad at their base, at their distal end with a spongy, nearly spherical capitulum of twice their breadth, provided with a very strong, angular, pyramidal, terminal spine (half as long as the arm). All four arms connected by a square patagium, arising immediately below the capitula, and perforated by four large interbrachial openings.

_Dimensions._--Radius of each arm (without the terminal spine) 0.25, basal breadth 0.05; length of the sides of the square patagium 0.3.

_Habitat._--Pacific, central area. Station 265, depth 2900 fathoms.

Subgenus 2. _Stephanastromma_, Haeckel.

_Definition._--Two opposite arms of the cross larger than the two others.

3. _Stephanastrum rhombus,_ Ehrenberg.

_Stephanastrum rhombus_, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 33; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Taf. xxv. fig. 1.

Two arms of the longitudinal axis one and a third times as long as two arms of the transverse axis. All four arms linear, about eight times as long as broad, at their distal end somewhat {550}thickened, club-shaped, with a pyramidal terminal spine. The ends of the arms are connected by a riband-shaped, straight, spongy patagium of the same breadth as the arms. Between the rhomboidal patagium and the arms remain four large rectangular triangles as interbrachial openings.

_Dimensions._--Radius of the longer arms 0.2, of the shorter 0.15; basal breadth 0.02; length of the sides of the rhombic patagium 0.25.

_Habitat._--Fossil in the rocks of Barbados.

Genus 238. _Dicranastrum_,[277] Haeckel, 1881, Prodromus, p. 460.

_Definition._--#Porodiscida# with four forked, spongy, or chambered arms, without a patagium; shell regular (not bilateral), with four equal arms crossed at right angles.

The genus _Dicranastrum_ comprises a number of very remarkable, hitherto unknown, Euchitonida, which are rather common in the Pacific (mainly on the surface), and characterised by the bifurcation of the cross-arms of the regular square shell. It bears therefore to its probable ancestral form, _Stauralastrum_, the same relation that in the triradiate Euchitonida _Chitonastrum_ does to _Dictyastrum_. The arms are commonly of very delicate structure, more or less spongy.

Subgenus 1. _Dicranaster_, Haeckel.

_Definition._--Each cross-arm with two simple branches.

1. _Dicranastrum furcatum_, n. sp. (Pl. 47, fig. 2).

Arms simply forked, three times as long as broad at their base, with eight blunt ends of the fork-branches. The simple proximal half of each arm about the same size as each branch of the dichotomous distal part, twice as long as broad. Edges of the arms ragged.

_Dimensions._--Radius of each arm 0.38, basal breadth 0.12; breadth of the forked part 0.3.

_Habitat._--Pacific, central area, Station 271, surface.

2. _Dicranastrum dichotomum_, n. sp.

Arms simply forked, four times as long as broad at their base; each arm with two blunt branches. The simple proximal part of each arm is three times as long and twice as broad as each branch of the dichotomous distal part. Ends of the arms blunt, truncated.

_Dimensions._--Radius of each arm 0.35, basal breadth 0.08; breadth of the forked part 0.2.

_Habitat._--South Pacific, Station 281, surface.

{551}3. _Dicranastrum cornutum_, n. sp. (Pl. 45, fig. 2).

_Hagiastrum cornutum_, Haeckel, 1879, Atlas (pl. xlv. fig. 2).

Four arms simply forked, four times as long as broad; each arm with two triangular diverging branches ending in strong conical spines. The simple basal part of each arm about of the same length as each branch of the distal part, twice as long as broad. Distance between the terminal spines of each arm nearly as great as its length.

_Dimensions._--Radius of the arm 0.24, basal breadth 0.05; breadth across the bifurcation 0.12.

_Habitat._--South Atlantic, Station 325, surface.

4. _Dicranastrum antilope_, n. sp.

Four arms simply forked, three times as long as broad; each arm with two lanceolate diverging branches, ending in strong angular spines. The simple basal part of each arm is twice as long as each branch of the distal part. Distance of the two terminal spines of each arm scarcely half as great as its length.

_Dimensions._--Radius of the arm 0.32, basal breadth 0.11; breadth of the branches 0.07.

_Habitat._--Tropical Atlantic (off Ascension), Station 342, surface.

Subgenus 2. _Tricranastrum_, Haeckel, 1881, Prodromus, p. 460.

_Definition._--Each cross arm with three terminal branches, one middle (perradial) and two lateral (adradial) branches.

5. _Dicranastrum wyvillei_, n. sp. (Pl. 47, fig. 3).

_Tricranastrum wyvillei_, Haeckel, 1879, Natürl. Schöpfungsgesch., p. 705, Taf. xvi. fig. 5.

Arms trifid, one and a half times as long as broad; each arm with three blunt terminal branches of equal size. The simple basal part of each arm twice as long as the trifid distal part. (The central capsule depicted in fig. 3, Pl. 47, has the same form as the skeleton, and is only a little smaller.)

_Dimensions._--Radius of the arm 0.4, basal breadth 0.12, greatest breadth (in the distal part) 0.24.

_Habitat._--Pacific, central area, Station 271, surface.

6. _Dicranastrum tricuspis_, n. sp.

Arms trifid, twice as long as broad; each arm with three pointed terminal branches, ending in strong conical spines, the middle branch somewhat larger than the other two. The simple basal part of each arm three times as long as the trifid distal part.

_Dimensions._--Radius of the arm 0.3, basal breadth 0.06, greatest breadth (in their distal part) 0.15.

_Habitat._--North Pacific, Station 244, surface.

{552}7. _Dicranastrum trifarium_, n. sp.

Arms trifid, three times as long as broad at their base; each arm with three pointed terminal branches, ending in strong sulcate spines; the middle branch twice as large as the two others. The simple basal part of each arm two and a half times as long as the trifid distal part.

_Dimensions._--Radius of the arm 0.35, basal breadth 0.03, greatest breadth (in the distal part) 0.05.

_Habitat._--South Pacific, Station 298, surface.

Subgenus 3. _Tetracranastrum_, Haeckel.

_Definition._--Each cross-arm with four terminal branches, the two fork-branches being again bifurcated.

8. _Dicranastrum bifurcatum_, n. sp. (Pl. 47, figs. 1, 1_a_).

Arms doubly forked or quadripartite, six times as long as broad at their base; each arm in its proximal half simple, three times as long as broad; in its distal half doubly forked; the secondary branches with blunt, roundish ends, nearly as large as the primary branches. Central disk (fig. 1_a_) with three concentric rings around the central chamber; from its periphery radiate thin radial beams in the spongy framework of the delicate arms. The central capsule has the same form as the skeleton, and is only a little smaller.

_Dimensions._--Radius of the arm 0.45, basal breadth 0.08; breadth of the terminal branches 0.03.

_Habitat._--North Pacific, east of Japan, Station 241, surface.

Genus 239. _Myelastrum_,[278] Haeckel, 1881, Prodromus, p. 460.

_Definition._--#Porodiscida# with four forked, spongy, or chambered arms, without a patagium; shell bilateral, with paired different arms; two equal anterior arms of different shape from the two equal posterior arms.

The genus _Myelastrum_ differs from the foregoing _Dicranastrum_, the ancestral form, by the twofold differentiation of the four arms. Whilst in the latter all four arms are equal, separated by equal angles, here the two anterior arms are constantly different from the two posterior. The lateral angles between the two arm-pairs are equal, while the posterior and the anterior angle (between the two arms of each pair) are more or less different. The shell assumes, therefore, a very characteristic bilateral form, similar to the "quadricorn cross" of the grey central substance in the transverse section of the human medulla spinalis. Though the spongy shell is commonly a most delicate and {553}thin disk it nevertheless reaches unusual dimensions, its diameter in some species being more than a millimetre.

Subgenus 1. _Myelastrella_, Haeckel.

_Definition._--Posterior arms simple, undivided; anterior arms lobated or cleft, with one or more incisions at the distal end.

1. _Myelastrum medullare_, n. sp. (Pl. 47, fig. 13).

Anterior arms bifid, nearly square, with a shallow incision at their broad truncated end. Posterior arms somewhat smaller, nearly triangular, with simple blunt ends. Sagittal constriction three-fourths as large as the transverse one. Surface smooth.

_Dimensions._--Radius of the anterior arms 0.36, of the posterior 0.3; longitudinal constriction 0.24, transverse 0.36.

_Habitat._--Pacific, central area, Station 271, surface.

2. _Myelastrum spinale_, n. sp.

Anterior arms bifid, twice as long as broad, with a deep incision at their truncated end. Posterior arms slender, half as large, with simple blunt ends. Sagittal constriction one and a half times as large as the transverse. Surface spiny.

_Dimensions._--Radius of the anterior arms 0.4, of the posterior 0.2; longitudinal constriction 0.3, transverse 0.2.

_Habitat._--North Pacific, Station 248, surface.

3. _Myelastrum heteropterum_, n. sp. (Pl. 47, fig. 8).

Anterior arms trifid, about as long as broad, with two incisions at their broad truncated end. Posterior arms about half as large, simple, with rounded blunt ends. Sagittal constriction two-thirds as large as the transverse. Surface bristly.

_Dimensions._--Radius of the anterior arms 0.65, of the posterior 0.035; longitudinal constriction 0.4, transverse 0.6.

_Habitat._--South Pacific, Station 291, surface.

Subgenus 2. _Myelastromma_, Haeckel.

_Definition._--All four arms (posterior as well as anterior) lobated or cleft.

4. _Myelastrum octocorne_, n. sp. (Pl. 47, fig. 12).

All four arms with a deep incision in their distal half; anterior arms broader, but shorter than the posterior; in the anterior arms the two lobes are of the same size, in the posterior arms the {554}median lobe is longer than the lateral lobe. Sagittal constriction little smaller than the transverse. Surface of the disk rough.

_Dimensions._--Radius of the anterior arms 0.45, of the posterior 0.62; longitudinal constriction 0.25, transverse 0.3.

_Habitat._--Pacific, central area, Station 271, surface.

5. _Myelastrum farfalla_, n. sp. (Pl. 47, fig. 10).

All four arms with a shallow incision at their distal end. Anterior arms broader, but shorter than the posterior; in each arm the anterior lobe is shorter than the posterior. Sagittal constriction smaller than the transverse. Surface smooth.

_Dimensions._--Radius of the anterior arms 0.4, of the posterior 0.6; longitudinal constriction 0.5, transversal stricture 0.6.

_Habitat._--Pacific, central area, Station 274, surface.

6. _Myelastrum papilio_, n. sp. (Pl. 47, fig. 6).

All four arms with a shallow incision at their distal end. Anterior arms triangular, of the same breadth, but of the double length of the square posterior arms. Sagittal and transverse constrictions of the same length. Surface ciliated. (Resembles a butterfly.)

_Dimensions._--Radius of the anterior arms 0.7, of the posterior 0.4; longitudinal and transverse constrictions 0.4.

_Habitat._--North Pacific, near Japan, Station 241, surface.

7. _Myelastrum decaceros_, n. sp. (Pl. 47, fig. 7).

Anterior arms bifid, with one shallow incision at their distal end. Posterior arms of the same length, but much broader, trifid, with two incisions (one larger and one smaller). Sagittal and transverse constrictions of the same length. Surface spiny.

_Dimensions._--Radius of all four arms 0.4; longitudinal and transverse constrictions 0.35.

_Habitat._--Pacific, central area, Station 272, surface.

8. _Myelastrum dodecaceros_, n. sp. (Pl. 47, figs. 11, 11_a_).

Anterior arms trifid, with two shallow incisions at their distal end. Posterior arms about one-third larger, also trifid, with one deeper anterior and one shallower posterior incision. Sagittal constriction much longer than the transverse. Surface ciliated, covered with numerous thin and long radial bristles (fig. 11_a_).

_Dimensions._--Radius of the anterior arms 0.5, of the posterior 0.7; longitudinal constriction 0.5, transverse 0.35.

_Habitat._--Pacific, central area, Station 270, surface.

{555}9. _Myelastrum ciliatum_, n. sp.

Anterior arms trifid, with two shallow incisions. Posterior arms somewhat smaller, also trifid, with two deeper incisions. Sagittal constriction a little larger than the transverse. Margin of the disk ciliated, with radial bristle-shaped spines, as prolongations of the inner radial beams, arising from the central disk.

_Dimensions._--Radius of the anterior arms 0.6, of the posterior 0.5; longitudinal constriction 0.4, transverse 0.35.

_Habitat._--South Pacific, Station 288, surface.

10. _Myelastrum lobatum_, n. sp.

Anterior arms somewhat broader but shorter than the posterior arms. Each arm four-lobed, with three terminal shallow incisions of nearly equal size. Sagittal constriction smaller than the transverse. Surface of the disk bristly.

_Dimensions._--Radius of the anterior arms 0.4, of the posterior 0.5; longitudinal constriction 0.3, transverse 0.35.

_Habitat._--North Pacific, Station 253, surface.

11. _Myelastrum rotula_, n. sp.

Anterior arms little broader than the posterior, but of the same length. Each arm four-lobed, with three terminal deep incisions of equal size. Sagittal and transverse constrictions equal. The whole disk nearly circular, resembles a wheel with sixteen spokes. Surface smooth.

_Dimensions._--Radius of all four arms 0.5; longitudinal and transverse constrictions 0.3.

_Habitat._--Pacific, central area, Station 274, surface.

12. _Myelastrum giganteum_, n. sp.

Anterior arms somewhat broader and shorter than the posterior. Each arm four-lobed, with three shallow terminal incisions, the middle incision twice as deep as the two laterals. Sagittal constriction a little larger than the transverse. Margin ciliated, with radial bristle-shaped spines as prolongations of the inner radial beams, proceeding from the central disk (as in _Myelastrum dodecaceros_, Pl. 47, figs. 11, 11_a_).

_Dimensions._--Radius of the anterior arms 0.6, of the posterior 0.8; longitudinal constriction 0.6, transverse 0.5.

_Habitat._--Pacific, central area, Station 271, surface.

{556}13. _Myelastrum anomalum_, n. sp. (Pl. 47, fig. 9).

All four arms of different size and form; anterior arms broader, posterior longer; one anterior arm trifid, the three other arms bifid; length of the branches unequal; all four angles between the arms unequal. (This anomalous form, seen only once, may be an individual abnormality.)

_Dimensions._--Radius of the arms 0.4 to 0.7; constrictions 0.3.

_Habitat._--North Pacific, Station 237, surface.

Genus 240. _Pentalastrum_,[279] Haeckel, 1881, Prodromus, p. 461.

_Definition._--#Porodiscida# with five simple, undivided, chambered arms, without a patagium.

The genus _Pentalastrum_ opens the small series of Euchitonida, in which the shell is not provided with three or four arms, as usual, but with five. All forms of this little group are rare. Some species resemble in their external form and in the articulation of their arms certain forms of Asterida. In _Pentalastrum_, the most simple genus, the five arms are simple, not forked, and without a patagium. It can be derived from _Dictyastrum_ or _Stauralastrum_ by increase of the number of arms.

Subgenus 1. _Pentalastrella_, Haeckel.

_Definition._--All five arms equal, with equal angles between them. Shell a regular pentagon.

1. _Pentalastrum asteracanthion_, n. sp.

All five arms equal, club-shaped, at their thickened obtuse end three times as broad as at their base, twice as long as broad. Angles between the arms equal.

_Dimensions._--Radius of each arm 0.2, basal breadth 0.03, distal breadth 0.08.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

2. _Pentalastrum astropecten_, n. sp.

All five arms equal, with five to six distinct, simple joints, the basal joint two-thirds as broad as the terminal joint, which bears a strong conical spine. Angles between the arms equal. (Resembles _Pentinastrum asteriscus_, Pl. 44, fig. 2, but has no patagium.)

_Dimensions._--Radius of each arm 0.14, basal breadth 0.024, distal breadth 0.036.

_Habitat._--Pacific, central area, Station 263, depth 2650 fathoms.

{557}Subgenus 2. _Pentalastromma_, Haeckel.

_Definition._--Arms of different sizes, one odd arm larger than the two others; the opposite odd angle generally different from the four other angles.

3. _Pentalastrum ophidiaster_, n. sp. (Pl. 44, fig. 3).

Arms nearly triangular, at their obtuse truncated distal end twice as broad as at their base. Four arms equal, with five joints each; the fifth arm twice as long, with seven joints. Angles between the arms nearly equal; the odd angle a little larger.

_Dimensions._--Radius of the larger odd arm 0.25, of the four smaller arms 0.15; basal breadth 0.035, distal breadth 0.07.

_Habitat._--Pacific, central area, Station 274, surface.

4. _Pentalastrum cometa_, n. sp.

Arms nearly cylindrical, at their obtuse truncated distal end one and a half times as broad as at their base. Posterior odd arm very large, with eleven joints, about three times as long as the two lateral arms (with five joints each) and four times as long as the two anterior arms (with three joints each). Angles between the paired arms different; the two lateral angles smaller than the two posterior, and these smaller than the odd anterior angle.

_Dimensions._--Radius of the odd posterior arm 0.5, of the lateral arms 0.25, of the anterior arms 0.18; basal breadth 0.05, distal breadth 0.08.

_Habitat._--South Pacific, Station 288, surface.

Genus 241. _Pentinastrum_,[280] Haeckel, 1881, Prodromus, p. 461.

_Definition._--#Porodiscida# with five simple, undivided, chambered arms, connected by a patagium.

The genus _Pentinastrum_ differs from the foregoing _Pentalastrum_ only in the development of a patagium or connecticulum between the arms, and bears therefore the same relation to it that _Histiastrum_ does to _Stauralastrum_, or _Hymeniastrum_ to _Dictyastrum_.

1. _Pentinastrum asteriscus_ , n. sp. (Pl. 44, fig. 2).

All arms equal, twice as long as broad, at their base two-thirds as broad as at their truncated distal end, which bears a strong, pyramidal, terminal spine. Each arm is divided by five transverse septa into six joints or chambers, and each of these by a radial beam into a pair of chambers. The five radial beams arise from the innermost chamber of the central disk, and end in the five terminal {558}spines. The diameter of the central disk is larger than the length of the arms. The angles between the arms are equal and filled up by an incomplete patagium, so that the whole disk forms a regular pentagon with five concave sides.

_Dimensions._--Radius of each arm (without terminal spine) 0.14; breadth at their base 0.02, at their terminal joint 0.03; radius of the central disk 0.06.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

2. _Pentinastrum goniaster_, n. sp.

? _Stephanastrum_ sp., Bury, 1862, Polycystins of Barbados, pl. xx. fig. 1.

All five arms equal, four times as long as broad, club-shaped, at their globose distal end twice as broad as at their base, and armed with a strong conical terminal spine. Diameter of the central disk equals only one-third of the length of the arms. The articulation of the spongy arms is somewhat obscure. Patagium complete, totally fills up the interbrachial spaces, so that the whole disk forms a regular pentagon with five rectilinear sides, except that the terminal spines project at the corners.

_Dimensions._--Radius of each arm 0.18, basal breadth 0.02, distal breadth 0.04; radius of the central disk 0.05.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms; also fossil in the rocks of Barbados.

Genus 242. _Pentophiastrum_,[281] n. gen.

_Definition._--#Porodiscida# with five forked chambered arms, without a patagium.

The genus _Pentophiastrum_ differs from the two preceding genera by the bifurcation of the five arms, and can be derived either from _Pentalastrum_ by the ramification of the distal ends of the arms, or from the similar _Myelastrum_ by the increase in the number of arms.

1. _Pentophiastrum dicranastrum_, n. sp.

All five arms equal, with equal angles between them. Each arm in the basal half simple, in the distal half forked; both branches of it equal, with obtuse ends. (This regular species resembles _Dicranastrum furcatum_, Pl. 47, fig. 2, but with five rays instead of four; also the form of the arms is more slender and the edges smooth.)

_Dimensions._--Radius of each arm 0.25, breadth 0.05.

_Habitat._--Equatorial Atlantic, Station 347, depth 2250 fathoms.

Subgenus _Pentophiastromma_, Haeckel.

_Definition._--Arms of different size, one odd arm opposite to the angle between both arm-pairs.

{559}2. _Pentophiastrum caudatum_, n. sp. (Pl. 47, fig. 5).

Arms in pairs different; four arms in the basal half simple, in the distal half forked; the fifth (posterior) odd arm simple, undivided, cylindrical; the anterior pair a little smaller than the posterior; the neighboring branches of the two pairs on each side larger than the two others. Axes of the arms and their branches straight.

_Dimensions._--Radius of the arms about 0.5, breadth 0.12.

_Habitat._--North Atlantic, Station 353, depth 2965 fathoms.

3. _Pentophiastrum forcipatum_, n. sp. (Pl. 47, fig. 4).

Arms in pairs different, all in the basal two thirds simple, in the distal third forked. Only in the posterior (odd) arm both branches are equal, in the four others unequal. The common axis of the posterior lateral pair is horizontal, perpendicular to the median line; the axes of the anterior pair are pincer-like, concavely curved towards the median line or principal axis.

_Dimensions._--Radius of the arms about 0.5, breadth 0.14.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

Genus 243. _Hexalastrum_,[282] Haeckel, 1881, Prodromus, p. 461.

_Definition._--#Porodiscida# with six simple chambered arms, without a patagium.

The genus _Hexalastrum_, together with the following _Hexinastrum_, encloses those _Euchitonida_ in which the number of the chambered arms surrounding the central disk amounts to six. This is the highest number of these articulated marginal appendages which is reached in any #Discoidea#. Formerly (1881) in my Prodromus, p. 459, I supposed that the same number was reached also by one Coccodiscid, and called this genus _Hexactura_. Afterwards I was convinced that this form was also a _Hexalastrum_.

1. _Hexalastrum palmanthum_, n. sp.

All six arms equal, with equal angles between them. Each arm club-shaped, three times as long as broad, twice as broad at the thickened distal end as at the base, without a terminal spine.

_Dimensions._--Radius of each arm 0.2, basal breadth 0.02, distal breadth 0.06.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

2. _Hexalastrum crinanthum_, n. sp.

All six arms equal, with equal angles between them. Each arm club-shaped, four times as long as broad, at the egg-shaped distal end three times as broad as in the linear basal part, provided {560}with numerous short conical spines and one longer terminal spine. (Resembles _Stauralastrum rhopalophorum_, Pl. 45, fig. 1, but with six rays instead of four.)

_Dimensions._--Radius of each arm 0.3, basal breadth 0.03, distal breadth 0.08.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

Subgenus _Hexalastromma_, Haeckel.

_Definition._--Arms more or less different in size or form; shell bilateral.

3. _Hexalastrum orchidaceum_, n. sp. (Pl. 44, fig. 5).

_Hexactura orchidacea_, Haeckel, 1881, Prodromus, p. 459.

Arms different in length, so that two unequal opposite odd arms determine the main axis, and the four other arms lie on both sides of this as two different pairs. The proportion of their relative length is the following:--anterior lateral arms five, anterior odd arm six; posterior lateral arms seven, posterior odd arm eight. Each arm is club-shaped, two to three times as long as broad, and divided into six to eight joints by five to seven transverse septa; its distal end is armed with a terminal spine and twice as broad as its base.

_Dimensions._--Radius of the posterior odd arm 0.4, of the anterior odd arm 0.3; of the posterior lateral pair 0.35, of the anterior lateral pair 0.25; basal breadth 0.08, distal breadth 0.16.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

Genus 244. _Hexinastrum_,[283] Haeckel, 1881, Prodromus, p. 461.

_Definition._--#Porodiscida# with six simple, undivided, chambered arms, connected by a patagium.

The genus _Hexinastrum_ differs from its ancestral form _Hexalastrum_ by the development of a patagium between the arms. The only observed species is regular.

1. _Hexinastrum geryonidum_, n. sp. (Pl. 44, fig. 4).

_Hexalastrum geryonidum_, Haeckel, 1879, Atlas (pl. xliv. fig. 4).

Disk quite regular with six radii; all six arms of the same size and form, at their broad, convexly rounded, smooth end five times as broad as at their narrow base, and little longer than broad. Each arm is divided by eight transverse septa into nine simple joints or chambers of the same height; the breadth of the distal chambers increases rapidly. The regular, hexagonal, central disk exhibits four concentric rings around the central chamber. Patagium between the arms incomplete, with concavely fluted edge.

_Dimensions._--Radius of each arm 0.15, basal breadth 0.016, distal breadth 0.08; radius of the central disk 0.04.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

{561}Family XXII. #PYLODISCIDA#, n. fam. (Pl. 48, figs. 12-20).

_Definition._--#Discoidea# without phacoid shell, with flat discoidal shell, in which a simple spherical central chamber is surrounded by one or two concentric triradial girdles; each girdle with three gates, separated by three simple arm-chambers. Surface of the disk with three open or latticed gates on each flat side.

The family #Pylodiscida# represents a new small but interesting group of #Discoidea#, which exhibits rather complex affinities to different groups of #Sphærellaria#. In my Prodromus (1881, p. 464) I had enumerated only two genera of this family, _Triopyle_ and _Hexapyle_, and had united them with _Tetrapyle_ and allied genera in the family Pylonida. Indeed, the resemblance of skeletal structure in the two groups is very great. The most simple forms of both groups exhibit a simple spherical latticed central chamber, which is surrounded by few latticed chambers of similar size and form, separated by open gates. But in the Pylonida these chambers are opposite in pairs, and form together a complete lattice-girdle around the central chamber, whereas in the Pylodiscida the chambers are not opposite in pairs in one axis, and form therefore only latticed half girdles, which arise from the central chamber like radial arms, and may perhaps better be called "arm-chambers"; their number is constantly three. The free open spaces between these three arm-chambers form three gates, comparable to the two or four gates of _Amphipyle_, _Tetrapyle_, &c., and become afterwards closed by lattice-work in a similar way in both groups. A more important difference between them is indicated by the further mode of growth. The Pylonida build new girdles in all three dimensive planes (alternating in the transverse, lateral and sagittal planes); their geometric fundamental form is therefore the "lentellipsis" or the "triaxial ellipsoid." The Pylodiscida, however, grow only at the periphery of the discoidal shell in one single plane (the equatorial plane); their fundamental form is therefore the biconvex lens or the flat disk (a shortened cylinder). This important difference is my deciding motive, in separating the latter from the former and in regarding the Pylodiscida as true #Discoidea#, the more so as they can easily be derived from _Archidiscus_, the fundamental and ancestral form of the Porodiscida.

One single form of _Archidiscus_ seems to be of peculiar importance in this relation, viz., _Archidiscus hexoniscus_ (Pl. 48, fig. 10). In this species the simple central chamber is surrounded by a latticed ring or girdle, composed of six equal chambers of the same size and form, all lying in the same plane with the central chamber. In a nearly allied species, viz., _Archidiscus pyloniscus_, the six ring-chambers are different, three smaller (with denser network) alternating with three larger (of looser network); if we imagine the network of the latter reduced to a marginal bar we get _Triopyle_, and if also this bar disappear by reduction we get _Triolena_, the most simple form of the Pylodiscida. {562}Even _Archidiscus pyloniscus_ may possibly represent the same form among the Porodiscida as _Triodiscus lenticula_ among the Pylodiscida; this important form indicates clearly the close affinity of the two families.

If we take the latter, nearly identical form as the common starting point of both families of Cyclodiscaria, then probably _Triopyle_ and _Triolene_ must be regarded as retrograde forms, derived from _Triodiscus_ in the one case, from _Archidiscus_ in the other, by reduction of three interradial arm-chambers, whilst three perradial only remain. But it is also possible that the most simple form, _Triolene_, originated independently from some _Cenosphæra_, three simple radial chambers, like the latticed central chamber, being derived from the latter by apposition in three equidistant radii, whilst three other radii between them remained free. In this case the other genera of Pylodiscida are derived from their ancestral form _Triolene_.

Adopting this latter view, we find that all eight genera of Pylodiscida, here distinguished, may be regarded as following members of a continuous series. If the three simple arm-chambers of _Triolene_, surrounding the equal central chamber, become united at their distal ends by a concentric equatorial ring, then originates _Triopyle_; and this graduates into _Triodiscus_ by fenestration of the three open gates between the three latticed arms. Whilst these three genera form together the subfamily Triopylida, a second family, Hexapylida, is composed of three other analogous genera, in which the same process of development becomes repeated.

_Pylolena_, the most simple form of Hexapylida, arises from _Triodiscus_ by the development of three new arm-chambers (of the second order) which are apposed at the distal end of the three primary arm-chambers (of the first order) in the same radius. If the distal ends of these three secondary arm-chambers become united by a concentric latticed ring or girdle, we get _Hexapyle_ (with six open gates, two in each radius), and if its six gates become afterwards closed by loose lattice-work, we arrive at _Pylodiscus_ (a repetition of _Triodiscus_).

A third subfamily, Discopylida, is formed by the building of a chambered equatorial girdle around the margin of _Pylodiscus_. This girdle has quite the same structure as the similar chambered rings or girdles of the Porodiscida and Coccodiscida. Between the two sieve-plates of the disk surface is enclosed a variable number (twelve to twenty-four or more) of chambers, imperfectly separated by radial beams, which connect the margin of the _Pylodiscus_-shell with an outer peripheral concentric ring. In _Discozonium_ this marginal ring is perfect, whilst in _Discopyle_ it is interrupted by a peculiar large opening, a "marginal osculum" surrounded by a corona of spines, quite the same remarkable formation which we encountered in _Ommatodiscus_ among the Porodiscida.

All Pylodiscida are therefore triradial (with three perradial arms and three interradial gates between them), and many of them have a great resemblance to certain triradial Porodiscida and Spongodiscida, perhaps not only a morphological resemblance, but also {563}a true phylogenetic relation. But it is remarkable that we do not find further forms of development in this family, by multiplication either of the arm-chambers (further growth in the three perradii) or of the concentric chambered rings (in the periphery of the disk margin).

The central capsule of the Pylodiscida is constantly flat, discoidal, and enclosed between the two sieve-plates of the surface. Its form is either circular or triangular.

_Synopsis of the Genera of the Pylodiscida._

------------------------------------------------------------------------- I. Subfamily Triopylida. Three gates between three simple arm-chambers. ----------------------------------------------------------------------- Three gates open, without a barring equatorial girdle, 245. _Triolena_.

Three gates barred by a { Gate-faces simple, 246. _Triopyle_. latticed equatorial { girdle. { Gate-faces latticed, 247. _Triodiscus_. ------------------------------------------------------------------------- II. Subfamily Hexapylida. Six gates between three double arm-chambers (three inner and three outer); no chambered marginal girdle. ------------------------------------------------------------------------- Three outer gates open, without a barring equatorial girdle, 248. _Pylolena_.

{ Both faces of the outer Three outer gates barred { gates simple, 249. _Hexapyle_. by a latticed (second) { equatorial girdle. { Both faces of the outer { gates latticed, 250. _Pylodiscus_. ------------------------------------------------------------------------- III. Subfamily Discopylida. Six gates between three double arm-chambers. ------------------------------------------------------------------------ { No peculiar osculum on In the equatorial plane { the margin of the disc, 251. _Discozonium_. on the margin of the { Pylodiscus-shell is a { One pecuiar osculum (with chambered equatorial { a corona of spines) on girdle. { the margin of the disc, 252. _Discopyle_.

Subfamily 1. TRIOPYLIDA, Haeckel.

_Definition._--#Pylodiscida# with a simple, spherical or lenticular, central chamber, surrounded by three simple arm-chambers, which are separated by three notches or gates.

Genus 245. _Triolena_,[284] n. gen.

_Definition._--#Pylodiscida# with a simple, spherical or lenticular, central chamber, surrounded by three simple arm-chambers. Notches between the three arms open.

The genus _Triolena_ is the most simple form of all Pylodiscida, and must be regarded as their common ancestral form, from an ontogenetic as well as a phylogenetic point of view. The small shell is composed of a simple, spherical or lenticular, latticed, central chamber, and of three simple, surrounding equal arms, which are also simple latticed chambers, lie in the equatorial plane, and are separated by three equal angles or open gates.

{564}1. _Triolena primordialis_, n. sp. (Pl. 48, fig. 12).

Arm-chambers trapezoid, nearly square, of the same size as the circular, lenticular, primordial, central chamber. Surface of the disk smooth.

_Dimensions._--Diameter of the shell 0.045, of the central chamber 0.015, of each arm 0.015.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

2. _Triolena tribelone_, n. sp.

Arm-chambers lanceolate, of the same breadth as and twice the length of the triangular, central chamber; at the pointed end of each arm is a conical terminal spine (in the equatorial plane). Surface of the disk thorny.

_Dimensions._--Diameter of the shell 0.05, of the central chamber 0.015; length of the arms 0.02, breadth 0.016.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

3. _Triolena trispinosa_, n. sp.

Arm-chambers ovate, in the basal half nearly as broad as the hexagonal central chamber, at the pointed distal end with a strong conical radial spine of double the length. Surface rough.

_Dimensions._--Diameter of the shell 0.055, of the central chamber 0.02.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

4. _Triolena hexabelone_, n. sp.

Arm-chambers nearly triangular, at the base half as broad as the hexagonal central chamber, at the truncate distal end one and a half times as broad, and armed with two radial conical spines (in the equatorial plane). Surface of the disk smooth.

_Dimensions._--Diameter of the shell 0.06, of the central chamber 0.02.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

5. _Triolena trigonalis_, n. sp.

Arm-chambers nearly triangular, at the base half as broad as the circular central chamber, at the concave lunulate distal end twice as broad, and armed with four conical radial spines (two on each side of the equatorial plane). Surface thorny.

_Dimensions._--Diameter of the shell 0.05, of the central chamber 0.015.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

{565}Genus 246. _Triopyle_,[285] Haeckel, 1881, Prodromus, p. 464.

_Definition._--#Pylodiscida# with a simple, spherical or lenticular, central chamber, surrounded by three simple arm-chambers. Notches between the three arms transformed into gates by a connecting equatorial girdle.

The genus _Triopyle_ differs from the preceding _Triolene_ in the development of a simple ring or latticed equatorial girdle, which connects the distal ends of the three arm-chambers, and transforms the open notches between them into three gates. The ring may be circular, triangular, or hexagonal.

1. _Triopyle circulus_, n. sp.

Disk circular, three times as broad as the hexagonal central chamber. Three arm-chambers trapezoidal, at the convex distal end as broad, at the base half as broad as the three circular gates between them. Surface smooth. No marginal spines on the girdle.

_Dimensions._--Diameter of the disk 0.045, of the gates 0.015.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

2. _Triopyle hexagona_, n. sp. (Pl. 48, fig. 13).

Disk hexagonal, three times as broad as the circular central chamber. Three arm-chambers trapezoidal, at the truncated distal end as broad, at the base half as broad as the three triangular gates between them. Surface smooth. No marginal spines.

_Dimensions._--Diameter of the disk 0.05, of the gates 0.02.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

3. _Triopyle trigona_, n. sp.

Disk triangular, four times as broad as the circular central chamber. Three arm-chambers nearly triangular, at the narrow base half as broad, at the distal end twice as broad as the circular or roundish gates. Surface smooth. On the margin (in the equatorial plane) three strong pyramidal spines (at the end of the arms).

_Dimensions._--Diameter of the disk 0.04, of the gates 0.015.

_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.

4. _Triopyle cordigera_, n. sp.

Disk hexagonal, four times as broad as the hexagonal central chamber. Three arm-chambers triangular, at the base half as broad as at the truncated distal end, about the same size as the {566}three heart-shaped gates. On the six corners of the margin (which forms a regular hexagon) are six pyramidal radial spines, as prolongations of the arm-edges.

_Dimensions._--Diameter of the disk 0.05, of the gates 0.02.

_Habitat._--Indian Ocean, Ceylon, surface, Haeckel.

5. _Triopyle renigera_, n. sp.

Disk hexagonal, five times as broad as the circular central chamber. Three arm-chambers trapezoidal, at the base one-third, at the distal end two-thirds as broad as the three kidney-shaped gates. On the six corners of the margin (which forms an irregular hexagon) six conical radial spines, as prolongations of the arm-edges.

_Dimensions._--Diameter of the disk 0.06, of the gates 0.02.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

6. _Triopyle spinigera_, n. sp.

Disk roundish, triangular, four times as broad as the triangular central chamber, which is armed with three radial spines between the arms. Arm-chambers club-shaped, at the narrow base one-fourth, at the distal end half as broad as the square gates. On the margin twelve large conical spines, two opposite on each face of the distal end of each arm-edge. Three smaller radial spines on the three corners of the girdle (in the same interradial meridian planes as the three spines of the central chamber). Compare _Triodiscus spinosus_.

_Dimensions._--Diameter of the disk 0.05, of the gates 0.02.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

Genus 247. _Triodiscus_,[286] n. sp.

_Definition._--#Pylodiscida# with a simple, spherical or lenticular, central chamber, surrounded by three simple arm-chambers. Notches between the three arms closed by lattice-work and by an equatorial girdle.

The genus _Triodiscus_ differs from the preceding _Triopyle_ in the development of loose lattice-work on both sides of the discoidal shell. This network closes the gates and transforms the whole shell into a fenestrated lens. The singular species of _Triodiscus_ correspond to certain species of _Triopyle_.

1. _Triodiscus lenticula_, n. sp.

Disk circular, lenticular, three times as broad as the central chamber. Three arm-chambers trapezoidal, of the same size and form as the three gates between them, which are closed by a loose {567}delicate network (differs from _Triopyle circulus_ by the production of the two convex latticed plates, which envelop the whole lens). Margin smooth.

_Dimensions._--Diameter of the disk 0.045, of the gates 0.015.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

2. _Triodiscus trigonus_, n. sp.

Disk triangular, four times as broad as the central chamber. Three arm-chambers at the base half as broad, at the distal end twice as broad as the roundish gates. Surface smooth. On the three corners of the margin (in the arm-radius) three strong spines. (Differs from _Triopyle trigona_ only in the loose framework closing the gates.)

_Dimensions._--Diameter of the disk 0.04, of the gates 0.015.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

3. _Triodiscus spinosus_, n. sp. (Pl. 48, fig. 14).

Disk subcircular, four times as broad as the triangular central chamber. Three arm-chambers club-shaped, at the base one-third, at the distal end two-thirds as broad as the semicircular gates. Surface thorny. On the margin fifteen larger radial spines, three on the corners of the disk (in the radius of the gates), twelve on the two faces of the arms ends (two opposite on the edge of each end.) (Differs from _Triopyle spinigera_ mainly by the delicate hexagonal network closing the gates.)

_Dimensions._--Diameter of the disk 0.05, of the gates 0.02.

_Habitat._--North Atlantic, Canary Islands (Lanzerote, Haeckel).

Subfamily 2. HEXAPYLIDA, Haeckel.

_Definition._--#Pylodiscida# with triopyle-shaped medullary shell, surrounded by three distal arm-chambers, which are separated by three open notches or gates.

Genus 248. _Pylolena_,[287] n. gen.

_Definition._--#Pylodiscida# with triopyle-shaped medullary shell, surrounded by three distal arm-chambers. Notches between the three arms open.

The genus _Pylolena_ opens the series of the Hexapylida, or of those Pylodiscida in which the centre of the shell is formed by a tri-radiated medullary shell like _Triopyle_. In the equatorial plane of this triopyle-shaped disk are developed on its margin three distal arm chambers, as prolongations of the three arms of _Triopyle_, but much larger. In _Pylolene_ the three angles or notches between the distal arms remain open, repeating the form of _Triolene_.

{568}1. _Pylolena inermis_, n. sp.

Arms club-shaped, at the base half as broad, at the rounded distal end as broad as the triopyle-shaped medullary shell. Surface and margin smooth.

_Dimensions._--Diameter of the cortical shell 0.15, of the medullary shell 0.05.

_Habitat._--Equatorial Atlantic, Station 347, surface; Central Pacific, Station 272, surface.

2. _Pylolena armata_, n. sp. (Pl. 48, fig. 15).

Arms trapezoid, at the base half as broad, at the distal end twice as broad as the triopyle-shaped medullary shell. Surface and margin thorny. Twelve strong conical spines at the distal end of the three arms, two opposite on both faces of the arm-edges.

_Dimensions._--Diameter of the cortical shell 0.2, of the medullary shell 0.06.

_Habitat._--South Atlantic, Station 325, surface.

Genus 249. _Hexapyle_,[288] Haeckel, 1881, Prodromus, p. 464.

_Definition._--#Pylodiscida# with triopyle-shaped medullary shell, surrounded by three distal arm-chambers. Notches between the three arms transformed into gates by a connecting equatorial girdle.

The genus _Hexapyle_ differs from the preceding _Pylolene_ in the development of an equatorial ring or latticed girdle, which connects the free extremities of the three distal ends and transforms the open notches between them into gates. It simulates therefore the formation of _Triopyle_, from which it differs by duplication of the arm-joints and of the gates (in each radius occur one proximal and one distal gate).

1. _Hexapyle triangula_, n. sp.

Cortical shell triangular, with three rounded corners, three times as broad as the triangular triopyle-shaped medullary shell. Surface smooth or rough, but not spiny. Three arms two-thirds as broad as the three egg-shaped gates of each side.

_Dimensions._--Diameter of the cortical shell (or length of one side of the triangle) 0.15, of the medullary shell 0.05; breadth of the gates 0.06, of the bridges between them 0.04.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

2. _Hexapyle sexangula_, n. sp.

Cortical shell hexagonal, with six equal sides, four times as broad as the triangular triopyle-shaped medullary shell. Surface rough, but not spiny. Three arms (on their smallest part) half as broad as the three triangular gates (on their broadest part).

{569}_Dimensions._--Diameter of the cortical shell 0.16, of the medullary shell 0.04; breadth of the gates 0.06, of the bridges 0.03.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

3. _Hexapyle circularis_, n. sp.

Cortical shell circular, four times as broad as the triangular, Triopyle-shaped medullary shell. Surface smooth. Three arms half as broad as the three kidney-shaped gates on each side of the shell.

_Dimensions._--Diameter of the cortical shell 0.2, of the medullary shell 0.05; breadth of the gates 0.08, of the bridges between them 0.04.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

4. _Hexapyle triacantha_, n. sp.

Cortical shell triangular, thorny, with three pointed corners, prolonged into three strong conical radial spines; its diameter four times as great as that of the medullary shell. Three arms of the same breadth as the three egg-shaped gates of each side.

_Dimensions._--Diameter of the cortical shell (or length of one side of the triangle, without spines) 0.2, of the medullary shell 0.05; breadth of the gates and of the bridges between them 0.06.

_Habitat._--Indian Ocean, surface; Madagascar, Rabbe.

5. _Hexapyle hexacantha_, n. sp.

Cortical shell hexagonal, thorny, three times as broad as the medullary shell. Six stronger conical radial spines on the six corners at equal distances, lying in the equatorial plane of the disk. Three half girdles half as broad as the three triangular gates of each side.

_Dimensions._--Diameter of the cortical shell 0.15, of the medullary shell 0.05; breadth of the gates 0.05, of the bridges 0.025.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

6. _Hexapyle dodecantha_, n. sp. (Pl. 48, fig. 16).

Cortical shell triangular, thorny, with rounded corners, three and a half times as broad as the medullary shell. Twelve stronger radial spines, six opposite in pairs on each side of the discoidal shell, as prolongations of the lateral edges of the triangular gates, which are about the same breadth as the half girdles between them.

_Dimensions._--Diameter of the cortical shell 0.21, of the medullary shell 0.06; breadth of the gates and of the bridges 0.06.

_Habitat._--Pacific, central area, Station 270, surface.

{570}7. _Hexapyle polyacantha_, n. sp.

Cortical shell circular, thorny, with a circle of numerous conical radial spines in the periphery; its diameter nearly three times as great as that of the medullary shell. Three half-girdles half as broad as the three kidney-shaped gates on each side of the discoidal shell.

_Dimensions._--Diameter of the cortical shell 0.11, of the medullary shell 0.04; breadth of the gates 0.04, of the bridges between them 0.02.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

Genus 250. _Pylodiscus_,[289] n. gen.

_Definition._--#Pylodiscida# with _Triopyle_-shaped medullary shell, surrounded by three distal arm-chambers. Notches between the three arms closed by lattice-work and by an equatorial girdle.

The genus _Pylodiscus_ differs from _Hexapyle_ in the development of two convex plates of lattice-work, which close the six open gates and transform the disk into a biconvex fenestrated lens. _Pylodiscus_ simulates therefore the characteristic form of _Triodiscus_; but whilst in the latter we find only three arm-joints and three simple gates, their number is doubled in the former.

1. _Pylodiscus triangularis_, n. sp. (Pl. 48, fig. 17).

Cortical shell triangular, with rounded corners, three times as broad as the triangular, _Triopyle_-shaped medullary shell. Three arms about as broad as the three egg-shaped gates between them. (Differs from _Hexapyle triangula_ only by the delicate network of both triangular convex covering plates, which close the open gates.) Six larger and many smaller spines on the margin of the disk.

_Dimensions._--Diameter of the disk 0.15, of the gates 0.05.

_Habitat._--Pacific, central area, Station 270, depth 2925 fathoms.

2. _Pylodiscus sexangularis_, n. sp.

Cortical shell hexangular, equilateral, four times as broad as the circular, _Triopyle_-shaped medullary shell. Surface spiny. Three arms nearly of the same form and size as the three triangular gates between them. (Similar to _Hexapyle sexangularis_, but differing in the irregular loose network closing the gates.)

_Dimensions._--Diameter of the disk 0.18, of the gates 0.06.

_Habitat._--North Pacific, south of Japan, Station 237, surface

{571}3. _Pylodiscus cardiopylus_, n. sp.

Cortical shell hexangular, equilateral, five times as broad as the triangular, _Triopyle_-shaped medullary shell. Surface smooth. Three arms triangular, at the distal end as broad as the three heart-shaped gates. On the margin six strong pyramidal spines in the equatorial plane (adradial, as prolongations of the lateral arm-edges).

_Dimensions._--Diameter of the disk 0.15, of the gates 0.05.

_Habitat._--Indian Ocean, Sunda Strait, Rabbe.

4. _Pylodiscus nephropylus_, n. sp.

Cortical shell circular, three times as broad as the circular, _Triopyle_-shaped medullary shell. Surface spiny. Three arms trapezoidal, half as broad as the three kidney-shaped gates. On the margin twelve stronger, conical, radial spines, opposite in pairs on both sides of the disk, disposed in six pairs at the distal end of the arms.

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.06.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

Subfamily 3. DISCOPYLIDA, Haeckel.

_Definition._--#Pylodiscida# with _Triopyle_-shaped medullary shell and _Pylodiscus_-shaped cortical shell, which is surrounded by a marginal chambered equatorial girdle.

Genus 251. _Discozonium_,[290] n. gen.

_Definition._--#Pylodiscida# with _Triopyle_-shaped medullary shell and _Pylodiscus_-shaped cortical shell, which is surrounded by an equatorial chambered girdle. No peculiar osculum on the margin of the disk.

The genus _Discozonium_ and the following _Discopyle_ make up together the small group of the Discopylida, or those Pylodiscida in which a discoidal shell like _Pylodiscus_ is surrounded by a marginal equatorial girdle; this girdle is divided into twelve to twenty-four or more chambers by radial beams, which are the external prolongations of the radial marginal spines of _Pylodiscus_. The latter genus bears therefore to _Discozonium_ the same relation as _Sethodiscus_ in the other #Discoidea# does to _Lithocyclia_, or _Phacodiscus_ to _Coccodiscus_.

1. _Discozonium cyclonium_, n. sp.

Disk circular, lenticular, with smooth margin, three times as broad as the triangular, _Triopyle_-shaped medullary shell. Three gates of the cortical shell kidney-shaped, twice as broad as the three {572}arms. Chambered equatorial girdle with twenty to twenty-four subregular chambers (similar to _Discopyle osculata_, Pl. 48, fig. 19, but without any marginal osculum).

_Dimensions._--Diameter of the disk 0.2, of the cortical shell 0.14, of the medullary shell 0.07.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

2. _Discozonium trigonium_, n. sp.

Disk triangular, with thorny margin, four times as broad as the triangular, _Triopyle_-shaped medullary shell. Three gates of the cortical shell egg-shaped, scarcely as broad as the three arms. Chambered equatorial girdle with twenty-four to thirty irregular chambers.

_Dimensions._--Diameter of the disk 0.24, of the cortical shell 0.2, of the medullary shell 0.06.

_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.

3. _Discozonium hexagonium_, n. sp. (Pl. 48, fig. 18).

Disk hexagonal, with spiny margin, four times as broad as the triangular, _Triopyle_-shaped medullary shell. Three gates of the cortical shell kidney-shaped, one and a half times as broad as the arms. Chambered equatorial girdle with twelve large regular chambers; the radial beams between them are prolonged into twelve strong pyramidal marginal spines (three perradial on the ends of the arms, three interradial on the radii of the gates, six adradial between the former and latter).

_Dimensions._--Diameter of the disk 0.2, of the cortical shell 0.12, of the medullary shell 0.05.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

Genus 252. _Discopyle_,[291] n. gen.

_Definition._--#Pylodiscida# with _Triopyle_-shaped medullary shell and _Pylodiscus_-shaped cortical shell, which is surrounded by an equatorial chambered girdle. One peculiar osculum, surrounded by a corona of spines, on the margin of the disk.

The genus _Discopyle_ differs from the preceding genus _Discozonium_ in the development of a peculiar marginal osculum, and bears therefore to it the same relation as, in the Porodiscida, _Ommatodiscus_ does to _Porodiscus_ (compare above, p. 500). This peculiar osculum is here also surrounded by a corona of spines, and serves probably for the exit or outlet of a bunch of pseudopodia or a "sarcode-flagellum." Only two species of _Discopyle_ have been observed, which represent perhaps better two different genera; in one species the disk is circular, in the other elliptical. In this latter the osculum lies on one pole of the main axis.

{573}1. _Discopyle osculata_, n. sp. (Pl. 48, fig. 19).

Disk circular with spiny margin, three times as broad as the triangular, _Triopyle_-shaped medullary shell. Three gates of the cortical shell kidney-shaped, on the inside with an interradial spine, twice as broad as the three pentagonal arms. Chambered equatorial girdle with twenty-four subregular chambers, in the radius of one odd gate with a large marginal osculum, which is as broad as the medullary shell, and surrounded by a dense corona of twenty to thirty strong conical spines.

_Dimensions._--Diameter of the disk 0.15, of the cortical shell 0.1, of the medullary shell 0.05, of the marginal osculum 0.06.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

2. _Discopyle elliptica_, n. sp. (Pl. 48, fig. 20).

Disk elliptical, four-fifths as broad as long, with spiny margin, three times as broad as the triangular, _Triopyle_-shaped medullary shell. Three gates of the cortical shell roundish, on the inside with an interradial spine, little broader than the quadrangular arms. Chambered equatorial girdle with twenty to thirty irregular chambers, on one pole of the main axis with a large marginal osculum, which is one-third as broad as the length of the main axis, and armed with a corona of twenty to thirty short conical spines. The osculum does not correspond to a certain radius.

_Dimensions._--Diameter of the disk 0.15, of the cortical shell 0.08, of the medullary shell 0.04, of the marginal osculum 0.05.

_Habitat._--Central Pacific, Station 267, depth 2700 fathoms.

Family XXIII. #SPONGODISCIDA#, Haeckel (Pl. 41, fig. 11).

_Spongodiscida et Spongocyclida_, Haeckel, 1862, Monogr. d. Radiol., pp. 452, 460, 469. _Spongodiscida_, Haeckel, 1881, Prodromus, p. 461. _Calodictya_, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 53 (_partim_).

_Definition._--#Discoidea# without a phacoid shell, with a flat discoidal shell, in which a simple spherical central chamber is surrounded by an irregular spongy framework (sometimes with concentric rings around the central chamber). Surface of the disk quite spongy, without porous sieve-plates.

The family #Spongodiscida# is the sixth and last family of the #Discoidea#, and bears to the other families of this group the same relation as the family Spongosphærida does to the other #Sphæroidea#, or the Spongurida to the other #Prunoidea#. Its characteristic structure consists in the irregular spongy framework of the disk, and mainly in the rough, irregular shape of its spongy surface, which is never covered with porous plates (neither phacoid shell nor corresponding sieve-plates), as in all other #Discoidea#. Of course a little spongy structure occurs also in many Porodiscida {574}and even in some Coccodiscida (principally in the peripheral part of the disk or its chambered arms); but both flat (or convex) surfaces of the disk (at least in the central part) remain here constantly as simple lattice-plates, whilst in all Spongodiscida the whole surface of the disk is spongy.

When I constituted the family Spongodiscida in my Monograph (1862, pp. 452, 460) I had separated from them the Spongocyclida, exhibiting in the central part of the disk a more or less distinct concentric arrangement of the spongy chambers, whilst in the former the delicate spongy framework is quite irregular, composed of branched siliceous threads, connected and interwoven in all directions. But in all Spongocyclida the whole surface of the spongy disk is quite as irregularly rough and deprived of smooth sieve-plates as in all true Spongodiscida, and the more or less concentric structure of the central part of the disk in the former (very variable and often scarcely able to be recognised) seems not sufficient to separate both groups; even the single genera cannot be sufficiently separated by this character. I now therefore give up entirely the group of Spongocyclida (as already done in my Prodromus, 1881). Nevertheless the concentric annular structure in the dark central part of some Spongodiscida is very interesting as transition to the Porodiscida; it indicates already that the former are derived from the latter. Even the single genera in both families are corresponding.

In the new system of "Polycystina," which Ehrenberg gave, 1875 (Abhandl. d. k. Akad. d. Wiss. Berlin, p. 157), are enumerated under the _Calodictya_ four genera "with spongy disk," viz., _Spongodiscus_, _Rhopalodictyum_, _Dictyocoryne_, _Spongaster_. Indeed these four genera, which I here retain, are true Spongodiscida, and must be separated from the other _Calodictya_, the greater part of which are Porodiscida. The number of species of true Spongodiscida now amounts to sixty-seven, which I dispose in thirteen genera.

The whole family may be divided into three subfamilies. The first of these are the Spongophacida (corresponding to the Trematodiscida among the Porodiscida), in which the circular margin of the spongy disk bears no radial appendages; either the margin is quite simple, spongy (_Spongodiscus_), or surrounded by a hyaline, solid, or porous equatorial girdle (_Spongophacus_). The disk is either more lenticular (biconvex) or more flat discoidal (a shortened cylinder), rarely a little biconcave (thicker at the margin than in the centre). The spongy framework of the solid disk is either quite irregular (_Spongodisculus_), or in the central part with concentric circular rings (_Spongocyclia_), or in the central part spirally convoluted (_Spongospira_).

The second subfamily, Spongotrochida, corresponds to the Stylodictyida (among the #Porodiscida#), and is distinguished by solid radial spines on the margin of the disk, disposed in the equatorial plane either irregularly or regularly (after the same order as in the other families of #Discoidea#).

The third subfamily, Spongobrachida, correspond perfectly to the Euchitonida {575}(among the Porodiscida), bearing on the disk-margin two, three, or four spongy arms, commonly disposed regularly in the equatorial plane. Here also occurs the peculiar formation of a "patagium," or of an interbrachial spongy framework different from that of the arms, which connects the arms like a web-membrane in the equatorial plane.

The spongy framework exhibits in all these Spongodiscida no remarkable differences, being everywhere composed of fine branched solid siliceous threads, interwoven in all directions, with irregular meshes of very different size.

The central capsule of all Spongodiscida is filled up with the same spongy framework which covers also both its sides. It grows according to the enveloping skeleton, but remains constantly smaller. The form of the central capsule is circular (lenticular or discoidal) in the Spongophacida and Spongotrochida, whilst in the Spongobrachida it enters into the radial spongy arms, developed from the margin of the spongy disk.

_Synopsis of the Genera of the Spongodiscida._

{Spongy disk with simple I. Subfamily { margin (without peculiar Spongophacida. { equatorialgirdle), 253. _Spongodiscus_. Spongy disk { without radial {Spongy disk with a peculiar appendages. { (solid or porous) equatorial { girdle, 254. _Spongophacus_.

{ {Two opposite { { spines, 255. _Spongolonche_. II. Subfamily {Few (two, { Spongotrochida. { three, or {Three marginal Spongy disk with { four) radial { spines, 256. _Spongotripus_. solid radial { spines { spines on the { regularly {Four crossed margin (in the { disposed. { spines, 257. _Spongostaurus_. equatorial { plane). { {Spines only {Numerous (five { on the { to ten or { margin { more) radial { (equatorial), 258. _Stylotrochus_. { spines, { { often {Spines on both { irregularly { sides of the { disposed. { disk, 259. _Spongotrochus_.

{ {Without a {Two arms, { patagium, 260. _Spongolena_. { opposite in { { one axis. {With a { { patagium, 261. _Spongobrachium_. III. Subfamily { Spongobrachida. { {Without Spongy disk with { { a patagium, 262. _Rhopalodictyum_. spongy radial {Three arms on { arms on the { the margin. {With a margin (in the { { patagium, 263. _Dictyocoryne_. equatorial { plane). { {Without { { a patagium, 264. _Spongasteriscus_. {Four arms in { { cross form. {With a { { patagium, 265. _Spongaster_.

Subfamily 1. SPONGOPHACIDA, Haeckel, 1881, Prodromus, p. 461.

_Definition._--#Spongodiscida# with a simple circular disk, without radial appendages on the margin (neither solid spines nor chambered arms).

{576}Genus 253. _Spongodiscus_,[292] Ehrenberg, 1854, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 237.

_Definition._--#Spongodiscida# with a simple circular disk, without radial appendages and without an equatorial girdle on the margin.

The genus _Spongodiscus_ represents the most simple and primitive form of the Spongodiscida, or of those #Discoidea# in which the central disk is more or less spongy, composed of an irregular fine framework. In my Monograph (1862, pp. 452, 460, 469) I had separated the true _Spongodiscus_ (first described by Ehrenberg, _loc. cit._) and the _Spongocyclia_; the former being characterised by the irregular spongy framework of the whole disk, whilst in the latter this framework includes in the central part some concentric circular rings (approaching _Porodiscus_). In the same way afterwards Stöhr (1880, _loc. cit._) separated the genus _Spongospira_ as spongy disks, which include in the central part some spiral convolutions. But as these differences are rather inconstant and not sharply discernible, I think it now better to regard these three forms as subgenera of _Spongodiscus_. All three have the common simple circular disk, without any marginal appendages.

Subgenus 1. _Spongodisculus_, Haeckel.

_Definition._--Spongy framework of the disk quite irregular, without concentric rings or spiral convolutions.

1. _Spongodiscus mediterraneus_, Haeckel.

_Spongodiscus mediterraneus_, Haeckel, 1862, Monogr. d. Radiol., p. 461, Taf. xii. figs. 14, 15.

Spongy disk plain on both sides, with quite an irregular framework, without concentric rings and without radial piercing beams. Texture everywhere uniform; meshes eight to ten times as broad as the bars.

_Dimensions._--Diameter of the disk 0.08 to 0.24, of the meshes 0.005 to 0.008.

_Habitat._--Mediterranean (Messina), Haeckel; also fossil in the Tertiary rocks of Sicily (Grotte), Stöhr.

2. _Spongodiscus radiatus_, n. sp.

Spongy disk plain on both sides, with quite irregular framework, without concentric rings, but with numerous piercing radial beams which are not prolonged into marginal spines. Texture everywhere uniform; meshes once and a half to twice as broad as the bars.

_Dimensions._--Diameter of the disk 0.12 to 0.15, of the meshes 0.002 to 0.003.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

{577}3. _Spongodiscus resurgens_, Ehrenberg.

_Spongodiscus resurgens_, Ehrenberg, 1854, Mikrogeol., Taf. xxxvB. B. iv., fig. 16.

_Spongodiscus resurgens_, Stöhr, 1880, Palæontogr., xxvi. p. 117, Taf. vi. fig. 11.

Spongy disk lenticular, biconvex, in the darker centre much thicker than towards the thin periphery, with an irregular framework, without concentric rings, but with numerous piercing radial beams. Texture equal; meshes three to four times as broad as the bars.

_Dimensions._--Diameter of the disk 0.1 to 0.3, of the meshes 0.003 to 0.006.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface; also fossil in the Tertiary rocks of Sicily and Barbados.

4. _Spongodiscus favus_, Ehrenberg.

_Spongodiscus favus_, Ehrenberg, 1861, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 301.

Spongy disk lenticular, biconvex, in the darker centre much thicker than towards the periphery, with an irregular framework, without concentric rings. Texture different, in the outer half with numerous radial beams and loose network, the meshes of which are three to four times as large as in the darker and denser framework of the centre.

_Dimensions._--Diameter of the disk 0.2, of the outer meshes 0.008 to 0.012, of the inner meshes 0.002 to 0.003.

_Habitat._--North Atlantic, Greenland, Færöe Channel (John Murray), surface.

5. _Spongodiscus biconcavus_, n. sp.

Spongy disk biconcave, in the peripheral, ring-like, thickened part twice as thick as in the hollowed central part, with an irregular framework, without concentric rings. Texture different, in the outer half looser than in the inner, darker part; meshes of the outer part five to six times, of the inner twice to three times, as broad as the bars.

_Dimensions._--Diameter of the disk 0.25, of the outer meshes 0.01 to 0.012, of the inner 0.004 to 0.006.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

Subgenus 2. _Spongocyclia_, Haeckel, 1862, Monogr. d. Radiol., p. 469.

_Definition._--Spongy framework of the disk in the inner part with concentric, circular rings, in the outer part irregular.

{578}6. _Spongodiscus cycloides_, Haeckel.

_Spongodiscus cycloides_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 843.

_Spongocyclia cycloides_, Haeckel, 1862, Monogr. d. Radiol., p. 469, Taf. xxviii. fig. 1.

Spongy disk on both sides plain, in the central part with five to ten concentric, circular rings, in the peripheral part quite irregularly and densely spongy. Meshes twice to four times as broad as the bars.

_Dimensions._--Diameter of the disk 0.1 to 0.2, of the meshes 0.003 to 0.006.

_Habitat._--Mediterranean (Messina), North Atlantic (Canary Islands).

7. _Spongodiscus spongocyclia_, Haeckel.

_Spongocyclia triangularis_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 119, Taf. vii. fig. 5.

Spongy disk lenticular, in the thicker central part with eleven to twelve circular, concentric rings, in the thinner, peripheral zone irregularly spongy. Meshes twice to four times as broad as the bars. (The triangular form in the specimen figured by Stöhr is accidental, produced by the broken margin.)

_Dimensions._--Diameter of the disk 0.2 to 0.3, of the meshes 0.006 to 0.008.

_Habitat._--Fossil in Tertiary rocks of Barbados (Haeckel) and Sicily (Stöhr).

Subgenus 3. _Spongospira_, Stöhr, 1880, Palæontogr., vol xxvi. p. 120.

_Definition._--Spongy framework of the disk in the inner part with spiral convolutions, in the outer part irregular.

8. _Spongodiscus florealis_, Haeckel.

_Spongospira florealis_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 120, Taf. vii. fig. 6.

Spongy disk lenticular, in the thicker central part with five to six spiral convolutions, in the outer peripheral zone irregularly spongy. No radial beams piercing the framework. Meshes three to four times as broad as the bars.

_Dimensions._--Diameter of the disk 0.26, of the meshes 0.006 to 0.008.

_Habitat._--Fossil in Tertiary rocks of Sicily (Grotte), Stöhr.

9. _Spongodiscus spiralis_, n. sp.

_Spongospira spiralis_, Haeckel, 1881, Prodromus.

Spongy disk on both sides plain, with twelve to sixteen spiral convolutions in the central part, with irregular, spongy framework in the outer part, pierced by numerous interrupted radial beams. Meshes five to six times as broad as the bars.

_Dimensions._--Diameter of the disk 0.2 to 0.3, of the meshes 0.01 to 0.012.

_Habitat._--Antarctic Ocean, Station 157, depth 1950 fathoms.

{579}Genus 254. _Spongophacus_,[293] Haeckel, 1881, Prodromus, p. 461.

_Definition._--#Spongodiscida# with a simple circular disk, without radial appendages, on the margin surrounded by a thin porous or solid equatorial girdle.

The genus _Spongophacus_, represented hitherto only by a single but interesting species, differs from _Spongodiscus_ by the peculiar girdle which surrounds the margin of the disk in the equatorial plane. It simulates the same formation as _Perichlamydium_ in the Porodiscida, and resembles also _Periphæna_, &c., in the Phacodiscida.

1. _Spongophacus periphæna_, n. sp.

Spongy disk lenticular, with an irregular, dense framework, in the centre darker than in the peripheral part. Margin of the disk very thin, surrounded by a broad, circular girdle, lying in the equatorial plane, about as broad as the half radius of the spongy disk. The inner part of the girdle is perforated by numerous irregular, small pores, which pass over gradually into the spongy meshes; the outer part is quite homogeneous, solid, transparent, with an extremely thin margin.

_Dimensions._--Diameter of the disk 0.2; breadth of the girdle 0.05.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

Subfamily 2. SPONGOTROCHIDA, Haeckel, 1881, Prodromus, p. 461.

_Definition._--#Spongodiscida# with a circular disk, the margin of which is armed with solid radial spines, situated in the equatorial plane (rarely also on both sides of the disk with radial spines).

Genus 255. _Spongolonche_,[294] Haeckel, 1881, Prodromus, p. 461.

_Definition._--#Spongodiscida# with two solid marginal spines, opposite in one equatorial diameter of the disk.

The genus _Spongolonche_ opens the series of the Spongotrochida, or of those Spongodiscida in which the margin of the disk is armed with solid radial spines, situated in the equatorial plane. _Spongolonche_ possesses only two such spines, opposite in one equatorial diameter of the disk; it corresponds therefore to _Stylocyclia_ among the Coccodiscida, to _Xiphodictya_ among the Porodiscida.

{580}1. _Spongolonche conostyla_, n. sp..

Spongy disk circular, with irregular framework, without concentric rings. Both opposite radial spines conical, about as long as the radius of the disk, and four times as long as broad at the base. Margin of the disk nearly smooth.

_Dimensions._--Diameter of the disk 0.16; length of the radial spines 0.18, basal thickness 0.045.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

2. _Spongolonche amphistyla_, n. sp.

Spongy disk circular, with four to six concentric rings in the inner part, with quite an irregular framework in the outer part. Both opposite radial spines cylindrical, twice to three times as long as the diameter of the disk, at the base about as broad as two meshes of the framework. Margin of the disk ciliated.

_Dimensions._--Diameter of the disk 0.2; length of the radial spines 0.4 to 0.6, basal thickness 0.01.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

Genus 256. _Spongotripus_,[295] Haeckel, 1881, Prodromus, p. 461.

_Definition._--#Spongodiscida# with three solid radial spines on the margin of the circular or triangular disk.

The genus _Spongotripus_ is characterised by three marginal spines, which are commonly regularly disposed, more rarely in a bilateral or an irregular manner. It corresponds to _Trigonocyclia_ among the Coccodiscida, to _Tripodictya_ among the Porodiscida.

Subgenus 1. _Spongotripodiscus_, Haeckel.

_Definition._--Radial spines of equal size and distance; triangle regular.

1. _Spongotripus regularis_, n. sp.

Spongy disk circular; three radial spines on its margin of equal size and equidistant, strong, conical, about as long as the diameter of the disk, and five times as long as broad at the base.

_Dimensions._--Diameter of the disk 0.15; length of the spines 0.16, basal breadth 0.03.

_Habitat._--Pacific, central area, Station 272, surface.

{581}2. _Spongotripus neumayri_, Haeckel.

_Spongechinus neumayri_, Dunikowski, 1882, Denskchr. d. k. Akad. d. Wiss. Wien, xlv. p. 28, Taf. v. fig. 59.

Spongy disk circular, nearly spherical; three radial spines on its margin of equal size and equidistant, pyramidal, nearly as long as the diameter of the disk, and three times as long as broad at the base.

_Dimensions._--Diameter of the disk 0.15 to 0.2; length of the spines 0.11, basal breadth 0.04.

_Habitat._--Fossil in the Jura of the Alps and in Tertiary rocks of Barbados.

3. _Spongotripus strepsiceros_, n. sp.

Spongy disk circular; three radial spines on its margin of equal size and equidistant, angular, twice as long as the diameter of the disk, spirally twisted like the horns of Antilope strepsiceros.

_Dimensions._--Diameter of the disk 0.15; length of the spines 0.3, basal breadth 0.02.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

Subgenus 2. _Spongotripodium_, Haeckel.

_Definition._--Radial spines of different size or at different distances; triangle either isosceles or irregular.

4. _Spongotripus ypsilon_, n. sp.

Spongy disk triangular, isosceles, with convex sides; three spines angular, of different size and at different distances; the odd spine straight and twice as long as the two paired spines, which are more approximated and curved concavely one to the other, like y.

_Dimensions._--Diameter of the disk 0.12; length of the odd spine 0.2, of the paired spines 0.1, basal breadth 0.04.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

5. _Spongotripus irregularis_, n. sp.

Spongy disk circular; three spines conical, irregularly curved, all three of different size, and at irregular distances; once to three times as long as the diameter of the disk; margin of the disk thorny.

_Dimensions._--Diameter of the disk 0.1; length of the spines 0.1 to 0.3, basal breadth 0.05.

_Habitat._--South Pacific, Station 300, depth 1375 fathoms.

{582}Genus 257. _Spongostaurus_,[296] Haeckel, 1881, Prodromus, p. 461.

_Definition._--#Spongodiscida# with four solid radial spines on the margin of the circular or square disk, commonly crossed in two equatorial diameters perpendicular one to another.

The genus _Staurodictya_ exhibits four marginal spines in cross form. Commonly the cross is regular and rectangular, the four spines being opposite in pairs in two perpendicular diameters; sometimes more or less irregular. The genus repeats _Staurodictya_ among the Porodiscida, _Staurocyclia_ among the Coccodiscida.

1. _Spongostaurus cruciatus_, n. sp.

Spongy disk circular; four radial spines on its margin opposite in two crossed equatorial diameters, perpendicular one to another, conical, about as long as the diameter of the disk.

_Dimensions._--Diameter of the disk 0.16; length of the spines 0.18, basal breadth 0.04.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

2. _Spongostaurus serratus_, n. sp.

Spongy disk circular; four crossed radial spines very large, twice to three times as long as the diameter of the central disk, serrated on both edges, with two rows of strong conical perpendicular teeth (similar to the saw of _Pristis antiquorum_).

_Dimensions._--Diameter of the disk 0.1; length of the spines 0.2 to 0.3, breadth 0.02.

_Habitat._--Indian Ocean, Madagascar, Rabbe, surface.

3. _Spongostaurus hastatus_, n. sp.

Spongy disk square, with concave sides; four crossed radial spines cylindrical, on the broader distal end spear-shaped or nearly lanceolate, one and a half times as long as the diameter of the disk.

_Dimensions._--Diameter of the disk 0.13; length of the spines 0.2, basal breadth 0.01, distal breadth 0.03.

_Habitat._--Tropical Atlantic, Station 347, surface.

4. _Spongostaurus quadratus_, n. sp.

Spongy disk square, with rectilinear sides; four crossed radial spines pyramidal, arising from the corners of the square, about as long as its half diagonal.

_Dimensions._--Diameter of the disk 0.16; length of the spines 0.08, basal breadth 0.02.

_Habitat._--Pacific, central area, Station 271, surface.

{583}Genus 258. _Stylotrochus_,[297] Haeckel, 1862, Monogr. d. Radiol., p. 463.

_Definition._--#Spongodiscida# with numerous solid radial spines on the margin of the disk (five to ten or more), all situated in the equatorial plane.

The genus _Stylotrochus_ comprises those Spongodiscida in which the margin of the circular disk bears numerous radial spines. All these spines lie in the same equatorial plane, whilst in the following genus they are disposed over the whole surface of the disk. _Stylotrochus_ corresponds to _Astrocyclia_ among the Coccodiscida, to _Stylodictya_ among the Porodiscida. The spongy framework of the disk is either quite irregular (_Stylotrochiscus_), or includes in the middle part some concentric circular rings (_Stylospongia_).

Subgenus 1. _Stylotrochiscus_, Haeckel.

_Definition._--Spongy framework of the whole disk irregular, without concentric circular rings or spiral convolutions.

1. _Stylotrochus arachnius_, Haeckel.

_Spongotrochus arachnius_, Haeckel, 1862, Monogr. d. Radiol., p. 464.

Spongy framework of the whole disk irregular. Eight to twelve marginal spines very long and thin, bristle-shaped, twice to four times as long as the diameter of the disk. (Very similar to the common _Stylodictya arachnia_, but without concentric circular rings and sieve-plates, with quite irregular network of fine bars.)

_Dimensions._--Diameter of the disk 0.12 to 0.15; length of the radial spines 0.2 to 0.6, basal breadth 0.001.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface; also fossil in Tertiary rocks of Barbados and the Mediterranean.

2. _Stylotrochus craticulatus_, Haeckel.

_Spongotrochus craticulatus_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 118, Taf. vi. fig. 12.

? _Spongodiscus aculeatus_, Ehrenberg, 1854, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 246.

Spongy framework of the whole disk irregular. Sixteen to twenty short marginal spines (twice to four times as long as the diameter of one mesh of the framework), free prolongations of internal radial beams which arise from the darker centre of the disk. (The interruption of the disk-margin on one point of its circumference, figured by Stöhr as osculum or "Mündungs-Oeffnung," is probably an accidental abnormality; I did not find it in other specimens.)

{584}_Dimensions._--Diameter of the disk 0.2 to 0.25; length of the radial spines 0.005 to 0.018, basal breadth 0.001 to 0.003.

_Habitat._--Pacific, central area, Stations 266 to 268, surface; fossil in Barbados and Sicily.

3. _Stylotrochus helianthus_, n. sp.

Spongy framework of the whole disk irregular. Thirty to fifty very large, conical radial spines, about as long as the diameter of the disk, and at the base two to four times as broad as one mesh of the framework (without internal prolongations).

_Dimensions._--Diameter of the disk 0.15 to 0.2; length of the radial spines 0.16 to 0.24, basal breadth 0.008 to 0.016.

_Habitat._--Pacific, central area, Station 272, surface.

4. _Stylotrochus rhabdostylus_, Haeckel.

_Spongosphæra rhabdostyla_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 256, Taf. xxvi. figs. 1, 2.

Spongy framework of the whole disk irregular. Four very large marginal primary spines crossed in two equatorial diameters, perpendicular one to another, and between them numerous (twelve to twenty or more) smaller secondary spines. The latter arise from the margin, whilst the former pierce the disk and are nearly united in its centre. All the spines are cylindrical, the smaller as broad as one mesh, the larger three to six times as broad.

_Dimensions._--Diameter of the disk 0.2; length of the four main spines 0.15 to 0.3, breadth 0.01 to 0.02; length of the accessory spines 0.05 to 0.1, breadth 0.005.

_Habitat._--Fossil in the rocks of Barbados.

5. _Stylotrochus heteracanthus_, Haeckel.

_Spongotrochus heteracanthus_, Haeckel, 1862, Monogr. d. Radiol., p. 464.

Spongy framework of the whole disk irregular. Ten very long needle-shaped marginal spines (symmetrically distributed), and between them numerous very fine, shorter, accessory, bristle-shaped spines.

_Dimensions._--Diameter of the disk 0.16; length of the main spines 0.16, basal breadth 0.002; length of the secondary spines 0.03.

_Habitat._--Mediterranean (Messina), surface.

Subgenus 2. _Stylospongia_, Haeckel, 1862, Monogr. d. Radiol., p. 473.

_Definition._--Spongy framework of the disk in the inner part with concentric rings or spiral convolutions, in the outer part quite irregular.

{585}6. _Stylotrochus huxleyi_, Haeckel.

_Stylospongia huxleyi_, Haeckel, 1862, Monogr. d. Radiol., p. 473, Taf. xxviii. fig. 7.

Spongy framework of the disk in the inner part with five concentric rings, in the outer part quite irregular. Ten marginal spines, conical at the base, about as long as the radius of the disk, without inner piercing prolongations.

_Dimensions._--Diameter of the disk 0.12; length of the radial spines 0.06, basal breadth 0.003.

_Habitat._--Mediterranean (Messina), Haeckel.

7. _Stylotrochus geddesii_, n. sp. (Pl. 41, fig. 11).

_Stylospongidium geddesii_, Haeckel, 1881, Atlas (pl. xli. fig. 11).

Spongy framework of the disk in the inner part with four to eight concentric rings (or partially spiral convolutions), in the outer part quite irregular. Thirty to fifty pyramidal marginal spines of variable size, one-fourth to one-half as long as the radius of the disk, outer prolongations of inner piercing radial beams, which arise from various concentric rings. I call this interesting species, which is intermediate between _Stylodictya_ and _Stylotrochus_, in honour of the morphologist Mr. Patrick Geddes of Edinburgh.

_Dimensions._--Diameter of the disk 0.15 to 0.25; length of the radial spines 0.03 to 0.06, basal breadth 0.004 to 0.01.

_Habitat._--Pacific, central area, Stations 270 to 274, in 2350 to 2925 fathoms.

Genus 259. _Spongotrochus_,[298] Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 844.

_Definition._--#Spongodiscida# with numerous solid radial spines (five to ten or more), which are scattered over the whole surface and the margin of the disk, or regularly disposed on both sides of it.

The genus _Spongotrochus_ differs from the foregoing and nearly allied genus by the distribution of the numerous radial spines. These are not confined to the margin of the disk, but also scattered on its whole surface, and sometimes symmetrically disposed on both its sides in a regular manner. Also in this genus the spongy framework is sometimes quite irregular (_Spongotrochiscus_), at other times in the middle part with enclosed concentric rings (_Stylospongidium_).

Subgenus 1. _Spongotrochiscus_, Haeckel, 1862, Monogr. d. Radiol., p. 463.

_Definition._--Spongy framework of the whole disk irregular, without concentric rings or spiral convolutions.

{586}1. _Spongotrochus brevispinus_, Haeckel.

_Spongotrochus brevispinus_, Haeckel, 1862, Monogr. d. Radiol., p. 462, Taf. xxvii. figs. 4, 5.

Spongy framework of the whole disk irregular, everywhere equal. The whole surface of the disk covered with numerous short, needle-shaped, radial spines, about as long as the thickness of the disk, which is one-fifth of its diameter.

_Dimensions._--Diameter of the disk 0.18; length of the radial spines 0.03 to 0.04, basal breadth 0.002.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

2. _Spongotrochus multispinus_, n. sp.

Spongy framework of the whole disk irregular, in the centre darker. The whole surface of the disk covered with numerous conical radial spines, about as long as the radius of the disk.

_Dimensions._--Diameter of the disk 0.22; length of the radial spines 0.1, basal breadth 0.008.

_Habitat._--Pacific, central area, Stations 271 to 274, surface.

3. _Spongotrochus longispinus_, Haeckel.

_Spongotrochus longispinus_, Haeckel, 1862, Monogr. d. Radiol., p. 463, Taf xxvii. figs. 2, 3.

Spongy framework of the whole disk irregular, everywhere equal. Surface thorny. Twenty long, needle-shaped, radial spines, about as long as the diameter of the disk, symmetrically distributed in pairs on both flat sides of the disk, so that the opposite pairs lie in five equidistant, meridian planes (compare the figures).

_Dimensions._--Diameter of the disk 0.2; length of the twenty radial spines 0.2, basal breadth 0.001.

_Habitat._--Mediterranean (Messina), surface.

Subgenus 2. _Stylospongidium_, Haeckel, 1881, Prodromus, p. 460.

_Definition._--Spongy framework of the disk in the inner part with concentric rings or spiral convolutions, in the outer part quite irregular.

4. _Spongotrochus scutella_, n. sp.

_Spongotrochus ehrenbergii_, Bütschli, 1882, L. N. 41, Taf. xxvi. figs. 1_a_, 1_b_.

Spongy framework of the disk in the inner part with four to six concentric rings, in the outer part quite irregular. The whole surface of the disk covered with bristle-shaped radial spines, about half as long as the radius of the disk.

_Dimensions._--Diameter of the disk 0.24; length of the radial spines 0.06, basal breadth 0.02.

_Habitat._--Antarctic Ocean, Station 157, depth 1950 fathoms.

{587}5. _Spongotrochus parma_, n. sp.

Spongy framework of the disk in the inner part with five to eight spiral convolutions (or partly concentric rings), in the outer part quite irregular. Thirty to forty long, bristle-shaped, radial spines, about as long as the diameter of the disk, disposed on both flat sides of the disk, but not on the margin.

_Dimensions._--Diameter of the disk 0.16; length of the radial spines 0.18, basal breadth 0.003.

_Habitat._--South Atlantic, Station 325, surface.

Subfamily 3. SPONGOBRACHIDA, Haeckel, 1881, Prodromus, p. 461.

_Definition._--#Spongodiscida# with two or more (commonly three or four) spongy radial arms on the margin of the disk, situated in its equatorial plane (with or without a connecting patagium between the arms).

Genus 260. _Spongolena_,[299] n. gen.

_Definition._--#Spongodiscida# with two opposite spongy arms on the margin of the disk, without a connecting patagium.

The genus _Spongolena_ opens the series of the Spongobrachida, or of the Spongodiscida provided with radial spongy arms on the margin of the disk. _Spongolena_ is the most simple form of this subfamily, and bears only two simple opposite arms, without a connecting patagium. It corresponds to _Amphibrachium_ (Porodiscida) and to _Diplactura_ (Coccodiscida). Also there is no patagium. _Spongolena_ may easily be confounded with _Spongurus_ (compare my Prodromus, 1881, p. 461); but in the true _Spongurus_ (an ellipsoid) the transverse section is circular, in _Spongolena_ elliptical.

1. _Spongolena rhopalura_, n. sp.

Arms club-shaped, three times as long as broad, at the rounded distal end twice as broad as at the base, and twice as long as the diameter of the circular central disk. Surface nearly smooth.

_Dimensions._--Radius of the arms (or the distance from the centre to the distal arm-end) 0.16, distal breadth 0.05, basal breadth 0.03.

_Habitat._--Pacific, central area, Station 273, depth 2350 fathoms.

2. _Spongolena spongura_, n. sp.

Arms nearly cylindrical, twice as long as broad, and a little longer than the diameter of the elliptical central disk. Surface thorny, some longer bristle-shaped spines on the distal end of the {588}arms. (Very similar to the ellipsoid _Spongurus cylindricus_, Monogr. d. Radiol., p. 465, Taf. xxvii. fig. 1, but differs in the compressed lenticular (not ellipsoidal) form of the central disk; the transverse section of the arm is elliptical, not circular.)

_Dimensions._--Radius of the arms 0.1, breadth 0.04.

_Habitat._--Pacific, central area, Station 270, depth 2925 fathoms.

3. _Spongolena cypselura_, n. sp.

Arms nearly triangular, not longer than broad, about half as large as the elliptical central disk, at the broader distal end with two very large, widely divergent lateral spines, and between them several smaller, like the tail of a swallow. Surface thorny.

_Dimensions._--Radius of the arms 0.2, distal breadth (without spines) 0.15, basal breadth 0.07.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

Genus 261. _Spongobrachium_,[300] Haeckel, 1881, Prodromus, p. 461.

_Definition._--#Spongodiscida# with two opposite spongy arms on the margin of the disk, connected by a spongy patagium of different texture.

The genus _Spongobrachium_ differs from the foregoing only in the loose spongy patagium, which envelops both opposite spongy arms. It corresponds to _Amphymenium_ among the Porodiscida and to _Amphiactura_ among the Coccodiscida.

1. _Spongobrachium ellipticum_, Haeckel.

_Spongocyclia elliptica_, Haeckel, 1862, Monogr. d. Radiol., p. 470, Taf. xxviii. fig. 2.

_Spongodiscus ellipticus_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 844.

Arms nearly square, scarcely as long and broad as the radius of the circular central disk, at the broader distal end truncated. Patagium complete, enveloping the whole disk with the arms, and forming a larger elliptical disk of looser framework. (In my Monograph, 1862, _loc. cit._, I had not distinguished the opposite darker arms, opposite in the longer axis of the elliptical disk, from the enveloping looser framework of the patagium. In larger specimens of the Challenger collection this distinction is very evident.)

_Dimensions._--Radius of the arms 0.12, breadth 0.05; major axis of the elliptical patagium 0.24, minor 0.16.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

2. _Spongobrachium lanceolatum_, n. sp.

Arms club-shaped, twice as long as broad, at the distal end pointed, five times as long as the radius of the circular central disk. Patagium complete, enveloping the whole disk with the arms, {589}and forming a larger lanceolate disk of looser framework. (Similar in form to _Amphymenium pupula_, Pl. 44, fig. 8, but with an irregular spongy framework and pointed ends.)

_Dimensions._--Radius of the arms 0.16, breadth 0.05; major axis of the lanceolate patagium 0.32, minor axis 0.12.

_Habitat._--Pacific, central area, Station 270, surface.

Genus 262. _Rhopalodictyum_,[301] Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 830.

_Definition._--#Spongodiscida# with three spongy arms on the margin of the circular or triangular disk, without a connecting patagium.

The genus _Rhopalodictyum_ comprises those very common forms of Spongodiscida in which the margin of the disk is provided with three simple, free, spongy arms. It corresponds to _Dictyastrum_ and _Rhopalastrum_ among the Porodiscida, to _Trigonactura_ among the Coccodiscida. The typical species of this genus is _Rhopalodictyum abyssorum_ of Ehrenberg, the only species figured by him. His diagnosis of the genus was very insufficient, and agreed with that of his _Dictyastrum_ (compare above the improved diagnosis of this genus, p. 526, and my Monograph, p. 466).

Subgenus 1. _Rhopalodictya_, Haeckel.

_Definition._--Triangular shell regular, with three arms of equal size and equidistant.

1. _Rhopalodictyum abyssorum_, Ehrenberg.

_Rhopalodictyum abyssorum_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 299, Taf. viii. fig. 17.

Arms of equal size and equidistant, club-shaped, about as long as the diameter of the triangular central disk, and a little longer than the breadth of the pear-shaped rounded distal end. Surface rough.

_Dimensions._--Radius of the arms 0.11, basal breadth 0.03, distal breadth 0.06.

_Habitat._--Cosmopolitan; Atlantic, Indian, Pacific; tropical zone, surface.

2. _Rhopalodictyum truncatum_, Ehrenberg.

_Rhopalodictyum truncatum_, Ehrenberg, 1861, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 301.

? _Dictyastrum angulatum_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 289, Taf. viii. fig. 18.

Arms of equal size and equidistant, nearly square, with straight edges, towards the truncated end a little broader, about of the same diameter as the central triangular disk. This species is indicated {590}by Ehrenberg only by the short diagnosis, "Radiis stellæ tribus apice truncatis." It is probably identical with his figure of _Dictyastrum angulatum_ (_loc. cit._). This latter name I have retained for the similar Porodiscid (above, p. 526), mainly because the genera _Dictyastrum_ and _Rhopalodictyum_, according to the insufficient diagnosis of Ehrenberg, seem to be identical. (Compare my Monograph, 1862, p. 466.)

_Dimensions._--Radius of each arm 0.13, basal breadth 0.09, distal breadth 0.1.

_Habitat._--Tropical Pacific, Philippine Sea, Station 200, depth 250 fathoms; Atlantic (Mexican Gulf Stream).

3. _Rhopalodictyum subacutum_, Ehrenberg.

_Rhopalodictyum subacutum_, Ehrenberg, 1861, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 301.

Arms of equal size and equidistant, club-shaped, three times as long as the diameter of the central disk, which equals the breadth of the thickened distal end; the latter is armed with a strong pyramidal terminal spine. (The diagnosis of Ehrenberg is "Radiis stellæ tribus, apice cuneatis subacutis.")

_Dimensions._--Radius of the arms 0.2, basal breadth 0.04, distal breadth 0.07.

_Habitat._--North Atlantic, surface and various depths; Greenland; Mexican Gulf Stream; Færöe Channel (John Murray).

4. _Rhopalodictyum bifidum_, n. sp.

Arms of equal size and equidistant, in the distal half forked, twice as long as the diameter of the central disk; both fork branches half as broad as the simple basal part, truncated at the distal end.

_Dimensions._--Radius of the arms 0.16, basal breadth 0.08, distal breadth 0.04.

_Habitat._--North Pacific, Station 237, surface.

Subgenus 2. _Triactinosphæra_, Dunikowski, 1882, Denkschr. d. k. Akad. d. Wiss. Wien, vol. 45, ii. p. 192.

_Definition._--Triangular shell bilateral or irregular, with three arms of different size or distance.

5. _Rhopalodictyum zittelii_, Haeckel.

_Triactinosphæra zittelii_, Dunikowski, 1882, Denkschr. d. k. Akad. d. Wiss, Wien, vol. 45, ii. p. 192.

Arms of different size and at unequal distances, one odd arm being a little shorter than the two paired arms; the odd angle between the latter is larger than the paired angles between them and the {591}former. Arms club-shaped, their basal semi-cylindrical, half as broad as the spherical distal half, which bears a strong, conical, terminal spine. The discoverer of this remarkable, very old, Liassic species, Dunikowski, supposes that it is not a true Discoid, from the absence of a central disk; in my opinion the central disk (nearly spherical) has the same relation to the arms as in many other #Discoidea#, their equatorial plane is the same.

_Dimensions._--Radius of the odd arm 0.18, of the paired arms 0.24; basal breadth 0.08, distal breadth 0.16.

_Habitat._--Fossil in the Alpine Lias, Schafberg, near Salzburg, Dunikowski.

6. _Rhopalodictyum elongatum_, n. sp.

Arms of different size and at unequal distances, one odd arm being twice as long as both paired arms; the odd angle between the latter much larger than both equal paired angles. Arms nearly cylindrical, little flattened, three to six times as long as broad, with rounded blunt distal end.

_Dimensions._--Radius of the arms 0.15 to 0.3, breadth 0.05.

_Habitat._--Pacific, central area, Station 274, surface.

7. _Rhopalodictyum curvatum_, n. sp.

Arms of different size and at unequal distances, irregular, more or less curved, nearly cylindrical, five to ten times as long as broad, with rounded blunt distal end. (There were observed only two specimens of this remarkable irregular species; in one specimen all three arms were simple, in the other one odd arm forked. The length of the arms and the size of the angles between them seems to be very different and variable.)

_Dimensions._--Radius of the arms 0.3 to 0.6 to 1.15, breadth 0.06 to 0.12.

_Habitat._--Pacific, central area, Station 271, surface.

Genus 263. _Dictyocoryne_,[302] Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 830.

_Definition._--#Spongodiscida# with three spongy arms on the margin of the circular or triangular disk, connected by a spongy patagium of different texture.

The genus _Dictyocoryne_ differs from the foregoing _Rhopalodictyum_ only in the patagium, connecting the three spongy arms, and bears to it the same relation as in the Porodiscida _Euchitonia_ does to _Rhopalastrum_. The typical species of this genus is _Dictyocoryne profunda_, the only species figured by Ehrenberg. After his {592}insufficient diagnosis _Dictyocoryne_ was identical with his _Spongaster_ (compare my Monograph, p. 467); but as the type of this latter genus (_Spongaster tetras_) figured by him, 1872, had four crossed arms, we retain this genus here separate.

Subgenus 1. _Dictyocorynula_, Haeckel.

_Definition._--Triangular shell regular, with three arms of equal size and equal distance.

1. _Dictyocoryne profunda_, Ehrenberg.

_Dictyocoryne profunda_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 307, Taf. vii. fig. 23.

Arms of equal size and equidistant, club-shaped, in the outer circular half three times as broad as in the inner cylindrical half, and much larger than the small triangular central disk. Patagium complete, forming an equilateral triangle with rounded corners.

_Dimensions._--Radius of the arms 0.14, basal breadth 0.025, distal breadth 0.07.

_Habitat._--Pacific, Philippine Sea, depth 3300 fathoms, Ehrenberg; Station 198, depth 2150 fathoms; Station 274, depth 2750 fathoms.

2. _Dictyocoryne tetradiscus_, n. sp.

Arms of equal size and equidistant, club-shaped, their outer circular half is quite as large as the circular central disk, and is connected with it by the thin cylindrical inner half, which is scarcely one-fourth as broad. Patagium complete, forming an equilateral triangle with rounded corners and convex sides.

_Dimensions._--Radius of the arms 0.16, basal breadth 0.02, distal breadth 0.08.

_Habitat._--Pacific, central area, Stations 271 to 274, in 2350 to 2750 fathoms.

3. _Dictyocoryne euchitonia_, Haeckel.

_Dictyocoryne euchitonia_, Haeckel, 1862, Monogr. d. Radiol., p. 468.

Arms of equal size and equidistant, lanceolate, twice as long as broad in the distal part, and three times as long as the small circular central disk. Patagium complete, forming an equilateral triangle with pointed corners. (Very similar to _Euchitonia köllikeri_, Monograph, 1862, p. 511, Taf. xxxi. fig. 6, but quite spongy, not concentric.)

_Dimensions._--Radius of the arms 0.15, basal breadth 0.03, distal breadth 0.06.

_Habitat._--Mediterranean (Messina), Haeckel.

{593}4. _Dictyocoryne trigona_, n. sp.

Arms of equal size and equidistant, lanceolate, three times as long as broad in the middle part, and as the diameter of the triangular central disk; their distal end armed with a strong conical radial spine. Patagium complete, forming an equilateral triangle with pointed corners.

_Dimensions._--Radius of the arms 0.2, basal breadth 0.02, distal breadth 0.06.

_Habitat._--North Atlantic, Canary Islands, surface.

Subgenus 2. _Dictyocorynium_, Haeckel.

_Definition._--Triangular shell bilateral or irregular, with three arms of different sizes or at different distances.

5. _Dictyocoryne charybdaea_, Haeckel.

_Spongocyclia charybdaea_, Haeckel, 1862, Monogr. d. Radiol., p. 472, Taf. xxviii. figs. 5, 6.

_Spongodiscus charybdaeus_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 844.

Arms at different distances, nearly equilateral triangular, scarcely half as long as the radius of the large circular central disk. Both paired arms touching at their bases, separated by a great distance from the opposite odd arm. Patagium complete, nearly pentagonal. (The illustration in my Monograph, in the coloured plate xxviii., is better than my description, as I had not exactly separated the arms from the patagium.)

_Dimensions._--Radius of the arms 0.18, basal breadth 0.08.

_Habitat._--Mediterranean (Messina), surface.

6. _Dictyocoryne pentagona_, Stöhr.

_Dictyocoryne pentagona_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 118, Taf. vii. fig. 2.

Arms at different distances, club-shaped, little longer than broad at their rounded distal end. Both paired arms smaller and more approximate than the opposite odd arm. Patagium complete, very large, enveloping the whole shell, and forming a pentagon with rectilinear base and transverse constriction, and with five rounded corners.

_Dimensions._--Radius of the arms 0.1 to 0.15, middle breadth 0.04.

_Habitat._--Fossil in the Tertiary rocks of Sicily, Grotte, Stöhr.

7. _Dictyocoryne agrigentina_, Stöhr.

_Dictyocoryne agrigentina_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 118, Taf. vii. fig. 1.

Arms at different distances, club-shaped, about twice as long as broad, and smaller than the large triangular central disk. Both paired arms smaller and more approximate than the opposite odd {594}arm. Patagium incomplete, enveloping only the basal half of the arms as a circular spongy disk of loose framework.

_Dimensions._--Radius of the arms 0.18, basal breadth 0.05, distal breadth 0.08.

_Habitat._--Fossil in the Tertiary rocks of Sicily, Grotte, Stöhr.

8. _Dictyocoryne echinata_, n. sp.

Arms unequal and at different distances, club-shaped, in the distal half twice as broad as in the basal half, three times as long as the small triangular central disk, at their distal end armed with one larger and several smaller conical spines. Both paired arms with touching bases, and only half as large as the doubly remote odd arm. Patagium incomplete, enveloping only the basal half of the arms, and forming a circular disk of looser framework. Surface thorny.

_Dimensions._--Radius of the arms 0.15 to 0.2, basal breadth 0.03, distal breadth 0.06.

_Habitat._--South Atlantic, Station 325, surface.

Genus 264. _Spongasteriscus_,[303] Haeckel, 1862, Monogr. d. Radiol., p. 474 (_sensu restricto_).

_Definition._--SPONGODISCIDA with four spongy arms on the margin of the circular or quadrangular disk, crossed in two equatorial diameters, without a connecting patagium.

The genus _Spongasteriscus_ (in the restricted definition here stated) exhibits on the margin of the disk four spongy arms, which form either a regular or a bilateral cross. It corresponds to _Stauralastrum_ and _Myelastrum_ among the Porodiscida, to _Astractura_ among the Coccodiscida.

Subgenus 1. _Spongasteriscinus_, Haeckel.

_Definition._--Cross formed by the four arms regular, rectangular, with equal-sized and equidistant arms.

1. _Spongasteriscus ovatus_, n. sp.

Arms at equal distances, forming a regular, rectangular cross, egg-shaped, with a broader rounded distal end, one and a third times as long as broad, and three times as long as the radius of the central disk; in the latter three to four concentric rings.

_Dimensions._--Radius of the arms 0.1, greatest breadth 0.06.

_Habitat._--Western Tropical Pacific, Station 225.

{595}2. _Spongasteriscus clavatus_, n. sp.

Arms at equal distances, forming a regular, rectangular cross, club-shaped, about as long as the diameter of the central disk, and at their rounded distal end one and a third times as long as broad, at their narrow base only one third as broad. In the centre five to six concentric rings.

_Dimensions._--Radius of the arms 0.13, distal breadth 0.06, basal breadth 0.02.

_Habitat._--Pacific, central area. Station 271, surface.

3. _Spongasteriscus mucronatus_, n. sp.

Arms at equal distances, forming a regular, rectangular cross, club-shaped, three times as long as the radius of the central disk, in the distal half nearly circular, three to four times as broad as at the narrow base. The rounded distal end armed with a strong pyramidal spine. In the centre no concentric rings. (Similar to _Stauralastrum rhopalophorum_, Pl. 45, fig. 1, but quite spongy.)

_Dimensions._--Radius of the arms 0.12, basal breadth 0.03, distal breadth 0.02.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

4. _Spongasteriscus furcatus_, n. sp.

Arms at equal distances, forming a regular, rectangular cross, in the distal third forked; both fork branches half as long as the basal undivided part of the arm, which is twice as long as broad. Distal ends of the eight branches blunt, rounded. In the central disk no concentric rings.

_Dimensions._--Radius of the arms 0.12, basal breadth 0.03; distal breadth of the branches 0.02.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

5. _Spongasteriscus armatus_, n. sp.

Arms at equal distances, forming a rectangular, regular cross, in the distal half forked; both fork branches of the same length as the basal undivided part of the arm, which is nearly square. Distal ends of the eight branches armed with a strong pyramidal spine. In the central disk no concentric rings. (Similar to _Dicranastrum cornutum_, Pl. 45, fig. 2, but quite spongy.)

_Dimensions._--Radius of the arms 0.18, basal breadth 0.03, distal breadth 0.015.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

Subgenus 2. _Spongasterisculus_, Haeckel.

_Definition._--Cross formed by the four arms, bilateral or irregular, with the arms at different distances.

{596}6. _Spongasteriscus quadricornis_, Haeckel.

_Spongasteriscus quadricornis_, Haeckel, 1862, Monogr. d. Radiol., p. 474, Taf. xxviii. figs. 8-10.

_Spongodiscus quadricornis_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 844.

Arms at different distances, forming a bilateral or irregular cross, grouped in two opposite pairs; their form equilateral triangular; their length smaller than the radius of the large circular central disk, which exhibits in the interior eight to sixteen concentric rings.

_Dimensions._--Radius of the arms 0.2, of the central disk 0.13; basal breadth of the arms 0.08.

_Habitat._--Mediterranean (Messina), Haeckel, surface.

7. _Spongasteriscus tetraceros_, Haeckel.

_Spongasteriscus tetraceros_, Haeckel, 1862, Monogr. d. Radiol., p. 475.

Arms at different distances, forming a bilateral or irregular cross, grouped in two opposite pairs; their form isosceles triangular; their length larger than the radius of the large elliptical central disk, which exhibits in the interior six to twelve concentric rings.

_Dimensions._--Radius of the arms 0.16, of the central disk 0.1; basal breadth of the arms 0.06.

_Habitat._--Mediterranean (Messina), North Atlantic (Canary Islands), surface.

8. _Spongasteriscus myelastrum_, n. sp.

Arms at different distances, forming a bilateral or irregular cross, grouped in two opposite pairs; the arms of one pair broader and shorter than the arms of the other pair. Each arm in its basal half simple, in the distal half forked; ends of the fork branches blunt. In the central disk no concentric rings. (Similar to _Myelastrum octocorne_, Pl. 47, fig. 12, but quite spongy.)

_Dimensions._--Radius of the arms 0.2, basal breadth 0.05, distal breadth 0.02.

_Habitat._--North Pacific, Station 236, surface.

Genus 265. _Spongaster_,[304] Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 833.

_Definition._--#Spongodiscida# with four spongy arms on the margin of the circular or quadrangular disk, connected by a spongy patagium of different texture.

The genus _Spongaster_ differs from the foregoing _Spongasteriscus_ in the patagium connecting the spongy arms, and bears therefore to it the same relation as, in the Porodiscida, _Histiastrum_ does to _Stauralastrum_, or, in the Coccodiscida, _Stauractura_ does to _Astractura_. The typical specimen, figured by Ehrenberg (_Spongaster tetras_), exhibits a regular, square disk, as also some other species. In a certain number of other species (formerly united by me with _Spongocyclia_) the quadrangular disk is bilateral.

{597}Subgenus 1. _Spongastrella_, Haeckel.

_Definition._--Cross formed by the four arms regular, rectangular, with the arms of equal size and equidistant.

1. _Spongaster tetras_, Ehrenberg.

_Spongaster tetras_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 299, Taf. vi. (iii.) fig. 8.

_Dictyocoryne tetras_, Haeckel, 1862, Monogr. d. Radiol., p. 469.

Arms at equal distances, forming a rectangular, regular Myelastrum, papiliocross, club-shaped, about twice as long as the diameter of the square central disk and eight times as long as broad at their base. Distal ends rounded, perfectly enclosed by the complete patagium, which forms a regular square, with slightly concave sides.

_Dimensions._--Radius of the arms 0.12, distal breadth 0.03, basal breadth 0.015; length of the square side 0.2.

_Habitat._--Cosmopolitan; Atlantic, Indian, Pacific, surface and in various depths.

2. _Spongaster quadratus_, n. sp.

Arms at equal distances, forming a regular, rectangular cross, club-shaped, about four times as long as the diameter of the central circular disk, and five times as long as broad at the base. Basal third of the arms square; distal two thirds triangular, three times as broad, with a truncated distal end. Patagium complete, perfectly enveloping the arms, and bordered by an elegant, radially striated, broad edge, forming a regular square. (Similar to _Histiastrum quadratum_, Pl. 46, fig. 4, but quite spongy.)

_Dimensions._--Radius of the arms 0.15, distal breadth 0.06, basal breadth 0.02; length of the square side 0.25.

_Habitat._--Pacific, central area, Stations 270 to 274, depths 2350 to 2925 fathoms.

3. _Spongaster cruciatus_, n. sp.

Arms at equal distances, forming a rectangular, regular cross, lanceolate, three times as long as broad and as the diameter of the central circular disk. Ends of the arms provided with a short conical spine. Patagium incomplete, enveloping only the basal half of the arms, forming a regular square with concave sides.

_Dimensions._--Radius of the arms 0.18, greatest breadth 0.05; length of the square side 0.2.

_Habitat._--South Pacific, Station 288, surface.

{598}4. _Spongaster pentacyclus_, n. sp.

Arms at equal distances, forming a rectangular, regular cross, of the same size and form as the circular central disk, so that the dark interior part of the shell is composed of five equal circular disks, situated in a quincuncial manner. The clearer complete patagium, enveloping the whole cross perfectly, forms a regular square with rounded edges.

_Dimensions._--Radius of the arms 0.2; diameter of each of the five circular disks 0.01; length of the square side 0.35.

_Habitat._--West Indies, Cuba, surface (Thomson).

Subgenus 2. _Spongastromma_, Haeckel.

_Definition._--Cross formed by the four arms bilateral or irregular, with the arms at different distances.

5. _Spongaster orthogonus_, Haeckel.

_Spongocyclia orthogona_, Haeckel, 1862, Monogr. d. Radiol., p. 471, Taf. xxviii. fig. 3.

_Spongodiscus orthogonus_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 844.

Arms at different distances, forming a bilateral cross, grouped in two opposite pairs of equal size and similar form. Arms club-shaped, about as long as the diameter of the central circular disk, enveloped perfectly by the complete patagium, which forms a regular rectangle, the longer side of which is one and a half times as long as the shorter side. (The arms in my figure are not distinctly enough marked.)

_Dimensions._--Radius of the arms 0.08, breadth 0.02; length of the larger side of the rectangle 0.15, of the smaller 0.1.

_Habitat._--Mediterranean (Messina), surface.

6. _Spongaster scyllaeus_, Haeckel.

_Spongocyclia scyllaea_, Haeckel, 1862, Monogr. d. Radiol., p. 471, Taf. xxviii. fig. 4.

_Spongodiscus scyllaeus_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 844.

Arms at different distances, forming a bilateral cross, grouped in two opposite pairs of different size and form, one pair smaller and less divergent than the other. Arms club-shaped, little longer than the radius of the central circular disk, enveloped perfectly by the complete patagium, which forms a trapezium; the convergent longer sides of the latter are one and a half times as long as the larger, and twice as long as the smaller parallel side. (The arms are in my figure, _loc. cit._, not distinctly enough marked.)

_Dimensions._--Radius of the arms 0.12 to 0.14, breadth 0.02; length of both convergent sides 0.24, of the larger parallel side 0.18, of the smaller 0.12.

_Habitat._--Pacific, central area, Station 272, surface; Mediterranean (Messina).

{599}----

Suborder VI. LARCOIDEA, Haeckel, 1883 (Pls. 9, 10, 49, 50).

_Definition_.--SPUMELLARIA with lentelliptical central capsule (rarely somewhat modified or allomorphic), with a lentelliptical fenestrated siliceous shell (often modified or allomorphic, and sometimes quite irregular). Growth different in the three unequal dimensive axes, perpendicular one to another. The typical Lentellipsis is characterised by three elliptical dimensive planes of different sizes, perpendicular one to another.

The section #Larcoidea#, the fourth and last of the #Sphærellaria#, comprises all those forms of this group in which the fenestrated shell originally is lentelliptical, characterised by different growth in three different axes, perpendicular one to another, all three equal on both poles. The geometrical fundamental form of the shell is therefore a lentellipsis or a triaxial ellipsoid; and this typical form is preserved completely in the majority of #Larcoidea# in the pure geometrical form of the central capsule.

The three dimensive axes, which determine the typical form of #Larcoidea#, are commonly differentiated in such a way, that the first, the longitudinal or principal axis, is the longest; both its poles, oral and aboral (or anterior and posterior) are equal. The second, the lateral or transverse axis, is commonly less than the first, greater than the third axis; both its poles are the equal lateral poles (right and left not differentiated). The third dimensive axis, the equatorial or sagittal axis, is commonly the shortest; both its equal poles are the sagittal poles (dorsal and ventral poles not different). The relative size of the three dimensive axes in the human body exhibits similar relations.

The three dimensive planes of the #Larcoidea#, the sagittal, lateral, and transverse planes, are elliptical, all three of different sizes. The first plane, the median or sagittal plane, is commonly as regards size between the two others; its major axis is the principal, its minor the sagittal axis; it separates the right half of the body from the left. The second plane or lateral plane, is commonly larger than the two others; its major axis the principal, its minor the transverse axis; it separates the dorsal half of the body from the ventral. The third plane, the equatorial or zonal plane, is commonly less than the two others; its major axis the lateral, its minor the sagittal axis; it separates the two principal halves of the body, the oral and aboral halves.

In my Monograph (1862) only very few forms of #Larcoidea# are described, _Tetrapyle_ and _Lithelius_ (the latter representing a peculiar family, Lithelida). In my Prodromus (1881, pp. 463, 464) I disposed all observed forms of #Larcoidea# in two different families, the Pylonida and Lithelida. The rich materials of the Challenger collection have since offered an astonishing number of new and interesting forms of this section, so that I can enumerate here fifty-one genera and two hundred and sixty-five species. I dispose them here in four subsections and nine families. Three of these have regular lentelliptical shells, which are not articulate, and {600}without annular constrictions (Larcarida, Larnacida, Pylonida); these form the subsection Pylolarcida. Two other families (Tholonida and Zonarida) are distinguished by annular constrictions, which divide the regular lentelliptical shell into a number of dome-shaped chambers or cupolas; we call these Thololarcida. A third group, Spirolarcida, comprises the #Larcoidea# with spiral growth; the two families of Lithelida and Streblemida. Finally a fourth group the Sorolarcida is formed by the #Larcoidea# with irregular shells, also two families, the Phorticida and Soreumida.

The first family of #Larcoidea#, the Larcarida, contains the most simple forms, beginning with _Cenolarcus_, a quite simple lentelliptical latticed shell. In _Coccolarcus_ we find already two concentric shells, connected by radial beams, an inner medullary and an outer cortical shell. In _Spongolarcus_ the lentelliptical shell becomes spongy.

The second family, Larnacida, is very similar to the Larcarida, and seems to diverge only by the different mode of connection between the two concentric lentelliptical shells. But in truth this slight difference is of great morphological importance, as it depends on a quite different and peculiar mode of growth. In the foregoing Larcarida (_Coccolarcus_, &c.), the concentric shells originate in the same manner as in the concentric #Prunoidea# and #Sphæroidea#, by radial beams, which arise from the surface of the inner (medullary) shell and become connected by a network to form the outer (cortical) shell. Here, in the Larnacida, a quite similar shell originates in a quite different way, first arrived at in the Pylonida (_Trizonium_). Both concentric shells become here connected by peculiar lattice girdles, which are developed in the perimeter of the three elliptical dimensive planes. Firstly, on both sides of a simple, spherical, or lentelliptical central chamber, arise two lateral wings (on the poles of the transverse axis), and build around the former a transverse girdle. This is crossed by a larger lateral girdle, the minor axis of which is the major of the former, and perpendicular to both girdles is yet developed a third, the sagittal girdle. If the open fissures or "gates" between these three girdles become closed by network, we obtain _Larnacilla_, the probable ancestral form of all Larnacida.

Whilst in _Larnacilla_ and _Larnacidium_ this typical trizonal lentelliptical shell constitutes by itself alone the whole skeleton, in the other Larnacida it becomes overgrown by outer envelops, and so becomes enclosed in the interior of the central capsule as a "_Larnacilla_-shaped medullary shell." If the enclosing external envelops be simply latticed, we get the subfamily Larnacalpida; if they be spongy, we get the Larnacospongida.

The third family, Pylonida, is the most important of all #Larcoidea#, as not only the largest and most interesting number of species belong to it, but also many other genera (far the greater part of all #Larcoidea#) may be derived from it. The peculiar character of the Pylonida is determined by the imperfect fenestration of the lentelliptical shell growing in the three dimensive axes in a quite different manner. Each elliptical dimensive plane becomes circumscribed by an elliptical latticed girdle (or fenestrated {601}ring), and between these three girdles (perpendicular one to another) remain wide open fissures of the shell or "gates" (_Pylæ_). The beginning of the shell-building is the same as in _Larnacilla_, the most simple form of Larnacida. From a quite simple medullary shell, a spherical, subspherical, ellipsoidal, or lentelliptical central chamber, arise two latticed wings, opposite on the poles of the transverse axis (_Monozonium_). Both wings are short and wide hollow fenestrated tubes, the axes of which are parallel to the principal axis. Therefore they form together with the central chamber an elliptical transverse girdle. This first girdle becomes crossed by a second lateral girdle; from both poles of the transverse axis arise latticed wings, which unite on the poles of the principal axis, therefore the minor axis of this second larger ring is the major axis of the first smaller ring (_Dizonium_). Between the two crossed rings remain four wide open gates. Now follows the development of a third sagittal girdle, arising from both poles of the principal axis and overgrowing the four gates. But as this third girdle is larger than the second, four other larger gates arise between the two (in planes perpendicular to the former four gates). Now we have the characteristic and most important trizonal shell (_Trizonium_), composed of three elliptical lattice-girdles of different size, perpendicular one to another, and enclosing a simple central chamber. If the four gates of this _Trizonium_ become closed by lattice-work, it passes over into _Larnacilla_, the most important ancestral form of the Larnacida.

This most significant "trizonal shell," either incompletely latticed in _Trizonium_ (with four open gates), or completely latticed by fenestration of the four gates, in _Larnacilla_, is to be found in far the greater part of all #Larcoidea#, representing the medullary shell, which is overgrown by an outer cortical shell. In many #Larcoidea#, in which this "_Larnacilla_-shell" is absent, it is perhaps lost by phylogenetic reduction, or retrograde metamorphosis.

The same process of triple girdle-building, by which the typical _Trizonium_-shell or _Larnacilla_-shell is produced (Haplozonaria), is repeated once or twice in the larger forms of Pylonida. The first system of three girdles (perpendicular one to another) becomes overgrown by a second system of the same formulation in the Diplozonaria, and this becomes overgrown by a third system in the Triplozonaria; in the highest genus of this group, _Pylozonium_, we find not less than nine girdles (three systems, each of three girdles). Till now only one genus of the whole polymorphous family was well known, _Tetrapyle_ (with five girdles, three of the medullary, two of the cortical shell). If the gates between the girdles remain open, all these forms must be regarded as Pylonida; if the gates afterwards become closed by a network, they pass over into other families.

The fourth family of the _Larcoidea_ is the Tholonida, distinguished by the polythalamous shell being composed of a certain number of roundish or hemispherical chambers (domes or cupolas), which surround a primordial central chamber in quite regular disposition, lying opposite in pairs on the poles of the three dimensive axes. {602}If we imagine that each "wing" (or open half-girdle) of the Pylonida becomes closed by a lattice-work, and so transformed into a hemispherical or roundish cupola, we obtain the characteristic shell of the Tholonida. Indeed every girdle of the former corresponds to a pair of opposite domes of the latter. The axis of each pair of domes is one of the three dimensive axes.

The primordial chamber of the Tholonida (or the central chamber, around which all cupolas are regularly disposed) is either a simple lentelliptical lattice-shell, like _Cenolarcus_, or it is a trizonal shell (with an enclosed concentric medullary shell), like _Larnacilla_. As in both cases the building and the disposition of the cupolas around it are quite the same, we can suppose that the whole family of Tholonida may have been derived originally from _Larnacilla_ (or _Trizonium_), and that the Cenotholida (with a simple central chamber) are sprung from the Coccotholida (with a _Larnacilla_-shaped central chamber) by reduction and loss of the original medullary shell.

The family Tholonida can be divided into three subfamilies according to the disposition of the cupola-pairs in one, two, or three dimensive axes. In the Cubotholida lie two cupolas on the poles of the transverse axis of the central chamber (corresponding to _Amphipyle_); in the Staurotholida we find four cupolas crosswise disposed, on the poles of the transverse and principal axes (corresponding to _Tetrapyle_); in the Cubotholida are at least six cupolas, on the poles of all three dimensive axes (corresponding to _Tholonium_). In all three cases the number of cupolas may be augmented by the secondary apposition of other chambers or domes in the same disposition. Sometimes also the whole cortical shell becomes enclosed by an external veil or mantle of delicate network. The lentelliptical (or often nearly cubical) central chamber becomes often reduced, so that its sides are incompletely latticed or widely opened; in some Cubotholida only the twelve edges of the eight cornered cubical central chamber remain; its six sides are quite open and only over-vaulted by the six hemispherical cupolas. From the opposite points of the latter (in the deep annular constrictions between them) often arise radial spines, and these lie commonly in diagonal planes, separating the dome-pairs.

A similar dome-building or a composition of the polythalamous shell by pairs of cupolas we find also in the next (fifth) family, the Zonarida. But here the true cause of the peculiar dome-structure is quite different, not an apposition of new chambers, but the constriction of a cortical shell-like _Larnacalpis_ by two or more constrictions. These constrictions lie in dimensive planes (or in planes parallel to these), and therefore the cupolas are (all or partly) in diagonal planes, a condition quite opposite to that found in the Tholonida. One of the annular constrictions is constantly in the sagittal plane (separating the right and left halves of the shell). The number of the constrictions in the few genera is two, three, and four, and therefore the number of the cupolas four, six, or eight. As this cortical shell constantly encloses a trizonal medullary shell (or _Larnacilla_-shell), we cannot doubt that the Zonarida must be derived from the Larnacida.

{603}Whilst in all the foregoing five families of #Larcoidea# the shell-form is regular and their geometrical fundamental form is a lentellipsis (or a triaxial ellipsoid, with three unequal isopolar dimensive axes), in the four remaining families of this suborder the shell becomes bilateral or irregular (with the poles of the axes unequal). In two of these families (Lithelida and Streblemida) the growth of the shell becomes spiral, in the last two families (Soreumida and Phorticida) quite irregular. But as in all four families we encounter the typical trizonal medullary shell (or _Larnacilla_-shell), we are convinced that they must be derived (wholly or partially) from the Larnacida.

The Lithelida (the sixth family) are #Larcoidea# with spiral growth and bilateral form (like _Nautilus_); therefore the spiral line lies in one plane and this spiral plane divides the whole shell into two symmetrical halves (right and left). The axis of the spiral (around which the shell winds) is a straight line, one of the three dimensive axes. In the greater part of Lithelida (in the Larcospirida) the primordial of central chamber of the polythalamous shell is a trizonal medullary shell or _Larnacilla_-shell, and the growth of the first spiral turning begins as the development of the first (transverse) cortical girdle of _Amphipyle_; but as one wing (or lateral half) of this girdle grows more rapidly than the other, it overgrows the latter and begins the spiral winding; if the other wing follow and overgrow the first, the spiral becomes double. Each of the three dimensive girdles (of the Pylonida) may begin the spiral winding. There can be no doubt that all these Lithelida (the Larcospirida) must be derived from the Pylonida, by unequal growth of the two halves of one girdle. Perhaps from these may also derived the other part of this family, the Spiremida (_Spirema_ and _Lithelius_); in these the primordial chamber of the spiral shell is simple, and may be derived by reduction of the original _Larnacilla_-shell. But it is also possible that the Spiremida proceed directly from the Larcarida, and that their ancestors did not possess a _Larnacilla_-shell.

The Streblemida (the seventh family) are #Larcoidea# with spiral growth and asymmetrical form of the polythalamous shell (like _Helix_ or _Turrilites_); therefore the spiral line is twisted like a winding stair, and the spiral face is curved and divides the shell into two unequal halves. The Streblemida have the same likeness and relation to the turbinoid Foraminifera (_Rotalia_, _Globigerina_, &c.) as the Lithelida to the nautiloid Foraminifera (_Polystomella_, _Nummulina_, &c.). As in these calcareous Rhizopods also the peculiar growth of the siliceous Streblemida begins from a primordial chamber to which a variable number of roundish chambers (of increasing size) is apposed. But the building of these chambers and of their septa is by no means so regular and complete as in the greater number of turbinoid Foraminifera. As in a part of this family the primordial chamber is _Larnacilla_-shell, these also may be derived from the Larnacida, but the other part (with simple central chamber) is perhaps produced directly from the Larcarida.

The eighth family, Soreumida, is perhaps derived from the Streblemida by the loss of the spiral growth. The polythalamous shell is similar to the latter, but the chambers are {604}aggregated without any order, like the Acervulinida among the Foraminifera. In some cases also here the primordial chamber is a trizonal _Larnacilla_-shell, in other cases it is a simple, subspherical or lentelliptical shell.

The last family, the Phorticida, is formed of irregular #Larcoidea#, in which a lentelliptical trizonal _Larnacilla_-shell (as an inner medullary shell) is enveloped by an irregular, latticed, or spongy cortical shell. They can be regarded as abnormalities or irregular deformities of Larnacida or Pylonida.

The central capsule of the #Larcoidea# is originally lentelliptical and preserves this form, the "triaxial ellipsoid," in the greater number of genera. In some groups it follows the prevalent growth of the shell in the direction of one of the three dimensive axes, and becomes prolonged in this way. In many chambered forms (particularly Tholonida and Zonarida) the growing central capsule gets constricted, corresponding to the constrictions of the shell. In the Soreumida and Phorticida its form often becomes irregular. But in general for the greater number of #Larcoidea# the lentelliptical form of their central capsule is quite characteristic.

_Synopsis of the Families of_ #Larcoidea#.

------------------------------------------------------------------------- #Larcoidea# with a regular or symmetrical shell, the growth of which is determined by the three dimensive axes. (Both poles of each axis are equal.) ------------------------------------------------------------------------- {Medullary shell absent or Cortical shell completely { simple (spherical or latticed, without external { lentelliptical), 1. LARCARIDA. gates (or interzonal { fissures), without annular {Medullary shell trizonal or constrictions and domes. { _Larnacilla_-shaped { (composed of three { dimensive girdles), 2. LARNACIDA.

Cortical shell incompletely latticed, with two to four or more symmetrically disposed gates or fissures remaining between latticed dimensive girdles, 3. PYLONIDA.

Cortical shell completely }Constrictions of the latticed, without external } cortical shell in gates (or interzonal } diagonal planes; domes fissures), with two or } in dimensive axes, 4. THOLONIDA. more annular constrictions,} which separate three to }Constrictions of the six or more dome-shaped } cortical shell in protuberances. } dimensive planes; domes } in diagonal axes, 5. ZONARIDA. ------------------------------------------------------------------------- #Larcoidea# with a symmetrical or irregular shell, either with spiral growth or with quite irregular growth. (Both poles of one axis are different.) ------------------------------------------------------------------------- {Spiral cortical shell bilateral { (with plane spiral), 6. LITHELIDA. Cortical shell with { spiral growth. {Spiral cortical shell { asymmetrical (with ascending { spiral), 7. STREBLEMIDA.

{Cortical shell simple, with { one single chamber, 8. PHORTICIDA. Cortical shell with quite { irregular growth. {Cortical shell composed of { a number of heaped up { or aggregated chambers, 9. SOREUMIDA.

{605}Family XXIV. #LARCARIDA#, Haeckel, 1883 (Pl. 50, figs. 1, 2).

_Definition._--#Larcoidea# with a regular, completely latticed, lentelliptical cortical shell, without open gates and annular constrictions; medullary shell absent or simple (not trizonal), connected with the cortical shell by radial beams.

The family #Larcarida# opens the long series of #Larcoidea# as the most simple group of this suborder. It commences with _Cenolarcus_, a quite simple lentelliptical latticed shell, which is characterised by three unequal isopolar dimensive axes, perpendicular one to another. The major of these three axes is the longitudinal or principal, the middle is the lateral or transverse, and the minor is the equatorial or sagittal axis (as in the human body). Among the three dimensive planes, which are determined by pairs of these axes, the lateral plane is the largest (halved by the crossed principal and lateral axes). The intermediate is the sagittal plane or median plane (halved by the crossed principal and sagittal axes). The smallest is the equatorial plane or transverse plane (halved by the crossed lateral and sagittal axes). Therefore the shell has all the characters of the true _Lentellipsis_ or of the "triaxial ellipsoid," and its axes agree with the three axes of the "rhombic crystalline system."

In the three subfamilies of Larcarida this lentelliptical shell assumes a different shape: in the Cenolarcida it remains simple, in the Spongolarcida it becomes spongy (sometimes quite filled out with a spongy framework), in the Coccolarcida it is composed of two or more concentric lentelliptical shells (at least an inner medullary and one outer cortical shell). These shells are simply connected by radial beams, and not, as in the Larnacida, by latticed wings (or half girdles).

The network of the Larcarida shell is sometimes regular, commonly irregular (as in the greater number of #Larcoidea#). The surface of the shell is sometimes smooth or thorny, at other times covered with radial spines. These are often symmetrically disposed, either on the poles of the dimensive axes or in crossed diagonal planes.

The central capsule is a true "lentellipsis" in a geometrical sense; it is halved by three elliptical dimensive planes of different sizes, perpendicular one to another. In the Cenolarcida the central capsule lies freely inside the simple (cortical) shell, only separated from it by the jelly-mantle. In the Coccolarcida it contains the medullary shell, and is enclosed by the simple or double cortical shell, perforated by the radial beams connecting the two shells. The spongy shell of the Spongolarcida exhibits a different relation to the central capsule: in _Spongolarcus_ the latter lies freely in the internal cavity of the spongy shell; in _Stypolarcus_, where this cavity is quite filled with a spongy network, the central capsule also contains a part of it.

The morphological and phylogenetic relations of the Larcarida to the other families of SPUMELLARIA admit of a different explanation. As this family contains the {606}most simple forms of all #Larcoidea#, we can regard the _Cenolarcus_ as the common ancestral form of this group, having originated from _Actilarcus_ (or the lentelliptical _Actissa_) by the building of a simple lentelliptical lattice-shell. But it is also possible that a part of the Larcarida (or all?) descend from Larnacida by reduction or loss of the original _Larnacilla_-shell (compare _Cenolarcus triaxonius_, p. 607).

_Synopsis of the Genera of the Larcarida._

------------------------------------------------------------------------- I. Subfamily Cenolarcida. Shell simple, latticed (lentelliptical cortical shell). ------------------------------------------------------------------------- Without radial spines, 266. _Cenolarcus_.

With radial spines, 267. _Larcarium_. ------------------------------------------------------------------------- II. Subfamily Coccolarcida. Shell composed of two or more concentric latticed shells (inner medullary and outer cortical). ------------------------------------------------------------------------- Without radial spines, 268. _Coccolarcus_.

With radial spines, 269. _Larcidium_. ------------------------------------------------------------------------- III. Subfamily Spongolarcida. Shell spongy, partly or whole composed of a spongy framework. ------------------------------------------------------------------------- With an internal cavity, 270. _Spongolarcus_.

Without an internal cavity, 271. _Stypolarcus_.

Subfamily 1. CENOLARCIDA, Haeckel.

_Definition._--#Larcarida# with a simple, lentelliptical latticed shell (cortical shell without a medullary shell).

Genus 266. _Cenolarcus_,[305] n. gen.

_Definition._--#Larcarida# with a simple, lentelliptical latticed shell, without a medullary shell, without radial spines.

The genus _Cenolarcus_ begins the group of #Larcoidea# as the most simple form of this suborder. It corresponds to _Cenosphæra_ among the #Sphæroidea#, to _Cenodiscus_ among the #Discoidea#, to _Cenellipsis_ among the #Prunoidea#. The simple latticed shell is distinguished from that of the three other genera by its typical lentelliptical form, a triaxial ellipsoid with three dimensive axes of unequal length. Probably _Cenolarcus_ is the original ancestral form of the #Larcoidea#, derived from _Actilarcus_ (the lentelliptical _Actissa_) by the formation of a simple fenestrated shell around the lentelliptical central capsule. But possibly also some species of _Cenolarcus_ may be derived from _Coccolarcus_ or _Larnacilla_ by reduction and loss of the medullary shell (compare _Cenolarcus triaxonius_, n. sp.).

{607}1. _Cenolarcus primordialis_, n. sp. (Pl. 50, figs. 7, 7_a_, 7_b_).

Network of the shell regular, with circular, hexagonally framed pores, twice as broad as the elevated bars; about ten pores on the half meridian, eight on the half equator. Surface a little rough. Proportion of the three dimensive axes = 2 : 2.5 : 3.

_Dimensions._--Principal axis (or length) 0.12, transverse axis (or breadth) 0.1, sagittal axis (or thickness) 0.08; pores 0.01, bars 0.005.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

2. _Cenolarcus dimensivus_, n. sp.

Network of the shell regular, with circular pores (without hexagonal frames), three times as broad as the thin bars; about twelve pores on the half meridian, nine on the half equator. Surface thorny. Proportion of the three dimensive axes = 3 : 4 : 5.

_Dimensions._--Principal axis 0.15, transverse axis 0.12, sagittal axis 0.09; pores 0.012, bars 0.004.

_Habitat._--North Pacific, Station 244, surface.

3. _Cenolarcus triaxonius_, n. sp.

Network of the shell regular, with circular, hexagonally framed pores, four times as broad as the thin bars; about twelve pores on the half meridian, nine on the equator. Surface smooth. From the inner surface of the shell arise six very thin radial beams, opposite in pairs in the three dimensive axes; all six beams end freely in a little knob, at an equal distance from the centre; therefore this remarkable species seems to have lost a medullary shell (descending from _Coccolarcus_ or _Larnacilla_?). Proportion of the three dimensive axes = 2 : 2.5 : 3.

_Dimensions._--Principal axis 0.13, transverse axis 0.11, sagittal axis 0.09; pores 0.012, bars 0.03.

_Habitat._--Tropical Atlantic, Station 338, depth 1990 fathoms.

4. _Cenolarcus lentellipticus_, n. sp.

Network of the shell regular, with circular pores of the same breadth as the thick bars; about eighteen pores on the half meridian, fourteen on the half equator. Surface smooth. Proportion of the three dimensive axes = 2 : 3 : 4.

_Dimensions._--Principal axis 0.16, transverse axis 0.12, sagittal axis 0.08; pores and bars 0.004.

_Habitat._--Western Tropical Pacific, Station 224, surface.

5. _Cenolarcus minimus_, n. sp.

Network of the shell subregular, with very small circular pores of the same breadth as the bars; only four pores on the half meridian, three on the half equator. Surface smooth. Proportion of the three dimensive axes = 3 : 4 : 5.

{608}_Dimensions._--Principal axis 0.05, transverse 0.04, sagittal axis 0.03; pores and bars 0.006.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

Genus 267. _Larcarium_,[306] n. gen.

_Definition._--#Larcarida# with a simple, lentelliptical latticed shell, without a medullary shell; surface covered with radial spines.

The genus _Larcarium_ differs from _Cenolarcus_ only in the possession of radial spines on the surface of the simple fenestrated lentelliptical shell. These spines are commonly disposed symmetrically, opposite in pairs, either on the poles of the three dimensive axes, or on the poles of certain diagonal axes. Larcarium differs from the similar genera _Larcidium_, _Larnacidium_, and _Larnacantha_ by the absence of any medullary shell.

1. _Larcarium amphistylum_, n. sp.

Shell thorny, with two large conical spines, opposite on both poles of the principal axis, somewhat longer than it. Network of the shell regular, with circular, hexagonally framed pores, twice as broad as the bars; about twelve pores on the half meridian, ten on the half equator. Proportion of the three dimensive axes = 3 : 4 : 5.

_Dimensions._--Principal axis (or length) 0.15, transverse axis (or breadth) 0.12, sagittal axis (or thickness) 0.09; pores 0.01, bars 0.005.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

2. _Larcarium staurostylum_, n. sp.

Shell smooth, with four short three-sided pyramidal spines of equal length, opposite in pairs on the poles of the principal and lateral axes. Network of the shell regular, with circular pores of the same breadth as the bars; about eight pores on the half meridian, six on the half equator. Proportion of the three dimensive axes = 2 : 2.5 : 3.

_Dimensions._--Length of the shell 0.12, breadth 0.1, thickness 0.08; pores and bars 0.006.

_Habitat._--South Pacific, Station 300, depth 1375 fathoms.

3. _Larcarium hexastylum_, n. sp.

Shell smooth, with six short conical spines of equal length (= the shortest axis of the shell), opposite in pairs on the poles of the three dimensive axes. Network of the shell subregular, with {609}circular pores three times as broad as the bars; about eleven pores on the half meridian, nine on the half equator. Proportion of the three dimensive axes = 3 : 4 : 5.

_Dimensions._--Length of the shell 0.1, breadth 0.08, thickness 0.06, pores 0.006; bars 0.002.

_Habitat._--North Pacific, Station 244, surface.

4. _Larcarium axostylum_, n. sp.

Shell thorny, with six strong conical radial spines, opposite in pairs on the poles of the three dimensive axes. All three pairs are of different sizes, the length of each spine corresponding nearly to the size of the shell-axis, of which it is the prolongation. Network of the shell subregular, with circular pores twice as broad as the bars; ten on the half meridian, eight on the half equator. Proportion of the three dimensive axes = 2 : 3 : 4.

_Dimensions._--Length of the shell 0.12, breadth 0.09, thickness 0.06; pores 0.01, bars 0.005.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

5. _Larcarium octostylum_, n. sp.

Shell thorny, with eight thin cylindrical radial spines, opposite in pairs in two crossed diagonal planes. Network of the shell irregular, with roundish pores, twice to four times as broad as the bars; nine to eleven on the half meridian, five to seven on the half equator. Proportion of the three dimensive axes = 3 : 4 : 5.

_Dimensions._--Length of the shell 0.11, breadth 0.09, thickness 0.07; pores 0.006 to 0.012, bars 0.003.

_Habitat._--Pacific, central area, Station 267, surface.

6. _Larcarium polystylum_, n. sp.

Shell thorny, with numerous (twenty to thirty) stronger conical radial spines, about as long as the shortest axis of the shell. Network of the shell irregular, with roundish pores, twice to four times as broad as the bars; seven to eight on the half meridian, five to six on the half equator. Proportion of the three dimensive axes = 1 : 2 : 3.

_Dimensions._--Length of the shell 0.09, breadth 0.06, thickness 0.03; pores 0.006 to 0.012, bars 0.003.

_Habitat._--South Atlantic, Station 323, surface.

7. _Larcarium chætostylum_, n. sp.

Shell bristly, with very numerous (sixty to eighty or more) very thin, bristle-like, radial spines, somewhat longer than the longest axis of the shell. Network irregular, with very small roundish pores, about the same size as the bars; sixteen to eighteen on the half meridian, thirteen to fifteen on the half equator. Proportion of the three dimensive axes = 1 : 1.5 : 2.

{610}_Dimensions._--Length of the shell (without spines) 0.13, breadth 0.1, thickness 0.07; pores and bars 0.004 to 0.006.

_Habitat._--Pacific, central area, Station 273, surface.

Subfamily 2. COCCOLARCIDA, Haeckel.

_Definition._--#Larcarida# with encased lentelliptical shell, composed of two or more concentric lentelliptical latticed shells, which are united by radial beams (at least one inner medullary shell and one outer cortical shell).

Genus 268. _Coccolarcus_,[307] n. gen.

_Definition._--#Larcarida# with two concentric latticed shells, an outer lentelliptical cortical shell, and an inner (spherical or lentelliptical) medullary shell, both connected by radial beams. Surface without radial spines.

The genus _Coccolarcus_ differs from _Cenolarcus_ by the possession of an internal medullary shell. This is quite simple, either spherical or lentelliptical, and connected with the outer cortical shell by a number of radial beams. In the similar _Larnacilla_ this connection is effected by four internal latticed lamellæ (the half lateral wings of the transverse girdle); therefore we find here four internal gates (on the poles of the principal axis), absent in _Coccolarcus_.

1. _Coccolarcus lentellipsis_, n. sp.

Cortical shell with smooth surface and regular network; pores circular, twice as broad as the bars; about thirteen on the half meridian, eleven on the half equator. Proportion of the three dimensive axes = 3 : 4 : 5. Medullary shell spherical, half as broad as the transverse radius.

_Dimensions._--Principal axis (or length) of the cortical shell 0.15, transverse axis (or breadth) 0.12, sagittal axis (or thickness) 0.09; pores 0.01, bars 0.005; diameter of the medullary shell 0.03.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

2. _Coccolarcus platellipsis_, n. sp.

Cortical shell with thorny surface and irregular network; pores roundish, twice to three times as broad as the bars; sixteen to eighteen on the half meridian, ten to twelve on the half equator. Proportion of the three dimensive axes = 1 : 2 : 3. Medullary shell lentelliptical, one-third as large as the cortical shell.

{611}_Dimensions._--Length of the cortical shell 0.17, breadth 0.11, thickness 0.06; pores 0.008 to 0.012, bars 0.004; medullary shell 0.03 to 0.06.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

Genus 269. _Larcidium_,[308] n. gen.

The genus _Larcidium_ differs from the foregoing _Coccolarcus_ only in the possession of radial spines, and bears to it the same relation that _Larcarium_ does to _Cenolarcus_. The spines are commonly symmetrically disposed, opposite in pairs in the dimensive axes, sometimes also in diagonal axes.

1. _Larcidium dissacanthum_, n. sp.

Cortical shell with thorny surface and regular network; pores circular, hexagonally framed, three times as broad as the bars; about thirteen on the half meridian, eleven on the half equator. Proportion of the three dimensive axes = 2 : 3 : 5. Medullary shell spherical, one-fourth as broad as the cortical, connected with it by two thin beams, lying in the principal axis, and prolonged on its poles into two strong conical spines, somewhat longer than the greatest axis.

_Dimensions._--Length of the cortical shell (or principal axis) 0.15, breadth 0.09, thickness 0.07; pores 0.015, bars 0.005; medullary shell 0.025.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

2. _Larcidium hexacanthum_, n. sp.

Cortical shell with smooth surface and regular network; pores circular, twice as broad as the bars; about eleven on the half meridian, nine on the half equator. Proportion of the three axes = 2 : 2.5 : 3. Medullary shell spherical, one-third as broad as the cortical. On the surface six strong, three-sided pyramidal spines, all about as long as the breadth of the cortical shell.

_Dimensions._--Length of the cortical shell 0.12, breadth 0.1, thickness 0.08; pores 0.01, bars 0.005; medullary shell 0.035.

_Habitat._--Pacific, central area. Station 266, surface.

3. _Larcidium axacanthum_, n. sp.

Cortical shell with rough surface and irregular network; pores roundish, twice to four times as broad as the bars; about fifteen to nineteen on the half meridian, twelve to fourteen on the half {612}equator. Proportion of the three axes = 2 : 3 : 4. Medullary shell lentelliptical, of the same form and structure as the cortical, but only one-third as large, connected with it by six thin radial beams, lying in pairs in the three dimensive axes; on the outside they are prolonged into six strong conical radial spines, which are in pairs of different size (as in _Larcarium axostylum_); the length of each spine nearly equals the axis of the cortical shell, of which it is the prolongation.

_Dimensions._--Length of the cortical shell (and the principal spines) 0.18, breadth of it (and length of the lateral spines) 0.135, thickness of it (and length of the sagittal spines) 0.09; pores 0.005 to 0.013, bars 0.003.

_Habitat._--Pacific, central area, Station 271, surface.

4. _Larcidium octacanthum_, n. sp.

Cortical shell thorny, with irregular network; pores roundish, once to four times as broad as the bars; about thirteen to fifteen on the half meridian, eleven to thirteen on the half equator. Proportion of the three axes = 1 : 2.5 : 4. Medullary shell lentelliptical, one-fifth as large as the cortical, connected with it by eight radial beams, which are situated in two crossed diagonal planes (opposite in pairs), and are prolonged on the surface into eight long and thin cylindrical radial spines similar to _Tetrapyle octacantha_.

_Dimensions._--Length of the cortical shell 0.16, breadth 0.11, thickness 0.045; pores 0.003 to 0.012, bars 0.003; medullary shell 0.02 to 0.03.

_Habitat._--Pacific, central area, Station 263, depth 2650 fathoms.

5. _Larcidium dodecanthum_, n. sp. (Pl. 50, figs. 8, 8_a_).

Cortical shell rough, with irregular network; pores roundish, twice to four times as broad as the bars; about twelve to fourteen on the half meridian, eight to ten on the half equator. Proportion of the three axes = 2 : 3 : 4. Medullary shell lentelliptical, one-third as large as the cortical, connected with it by twelve thin radial beams, which are prolonged outside into twelve strong conical radial spines, about half as long as the breadth of the shell.

_Dimensions._--Length of the cortical shell 0.14, breadth 0.1, thickness 0.07; pores 0.008 to 0.015, bars 0.004; medullary shell 0.04 to 0.05.

_Habitat._--South Pacific, Station 288, surface.

6. _Larcidium polyacanthum_, n. sp.

Cortical shell spiny, with irregular network; pores roundish, once to twice as broad as the bars; about ten to twelve on the half meridian, six to eight on the half equator. Proportion of the three axes = 1 : 2 : 3. Medullary shell lentelliptical, half as large as the cortical shell, connected with it by numerous (twenty to twenty-five) radial beams, which are prolonged outside into three-sided pyramidal spines, about as long as the breadth of the shell.

_Dimensions._--Length of the cortical shell 0.18, breadth 0.12, thickness 0.06; pores 0.01 to 0.015, bars 0.008; medullary shell 0.03 to 0.09.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

{613}Subfamily 3. SPONGOLARCIDA, Haeckel.

_Definition._--#Larcarida# with spongy lentelliptical shell (with or without enclosed medullary shell).

Genus 270. _Spongolarcus_,[309] n. gen.

_Definition._--#Larcarida# with lentelliptical spongy shell, containing a central cavity of the same form, without medullary shell (without radial spines).

The genus _Spongolarcus_ differs from _Cenolarcus_ (its probable ancestral form) only in the development of spongy framework forming the wall of the hollow lentelliptical shell. It corresponds, therefore, to _Plegmosphæra_ among the #Sphæroidea#, and to _Spongellipsis_ among the #Prunoidea#. From these two similar spongy #Sphærellaria# it differs in its characteristic lentelliptical form, with three dimensive axes of unequal length.

1. _Spongolarcus lentellipsis_, n. sp.

Spongy network of the shell very loose, its meshes fifteen to twenty times as broad as the bars. Surface of the shell nearly smooth; diameter of its internal cavity twice as large as the thickness of its wall. Proportion of the three dimensive axes = 2 : 3 : 4.

_Dimensions._--Length 0.16, breadth 0.12, height 0.08; thickness of the spongy wall 0.05.

_Habitat._--Pacific, central area, Station 274, surface.

2. _Spongolarcus triaxonius_, n. sp.

Spongy network of the shell rather loose, its meshes twelve to sixteen times as broad as the bars. Surface of the shell rough; diameter of its internal cavity about eight times as large as the thickness of its wall. Proportion of the three dimensive axes = 2 : 2.5 : 3.

_Dimensions._--Length 0.25, breadth 0.2, height 0.16; thickness of the spongy wall 0.025.

_Habitat._--North Pacific, Station 253, surface.

3. _Spongolarcus dimensivus_, n. sp.

Spongy network of the shell dense, its meshes four to eight times as broad as the bars. Surface of the shell thorny; diameter of its internal cavity about fifteen times as large as the thickness of its wall. Proportion of the three dimensive axes = 3 : 4 : 5.

_Dimensions._--Length 0.2, breadth 0.16, height 0.12; thickness of the spongy wall 0.01.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

{614}4. _Spongolarcus amphicentria_, Haeckel.

? _Amphicentria salpa_, Ehrenberg, 1861, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 296; Abhandl. d. k. Akad. d. Wiss. Berlin, 1872, Taf. ii. fig. 18.

? _Spongurus salpa_, Haeckel, 1862, Monogr. d. Radiol., p. 466.

Spongy network of the shell compact, its meshes about the same breadth as the bars. Surface of the shell spiny, with some larger spines around the poles of the axis; diameter of the internal cavity about six times as large as the thickness of its wall. Proportion of the three dimensive axes = 1 : 2 : 3. (Perhaps this _Spongolarcus_ is identical with _Amphicentria salpa_, very imperfectly described and figured by Ehrenberg, _loc. cit._?)

_Dimensions._--Length 0.14, breadth 0.09, height 0.05; thickness of the spongy wall 0.015.

_Habitat._--North Atlantic; off Greenland, 1000 fathoms, Ehrenberg; Station 64, depth (2700) fathoms.

Genus 271. _Stypolarcus_,[310] n. gen.

_Definition._--#Larcarida# with lentelliptical spongy shell, composed of compact spongy framework, without central cavity and medullary shell (without radial spines).

The genus _Stypolarcus_ differs from _Spongolarcus_ in the absence of any central cavity. This is quite filled up by spongy framework, which forms the whole mass of the lentelliptical body. _Stypolarcus_ bears therefore the same relation to _Spongolarcus_ that _Styptosphæra_ does to _Plegmosphæra_.

1. _Stypolarcus spongiosus_, n. sp.

Lentelliptical shell composed in the whole mass of loose, spongy framework of similar texture, with irregular meshes, about ten to twenty times as broad as the thin bars. Surface rough, without radial spines. Proportion of the three axes = 3 : 4 : 5.

_Dimensions._--Length 0.2, breadth 0.16, height 0.12.

_Habitat._--Antarctic Ocean, Station 157, depth 1950 fathoms.

Family XXV. #LARNACIDA#, Haeckel, 1883 (Pl. 50, figs. 3-8).

_Definition._--#Larcoidea# with a regular, completely latticed, lentelliptical cortical shell, without open gates and annular constrictions; either this cortical shell or the enclosed medullary shell is trizonal, composed of three elliptical, latticed, dimensive girdles of different sizes, perpendicular one to another.

{615}The family #Larnacida# immediately follows the Larcarida as the next simple group of all #Larcoidea#; some genera of both groups (such as _Larnacalpis_ and _Coccolarcus_, or _Larnacantha_ and _Larcidium_) may easily be confounded from their being so much alike. In both the lentelliptical shell is composed of two concentric shells, an inner (medullary) and an outer (cortical) shell. But the connection between these shells and the construction of the inner shell is quite different in the two groups. Whilst in the Larcarida the medullary shell is connected with the cortical shell simply by radial beams, here in the Larnacida this connection is effected by two latticed lamellæ, which are the lateral wings of a transverse girdle. Therefore we encounter here for the first time that peculiar mode of growth which characterises the greater part of the #Larcoidea#, but particularly the Pylonida. But whilst in the Pylonida between the three crossed lattice-girdles, remain four open gates, here in the Larnacida the gates become closed by lattice-work; the lentelliptical cortical shell becomes perfect.

The most simple genus of Larnacida, and no doubt the common ancestral form of this whole family, is _Larnacilla_ (Pl. 50, figs. 1, 1_a_, 1_b_). The most important shell of this typical genus is composed of a simple lentelliptical medullary shell and of three elliptical latticed girdles surrounding it, perpendicular one to another. These three "dimensive girdles" lie in the perimeter of the three dimensive planes, the minor (and first) in the equatorial plane, the second (and major) in the lateral plane, the third (and intermediate) in the sagittal plane. Therefore we have before us the same "trizonal shell" as in the important genus _Trizonium_ among the Pylonida. But whilst in _Trizonium_, as in all Pylonida, the four gates between the girdles remain open, here in _Larnacilla_ they become perfectly closed by lattice-work.

The formation of the typical "_Larnacilla_-shell" begins with a simple, spherical or lentelliptical lattice-shell, from both sides of which arise two latticed "lateral wings" opposite on the poles of the transverse axis. These two wings are comparable to the lateral chambers of _Tholartus_ (among the Tholonida), but differ by two large openings. Each wing is a short cylindrical tube with latticed wall, open at both ends; the axis of the tube (going through the centre of the open ends) is parallel to the principal axis of the whole shell (and of the central chamber). Therefore both wings form together a transverse ring, the middle of which encloses the central chamber. The distal parts of both wings grow towards the poles of the principal axis; if they became united here, the second (lateral) girdle would be complete. Between it and the first girdle four open gates remain ("_Tetrapyle_"); but these become overgrown by the third or sagittal girdle, and at last the gates between this and the two other girdles become closed by lattice-work. This perfect fenestration of the trizonal cortical shell, and the complete closing of the gates between the girdles by network, is the only difference between _Trizonium_ and _Larnacilla_.

In _Larnacilla_ and in the nearly allied _Larnacidium_ (only differing by radial spines {616}on the surface) the "trizonal shell" is an external or "cortical shell," enclosing the central capsule, the interior of which only contains the simple central chamber and the jointed proximal parts of both lateral wings. In the other genera of Larnacida (by proceeding growth) this trizonal _Larnacilla_-shell becomes enclosed by the growing central capsule and is now only a "medullary shell," whilst on the outside of the central capsule in the same manner is developed an outer cortical shell (_Larnacalpis_, _Larnacantha_); and perhaps the same process may be repeated. But sometimes also this cortical shell becomes doubled by a simple envelop of network (_Larnacoma_). In the Larnacospongida the cortical shell is composed of a spongy framework (corresponding to the Spongolarcida in the foregoing family).

The lattice-work of the Larnacida is commonly irregular (as in most other #Larcoidea#), and its pores have little signification for the different species. On the outer surface often arise radial spines, symmetrically disposed either in dimensive planes or in diagonal planes.

The central capsule is constantly a true lentellipsis or a "triaxial ellipsoid," characterised by three halving, elliptical dimensive planes, perpendicular one to another. It bears a different relation to the skeleton in the two subfamilies of Larnacida. In the first subfamily, the Larnacillida (_Larnacilla_, _Larnacidium_), the central capsule encloses only the simple spherical or lentelliptical central chamber ("simple medullary shell"), and is enveloped by the trizonal cortical shell. In the other subfamily, the Larnacalpida (_Larnacalpis_, _Larnacospongus_, &c.), this trizonal "_Larnacilla_-shell" becomes enclosed by the overgrowing central capsule, which now becomes enveloped by an external, latticed or spongy, lentelliptical "cortical shell."

_Synopsis of the Genera of Larnacida._

------------------------------------------------------------------------- I. Subfamily Larnacillida. Medullary shell simple, spherical or subspherical. Cortical shell lentelliptical, trizonal; between them four gates. ------------------------------------------------------------------------- Shell without radial spines, 272. _Larnacilla_.

Shell with radial spines, 273. _Larnacidium_. ------------------------------------------------------------------------- II. Subfamily Larnacalpida. Medullary shell _Larnacilla_-shaped, double; the inner spherical or subspherical, the outer lentelliptical and trizonal. ------------------------------------------------------------------------- { { Without radial { Cortical { spines, 274. _Larnacalpis_. { shell { Cortical shell simple { simple. { With radial or double, but not { { spines, 275. _Larnacantha_. spongy. { { Cortical shell double, { without radial spines, 276. _Larnacoma_.

{ Shell without radial Cortical shell simple { spines, 277. _Larnacospongus_. or double, wholly or { partly spongy. { Shell with radial spines, 278. _Larnacostupa_.

{617}Subfamily 1. LARNACILLIDA, Haeckel.

_Definition._--#Larnacida# with a simple, spherical or lentelliptical, medullary shell, connected by the lateral wings of a latticed transverse girdle with the simple lentelliptical trizonal cortical shell; the central capsule encloses the former and is enveloped by the latter.

Genus 272. _Larnacilla_,[311] n. gen.

_Definition._--#Larnacida# with a simple lentelliptical cortical shell, connected by the lateral wings of a latticed transverse girdle with the simple, spherical or lentelliptical, medullary shell. Surface without radial spines.

The genus _Larnacilla_ represents the most simple form of Larnacida, and at the same time the most important common ancestral form, from which the greater number of #Larcoidea# may be derived, viz., all those genera which possess the characteristic "_Larnacilla_-shaped medullary shell." This typical form of medullary shell may be derived from the genus _Trizonium_ among the Pylonida by the closing of the four open gates of this genus. The free opening of these four gates becomes overgrown and closed by lattice-work, developed from the free edges of the three crossed girdles, and thus finally all three girdles are united in the form of a simple lentelliptical shell (Pl. 50, figs. 1, 1_a_, 1_b_). Seen from the sagittal poles (or from the poles of the shortest axis, fig. 1), the shell exhibits on both sides of the small spherical medullary shell the two lateral wings of the transverse girdle from the face; seen from the lateral poles (or from the poles of the transverse axis, fig. 1_a_), one of these wings appears in the optical section as an oblong ring, which seemingly encloses the concentric medullary shell, and on both sides is grown together with the sagittal girdle; seen from the principal poles (or from the poles of the longitudinal axis, fig. 1_b_), both wings exhibit their elliptical opening (at the right and left from the central medullary shell). The two concentric shells are only connected by the two lateral tube-like wings of the transverse girdle; the lateral and the sagittal girdles have no connection with the medullary shell. The latter is sometimes spherical, at other times lentelliptical.

1. _Larnacilla typus_, n. sp. (Pl. 50, fig. 1, 1_a_, 1_b_).

Cortical shell with smooth surface and with subregular network; pores twice as broad as the bars; about twelve pores on the half meridian, ten on the half equator. Proportion of the three dimensive axes = 2 : 3 : 4. Internal four gates (between transverse and lateral girdles) roundish-triangular, little broader than high. Medullary shell spherical, scarcely one-third as broad as the lentelliptical cortical shell.

{618}_Dimensions._--Length of the cortical shell (or principal axis) 0.13, breadth of it (or transverse axis) 0.1, height of it (or sagittal axis) 0.07; pores 0.006, bars 0.003; medullary shell (diameter) 0.03.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

2. _Larnacilla prometor_, n. sp.

Cortical shell with rough surface and regular network; pores three times as broad as the bars; about ten on the half meridian, eight on the half equator. Proportion of the three axes = 1 : 2 : 3. Internal four gates (between transverse and lateral girdles) kidney-shaped, twice as broad as high. Medullary shell lentelliptical, of the same form as the external cortical shell, but only one third as large.

_Dimensions._--Length of the cortical shell 0.15, breadth 0.1, height 0.05, pores 0.015, bars 0.005; medullary shell 0.02 to 0.05.

_Habitat._--Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.

3. _Larnacilla subglobosa_, n. sp.

Cortical shell nearly spherical, with thorny surface and irregular network; pores roundish, twice to four times as broad as the bars; twelve to sixteen in the half circumference. Proportion of the three axes very little different = 1.3 : 1.4 : 1.5. Internal four gates elliptical, one and a half times as broad as high. Medullary shell spherical, one-fourth as broad as the cortical shell.

_Dimensions._--Length of the cortical shell 0.15, breadth 0.14, height 0.13; pores 0.006 to 0.012, bars 0.003; medullary shell 0.035.

_Habitat._--Pacific, central area. Station 266, depth 2750 fathoms.

4. _Larnacilla medullaris_, n. sp.

Cortical shell lentelliptical, with smooth surface and irregular network; pores roundish, very small, scarcely as broad as the bars; about eight to nine on the half meridian, six to seven on the half equator. Proportion of the three axes = 3 : 4 : 6. Internal four gates elliptical. Medullary shell spherical, scarcely one-third as broad as the cortical shell. (This small species may be only the medullary shell of some other Larcoid, the cortical shell of which is not yet formed.)

_Dimensions._--Length of the cortical shell 0.06, breadth 0.04, height 0.03; pores and bars about 0.004; medullary shell 0.013.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

Genus 273. _Larnacidium_,[312] n. gen.

{619}The genus _Larnacidium_ has the same shell-formation as the foregoing _Larnacilla_, and differs from it only in the possession of radial spines on the surface, which in all known species exhibit a symmetrical disposition. From the nearly allied genus _Larcidium_ it differs in the characteristic mode of connection between the two shells, owing to the different kind of growth. In _Larcidium_ this connection is effected only by radial beams, whereas in _Larnacidium_ (as in all Larnacida) by two lateral latticed tubes, the wings of the primary transverse girdle.

1. _Larnacidium staurobelonium_, n. sp.

Cortical shell smooth, with four strong conical, radial spines in the lateral plane, opposite in pairs, two on the poles of the principal and two on the poles of the transverse axis. Pores subregular, circular, twice as broad as the bars; about twelve on the half meridian. Proportion of the three axes = 2 : 3 : 4. Medullary shell spherical, one-third as broad as the cortical shell.

_Dimensions._--Length of the cortical shell 0.12, breadth 0.09, height 0.06; pores 0.008, bars 0.04; medullary shell 0.03.

_Habitat._--North Pacific Station 244, depth 2900 fathoms.

2. _Larnacidium hexabelonium_, n. sp.

Cortical shell thorny, with six strong, three-sided pyramidal, radial spines, lying opposite in pairs on the poles of the three dimensive axes. Pores subregular, circular, three times as broad as the bars; about fourteen on the half meridian. Proportion of the three axes = 2 : 2.5 : 3. Medullary shell spherical, one-third as broad as the cortical shell.

_Dimensions._--Length of the cortical shell 0.14, breadth 0.11, height 0.08; pores 0.01, bars 0.003; medullary shell 0.04.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

3. _Larnacidium polybelonium_, n. sp.

Cortical shell very spiny, with numerous (twenty to thirty or more) larger thin radial spines, about as long as the shell. Pores irregular, twice to five times as broad as the bars; about sixteen on the half meridian. Proportion of the three axes = 2 : 2.5 : 3. Medullary shell lentelliptical, half as large as the cortical shell.

_Dimensions._--Length of the cortical shell 0.11, breadth 0.09, height 0.07; pores 0.004 to 0.01, bars 0.002; length of the medullary shell 0.06, breadth 0.05, height 0.04.

_Habitat._--Western Tropical Pacific, Station 225. depth 4475 fathoms.

Subfamily 2. LARNACALPIDA, Haeckel.

_Definition._--#Larnacida# with a double, trizonal, _Larnacilla_-shaped medullary shell, enclosed in the central capsule, and enveloped by a simple or double, latticed or spongy, lentelliptical, cortical shell.

{620}Genus 274. _Larnacalpis_,[313] n. gen.

_Definition._--#Larnacida# with a simple lentelliptical cortical shell, without radial spines. Medullary shell double, _Larnacilla_-shaped.

The genus _Larnacalpis_ represents the most simple form of the sub-family Larnacalpida, and is very important as the common original form of all those #Larcoidea# in which a double _Larnacilla_-shaped medullary shell is surrounded by a simple, perfectly closed, latticed, lentelliptical cortical shell. Therefore the same typical, trizonal, lentelliptical shell, which in _Larnacilla_ represents the external envelop (or cortical shell) of the central capsule, here in _Larnacalpis_ becomes enclosed as an internal nucleus (or medullary shell) in the interior of the central capsule, and this latter becomes overgrown by a new lentelliptical cortical shell. The connection between the two shells of _Larnacalpis_ is either effected by a number of radial beams (e.g., in _Larnacalpis triaxonia_ by six beams situated in the three dimensive axes), or by two lateral, latticed, tube-like wings, which are repetitions of the smaller lateral wings connecting its external shell with the internal medullary shell (as in _Larnacalpis lentellipsis_). The latter species may be regarded as a _Pylonium_ with a completely latticed shell.

1. _Larnacalpis lentellipsis_, n. sp. (Pl. 50, figs. 2, 2_a_, 2_b_).

Cortical shell with thorny surface and irregular network; pores roundish, twice to four times as broad as the bars; about sixteen on the half meridian, twelve on the half equator. Proportion of the three dimensive axes = 2 : 3 : 4. Medullary shell one-third as large as the cortical, with four elliptical internal gates, connected with it by two opposite beams in the principal axis and by two latticed wings in the transverse axis; therefore between the two shells are four large kidney-shaped gates, halved by the polar beams (as in _Octopyle_).

_Dimensions._--Length of the cortical shell (or principal axis) 0.14, breadth (or transverse axis) 0.11, height (or sagittal axis) 0.07; pores 0.01 to 0.02, bars 0.005; length of the medullary shell 0.05, breadth 0.04, height 0.03.

_Habitat._--Pacific, central area, Station 273, depth 2600 fathoms.

2. _Larnacalpis phacodiscus_, n. sp.

Cortical shell with thorny surface and regular network; pores circular, twice as broad as the bars; about ten on the half meridian, eight on the half equator. Proportion of the three axes = 2 : 2.5 : 3. Medullary shell half as large as the cortical, with four kidney-shaped internal gates.

_Dimensions._--Length of the cortical shell 0.13, breadth 0.11, height 0.09; pores 0.012, bars 0.006; length of the medullary shell 0.06, breadth 0.045, height 0.03.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

{621}3. _Larnacalpis macrococcus_, n. sp.

Cortical shell with spiny surface and regular network; pores circular, small, of the same breadth as the bars; about twenty-two on the half meridian, nineteen on the half equator. Proportion of the three axes = 2 : 3 : 4. Medullary shell two-thirds as large as the cortical, with four wide internal semicircular gates.

_Dimensions._--Length of the cortical shell 0.1, breadth 0.075, height 0.05; pores and bars 0.003; length of the medullary shell 0.066, breadth 0.05, height 0.032.

_Habitat._--Western Tropical Pacific, Station 224, depth 1850 fathoms.

4. _Larnacalpis subsphærica_, n. sp.

Cortical shell with rough surface and irregular network; roundish pores twice to five times as broad as the bars; about twenty-four on the half meridian, twenty-one on the half equator. Proportion of the three axes = 1.2 : 1.3 : 1.4. Medullary shell half as large as the cortical, with four elliptical internal gates.

_Dimensions._--Length of the cortical shell 0.14, breadth 0.13, height 0.12; pores 0.004 to 0.01, bars 0.002; length of the medullary shell 0.08, breadth 0.07, height 0.06.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

5. _Larnacalpis triaxonia_, n. sp. (Pl. 50, fig. 3).

Cortical shell with smooth surface and peculiar network, composed of four meridian rows of larger pores (five large elliptical pores on each half meridian, the largest in the equator) and numerous small irregular pores between them. Proportion of the three axes = 2 : 3 : 4. Medullary shell with four semicircular internal gates, about one-fourth as large as the cortical, connected with it by six thin radial beams, opposite in pairs in the three dimensive axes.

_Dimensions._--Length of the cortical shell 0.14, breadth 0.1, height 0.07; large pores 0.03, small pores 0.002 to 0.01, bars 0.002 to 0.01; length of the medullary shell 0.04, breadth 0.03, height 0.02.

_Habitat._--Pacific, central area, Station 263, depth 2650 fathoms.

Genus 275. _Larnacantha_,[314] n. gen.

_Definition._--#Larnacida# with a simple lentelliptical cortical shell, armed with symmetrically disposed radial spines. Medullary shell double, _Larnacilla_-shaped.

The genus _Larnacantha_ has the same characteristic shell-formation as the foregoing _Larnacalpis_, and differs from it only in the possession of radial spines, which are symmetrically distributed on the surface in a definite order. Commonly these spines are external prolongations of the internal radial beams, which connect the double _Larnacilla_-shaped medullary shell with the simple lentelliptical cortical shell.

{622}1. _Larnacantha dissacantha_, n. sp.

Cortical shell smooth, with two large cylindrical spines, opposite on the poles of the principal axis, and somewhat longer than it. Pores regular, circular, three times as broad as the bars; about eleven on the half meridian. Proportion of the three axes = 2 : 3 : 4. Medullary shell one-third as large as the cortical shell.

_Dimensions._--Length of the cortical shell (principal axis) 0.13, breadth (transverse axis) 0.1, height (sagittal axis) 0.07; pores 0.009, bars 0.003; length of the _Larnacilla_-shaped medullary shell 0.045.

_Habitat._--North Pacific, Station 256, depth 2950 fathoms.

2. _Larnacantha stauracantha_, n. sp.

Cortical shell smooth, with four large conical spines in the lateral plane, two larger opposite on the poles of the principal, two smaller on those of the transverse axis. Pores regular, circular, twice as broad as the bars; about seventeen on the half meridian. Proportion of the three axes = 3 : 3.5 : 4. Medullary shell one-third as large as the cortical shell.

_Dimensions._--Length of the cortical shell 0.15, breadth 0.13, height 0.11; pores 0.008, bars 0.004; length of the medullary shell 0.05.

_Habitat._--Pacific, central area, Station 274, surface.

3. _Larnacantha quadricornis_, n. sp.

Cortical shell spiny, with four strong, horn-like curved spines in the lateral plane, opposite in pairs on the poles of the crossed diagonal axes. Pores irregular, roundish, twice to four times as broad as the bars; about fourteen on the half meridian. Proportion of the three axes = 2 : 3 : 4. Medullary shell one-third as large as the cortical shell.

_Dimensions._--Length of the cortical shell 0.14, breadth 0.11, height 0.07; pores 0.006 to 0.012, bars 0.003; length of the medullary shell 0.05.

_Habitat._--Pacific, central area, Station 270, surface.

4. _Larnacantha hexacantha_, n. sp. (Pl. 50, fig. 4).

Cortical shell thorny, with six strong conical radial spines in the lateral plane, two opposite on the poles of the principal axis, four others opposite in pairs on the poles of the two crossed diagonal axes. Pores with peculiar distribution; twelve large elliptical pores (nearly of the size of the medullary shell) symmetrically disposed in four crossed meridians (between the sagittal and the lateral meridians), separated by bands of smaller irregular pores. Proportion of the three axes = 3 : 4 : 5. Medullary shell hexagonal, one-third as large as the cortical shell.

_Dimensions._--Length of the cortical shell 0.14, breadth 0.11, height 0.08; large pores 0.04, small pores 0.003 to 0.01, bars 0.004; length of the medullary shell 0.05.

_Habitat._--Pacific, central area, Station 263, depth 2650 fathoms.

{623}5. _Larnacantha bicruciata_, n. sp. (Pl. 50, fig. 5).

Cortical shell thorny, in the lateral plane with eight strong conical radial spines, alternating with eight smaller spines; four of the eight stronger spines opposite on the poles of the principal and transverse axes (in the figure 5, by mistake, not represented large enough), four others between those, opposite on the poles of the two crossed diagonal axes. Pores with a peculiar disposition; on both flat sides of the lentellipsis an elliptical ring of eight large elliptical pores (alternating with the eight stronger radial spines), separated by bands of smaller irregular pores. Proportion of the three axes = 2 : 3 : 4. Medullary shell nearly half as long as the cortical shell.

_Dimensions._--Length of the cortical shell 0.16, breadth 0.13, height 0.08; large pores 0.03, small pores 0.003 to 0.01, bars 0.006; length of the medullary shell 0.07.

_Habitat._--Indian Ocean, surface, Madagascar (Rabbe).

6. _Larnacantha octacantha_, n. sp.

Cortical shell thorny, with eight long and thin, cylindrical, radial spines, lying opposite in pairs in two crossed diagonal planes. Pores irregular, roundish, twice to five times as broad as the bars; about sixteen on the half meridian. Proportion of the three axes = 1 : 1-1/3 : 2. Medullary shell scarcely one-fourth as long as the cortical shell. (This species resembles closely the common _Tetrapyle octacantha_, from which it seems to be developed by a complete over-growing of the four gates, which become closed by a network connecting the free edges of the transverse and lateral girdles.)

_Dimensions._--Length of the cortical shell 0.18, breadth 0.13, height 0.1; pores 0.005 to 0.015, bars 0.003; length of the medullary shell 0.04.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

7. _Larnacantha cladacantha_, n. sp.

Cortical shell very spiny, with eight longer ramified spines, lying opposite in pairs in two crossed diagonal planes; each spine with two to six irregular, lateral branches. Pores irregular, roundish, twice to three times as broad as the bars; about twelve on the half meridian. Proportion of the three axes = 5 : 6 : 7. Medullary shell nearly half as long as the cortical shell. (Differs from the foregoing by the branching spines end the larger medullary shell.)

_Dimensions._--Length of the cortical shell 0.15, breadth 0.13, height 0.11; pores 0.01 to 0.015, bars 0.005; length of the medullary shell 0.07.

_Habitat._--Indian Ocean, surface, Cocos Islands (Rabbe).

8. _Larnacantha prismatica_, n. sp. (Pl. 50, fig. 6).

Cortical shell smooth, four-sided prismatic, with eight short, parallel, three-sided pyramidal spines; these lie opposite in pairs in four parallel longitudinal lines, as prolongations of the four {624}lateral edges of the prism, and arise from its eight corners. Pores regular, circular, three times as broad as the bars; about fourteen on the half meridian. Proportion of the three axes = 2 : 3 : 4. Medullary shell half as long as the cortical shell.

_Dimensions._--Length of the cortical shell 0.11, breadth 0.07, height 0.05; pores 0.006, bars 0.002; length of the medullary shell 0.06.

_Habitat._--Pacific, central area, Station 263, depth 2650 fathoms.

9. _Larnacantha decacantha_, n. sp.

Cortical shell thorny, with ten short and stout, conical, radial spines, two opposite on the poles of the principal axis (as prolongations of inner axial beams), eight others opposite in pairs in two crossed diagonal planes. Pores irregular, roundish, twice to four times as broad as the bars; about sixteen on the half meridian. Proportion of the three axes = 3 : 3.75 : 4. Medullary shell about one-third as long as the cortical shell.

_Dimensions._--Length of the cortical shell 0.16, breadth 0.15, height 0.12; pores 0.008 to 0.016, bars 0.004; length of the medullary shell 0.06.

_Habitat._--North Atlantic, Station 354, surface.

10. _Larnacantha dodecantha_, n. sp.

Cortical shell nearly smooth, but with twelve strong conical radial spines; four in the lateral plane opposite in pairs (two on the poles of the principal, and two on the poles of the transverse axis); eight others opposite in pairs in two crossed diagonal planes. Pores with a peculiar disposition: twelve large elliptical pores in two crossed meridian planes (alternating with the twelve spines), separated by bands of irregular small pores. Proportion of the three axes = 1 : 1.5 : 2. Medullary shell hexagonal, one-third as long as the cortical shell.

_Dimensions._--Length of the cortical shell 0.15, breadth 0.11, height 0.08; large pores 0.03, small pores 0.005 to 0.01, bars 0.003; length of the medullary shell 0.05.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

11. _Larnacantha drymacantha_, n. sp.

Cortical shell very spiny, on the whole surface covered with a forest of numerous (thirty to fifty or more) large branched spines, about the length of the shell; each spine with three to nine lateral branches, simple or forked (very similar to _Cromyodrymus abietinus_, Pl. 30, fig. 6). Pores very irregular, roundish. Proportion of the three axes = 2 : 2.5 : 3. Medullary shell half as long as the cortical shell.

_Dimensions._--Length of the cortical shell 0.16, breadth 0.13, height 0.1; pores 0.005 to 0.015, bars 0.03; length of the medullary shell 0.08.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

{625}Genus 276. _Larnacoma_,[315] n. gen.

_Definition._--#Larnacida# with double lentelliptical cortical shell, without radial spines. Medullary shell double, _Larnacilla_-shaped.

The genus _Larnacoma_ has originated from the nearly allied _Larnacalpis_ by duplication of the cortical shell. Whilst in both genera the connection between the _Larnacilla_-shaped medullary shell and the primary cortical shell is the same, many short radial beams arise from the surface of the latter in _Larnacoma_, which at constant equal distances from it unite by a network forming the secondary or outer cortical shell. It differs from the similar Druppulida (_Cromyodruppa_) by the sagittal flattening of the lentelliptical shell and the _Larnacilla_-form of the double medullary shell.

1. _Larnacoma lentellipticum_, n. sp.

Shell with smooth surface and elliptical perimeter, one and a third times as long as broad. All four shells lentelliptical. Distance between the two cortical shells about twice as great as the distance of the inner cortical and outer medullary shell. Network of both outer shells irregular, with large roundish pores, twice to six times as broad as the bars.

_Dimensions._--Length (or principal axis) of the first (innermost) shell 0.03, second 0.08, third 0.16, fourth (outermost) 0.27, breadth (or transverse axis) corresponding--(A) 0.02, (B) 0.05, (C) 0.11, (D) 0.2.

_Habitat._--South Atlantic, Station 323, depth 1900 fathoms.

2. _Larnacoma quadruplex_, n. sp.

Shell with thorny surface and elliptical perimeter, one and a fifth times as long as broad. All four shells lentelliptical. Distance between the two cortical shells somewhat smaller than the distance between the inner cortical and outer medullary shell. Network of both outer shells irregular, with large roundish pores, twice to ten times as broad as the bars.

_Dimensions._--Length of the first shell 0.02, second 0.06, third 0.15, fourth 0.24; breadth corresponding--(A) 0.016, (B) 0.04, (C) 0.11, (D) 0.2.

_Habitat._--South Atlantic, Station 335, depth 1425 fathoms.

3. _Larnacoma hexagonium_, n. sp.

Shell with thorny surface and hexagonal perimeter, as long as broad. All four shells hexagonal, connected by six piercing radial beams (two in the principal axis, four others in two crossed diagonals). Distance between the two cortical shells somewhat greater than the distance between the inner cortical and outer medullary shell. Network of both outer shells subregular, with small circular pores, twice as broad as the bars.

{626}_Dimensions._--Length of the first shell 0.02, second 0.05, third 0.09, fourth 0.16; breadth corresponding--(A) 0.015, (B) 0.035, (C) 0.065, (D) 0.12.

_Habitat._--South Atlantic, west of Tristan da Cunha, Station 332, depth 2200 fathoms.

Genus 277. _Larnacospongus_,[316] n. gen.

_Definition._--#Larnacida# with spongy lentelliptical cortical shell, without radial spines. Medullary shell double, _Larnacilla_-shaped.

The genus _Larnacospongus_ differs from the nearly allied genera _Larnacalpis_ and _Larnacoma_ by the spongy texture of the lentelliptical cortical shell whilst the enclosed medullary shell in both genera is the same trizonal _Larnacilla_-shell. Therefore _Larnacospongus_ (and the following nearly related _Larnacostupa_) can be derived directly by development of a spongy envelop either from _Larnacilla_ and _Larnacalpis_, or from _Trizonium_ and _Amphipyle_. But some species of these spongy genera appear to be derived rather from _Tetrapyle_ or _Pylonium_, perhaps also from _Cubotholus_. Their phylogenetic origin may be explained in different ways.

1. _Larnacospongus larnacillifer_, n. sp.

Cortical shell lentelliptical, one and a half times as long as broad, with rough surface and rather loose spongy framework, directly enclosing a trizonal _Larnacilla_-shell of the same form, but of only one-third its size.

_Dimensions._--Length of the whole shell 0.17, breadth 0.12; length of the medullary shell 0.06, breadth 0.04.

_Habitat._--South Atlantic, east coast of Patagonia, Station 319, surface.

2. _Larnacospongus tetrapylifer_, n. sp.

Cortical shell lentelliptical, one and a third times as long as broad, with thorny surface; composed of an outer envelop of loose spongy framework and an inner lattice-shell with four kidney-shaped gates, like _Tetrapyle;_ the latter encloses a trizonal medullary shell of one-fourth its size.

_Dimensions._--Length of the whole shell 0.22, breadth 0.16; length of the medullary shell 0.045, breadth 0.035.

_Habitat._--South Atlantic, west of Tristan da Cunha, Station 332, surface.

{627}Genus 278. _Larnacostupa_,[317] n. gen.

_Definition._--#Larnacida# with spongy lentelliptical cortical shell, with radial spines on the surface. Medullary shell double, _Larnacilla_-shaped.

The genus _Larnacostupa_ differs from the preceding Larnacospongus only in the possession of radial spines, covering either the whole surface irregularly or disposed in a certain symmetrical order.

1. _Larnacostupa octacantha_, n. sp.

Cortical shell lentelliptical, with thorny surface, and rather dense, irregular, spongy framework, which arises from an inner latticed cortical shell, like that of _Tetrapyle_ or _Pylonium_. This latter is twice as large as the enclosed _Larnacilla_-shell. Eight long and thin, cylindrical, radial spines, opposite in pairs in two diagonal planes. (Seems to be the common _Tetrapyle octacantha_, enveloped by an outer spongy framework mantle.)

_Dimensions._--Length of the whole shell (without spines) 0.22, breadth 0.16; length of the medullary shell 0.06, breadth 0.04.

_Habitat._--Indian Ocean, Madagascar, Rabbe, surface.

2. _Larnacostupa spinosa_, n. sp.

Cortical shell lentelliptical, about one and a half times as long as broad, with very lax and irregular spongy framework, arising from a nearly quadrangular lattice-shell like that of _Tetrapyle_; this latter encloses a _Larnacilla_-shell of half its size. Whole surface covered with thin bristle-like radial spines, of about the length of the shell.

_Dimensions._--Length of the whole shell (without spines) 0.18, breadth 0.12; length of the medullary shell 0.05, breadth 0.035.

_Habitat._--Antarctic Ocean, off Kerguelen, Station 150, surface.

3. _Larnacostupa dendrophora_, n. sp.

Cortical shell nearly spherical, scarcely longer than broad, with lax, irregular spongy framework, arising from a lentelliptical trizonal medullary shell (like _Larnacilla_). Whole surface covered with thin arborescent radial spines, about half as long as the shell, each spine with three to six irregular branches.

_Dimensions._--Length of the whole shell (without spines) 0.15, breadth 0.13; length of the medullary shell 0.07, breadth 0.04.

_Habitat._--Antarctic Ocean, Station 154, surface.

{628}Family XXVI. #PYLONIDA#, Haeckel, 1881 (Pl. 9).

_Pylonida_, Haeckel, 1881, Prodromus, p. 463.

_Definition._--#Larcoidea# with regular, incompletely latticed cortical shell, distinguished by two to four or more symmetrically disposed gates or large fissures remaining between one to three latticed dimensive girdles (perpendicular one to another). One, two, or three concentric systems of such girdles (each system with three girdles) may be developed.

The family #Pylonida# is the most important and interesting among all the #Larcoidea#, not only because it is much richer in different and peculiar forms than the other families of this section, but also because it has direct and very complex relations to all the other families of #Larcoidea#. It is even possible that the Pylonida represent the original ancestral group of the whole section, and that the apparently simpler group of the Larcarida must be derived from the former by retrogressive metamorphosis.

Till the year 1881 the family Pylonida, which here now exhibits ten genera with eighty-six species, was only represented by one single species, accurately described and extensively illustrated by Johannes Müller in 1858, the well known and widely distributed cosmopolitan _Tetrapyle octacantha_ (Abhandl. d. k. Akad. d. Wiss. Berlin, p. 33, Taf. iii.). A slight modification of it was afterwards described by Ehrenberg as _Schizomma quadrilobum_ (Abhandl. d. k. Akad. d. Wiss. Berlin, 1872, Taf. ii. fig. 12). A more accurate description of it, with a good explanation of its characteristic growth, was given in 1879 by Richard Hertwig in his Organismus der Radiolarien (pp. 52-54, Taf. iv. figs. 7, 8; Taf. vi. figs. 2, 5). In my Prodromus (1881, p. 463) I constituted for a large number of allied species, detected in the Challenger collection, the special family Pylonida, and distinguished among it twelve different genera. However, I think it now better to restrict the definition of the family as given in the above definition, and to remove from it a number of genera formerly with it united, as the genera _Triopyle_ and _Hexapyle_, appertaining to the #Discoidea#.

The characteristic type of all true Pylonida is clearly demonstrated by their peculiar mode of growth, the consequence of which is the imperfect lattice-work of the fenestrated larcoid shell. This remarkable growth is effected by the development of elliptical latticed girdles (or rings), which enclose a quite simple, spherical, subspherical, or lentelliptical primordial shell. The girdles lie in three different planes, perpendicular to one another, and are of different sizes; each girdle being somewhat larger than the foregoing and somewhat smaller than the following girdle. Between these latticed girdles remain on the surface of the shell large openings or "gates," which are not closed by network, and it is just the symmetrical disposition and form of these open "gates," separated and enclosed by the fenestrated girdles, which give to the Pylonida their characteristic appearance.

{629}To understand clearly this peculiar constitution of the Pylonida-shell by a system of alternating girdles, developing one after the other it is indispensable to pay careful attention to the three different elliptical dimensive planes, which characterise all #Larcoidea#, and to the three different dimensive axes, which bisect those planes. The girdle which first develops around simple primordial shell or central chamber is the transverse girdle, lying in the equatorial plane; then comes, secondly, the lateral girdle, lying in the lateral plane; and thirdly follows the sagittal girdle, lying in the sagittal or median plane. The three simplest genera of the Pylonida--_Monozonium_, _Dizonium_, _Trizonium_--represent these three different stages, with one, two, or three girdles. These three genera constitute the first subfamily, Haplozonaria (with one single system of girdles); all three girdles lie in the surface of a simple lentelliptical cortical shell.

From this first subfamily the other two subfamilies of Pylonida must be derived, by repetition of the same characteristic process of growth. In the Diplozonaria a second system of girdles has been developed, constituting a second (outer) cortical shell of lentelliptical form, concentric with the first. Also in this second system the transverse girdle is first developed, secondly the lateral girdle, thirdly the sagittal girdle. The three genera _Amphipyle_, _Tetrapyle_ (with _Octopyle_), and _Pylonium_ represent these three different stages of growth.

Commonly the growth of the Pylonida stops with the completion of the second system but sometimes the same process is once repeated and a third system of girdles is formed, constituting a third lentelliptical shell; in this case also the succession of the three latticed girdles is the same; firstly the (third) transverse girdle is formed, secondly the (third) lateral girdle, and thirdly the (third) sagittal girdle. Each of these three girdles of the third system encloses concentrically the corresponding girdles of the second and first system. The three corresponding genera of this third subfamily (Triplozonaria) are _Amphipylonium_, _Tetrapylonium_, and _Pylozonium_. But in general this highest number of girdles (nine) is very seldom reached; commonly the growth of the Pylonida stops with five girdles (_Tetrapyle_ and _Octopyle_). More than nine girdles I have never observed, though there remains the possibility of the apposition of a fourth system owing to the peculiar imperfect character of the growth itself.

The central or primordial chamber of the shell, with which in all Pylonida the shell-building commences, is a quite simple, very small fenestrated shell. Commonly one sees on the surface only five to ten small pores (three to four on the diameter). Its form seems to be sometimes spherical, sometimes elongated, ellipsoidal or probably lentelliptical. It may be originally a small _Cenolarcus_. This simple central chamber, the true "medullary shell" of the small Haplozonaria, is quite different from the medullary shell of the larger Diplozonaria, and particularly of the well-known _Tetrapyle_. The former observers, J. Müller as well as R. Hertwig, have described in these forms also the medullary shell as a simple spherical or oblong body. But a careful {630}comparison of many hundred specimens of them and of their dimensions, has convinced me that this was an error, and that the small spherical or elliptical medullary shell of _Tetrapyle_ and the other Diplozonaria possesses already the same complex structure, composed of a system of three girdles, as _Trizonium_ and _Larnacilla_. Whilst in the Haplozonaria probably the simple central chamber only represents the medullary shell (enclosed in the central capsule), and the first system of girdles (complete in _Trizonium_) the external cortical shell, with the progressive growth this latter becomes enclosed in the central capsule and so constitutes the "trizonal medullary shell" of the Diplozonaria and Triplozonaria.

A very difficult matter is the mode of connection between the cortical and medullary shell. In most of the Pylonida it seems that the first or transverse girdle (in each system) is produced by the formation of two lateral wings or chambers (one on each side of the medullary shell), so that each wing (or half girdle) represents a short and wide, nearly cylindrical tube, the axis of which (with free openings on both poles) is parallel to the principal axis of the medullary shell. In this case (probably the ordinary one) both principal faces of the medullary shell itself (dorsal and ventral face) constitute the middle part of the first girdle whilst its lateral parts are formed by the wings (comparable to the lateral chambers of _Amphitholus_).

In the second case (probably a much rarer one) there is a free ring-shaped space between the medullary shell and the first (transverse) girdle, and both are connected by a small number of very short and small radial beams (R. Hertwig, _loc. cit._, p. 52, line 19 to 21 from above). This mode of connection would be the same as is common between the concentric shells of the #Sphæroidea# and #Prunoidea#. The distinction between these two different modes of connection is often very difficult.

The second or lateral girdle is commonly not in direct connection with the medullary shell, or only by some scattered radial beams (mainly in the principal axis). This lateral guide arises by prolongation of both wings of the transverse girdle in the lateral plane, so that from both sides (right and left) they become united on the poles of the principal axis. The minor axis of the elliptical lateral ring (thus formed) is therefore the major axis of the foregoing (transverse) elliptical ring; the major axes of both are perpendicular one to another. The major axis of the lateral ring is the principal (or longitudinal) axis of the whole body.

The third or sagittal girdle becomes developed from the second almost in the same manner as the second from the first. On both poles of the principal axis two latticed wings arise from the lateral girdle, growing further in the direction of an elliptical ring, which represents the perimeter of the sagittal plane or median plane. These wings are already mentioned by J. Müller as "prominent roofs, protecting the gates of the _Tetrapyle_-shell." If these roofs grow towards the equatorial plane of the shell and become united in pairs on the poles of the sagittal axis, the third girdle becomes {631}complete. R. Hertwig supposes that the minor axis of this sagittal girdle is constantly at the same time the major axis of the lateral girdle, but this is not always the case. Very often the size of both these girdles is nearly the same, or one is not much larger than the other. In this case the principal axis of the body is the major axis of the second as well as of the third girdle.

The characteristic "gates" of the Pylonida, or the large wide openings in their cortical shell, remaining between the crossed latticed girdles, are in general roundish, sometimes nearly circular, commonly more elliptical, kidney-shaped or semilunar, their special form varying much according to the different form of the girdles. The narrowest part of each girdle, or its "isthmus," in the case of the halves of the transverse girdle is commonly at their origin from the medullary shell, in the case of the halves of the lateral girdle at the poles of the principal axis, and in the case of the halves of the sagittal girdle at the poles of the sagittal axis. The number of the gates is quite constant in the different genera. If only one girdle (the transverse) be developed, we find only two large gates, between the two wings on the poles of the principal axis (in _Monozonium_, _Amphipyle_, _Amphipylonium_). In all other cases there are four gates (determining the original name "_Tetrapyle_"), as well if only two or if all three girdles be completed. If two girdles be complete (in _Dizonium_, _Tetrapyle_, _Tetrapylonium_) the four gates lie opposite in pairs on the sagittal faces (two anterior and two posterior gates), and are limited by the transverse and lateral girdles. If all three girdles be complete (in _Trizonium_, _Pylonium_, _Pylozonium_) the four gates lie opposite in pairs on the lateral faces (two dorsal and two ventral gates), and are limited by the sagittal and the transverse girdles. If we turn the shell through an angle of 90°, we have the same aspect as in the former group. A sagittal septum sometimes becomes developed, beginning with two polar beams, rising from the poles of the principal axis. If these polar beams become branched and connected with the middle part of the lateral girdle, we get a latticed vertical septum, which divides the four gates of _Tetrapyle_ into eight gates, _Octopyle_.

The lattice-work of the Pylonida is commonly very variable and irregular, with roundish meshes of very unequal size, therefore without value in the determination of the species. Commonly the outside of the shell is thorny, and often distinguished by larger radial spines, symmetrically disposed. We can separate these into two groups; "dimensive" spines, lying in one of the three dimensive axes (principal, transverse, or sagittal), and "diagonal" spines, lying crossed in pairs in diagonal axes. Among these latter eight diagonal wing-spines, which arise from the lateral edges of the four gates, are particularly remarkable; they are not only characteristic of _Tetrapyle octacantha_, but also of a large number of other Pylonida, and form the starting-point for many specific forms.

The shell of the Pylonida is characterised by extraordinary variability and great {632}inclination to individual abnormalities, formation of varieties and transitions into other families, hence derived, as Larnacida, Tholonida, Lithelida, &c.

The central capsule in all Pylonida, in which I could observe it, was a true lentellipsis (or a "triaxial ellipsoid" in the geometrical sense, with the three unequal isopolar axes of the "rhombic octahedron"). In the living Pylonida it is commonly coloured pink or scarlet. During growth its dimensions are probably more or less changed, and perhaps the axes alternate. Regarding the relation of the central capsule to the skeleton, we can distinguish two different groups, quite as in the nearly allied Larnacida. In the Haplozonaria (as also in the Larnacillida) the central capsule encloses only the central chamber and is enveloped by the first system of girdles, whereas in the Diplozonaria and Triplozonaria (as in the Larnacalpida) that "trizonal shell" becomes enclosed (as the "medullary shell") in the central capsule, which is now enveloped by the second system of girdles as the "cortical shell."

_Synopsis of the Genera of Pylonida._

------------------------------------------------------------------------- I. Subfamily Haplozonaria. One system of girdles. Medullary shell simple, spherical or lentelliptical; cortical shell simple, with one, two, or three girdles. ------------------------------------------------------------------------- Cortical shell only with one latticed (transverse) girdle, 279. _Monozonium_.

Cortical shell with two perfect girdles (transverse and lateral), 280. _Dizonium_.

Cortical shell with three perfect girdles (transverse, lateral, and sagittal), 281. _Trizonium_. ------------------------------------------------------------------------- II. Subfamily Diplozonaria. Two systems of concentric girdles. Medullary shell trizonal, with three perfect girdles; cortical shell simple, with one, two or three girdles. ------------------------------------------------------------------------- Cortical shell only with one perfect (transverse) girdle, 282. _Amphipyle_.

Cortical shell with two { Four gates simple, 283. _Tetrapyle_. perfect girdles (the { transverse and lateral).{ Four gates bisected by { a sagittal septum, 284. _Octopyle_.

Cortical shell with three perfect girdles (transverse, lateral, and sagittal), 285. _Pylonium_. ------------------------------------------------------------------------- III. Subfamily Triplozonaria. Three systems of concentric girdles. Medullary shell trizonal, with three perfect girdles, quite as the inner cortical shell; outer cortical shell with one, two, or three girdles. ------------------------------------------------------------------------- Outer cortical shell (third system) only with one perfect (transverse) girdle, 286. _Amphipylonium_.

Outer cortical shell with two perfect girdles (transverse and lateral), 287. _Tetrapylonium_.

Outer cortical shell with three perfect girdles (transverse, lateral, and sagittal), 288. _Pylozonium_.

Subfamily 1. HAPLOZONARIA, Haeckel.

_Definition._--#Pylonida# with one single system of fenestrated girdles (with one, two, or three girdles, lying in one lentelliptical face).

{633}Genus 279. _Monozonium_,[318] n. gen.

_Definition._--#Pylonida# with simple, spherical or subspherical, central chamber, surrounded by one single (transverse) latticed girdle.

The genus _Monozonium_ is the most simple and primitive of all Pylonida, and may be regarded as their common ancestral form; it may probably be derived phylogenetically either directly from _Cenosphæra_ or from _Lentellipsis_, either by apposition of two imperfect lateral chambers, or by surrounding it with an equatorial latticed girdle. This transverse girdle is composed of three parts, the central chamber and two lateral wings, which represent two short hollow latticed tubes, the axes of which are parallel to the principal axis. On both principal sides (on the anterior and posterior faces) there are two large open gates as in _Amphipyle_. If we imagine the openings of the tube-shaped lateral wings closed by lattice-work, _Monozonium_ becomes transformed into _Tholartus_, the most simple form of Tholonida. Probably in all Pylonida the ontogeny of the shell begins with the formation of a _Monozonium_.

Subgenus 1. _Monozonaris_, Haeckel.

_Definition._--Shell smooth or rough, without radial spines or thorns.

1. _Monozonium primordiale_, n. sp.

Central chamber of the shell spherical, smooth, with three to four pores on the half equator. Both wings of the girdle of the same breadth, but of twice the length of the central chamber, with three to four longitudinal rows of pores. No radial spines.

_Dimensions._--Diameter of the central chamber 0.02; breadth of the wings 0.02, length 0.04; pores and bars 0.003.

_Habitat._--Pacific, central area, Station 271, surface.

2. _Monozonium alatum_, n. sp. (Pl. 9, fig. 1).

Central chamber of the shell lentelliptical, smooth, one and a half times as long as broad, with three to four pores on the half equator. Both wings of the girdle twice as broad, and somewhat longer than the central chamber, with five to six longitudinal rows of pores. No radial spines.

_Dimensions._--Length of the central chamber 0.03, breadth 0.02; breadth of the wings 0.04, length 0.05; pores and bars 0.004.

_Habitat._--North Pacific, Station 241, surface.

_Monozonium hartingii_ = _Haliomma amphiaspis_, Harting, 1863 (L. N. 18, p. 15, pl. 2, fig. 43).

{634}Subgenus 2. _Monozonitis_, Haeckel.

_Definition._--Shell with radial spines or thorns, symmetrically disposed.

3. _Monozonium pleurostylum_, n. sp.

Central chamber spherical, smooth, with four to five pores on the half equator. Both wings of the girdle of the same breadth, but somewhat longer than the central chamber, with four to five longitudinal rows of pores. On the poles of the lateral axis two opposite strong conical spines (one in the middle of each wing).

_Dimensions._--Diameter of the central chamber 0.025; breadth of the wings 0.025, length 0.03; pores and bars 0.005.

_Habitat._--Pacific, central area, Station 265, surface.

4. _Monozonium amphistylum_, n. sp.

Central chamber lentelliptical, one and a half times as long as broad, with three to four pores on the half equator. Breadth and length of each wing somewhat greater than that of the central chamber. On the latter two strong conical spines, opposite on the poles of the principal or longitudinal axis.

_Dimensions._--Length of the central chamber 0.03, breadth 0.02; breadth of the wings 0.025, length 0.04; pores and bars 0.004.

_Habitat._--South Atlantic, Station 332, surface.

5. _Monozonium staurostylum_, n. sp.

Central chamber lentelliptical, one and a third times as long as broad, with four to five pores on the half equator. Both wings of the girdle have the same breadth, but one and a half times the length of the central chamber. Four conical radial spines, two opposite on the poles of the lateral, two on the poles of the principal axis.

_Dimensions._--Length of the central chamber 0.028, breadth 0.021; breadth of the wings 0.02, length 0.04.

_Habitat._--South Pacific, Station 295, surface.

Genus 280. _Dizonium_,[319] n. gen.

_Definition._--#Pylonida# with simple, spherical or subspherical, central chamber, surrounded by two crossed latticed girdles, one smaller (primary) transverse and one larger (secondary) lateral girdle.

The genus _Dizonium_ differs from the preceding _Monozonium_ in the possession of two crossed elliptical lattice-girdles. The smaller girdle, immediately surrounding the {635}central chamber, is the transverse girdle (the single girdle of _Monozonium_). On the poles of its major axis (the transverse axis) it is connected with the larger girdle, the elliptical perimeter of which circumscribes the lateral plane. The minor axis of this latter is the major axis of the former. Between the two crossed girdles remain four larger openings or gates, quite as in _Tetrapyle_. But whilst in _Tetrapyle_ the enclosed medullary shell is a trizonal _Larnacilla_-shell, here in _Dizonium_ it is a simple spherical or lentelliptical chamber.

Subgenus 1. _Dizonaris_, Haeckel.

_Definition._--Shell smooth or rough, without radial spines or thorns.

1. _Dizonium circulare_, n. sp.

Central chamber of the shell spherical, smooth, with four to five pores on the half equator. Lateral girdle circular, three times as broad as the former. Four gates semilunar, twice as broad as high. No radial spines.

_Dimensions._--Diameter of the central chamber 0.02, of the lateral girdle 0.06; height of the gates 0.02, breadth 0.04.

_Habitat._--Pacific, central area, Station 274, surface.

2. _Dizonium ellipticum_, n. sp.

Central chamber of the shell elliptical, smooth, with three to four pores on the half equator. Lateral girdle elliptical, three times as long and broad as the central chamber. Four gates kidney-shaped, twice as broad as high. No radial spines.

_Dimensions._--Length of the central chamber 0.03, breadth 0.02; length of the lateral girdle 0.09, breadth 0.06; height of the gates 0.02, breadth 0.038.

_Habitat._--South Pacific, Station 288, surface.

3. _Dizonium transversum_, n. sp.

Central chamber of the shell spherical, rough, with five to six pores on the half equator. Lateral girdle transverse-elliptical, so that its longer axis corresponds to the lateral axis of the transverse girdle, and equals four times the diameter of the central chamber. Four gates kidney-shaped, four times as broad as high. No radial spines.

_Dimensions._--Diameter of the central chamber 0.02; length of the lateral girdle 0.05, breadth 0.08; height of the gates 0.01, breadth 0.04.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

{636}Subgenus 2. _Dizonitis_, Haeckel.

_Definition._--Shell with radial spines or thorns, symmetrically disposed.

4. _Dizonium pleuracanthum_, n. sp. (Pl. 9, fig. 2).

Central chamber of the shell nearly spherical, smooth. Lateral girdle elliptical, one and a third times as long as broad, three times as long as the central chamber. Four gates transverse-elliptical, one and a half times as broad as high. Two conical spines, opposite on the poles of the lateral axis.

_Dimensions._--Diameter of the central chamber 0.03; length of the lateral girdle 0.1, breadth 0.075; height of the gates 0.026, breadth 0.04.

_Habitat._--Western Tropical Pacific, Station 224, depth 1850 fathoms.

5. _Dizonium amphacanthum_, n. sp.

Central chamber elliptical. Lateral girdle elliptical, twice as long as broad. Four gates heart-shaped, about as high as broad. Two conical spines, opposite on the poles of the principal axis.

_Dimensions._--Length of the central chamber 0.03, breadth 0.02; length of the lateral girdle 0.1, breadth 0.05; height and breadth of the gates 0.03.

_Habitat._--Pacific, central area, Station 270, depth 2925 fathoms.

6. _Dizonium stauracanthum_, n. sp. (Pl. 9, fig. 3).

Central chamber spherical. Lateral girdle elliptical, one and a third times as long as broad. Four gates elliptical, one and a half times as broad as high, halved by an axial beam (as in _Octopyle_). Four conical radial spines opposite in pairs, two on the poles of the principal, two on the poles of the transverse axis.

_Dimensions._--Diameter of the central chamber 0.025; length of the lateral girdle 0.09, breadth 0.06; height of the gates 0.024, breadth 0.036.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

7. _Dizonium octacanthum_, n. sp.

Central chamber spherical. Lateral girdle elliptical, one and a half times as long as broad. Four gates kidney-shaped, twice as broad as high. Eight radial spines, opposite in pairs in two crossed diagonal planes.

_Dimensions._--Diameter of the central chamber 0.02; length of the lateral girdle 0.075, breadth 0.05; height of the gates 0.02, breadth 0.04.

_Habitat._--Pacific, central area, Station 272, surface.

{637}Genus 281. _Trizonium_,[320] n. gen.

_Definition._--#Pylonida# with simple, spherical or subspherical, central chamber, surrounded by three latticed girdles, one smaller (primary) transverse, one larger (secondary) lateral, and one (tertiary) sagittal girdle.

The genus _Trizonium_ represents the most highly developed form of the Haplozonaria, with three complete elliptical latticed girdles, crossed at right angles and lying in the perimeter of the three dimensive planes. Commonly the first (transverse) girdle is the smallest, immediately connected with the spherical or lentelliptical central chamber. The minor axis of the second (lateral) girdle is identical with the major axis of the first girdle. The third (sagittal) girdle is either larger than both others, or intermediate between them. If the four gates between the girdles become afterwards closed by lattice-work, the "trizonal shell" of _Trizonium_ passes over into the typical _Larnacilla_, the ancestral form of a great many #Larcoidea#.

Subgenus 1. _Trizonaris_, Haeckel.

_Definition._--Shell smooth or rough, without radial spines or thorns.

1. _Trizonium tricinctum_, n. sp. (Pl. 9, fig. 4).

Central chamber of the shell elliptical. Lateral girdle elliptical, one and a half times as long as broad. Four gates kidney-shaped, one and a half times as broad as high. Ten to eleven pores on the half equator, fourteen to sixteen on the half meridian of the lentelliptical shell. No radial spines on the surface.

_Dimensions._--Length of the central chamber 0.024, breadth 0.016; length of the lateral girdle 0.075, breadth 0.05; height of the four gates 0.026, breadth 0.04.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

2. _Trizonium constrictum_, n. sp.

Central chamber elliptical. Lateral girdle violin-shaped, on both sides in the middle constricted, twice as long as broad. Four gates transverse-elliptical, twice as broad as high. Eight to nine pores on the half equator, twelve to thirteen on the half meridian. No radial spines.

_Dimensions._--Length of the central chamber 0.03, breadth 0.02; length of the lateral girdle 0.09, breadth (in the middle) 0.045; height of the gates 0.022, breadth 0.044.

_Habitat._--Pacific, central area, Station 263, surface.

{638}3. _Trizonium hexagonium_, n. sp.

Central chamber spherical. Lateral girdle hexagonal, with parallel sides, twice as long as broad. Four gates triangular, twice as broad as high. Eleven to twelve pores on the half equator, sixteen to eighteen on the half meridian. No radial spines.

_Dimensions._--Diameter of the central chamber 0.025; length of the lateral girdle 0.08, breadth 0.04; height of the gates 0.018, breadth 0.036.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

4. _Trizonium octogonium_, n. sp.

Central chamber spherical. Lateral girdle octagonal; two lateral sides of the octagon twice as long as the two polar sides and the four diagonal sides. Four gates hexagonal, one and a half times as broad as high. Nine to ten pores on the half equator, twelve to fourteen on the half meridian. No radial spines.

_Dimensions._--Diameter of the central chamber 0.02; length of the lateral girdle 0.01, breadth 0.07; height of the gates 0.04, breadth 0.06.

_Habitat._--Indian Ocean, surface; Ceylon, Haeckel.

Subgenus 2. _Trizonitis_, Haeckel.

_Definition._--Shell with radial spines or thorns, symmetrically disposed.

5. _Trizonium pleurobelonium_, n. sp.

Central chamber spherical. Lateral girdle elliptical, one and a third times as long as broad. Four gates nearly circular. Ten to eleven pores on the half equator, fifteen to sixteen on the half meridian. Two opposite conical spines on the poles of the lateral axis.

_Dimensions._--Diameter of the central chamber 0.02; length of the lateral girdle 0.08, breadth 0.06; height and breadth of the gates 0.025.

_Habitat._--South Atlantic, off Buenos Ayres, Station 323, depth 1900 fathoms.

6. _Trizonium amphibelonium_, n. sp.

? _Echinosphæra datura_, R. Hertwig (partim), 1879, Organismus d. Radiol., p. 54, Taf. iv. figs. 8, 8_a_.

Central chamber lentelliptical. Lateral girdle lanceolate, nearly one and a half times as long as broad. Four gates subtriangular. Eight to nine pores on the half equator, ten to twelve on the half meridian. Two opposite thin and long spines on the poles of the principal axis, numerous shorter radial spines on the whole surface. Possibly this species is identical with one of the three different #Larcoidea# which R. Hertwig has described as _Echinosphæra datura_. His fig. 8, Taf. iv., would be the aspect from the sagittal girdle.

{639}_Dimensions._--Length of the central chamber 0.04, breadth 0.025; length of the lateral girdle 0.11, breadth 0.08; height of the gates 0.03, breadth 0.04.

_Habitat._--Mediterranean (Genoa), Haeckel, (Messina), R. Hertwig, surface; Tropical Atlantic, Station 348, surface.

7. _Trizonium staurobelonium_, n. sp.

Central chamber spherical, with two opposite polar beams. Lateral girdle elliptical, one and a half times as long as broad. Four gates transverse-elliptical, half as high as broad. Ten to eleven pores on the half equator, fourteen to fifteen on the half meridian. Four conical radial spines, two on the poles of the lateral, two on the poles of the principal axis.

_Dimensions._--Diameter of the central chamber 0.02; length of the lateral girdle 0.075, breadth 0.05; height of the gates 0.014, breadth 0.028.

_Habitat._--North Pacific, Station 241, depth 2300 fathoms.

8. _Trizonium hexabelonium_, n. sp.

Central chamber elliptical. Lateral girdle hexagonal, one and a half times as long as broad. Four gates rhombic, two-thirds as high as broad. Eight to nine pores on the half equator, twelve to thirteen on the half meridian. Six radial spines in the lateral plane, opposite in pairs on the six corners of the lateral girdle (two principal and four diagonal).

_Dimensions._--Length of the central chamber 0.024, breadth 0.018; length of the lateral girdle 0.06, breadth 0.04; height of the gates 0.02, breadth 0.03.

_Habitat._--Pacific, central area, Station 263, depth 2650 fathoms.

9. _Trizonium octobelonium_, n. sp.

Central chamber elliptical. Lateral girdle hexagonal, one and one-third times as long as broad. Four gates kidney-shaped or nearly rhombic, twice as broad as high. Eleven to twelve pores on the half equator, sixteen to seventeen on the half meridian. Eight radial spines, opposite in pairs in two crossed diagonal planes. (An intermediate stage between _Dizonium octacanthum_ and _Amphipyle octostyle_.)

_Dimensions._--Length of the central chamber 0.03, breadth 0.024; length of the lateral girdle 0.09, breadth 0.07; height of the gates 0.025, breadth 0.05.

_Habitat._--Indian Ocean, Madagascar, Rabbe, surface.

10. _Trizonium decabelonium_, n. sp.

Central chamber elliptical. Lateral girdle hexagonal, one and a half times as long as broad. Four gates rhombic, twice as broad as high. Twelve to thirteen pores on the half equator, seventeen to eighteen on the half meridian. Ten radial spines, two opposite on the two poles of the principal axis, eight others opposite in pairs in two crossed diagonal planes.

{640}_Dimensions._--Length of the central chamber 0.04, breadth 0.03; length of the lateral girdle 0.12, breadth 0.08; height of the gates 0.03, breadth 0.06.

_Habitat._--North Atlantic, Station 353, surface.

11. _Trizonium dodecabelos_, n. sp.

Central chamber spherical. Lateral girdle octagonal, nearly twice an long as broad. Four gates hexagonal, one and a half times as broad as high. Nine to ten pores on the half equator, fifteen to sixteen on the half meridian. Twelve radial spines, four in the lateral plane, in pairs on both sides of the poles of the principal axis, eight others opposite in pairs in two crossed diagonal axes.

_Dimensions._--Diameter of the central chamber 0.025; length of the lateral girdle 0.1, breadth 0.06; height of the gates 0.033, breadth 0.05.

_Habitat._--Pacific, central area, Station 272, surface.

Subfamily 2. DIPLOZONARIA, Haeckel.

_Definition._--#Pylonida# with two concentric systems of fenestrated girdles, lying in two concentric lentelliptical faces (every one system with one to three girdles, lying in one lentelliptical face).

Genus 282. _Amphipyle_,[321] Haeckel, 1881, Prodromus, p. 463.

_Definition._--#Pylonida# with trizonal lentelliptical medullary shell, surrounded by one single (transverse) latticed cortical girdle.

The genus _Amphipyle_ opens the large series of Diplozonaria, comprising all Pylonida, the shell of which is composed of two concentric systems of latticed girdles; the first system constituting the characteristic "trizonal medullary shell" or "_Larnacilla_-shell;" the second system composed of one to three girdles of the second order. The first system lies inside, the second outside the central capsule. In _Amphipyle_ only the first (transverse) girdle of the second system becomes developed, and therefore on both poles of the principal axis are two large open gates. _Amphipyle_ repeats the two-winged form of _Monozonium_; but whilst the medullary shell in this latter is a simple central chamber, it is here a trizonal _Larnacilla_-shell.

Subgenus 1. _Amphipylissa_, Haeckel.

_Definition._--Cortical shell smooth or thorny, but without large, symmetrically disposed spines.

{641}1. _Amphipyle aceros_, n. sp.

Cortical shell quite smooth, without any spines or thorns. Both lateral wings (or opposite half girdles) semilunar, with convex lateral crest, three times as long as broad; twice as broad as the trizonal lentelliptical medullary shell.

_Dimensions._--Length of the medullary shell 0.05, breadth 0.03; length of each lateral wing (or principal dimension of the latticed girdle) 0.18, breadth of it (or transverse dimension of each girdle-tube) 0.06.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

2. _Amphipyle stenoptera_, n. sp.

Cortical shell smooth, without spines. Both lateral wings of the same breadth as the lentelliptical medullary shell, but five times as long as broad, prolonged on both ends into cylindrical latticed tubes, with rectilinear lateral crest.

_Dimensions._--Length of the medullary shell 0.06, breadth 0.04; length of each cylindrical lateral wing 0.2, breadth 0.04.

_Habitat._--South Atlantic, off Ascension Island, Station 343, surface.

3. _Amphipyle platyptera_, n. sp.

Cortical shell thorny, but without larger spines. Both lateral wings nearly triangular, very broad and short, four times as broad as the medullary shell between them, and only twice as long as broad, with rectilinear lateral crest.

_Dimensions._--Length of the medullary shell 0.05, breadth 0.25; length of each lateral wing 0.18, breadth 0.09.

_Habitat._--Indian Ocean, Ceylon, Haeckel, surface.

Subgenus 2. _Amphipylura_, Haeckel.

_Definition._--Cortical shell armed with large, symmetrically disposed spines.

4. _Amphipyle amphiceros_, n. sp.

Cortical shell with two conical spines on the poles of the longitudinal axis (of the lentelliptical medullary shell), without other large spines, but with small thorns on the surface; two to three longitudinal rows of irregular, roundish pores on each half wing of the cortical girdle.

_Dimensions._--Length of the medullary shell (or principal axis) 0.06, breadth (or transverse axis) 0.04; length of each lateral wing 0.2, breadth of it 0.05.

_Habitat._--Western Tropical Pacific, Station 222, surface.

{642}5. _Amphipyle tetraceros_, n. sp. (Pl. 9, fig. 5).

Cortical shell with smooth surface, and with four strong conical spines in the lateral plane, opposite in pairs on the ends of the concave lateral crests (one pair on the end-points of the lateral line of each wing); four to five longitudinal rows of irregular, roundish pores on each half wing of the cortical girdle. Surface of the medullary shell spiny.

_Dimensions._--Length of the medullary shell 0.08, breadth of the same 0.05; length of each lateral wing 0.16, breadth 0.04.

_Habitat._--Pacific, central area, Station 271, surface.

6. _Amphipyle stauroceros_, n. sp.

Cortical shell with four strong conical spines, two on the poles of the longitudinal axis, two opposite on the poles of the transverse axis (perpendicular to the former). Three to four longitudinal rows of irregular, roundish pores on each half wing of the cortical girdle, about six pores in the longest row. Lateral crest convex.

_Dimensions._--Length of the medullary shell 0.05, breadth 0.03; length of each lateral wing 0.15, breadth 0.08.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

7. _Amphipyle amphiptera_, n. sp. (Pl. 9, fig. 7).

Cortical shell with six strong conical spines, lying in the lateral plane in three parallel longitudinal lines; two on the poles of the longitudinal axis, two others on the poles of the wing axes, which are parallel to the former. Two to three longitudinal rows of irregular, roundish pores on each half wing of the cortical girdle, about eight pores in the longest row. Lateral crest convex, thorny.

_Dimensions._--Length of the medullary shell 0.06, breadth 0.045; length of each lateral wing 0.09, breadth 0.035.

_Habitat._--Western Tropical Pacific, Station 224, surface.

8. _Amphipyle hexaceros_, n. sp.

Cortical shell thorny, with six strong conical spines lying in the lateral plane; two on the poles of the lateral axis (in the central point of each wing), two on the end-points of the triangular crest of each wing (on both poles of the longitudinal wing-axis).

_Dimensions._--Length of the medullary shell 0.06, breadth 0.04; length of each lateral wing 0.13, breadth 0.07.

_Habitat._--South Pacific, Station 291, surface.

{643}9. _Amphipyle octoceros_, n. sp.

Cortical shell thorny, with eight long radial spines, lying in two crossed diagonal planes, opposite in pairs. These eight horns are the prolongations of the anterior and posterior edges of each wing, on both sides of its lateral plane; they are of great importance, as appearing (by heredity) in many other Pylonida (_e.g._, in _Tetrapyle octacantha_). Lateral crest of each wing without spines, slightly convex.

_Dimensions._--Length of the medullary shell 0.07, breadth 0.05; length of each lateral wing 0.15, breadth 0.06.

_Habitat._--Pacific, central area, Stations 270 to 274, surface.

10. _Amphipyle cladoceros_, n. sp.

Cortical shell spiny, with eight strong ramified radial spines, lying in the same two crossed diagonal planes as in the preceding species. It differs from this in the ramification of the eight horns, which bear six to nine irregular lateral branches, partly simple, partly bifurcate. Lateral crest of each wing spiny, convex.

_Dimensions._--Length of the medullary shell 0.06, breadth 0.045; length of each lateral wing (without spines) 0.2, breadth 0.09.

_Habitat._--Indian Ocean, surface, Madagascar, Rabbe.

11. _Amphipyle decaceros_, n. sp.

Cortical shell spiny, with ten strong conical spines; eight lying in two crossed diagonal planes, in the same disposition (opposite in pairs) as in both preceding species; two others opposite on the poles of the principal axis, arising from both poles of the medullary shell (columella-beams). Spiny crest of the wings convex, semilunar.

_Dimensions._--Length of the medullary shell 0.04, breadth 0.03; length of each lateral wing 0.12, breadth 0.04.

_Habitat._--North Atlantic, Station 354, surface.

12. _Amphipyle dodecaceros_, n. sp.

Cortical shell thorny, with twelve large cylindrical spines; eight lying in two crossed diagonal planes, in the same disposition (opposite in pairs) as in the three preceding species; four others crossed at right angles in the lateral plane, two opposite on the poles of the principal, two on the poles of the lateral axis (the latter shorter). Both lateral wings nearly rhombic.

_Dimensions._--Length of the medullary shell 0.06, breadth 0.04; length of the lateral wings 0.15, breadth 0.05.

_Habitat._--South Atlantic, coast of Brazil, Rabbe, surface.

{644}13. _Amphipyle callizona_, n. sp. (Pl. 9, fig. 6).

Cortical shell smooth, with sixteen strong and short conical spines, lying opposite in pairs in two crossed diagonal planes; each lateral wing four-sided prismatic, its lateral face concave, both ends truncated, and each end provided with four divergent spines. Length of the wings somewhat greater, but breadth smaller, than that of the medullary shell.

_Dimensions._--Length of the medullary shell 0.07, breadth 0.05; length of the lateral wings 0.09, breadth 0.03.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

Genus 283. _Tetrapyle_,[322] J. Müller, 1858, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 154.

_Definition._--#Pylonida# with trizonal lentelliptical medullary shell, surrounded by two crossed latticed cortical girdles, one smaller (primary) transverse, and one larger (secondary) lateral girdle. Four gates between the two cortical girdles simple, without a sagittal septum.

The genus _Tetrapyle_, till 1881 the only known genus of the whole family, was founded by Johannes Müller in 1858, and clearly illustrated by the Mediterranean (and common cosmopolitan) _Tetrapyle octacantha_, hitherto the best known type of this family. Afterwards (1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 832) Ehrenberg founded the genus _Schizomma_ for a nearly allied form, which exhibits only slight specific differences (compare my Monograph, 1862, p. 434). Some good remarks on the structure of this typical genus and its relations to other Pylonida are to be found in Richard Hertwig's Organismus, &c., 1879, p. 52, but the true trizonal structure of the medullary shell in this genus was not recognised by him, so that his description agrees more with _Dizonium_. We confine here the genus _Tetrapyle_ to those Pylonida for which _Tetrapyle octacantha_ of J. Müller remains the determining type; the cortical shell is composed only of two perfect lattice-girdles (the transverse and lateral), between which four wide gates remain open. This structure is similar to that of _Dizonium_; but whilst here the medullary shell is a simple central chamber, in _Tetrapyle_ it is a complete trizonal or _Larnacilla_-shell.

Subgenus 1. _Tetrapylissa_, Haeckel.

_Definition._--Cortical shell smooth or thorny, but without large, symmetrically disposed spines.

{645}1. _Tetrapyle circularis_, n. sp. (Pl. 9, fig. 8).

Cortical shell rough, without radial spines. Lateral girdle circular, therefore the longitudinal axis is equal to the transverse. Four gates kidney-shaped, twice as broad as high. In each half wing of the transverse girdle six to seven longitudinal rows of irregular, roundish pores.

_Dimensions._--Medullary shell 0.05 long, 0.04 broad; cortical shell 0.15 long and broad; gates 0.04 high, 0.08 broad.

_Habitat._--Pacific, central area, Station 263, surface.

2. _Tetrapyle circopyle_, n. sp.

Cortical shell smooth, without radial spines. Lateral girdle elliptical, one and a half times as long as broad. Four gates nearly circular. On each half wing of the transverse girdle four to five rows of subregular, circular pores. (Similar to _Tetrapyle pleuracantha_, Pl. 9, fig. 9, but without lateral spines.)

_Dimensions._--Medullary shell 0.04 long, 0.03 broad; cortical shell 0.16 long, 0.11 broad; gates 0.05 high and broad.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

3. _Tetrapyle quadriloba_, Haeckel.

_Tetrapyle quadriloba_, Haeckel, 1862, Monogr. d. Radiol., p. 436.

_Schizomma quadrilobum_, Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 815; Abhandl. d. k. Akad. d. Wiss. Berlin, 1872, Taf. x. figs. 12-14.

Cortical shell thorny, without regular, radial spines. Lateral girdle elliptical, one and a half times as long as broad. Four gates nearly circular. On each half wing of the transverse girdle three to four rows of irregular, roundish pores.

_Dimensions._--Medullary shell 0.06 long, 0.04 broad; cortical shell 0.16 long, 0.1 broad; diameter of the gates 0.05.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian Ocean, Pacific, surface.

4. _Tetrapyle nephropyle_, n. sp.

Cortical shell thorny, without radial spines. Lateral girdle elliptical, one and a third times as long as broad. Four gates kidney-shaped, nearly twice as broad as high, with two prominent polar spines on the poles of the longitudinal axis of the medullary shell. On each half wing of the transverse girdle three to four longitudinal rows of large roundish pores.

_Dimensions._--Medullary shell 0.06 long, 0.04 broad; cortical shell 0.24 long, 0.18 broad; gates 0.05 high, 0.08 broad.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

{646}5. _Tetrapyle cardiopyle_, n. sp.

Cortical shell rough, without radial spines. Lateral girdle with hexagonal contour, nearly cylindrical in the middle part, conical at both ends, twice as long as broad. Four gates heart-shaped, about as high as broad. On each half wing of the transverse girdle three to four longitudinal rows of subregular, polygonal pores.

_Dimensions._--Medullary shell 0.04 long, 0.02 broad; cortical shell 0.14 long, 0.07 broad; gates 0.05 high and broad.

_Habitat._--Eastern Tropical Atlantic, Station 348, depth (2450) fathoms.

Subgenus 2. _Tetrapylura_, Haeckel.

_Definition._--Cortical shell armed with large, symmetrically disposed spines.

6. _Tetrapyle fusiformis_, n. sp.

Cortical shell rough, with two strong conical spines on the poles of the longitudinal axis. Lateral girdle spindle-shaped, one and a half times as long as broad. Four gates kidney-shaped, twice as broad as high. On each half wing of the transverse girdle four to five longitudinal rows of irregular, roundish pores.

_Dimensions._--Medullary shell 0.07 long, 0.05 broad; cortical shell 0.18 long, 0.12 broad; gates 0.04 high, 0.08 broad.

_Habitat._--Western Tropical Atlantic, Mexican Gulf Stream, depth 1500 fathoms, Schaffner.

7. _Tetrapyle pleuracantha_, n. sp. (Pl. 9, fig. 9).

Cortical shell rough, with two strong conical spines on the poles of the transverse axis. Lateral girdle elliptical, one and half times as long as broad. Four gates subcircular or nearly hexagonal, about as high as broad. On each half wing of the transverse girdle three to four longitudinal rows of very irregular pores.

_Dimensions._--Medullary shell 0.045 long, 0.035 broad; cortical shell 0.16 long, 0.11 broad; gates 0.045 high and broad.

_Habitat._--Western Tropical Pacific, off New Guinea, Stations 222 to 224, depths 1850 to 2450 fathoms.

8. _Tetrapyle transversa_, n. sp.

Cortical shell thorny, with two strong conical lateral spines on the poles of the transverse axis. Lateral girdle elliptical, only four-fifths as long as broad. Four gates elliptical, twice as broad as high, with two prominent spines on the poles of the longitudinal axis of the medullary shell. On each half wing of the transverse girdle five to six longitudinal rows of subregular, roundish pores. (Similar to _Octopyle transversa_, but without sagittal septum and with stronger lateral spines.)

{647}_Dimensions._--Medullary shell 0.05 long, 0.035 broad; cortical shell 0.12 long, 0.15 broad; gates 0.03 high, 0.06 broad.

_Habitat._--Southern Pacific, Station 290, surface.

9. _Tetrapyle cruciata_, n. sp.

Cortical shell smooth, with four strong radial spines, two on the poles of the longitudinal axis, two on the poles of the transverse axis. Lateral girdle nearly circular, quite as long as broad. Four gates kidney-shaped, twice as broad as high. On each half wing of the transverse girdle five to six rows of subregular, circular pores.

_Dimensions._--Medullary shell 0.06 long, 0.05 broad; cortical shell 0.16 long and broad; gates 0.05 high, 0.09 broad.

_Habitat._--South Atlantic, Station 330, surface.

10. _Tetrapyle staurophora_, n. sp.

Cortical shell thorny, with four strong radial spines, two on the poles of the longitudinal axis, two on the poles of the transverse axis. Lateral girdle elliptical, one and a half times as long as broad. Four gates nearly hexagonal, quite as high as broad. On each half wing of the transverse girdle three to four longitudinal rows of irregular, roundish pores.

_Dimensions._--Medullary shell 0.06 long, 0.04 broad; cortical shell 0.18 long, 0.12 broad; gates 0.08 high and broad.

_Habitat._--Western Tropical Atlantic, coast of Brazil, Rabbe, surface.

11. _Tetrapyle quadricornis_, n. sp.

Cortical shell thorny, with four strong horn-like curved spines, lying in the lateral plane and converging in pairs towards the poles of the transverse axis. Lateral girdle elliptical, one and a third times as long as broad. Four gates kidney-shaped, twice as broad as high. On each half wing of the transverse girdle four to five rows of irregular, roundish pores. (May be only the young form of _Pylonium quadricorne_, Pl. 9, fig. 14.)

_Dimensions._--Medullary shell 0.05 long, 0.04 broad; cortical shell 0.16 long, 0.12 broad; gates 0.03 high, 0.07 broad.

_Habitat._--Pacific, central area, Stations 270 to 274, surface.

12. _Tetrapyle tetracantha_, n. sp.

Cortical shell thorny, with four strong radial spines lying in the lateral plane and in pairs in its two crossed diagonal axes. Lateral girdle elliptical, constricted in the middle, nearly twice as long as broad. Four gates kidney-shaped, one and a half times as broad as high. On each half wing of the transverse girdle three to four longitudinal rows of large, irregular, roundish pores. {648}(Similar to _Tetrapylonium quadrangulare_, Pl. 49, fig. 15, but without a sagittal girdle and with stronger lateral spines.)

_Dimensions._--Medullary shell 0.06 long, 0.04 broad; cortical shell 0.18 long, 0.1 broad; gates 0.007 high, 0.01 broad.

_Habitat._--North Atlantic, Canary Islands, Station 353, surface.

13. _Tetrapyle quadrigata_, n. sp.

Cortical shell thorny, with four brush-like groups of radial spines on the four diagonal corners of the lateral plane, opposite in pairs in diagonal axes. Lateral girdle nearly square, somewhat broader than long. Four gates kidney-shaped, twice as broad as high. On each half wing of the transverse girdle five to six longitudinal rows of irregular, roundish pores.

_Dimensions._--Medullary shell 0.06 long, 0.04 broad; cortical shell 0.14 long, 0.15 broad; gates 0.03 high, 0.07 broad.

_Habitat._--Pacific, central area, Station 270, surface.

14. _Tetrapyle octacantha_, J. Müller.

_Tetrapyle octacantha_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 33, Taf. ii. figs. 1-6.

_Tetrapyle octacantha_, Haeckel, 1862, Monogr. d. Radiol., p. 435.

_Tetrapyle octacantha_, R. Hertwig, 1879, Organismus d. Radiol., p. 52, Taf. iv. fig. 7, Taf. vi. figs. 2, 5, 5_a._

Cortical shell thorny, with eight long and thin, cylindrical radial spines, lying in two crossed diagonal planes, opposite in pairs. These eight characteristic diagonal spines (or "angular spines") are the same as in _Amphipyle octoceros_ and many other Pylonida, and arise as prolongations of the proximal edges of the four gates (or of the lateral wings on the eight points, where they are intersected by the edges of the lateral ring). This cosmopolitan, widely distributed and very variable species was a long time the only known species of all the Pylonida, and very accurately first described (1858) by Johannes Müller, afterwards (1879) by R. Hertwig. But in the descriptions of these authors also some different species (such as the following) may be confounded with the true typical _Tetrapyle octacantha_. The four gates of this species are transverse-elliptical or almost triangular, nearly twice as broad as high.

_Dimensions._--Length of the medullary shell 0.04, breadth 0.03; length of the cortical shell 0.18, breadth 0.13; height of the gates 0.05, breadth 0.08.

_Habitat._--Cosmopolitan; very common in all warmer seas, Mediterranean, Atlantic, Indian, Pacific, surface.

15. _Tetrapyle cladacantha_, n. sp.

Cortical shell thorny, with eight strong ramified radial spines, lying opposite in pairs in two crossed diagonal planes, as in the preceding species. It differs from this by the peculiar ramification of the eight spines, which bear two to eight simple or furcate lateral branches arising under {649}right angles (already commencing in a transitional variety of _Tetrapyle octacantha_, J. Müller, _loc. cit._, Taf. ii. figs. 5, 6). Four gates transverse-elliptical, one and a half times as broad as high.

_Dimensions._--Medullary shell 0.05 long, 0.04 broad; cortical shell 0.16 long, 0.13 broad; gates 0.05 high, 0.08 broad.

_Habitat._--Mediterranean (Corfu), Haeckel, surface.

16. _Tetrapyle pluteus_, Haeckel.

_Tetrapyle octacantha_, var., J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. iii. figs. 7-12.

Cortical shell thorny, with eight strong radial spines, lying opposite in pairs, as in the two foregoing species. On the distal edge each of the four triangular gates is protected by a prominent roof of lattice-work (or "pluteus"), which arises from the distal part of the lateral girdle and connects the two angular diagonal spines of each gate. Therefore the shell assumes the characteristic form very well represented by J. Müller in his fig. 11 (seen from the lateral side) and fig. 7 (seen from the pole of the principal axis).

_Dimensions._--Medullary shell 0.04 long, 0.03 broad; cortical shell 0.15 long, 0.11 broad; gates 0.045 high, 0.07 broad.

_Habitat._--Mediterranean, Atlantic, Stations 348 to 353, &c., surface.

17. _Tetrapyle turrita_, n. sp. (Pl. 9, fig. 10).

Cortical shell smooth, but with ten strong conical spines, two on the poles of the principal axis, eight others symmetrically distributed on both sides of the distal edge of the four roundish gates, and directed towards the transverse axis. Lateral girdle lanceolate, twice as long as broad.

_Dimensions._--Medullary shell 0.05 long, 0.04 broad; cortical shell 0.2 long, 0.1 broad; gates 0.05 high, 0.07 broad.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

18. _Tetrapyle dodecaceros_, n. sp.

Cortical shell thorny, with twelve stronger conical spines, eight diagonal spines in two crossed planes (as in _Tetrapyle octacantha_), and four others in the lateral plane, in pairs on both sides of a deep sagittal constriction of the quadrangular lateral girdle. Four gates kidney-shaped, twice as broad as high. On each half wing of the transverse girdle five to six longitudinal rows of irregular, roundish pores.

_Dimensions._--Medullary shell 0.06 long, 0.04 broad; cortical shell 0.18 long, 0.14 broad; gates 0.04 high, 0.08 broad.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

{650}Genus 284. _Octopyle_,[323] Haeckel, 1881, Prodromus, p. 464.

_Definition._--#Pylonida# with trizonal lentelliptical medullary shell, surrounded by two crossed, latticed, cortical girdles; one smaller (primary) transverse, and one larger (secondary) lateral girdle. Four gates between the two cortical girdles divided by a sagittal septum into eight gates.

The genus _Octopyle_ comprises those Pylonida which are distinguished from the nearly allied _Tetrapyle_ by the development of a sagittal septum, dividing the four gates of the latter into eight separate gates. The septum begins with the formation of two axial rods or columellæ, which afterwards become branched; the branches communicating one with another and with the middle parts of the lateral girdle (on the poles of the principal axis), there is formed a latticed septum in the sagittal plane, which separates more or less incompletely the right and left halves of the shell. The four gates of _Tetrapyle_ become halved by this septum, and their number doubled.

Subgenus 1. _Octopylissa_, Haeckel.

_Definition._--Cortical shell smooth or thorny, but without larger symmetrically disposed spines.

1. _Octopyle ovulina_, n. sp.

Cortical shell lentelliptical, smooth, without thorns. Lateral girdle elliptical, one and a third times as long as broad. Transverse girdle narrow, with two pores on the isthmus (or on the narrowest part of each quadrant). Sagittal septum as long as the elliptical medullary shell. Eight gates egg-shaped.

_Dimensions._--Length of the medullary shell 0.05, breadth 0.035; length of the cortical shell 0.16, breadth 0.12.

_Habitat._--Pacific, central area, Station 274, surface.

2. _Octopyle quadrata_, n. sp.

Cortical shell thorny, nearly square, of equal length and breadth. Lateral girdle quadrangular, with rounded edges, of equal length and breadth. Transverse girdle narrow, with three pores on the isthmus. Sagittal septum of the same length as the subspherical medullary shell. Eight gates nearly circular.

_Dimensions._--Diameter of the medullary shell 0.04, of the cortical shell 0.14.

_Habitat._--Northern Pacific, Station 244, depth 2900 fathoms.

{651}3. _Octopyle subglobosa_, n. sp.

Cortical shell nearly spherical, thorny, of equal length and breadth. Lateral girdle broad, nearly circular. Transverse girdle broad, with four pores on the isthmus. Sagittal septum shorter than the subspherical medullary shell. Eight gates egg-shaped.

_Dimensions._--Diameter of the medullary shell 0.05, of the cortical shell 0.13.

_Habitat._--Southern Pacific, Station 300, depth 1375 fathoms.

4. _Octopyle transversaria_, n. sp.

Cortical shell thorny, transverse-elliptical. Lateral girdle very broad, one and a third times as broad as long. Transverse girdle also very broad, with five pores on the isthmus. Sagittal septum shorter than the elliptical medullary shell. Eight gates small, roundish.

_Dimensions._--Length of the medullary shell 0.05, breadth 0.04; length of the cortical shell 0.11, breadth 0.15.

_Habitat._--Western Tropical Pacific, Station 224, depth 1850 fathoms.

Subgenus 2. _Octopylura_, Haeckel.

_Definition._--Cortical shell armed with large, symmetrically disposed spines.

5. _Octopyle amphistyle_, n. sp.

Cortical shell smooth, nearly spindle-shaped, about twice as long as broad. Transverse girdle broad, with four large pores on the isthmus. Lateral girdle lanceolate. Sagittal septa about as long as the medullary shell, prolonged at both poles of the principal axis into two opposite, strong, angular spines. Eight gates obliquely quadrangular.

_Dimensions._--Length of the medullary shell 0.07, breadth 0.05; length of the cortical shell 0.2, breadth 0.12.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

6. _Octopyle staurostyle_, n. sp.

Cortical shell nearly rhombic, smooth, one and a half times as long as broad, with four strong, conical, radial spines, two on the poles of the principal axis (as prolongations of the sagittal septa), two others on the poles of the transverse axis. Transverse girdle narrow, with two pores on the isthmus. Sagittal septa longer than the medullary shell. Eight gates triangular.

_Dimensions._--Length of the medullary shell 0.04, breadth 0.03; length of the cortical shell 0.18, breadth 0.12.

_Habitat._--Tropical Atlantic, Station 347, depth 2250 fathoms.

{652}7. _Octopyle tetrastyle_, n. sp.

Cortical shell lentelliptical, with rough surface and four angular radial spines in the lateral plane, opposite in pairs in two crossed diagonals. Lateral girdle nearly rectangular (each angle with one spine), one and a third times as long as broad. Sagittal septum longer than the hexagonal medullary shell. Eight gates egg-shaped.

_Dimensions._--Length of the medullary shell 0.05, breadth 0.03; length of the cortical shell 0.16, breadth 0.12.

_Habitat._--North Atlantic, Station 354, surface.

8. _Octopyle tetraptera_, n. sp.

Cortical shell quadrangular, with thorny surface and four latticed wing-like prolongations on the corners of the quadrangle, opposite in pairs in two crossed diagonals, each wing supported by a strong radial spine. Lateral girdle quadrangular, one and a half times as long as broad. On the isthmus of the transverse girdle four pores. Sagittal septum longer than the hexagonal medullary shell. Eight gates triangular.

_Dimensions._--Length of the medullary shell 0.07, breadth 0.04; length of the cortical shell 0.24, breadth 0.16.

_Habitat._--Pacific, central area, Station 271, surface.

9. _Octopyle stenozona_, n. sp. (Pl. 9, fig. 11).

Cortical shell quadrangular, with thorny surface, and four conical spines in the lateral plane, on the points, where both cortical girdles are crossed. Lateral girdle very narrow, nearly square, with rounded corners, of equal length and breadth. On the isthmus of the narrow transverse girdle only one pore. Sagittal septum of the same length as the subspherical medullary shell. Eight gates irregular roundish or nearly circular.

_Dimensions._--Diameter of the medullary shell 0.04, of the cortical shell 0.14.

_Habitat._--Tropical Atlantic, Station 338, depth 1990 fathoms.

10. _Octopyle euryzona_, n. sp.

Cortical shell nearly quadrangular, very thorny, with four bunches of stronger radial spines on the four corners. Lateral girdle broad, with rounded edges of the quadrangle, little longer than broad. On the isthmus of the broad transverse girdle four pores. Sagittal septum of the same length as the elliptical medullary shell, with many radial beams. Eight gates nearly square.

_Dimensions._--Length of the medullary shell 0.05, breadth 0.035; length of the cortical shell 0.16, breadth 0.14.

_Habitat._--Southern Atlantic, Station 332, depth 2200 fathoms.

{653}11. _Octopyle hexastyle_, n. sp.

Cortical shell nearly rectangular, thorny, with six strong radial spines in the lateral plane, two opposite on the poles of the principal axis (prolongations of the principal beam at the sagittal septum), four others on the truncate corners of the quadrangular lateral girdle, which is one and a half times as long as broad. On the isthmus of the broad transverse girdle three pores. Sagittal septum longer than the hexagonal medullary shell. Eight egg-shaped gates.

_Dimensions._--Length of the medullary shell 0.05, breadth 0.04; length of the cortical shell 0.18, breadth 0.12.

_Habitat._--Northern Atlantic, surface; Canary Islands, Station 9, depth 3150 fathoms.

12. _Octopyle sexangulata_, n. sp. (Pl. 9, fig. 12).

Cortical shell thorny, hexagonal, with six strong conical radial spines on the six corners of the lateral girdle, lying in the lateral plane, two opposite on the poles of the transverse axis, four others in pairs on both sides of the annular sagittal constriction, which is only twice as long as the elliptical medullary shell. Transverse girdle broad, with five pores on the isthmus. Eight gates roundish, smaller than the medullary shell.

_Dimensions._--Length of the medullary shell 0.045, breadth 0.035; length of the cortical shell 0.11, breadth 0.13.

_Habitat._--Pacific, central area, Station 270, surface.

13. _Octopyle octostyle_, n. sp.

Cortical shell elliptical, thorny, with eight long cylindrical radial spines, lying in two crossed diagonal planes, opposite in pairs, quite as in the nearly related _Tetrapyle octacantha_. It differs from this species by the perfect, latticed, vertical sagittal septum, which divides every gate into two triangular halves. Lateral girdle elliptical, one and a third times as long as broad. Transverse girdle on the isthmus with three pores. Septum longer than the elliptical medullary shell.

_Dimensions._--Length of the medullary shell 0.06, breadth 0.045; length of the cortical shell 0.16, breadth 0.12.

_Habitat._--South Pacific, Station 288, surface.

14. _Octopyle obtecta_, n. sp.

Cortical shell quadrangular, thorny, with eight strong diagonal spines, lying in two crossed planes, and arising from the proximal edges of the gates in the same way as in the foregoing species. It differs from this by four prominent latticed roofs, which arise from the distal edge of the gates and connect the diagonal spines of one gate. _Octopyle obtecta_ bears therefore the same relation to _Octopyle octostyle_ that _Tetrapyle pluteus_ does to _Tetrapyle octacantha_.

_Dimensions._--Length of the medullary shell 0.055, breadth 0.04; length of the cortical shell 0.16, breadth 0.12.

_Habitat._--Indian Ocean, surface, Madagascar, Rabbe.

{654}15. _Octopyle decastyle_, n. sp. (Pl. 9, fig. 13).

Cortical shell thorny, nearly quadrangular, with ten stronger radial spines, two opposite on the poles of the principal axis (as prolongations of the axial beams), eight others opposite in pairs in two diagonal planes (as in the foregoing species). Lateral girdle nearly square, with slightly convex lateral faces, slightly concave principal faces. Transverse girdle broad, with four pores on the isthmus. Sagittal septum of the same length as the hexagonal medullary shell. Eight gates elliptical or irregular roundish.

_Dimensions._--Length of the medullary shell 0.05, breadth 0.032; diameter of the cortical shell 0.15.

_Habitat._--Western Tropical Pacific, Station 224, depth 1850 fathoms.

Genus 285. _Pylonium_,[324] Haeckel, 1881, Prodromus, p. 464.

_Definition._--#Pylonida# with trizonal lentelliptical medullary shell surrounded by three crossed latticed cortical girdles, one smaller (primary) transverse, one larger (secondary) lateral, and one (tertiary) sagittal girdle.

The genus _Pylonium_ is the most highly developed among the Diplozonaria, with six complete latticed girdles, three on the medullary shell, three on the cortical shell, the latter corresponding to the former. In each of the two systems the transverse girdle is smaller than the lateral; the sagittal girdle may be smaller or larger than the lateral girdle. _Pylonium_ repeats the typical form of _Trizonium_; but whilst in this latter the medullary centre of the shell is a simple spherical chamber, here in _Pylonium_ it is a true trizonal or _Larnacilla_-shaped medullary shell.

Subgenus 1. _Pylonissa_, Haeckel.

_Definition._--Cortical shell smooth or thorny, but without large, symmetrically disposed spines.

1. _Pylonium circozonium_, n. sp.

Cortical shell thorny, without radial spines; all its three girdles nearly of the same size, subcircular, very narrow, only with one to two rows of pores. Four gates subcircular.

_Dimensions._--Principal axis 0.12, transverse axis 0.11; diameter of the subspherical medullary shell 0.05.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

{655}2. _Pylonium hexazonium_, n. sp.

Cortical shell smooth, without symmetrical radial spines. Transverse girdle elliptical, one and a half times as long as broad. Lateral and sagittal girdles nearly circular. Four gates egg-shaped.

_Dimensions._--Principal axis 0.16, transverse axis 0.15; diameter of the subspherical medullary shell 0.04.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

3. _Pylonium nephropylium_, n. sp.

Cortical shell thorny, without radial spines. All its three girdles elliptical, one and a third times as long as broad. Four gates kidney-shaped, nearly twice as broad as high.

_Dimensions._--Principal axis 0.17, transverse axis 0.13; length of the lentelliptical medullary shell 0.04, breadth 0.03.

_Habitat._--Pacific, central area, Station 273, depth 2350 fathoms.

Subgenus 2. _Pylonura_, Haeckel.

_Definition._--Cortical shell armed with large, symmetrically disposed spines.

4. _Pylonium quadricorne_, n. sp. (Pl. 9, fig. 14).

Cortical shell thorny, with four strong horn-like curved spines in the lateral plane. All its three girdles elliptical, one and a third times as long as broad. Four gates kidney-shaped, twice as broad as high. (This species is a further developmental stage of _Tetrapyle quadricornis_, with perfect sagittal girdle.)

_Dimensions._--Principal axis 0.16, transverse axis 0.12; length of the medullary shell 0.05, breadth 0.04.

_Habitat._--Pacific, central area, Stations 270 to 274, surface; Indian Ocean, Madagascar, Rabbe, surface.

5. _Pylonium octacanthum_, n. sp.

Cortical shell thorny, with eight long and thin cylindrical radial spines, lying in two crossed diagonal planes, opposite in pairs, and arising from the eight points where the transverse girdle is crossed by the lateral girdle. All three girdles elliptical, one and a half times as long as broad; four gates triangular. (This species is a further developmental stage of _Tetrapyle octacantha_, with perfect sagittal girdle.)

_Dimensions._--Principal axis 0.18, transverse axis 0.13; length of the medullary shell 0.03 to 0.04.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

{656}6. _Pylonium stenozonium_, n. sp.

Cortical shell thorny, with eight short conical radial spines, lying in two crossed diagonal planes (as in the foregoing species). All three girdles nearly of the same size, subcircular, very narrow, only with one to two rows of pores. Four gates kidney-shaped.

_Dimensions._--Principal axis 0.15, transverse axis 0.14; diameter of the quadrangular medullary shell 0.04.

_Habitat._--Equatorial Atlantic, Station 347, surface.

Subfamily 3. TRIPLOZONARIA, Haeckel.

_Definition._--#Pylonida# with three concentric systems of fenestrated girdles, lying in three concentric lentelliptical faces (every system with one to three girdles lying in one lentelliptical face).

Genus 286. _Amphipylonium_,[325] Haeckel, 1881, Prodromus, p. 463.

_Definition._--#Pylonida# with trizonal lentelliptical medullary shell, surrounded by a double latticed cortical shell; inner cortical shell _Pylonium_-shaped, with three perfect crossed girdles; outer cortical shell only represented by a single (transverse) girdle.

The genus _Amphipylonium_ opens the series of Triplozonaria, or of those Pylonida in which the shell is composed of three concentric systems of latticed girdles. The first (and innermost) system represents the complete trizonal medullary shell, which is probably a lentelliptical _Larnacilla_-shell. The first and intermediate system is formed of a complete trizonal cortical shell of the same form, but much larger (like _Pylonium_). The third (and outermost) system is represented by one to three latticed girdles, corresponding to the former and forming an outer or second cortical shell. In _Amphipylonium_ (as the most simple form of the Triplozonaria) there is only developed the first (transverse) girdle of the third system. It repeats therefore the form of _Amphipyle_, the cortical shell of which is here double (Prodromus, 1881, p. 463).

1. _Amphipylonium semilunare_, n. sp.

Inner cortical shell lentelliptical, one and a half times as long as broad, with smooth surface and four semilunar gates. Transverse girdle of the outer cortical shell with two smooth semilunar wings, with convex, smooth lateral crests; each wing as broad as the transverse girdle of the inner cortical shell and twice as long as its lateral girdle.

_Dimensions._--Length of the lentelliptical medullary shell 0.04, breadth 0.03; length of the inner cortical shell 0.15, breadth 0.1; length of each lateral wing of the outer cortical shell 0.3, breadth 0.1.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

{657}2. _Amphipylonium spinosissimum_, n. sp.

Inner cortical shell lentelliptical, one and a third times as long as broad, with thorny surface and four kidney-shaped gates. Transverse girdle of the outer cortical shell very spiny, with two semilunar wings, with convex thorny lateral crests; each wing one and a half times as broad as the transverse girdle of the inner cortical shell, and one and a half times as long as its lateral girdle.

_Dimensions._--Length of the lentelliptical medullary shell 0.05, breadth 0.03; length of the inner cortical shell 0.16, breadth 0.12; length of each lateral wing of the outer cortical shell 0.24, breadth 0.18.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

3. _Amphipylonium tetraceros_, n. sp.

Inner cortical shell hexagonal, one and a half times as long as broad, with smooth surface and four transverse elliptical gates. Transverse girdle of the outer cortical shell smooth, with rectilinear smooth lateral crests, which are prolonged at both ends into strong conical spines (therefore four spines in the lateral plane); each wing of the same breadth as the transverse girdle of the inner cortical shell, and twice as long as its lateral girdle.

_Dimensions._--Length of the hexagonal medullary shell 0.03, breadth 0.02; length of the inner cortical shell 0.12, breadth 0.08; length of each lateral wing of the outer cortical shell 0.24, breadth 0.08.

_Habitat._--Northern Pacific, Station 253, depth 3125 fathoms.

4. _Amphipylonium octoceros_, n. sp.

Inner cortical shell quadrangular, one and a third times as long as broad, with thorny surface and four kidney-shaped gates. Transverse girdle of the outer cortical shell thorny, constricted at the equator, with concave thorny lateral crests, and with eight strong radial spines, opposite in pairs and lying in two crossed diagonal planes; each wing narrower than the transverse girdle of the inner cortical shell and twice as long as its lateral girdle.

_Dimensions._--Length of the subspherical medullary shell 0.04, breadth 0.035; length of the inner cortical shell 0.14, breadth 0.11; length of each lateral wing of the outer cortical shell 0.26, breadth 0.09.

_Habitat._--Southern Pacific, Station 295, depth 1500 fathoms.

Genus 267. _Tetrapylonium_,[326] Haeckel, 1881, Prodromus, p. 464.

{658}The genus _Tetrapylonium_ represents a further developmental stage of the foregoing _Amphipylonium_; whilst in this latter the outer cortical shell (or the third system of girdles) is formed only by a transverse girdle, here this is crossed by a lateral girdle. _Tetrapylonium_ repeats therefore the typical form of _Tetrapyle_, but with doubled cortical shell (Prodromus, 1881, p. 464).

1. _Tetrapylonium pantellipticum_, n. sp.

Outer cortical shell elliptical, one and a third times as long as broad, with smooth surface and four elliptical gates. Inner cortical shell elliptical, with smooth surface and four elliptical gates which repeat the form of the four outer gates, but are of half the size. Transverse girdle broad, with five pores on the isthmus.

_Dimensions._--Length (or principal axis) of the first shell (medullary shell) 0.04, breadth (or transverse axis) 0.03; length of the second (or inner cortical) shell 0.12, breadth 0.09; length of the third (or outer cortical) shell 0.18, breadth 0.14.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

2. _Tetrapylonium reniforme_, n. sp.

Outer cortical shell elliptical, one and a half times as long as broad, with thorny surface and four large kidney-shaped gates. Inner cortical shell of the same form, but one-third smaller, also with four kidney-shaped gates. Transverse girdle small, but with two pores on the isthmus.

_Dimensions._--Length of the first (innermost) shell 0.03, breadth 0.02; length of the second (middle) shell 0.14, breadth 0.08; length of the third (outermost) shell 0.2, breadth 0.11.

_Habitat._--Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.

3. _Tetrapylonium quadrangulare_, n. sp. (Pl. 9, fig. 15).

Outer cortical shell nearly quadrangular, one and a third times as long as broad, with four rounded corners, from which arise in the lateral plane four three-sided pyramidal radial spines, opposite in pairs in two crossed diagonal axes. Surface thorny; four gates elliptical or nearly quadrangular. Inner cortical shell more elliptical, by one half smaller, with broader transverse girdle and four kidney-shaped gates. Medullary shell nearly spherical, of half the size.

_Dimensions._--Length of the first shell 0.045, breadth 0.035; length of the second shell 0.1, breadth 0.07; length of the third shell 0.16, breadth 0.11.

_Habitat._--South Atlantic, off Tristan da Cunha, Station 332, depth 2200 fathoms.

4. _Tetrapylonium octacanthum_, n. sp.

Outer cortical shell elliptical, one and a third times as long as broad, with thorny surface, and eight long and thin radial spines arising from the corners of the four triangular gates, and lying {659}opposite in pairs in two crossed diagonal planes. Inner cortical shell of the same shape, but two-thirds smaller, also thorny. Transverse girdle broad, with four pores on the isthmus. (This species appears to be the common _Tetrapyle octacantha_, with doubled cortical shell.)

_Dimensions._--Length of the first shell 0.04, breadth 0.03; length of the second shell 0.16, breadth 0.12; length of the third shell 0.24, breadth 0.18.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

5. _Tetrapylonium armatum_, n. sp.

Outer cortical shell nearly quadrangular, one and a fourth times as long as broad, with very spiny surface. Between numerous smaller (simple or branched) thorns arise twelve larger radial spines, symmetrically distributed, eight wing-spines crossed in two diagonal planes (as in _Tetrapylonium octacanthum_) and four corner spines on the four rounded corners of the lateral plane (as in _Tetrapylonium quadrangulare_). Therefore this species combines the armature of both foregoing species. Four gates kidney-shaped. Inner cortical shell elliptical, smooth, three-fourths smaller.

_Dimensions._--Length of the first shell 0.045, breadth 0.035; length of the second shell 0.18, breadth 0.15; length of the third shell 0.25, breadth 0.2.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

Genus 288. _Pylozonium_,[327] n. gen.

_Definition._--#Pylonida# with trizonal lentelliptical medullary shell, surrounded by double latticed cortical shell; inner cortical shell as well as the outer _Pylonium_-shaped, each with three perfect crossed girdles (transverse, lateral, and sagittal).

The genus _Pylozonium_ is the most highly developed form of the Pylonida, as all three systems of concentric girdles here become fully developed, each system with three perfect girdles. In this genus only among all the Pylonida we find nine complete latticed girdles, and in each of the three dimensive planes three concentric elliptical girdles. The first system forms the medullary shell, the second system the inner cortical shell, and the third system the outer cortical shell.

1. _Pylozonium novemcinctum_, n. sp.

Outer cortical shell lentelliptical, thorny, one and a third times as long as broad, without radial spines, with four kidney-shaped gates. Inner cortical shell of the same shape, but one-third smaller, four times as large as the lentelliptical medullary shell.

_Dimensions._--Length of the medullary shell 0.04, breadth 0.03; length of the inner cortical shell 0.16, breadth 0.12; length of the outer cortical shell 0.24, breadth 0.18.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

{660}2. _Pylozonium octacanthum_, n. sp. (Pl. 9, fig. 16).

Outer cortical shell lentelliptical, one and a third times as long as broad, with thorny surface and eight long and thin radial spines arising from the corners of the four elliptical gates, and lying opposite in pairs in two crossed diagonal planes. Inner cortical shell of the same shape but one-fourth smaller, about twice as large as the lentelliptical medullary shell.

_Dimensions._--Length of the medullary shell 0.065, breadth 0.045; length of the inner cortical shell 0.18, breadth 0.12; length of the outer cortical shell 0.24, breadth 0.18.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

Family XXVII. #THOLONIDA#, n. fam. (Pl. 10).

_Definition._--#Larcoidea# with regular, completely latticed cortical shell, which is composed of two to six or more hemispherical or cap-shaped domes (vaulted chambers or cupolas). The domes lie opposite in pairs on the poles of the three dimensive axes, are separated by annular constrictions, and surround a simple or _Larnacilla_-shaped central chamber.

The family #Tholonida# represents a peculiar and very remarkable group of the #Larcoidea#, distinguished from the other groups of this suborder by the characteristic form of the shell, composed of a variable number of hemispherical domes or cupolas. The middle and original part of the shell is constantly formed of an elliptical or subspherical central chamber, which often, but not constantly, contains a small medullary shell. An even number (two, four, six, or more) of domes is attached to the poles of the three dimensive axes of the central chamber; according as only one, or two, or all three axes develop cupolas, we distinguish in this family three different subfamilies (the Amphitholida, Staurotholida, and Cubotholida). The Amphitholida (or Tholonida monaxonia) form cupolas only on the two poles of one single axis, and this axis corresponds to the minor (or transverse) axis of the central chamber, we find here therefore constantly at least two lateral cupolas (Pl. 10, figs. 1-7). The Staurotholida (or Tholonida diaxonia) form cupolas on the poles of two axes perpendicular one to another; these two axes are the major (principal) and the minor (transverse) axis of the central chamber, we find here therefore constantly at least four cupolas crossed in pairs (Pl. 10, figs. 8-11). The Cubotholida (or Tholonida triaxonia) form cupolas on the poles of all three dimensive axes (perpendicular one to another); corresponding to the principal, transverse, and sagittal axes of the lentelliptical central chamber; therefore we find here constantly at least six cupolas, attached in pairs on the six sides of the central chamber (Pl. 10, figs. 12-17).

The number of genera and species in the family #Tholonida# is rather large, but the number of individuals is much smaller than in most of the other SPUMELLARIA, and {661}particularly than in the nearly allied Pylonida; the greater number of the species are very rare. Besides this they seem to be very variable and inclined to produce numerous abnormalities. Very often intermediate forms of transition are to be found between the Tholonida and other #Larcoidea#, particularly the Pylonida and Lithelida. In many species the thick-walled shell is very opaque, and offers great difficulties to the clear study; in the greater number the structure of the shell cannot be understood completely without rolling the shell to the different sides; and the distinction between the Staurotholida and Cubotholida is often very difficult.

The primordial chamber of the Tholonida, or the central chamber in which its growth begins, is either a simple lentelliptical shell (without enclosed medullary shell), like _Cenolarcus_, or it is a trizonal shell, like _Larnacilla_, and contains a small concentric medullary shell. But this important inner shell of the central chamber offers peculiar difficulties for study. In many cases (probably in the greater number) there is no doubt the same characteristic trizonal medullary shell, which we found in the Larnacida and Pylonida, and this is our principal argument, if we regard the Tholonida as #Larcoidea#, which are most nearly allied to both these families, and in which the fenestrated open cortical girdles of the Pylonida are replaced by fenestrated closed cupolas or domes; the characteristic "gates" or large fissures in the cortical shell of the former are therefore here perfectly closed by network. The Tholonida agree in this point with the Larnacida, but are distinguished from them by the prominent vaultings of the hemispherical cupolas or domes, which give them a peculiar appearance. Each pair of domes (opposite on both poles of one dimensive axis) corresponds to one single girdle of the Pylonida.

Regarding the absence or presence of a medullary shell in the central chamber, we may divide the Tholonida into two groups, Cenotholida (without medullary shell) and Coccotholida (with medullary shell). The absence of the medullary shell in many Tholonida may be either primary (original) or secondary (by reduction and loss of it). Probably in the larger proportion (if not always?) its absence is the consequence of reduction and loss, and in this case the Cenotholida must be derived phylogenetically from the Coccotholida, but possibly often (or always?) the contrary may also be the case. At present we cannot find certain arguments for one opinion or the other.

The connection between the medullary (internal) and the cortical (external) shell of the central chamber in the Coccotholida is effected by two lateral wings of a latticed transverse girdle; on both sides of the latter remain the four internal open "gates" of the Pylonida and Larnacida. Very often the limiting edges of these four gates are prolonged into eight external radial spines which lie opposite in pairs in two crossed diagonal planes, and correspond to the eight portal-spines of _Tetrapyle octacantha_. Besides these, we often find four other beams opposite in pairs in the two crossed axes (principal and lateral). Very often also these radial beams (between medullary and {662}cortical shells) are prolonged on the outside into prominent free radial spines. But other spines may also arise from the surface. Very remarkable is the presence of twenty symmetrically disposed radial spines in some forms of Amphitholida (_Amphitholus acanthometra_ and _Amphitholonium acanthonium_, &c.). It recalls the twenty radial spines of the #Acanthonida#, though the laws of distribution in the two similar cases are quite different.

The cortical shell of the Tholonida remains either simple, or it becomes doubled by formation of an outer veil or envelope. This outer cortical shell or "veil" may either repeat completely the typical form of the inner with its cupolas, or it may form an ellipsoidal envelope without dome-shaped partitions. Its network is either like that of the inner, or it is very delicate and irregular, spider-web like. The connection between the two cortical shells is effected by a variable number of radial beams, often prolonged on the outside into radial spines.

The growth of the Tholonida by apposition of new chambers is very characteristic, constantly pairs of chambers originating at both opposite poles of the three dimensive axes, firstly on the transverse axis, secondly on the principal axis, thirdly on the sagittal axis. It is possible that by repeated apposition of new chambers the Tholonida are transformed into #Discoidea#, but commonly the number of domes is restricted, two in the Amphitholida, four in the Staurotholida, six in the Coccotholida. If new chambers in an irregular manner or in a spiral order be opposed to those first formed pairs of chambers, the Tholonida may be transformed into Soreumida, Streblemida, or Lithelida. The phylogenetic connection between these families is probably very complex and very worthy of further research.

The network of the shell in the Tholonida is sometimes regular, with circular (often hexagonally framed) pores of equal size, sometimes irregular, with roundish pores of unequal size. Commonly the shell is thick and compact; in those genera in which the cortical shell is doubled, the inner is commonly compact, the outer a very delicate veil.

The central capsule of the Tholonida is originally always enclosed by the central chamber, and like this of lentelliptical form, a triaxial ellipsoid. With the apposition of cupolas the growing central capsule may form dome-shaped protuberances which enter into the former. So we may find in the Amphitholida a central capsule with three joints (separated by two annular parallel constrictions), in the Staurotholida a cross-shaped capsule (with four caps around the central lentellipsis), in the Cubotholida a clustered capsule with six caps, surrounding six sides of the cubical central mass. In the Coccotholida (with medullary shell in the central chamber) the latter encloses in the centre the nucleus of the cell. The calymma, or the jelly-veil between the central capsule and the enveloping shell, probably always exhibits annular constrictions, corresponding to those which separate the cupolas of the shell. All these anatomical peculiarities in the Tholonida require a further accurate study.

{663}_Synopsis of the Genera of Tholonida._

------------------------------------------------------------------------- I. Subfamily Amphitholida. Cupolas developed only in the direction of one single axis (commonly two cupolas). (Tholonida unidimensiva.) ------------------------------------------------------------------------- {Two simple cupolas { (without veil), 289. _Tholartus_. Central chamber simple, { without medullary shell. {Two double cupolas { (with veil), 290. _Tholodes_.

{Two simple cupolas Central chamber { (without veil), 291. _Amphitholus_. _Larnacilla_-shaped, with { enclosed medullary shell. {Two double cupolas { (with veil), 292. _Amphitholonium_. ------------------------------------------------------------------------- II. Subfamily Staurotholida. Cupolas developed in the direction of two axes perpendicular one to another (commonly four cupolas). (Tholonida bidimensiva.) ------------------------------------------------------------------------- {Four simple cupolas { (without veil), 293. _Tholostaurus_. Central chamber simple, { without medullary shell. {Four double cupolas { (with veil), 294. _Tholoma_.

{Four simple cupolas Central chamber { (without veil), 295. _Staurotholus_. _Larnacilla_-shaped, with { enclosed medullary shell. {Four double cupolas { (with veil), 296. _Staurotholonium_. ------------------------------------------------------------------------- III. Subfamily Cubotholida. Cupolas developed in the direction of three axes perpendicular one to another (commonly six cupolas). (Tholonida tridimensiva.) ------------------------------------------------------------------------- {Six simple cupolas { (without veil), 297. _Tholocubus_. Central chamber simple, { without medullary shell. {Six double cupolas { (with veil), 298. _Tholonium_.

{Six simple cupolas Central chamber { (without veil), 299. _Cubotholus_. _Larnacilla_-shaped, with { enclosed medullary shell. {Six double cupolas { (with veil), 300. _Cubotholonium_.

Subfamily 1. AMPHITHOLIDA, Haeckel.

_Definition._--#Tholonida# with monaxial growth; cupolas opposite on the poles of one axis. (Shell commonly three-chambered, with two domes on both sides of the central chamber.)

Genus 289. _Tholartus_,[328] n. gen.

_Definition._--#Tholonida# with simple cortical shell (without external veil); with two hemispherical cupolas, opposite on the poles of one axis; central chamber between them simple (without medullary shell).

{664}The genus _Tholartus_ (Pl. 10, fig. 1) represents the most simple form of all Tholonida, a three-jointed simple cortical shell without medullary shell; two hemispherical cupolas or domes are attached on both lateral sides of a simple triaxial ellipsoidal central chamber, corresponding to the poles of its lateral or transverse axis. _Tholartus_ may be regarded as the common ancestral form of all Tholonida, and may be derived either from the Pylonida _Monozonium_ (by complete lattice-locking of the lateral wings) or from the Ellipsida _Cenellipsis_ (by development of two lateral protuberances on the poles of the transverse axis). But it is also possible that the absence of the medullary shell is produced by reduction, and in this case _Tholartus_ may be descended from _Amphitholus_.

Subgenus 1. _Tholartella_, Haeckel.

_Definition._--Surface of the shell smooth or rough, without radial spines.

1. _Tholartus tricolus_, n. sp. (Pl. 10, fig. 1).

Central chamber one and a half times as high and as broad as both cupolas. Surface of the shell rough. Pores regular, circular, without hexagonal frames, three times as broad as the bars; about sixteen on the half meridian of the central chamber (or its vertical diameter).

_Dimensions._--Length of the shell (major axis of the central chamber, vertical) 0.1, breadth of the shell (major axis of the whole three-chambered shell, horizontal) 0.13; pores 0.01, bars 0.003.

_Habitat._--Pacific, central area, Station 270, depth 2925 fathoms.

2. _Tholartus paniscus_, n. sp.

Central chamber of the same breadth, but of the double height of both cupolas. Surface of the shell rough. Pores regular, circular, with hexagonal frames, of the same breadth as the bars; eight to ten on the half meridian of the central chamber.

_Dimensions._--Length of the shell (major axis of the central chamber, vertical) 0.12, breadth of the shell (major axis of the whole three-chambered shell, horizontal) 0.15; pores and bars 0.008.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

3. _Tholartus isocolus_, n. sp.

Central chamber of the same breadth and height as both cupolas. Surface of the shell smooth. Pores irregular, roundish, once to three times as broad as the bars; ten to fifteen on the half meridian of the central chamber.

_Dimensions._--Length of the shell 0.11, breadth 0.14; pores 0.004 to 0.01, bars 0.003.

_Habitat._--Pacific, central area, Station 270, depth 2925 fathoms.

{665}Subgenus 2. _Tholartissa_, Haeckel.

_Definition._--Surface of the shell with radial spines.

4. _Tholartus tripanis_, n. sp.

Central chamber of the same size as both cupolas. Surface of the shell thorny, everywhere covered with short conical radial spines, about as long as the cupolas. Pores regular or subregular, circular, twice as broad as the bars; eight to ten on the half meridian.

_Dimensions._--Length of the shell 0.1, breadth 0.12; pores 0.01, bars 0.005.

_Habitat._--South Pacific, Station 295, surface.

5. _Tholartus sagitta_, n. sp.

Central chamber twice as large as both cupolas. Surface of the shell spiny, with eight to twelve regularly (?) distributed radial spines, radiating from the two constrictions between the three chambers. Spines needle-shaped, very thin and long. Pores subregular or irregular, roundish or circular, about three times as broad as the bars; twelve to sixteen on the half meridian.

_Dimensions._--Length of the shell 0.11, breadth 0.15; pores 0.01, bars 0.003.

_Habitat._--North Pacific, Station 244, surface.

Genus 290. _Tholodes_,[329] n. gen.

_Definition._--#Tholonida# with double cortical shell (with external veil), with two hemispherical cupolas, opposite on the poles of one axis; central chamber between them simple (without medullary shell).

The genus _Tholodes_ (Pl. 10, fig. 2) differs from _Tholartus_, its probable ancestral form, only in the duplication of the shell; the outer shell has exactly the same three-jointed form as the inner; both are connected by eight radial beams, lying in two diagonal planes and corresponding to the eight frontal spines of _Tetrapyle octacantha_. Possibly _Tholodes_ may also be descended from _Amphitholonium_ by loss of the medullary shell. I have observed only one single specimen of this genus.

1. _Tholodes cupula_, n. sp. (Pl. 10, fig. 2).

Outer shell of the same form and structure as the inner shell. Central chamber larger than both cupolas. Surface a little rough, without radial spines. Distance of both shells equals the height of the outer cupolas. Pores of both shells regular, circular, three times as broad as the {666}bars; six to seven in the semicircle of one inner cupola, ten to twelve in the semicircle of one outer cupola. Both shells are connected by eight radial beams, crossed in two diagonal planes.

_Dimensions._--Major axis of the outer shell 0.1, minor 0.065; major axis of the inner shell 0.05, minor 0.04; pores 0.006, bars 0.002.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

Genus 291. _Amphitholus_,[330] n. gen.

_Definition._--#Tholonida# with simple cortical shell (without external veil), with two hemispherical cupolas, opposite on the poles of one axis; central chamber (between them) _Larnacilla_-shaped, with medullary shell.

The genus _Amphitholus_ is the most simple form of all Coccotholida (or all Tholonida provided with medullary shell). Its simple cortical shell exhibits, like _Tholartus_, two lateral hemispheric cupolas, attached on both sides of a lentelliptical central chamber (on the poles of its transverse axis). The central chamber has the form of a triaxial ellipsoid, and contains, like _Larnacilla_, a small medullary shell, connected with it by the wings of a latticed transverse girdle. _Amphitholus_ may be derived either from _Tholartus_ by secondary production of a cortical shell, or (more probably) from _Larnacilla_ by apposition of two lateral dome-shaped protuberances. In the latter case it may be regarded as an _Amphipyle_, the lateral open wings of which are closed by lattice-work.

Subgenus 1. _Amphitholissa_, Haeckel.

_Definition._--Surface of the shell smooth or rough, without radial spines.

1. _Amphitholus artiscus_, n. sp. (Pl. 10, fig. 3).

Central chamber of the same height as both cupolas. Surface of the cortical shell rough. Pores regular, circular, with prominent hexagonal frames, twice as broad as the bars; eight to ten in the basal semicircle of one cupola.

_Dimensions._--Major axis of the shell 0.16, minor axis 0.1; pores 0.008, bars 0.004.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

2. _Amphitholus artidium_, n. sp.

Central chamber one-fourth higher than both cupolas. Surface of the cortical shell smooth. Pores irregular, roundish, once to three times as broad as the bars. (Very similar to _Tholartus_ tricolus, Pl. 10, fig. 1, but different by the medullary shell.)

_Dimensions._--Major axis of the shell 0.15, minor axis 0.12; pores 0.004 to 0.01, bars 0.003.

_Habitat._--North Pacific, Station 241, depth 2300 fathoms.

{667}Subgenus 2. _Amphitholura_, Haeckel.

_Definition._--Surface of the shell with radial spines or thorns.

3. _Amphitholus octacanthus_, n. sp.

Central chamber about twice as high and broad as both cupolas. From the surface arise, symmetrically distributed, eight stout conical radial spines, lying in two diagonal planes, as prolongations of the eight wing-beams, which connect the _Tetrapyle_-shaped medullary shell with the two ring-like constrictions of the cortical shell. Pores of the latter regular, circular, twice as broad as the bars; ten to twelve in the basal semicircle of one cupola.

_Dimensions._--Major axis of the shell 0.15, minor 0.12; pores 0.01, bars 0.005.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

4. _Amphitholus dodecanthus_, n. sp.

Central chamber a little larger than both cupolas. From the surface arise twelve strong conical radial spines, four on the poles of the major and the minor axis of the shell, lying in the lateral plane; eight others lying in two diagonal planes, as prolongations of the eight wing-beams, which connect the _Tetrapyle_-shaped medullary shell with the two ring-like constrictions of the cortical shell. Pores of the latter irregular, roundish, twice to four times as broad as the bars; sixteen to eighteen in the basal semicircle of one cupola.

_Dimensions._--Major axis of the shell 0.15, minor 0.11; pores 0.004 to 0.008, bars 0.002.

_Habitat._--North Pacific, Station 256, surface.

5. _Amphitholus acanthometra_, n. sp. (Pl. 10, figs. 5, 6).

Central chamber about twice as broad and as high as both cupolas. On the surface quite symmetrically distributed twenty long and strong cylindrical radial spines; eight in the sagittal plane or in the meridian plane of the central chamber (four opposite in pairs in the principal and the sagittal axes, four others in the middle between the principal and the sagittal spines); four in the horizontal transverse plane, on both sides of the poles of the major or lateral axis; and eight in diagonal planes (corresponding to the eight wing-spines of _Tetrapyle octacantha_). In the centre of the central chamber is a distinct trizonal medullary shell like that of _Tetrapyle_, with two vertical columella beams. Pores of the cortical shell subregular, circular, with elevated hexagonal frames, about four times as broad as the bars; five to seven in the semicircle of one cupola. (This remarkable species differs from _Tholartus vicenus_ in the possession of a medullary shell, from _Amphitholonium acanthometra_ by the simple cortical shell. Compare these species).

_Dimensions._--Major axis of the shell 0.14 to 0.16, minor axis 0.10 to 0.12; pores 0.015, bars 0.004; major axis of the medullary shell 0.04 to 0.05, minor (horizontal) axis 0.02 to 0.03; length of the twenty radial spines 0.18 to 0.24, basal breadth 0.01.

_Habitat._--South Pacific, Station 300, depth 1375 fathoms.

{668}6. _Amphitholus armatus_, n. sp.

Central chamber twice as broad, but of the same height, as the flat vaulted cupolas. Surface armed with thirty to forty very large three-sided prismatic spines, longer than the major axis of the shell. Pores irregular, roundish, twice to five times as broad as the bars; eight to nine on the basal semicircle of one cupola.

_Dimensions._--Major axis of the shell 0.15, minor axis 0.1; pores 0.006 to 0.015, bars 0.003; length of the spines 0.2 to 0.25, breadth 0.01.

_Habitat._--North Atlantic, Station 353, surface.

7. _Amphitholus polyacanthus_, n. sp.

Central chamber of the same breadth and height as both cupolas. Surface armed with very numerous (sixty to eighty) strong conical spines, about as long as the minor axis of the shell. Pores subregular, circular, twice as broad as the bars; sixteen to eighteen in the basal semicircle of one cupola.

_Dimensions._--Major axis of the shell 0.13, minor 0.08; pores 0.006, bars 0.003; length of the radial spines 0.09, breadth 0.006.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

8. _Amphitholus panicium_, n. sp. (Pl. 10, fig. 4).

Central chamber ellipsoidal, nearly twice as broad, but of the same height, as both cupolas. Whole surface thorny; the largest radial thorns about as long as the medullary shell. Pores irregular, roundish, twice to four times as broad as the bars. On the base of each cupola a circle of ten to twelve larger square pores, separated by radial beams, which are prolonged into stouter free spines. This remarkable formation of the cupolas, very rare in this family, recalls the characteristic formation of the distal chambers of the Panartida and Zygartida (_e.g._, Pl. 40, figs. 4, 8, &c.), where it is very common.

_Dimensions._--Major axis of the shell 0.15, minor 0.1; pores 0.005 to 0.012, bars 0.003; large square pores 0.02; axes of the medullary shell 0.03 and 0.02.

_Habitat._--Indian Ocean, Madagascar, Rabbe, surface.

Genus 292. _Amphitholonium_,[331] n. gen.

_Definition._--#Tholonida# with double cortical shell (with external veil), with two hemispherical cupolas, opposite on the poles of one axis; central chamber (between them) _Larnacilla_-shaped, with medullary shell.

The genus _Amphitholonium_ differs from the nearly allied _Amphitholus_ (probably its ancestral form) only in the duplication of the cortical shell; the outer has the {669}same three-jointed form as the inner, and is connected with it by a variable number of radial beams. From the similar _Tholodes_ it differs in the possession of a medullary shell.

1. _Amphitholonium tricolonium_, n. sp. (Pl. 10, fig. 7).

Outer cortical shell smooth, of the same three-jointed form as the inner, at an equal distance from it throughout the whole circumference; central chamber higher-vaulted than both cupolas. Network of the outer shell delicate, with subregular, circular pores. Pores of the thick-walled inner shell subregular, circular, with hexagonal frames, three times as broad as the bars; eight to ten in the basal semicircle of one cupola.

_Dimensions._--Major axis of the outer cortical shell 0.2, minor axis 0.15; major axis of the inner cortical shell 0.16, minor axis 0.11; pores 0.01, bars 0.0035.

_Habitat._--South Pacific, Station 302, depth 1450 fathoms.

2. _Amphitholonium octostylium_, n. sp.

Outer cortical shell lentelliptical, smooth, not articulated, at a varying distance from the three-jointed inner shell; central chamber of the latter twice as high as both hemispherical cupolas. Network of the outer shell very thin, cob-web like. Pores of the inner shell subregular, roundish, twice as broad as the bars; six to seven in the semicircle of one cupola. Eight thin and long, bristle-shaped, radial spines, opposite in pairs in two crossed diagonal planes.

_Dimensions._--Major axis of the outer cortical shell 0.16, minor 0.12; major axis of the inner cortical shell 0.12, minor 0.09; pores 0.01, bars 0.005.

_Habitat._--Pacific, central area, Station 273, depth 2350 fathoms.

3. _Amphitholonium acanthonium_, n. sp.

Outer cortical shell of the same three-jointed form as the inner, at a uniform distance from it; central chamber higher vaulted than both cupolas. Network of the outer shell irregular, delicate, of the inner regular, strong, with circular, hexagonally framed pores, three times as broad as the bars; eight to nine in the semicircle of one cupola. On the surface, quite symmetrically disposed, twenty long and strong, cylindrical, radial spines; eight in the sagittal plane, four in the transverse plane; eight in two diagonal planes between the former and the latter. The remarkable geometric disposition of the twenty spines is in this species quite the same as in _Amphitholus acanthometra_. It differs from this nearly allied species in the double cortical shell.

_Dimensions._--Major axis of the outer cortical shell 0.18, minor 0.14; major axis of the inner cortical shell 0.14, minor 0.1; pores 0.012, bars 0.004.

_Habitat._--South Pacific, Station 295, surface.

{670}Subfamily 2. STAUROTHOLIDA, Haeckel.

_Definition._--#Tholonida# with diaxial growth; cupolas crossed in pairs, opposite on the poles of two axes, perpendicular one to another. (Shell commonly five-chambered, with four domes, cross-wise surrounding the central chamber.)

Genus 293. _Tholostaurus_,[332] n. gen.

_Definition._--#Tholonida# with simple cortical shell (without external veil), composed of four hemispherical cupolas in cross-form, opposite in pairs on the poles of two axes perpendicular one to another; central chamber simple (without medullary shell).

The genus _Tholostaurus_ is the most simple form of the Staurotholida, or the Tholonida with four crossed hemispherical cupolas, lying on the poles of two axes perpendicular one to another. The central chamber communicates by four wide openings with the four domes, and contains no medullary shell. _Tholostaurus_ may originate either from _Tholartus_ by apposition of two opposite cupolas between the first pair, or from _Staurotholus_ by loss of the medullary shell.

Subgenus 1. _Tholostaurantha_, Haeckel.

_Definition._--Surface of the shell smooth or rough, without radial spines.

1. _Tholostaurus quadrigatus_, n. sp.

All four cupolas nearly of the same size and form, subregular. Surface smooth, without radial spines. Pores subregular, circular, four times as broad as the bars; eight to ten pores in the basal semicircle of one cupola.

_Dimensions._--Diameter of the shell 0.12; pores 0.008, bars 0.002.

_Habitat._--Pacific, central area, Station 272, surface.

2. _Tholostaurus cruciformis_, n. sp.

Two opposite cupolas larger than the two others. Surface rough, without radial spines. Pores regular, circular, hexagonally framed, twice as broad as the bars; twelve to fourteen in the basal semicircle of one cupola.

_Dimensions._--Major axis of the shell 0.16, minor axis 0.12; pores 0.006, bars 0.003.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

{671}Subgenus 2. _Tholostauroma_, Haeckel.

_Definition._--Surface of the shell with radial spines or thorns.

3. _Tholostaurus tetrabelonis_, n. sp.

All four cupolas nearly of the same size and form, subregular. Pores regular, circular, hexagonally framed, twice as broad as the bars; twelve to fourteen in the semicircle of one cupola. Four long and stout conical radial spines, two vertical on the poles of the principal axis, two horizontal on the poles of the transverse axis.

_Dimensions._--Major axis of the shell 0.15, minor 0.13; pores 0.006, bars 0.003.

_Habitat._--South Pacific, Station 288, surface.

4. _Tholostaurus octobelonis_, n. sp.

Two opposite cupolas larger than the two others. Pores subregular, circular, three times as broad as the bars; ten to twelve in the semicircle of one cupola. Eight long and thin, needle-shaped, radial spines, in pairs crossed in two diagonal planes.

_Dimensions._--Major axis of the shell 0.16, minor 0.12; pores 0.01, bars 0.003.

_Habitat._--South Pacific, Station 291, surface.

5. _Tholostaurus dodecabelos_, n. sp.

Two opposite cupolas larger than the two others. Pores irregular, roundish, twice to three times as broad as the bars; six to eight in the semicircle of one cupola. Twelve thin and long radial spines, four on the poles of the two crossed axes (principal and lateral), eight crossed in two diagonal planes.

_Dimensions._--Major axis of the shell 0.14, minor 0.11; pores 0.006 to 0.01, bars 0.003.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

6. _Tholostaurus polybelonis_, n. sp.

Two opposite cupolas larger than the two others. Pores circular, hexagonally framed, of the same breadth as the bars; ten to twelve in the semicircle of one cupola. Numerous (twenty to thirty or more) thin, bristle-like, radial spines, about as long as the radius of the shell.

_Dimensions._--Major axis of the shell 0.15, minor axis 0.12; pores and bars 0.007.

_Habitat._--Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.

Genus 294. _Tholoma_,[333] n. gen.

_Definition._--#Tholonida# with double cortical shell (with external veil), composed of four hemispherical cupolas in cross-form, opposite in pairs on the poles of two axes perpendicular one to another; central chamber simple (without medullary shell).

{672}The genus _Tholoma_ (Pl. 10, figs. 10, 13) differs from the preceding _Tholostaurus_ (its probable ancestral form) only in the duplication of the shell. The outer (secondary) shell has the same cross-form as the inner (primary) shell. In the two observed species the growth seems to be different, in the first species all four cupolas of each cross being of the same size, form, and age; in the second two opposite cupolas, larger and apparently older than the other two. _Tholoma_ is possibly the offspring of _Staurotholonium_, from which it may have been produced by loss of the medullary shell.

Subgenus 1. _Tholomantha_, Haeckel.

_Definition._--Surface of the shell smooth, without radial spines.

1. _Tholoma quadrigeminum_, n. sp. (Pl. 10, fig. 10).

All four chambers in each cortical shell nearly equal, subregular. Surface smooth, without radial spines. Structure of the network in both shells similar. Pores regular, circular, twice as broad as the bars; six to eight in the basal semicircle of one inner, ten to twelve in the semicircle of one outer cupola.

_Dimensions._--Diameter of the outer shell 0.14, of the inner 0.09; pores 0.006, bars 0.003.

_Habitat._--South Pacific, Station 302, surface.

Subgenus 2. _Tholomura_, Haeckel.

_Definition._--Surface of the shell with radial spines.

2. _Tholoma metallasson_,[334] n. sp. (Pl. 10, fig. 13).

Two opposite chambers in each cortical shell larger than the two others; the larger chambers of the inner shell corresponding to the smaller chambers of the outer shell. Network in both shells of the same structure, regular, with circular, hexagonally framed pores of the same breadth as the bars; eight to ten in the semicircle of an inner, fourteen to sixteen in the semicircle of an outer cupola. Numerous (twenty to thirty or more) thin, cylindrical, bristle-shaped, long radial spines, symmetrically disposed.

_Dimensions._--Major axis of the outer shell 0.26, minor axis 0.2; major axis of the inner shell 0.16, minor axis 0.13; pores and bars 0.006.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

Genus 295. _Staurotholus_,[335] n. gen.

_Definition._--#Tholonida# with simple cortical shell (without external veil), composed of four hemispherical cupolas in cross-form, opposite in pairs on the poles of {673}two axes perpendicular one to another; central chamber _Larnacilla_-shaped (with enclosed medullary shell).

The genus _Staurotholus_ differs from _Tholostaurus_ in the possession of a medullary shell in the central chamber, and may be derived from this genus by its production. But it may also be derived from _Amphitholus_ by apposition of two secondary opposite cupolas between the two primary cupolas. The symmetrical position of an increasing number of radial spines in the different species is remarkable (resembling _Tholostaurus_ as well as _Amphitholus_).

Subgenus 1. _Staurotholissa_, Haeckel.

_Definition._--Surface of the shell smooth or rough, without radial spines.

1. _Staurotholus quadratus_, n. sp.

Surface of the cortical shell smooth. All four cupolas nearly of the same size and form; therefore principal and lateral axes equal. Pores regular, circular, with hexagonal frames, twice as broad as the bars; eight to ten on the basal semicircle of one cupola. Medullary shell square.

_Dimensions._--Diameter of the cortical shell 0.15; pores 0.01, bars 0.005.

_Habitat._--South Atlantic, Station 323, depth 1900 fathoms.

2. _Staurotholus cruciatus_, n. sp.

Surface of the cortical shell rough. The two principal cupolas somewhat larger than the two lateral cupolas; therefore the longitudinal axis longer than the transverse. Pores irregular, roundish, twice to three times as broad as the bars; twelve to sixteen in the semicircle of one cupola.

_Dimensions._--Major axis of the shell 0.16, minor 0.13; pores 0.005 to 0.009, bars 0.003.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

Subgenus 2. _Staurotholura_, Haeckel.

_Definition._--Surface of the shell with radial spines.

3. _Staurotholus tetrastylus_, n. sp. (Pl. 10, fig. 8).

The two principal cupolas smaller than the two lateral cupolas. Pores subregular, circular, three times as broad as the bars; six to eight in the semicircle of one cupola. Medullary shell elliptical. On the surface four long cylindrical radial spines; two in the principal and two in the lateral axis.

_Dimensions._--Major axis of the cortical shell 0.15, minor 0.12; pores 0.012, bars 0.004.

_Habitat._--South Pacific, Station 166, surface.

{674}4. _Staurotholus octostylus_, n. sp.

The two lateral cupolas larger than the two principal cupolas. Pores subregular, circular, twice as broad as the bars; ten to twelve in the semicircle of one cupola. Medullary shell hexagonal, connected with each ring-like constriction by eight strong cylindrical radial spines (longer than the whole shell), lying in two crossed meridian planes, and corresponding to the eight diagonal wing-spines of _Tetrapyle octacantha_.

_Dimensions._--Major axis of the cortical shell 0.12, minor 0.1; pores 0.008, bars 0.004.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

5. _Staurotholus decastylus_, n. sp.

The two principal cupolas twice as broad and high as the two lateral cupolas. Pores subregular, circular, four times as broad as the bars; six to eight in the semicircle of one cupola. Ten long and thin radial spines with thickened conical bases, about as long as the major axis of the shell, by inner prolongations connected with the lentelliptical medullary shell; two polar spines in the principal axis, eight wing-spines in two crossed diagonal planes.

_Dimensions._--Major axis 0.12, minor 0.1; pores 0.012, bars 0.003.

_Habitat._--Western Tropical Pacific; Station 224, depth 1850 fathoms.

6. _Staurotholus dodecastylus_, n. sp. (Pl. 10, fig. 9).

The two lateral cupolas larger than the two principal cupolas. Pores subregular, circular, three times as broad as the bars; five to seven in the semicircle of one cupola. Twelve strong cylindrical radial spines, four on the poles of the two larger axes (two principal and two lateral), eight wing-spines in two crossed diagonal planes. Medullary shell hexagonal.

_Dimensions._--Major (lateral) axis 0.11, minor (principal) 0.09; pores 0.009, bars 0.003.

_Habitat._--Tropical Atlantic, Station 348, surface.

7. _Staurotholus polystylus_, n. sp.

The two principal cupolas larger than the two lateral cupolas. Pores irregular, roundish, twice to three times as broad as the bars; ten to twelve in the semicircle of one cupola. On the surface numerous thin bristle-shaped spines (twenty to thirty or more).

_Dimensions._--Major axis 0.14, minor 0.11; pores 0.006 to 0.01, bars 0.003.

_Habitat._--North Pacific, Station 231, surface.

Genus 296. _Staurotholonium_,[336] n. gen.

{675}The genus _Staurotholonium_ differs from the nearly allied _Staurotholus_ (its probable ancestral form) only in the duplication of the cortical shell. The outer shell commonly repeats the cross-form of the inner, with four corresponding cupolas; but sometimes the four cupolas of the outer shell alternate in size and form with those of the inner, or the outer shell forms a simple lenticular envelope around the inner. From the similar _Tholoma_, _Staurotholonium_ differs in the possession of a medullary shell in the central chamber.

Subgenus 1. _Staurotholodes_, Haeckel.

_Definition._--Surface of the outer cortical shell smooth or rough, without radial spines.

1. _Staurotholonium biquadratum_, n. sp.

Outer cortical shell smooth, of the same regular crucial form as the inner, equidistant from it everywhere. Form and structure of both cortical shells nearly the same, but the outer about twice as large as the inner; both connected only by eight diagonal beams. All four cupolas of each cortical shell regular, of the same size. Pores regular, circular, twice as broad as the bars; six to eight in the basal semicircle of each cupola. Medullary shell square. (Similar to _Staurotholus quadratus_, but differs by the double cortical shell.)

_Dimensions._--Diameter of the outer cortical shell 0.16, of the inner 0.08, of the medullary shell 0.04; pores of the inner cortical shell 0.006, bars 0.003.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

2. _Staurotholonium bicruciatum_, n. sp.

Outer cortical shell rough, twice as large as the inner, of the same form and structure, at an equal distance from it. In both shells the principal cupolas are larger than the lateral. Pores irregular, roundish, in the outer shell four times, in the inner twice as large as the bars; eight to ten in the basal semicircle of one cupola. (Similar to _Staurotholus cruciatus_, but differs mainly in the double cortical shell.) Medullary shell lentelliptical.

_Dimensions._--Major (longitudinal) axis of the outer cortical shell 0.016, of the inner 0.08; minor (transverse) axis of the former 0.14, of the latter 0.07; medullary shell 0.03 to 0.04.

_Habitat._--Pacific, central area, Station 267, depth 2700 fathoms.

3. _Staurotholonium alternatum_, n. sp.

Outer cortical shell smooth, very different from the inner; in the outer the two principal cupolas are larger than the two lateral; in the inner inversely smaller. Pores subregular, circular, in the outer shell four times, in the inner shell twice as broad as the bars; ten to twelve pores in the basal semicircle of one cupola.

{676}_Dimensions._--Major axis (length) of the outer cortical shell 0.15, minor (breadth) 0.13; pores 0.012, bars 0.003; major axis (length) of the inner cortical shell 0.11, minor axis (breadth) 0.09; pores 0.006, bars 0.003.

_Habitat._--Indian Ocean, surface, Madagascar, Rabbe.

4. _Staurotholonium lenticulare_, n. sp.

Outer cortical shell smooth, lenticular, with circular circumference, with very delicate irregular network and small roundish pores. Its distance from the inner much greater in the four diagonal points than in the four polar points. Inner cortical shell regular, cross-like, with four cupolas of similar size and form. Pores subregular, circular, twice as broad as the bars; eight to ten in the basal semicircle of one cupola. Medullary shell lenticular.

_Dimensions._--Diameter of the outer cortical shell 0.16, of the inner 0.12; pores of the inner 0.008, bars 0.004.

_Habitat._--North Atlantic, Station 353, surface.

Subgenus 2. _Staurotholoma_, Haeckel.

_Definition._--Surface of the outer cortical shell with radial spines or thorns.

5. _Staurotholonium octodoratium_, n. sp.

Outer cortical shell of the same form and structure as the inner, but twice as large, both principal domes somewhat larger than both lateral. Pores subregular, circular, of the same breadth as the bars; five to six in the semicircle of one inner, eight to ten of one outer cupola. Eight thin and long bristle-like spines, opposite in pairs in two crossed diagonal planes.

_Dimensions._--Major axis of the outer cortical shell 0.15, minor 0.12; major axis of the inner cortical shell 0.07, minor 0.06; pores and bars 0.005.

_Habitat._--North Pacific, Station 231, surface.

6. _Staurotholonium octodoronium_, n. sp. (Pl. 10, fig. 11).

Outer cortical shell of the same form as the inner, both little distant; network of the outer irregular and delicate. Pores of the inner regular, circular, twice as broad as the bars; seven to nine in the basal semicircle of one cupola. Both lateral domes larger than the principal. Eight long and thin, cylindrical radial spines opposite in pairs in two crossed diagonal planes.

_Dimensions._--Major axis of the outer cortical shell 0.2, minor 0.18; major axis of the inner cortical shell 0.16, minor 0.14; pores 0.008, bars 0.004.

_Habitat._--South Pacific, Station 288, surface.

{677}Subfamily 3. CUBOTHOLIDA, Haeckel.

_Definition._--#Tholonida# with triaxial growth; cupolas lying in pairs on the six sides of a cubical central chamber, opposite at the poles of three axes perpendicular one to another. (Shell commonly seven-chambered, with six domes surrounding the central chamber.)

Genus 297. _Tholocubus_,[337] n. gen.

_Definition._--#Tholonida# with simple cortical shell (without external veil), composed of six hemispherical cupolas, opposite in pairs on the poles of three axes perpendicular one to another, covering six sides of the simple cuboidal central chamber (without medullary shell).

The genus _Tholocubus_ is the most simple form of the Cubotholida, or of the Tholonida with domes situated in three axes perpendicular one to another; six hemispherical cupolas lying on the six sides of a cuboidal central chamber; this latter contains no medullary shell. _Tholocubus_ may be derived phylogenetically either from _Tholostaurus_ by apposition of two opposite domes on the flat sides of the cross-shell, or from _Cubotholus_ by loss of the medullary shell.

Subgenus 1. _Tholocubulus_, Haeckel.

_Definition._--Surface of the shell smooth or rough, without radial spines.

1. _Tholocubus tessellatus_, n. sp. (Pl. 10, fig. 12).

Surface of the shell smooth, without radial spines. Pores regular, circular, hexagonally framed, twice as broad as the bars; eight to twelve pores on the semicircle of one cupola. Principal cupolas smaller than the lateral, larger than the sagittal cupolas.

_Dimensions._--Diameter of the shell 0.15; pores 0.01, bars 0.005.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

2. _Tholocubus tesserarius_, n. sp.

Surface of the shell rough, without radial spines. Pores irregular, roundish, once to three times as broad as the bars; twelve to sixteen pores in the semicircle of one cupola. All six cupolas nearly of the same size.

_Dimensions._--Diameter of the shell 0.16; pores 0.004 to 0.008, bars 0.003.

_Habitat._--North Atlantic, Station 353, depth 2965 fathoms.

{678}Subgenus 2. _Tholocubitus_, Haeckel.

_Definition._--Surface of the shell with radial spines or thorns.

3. _Tholocubus tesseralis_, n. sp. (Pl. 10, fig. 16).

Surface of the shell with numerous (eight to sixteen) thin and long, bristle-shaped radial spines (the greater part broken off in the figured specimen); pores subregular, circular, three to four times as broad as the bars; ten to twelve in the semicircle of one cupola.

_Dimensions._--Major axis of the shell 0.16, minor axis 0.14; pores 0.01, bars 0.0027.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

Genus 298. _Tholonium_,[338] n. gen.

_Definition._--#Tholonida# with double cortical shell (with external veil), composed of six hemispherical cupolas, opposite in pairs on the poles of three axes perpendicular one to another, covering six sides of the simple cuboidal central chamber (without medullary shell).

The genus _Tholonium_ (Pl. 10, fig. 17) differs from the preceding _Tholocubus_ only in the duplication of the cortical shell. The outer (secondary) shell forms either a simple (spheroidal or ellipsoidal) thin veil around the inner (primary) shell, or both shells are of the same form, with six corresponding cupolas. Possibly _Tholonium_ is the offspring of _Cubotholonium_, having originated by loss of the medullary shell.

Subgenus 1. _Tholonetta_, Haeckel.

_Definition._--Surface of the shell smooth or rough, without radial spines or thorns.

1. _Tholonium bicubicum_, n. sp.

Outer shell with six hemispherical dome-shaped protuberances, corresponding in those of the inner shell. Both shells connected by numerous radial beams. Surface of the outer shell smooth; its network nearly of the same shape as that of the inner, with subregular, circular pores, twice as broad as the bars; ten to fifteen pores on the semicircle of one cupola.

_Dimensions._--Diameter of the outer shell 0.14, of the inner 0.12; pores of the latter 0.006, bars 0.003.

_Habitat._--South Atlantic, Station 325, depth 2650 fathoms.

{679}2. _Tholonium ellipticum_, n. sp.

Outer shell ellipsoidal, without dome-shaped protuberances, with smooth surface, without radial spines; network delicate, with subregular, circular pores. Inner shell with regular, circular, hexagonally framed pores, twice as broad as the bars; ten to twelve pores on the semicircle of one cupola.

_Dimensions._--Major axis of the outer shell 0.16, minor axis 0.14; major axis of the inner shell 0.14, minor axis 0.12; pores 0.008, bars 0.004.

_Habitat._--Pacific central area, Station 267, depth 2700 fathoms.

3. _Tholonium sphæricum_, n. sp.

Outer shell spherical, without dome-shaped protuberances, with smooth surface, without radial spines; network very delicate, with very small subregular, circular pores. Inner shell with regular, circular pores of the same breadth as the bars; fourteen to sixteen on the basal semicircle of one cupola.

_Dimensions._--Diameter of the spherical outer shell 0.15, inner shell 0.12; pores and bars of the inner shell 0.005.

_Habitat._--Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.

Subgenus 2. _Tholonilla_, Haeckel.

_Definition._--Surface of the outer shell covered with radial spines or thorns.

4. _Tholonium hexonium_, n. sp. (Pl. 10, fig. 17).

Outer shell ellipsoidal, without dome-shaped protuberances, covered with numerous (thirty to fifty) thin and long, bristle-shaped radial spines; network very delicate, irregular, with roundish pores. Inner shell with six marked hemispherical domes of somewhat different sizes; pores regular, circular, with prominent hexagonal frames, twice as broad as the bars; ten to twelve on the basal semicircle of one cupola.

_Dimensions._--Major axis of the outer shell 0.15, minor axis 0.14; major axis of the inner shell 0.13, minor axis 0.12; pores 0.008, bars 0.004.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

5. _Tholonium sphæronium_, n. sp.

Outer shell very thin walled, spherical, without dome-shaped protuberances, with smooth surface, excepting eight large radial spines, rising from the eight corners of the inner cubical central chamber. Pores of the outer shell very small, subcircular. Inner shell very thick walled, with six marked hemispherical domes; pores subregular, circular, with prominent hexagonal frames, twice as broad as the bars; six to eight on the semicircle of one cupola.

{680}_Dimensions._--Diameter of the spherical outer shell 0.15, inner shell 0.11; pores of the inner 0.01, bars 0.005.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

Genus 299. _Cubotholus_,[339] n. gen.

_Definition._--#Tholonida# with simple cortical shell (without external veil), composed of six hemispherical cupolas, opposite in pairs on the poles of three axes perpendicular one to another, covering six sides of the cuboidal _Larnacilla_-shaped central chamber (with medullary shell).

The genus _Cubotholus_ differs from _Tholocubus_ in the possession of a medullary shell in the central chamber, and may be derived from this genus by its production; but it may also be derived from _Staurotholus_ by apposition of two opposite domes on the flat sides of the cross-shell. Sometimes all six domes are of the same size and form, but commonly different in pairs.

Subgenus 1. _Cubotholissa_, Haeckel.

_Definition._--Surface of the shell smooth or rough, without radial spines.

1. _Cubotholus regularis_, n. sp. (Pl. 10, fig. 14).

On the six sides of the cubical central chamber six hemispherical cupolas of the same size and form. Surface smooth. Pores regular, circular, twice as broad as the bars; eight in the basal semicircle of each cupola. Medullary shell apparently spherical (?), connected with the eight corners of the central chamber by eight radial beams, regularly disposed. (This species is remarkable for the perfect symmetry of the shell, the six sides of which appear to be quite similar. It differs from the similar _Tholocubus regularis_ in the possession of a medullary shell.)

_Dimensions._--Diameter of the cortical shell (equal in all three dimensive axes) 0.15; pores 0.01, bars 0.005; diameter of the medullary shell 0.04.

_Habitat._--Pacific, central area, Station 273, depth 2350 fathoms.

2. _Cubotholus quadraticus_, n. sp.

Surface of the shell smooth. Both principal cupolas (on the poles of the longitudinal axis) larger than the four other cupolas, which have the same size and lie cross-wise in the equatorial plane. (Therefore two of the three fundamental axes equal, the third larger.) Pores subregular, circular, three times as broad as the bars; ten to twelve in the semicircle of each cupola-basis.

_Dimensions._--Major axis 0.16, minor axis 0.12; pores 0.012, bars 0.004.

_Habitat._--Indian Ocean, Zanzibar, Pullen; depth 2200 fathoms.

{681}3. _Cubotholus rhombicus_, n. sp.

Surface of the shell smooth. Both principal cupolas (on the poles of the longitudinal axis) larger than the two lateral (on the poles of the transverse axis), and these larger than the two sagittal cupolas (on the poles of the sagittal axis). Therefore all three fundamental axes unequal. Pores irregular, roundish, twice to four times as broad as the bars; eight to twelve in the basal semicircle of each cupola. Medullary shell lentelliptical.

_Dimensions._--Major (principal) axis 0.16, middle (lateral) axis 0.14, minor (sagittal) axis 0.12; pores 0.006 to 0.012, bars 0.003.

_Habitat._--South Atlantic, Station 335, depth 1425 fathoms.

Subgenus 2. _Cubotholura_, Haeckel.

_Definition._--Surface of the shell with radial spines or thorns.

4. _Cubotholus octoceras_, n. sp.

All six cupolas in pairs of different sizes. Both principal domes larger than the lateral domes, and these larger than the sagittal domes. Pores subregular, circular, twice as broad as the bars; eight to ten in the semicircle of each cupola. From the surface arise (at the intersecting points of every three cupolas) eight strong conical radial spines, about as long as the shell-axis; they lie in two diagonal planes, and are the external free prolongations of eight inner beams (homologous with the eight wing-spines of _Tetrapyle octacantha_), which connect the lentelliptical medullary shell with the eight corners of the cuboidal central chamber.

_Dimensions._--Major axis of the cortical shell 0.15, middle 0.13, minor 0.11; pores 0.008, bars 0.004; diameters of the medullary shell corresponding to 0.05, 0.04, 0.03.

_Habitat._--Western Tropical Pacific, Station 224, depth 1850 fathoms.

Genus 300. _Cubotholonium_,[340] n. gen.

_Definition._--#Tholonida# with double (or sometimes triple) cortical shell (with external veil), composed of six hemispherical cupolas, opposite in pairs on the poles of three axes perpendicular one to another, covering six sides of the cuboidal _Larnacilla_-shaped central chamber (with medullary shell).

The genus _Cubotholonium_ differs from the nearly allied _Cubotholus_ (its probable ancestral form) only in duplication of the cortical shell. I have observed only two species of this rare form, both rather different. In the first species the outer cortical shell forms a simple spherical thin veil around the inner, the six cupolas of which are nearly of the same form and size. In the second species each of the domes of the {682}inner cortical shell is protected by an outer larger cupola, and besides this the whole shell is enveloped by a thin ellipsoidal veil (Pl. 10, fig. 15). Therefore this species may be the representative of a peculiar genus, the most highly developed of all Tholonida--_Tholothauma_.

1. _Cubotholonium sphæroides_, n. sp.

Outer cortical shell (or veil) spherical, with smooth surface; network very delicate, with very thin bars and very small irregular, roundish pores. Inner cortical shell simple, composed of six hemispherical cupolas, surrounding the six sides of the cubical central chamber, which encloses a spherical medullary shell (one-third as large as itself). Network of the inner cortical shell regular, with circular pores of the same breadth as the bars, twelve to fourteen in the basal semicircle of one cupola.

_Dimensions._--Diameter of the spherical outer shell 0.2, of the inner cortical shell 0.15; pores and bars of the latter 0.006.

_Habitat._--Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.

2. _Cubotholonium ellipsoides_, n. sp. (Pl. 10, fig. 15).

_Tholothauma ellipsoides_, Haeckel, 1883, MS.

Outer cortical shell (or veil) ellipsoidal, with very thin irregular network and thorny surface. Inner cortical shell double, with six double, flatly vaulted cupolas, surrounding the six sides of the _Larnacilla_-shaped central chamber; the double domes of each shell are in opposite pairs somewhat larger than the alternating pairs. Pores subregular, circular, about the same breadth as the bars; eight to twelve in the basal semicircle of one cupola. Central chamber with ellipsoidal medullary shell. Radial spines short, very numerous.

_Dimensions._--Major axis of the outer cortical shell 0.28, minor 0.24; major axis of the inner cortical shell 0.16, minor axis 0.14; pores and bars 0.006; medullary shell 0.03.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

Family XXVIII. #ZONARIDA#, n. fam. (Pl. 50, figs. 9-12).

_Definition._--#Larcoidea# with regular, completely latticed cortical shell, distinguished by two to four or more annular constrictions, which lie (all or partly) in the dimensive planes (sagittal, transverse, or lateral), and by which four to eight or more vaulted cupolas or dome-like chambers become separated. In the centre of this chambered cortical shell lies constantly a trizonal or _Larnacilla_-shaped medullary shell.

The family #Zonarida# comprises a small number of peculiar #Larcoidea#, resembling the Tholonida in the composition of the polythalamous cortical shell by a number of cupolas or dome-shaped protuberances. But the disposition and origin of these latter {683}are quite different. Whilst in the Tholonida the axes of the domes are dimensive axes, and these are separated by annular constrictions lying in diagonal planes, in the Zonarida we find the contrary; the axes of the domes are here diagonal axes, and these are separated by annular constrictions lying in dimensive planes. However, this definition agrees absolutely only in the four-chambered _Zonarium_ and in the eight-chambered _Zonidium_, whilst in the six chambered _Zoniscus_ only four domes are disposed according to this law, two others, however, in the same manner as in the Tholonida. Therefore this genus is intermediate between both families.

_The Cortical Shell_ of the Zonarida is in all cases completely latticed and of regular lentelliptical fundamental form, as in the nearly allied Larnacida and Tholonida. The three dimensive axes are constantly of different sizes, each with two equal poles; commonly (as in the human body) the principal or longitudinal axis is the longest, the sagittal (or dorso-ventral) axis the shortest; the transverse (or lateral) axis being intermediate between them. Of the three dimensive planes the lateral plane is the largest (determined by the principal and transverse axes); the smallest is the equatorial plane (crossed by the transverse and sagittal axes); the sagittal plane (determined by the sagittal and principal axes) being intermediate between them.

The annular constrictions of the cortical shell which produce the dome-shaped protuberances are different in number in the three known genera--two, three, or four. To each constriction often (but not always) corresponds an internal latticed septum, which connects the cortical with the medullary shell. The number of the cupolas is always double the number of the annular constrictions by which they are separated, therefore four, six, or eight.

In all known Zonarida the sagittal septum is quite constant, but derived from the original axial rod, which lies in the principal axis. By ramification of this axial beam and reticular connection with the sagittal girdle arises the sagittal septum, which we found first in _Octopyle_, halving the four gates of _Tetrapyle_. Whilst this sagittal septum (between right and left halves of the body) is common to all three known genera of this family, the number and shape of the other annular constrictions are different. In _Zonarium_ (Pl. 50, fig. 9) we find only one transverse constriction (in the equatorial plane), in _Zoniscus_ (figs. 10, 11) two parallel transverse constrictions (parallel to the equatorial plane, on both sides of it). _Zonidium_ (fig. 12) is a combination of both foregoing genera; it has three parallel transverse constrictions (one in the equatorial plane, and one on each side of it).

_The Latticed Domes_ (cupolas or chambers) of the cortical shell exhibit correspondingly a different number and disposition in the three known genera. In _Zonarium_ are found only four crossed chambers, separated by the sagittal and transverse septa; the axes of the four crossed domes are diagonal axes, whilst in the similar _Staurotholus_ they are dimensive axes (principal and transverse axes). In _Zonidium_ we find eight domes, each cupola of _Zonarium_ being halved by a diagonal septum. _Zoniscus_ is intermediate {684}between the two foregoing genera, and has six cupolas, three on each side of the sagittal septum.

The inner communication of the cupolas or chambers is more or less free, the lattice-work of the separating septa between them commonly remaining more or less imperfect, or represented only by some isolated beams or meshes. The outer network of the cupolas is commonly irregular (as in the majority of #Larcoidea#), but sometimes distinguished by a small number of regularly disposed larger apertures (similar to the "gates" of the Pylonida). From the surface radial spines often arise in characteristic number and symmetrical disposition, commonly as prolongations of the septal axes or of the constricted edges.

The _Medullary Shell_ in all Zonarida is a true trizonal or _Larnacilla_-shaped lattice-shell (compare above, p. 600); its perimeter (or the first lateral girdle) is sometimes more elliptical, at other times more hexagonal; the hexagon is amphithect; both its lateral sides are often concave and commonly longer than the four other sides.

The _Central Capsule_ in all Zonarida is in a strict geometrical sense a true lentellipsis (compare above, p. 599); its principal axis is commonly one and a third to one and a half times as great as the transverse axis, and twice to three times as great as the sagittal axis. The lentelliptical central capsule encloses the trizonal medullary shell, whilst it is externally enveloped by the chambered cortical shell.

_Synopsis of the Genera of Zonarida._

Two annular constrictions and four cupolas, 301. _Zonarium_.

Three annular constrictions and six cupolas, 302. _Zoniscus_.

Four annular constrictions and eight cupolas, 303. _Zonidium_.

Genus 301. _Zonarium_,[341] n. gen.

_Definition._--#Zonarida# with four dome-shaped chambers of the cortical shell, separated by two annular constrictions (one sagittal and one transverse).

The genus _Zonarium_ is the most simple form of the Zonarida, and differs from the nearly allied _Larnacalpis_ by two ring-like constrictions, which are crossed at right angles, one in the sagittal (or median) plane, and one in the transverse (or equatorial) plane. By these two annular constrictions four egg-shaped or kidney-shaped chambers become imperfectly separated, which correspond to the quadrants of the lateral plane. The first cause of the marked constrictions may be the formation of the latticed sagittal septum, which is found first in _Octopyle_, as halving the four gates of {685}_Tetrapyle_. Between this septum and the constricted narrow transverse girdle the cortical shell grows out in the form of four vaulted cupolas; every two opposite domes are congruent, two neighbouring are symmetrically equal.

1. _Zonarium quadrigatum_, n. sp.

Cortical shell quadrangular, one and a half times as long as broad, with four rounded corners. Surface thorny, with numerous short radial spines. Sagittal constriction twice as long as the hexagonal medullary shell. Four cupolas kidney-shaped.

_Dimensions._--Length of the cortical shell 0.16, breadth 0.11; length of the medullary shell 0.06, breadth 0.04.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

2. _Zonarium quadrispinum_, n. sp.

Cortical shell quadrangular, nearly rectangular, about twice as long as broad, with four corners, from which arise four strong, three-sided pyramidal, radial spines (crossed in two diagonals of the lateral plane). Surface thorny, only smooth in the transverse constriction. Sagittal constriction three times as long as the lentelliptical medullary shell. Four cupolas elliptical or nearly quadrangular.

_Dimensions._--Length of the cortical shell 0.22, breadth 0.1; length of the medullary shell 0.07, breadth 0.05.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

3. _Zonarium octangulum_, n. sp. (Pl. 50, fig. 9).

Cortical shell octangular, one and a fourth times as long as broad, with eight strong conical spines on the eight corners; these are separated by four deep constrictions on the poles of the principal and transverse axes, and by four truncated planes on the poles of the crossed diagonal axes between the former. Sagittal constriction twice as long as the hexagonal medullary shell. Four cupolas kidney-shaped or nearly pentagonal.

_Dimensions._--Length of the cortical shell 0.15, breadth 0.12; length of the medullary shell 0.07, breadth 0.04.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

4. _Zonarium tetratholium_, n. sp.

Cortical shell quadrangular, with four rounded corners. Surface thorny, with sixteen stronger radial spines; eight of these lie in the lateral plane, in the same symmetrical disposition as in the foregoing species; eight others lie on both sides of the lateral plane, opposite in pairs in two crossed diagonal planes, in the same symmetrical disposition as in _Tetrapyle octacantha_. Sagittal {686}constriction three times as long as the lentelliptical medullary shell. Four cupolas obliquely elliptical.

_Dimensions._--Length of the cortical shell 0.16, breadth 0.12; length of the medullary shell 0.04, breadth 0.03.

_Habitat._--North Pacific, Station 241, depth 2300 fathoms.

Genus 302. _Zoniscus_,[342] n. gen.

_Definition._--#Zonarida# with six dome-shaped chambers of the cortical shell, separated by three annular constrictions (one sagittal and two transverse, parallel to the equatorial plane).

The genus _Zoniscus_ differs from _Zonarium_ as well as from _Zonidium_ by the development of the transverse girdle, which is not constricted, but on the contrary prominently vaulted in the equatorial plane. Therefore both wings of the transverse girdle form here two opposite lateral or "equatorial cupolas," as in _Amphitholus_. These are separated from four other domes (the "corner cupolas") by two transverse annular constrictions, which correspond to the free edges of the original transverse girdle. The corner domes of each pair are separated from each other by the sagittal septum.

1. _Zoniscus rectangulus_, n. sp.

Cortical shell nearly rectangular, with rounded corners, nearly one and a half times as long as broad. Surface thorny, without larger radial spines. Sagittal constriction scarcely half as long as the hexagonal medullary shell. Both equatorial cupolas (or wings of the transverse girdle) scarcely half as large as the four corner cupolas.

_Dimensions._--Length of the cortical shell 0.15, breadth 0.11; length of the medullary shell 0.07, breadth 0.045.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

2. _Zoniscus hexathalamus_, n. sp.

Cortical shell nearly elliptical, one and a third times as long as broad. Surface nearly smooth, without radial spines. Sagittal constriction three times as long as the lentelliptical medullary shell. Both equatorial cupolas about as large as the four corner cupolas.

_Dimensions._--Length of the cortical shell 0.12, breadth 0.09; length of the medullary shell 0.035, breadth 0.025.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

{687}3. _Zoniscus tetracanthus_, n. sp. (Pl. 50, fig. 10).

Cortical shell nearly quadrangular, one and a half times as long as broad, with four prominent corners, from which arise in the lateral plane four strong, three-sided pyramidal radial spines (opposite in pairs in two crossed diagonal axes). Surface thorny, with exception of the concave lateral sides. Sagittal constriction two and a half times as long as the hexagonal medullary shell. Both equatorial cupolas scarcely half as large as the four corner cupolas.

_Dimensions._--Length of the cortical shell 0.18, breadth 0.12; length of the medullary shell 0.07, breadth 0.04.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

4. _Zoniscus octacanthus_, n. sp.

Cortical shell nearly four-sided, prismatic, one and a third times as long as broad, with spiny surface. Eight longer thin radial spines opposite in pairs in two crossed diagonal planes (as in _Tetrapyle octacantha_). Sagittal constriction two and a half times as long as the hexagonal medullary shell. Both equatorial cupolas somewhat larger than the four corner cupolas.

_Dimensions._--Length of the cortical shell 0.16, breadth 0.12; length of the medullary shell 0.055, breadth 0.04.

_Habitat._--Pacific, central area, Station 263, depth 2650 fathoms.

5. _Zoniscus hexatholius_, n. sp. (Pl. 50, fig. 11).

Cortical shell nearly rectangular, with four rounded corners and deep sagittal constriction, one and a fourth times as long as broad with thorny surface. Twelve longer edged radial spines; eight opposite in pairs in two crossed diagonal planes (as in the foregoing species), four others in the lateral plane, opposite in pairs on both sides of the sagittal constriction, which is scarcely twice as long as the hexagonal, in the equatorial plane constricted medullary shell. Both equatorial cupolas nearly of the same size as the four corner cupolas.

_Dimensions._--Length of the cortical shell 0.16, breadth 0.13; length of the medullary shell 0.07, breadth 0.04.

_Habitat._--South Pacific, Station 300, depth 1375 fathoms.

Genus 303. _Zonidium_,[343] n. gen.

_Definition._--#Zonarida# with eight dome-shaped chambers of the cortical shell, separated by four annular constrictions (one sagittal, one transverse, and two others parallel to the latter).

The genus _Zonidium_ must be regarded as a _Zonarium_, in which the four cupolas (in the quadrants of the lateral plane) are halved by diagonal beams or latticed septa, {688}lying opposite in pairs in two crossed diagonal planes. Therefore the number of the septa (four) and the domes (eight) is here doubled. Among the eight cupolas we distinguish four median (on both sides of the sagittal plane) and four lateral (on both sides of the equatorial plane); both groups are of different size and form. Probably _Zonidium_ is derived from _Zonarium_ by lattice-connection between the eight diagonal wing-spines, which in both species of this genus are present, the same as in _Tetrapyle octacantha_.

1. _Zonidium octostylium_, n. sp.

Cortical shell nearly quadrangular, with rounded corners and thorny surface. Eight long and thin radial spines on both sides of the lateral plane opposite in pairs and lying in two crossed diagonal planes (as in _Tetrapyle octacantha_). Sagittal constriction three times as long as the lentelliptical medullary shell. Four medial cupolas (on both sides of the sagittal plane) somewhat larger than the four lateral cupolas (on both sides of the equatorial plane).

_Dimensions._--Length of the cortical shell 0.15, breadth 0.12; length of the medullary shell 0.05, breadth 0.03.

_Habitat._--Indian Ocean, Madagascar, Rabbe, surface.

2. _Zonidium octotholium_, n. sp. (Pl. 50, fig. 12).

Cortical shell nearly octangular, with spiny surface; twenty long and stout radial spines between numerous smaller spines; eight wing-spines opposite in pairs in two crossed diagonal planes (as in the preceding species); twelve other strong spines in the lateral plane (four longer opposite in pairs on the poles of the principal and transverse axes, eight others smaller, alternating between these and the diagonal spines). Sagittal constriction twice as long as the hexagonal medullary shell. Four median cupolas somewhat smaller than the four lateral cupolas.

_Dimensions._--Length of the cortical shell 0.18, breadth 0.15; length of the medullary shell 0.07, breadth 0.05.

_Habitat._--Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.

Family XXIX. #LITHELIDA#, Haeckel (Pl. 49, figs. 1-7).

_Lithelida_, Haeckel, 1862, Monogr. d. Radiol., p. 515.

_Definition._--#Larcoidea# with symmetrical spiral shell, divided by the spiral plane into two symmetrical halves; all windings of the spiral lie in this plane. Primordial chamber either simple or _Larnacilla_-shaped.

The family #Lithelida# comprises all those #Larcoidea# in which the growth of the latticed shell is spirally winding in one plane, _Nautilus_-like. They agree in the spiral growth with the following family. But in the Streblonida the spiral is screw-shaped, {689}ascending (like _Helix_). Therefore in these latter the geometrical fundamental form of the shell is asymmetrical or "dysdipleural," whereas in the Lithelida bilateral-symmetrical or "eudipleural." The lentelliptical or nearly spherical shell may be divided by a median section into two symmetrical halves; the right half is the mirror image of the left half.

When in 1862 I founded the family Lithelida in my Monograph (p. 515), I knew only one genus, _Lithelius_, with two species. The rich material of the Challenger collection contains a great number of similar spirally constructed #Larcoidea#, so that at the present time we may distinguish at least six genera. These belong to two different subfamilies, which may possibly be afterwards better separated as families. The first subfamily, Spiremida, possess a simple, spherical or subspherical, medullary shell; the second subfamily, Larcospirida, possess a trizonal or _Larnacilla_-shaped medullary shell. No doubt these latter must be derived from Pylonida, as we observe all stages of development starting from a simple _Trizonium_; but perhaps also the Spiremida have the same origin, their simple, spherical or subspherical, medullary shell being derived from a trizonal or _Larnacilla_-shaped medullary shell by reduction.

The general appearance in both subfamilies of the Lithelida is quite the same, and it requires a careful study of the medullary shell to distinguish certainly the Spiremida from the Larcospirida. This distinction is often not easy, particularly in the larger forms; the shell is often very opaque and difficult to understand. Only in one position, if the spiral axis be parallel to the axis of the eye of the observer, and the spiral plane be therefore fully seen in the optical plane of the microscope, the spiral line (or the axial section of the latticed spiral lamella) is distinctly observed; in all other positions the figure of the spiral is more or less indistinct, and the whole microscopical image often quite intricate and confused. The sufficient study of this family requires therefore the contemplation of the shell from different sides, and is the more difficult, as the variability of the Lithelida--as of the Pylonida--is extraordinarily great.

The description which I gave of _Lithelius_ (1862) in my Monograph is in some points erroneous, and was afterwards (1879) corrected by R. Hertwig, who explained particularly the near relation of it to _Tetrapyle_. Indeed the intermediate forms between the Lithelida and the Pylonida are so numerous and so evident in all stages of development, that the derivation of the former (at least of the Larcospirida) from the latter is quite clear. The analogy between the structure of the Lithelida and the calcareous (foraminiferous) Alveolinida is not so complete as I supposed it to be in my Monograph (1862); particularly the formation of the small chambers between the turnings of the spiral lamella is much more complete in the Alveolinida than in the Lithelida.

The cortical shell of all Lithelida has the same geometrical fundamental form as _Nautilus_ or as the nautiloid Polythalamia (_Polystomella_, _Nummulites_, &c.); therefore the shell is dipleural, being divided by the median plane into two symmetrical lateral halves. {690}Since the spiral line lies in the median plane, we will call it the spiral plane; it separates the right half from the left. The axis of the body, around which the spiral turns (without touching it), is the spiral axis. The latticed part of the cortical shell, which turns around them, is the spiral lamella. Only in one genus of our family, viz., _Tholospira_, are the spiral axis, the lateral axis, the spiral plane, and the sagittal plane quite as in _Nautilus_. In all other genera this disposition is different or is uncertain. This depends on the different part of the cortical shell, from which the spiral growth begins. In this respect we can distinguish four different modes.

In the Larcospirida (or the Lithelida with _Larnacilla_-shaped medullary shell) the spiral growth exhibits four quite different forms. It begins here with _Larcospira_, in which already the first cortical girdle of the Diplozonaria determines the spiral growth; one wing of this girdle, the transverse girdle of _Amphipyle_, grows more swiftly than the other, overgrows it, and thus turns around the principal axis. In _Pylospira_ the first or transverse girdle is already perfectly formed (as in _Amphipyle_), and the spiral growth is introduced by the second or lateral girdle of _Tetrapyle_; one wing of it (the right or the left) grows more swiftly than the other, overgrows it, and thus turns around the sagittal axis. In _Tholospira_ also the second girdle is complete, and the spiral growth begins from the third or sagittal girdle. One of its wings grows more swiftly than the other, overgrows it, and thus turns around the transverse axis. Consequently we see that each of the three dimensive planes of the lentelliptical Larcoid-body may be the spiral plane: in _Larcospira_ the transverse plane, in _Pylospira_ the lateral plane, in _Tholospira_ the sagittal plane. Correspondingly the spiral axis in the first genus is the principal, in the second the sagittal, in the third the transverse axis of the central _Larnacilla_-shell. Therefore in these three genera the spiral plane is the plane of the latticed girdle, which determines the spiral growth, one of both its wings overgrowing the other.

In each of the three above mentioned genera the spiral may be simple or double; it remains simple if only one of both wings of the turning girdle overgrow the other, and this latter remain a simple half girdle (or tube-like wing). Whereas the spiral becomes double if the second wing of the girdle afterwards follow the example of the first wing and now turn around it in the same direction. As this happens in all three genera, we can subdivide them into six subgenera.

A quite peculiar form of spiral growth is produced in _Spironium_, in which the direction of growth in both lateral wings of the transverse girdle is inverse from the beginning. The left wing grows against the posterior, the right wing against the anterior pole of the principal axis, turning around it in crossed, eight-like spirals. The whole shell afterwards assumes a lentelliptical form.

Commonly between the embracing spiral turnings or convolutions a great number of radial beams is developed, irregularly disposed and often branching; they support the {691}thin spiral lamellæ and give to the whole shell more solidity. Often these beams form imperfect radial septa, by which the spiral cavity of the turnings is divided into a variable number of chambers. But these chambers never become so regular and perfect as in the analogous nautiloid Polythalamia.

In many Lithelida the growth of the shell reaches a certain limit, concluding with the formation of a superficial latticed lamella of lentelliptical or nearly spherical form. In many other forms of the family this seems not to be the case; but these may possibly be younger forms, afterwards reaching the same limit.

The network of the shell in the Lithelida is commonly quite irregular, and so variable that its special conformation has usually no value in the determination of the species. The surface of the shell is often covered with radial spines, which are sometimes arborescent.

The central capsule seems always to preserve the same lentelliptical form (or triaxial ellipsoid) as in all other #Larcoidea#. With the increase of growth it encloses successively a larger part of the spiral cortical shell, but on the outside is constantly protected by the last turnings of the spiral, or by the lattice-lamella of the surface.

_Synopsis of the Genera of Lithelida._

------------------------------------------------------------------------- I. Subfamily Spiremida. Central medullary shell simple, spherical or lentelliptical. ------------------------------------------------------------------------- Surface of the cortical shell smooth or thorny, without radial spines, 304. _Spirema_.

Surface of the cortical shell covered with numerous simple or branched radial spines, 305. _Lithelius_. ------------------------------------------------------------------------- II. Subfamily Larcospirida. Central medullary shell double, trizonal or _Larnacilla_-shaped. ------------------------------------------------------------------------- The transverse girdle turns around the principal axis, 306. _Larcospira_.

The lateral girdle turns around the sagittal axis, 307. _Pylospira_.

The sagittal girdle turns around the transverse axis, 308. _Tholospira_.

Both wings of the transverse girdle turn around the principal axis in an opposite diagonal direction, 309. _Spironium_.

Subfamily 1. SPIREMIDA, Haeckel, 1881, Prodromus, p. 464.

_Definition._--#Lithelida# with simple, spherical or subspherical, medullary shell.

Genus 304. _Spirema_,[344] Haeckel, 1881, Prodromus, p. 464.

_Definition._--#Lithelida# with simple, spherical or subspherical, medullary shell, and lentelliptical or subspherical, spirally constructed cortical shell; surface smooth or thorny, without radial spines.

{692}The genus _Spirema_ begins the series of the Spiremida, or of those Lithelida in which the medullary shell presents a simple latticed sphere or ellipsoid, never composed of a double, trizonal or _Larnacilla_-shaped shell. In the present state of our knowledge we cannot say whether this simple medullary shell be a primary formation, or effected by secondary means, by reduction of a double _Larnacilla_-shaped medullary shell, which is constantly found in the Larcospirida. The species of this genus (as of all Lithelida) are difficult to distinguish, are transformistic, and incline very much to variations and abnormalities. The spiral may be simple or double.

Subgenus 1. _Spiremarium_, Haeckel.

_Definition._--Spiral convolutions of the cortical shell simple.

1. _Spirema lentellipsis_, n. sp.

Cortical shell lentelliptical, with smooth surface; proportion of its three dimensive axes = 4 : 5 : 6. In the median plane are visible four perfect turnings of the simple spiral, the breadth of which gradually increases towards the third convolution, finally decreasing; the broadest (third) turning three times as broad as the simple spherical medullary shell.

_Dimensions._--Length of the lentelliptical cortical shell 0.18, breadth 0.15, height 0.12; diameter of the spherical medullary shell 0.02.

_Habitat._--North Atlantic, Station 353, surface.

2. _Spirema melonia_, n. sp. (Pl. 49, fig. 1).

Cortical shell nearly spherical, with smooth surface; proportion of its three dimensive axes = 1.4 : 1.5 : 1.6. In the median plane are visible three perfect turnings of the simple spiral, all of the same breadth as the simple spherical medullary shell; the breadth of each convolution somewhat greater at the poles of the principal than at the poles of the sagittal axis.

_Dimensions._--Length of the shell 0.16, breadth 0.15, height 0.14; medullary shell 0.018.

_Habitat._--Pacific, central area, Station 271, surface.

3. _Spirema flustrella_, Haeckel.

_Flustrella haliomma_, Ehrenberg (1861), Abhandl. d. k. Akad. d. Wiss. Berlin, 1872, p. 293, Taf. ii. fig. 6.

Cortical shell egg-shaped, with thorny surface; proportion of its three axes = 4 : 5 : 6. In the median plane are visible three perfect turnings of the simple spiral, the first and second of about the same breadth as the simple spherical medullary shell, the third suddenly increasing, and finally three to four times as broad. Network of the surface irregular, with roundish pores.

_Dimensions._--Length of the shell 0.2, breadth 0.17, height 0.14; medullary shell 0.013.

_Habitat._--North Atlantic, Greenland, 1000 fathoms, Ehrenberg; Færöe Channel, John Murray.

{693}Subgenus 2. _Spiremidium_, Haeckel.

_Definition._--Spiral convolutions of the cortical shell double.

4. _Spirema diplospira_, n. sp.

Cortical shell lentelliptical, with smooth surface; proportion of its three dimensive axes = 6 : 7 : 8. In the median plane are visible three perfect turnings of a double spiral, the breadth of which gradually increases; the broadest (third) convolution three times as broad as the simple lentelliptical medullary shell.

_Dimensions._--Length of the shell 0.24, breadth 0.21, height 0.18; medullary shell 0.02.

_Habitat._--Tropical Pacific, Philippines, Station 200, depth 250 fathoms.

5. _Spirema subglobosum_, n. sp.

Cortical shell nearly spherical, with thorny surface; proportion of its three axes = 2 : 2.1 : 2.2. In the median plane are visible two perfect turnings of a double spiral, the breadth of which in the second convolution is four times as great as that of the first convolution and the simple spherical medullary shell.

_Dimensions._--Length of the shell 0.22, breadth 0.21, height 0.2; medullary shell 0.02.

_Habitat._--Tropical Atlantic, off Sierra Leone, Station 348, depth (2450) fathoms.

Genus 305. _Lithelius_,[345] Haeckel, 1862, Monogr. d. Radiol., p. 519.

_Definition._--#Lithelida# with simple, spherical or subspherical, medullary shell, and lentelliptical or subspherical, spirally constructed cortical shell; surface covered with numerous, simple or branched, radial spines.

The genus _Lithelius_, founded by me in 1862, and represented by two Mediterranean species, was at that time the only known form of this family, which now contains six genera and twenty-seven species. It differs from the foregoing _Spirema_ in the possession of numerous radial spines on the surface. These may be either simple or branched. The spiral may be simple or double, and according to this latter modification we distinguish two different subgenera.

Subgenus 1. _Lithospira_, Haeckel.

_Definition._--Spiral convolutions of the cortical shell simple.

1. _Lithelius spiralis_, Haeckel.

_Lithelius spiralis, Haeckel_, 1862, Monogr. d. Radiol., p. 519, Taf. xxvii. figs. 6, 7.

Cortical shell lentelliptical, one and a third times as long as broad, covered with very numerous (one hundred to one hundred and fifty or more) simple, bristle-shaped radial spines, about as long {694}as the shell. Spiral turnings simple, all nearly of the same breadth and scarcely broader than the simple spherical medullary shell.

_Dimensions._--Length of the cortical shell (with six spiral convolutions) 0.15, breadth 0.13; diameter of the medullary shell 0.012.

_Habitat._--Mediterranean, Messina, Haeckel, surface; Atlantic, Stations 348 to 353, surface.

2. _Lithelius primordialis_, R. Hertwig.

_Lithelius primordialis_, R. Hertwig, 1879, Organism. d. Radiol., p. 54, Taf. vi. figs. 4, 4_a_.

Cortical shell subspherical, covered with numerous simple, bristle-shaped radial spines, longer than the shell. Spiral turnings simple, with gradually increasing breadth, so that the beginning of the third spiral is twice as broad as the first and as the simple spherical medullary shell.

_Dimensions._--Diameter of the cortical shell (with two spiral convolutions) 0.12; diameter of the medullary shell 0.02.

_Habitat._--Mediterranean, Messina, R. Hertwig, surface.

3. _Lithelius alveolina_, Haeckel, 1862.

_Lithelius alveolina_, Haeckel, 1862, Monogr. d. Radiol., p. 520, Taf. xxvii. figs. 8, 9.

Cortical shell spherical, covered with simple, very numerous (two hundred to three hundred or more), short, bristle-shaped radial spines, scarcely half as long as the radius of the shell. Spiral turnings simple, with gradually increasing breadth, so that the beginning of the third spiral is three times as broad as the first and as the simple spherical medullary shell.

_Dimensions._--Diameter of the cortical shell (with four spiral convolutions) 0.2; diameter of the medullary shell 0.01.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, on many Stations, surface.

4. _Lithelius capreolus_, n. sp.

Cortical shell lentelliptical, one and a fourth times as long as broad, covered with numerous (eighty to one hundred and twenty or more) short, branched radial spines, about half as long as the radius of the shell; each spine once or twice dichotomous, with curved divergent branches. Spiral turnings simple, with gradually increasing breadth, so that the beginning of the third spiral is twice as broad as the first, and as the simple spherical medullary shell.

_Dimensions._--Length of the cortical shell (with four spiral convolutions) 0.18, breadth 0.14; diameter of the medullary shell 0.015.

_Habitat._--Pacific, central area, Station 274, surface.

Subgenus 2. _Drymospira_, Haeckel, 1881, Prodromus, p. 464.

_Definition._--Spiral convolutions of the cortical shell double.

{695}5. _Lithelius solaris_, n. sp. (Pl. 49, fig. 2).

Cortical shell spherical, covered with simple, very numerous (two hundred to three hundred) bristle-shaped radial spines, longer than the diameter of the shell. Spiral turnings double, both of the same breadth, gradually increasing with the growth of the shell and several times surpassing the diameter of the simple spherical medullary shell. (Pl. 49, fig. 2, exhibits only the first convolutions in the centre of the shell.)

_Dimensions._--Diameter of the cortical shell (with four spiral convolutions) 0.18; diameter of the medullary shell 0.02.

_Habitat._--Pacific, central area, Stations 266 to 272, surface and in various depths.

6. _Lithelius arborescens_, n. sp.

Cortical shell lentelliptical, one and a half times as long as broad, covered with numerous (fifty to eighty or more) branched radial spines, about as long as the greatest diameter of the shell; each spine with two to four lateral branches, which are again branched or dichotomous. Spiral turnings double, both of little different breadth, which increases considerably with the growth of the shell, so that the third turn is four times as broad as the simple spherical medullary shell.

_Dimensions._--Length of the cortical shell (with three spiral convolutions) 0.18, breadth 0.12; diameter of the medullary shell 0.01.

_Habitat._--North Atlantic, Færöe Channel, surface, John Murray.

Subfamily 2. LARCOSPIRIDA, Haeckel.

_Definition._--#Lithelida# with double, trizonal, or _Larnacilla_-shaped medullary shell.

Genus 306. _Larcospira_,[346] n. gen.

_Definition._--#Lithelida# with double, trizonal, or _Larnacilla_-shaped medullary shell; cortical shell subspherical or lentelliptical, constructed of a simple or double spiral of the transverse girdle (or primary cortical girdle); the spiral lamella revolving around the principal axis.

The genus _Larcospira_ begins the interesting series of the Larcospirida, or of those Lithelida in which the medullary shell is formed by a trizonal or _Larnacilla_-shaped lattice-shell, and the cortical shell by spiral turnings of one of the three girdles, which compose the cortical shell of the Pylonida. In _Larcospira_, as the oldest and most simple form of Larcospirida, the spiral is formed by the transverse girdle, or the first girdle of the Diplozonaria, the only cortical girdle of _Amphipyle_. If in this genus one of both wings of the transverse girdle grow stronger than the other and overgrow the latter, turning {696}around the principal axis, we reach the characteristic form of _Larcospirema_, the first subgenus of _Larcospira_; but if afterwards the second wing follow the example of the first, and overgrow it from the other side, we reach the typical form of the second subgenus, _Larcospironium_. In this latter subgenus the spiral becomes double, whilst in the former it remains simple.

Subgenus 1. _Larcospirema_, Haeckel.

_Definition._--Spiral convolutions or turns of the cortical shell simple; only one single wing of the transverse girdle turning around the principal axis.

1. _Larcospira lentelliptica_, n. sp.

Cortical shell with smooth surface, four times as long as the lentelliptical medullary shell. Perimeter of the lateral plane elliptical, one and a half times as long as broad, without constrictions. One lateral wing of the transverse girdle is more strongly developed and turns around the other in two to three simple spiral turns.

_Dimensions._--Length of the cortical shell 0.2, breadth 0.16; length of the medullary shell 0.05, breadth 0.04.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

2. _Larcospira quadrangula_, n. sp. (Pl. 49, fig. 3).

Cortical shell with thorny surface, three times as long as the lentelliptical medullary shell. Perimeter of the lateral plane nearly quadrangular, with four rounded corners (on the poles of two crossed diagonal axes), one and a third times as long as broad, with one sagittal constriction at the poles of the principal axis. One lateral wing of the transverse girdle turns around the other in one and a half to two simple spiral turns.

_Dimensions._--Length of the cortical shell 0.18, breadth 0.14; length of the medullary shell 0.06, breadth 0.04.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

3. _Larcospira sexangula_, n. sp.

Cortical shell with spiny surface, four times as long as the hexagonal medullary shell. Perimeter of the lateral plane nearly hexagonal, one and a half times as long as broad, with six rounded corners (two on the poles of the principal axis, four on the poles of two crossed diagonal axes), with three slight ring-like constrictions. One lateral wing of the transverse girdle turns around the other in two to two and a half simple spiral turns.

_Dimensions._--Length of the cortical shell 0.24, breadth 0.16; length of the medullary shell 0.06, breadth 0.04.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

{697}Subgenus 2. _Larcospironium_, Haeckel.

_Definition._--Spiral convolutions or turns of the cortical shell double; both wings of the transverse girdle turning around the principal axis.

4. _Larcospira oliva_, n. sp.

Cortical shell with smooth surface, six times as long as the lentelliptical medullary shell. Perimeter of the lateral plane elliptical, one and a fourth times as long as broad, without constrictions. Both lateral wings of the transverse girdle turn round one another and form one and a half to two double spiral turns.

_Dimensions._--Length of the cortical shell 0.25, breadth 0.2; length of the medullary shell 0.04, breadth 0.035.

_Habitat._--Antarctic Ocean, Station 157, depth 1950 fathoms.

Genus 307. _Pylospira_,[347] n. gen.

_Definition._--#Lithelida# with double, trizonal or _Larnacilla_-shaped medullary shell; cortical shell subspherical or lentelliptical, constructed of a single or double spiral of the lateral girdle (or second cortical girdle); the spiral lamella revolving round the sagittal axis.

The genus _Pylospira_ follows after _Larcospira_ as the second genus of Larcospirida; but in this latter the spiral of the cortical shell is formed by the transverse girdle (or the first lattice-girdle of the Diplozonaria), whilst in _Pylospira_ it is produced by the lateral girdle, or the second lattice-girdle of that group. Therefore _Pylospira_ may be derived phylogenetically from _Tetrapyle_ in the same manner as _Larcospira_ from _Amphipyle_. Whilst in this latter the first cause of the spiral turning, the unequal growth of both girdle-wings, proceeds from the transverse girdle, in _Pylospira_ it proceeds from the lateral girdle. One of its wings overgrows the other, turning around the sagittal axis. If the second wing do not become developed, the spiral remains simple and represents the subgenus _Pylospirema_; but if afterwards the second wing follow the example of the first and overgrow it from the other side, we reach the typical form of the second subgenus, _Pylospironium_, with a double spiral.

Subgenus 1. _Pylospirema_, Haeckel.

_Definition._--Spiral convolutions or turns of the cortical shell simple, only one single wing of the lateral girdle turning around the sagittal axis.

{698}1. _Pylospira tetrapyle_, n. sp.

Cortical shell with thorny surface, five times as long as the lentelliptical medullary shell. Perimeter of the lateral plane elliptical, one and a half times as long as broad. Four internal gates (as in _Tetrapyle_, between the complete lateral wings of the transverse girdle) kidney-shaped. One principal wing of the lateral girdle turns around the other in one and a half to two simple spiral turns.

_Dimensions._--Length of the cortical shell 0.21, breadth 0.15; length of the medullary shell 0.04, breadth 0.03.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

2. _Pylospira octopyle_, n. sp. (Pl. 49, fig. 4).

Cortical shell with thorny surface, three times as long as the lentelliptical medullary shell. Perimeter of the lateral plane elliptical or nearly hexagonal, with four rounded corners (on the poles of two crossed diagonal axes), one and a third times as long as broad. Eight internal egg-shaped gates (as in _Octopyle_), between the complete lateral wings of the transverse girdle, and two axial beams in the principal axis. One single wing of the lateral girdle turns around the other in two to three simple spiral turns.

_Dimensions._--Length of the cortical shell 0.18, breadth 0.14; length of the medullary shell 0.06, breadth 0.035.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

Subgenus 2. _Pylospironium_, Haeckel.

_Definition._--Spiral convolutions or turns of the cortical shell double; both wings of the lateral girdle turning around the sagittal axis.

3. _Pylospira cymbium_, n. sp.

Cortical shell with smooth surface, seven times as long as the lentelliptical medullary shell. Perimeter of the lateral plane elliptical, one and a third times as long as broad. Four internal kidney-shaped gates between the complete lateral wings of the transverse girdle (as in _Tetrapyle_). Both principal wings of the lateral girdle turn round one another in two to two and a half double spiral turns.

_Dimensions._--Length of the cortical shell 0.22, breadth 0.17; length of the medullary shell 0.03, breadth 0.025.

_Habitat._--Indian Ocean, Madagascar, Rabbe, surface.

{699}Genus 308. _Tholospira_,[348] n. gen.

_Definition._--#Lithelida# with double, trizonal or _Larnacilla_-shaped medullary shell; cortical shell subspherical or lentelliptical constructed of a simple or double spiral of the sagittal girdle (or third cortical girdle); the spiral lamella revolving around the transverse axis.

The genus _Tholospira_ represents the third genus of Larcospirida. Whilst the spiral growth of the cortical shell is produced in _Larcospira_ by the first (transverse) girdle of the Diplozonaria, in _Pylospira_ by the second (lateral) girdle, in _Tholospira_ it is effected by the third or sagittal girdle, which we found complete in _Pylonium_. If in this genus one wing of the sagittal girdle overgrow the other remaining one and turn around the transverse axis, we get _Tholospirema_, the first subgenus of our genus, with simple spiral; but if afterwards the second wing follow the example of the first, and overgrow it from the other side, we get _Tholospironium_, with double spiral.

Subgenus 1. _Tholospirema_, Haeckel.

_Definition._--Spiral convolutions or turns of the cortical shell simple, only one single wing of the sagittal girdle turning around the transverse axis.

1. _Tholospira nautiloides_, n. sp.

Cortical shell with smooth surface, five times as long as the lentelliptical medullary shell. Perimeter of the lateral plane elliptical, one and a half times as long as broad. Four internal kidney-shaped gates (between the lateral wings of the transverse girdle, as in _Tetrapyle_). One wing of the sagittal girdle turns around the other in two to two and a half simple spiral turns.

_Dimensions._--Length of the cortical shell 0.24, breadth 0.18; length of the medullary shell 0.05, breadth 0.04.

_Habitat._--Indian Ocean, between Ceylon and Socotra, Haeckel, surface.

2. _Tholospira spinosa_, n. sp.

Cortical shell covered with numerous (sixty to eighty or more) simple, bristle-like radial spines, about the length of the shell. Perimeter of the lateral plane nearly quadrangular, with four rounded corners (on the poles of two crossed diagonal axes), one and a half times as long as broad. Eight internal egg-shaped gates (between the lateral wings of the transverse girdle and two axial {700}beams in the principal axes, as in _Octopyle_). One wing of the sagittal girdle turns around the other in two to three simple spiral turns.

_Dimensions._--Length of the cortical shell 0.27, breadth 0.18; length of the medullary shell 0.04, breadth 0.03.

_Habitat._--South Pacific, Station 288, surface.

3. _Tholospira dendrophora_, n. sp. (Pl. 49, fig. 6).

Cortical shell covered with numerous (forty to fifty or more) branched radial spines, about half as long as the shell; each spine with two to six dichotomous branches. Perimeter of the lateral plane elliptical, one and a third times as long as broad. Eight internal egg-shaped gates, as in the foregoing species. One single wing of the sagittal girdle turns around the other in three to four spiral turns.

_Dimensions._--Length of the cortical shell 0.22, breadth 0.17; length of the medullary shell 0.05, breadth 0.04.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

Subgenus 2. _Tholospironium_, Haeckel.

_Definition._--Spiral convolutions of the cortical shell double; both wings of the sagittal girdle turning around the transverse axis.

4. _Tholospira hystrix_, n. sp.

Cortical shell covered with numerous (sixty to eighty or more) simple conical spines, about half as long as the shell. Perimeter of the lateral plane hexagonal, one and a half times as long as broad. Four internal kidney-shaped gates, as in _Tetrapyle_. Both wings of the sagittal girdle turn round one another in two to two and a half double spiral turns.

_Dimensions._--Length of the cortical shell 0.21, breadth 0.14; length of the medullary shell 0.04, breadth 0.03.

_Habitat._--North Atlantic, Station 354, surface.

5. _Tholospira cervicornis_, n. sp. (Pl. 49, fig. 5).

Cortical shell covered with numerous (forty to fifty or more) branched radial spines; each spine antler-shaped, about as long as the medullary _Larnacilla_-shell, with eight to twelve dichotomous branches (similar to _Cromyodrymus abietinus_, Pl. 30, fig. 6). Perimeter of the lateral plane elliptical, one and a third times as long as broad. Four internal kidney-shaped gates, as in _Tetrapyle_. Both wings of the sagittal girdle turn round one another in one and a half to two double spiral turns.

_Dimensions._--Length of the cortical shell 0.2, breadth 0.15; length of the medullary shell 0.03, breadth 0.025.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

{701}Genus 309. _Spironium_,[349] n. gen.

_Definition._--#Lithelida# with double, trizonal or _Larnacilla_-shaped medullary shell; cortical shell subspherical or lentelliptical, constructed of two crossed spirals, which arise from both lateral wings of one girdle (commonly the lateral girdle) and revolve in an opposite diagonal direction around the principal axis.

The genus _Spironium_ differs in a very remarkable manner from all foregoing Lithelida, and is distinguished by a quite peculiar mode of growth. It is most nearly allied to _Larcopyle_, and may, like this, be derived from _Amphipyle_ (or rather from _Larnacilla_, beginning to transform into _Amphipyle_). But whilst in _Larcopyle_ one of the two wings of the lateral girdle overgrows the other in the direction of the transverse axis (turning around the principal axis), here in _Spironium_ both lateral wings begin at the same time to grow out from the lateral sides of the _Larnacilla_-shaped medullary shell; the most remarkable thing is, however, that the direction of growth in the wings is diverse from the beginning: the left wing grows downwards and turns around the lower (aboral) pole of the principal axis, the right wing grows upwards and turns around the upper (oral) pole of the same axis. Thus both wings of the lateral girdle are crossed in diagonal axes, and with increasing growth one overgrows the other in the direction of these diagonals, so as to resemble the figure 8 in shape. The open gates remaining between the turnings of the girdle become afterwards closed on the surface by irregular lattice-work, and so the whole cortical shell assumes finally a spherical, ellipsoidal, or lentelliptical form. Its surface sometimes becomes covered with simple or branched radial spines. In the interior the eight characteristic egg-shaped gates of _Octopyle_ are commonly (or constantly?) visible, two strong radial beams in the principal axis arising from the poles of the lentelliptical medullary shell.

Subgenus 1. _Spironetta_, Haeckel.

_Definition._--Surface of the shell smooth or rough, but not with radial spines.

1. _Spironium octonium_, n. sp. (Pl. 49, fig. 7).

Cortical shell lentelliptical, its breadth (or transverse axis) surpassing considerably the length (or the principal axis). Surface thorny and somewhat hump-backed. The spiral wings of the transverse girdle have about the same breadth as the eight internal gates between them and the axial beams.

_Dimensions._--Length of the cortical shell (or principal axis) 0.15, breadth (or transverse axis) 0.2; length of the medullary shell 0.05, breadth 0.04.

_Habitat._--South Atlantic, west of Tristan da Cunha, Station 332, depth 2200 fathoms.

{702}2. _Spironium diagonale_, n. sp.

Cortical shell nearly spherical, four times as great as the subspherical medullary shell. Surface rough. The spiral wings of the transverse girdle about half as broad as the eight internal gates between them and the axial beams.

_Dimensions._--Diameter of the cortical shell 0.16, of the medullary shell 0.04.

_Habitat._--Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.

Subgenus 2. _Spironilla_, Haeckel.

_Definition._--Surface of the shell covered with simple or branched radial spines.

3. _Spironium spinosum_, n. sp.

Cortical shell subspherical, five times as great as the subspherical medullary shell. Surface covered with numerous (sixty to eighty or more) simple, bristle-like radial spines, longer than the shell. The spiral wings of the transverse girdle of about the same breadth as the eight internal gates between them and the axial beams.

_Dimensions._--Diameter of the cortical shell 0.2, of the medullary shell 0.04.

_Habitat._--Pacific, central area, Station 274, surface.

4. _Spironium arbustum_, n. sp.

Cortical shell lentelliptical, its breadth surpassing its length considerably. Surface covered with numerous (forty to sixty or more) thin radial spines, about as long as the greatest diameter of the shell; each spine with two to six lateral branches, which are either simple or again branched (similar to _Cromyodrymus abietinus_, Pl. 30, fig. 6). The spiral wings of the transverse girdle only half as broad as the eight internal gates between them and the strong beams of the principal axis.

_Dimensions._--Length of the cortical shell 0.12, breadth 0.15; length of the hexagonal medullary shell 0.05, breadth 0.04.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

Family XXX. #STREBLONIDA#, n. fam. (Pl. 49, figs. 8, 9).

_Definition._--#Larcoidea# with asymmetrical, spiral, polythalamous shell, composed of a variable number of roundish chambers, which form together an ascending spiral; both halves of the shell unequal. Primordial chamber either simple or _Larnacilla_-shaped.

The family #Streblonida# comprises those #Larcoidea# in which a number of chambers is arranged in an ascending spiral, round a simple or trizonal primordial chamber, like winding stairs. They show the same spiral structure as in the foregoing {703}family, but whilst in the Lithelida the spiral line lies in one plane (as in _Nautilus_), in the Streblonida it ascends like a screw (as in _Helix_). Therefore the former have the same relation, regarding the spiral structure, to the nautiloid Polythalamia as the latter to the turbinoid Foraminifera. Indeed the single forms of Streblemida repeat in their special structure the characteristic genera of Turbinoida, such as _Globigerina_, _Rosalina_, _Pulvinulina_, _Hastigerina_, &c. As in these calcareous turbinoid Foraminifera, so also in the analogous siliceous Streblonida the distinction of species is very difficult and open to many objections.

The number of species in this family is very small; all are rare and for the most part very opaque and difficult to understand, so that the following distinction of a dozen species can have only a provisional value. To get a complete idea of their peculiar structure, the shell must be turned and observed from different sides, and thus their full study requires yet much time and work. There are to be found evident transitional forms between them and the Lithelida on the one hand and the Soreumida on the other. Besides this, most species of Streblonida seem to have more inclination to individual varieties and abnormalities than the majority of the other Radiolaria.

The general form of the whole shell is in the Streblonida sometimes more egg-shaped or even subspherical, at other times more top-like or conical, sometimes nearly discoidal. The height of the shell (or the vertical axis of the ascending spiral) is occasionally larger, at other times smaller than the breadth (or the greatest horizontal diameter, perpendicular to the height). Some very flat forms seem to approach the Lithelida. With regard to the internal screw-formation, the shell of all Streblonida is asymmetrical.

The number of the aggregated incomplete chambers is commonly between ten and twenty, but ascends sometimes to thirty, forty, or more. Sometimes the size of all the chambers is nearly the same, sometimes they increase gradually, occasionally also very rapidly. The primordial chamber (or the first and oldest) seems to be commonly the smallest, and inversely, the last and youngest chamber, the largest. But sometimes (in _Streblopyle_) also the contrary may be the case. The form of the single chambers is very variable, from the spherical or hemispherical through all transitions leading to irregular roundish or longish forms. The network is commonly irregular, with small roundish pores of different sizes, but sometimes also regular, circular. The surface of the shell is commonly smooth or rough, rarely covered with radial spines. In most species the reticulation and particularly the separation of the chambers is more or less incomplete.

As in the Lithelida, so also in the Streblonida we can distinguish two subfamilies. In the Streblacanthida (_Streblonia_, _Streblacantha_) the primordial chamber is a simple, spherical, subspherical, or lentelliptical latticed shell. In the Streblopylida (_Streblopyle_) the primordial chamber is trizonal or _Larnacilla_-shaped, as in the greater number of #Larcoidea#, composed of three elliptical latticed girdles of unequal size, perpendicular one to another, and surrounding a simple central chamber. As in the Lithelida, so also {704}here we cannot certainly say whether the former have originated from the latter by reduction of the _Larnacilla_-shell, or whether both groups be of different origin. The latter is perhaps more probable. This family as well as the foregoing requires a much more careful study than I could give to it.

_Synopsis of the Genera of Streblonida._

------------------------------------------------------------------------- I. Subfamily Streblacanthida. Primordial chamber simple, spherical or lentelliptical. ------------------------------------------------------------------------- Shell without radial spines, 310. _Streblonia_.

Shell with radial spines, 311. _Streblacantha_. ------------------------------------------------------------------------- II. Subfamily Streblopylida. Primordial chamber trizonal or _Larnacilla_-shaped. ------------------------------------------------------------------------- Shell without radial spines, 312. _Streblopyle_.

Genus 310. _Streblonia_,[350] n. gen.

_Definition._--#Streblonida# with simple, spherical, subspherical, or lentelliptical primordial chamber, beginning the screw-like series of spirally ascending chambers. Surface smooth or thorny, without radial spines.

The genus _Streblonia_ contains those Streblonida in which a variable number of roundish, subspherical, or longish chambers form a screw-like aggregate, beginning with a quite simple primordial chamber. The special order of the complex spiral offers interesting resemblances to different genera of the calcareous Foraminifera, from which I have taken the corresponding name of the species. The whole form of the shell is sometimes more egg-shaped or subspherical, at other times more top-like or conical, occasionally very flat. Its surface is smooth or rough, but not covered with radial spines.

1. _Streblonia globigerina_, n. sp.

Shell subspherical, thick walled, clustered, with eight to ten nearly spherical chambers, of rapidly increasing size, the tenth chamber about twelve times as broad as the first. Breadth of the shell nearly equal to the height. Pores subregular, circular, hexagonally formed, of about the same breadth as the bars; about sixteen on the breadth of the tenth chamber. (Resembles very much the common _Globigerina_.)

_Dimensions._--Breadth of the shell 0.18, height 0.16.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

2. _Streblonia uvigerina_, n. sp.

Shell nearly egg-shaped, clustered, with eight to eleven subspherical chambers of gradually increasing size, the tenth chamber about six times as broad as the first. Breadth of the shell about {705}half its height. Pores of the shell subregular, circular, about twice as broad as the bars; about twenty on the breadth of the tenth chamber. (Resembles some species of _Uvigerina_.)

_Dimensions._--Breadth of the shell 0.11, height 0.23.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

3. _Streblonia polymorphina_, n. sp.

Shell egg-shaped, thin walled, with twelve to fourteen roundish chambers of rapidly increasing size, the tenth chamber about seven times as broad as the first. Breadth of the shell about two-thirds of the height. Pores irregular roundish, twice as broad as the bars; about twenty on the tenth chamber. (Resembles certain forms of _Polymorphina_.)

_Dimensions._--Breadth of shell 0.22, height 0.14.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

4. _Streblonia bulimina_, n. sp.

Shell nearly egg-shaped, thick walled, clustered, with fourteen to eighteen egg-shaped chambers of rapidly increasing size, the tenth chamber about eight times as broad as the first. Breadth of the shell about two-thirds of the height. Pores irregular, roundish, half as broad as the bars; about twelve on the breadth of the tenth chamber. (Resembles closely _Bulimina_.)

_Dimensions._--Breadth of the shell 0.17, height 0.24.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

5. _Streblonia rosalina_, n. sp.

Shell top-shaped or flatly conical, with twelve to sixteen chambers of gradually increasing size, the tenth chamber about four times as broad as the first. Breadth of the shell twice as large as the height. Pores subregular, circular, very small, of the same breadth as the bars; about twelve on the breadth of the tenth chamber. (Resembles some forms of _Rosalina_.)

_Dimensions._--Breadth of the shell 0.27, height 0.13.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

6. _Streblonia planorbulina_, n. sp.

Shell very flatly conical, nearly lenticular or discoidal, with twenty to twenty-five chambers of nearly equal size, the tenth chamber a little broader than the first. Breadth of the shell exceeds five to six times the height. Pores subregular, circular, very small, half as broad as the bars; about eight on the breadth of the tenth chamber. (Resembles closely _Planorbulina_.)

_Dimensions._--Breadth of the shell 0.3 to 0.4, height 0.06 to 0.07.

_Habitat._--Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.

{706}7. _Streblonia pulvinulina_, n. sp.

Shell top-shaped or flatly conical, with thirty to forty chambers of slowly increasing size, the tenth chamber about three times as broad as the first. Breadth of the shell exceeds three times the height. Pores circular, subregular, very small, about one-third as broad as the bars; about thirty in the breadth of the tenth chamber. (Resembles closely _Pulvinulina_.)

_Dimensions._--Breadth of the shell 0.25, height 0.08.

_Habitat._--Pacific, central area, Station 263, depth 2650 fathoms.

Genus 311. _Streblacantha_,[351] n. gen.

The genus _Streblacantha_ differs from the nearly allied _Streblonia_ only in the covering of radial spines, and bears therefore the same relation to it as _Hastigerina_ has to _Globigerina_ amongst the similar calcareous Polythalamia.

1. _Streblacantha siderolina_, n. sp. (Pl. 49, figs. 8, 8_a_).

_Streblonia siderolina_, Haeckel, 1883, MS.

Shell flatly conical, with fourteen to sixteen nearly hemispherical chambers of gradually increasing size, the tenth chamber about six times as broad as the first. Breadth of the shell nearly equal to the height. Pores subregular, circular, hexagonally framed, twice as broad as the bars; about nine pores on the breadth of the tenth chamber. Surface covered with numerous short conical radial spines, one-fourth to one-sixth as long as the diameter of the shell.

_Dimensions._--Breadth of the shell 0.15, height 0.17.

_Habitat._--South Pacific, Station 298, depth 2225 fathoms.

2. _Streblacantha calcarina_, n. sp.

Shell conical, with sixteen to eighteen roundish chambers of gradually increasing size, the tenth chamber about three times as broad as the first. Breadth of the shell about one and a half times the height. Pores irregular, roundish. Surface covered with numerous strong conical radial spines, about half as long as the diameter of the shell.

_Dimensions._--Breadth of the shell 0.24, height 0.17.

_Habitat._--South Pacific, Station 285, depth 2375 fathoms.

{707}3. _Streblacantha hastigerina_, n. sp.

Shell nearly spherical, clustered, with nine to eleven nearly spherical chambers of rapidly increasing size, the tenth chamber about six times as broad as the first. Breadth of the shell nearly equal to the height. Pores subregular, circular, of about the same breadth as the bars. Surface bristly, covered with numerous very thin and long, needle-shaped radial spines, longer than the diameter of the shell. (Resembles closely _Hastigerina_.)

_Dimensions._--Breadth of the shell 0.18, height 0.15.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

Genus 312. _Streblopyle_,[352] n. gen.

_Definition_.--#Streblonida# with trizonal lentelliptical medullary shell (composed like _Larnacilla_ of three elliptical dimensive girdles surrounding one simple central primordial chamber). From this begins a screw-like series of spirally ascending chambers. Surface smooth or thorny, without radial spines.

The genus _Streblopyle_ presents externally the same appearance and contour as _Streblonia_, and is composed like this of a variable number of chambers, ascending screw-like around the axis of the spiral shell. The first or primordial chamber, however, in which the growth begins, is in _Streblonia_ a simple spherical shell, but in _Streblopyle_ a trizonal shell or _Larnacilla_-shell (compare above, p. 600). The chambers are very incompletely separated, and comparatively much larger, their number much smaller than in _Streblonia_. The structure in the species of this genus is difficult to understand.

1. _Streblopyle helicina_, n. sp. (Pl. 49, fig. 9).

Shell helicoid, one and a third times as high as broad, with eight to twelve incomplete semizonal chambers, ascending spirally from the lateral half girdle of the lentelliptical medullary shell, octopyle-shaped, and enveloping it in three to four spiral turnings. The height of the whole cortical shell equals nearly five times the height of the trizonal medullary shell. Pores irregular, roundish. Surface of the shell rough or nearly smooth. (This species seems to be nearly allied to _Spironium octonium_.)

_Dimensions._--Breadth of the spiral cortical shell 0.18, height 0.24; breadth of the medullary shell 0.04, height 0.05.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

2. _Streblopyle spirulina_, n. sp.

Shell egg-shaped or nearly spherical, about as high as broad, with eight to nine semizonal chambers, ascending spirally from the subspherical trizonal medullary shell, and enveloping it in {708}four to five turnings. The sixth chamber twice as broad as the trizonal medullary shell. Pores irregular, roundish. Surface of the shell thorny.

_Dimensions._--Breadth of the spiral cortical shell 0.27, height 0.25; breadth of the medullary shell 0.05, height 0.06.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

Family XXXI. #PHORTICIDA#, Haeckel (Pl. 49, figs. 10, 11).

_Phorticida_, Haeckel, 1881, Prodromus, p. 464.

_Definition._--#Larcoidea# with quite irregular monothalamous shell, representing irregular modifications of an original lentelliptical latticed shell; the irregular cortical shell encloses a regular or subregular, lentelliptical or trizonal medullary shell.

The family Phorticida comprises a small number of #Larcoidea# in which a subregular, trizonal, lentelliptical medullary shell is enclosed by an irregular simple or spongy cortical shell. The lattice-work of the latter is sometimes simple and complete, at other times incomplete, with open gates (as in the Pylonida), sometimes also spongy. Its form is always more or less irregular, roundish, often dimply or tuberous; different from most other #Larcoidea#.

The medullary shell is constantly a regular or subregular _Larnacilla_-shell, composed of three elliptical latticed girdles of different sizes, perpendicular one to another. This leaves no doubt that the Phorticida are true #Larcoidea#. The connection of it with the cortical shell is rarely effected by radial beams, commonly by two opposite latticed wings, which are identical with the lateral halves of the transverse girdle in the Pylonida diplozonaria (_Amphipyle_, _Tetrapyle_). Often also between this transverse and a second (lateral) girdle there remain large open gates, so that the affinity between these Phorticida and the Pylonida cannot be doubted. In other cases these gates become closed, so that they more nearly approach the Larnacida. From both families they differ by the irregularity of the papillate or tuberous cortical shell. The network is more or less irregular, its surface often thorny, but never covered with symmetrically disposed radial spines.

The central capsule is lentelliptical, encloses the medullary shell, and is enveloped by the cortical shell, as in the nearly allied Pylonida and Larnacida, of which the Phorticida may be regarded as irregular aberrant forms.

_Synopsis of the Genera of Phorticida._

Cortical shell simply latticed, 313. _Phorticium_.

Cortical shell spongy, 314. _Spongophortis_.

{709}Genus 313. _Phorticium_,[353] Haeckel, 1881, Prodromus, p. 464.

_Definition._--#Phorticida# with irregular cortical shell of simple lattice-work, enclosing a lentelliptical _Larnacilla_-shaped medullary shell.

The genus _Phorticium_ comprises all Phorticida in which the irregular cortical shell is formed by simple lattice-work, not by spongy framework. We can divide this genus into two subgenera: in _Phortopyle_ (as in the _Pylonida_) the lattice-work of the cortical shell exhibits large openings or gates; in _Phortolarcus_ these gates are perfectly closed by network; the former may be regarded as abnormal or irregular Pylonida, the latter as modifications of Larnacida.

Subgenus 1. _Phortopyle_, Haeckel.

_Definition._--Lattice-work of the irregular cortical shell incomplete, with large openings or gates.

1. _Phorticium pylonium_, n. sp. (Pl. 49, fig. 10).

Cortical shell irregular, roundish, about three times as large as the enclosed lentelliptical, regular, _Larnacilla_-shell, connected with it by some radial beams and irregularly latticed girdles; between these remain four to eight large open gates of irregular roundish form and size; and these gates are the same as in _Tetrapyle_ and _Octopyle_. This very variable species may be regarded as a monstrosity of those genera of Pylonida; it is very common, but all individuals are more or less unequal; some specimens approach to some common species of _Tetrapyle_. The surface of the shell is more or less spiny.

_Dimensions._--Diameter of the irregular cortical shell 0.12 to 0.18; length of the lentelliptical medullary shell 0.05 to 0.06, breadth 0.035 to 0.045.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, &c., common, surface and in various depths.

2. _Phorticium spironium_, n. sp.

Cortical shell irregular, roundish, tuberous, about four times as large as the enclosed subregular _Larnacilla_-shell, connected with it by some irregular radial beams, and by opposite, spirally begining, irregularly latticed girdles, comparable to those of _Spironium_; between them remain six to twelve large open gates of irregular size and form. Surface rough. The resemblance to some forms of _Spironium_ makes it probable that this species is a deformity or monstrosity of that genus.

_Dimensions._--Diameter of the irregular cortical shell 0.12 to 0.2, of the lentelliptical medullary shell 0.03 to 0.06.

_Habitat._--Pacific, central area, Stations 270 to 274, surface, and in various depths.

{710}Subgenus 2. _Phortolarcus_, Haeckel.

_Definition._--Lattice-work of the irregular cortical shell complete, without large openings or gates.

3. _Phorticium deforme_, n. sp.

Cortical shell irregular, roundish or longish, three times as large as the enclosed subregular, lentelliptical _Larnacilla_-shell, connected with it by two opposite latticed wings (the halves of the transverse girdle of _Tetrapyle_). Network of the cortical shell irregular, dense, perfectly closed, without larger openings or gates. Surface thorny. (May be regarded as a monstrous form of _Larnacalpis_.)

_Dimensions._--Diameter of the irregular cortical shell 0.15 to 0.18, of the medullary shell 0.04 to 0.06.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

4. _Phorticium abnorme_, n. sp.

Cortical shell irregular, roundish, tuberous, with five to ten quite irregular or nearly hemispherical protuberances, which resemble the cupolas of Zonarida. The regular lentelliptical _Larnacilla_-shell is one-third to one-fourth as large as the enclosing cortical shell, and is connected with it by some irregular radial beams. Lattice-work completely closed, without gates. Surface spiny. (May be regarded as an anomalous form of _Zonidium_; as in the other species of this variable genus, the individuals are very unequal.)

_Dimensions._--Diameter of the irregular cortical shell 0.12 to 0.2, of the medullary shell 0.03 to 0.05.

_Habitat._--Atlantic and Pacific, tropical zone, surface, and at various depths.

Genus 314. _Spongophortis_,[354] Haeckel, 1881, Prodromus, p. 464.

_Definition._--#Phorticida# with irregular cortical shell of spongy framework, enclosing a lentelliptical _Larnacilla_-shaped medullary shell.

The genus _Spongophortis_ differs from _Phorticium_ in the spongy framework of the cortical shell. This encloses the inner _Larnacilla_-shaped medullary shell either directly, or both shells are separated by a hollow interval, and connected either by radial beams or by latticed lamellæ. Perhaps both these subgenera might be better separated as genera.

{711}Subgenus 1. _Stypophorticium_, Haeckel.

_Definition._--Spongy cortical shell immediately enclosing the lentelliptical medullary shell, without hollow interval.

1. _Spongophortis spongiosa_, n. sp.

Cortical shell irregular, roundish, rough or tuberous, composed of loose spongy framework, which immediately envelops the lentelliptical central _Larnacilla_-shell; the diameter of the former becomes about five to six times as large as that of the latter.

_Dimensions._--Diameter of the spongy cortical shell 0.15 to 0.25, of the trizonal medullary shell 0.03 to 0.04.

_Habitat._--Pacific, central area, Station 274, surface.

Subgenus 2. _Spongophorticium_, Haeckel.

_Definition._--Spongy cortical shell separated by a hollow interval from the lentelliptical medullary shell.

2. _Spongophortis radiosa_, n. sp.

Cortical shell irregular, roundish, four to five times as large as the enclosed lentelliptical _Larnacilla_-shell, with which it is connected by ten to twenty irregularly disposed radial beams. Spongy framework compact, about as thick as the medullary shell. Surface covered with numerous short, bristle-shaped, radial spines.

_Dimensions._--Diameter of the spongy cortical shell 0.15 to 0.2, of the trizonal medullary shell 0.035 to 0.045.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

3. _Spongophortis larnacilla_, n. sp. (Pl. 49, figs. 11_a_-11_d_).

Cortical shell irregular, roundish, tuberous, three to four times as large as the enclosed lentelliptical _Larnacilla_-shell, connected with it by two opposite latticed wings (the halves of the transverse girdle of _Tetrapyle_). Spongy framework compact, about half as thick as the medullary shell. Surface rough. (May be regarded as an abnormal _Tetrapyle_ or _Larnacalpis_, with an irregular spongy cortical shell.)

_Dimensions._--Diameter of the spongy cortical shell 0.16 to 0.2, of the trizonal medullary shell 0.04 to 0.06.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

{712}Family XXXII. #SOREUMIDA#, Haeckel (Pl. 49, figs. 12, 13).

_Soreumida_, Haeckel, 1881, Prodromus, p. 464.

_Definition._--#Larcoidea# with quite irregular polythalamous shell, composed of a variable number of chambers, aggregated without any definite order. Primordial chamber either simple or _Larnacilla_-shaped.

The family #Soreumida# contains a small number of #Larcoidea#, different from most other #Sphærellaria# in the complete irregularity of the polythalamous shell, which is composed of a variable number of roundish chambers or subspherical latticed shells, aggregated in the form of an irregular heap. We can distinguish in this family only two genera, with very different structure of the central medullary shell or the first chamber beginning the growth; and these correspond to the two subfamilies of the nearly allied Streblonida (p. 704). In _Soreuma_ (as in _Streblonia_) the first or primordial chamber, from which the growth begins, is like the others, a simple spherical or irregular roundish lattice-shell. In _Sorolarcus_, however (as in _Streblopyle_), the first or primordial chamber is a trizonal or _Larnacilla_-shell. It is not improbable that the former originated phylogenetically from _Streblonia_, the latter from _Streblopyle_, by loss of the original spiral order of growth. But it is also possible that these groups have no nearer relation. Among the calcareous Foraminifera a very similar form is represented by _Acervulina_ and its allies.

The general form of the whole shell in the Soreumida is sometimes more egg-shaped or lentelliptical, at other times even subspherical, occasionally quite irregular, tuberous, or clustered. The number of the aggregated chambers is very variable, in _Sorolarcus_ between ten and thirty, in _Soreuma_ ascending to fifty to eighty, sometimes from one hundred to one hundred and fifty and more. Their size is sometimes nearly equal, at other times very different, their form commonly very irregular, roundish, but sometimes also subspherical or egg-shaped. The network of the shell is also commonly irregular, with roundish pores of different sizes. The surface is usually smooth or rough, rarely covered with radial spines.

The central capsule is not known, as I observed only a few skeletons of this family.

_Synopsis of the Genera of Soreumida._

Primordial chamber of the shell simple, subspherical or roundish, 315. _Soreuma_.

Primordial chamber of the shell trizonal or _Larnacilla_-shaped, 316. _Sorolarcus_.

Genus 315. _Soreuma_,[355] Haeckel, 1881, Prodromus, p. 464.

_Definition._--#Soreumida# with numerous chambers, aggregated without any regularity around one simple, spherical or subspherical, central chamber.

{713}The genus _Soreuma_ contains those Soreumida in which no trace of any regular structure is found, but all the chambers of the irregular shell are without any order, aggregated around a simple spherical or subspherical central chamber or medullary shell. _Soreuma_ may have originated either from _Sorolarcus_ by loss of the central _Larnacilla_-shell or from _Cenolarcus_ by irregular apposition of new chambers around the lentelliptical central chamber or simple Larcoid-shell. Some species seem to exhibit a transition to _Sorolarcus_. Owing to the absolute irregularity of the polythalamous shell _Soreuma_ resembles _Acervulina_ among the Foraminifera.

Subgenus 1. _Soreumium_, Haeckel.

_Definition._--Shell without radial spines.

1. _Soreuma irregulare_, n. sp. (Pl. 49, fig. 12).

Shell irregular, clustered, or tuberous, composed of a large number (one hundred and twenty to one hundred and fifty or more) of irregular, roundish chambers of very different sizes, the largest four to five times as broad as the smallest. Network very delicate, with very small roundish pores, to five times as broad as the bars. Surface thorny.

_Dimensions._--Diameter of the shell 0.3, of the single chambers 0.02 to 0.08.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

2. _Soreuma acinosum_, n. sp.

Shell irregularly lentelliptical, with different growth in the three dimensions, composed of a large number (forty to sixty or more) of irregular, roundish chambers of very different sizes, the largest six to eight times as broad as the smallest. Pores subregular, circular, twice as broad as the bars. Surface smooth.

_Dimensions._--Length of the shell 0.21, breadth 0.17, height 0.13; diameter of the largest chambers 0.03, of the smallest 0.004.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

3. _Soreuma subglobosum_, n. sp.

Shell nearly spherical, composed of a variable number (twelve to fifteen or more) of irregularly aggregated subspherical chambers of nearly equal size. Pores subregular, circular, twice as broad as the bars. Surface thorny.

_Dimensions._--Diameter of the shell 0.25, of the largest chambers 0.04, of the smallest 0.005.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

{714}4. _Soreuma acervulina_, n. sp.

Shell quite irregular, cloddy, or tuberous, composed of twenty to thirty (or more) roundish chambers of almost uniform size, the largest twice to three times as broad as the smallest. Pores irregular, roundish. Surface smooth.

_Dimensions._--Diameter of the shell 0.18 to 0.24, of the largest chambers 0.06, of the smallest 0.02.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

Subgenus 2. _Soreumidium_, Haeckel.

_Definition._--Shell with radial spines.

5. _Soreuma spinosum_, n. sp.

Shell quite irregular, cloddy, or tuberous, composed of thirty to forty subspherical chambers of nearly the same size. Pores subregular, circular, twice as broad as the bars; on the equator of each chamber six to eight pores. Surface thorny, covered with irregularly scattered conical radial spines, about as long as the diameter of the chambers.

_Dimensions._--Diameter of the shell 0.17 to 0.25, of the chambers 0.04.

_Habitat._--North Pacific, Station 241, depth 2300 fathoms.

6. _Soreuma setosum_, n. sp.

Shell nearly spherical, composed of sixty to seventy (or more) irregular, roundish chambers of very different sizes, the largest five to six times as broad as the smallest. Pores irregular, roundish. Surface bristly, covered with very numerous, long and thin, bristle-shaped radial spines, about as long as the diameter of the shell.

_Dimensions._--Diameter of the shell 0.28, of the chambers 0.005 to 0.03.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

Genus 316. _Sorolarcus_,[356] n. gen.

_Definition._--#Soreumida# with numerous chambers, aggregated irregularly around a trizonal medullary shell or _Larnacilla_-shell.

The genus _Sorolarcus_ comprises those Soreumida in which the heap of irregularly aggregated chambers encloses a central trizonal medullary shell, by which they demonstrate clearly their descent from Larnacida or Pylonida. The lentelliptical medullary {715}shell exhibits quite the same characteristic structure as that of _Larnacilla_, being composed of three elliptical latticed girdles, perpendicular one to another. In some species also the beginning of a second system of girdles is clearly indicated, so that there can be no doubt as to their derivation from _Amphipyle_ or _Tetrapyle_.

Subgenus 1. _Sorolarcium_, Haeckel.

_Definition._--Shell without radial spines.

1. _Sorolarcus larnacillifer_, n. sp. (Pl. 49, fig. 13).

Shell irregular, clustered, or tuberous, composed of twenty to thirty irregular, roundish chambers of very different size, the largest four to eight times as broad as the smallest, aggregated without order around a central, lentelliptical, _Larnacilla_-shaped medullary shell. Pores irregular, roundish, twice to four times as broad as the bars. Surface smooth or a little spiny.

_Dimensions._--Diameter of the whole shell 0.18, of the central _Larnacilla_-shell 0.05.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

2. _Sorolarcus tetrapylifer_, n. sp.

Shell irregularly roundish, clustered, composed of ten to twelve irregular rather long chambers of almost uniform size, the largest twice as broad as the smallest, aggregated without order around a central shell of the structure of _Tetrapyle_, which encloses an inner trizonal _Larnacilla_-shell of half the size. Pores irregular, roundish, twice to four times as broad as the bars. Surface spiny.

_Dimensions._--Diameter of the whole shell 0.25, of the outer (_Tetrapyle_-like) medullary shell 0.12, of the inner (_Larnacilla_-like) shell 0.06.

_Habitat._--Pacific, central area, Station 272, depth 2600 fathoms.

Subgenus 2. _Sorolarcidium_, Haeckel.

_Definition._--Shell with radial spines.

3. _Sorolarcus terminalis_, n. sp.

Shell nearly spherical, composed of fifteen to eighteen irregularly aggregated roundish chambers of nearly equal size; in the centre a lentelliptical _Larnacilla_-shell. Surface covered with numerous thin, bristle-like radial spines, somewhat longer than the shell.

_Dimensions._--Diameter of the whole shell 0.21, of the central _Larnacilla_-shell 0.05.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

{716}----

LEGION II. #ACANTHARIA#,

VEL ACTIPYLEA, VEL ACANTHOMETREA (PLS. 129-140).

_Acantharia_, Haeckel, 1881. _Actipylea_, Haeckel, 1882. _Acanthometrea_, Hertwig, 1879. _Panacantha_, Haeckel, 1878.

_Definition._--Radiolaria with simple membrane bounding the central capsule, which is everywhere perforated by innumerable fine pores (disposed either equally or symmetrically). Extracapsulum without phæodium. Skeleton centrogenous (its growth proceeding from the centre), acanthinic (organic, not siliceous). Fundamental form originally spherical.

The legion ACANTHARIA vel ACTIPYLEA, to the extent here defined, was constituted by me, 1878, in my Protistenreich (p. 102) under the name "PANACANTHA." A more accurate definition of this group was given in 1879 by Hertwig under the name ACANTHOMETREA. Both names were replaced by me, 1881, in my Prodromus (pp. 421, 465) by the more convenient name ACANTHARIA. This legion comprises all those Radiolaria which were first described by Johannes Müller, 1858, as _Acanthometrae_, and also an important part of his _Haliomma_. In my Monograph (1862, pp. 371-424) I disposed them in three families, Acanthometrida, Diploconida, and Dorataspida.

Although the number of genera and species in this legion is much increased by the rich collection of the Challenger, we can divide all ACANTHARIA into two different orders: #Acanthometra# (without complete lattice-shell) and #Acanthophracta# (provided with a complete lattice-shell).

The ACANTHARIA agree with the SPUMELLARIA in the structure of the simple capsule-membrane, which is perforated by numerous small pores (but constantly devoid of the large main opening, which the NASSELLARIA and PHÆODARIA possess, being hence united as "Merotrypasta"). We can therefore unite both former legions as "Holotrypasta" (compare above, pp. 5, 6); but in many ACANTHARIA (if not in all?) the numerous small pores of the capsule-membrane exhibit a certain peculiar arrangement not observed in the SPUMELLARIA; therefore the latter can be regarded as true "Peripylea" in opposition to the former as "Actipylea."

The peculiar main character of all ACTIPYLEA or ACANTHARIA is determined by the chemical constitution of their skeleton, which is not silex, but a peculiar organic substance, called by me in 1862 "acanthin" (Monogr. d. Radiol., pp. 30, 32). In all other Radiolaria the skeleton is composed of silex or of a silicate. But besides this {717}chemical difference, an important morphological character of the skeleton also separates the ACANTHARIA from all other Radiolaria: in the latter the skeleton is never centrogenous or arising from the centre of the capsule; in strict opposition to this general fact the skeleton of all ACANTHARIA is centrogenous, composed of radial spines, which arise from the central point of the capsule and pierce its membrane. These characteristic "radial spines of acanthin," arising from the centre, are never hollow (as formerly was supposed), but constantly solid. Their form is extremely variable, and most important for the distinction of genera and species; but more interesting from a general point of view is their peculiar arrangement or disposition.

The regular disposition of twenty radial spines has general value almost for all ACANTHARIA, with the exception only of the small group of #Actinelida#. In this latter group the number of radial spines is either more or less than twenty, and their disposition is either quite irregular or follows a peculiar rule. The number of individuals of these #Actinelida#, compared with that of the other ACANTHARIA, may be scarcely 1 per cent., whilst the latter have more than 99 per cent.; the number of observed species is in the former about 5 per cent., in the latter about 95 per cent. Nevertheless the small group of #Actinelida# is very important, being probably the ancestral group from which all other ACANTHARIA have been phylogenetically derived. These other ACANTHARIA, with twenty regularly disposed radial spines, represent the two large groups of #Acanthonida# and #Acanthophracta#. For short and clear distinction of these two groups of ACANTHARIA, we will call the #Actinelida# (with irregular number and disposition of radial spines) Adelacantha, in opposition to the Icosacantha (#Acanthonida# and #Acanthophracta#), which all possess twenty regularly disposed radial spines.

Johannes Müller, the great zoologist, to whom we are indebted for the first detection and accurate knowledge of the #Acanthometra#, already recognised the regularity in the peculiar disposition of their twenty radial spines (Abhandl. d. k. Akad. d. Wiss. Berlin, 1858, pp. 12, 37). In honour of my great master I have called this regular disposition the "Müllerian law of spine disposition," and have given a full explanation of it in my Monograph (1862, pp. 40-45, 371, 372). With regard to its general value for all Icosacantha (#Acanthonida# and #Acanthophracta#), we might also call this promorphological Müllerian law "the Icosacanthan law."

In 1862 I had already given the following precise definition of this "Icosacanthan law" (_loc. cit._, p. 40):--"Between two poles of a spineless axis are regularly disposed five parallel zones, each with four radial spines; the four spines of each zone are equidistant one from another, and also equidistant from each pole; and the four spines of each zone are so alternating with those of each neighbouring zone, that all twenty spines together lie in four meridian planes, which intersect one another at an angle of 45°." For the clear conception of this remarkable Müllerian law, and for the complete understanding of its high value for the complicated {718}morphology of all Icosacantha, it is the most profitable way to retain constantly in mind for comparison the figure of a terrestrial globe with its axis and zones. The axis of the globe is the spineless axis of all Icosacantha, around which all twenty spines are symmetrically disposed; it is perpendicular to the bisecting equatorial plane, in which lies the middle of the five parallel zones; therefore the four spines, crossed perpendicularly in this equatorial plane, are called the equatorial spines (_c_1 to _c_4 in the figures of Pls. 131-140); often, and mainly in the family Quadrilonchida (Pl. 131), these four equatorial spines are much larger or of a peculiar form, different from that of the sixteen other spines. Each pair of the four equatorial spines lies in one equatorial axis, and this latter is perpendicular to the crossing axis, in which lies the other pair of opposite spines. We may regard these two equatorial diameters, perpendicular one to another and to the spineless axis, as the two perradial axes or primary axes. Correspondingly the two meridian planes, which are determined by one perradial axis and the spineless axis, may be called the two primary or perradial meridian planes.

The globe is divided by the equatorial plane into two equal halves, the northern and the southern hemisphere. In each hemisphere there are disposed quite symmetrically eight radial spines, the distal ends of which fall in two parallel circles, a larger tropical circle (nearer to the equator) and a smaller polar circle (nearer to the pole of the spineless axis). Therefore we call the four spines of the former the "tropical spines" and the four spines of the latter the "polar spines." The angle between the former and the equatorial plane is about 30°, the angle between the latter and that plane about 60°.

The eight polar spines (four northern and four southern) lie in the same two meridian planes as the four equatorial spines. Therefore in each of these two perradial planes lie six radial spines, opposite in pairs; two equatorial and four polar spines. Commonly all eight polar spines are of the same size and form; and often they are also equal to the eight tropical spines; but in some cases (e.g., in some species of Quadrilonchida) they are much smaller than the twelve other spines, and sometimes even rudimentary. In all figures of the Pls. 131-140 (and also in my Monograph, 1862, Taf. xv.-xxii.) the polar spines of the northern circle are marked by the characters _a_1 to _a_4, the polar spines of the southern circle by the characters _e_1 to _e_4. In the first perradial meridian plane lie _a_1 and _a_3, _e_1 and _e_3, in the second _a_2 and _a_4, _e_2 and _e_4.

The eight tropical spines lie between the eight polar and the four equatorial spines, four in each hemisphere; their distal points fall in two parallel circles, which correspond exactly to the two tropics of the globe. Therefore the four northern tropical spines may be called "canceral spines" (as their ends fall in the Tropic of Cancer) and the four southern correspondingly "capricornal spines" (as their points lie {719}in the Tropic of the Capricorn). In the figures of the Pls. 131-140 (as well as in my Monograph, 1862, Taf. xv.-xxii.) the four northern or canceral spines are marked by the characters _b_1 to _b_4, and the four southern or capricornal spines by the characters _d_1 to _d_4. Also the eight tropical spines lie (crossed in pairs) in two meridian planes; they do not lie, however, in those perradial planes, in which are placed the twelve other spines; but in two different meridian planes, crossing the former at angles of 45°; we call these the "secondary" or "interradial" meridian planes. Each of these planes is determined by the spineless axis and by two crossed interradial or secondary axes; in each of the latter lie two opposite tropical spines. In the first interradial meridian plane lie _b_1 and _b_3, _d_1 and _d_3, in the second _b_2 and _b_4, _d_2 and _d_4.

It is a most interesting and important fact, that in all Icosacantha (#Acanthonida# and #Acanthophracta#) this regular disposition of the twenty spines (in five parallel zones and four meridian planes) becomes constantly preserved by heredity, whilst the form and size of the different spines are extremely varied by adaptation.

Only in a minority of the Icosacantha are all twenty spines perfectly equal or nearly equal in size and form; and then it is often very difficult to distinguish the different zones in their disposition. But in far the greater part the size or the form of the twenty spines becomes different in different zones; and then we can commonly distinguish easily the five different zones. Firstly, in all Quadrilonchida and Dorataspida, the four equatorial are distinguished from the sixteen other spines either by form or by size, and often in a very remarkable degree. As soon as these four principal spines are recognised, it is easy to determine also the sixteen others; for the eight polar spines lie in the same two (perradial) meridian planes as the former, whilst the eight tropical spines lie in two different (interradial) meridian planes, intersecting the two former at angles of 45°. Commonly, therefore, this distinction is rather easy.

In the majority of the Icosacantha all four equatorial spines are exactly of the same form and size. But in four families the two opposite spines of one equatorial axis are much larger, or of another form, than those of the crossing axis. This is the case in the Amphilonchida, Belonaspida, Hexalaspida, and Diploconida. Therefore we here call the major equatorial axis (with larger spines) the "hydrotomical axis," and the minor axis (with smaller spines) the "geotomical axis." Correspondingly, the meridian plane, in which the two larger equatorial spines are placed (_c_1, _c_3) and the appertaining four polar spines (_a_1, _a_3, _e_1, _e_3) may be called the "hydrotomical plane"; in the remarkable family of Hexalaspida (Pl. 139) all six spines of this hydrotomical plane are much larger than the other fourteen. Perpendicular to this plane is the second perradial meridian plane, which we call the "geotomical plane"; in it lie the two smaller equatorial spines (c2, c4) and the corresponding four polar spines (_a_2, _a_4, _e_2, _e_4). In some Hexalaspida (_Hexonaspis_ and _Hexacolpus_) the six spines of the hydrotomical plane become so preponderant that {720}the other fourteen spines appear rudimentary; and in some of them the two equatorial spines of the hydrotomical plane are much larger than the four polar spines of the same plane. This curious relation reaches its maximum in the Diploconida (Pl. 140).

The different development of the two equatorial axes (of the larger hydrotomical and the smaller geotomical axis) is the first and most important cause of the peculiar forms, which are produced in the four cited families. We derive these terms also from the metaphor of the terrestrial globe. The hydrotomical plane is that meridian plane of the globe which intersects almost only the water-hemisphere (the island of Ferro in the Atlantic, the island of Pandora in the Pacific). Perpendicular to this is the geotomical plane, the meridian of which intersects great land-masses in both hemispheres (Bombay in India, Athabasca in Canada). Both poles of the smaller geotomical axis are everywhere equal (the East Indian and the Western American). However, both poles of the larger hydrotomical axis (the eastern Atlantic and the western Pacific) are in some genera very different, _e.g._, in _Amphibelone_ among the Amphilonchida, and in _Zygostaurus_ among the Quadrilonchida. In this case we call the anterior (commonly more developed) pole of the hydrotomical axis the frontal pole, the opposite posterior (commonly smaller) the caudal pole (Pl. 131, figs. 7, 8; Pl. 132, figs. 9, 10). On both sides of these (right and left) lie symmetrically the two equal poles of the geotomical lateral axis.

The promorphology of the ACANTHARIA demonstrates that the geometrical fundamental form in those groups is different. In the majority of the ACANTHARIA, where the two equatorial axes are equal, that form is a double square-pyramid or a "quadrate octahedron"; the four equal equatorial spines indicate the two diagonals of the square, which is the common base of the united regular four-sided pyramids; their common axis is the spineless axis of the body; the ends of the polar spines fall on the edges of the pyramids, while the ends of the tropical spines fall on the halving lines of their faces. However, in those ACANTHARIA in which the two equatorial axes become different, the square double pyramid becomes changed into a rhombic double pyramid; the common base of the united pyramids is thus a rhombus; the hydrotomical axis is the larger, the geotomical axis the smaller diagonal of the rhombus.

Opposed to the Icosacantha, under the name "Adelacantha," is the small group of Actinelida, in which the number and disposition of the radial spines is variable, not determined by the Müllerian law. Probably this group is the common ancestral stock, from which the Icosacantha have been derived by gradual development of their peculiar disposition. Probably the oldest and most primitive form of all ACANTHARIA is _Actinelius_, in which a variable and undetermined (often very large) number of radial spines is united in one common central point, and therefore forms a needle-sphere. Whilst here all spines (often more than a hundred) are of equal size and form, in the nearly allied _Astrolophus_ large and small spines are intermingled. Both genera together form the small ancestral family of Astrolophida. In the strange family of Litholophida the radial spines do not {721}radiate within a spherical space (equally disposed in all directions), but within a quadrant or even an octant, forming a conical brush or pencil.

One very remarkable form of #Actinelida# is _Actinastrum_, forming the transition from these Adelacantha to the common regular Icosacantha. In the two observed species of _Actinastrum_ we find thirty-two radial spines, twenty of which are disposed after the Müllerian law, as in the Icosacantha. The other twelve are four interradial equatorial spines (lying in the two secondary meridian planes) and eight perradial tropical spines (lying in the two primary meridian planes). Therefore here in each primary meridian plane are placed ten spines (two equatorial, four tropical, and four polar spines), whereas in each secondary meridian plane are placed six spines (two equatorial and four tropical). But here also all thirty-two spines are so regularly placed that their free distal ends fall into five parallel zones, four in each polar zone, eight in each tropical zone, and eight in the equatorial zone.

_The Central Junction_ of the radial spines in the ACANTHARIA becomes effected in four different ways:--(1) by simple apposition of the pyramidal central ends or bases; (2) by a basal leaf-cross, or by broad wings, four on each spine, supported one upon the other; (3) by a central concrescence of the meeting bases of all the twenty spines, growing perfectly together; and (4) by a concrescence in pairs of every two opposite spines. The most common and probably the original mode of junction is the first--by pyramidal apposition; the spines at the central base are pointed in the form of a pyramid, and the triangular faces of the neighbouring pyramids are simply placed upon one another. Often the small basal pyramids are imperfectly separated from the spines by an annular constriction. Commonly the basal pyramids of the four equatorial spines are six-sided, those of the sixteen other spines five-sided.

The second mode of junction, by a basal leaf-cross, is developed from the first and appears as a strengthening or a mechanical elaboration of it. Immediately above the basal pyramid arise from its radial edges four thin and broad triangular leaves or wings, and the meeting edges of the neighbouring wings are in apposition one with the other, so that between the bases of every three or four neighbouring spines a hollow pyramidal space remains open. The apex of such a pyramidal space is directed towards the centre of the body, but separated from it by the small basal pyramid; its open base is directed outwards. The twenty-two hollow pyramidal spaces are disposed regularly in four different groups:--(A) Four equatorial spaces, four-sided, each limited by two equatorial and two tropical spines (one canceral and one capricornal); (B) eight perizonal spaces (four northern and four southern), four-sided, each limited by one equatorial, two tropical, and one polar spine; (C) eight peripolar spaces (four northern and four southern), three-sided, each limited by one tropical and two polar spines; (D) two polar spaces (one northern and one southern), four-sided, each limited by four neighbouring polar spines.

{722}The third mode of junction, by central concrescence of all twenty spines, was formerly regarded by me as an important peculiarity, sufficient for the separation of subfamilies and genera (Monogr. d. Radiol., 1862, pp. 399, 401; Prodromus, 1881, p. 466). But I found afterwards that in many species where the twenty spines commonly remain separated, accidentally they grow perfectly together and form one single piece of acanthin--a starrulet with twenty rays. Therefore I now think it is more natural to divide those species only into different subgenera.

A fourth and a very different mode of junction, quite sufficient for the distinction of different families, is the concrescence in pairs of every two opposite spines, lying in one diameter (in _Acanthochiasma_ and _Chiastolus_). Here we obtain a number of "diametral spines" (each composed of two originally opposed radial spines) and all these diametral spines are crossed loosely near the central point of the body without any solid and permanent apposition (Chiastolida). However, in some species of this peculiar family the central part of the diametral spines is twisted like a screw or spirally convoluted (Pl. 129, figs. 2, 3).

_The Form of the Radial Spines_ in the ACANTHARIA is extremely varied, and constitutes the main characters for the distinction of nearly four hundred species. But all these different forms may be reduced phylogenetically to three different fundamental forms:--(_a_) the cylindrical (with circular transverse section), (_b_) the two-edged (with elliptical or lanceolate transverse section), and (_c_) the four-edged (with square transverse section). No doubt the first (_a_) is the original primitive form, from which the two others are secondarily derived. Triangular spines never occur in the ACANTHARIA, whilst, however, they are common in the #Sphærellaria#. The first and original form, the cylindrical spine, is either a true cylinder of equal thickness in its whole length, or it is more or less conical. Rarely the spine is in the distal half spindle-shaped, and thicker than in the basal half. The second form, the two-edged spine, is more or less compressed from two opposite sides; its two edges are either more blunt, rounded, or more acute, sharp; its transverse section in the former case is elliptical, in the latter case lanceolate or rhomboidal. Sometimes the two edges are broader and in the form of two thin opposite wings. The two-edged spines may be occasionally shorter, triangular or lanceolate, at other times longer sword-shaped or linear. The third form, the four-edged spine, has constantly a square transverse section; the sides of this square are either even or concave; in the latter case the four edges are broadened and wing-like, but in the former case not. The quadrangular spines are either prismatic (of equal breadth throughout their whole length) or pyramidal (becoming gradually thinner towards the distal apex).

_The Apex of the Radial Spines_, or their free distal end, is in the majority of ACANTHARIA simple, conical. In the minority it is either truncated or bifid, or four-sided pyramidal, often with two, rarely with four prominent parallel teeth. In some forms {723}the bifid spines are so deeply cleft that they become forked. Much more interesting and more varied than these different forms of the distal end are those of the apophyses of the radial spines.

_The Apophyses of the Radial Spines_, or their "lateral transverse processes," are of the greatest importance for the morphological development of the whole subclass. Only in sixteen among the sixty-five genera of ACANTHARIA are the apophyses perfectly wanting; in the other genera they determine in the first place their general character. In the #Acanthometra# the apophyses remain perfectly free, whilst in the #Acanthophracta# their meeting ends or branches compose the latticed shell. All differences in form and shape of the apophyses can be reduced to only two primary modes; either the spine bears two opposite or four crossed apophyses; correspondingly all Acantharia apophysaria may be divided into two different main groups, the Zygapophysica (with two opposite lateral processes) and the Staurapophysica (with four crossed lateral processes opposite in pairs). Both groups have probably no direct phylogenetic connection, but seem to be derived independently from different stocks, and produce different families. The Zygapophysica are probably derived from Astrolonchida with two-edged spines (_Zygacantha_), and from this group arise the Diporaspida, the ancestral group of the majority of #Acanthophracta#. On the other hand the Staurapophysica are probably derived from Astrolonchida with four-edged spines (_Acanthonia_), and from this group arise the Tessaraspida. The apophyses of the #Acanthonida# are partly simple, partly branched or even latticed; the apophyses of the #Acanthophracta# are never simple, constantly branched and commonly latticed.

_The Malacoma_ (or the whole soft body of the ACANTHARIA as opposed to the skeleton) exhibits some peculiarities which distinguish them from the other Radiolaria, as well in the structure of the central capsule and its nucleus as in that of the enveloping extracapsular body and the pseudopodia.

The _Central Capsule_ is constantly spherical in the far greater number of the ACANTHARIA, viz., in the following six families:--Astrolophida, Chiastolida, Astrolonchida, Dorataspida, Sphærocapsida, and Phractopeltida. Among these six families the Astrolonchida and Dorataspida are far greater and far richer in different forms than all the other families. The central capsule becomes ellipsoidal or cylindrical, prolonged in one axis, in the three families, Amphilonchida, Belonapsida, and Diploconida; it becomes discoidal or lenticular, by the shortening of one axis, in two families, viz., in the Quadrilonchida and Hexalaspida. Finally, the peculiar family Litholophida is distinguished by the conical form of its central capsule.

_The Membrane_ of the central capsule in all ACANTHARIA is simple, commonly thin, sometimes very delicate; in some species it seems to be developed late, just immediately before the formation of the spores; but in no species is it completely missing. The membrane is constantly pierced by innumerable fine pores, for the emission of the {724}pseudopodia; but in many species (and probably more or less in all ACANTHARIA) there is recognisable a certain regularity in the disposition of the numerous pseudopodia and of the pores by which they radiate from the capsule. Sometimes these pores are disposed in a regular network of ramified lines, whilst the meshes of this network are devoid of pores; in other cases they form regular tufts or bushes between the radial spines. Probably in no ACANTHARIA are the pores of the capsule membrane so numerous and so equally distributed throughout as in the SPUMELLARIA; we may therefore call the former ACTIPYLEA (in opposition to the latter, as PERIPYLEA).

_The Nucleus_ of the ACANTHARIA is constantly excentric, whilst it is originally constantly central in the SPUMELLARIA. This excentric position is a necessary consequence of the centrogenous development of the radial spines. Probably connected with this peculiarity is the other, that the nucleus assumes a peculiar, complicated structure, and that in the greater number of ACANTHARIA it becomes cleft very early, and that this cleavage is effected by a peculiar kind of gemmation, first detected and very accurately described by R. Hertwig (compare his Organismus d. Radiol., 1879, pp. 10-24). However, in the young ACANTHARIA the nucleus is constantly simple, and in a certain number of species its cleavage takes place late (as in the greater number of SPUMELLARIA).

_The Endoplasm_, or the intracapsular sarcode, exhibits in the greater number of ACANTHARIA a more or less distinct radial arrangement; but this is often concealed by the different enclosed products of the endoplasm--oil-globules, vacuoles, red or different coloured pigment-granules, crystals, &c. Often it encloses a variable number of "yellow cells" (becoming green by mineral acids) to be considered as symbiotic xanthellæ.

_The Calymma_ or the jelly-veil, including the central capsule, in the ACANTHARIA is more or less voluminous, and commonly envelops the skeleton perfectly. In its surface is sometimes developed a peculiar network of "supporting fibres." A very peculiar product are the remarkable "Myophrisca" of the #Acanthometra#, which are wanting in the #Acanthophracta#; they were first detected by Johannes Müller, and figured as "Cilien-Kränze," afterwards explained by Hertwig as "contractile Fäden," similar to muscular fibrillæ (compare below).

_The Matrix_, placed between the calymma and central capsule, in the majority of the ACANTHARIA is a rather thin layer of granular exoplasm.

_The Pseudopodia_ arising from it are not so numerous as in the SPUMELLARIA, and not so equally disposed over the whole surface. Also their tendency to ramify, anastomose, and form networks seems to be much less developed. Commonly they are simple or little ramified. In many cases (and perhaps everywhere) there may be distinguished two different kinds of pseudopodia:--(1) Axopodia, or permanent pseudopodia (with axial filaments?), piercing the wall of the central capsule, and arising from the central mass of endoplasm; and (2) Collopodia, or variable pseudopodia (without axial filaments), arising outside the capsule from the matrix of extracapsular sarcode or from the {725}exoplasm on the surface of the calymma. These and other differentiations seem to indicate that the pseudopodia in the ACANTHARIA are more highly developed than in the SPUMELLARIA, and justify the denomination of the former as "Actipylea."

_Synopsis of the Orders and Suborders of_ ACANTHARIA.

------------------------------------------------------------------------- I. ACANTHOMETRA. Skeleton composed only of acanthinic radial spines not forming a complete lattice-shell. ------------------------------------------------------------------------- Radial spines in variable and indefinite number, disposed irregularly, 1. #Actinelida#.

Radial spines constantly twenty, disposed regularly after the Müllerian law of Icosacantha, 2. #Acanthonida#. ------------------------------------------------------------------------- II. ACANTHOPHRACTA. Skeleton composed of twenty acanthinic radial spines (disposed after the Müllerian law) and of a spherical or variously shaped complete lattice-shell. ------------------------------------------------------------------------- Radial spines all twenty of equal size; shell and central capsule spherical, 3. #Sphærophracta#.

Radial spines of different sizes; shell and central capsule ellipsoidal, discoidal, or heteromorphous, 4. #Prunophracta#.

----

Order III. ACANTHOMETRA, Johannes Müller, 1855.

_Acanthometra_, J. Müller, 1855, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin. _Acanthometrida_, Haeckel, 1862, Monogr. d. Radiol., p. 371. _Acanthometrea_, R. Hertwig, 1879, Organismus d. Radiol., p. 133. _Acanthonida et Litholophida_, Haeckel, 1881, Prodromus, pp. 465, 469.

_Definition._--ACANTHARIA without complete latticed shell.

The order #Acanthometra#, the third order of Radiolaria, comprises all those ACANTHARIA in which the acanthinic skeleton is only composed of radial spines arising from one common central point, but never forms a complete latticed shell. By the absence of such a latticed or fenestrated shell the #Acanthometra# differ principally from the nearly allied #Acanthophracta#, the second order of ACANTHARIA, which constantly possess such a complete shell.

Johannes Müller, who first detected and described the #Acanthometra# (in 1855, _loc. cit._), defined them as follows:--"Radiolaria without shell, with siliceous radial spines" (1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 46). He described and figured eighteen species of them, disposed in four genera (_Acanthometra_ with fifteen species, and _Zygacantha_, _Lithophyllium_, _Lithoptera_, each with a single species). Among those eighteen species, however, were two "Acanthometræ cataphractæ," appertaining to the following order, the #Acanthophracta#.

In my Monograph (1862, p. 371) all true #Acanthometra# were united into a single family, Acanthometrida, with the following definition:--"Skeleton composed of a number of radial spines, piercing the central capsule and united in its centre, without {726}latticed shell." In the majority of them I observed that the skeleton did not consist of silex, but of a very peculiar organic substance, which I called "acanthin." At that time I divided the family Acanthometrida into four subfamilies:--(1) Acanthostaurida, (2) Astrolithida, (3) Litholophida, (4) Acanthochiasmida. The two former now represent the suborder #Acanthonida#, the two latter the suborder #Actinelida#. The number of genera which I distinguished in my Monograph amounted to nine, the number of species to fifty. By the rich collections of the Challenger this number is so much increased that we can here describe twenty-seven genera and one hundred and sixty species.

Richard Hertwig in his work on the Organismus der Radiolarien (1879, pp. 6-25) adopted my family Acanthometrida, and gave a very accurate description of its anatomical structure. He confirmed my observations that the radial spines of this family are never hollow, but solid, and that their chemical substance is not silex, but the organic matter "acanthin." He found that the simple nucleus of the Acanthometrida is commonly very early cleft, and that the peculiar brushes of filaments on the calymma, described by Johannes Müller and by me as "Gallert-cilien," are peculiar "contractile filaments," comparable to the "muscle-fibrillæ" of some Infusoria, or the "Myophan-filaments" (Myophrisca).

The order #Acanthometra# is here divided into two different suborders of very unequal extent and value, the #Actinelida# and #Acanthonida#. The first may be regarded as the common ancestral stock, not only of the second, but of all ACANTHARIA. In the small group of #Actinelida# the number of radial spines is variable and commonly indefinite, often very large (more than a hundred); they are therefore Adelacantha. The second suborder, the #Acanthonida#, comprise by far the greatest part of the order, and possess constantly twenty radial spines, regularly disposed after the Müllerian law; they are therefore (like all #Acanthophracta#) Icosacantha (compare above, p. 717).

The #Actinelida# possess constantly simple radial spines, without any apophyses; their form is commonly very simple and primitive. This suborder comprises three small but very different families, the Astrolophida, Litholophida, and Chiastolida. The first family, the Astrolophida, is the original ancestral group. A large and variable, commonly indefinite number of radial spines is here united in the centre of the spherical central capsule and radiating within a spherical space. In the second family, the Litholophida, a small and variable number of radial spines (between ten and twenty) is united in the apex of a conical central capsule and radiating within the quadrant or octant of a spherical space. In the third family, the Chiastolida, a variable number of radial spines is grown together by pairs, in such a manner that every two opposite spines (placed originally in one axis of the spherical central capsule) forms a single "diametral spine"; all these diametral spines are not united in the centre of the central capsule but only crossed loosely near the centre.

{727}The #Acanthonida#, the second suborder of #Acanthometra#, embraces by far the greatest number in this order, viz., all those forms in which twenty radial spines are regularly disposed after the Müllerian law--Icosacantha (compare above, p. 717). The radial spines of this suborder are either simple or provided with transverse processes (either two opposite or four crossed apophyses). They are commonly united in the middle of the central capsule by their opposed basal ends, forming small pyramids; the meeting triangular faces of the neighbouring pyramids being propped one upon another. Above these small basal pyramids often arises a basal leaf-cross formed by four broad triangular leaves or wings with straight edges; the meeting thin edges of the neighbouring spines serve for strengthening the basal junction and form hollow pyramidal spaces or compartments, filled with the contents of the central capsule (compare p. 721). The suborder #Acanthonida# comprises three different families, the Astrolonchida, Quadrilonchida, and Amphilonchida. The first family, the Astrolonchida, comprises by far the greater number of the #Acanthonida#; those genera in which all twenty spines are perfectly equal or nearly equal in size and form. In the second family, the Quadrilonchida, the four equatorial spines are much larger (and often also of another form) than the sixteen other spines (often also the eight tropical larger than the eight polar spines). The third family, the Amphilonchida, is distinguished by the preponderating development of only two opposite equatorial spines, which are much larger (and often also of another form) than the eighteen other spines.

_Synopsis of the Suborders and Families of_ #Acanthometra#.

------------------------------------------------------------------------- Suborder I. ACTINELIDA. Number of the radial spines variable, either more or less than twenty, commonly disposed irregularly and not according to the Müllerian law. ------------------------------------------------------------------------- Radial spines very numerous (thirty to a hundred or more), radiating from a common centre within a spherical space, 1. ASTROLOPHIDA.

Radial spines between ten and twenty, radiating from one common point within a sphere-quadrant, 2. LITHOLOPHIDA.

Radial spines of variable number; every two opposite spines grown together in the centre; therefore numerous diametral spines are crossed freely in the centre, 3. CHIASTOLIDA. ------------------------------------------------------------------------- Suborder II. ACANTHONIDA. Number of the radial spines constantly twenty, disposed regularly according to the Müllerian law. ------------------------------------------------------------------------- All twenty radial spines nearly equal, and of the same size and form, 4. ASTROLONCHIDA.

Four equatorial spines much larger than (and often also of different form from) the sixteen other spines, 5. QUADRILONCHIDA.

Two opposite equatorial spines (or principal spines) much larger than (and often also of different form from) the eighteen other spines, 6. AMPHILONCHIDA.

{728}----

Suborder I. ACTINELIDA, Haeckel, 1882.

_Definition._--#Acanthometra# with a variable number of radial spines, which are commonly irregularly disposed, not according to the Icosacantha.

Family XXXIII. #ASTROLOPHIDA#, Haeckel.

_Astrolophida_, Haeckel, 1881, Prodromus, p. 469.

_Definition._--#Acantharia# with a variable number of simple radial spines, radiating within a spherical space from one common central point which is the centre of the spherical central capsule. No lattice shell.

The family #Astrolophida# comprises the simplest and the most primitive forms among all ACANTHARIA, and may therefore be regarded as the common ancestral stock of this whole legion or subclass of Radiolaria. The acanthinic skeleton is composed of a variable number of quite simple radial spines, which are united in the centre of the spherical central capsule and radiate, piercing its walls and the surrounding jelly-veil, within a spherical space.

The first observed form of this family is the ancestral genus _Actinelius_, two different species of which I detected in 1864 in the northern Mediterranean, at Villafranca, near Nice (compare Zeitschr. f. wiss. Zool., 1865, Bd. xv. p. 364, Taf. xxvi. fig. 4). Three other species of the same genus were afterwards found by me in the Challenger collections. Whilst in this _Actinelius_ all radial spines are of the same size, a new nearly allied genus, _Astrolophus_ (with two species), differs from it by the different size of the radial spines, a small number of very large spines being intermingled with a very large number of small spines. In these two genera, _Actinelius_ and _Astrolophus_ (the true "Astrolophida" _sensu strictiori_), the number of the radial spines is quite indeterminable and their arrangement quite irregular and variable.

A third remarkable genus, _Actinastrum_, differs from these two genera in the definite number and regular order of thirty-two radial spines, and may therefore perhaps better represent a peculiar family, Actinastrida. In this genus (of which two species were observed) the thirty-two radial spines are disposed in such a regular manner that they lie in four meridian planes, and that their distal ends fall into five parallel zones. These five zones and these four planes are the same as we find in all Icosacantha (compare above, p. 717). Also the constant twenty spines of these latter are present in _Actinastrum_; but their number is here enlarged by twelve other spines missing in the Icosacantha; four of these are secondary or interradial equatorial spines, lying opposite in pairs between the four primary or perradial equatorial spines; and eight are perradial tropical spines, lying between the eight interradial tropical spines. Therefore the {729}distal ends of the thirty-two radial spines are disposed regularly in five parallel zones, and while two zones (the two polar) contain only the points of every four spines, three zones (the single equatorial and the two tropical) contain the points of every eight spines. The four meridian planes are in _Actinastrum_ the same as in the Icosacantha, crossed in the spineless axis at angles of 45°. But in the Icosacantha each of the two perradial meridian planes contains six radial spines (two equatorial and four polar), each of the two interradial meridian planes only four tropical spines. Whereas in _Actinastrum_ each of the two primary or perradial meridian planes contains ten spines (two equatorial, four tropical, and four polar), each of the two secondary or interradial meridian planes six spines (two equatorial and four tropical). We find therefore altogether thirty-two radial spines in three orders; eight equatorial, sixteen tropical, and eight polar spines.

Only one other genus of Radiolaria exhibits the same characteristic disposition of thirty-two radial spines as _Actinastrum_, and this is _Chiastolus_; but here the two opposite spines of each pair are grown together and form one diametral spine; and the sixteen diametral spines are crossed in the centre of the capsule. In _Actinastrum_, as in _Astrolophus_ and _Actinelius_, the central ends or bases of all the spines are pyramidal, and the triangular faces of the neighbouring spines rest one upon another (as in the greater number of #Acanthonida#). The form of the radial spines in all Astrolophida is quite simple, without lateral processes or apophyses; chiefly cylindrical, more rarely compressed, two-edged or quadrangular.

The central capsule in all Astrolophida is spherical, and in the younger specimens contains a single large concentric and lobed nucleus, but in the older specimens a large number of small nuclei. The surrounding jelly-veil or calymma seems commonly to envelop the spines perfectly. The piercing pseudopodia radiate everywhere between the spines, and are very numerous and thin. The circulating granules in them are sometimes red (_Actinelius purpureus_).

_Synopsis of the Genera of Astrolophida._

Radial spines of indefinite {Spines of equal size, 317. _Actinelius_. number and of irregular { disposition. {Spines of unequal size, 318. _Astrolophus_.

Radial spines thirty-two, disposed regularly in five parallel zones, 319. _Actinastrum_.

Genus 317. _Actinelius_,[357] Haeckel, 1865, Zeitschr. f. wiss. Zool., Bd. xv. p. 364.

_Definition._--#Astrolophida# with a variable and undetermined number of simple radial spines, all of equal size, united in the centre of the spherical central capsule.

{730}The genus _Actinelius_ comprises the most simple and primitive forms among all ACANTHARIA, and may be regarded as the common ancestral stock of this whole legion. The spherical central capsule is pierced by numerous simple radial spines of equal size, the pyramidal bases of which are supported one upon another with their triangular faces in the centre of the capsule. The number and position of the spines are quite indefinite and variable. We may derive _Actinelius_ either from _Actissa_ (#Colloidea#) by development of acanthinic radial spines, or directly from _Actinosphærium_ (Heliozoa) by formation of a central capsule.

Subgenus 1. _Actinelarium_, Haeckel.

_Definition._--Radial spines cylindrical, conical, or spindle-shaped, their transverse section circular.

1. _Actinelius primordialis_, n. sp. (Pl. 129, fig. 1).

Spines sixty to eighty or more, cylindrical, at the distal end thickened, spindle-shaped. Apex simple. Base a small slender pyramid. Central capsule yellow. Granules of the sarcode colourless.

_Dimensions._--Length of the spines 0.3 to 0.4, breadth in the distal part 0.02, in the basal part 0.008.

_Habitat._--Central Pacific, Stations 265 to 274, surface.

2. _Actinelius purpureus_, Haeckel.

_Actinelius purpureus_, Haeckel, 1865, Zeitschr. f. wiss. Zool., Bd. xv. p. 364, Taf. xxvi. fig. 4.

Spines thirty to forty or more, cylindrical, very thin, a little thinner towards both ends. Apex simple. Base a small sulcate pyramid. Central capsule opaque, purple. Granules of the sarcode also purple.

_Dimensions._--Length of the spines 0.2 to 0.3, breadth 0.002.

_Habitat._--Mediterranean (Nice), Haeckel.

Subgenus 2. _Actinelidium_, Haeckel.

_Definition._--Radial spines compressed, two-edged; their transverse section elliptical or lanceolate.

3. _Actinelius protogenes_, n. sp.

Spines fifty to sixty, compressed, two-edged, gradually broadened towards the truncated distal end. Basal or proximal end thin, pyramidal. The spines of this species are similar to those of {731}_Actinastrum pentazonium_ (p. 733) and of _Chiastolus amphicopium_ (Pl. 129, fig. 3), but much more numerous, smaller, and not regularly disposed. These latter two Actinelida must be separated on account of the regular disposition of the thirty-two spines.

_Dimensions._--Length of the spines 0.2, basal breadth 0.008, distal breadth 0.02.

_Habitat._--South Pacific, Station 165, surface.

Subgenus 3. _Actinelonium_, Haeckel.

_Definition._--Radial spines quadrangular, prismatic, or pyramidal, their transverse section square.

4. _Actinelius pallidus_, Haeckel.

_Actinelius pallidus_, Haeckel, 1865, Zeitschr. f. wiss. Zool., Bd. xv. p. 364.

Spines eighty to one hundred and twenty or more, quadrangular, prismatic, of equal breadth throughout their whole length. Apex simple, truncate or pyramidal. Base a four-sided slender pyramid. Central capsule pale yellowish. Granules of the sarcode colourless.

_Dimensions._--Length of the spines 0.2 to 0.3, breadth 0.005.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific.

5. _Actinelius polyacanthus_, n. sp.

Spines two hundred to three hundred or more, quadrangular, pyramidal, gradually thinned towards the simple apex. Base a small three-sided pyramid. Central capsule opaque.

_Dimensions._--Length of the spines 0.12 to 0.18, basal breadth 0.012.

_Habitat._--South Pacific, Station 291, surface.

Genus 318. _Astrolophus_,[358] Haeckel, 1881, Prodromus, p. 469.

_Definition._--#Astrolophida# with a variable and undetermined number of simple radial spines of different sizes (large and small spines intermingled), which are united in the centre of the spherical central capsule.

The genus _Astrolophus_ differs from the nearly allied ancestral genus _Actinelius_ only in the unequal size of the numerous radial spines. In both observed species very numerous small spines are intermingled with a small number of large spines, and between them numerous spines of medium size. The small spines fill up the hollow spaces between the basal parts of the large spines.

{732}1. _Astrolophus stellaris_, n. sp.

Radial spines from one hundred to two hundred, of very different sizes, but of similar form; about sixteen to twenty very large spines, forty to fifty of medium size, and one hundred to one hundred and twenty much smaller. All spines cylindrical in the greater part of their length, with simple apex, gradually thickened towards the central part, conical, without edges. The base itself is a slender pyramid with four to eight edges.

_Dimensions._--Length of the largest spines 0.3 to 0.4, of the majority 0.1 to 0.2, of the smallest 0.05 to 0.1.

_Habitat._--South Pacific, Station 288, surface.

2. _Astrolophus solaris_, n. sp. (Pl. 132, figs. 12_a_, 12_b_).

Radial spines from two hundred to three hundred, of very different sizes, but of similar form; about twenty to thirty very large spines, sixty to eighty of medium size, and one hundred and twenty to one hundred and fifty much smaller. All spines cylindrical in the greater part of their length, with simple apex, gradually thickened and four-edged towards the central base. The base itself is a slender pyramid with four to eight edges; partly the faces, partly the edges of these basal pyramids rest one upon another, the points of the larger spines meeting in the centre.

_Dimensions._--Length of the largest spines 0.4 to 0.5, of the majority 0.2 to 0.3, of the smallest 0.1 to 0.16; basal thickness of the largest spines 0.015.

_Habitat._--South-east Pacific (off Juan Fernandez), Station 296, surface.

Genus 319. _Actinastrum_,[359] n. gen.

_Definition._--#Astrolophida# with thirty-two simple radial spines, regularly disposed within four meridian planes in such an order that their distal ends fall into five parallel zones. Central ends of the thirty-two spines supported one upon another in the centre of the spherical central capsule.

The genus _Actinastrum_ differs from the two preceding genera in the definite number and order of the thirty-two radial spines, which are disposed in a very remarkable manner. Twenty radial spines are disposed after the Müllerian law of Icosacantha (compare above, p. 717). The remaining twelve spines are four equatorial spines lying in the two secondary meridian planes, and eight tropical spines lying in the two primary meridian planes. We have therefore together eight equatorial, sixteen tropical, and eight polar spines (compare above, p. 729).

{733}1. _Actinastrum legitimum_, n. sp.

All thirty-two radial spines of equal size and similar form, cylindrical, conical at the distal end, at the central base pyramidal. Central capsule pellucid, colourless.

_Dimensions._--Length of the radial spines 0.3, breadth 0.004.

_Habitat._--South Pacific, Station 288, surface.

2. _Actinastrum pentazonium_, n. sp.

All thirty-two radial spines of equal size and similar form, compressed, two-edged, gradually becoming broader and thinner from the pyramidal central base towards the truncated distal end. Central capsule dark, opaque. (Compare the similar _Chiastolus amphicopium_, Pl. 129, fig. 3.)

_Dimensions._--Length of the radial spines 0.2, breadth at the base 0.005, at the distal end 0.02.

_Habitat._--South Pacific (west coast of Patagonia), Station 302, surface.

Family XXXIV. LITHOLOPHIDA, Haeckel.

_Litholophida_, Haeckel, 1862, Monogr. d. Radiol., p. 401.

_Definition._--ACANTHARIA with a variable number of simple radial spines radiating within a conical space (or within the quadrant of a sphere) from one common central point, which is the apex of the conical central capsule. No lattice-shell.

The family #Litholophida#, represented only by a single genus, _Litholophus_, differs from all other ACANTHARIA in the remarkable fact that the common point, from which the radial spines arise, is not the geometrical central point of the whole body, but is quite excentric in position, the apex of the conical or pyramidal central capsule. Therefore the spines form together a kind of brush or broom.

When I founded the family Litholophida in my Monograph (1862, p. 401) I knew only a single species, _Litholophus rhipidium_, observed very frequently in Messina. Another species, _Litholophus ligurinus_, was afterwards (1864) found by me at Nice. Six other species were detected in the preparations of the Challenger, some of them very frequent. All these eight species of _Litholophus_ are very nearly allied, and exhibit only slight differences in the form and number of the radial spines; their mode of excentric connection and the structure of the peculiar soft body is everywhere the same.

The radial spines in all observed Litholophida possess the form of the genus _Acanthonia_, _i.e._, they are quite simple, four-sided prismatic or quadrangular, with square transverse section; their four edges are sometimes smooth, at other times elegantly denticulate, commonly more or less prominent or wing-shaped. In the greater number of species they are very long and of nearly equal breadth, prismatic; in some species they are more pyramidal, thinned towards the distal end; the latter {734}is commonly truncated or broken off, sometimes pyramidal. The central end is everywhere thinned, more or less pyramidal, and the neighbouring spines are propped one upon another by the triangular faces of their small basal pyramids. A slight pressure is sufficient to destroy their connection.

The number and disposition of the radial spines seem to be variable and irregular, but require further researches. In four of the observed eight species I found constantly ten spines, in two other species from ten to twenty (commonly twelve or sixteen), and in two species twenty or more. A certain order or disposition of the spines within the conical space in which they radiate could nowhere be ascertained.

When I first observed _Litholophus_, I supposed that it might only be a mutilated or altered form of an _Acanthonia_. Afterwards, observing many specimens with ten spines, I was led to the suggestion that they were produced by self-division of an _Acanthonia_, and that the number of the spines in each half of the body might be afterwards doubled. But this suggestion seems to be refuted by the fact that in no other genus of the numerous ACANTHARIA is self-division observed, and that many hundreds of _Litholophus_ which I observed exhibit quite constantly only a single form of radial spines, that of _Acanthonia_--simple quadrangular spines without any apophyses.

Genus 320. _Litholophus_,[360] Haeckel, 1862, Monogr. d. Radiol., p. 401.

_Definition._--#Litholophida# with a variable number of quadrangular diverging radial spines, united with pyramidal bases in the apex of the conical central capsule.

The genus _Litholophus_, the only one of this family, exhibits the peculiarities just described, but might more nearly be defined as a typical "genus" by the quadrangular form of the radial spines, identical with those of _Acanthonia_.

The central capsule of _Litholophus_ is constantly conical or pyramidal, commonly opaque, of a dark brownish or reddish colour; it contains many small nuclei. It envelops the basal half of all radial spines in such a manner that their basal parts are united in its apex, and their distal parts pierce the rounded base of the conical capsule (Pl. 129, fig. 2).

The calymma or the jelly envelope of the central capsule is only developed at its base, where the spines radiate; at the conical mantle of the capsule it is very thin. The spines seem to be perfectly enclosed in the calymma and connected with it by the same contractile retinacula or "myophrisca" which we observe in the #Acanthonida#. The pseudopodia arise only from the rounded base of the conical capsule, and radiate between the spines, piercing the calymma, diverging within the conical space occupied by the fascicle of spines.

{735}Subgenus 1. _Litholopharium_, Haeckel.

_Definition._--Ten radial spines.

1. _Litholophus decimalis_, n. sp.

Ten radial spines, four-sided prismatic, with prominent smooth edges, of equal breadth throughout their whole length.

_Dimensions._--Length of the spines 0.2 to 0.3, breadth 0.006.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface.

2. _Litholophus pyramidalis_, n. sp.

Ten radial spines, four-sided pyramidal, with prominent smooth edges, gradually thickened from the small pyramidal base towards the truncated distal end.

_Dimensions._--Length of the spines 0.3 to 0.4, breadth in the basal part 0.002, in the middle part 0.006, in the distal part 0.012 to 0.02.

_Habitat._--Central Pacific, Station 266, surface.

3. _Litholophus decapristis_, n. sp. (Pl. 129, fig. 2).

Ten radial spines, four-sided prismatic, with prominent, elegantly denticulated edges, of equal breadth in their whole length.

_Dimensions._--Length of the spines 0.2 to 0.4, breadth 0.008.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

4. _Litholophus decastylus_, n. sp.

Ten radial spines, four-winged pyramidal, with broad and thin, elegantly denticulated edges, gradually thickened from the small pyramidal base towards the truncated distal end.

_Dimensions._--Length of the spines 0.2 to 0.3, breadth in the basal part 0.002, in the middle part 0.005, in the distal part 0.015.

_Habitat._--South Atlantic, Station 332, surface.

Subgenus 2. _Litholophidium_, Haeckel.

_Definition._--Number of the radial spines variable, between ten and twenty, commonly twelve to sixteen.

{736}5. _Litholophus ligurinus_, Haeckel.

_Litholophus ligurinus_, Haeckel, 1865, Zeitschr. f. wiss. Zool., Bd. xv. p. 366.

Spines of variable number, from eleven to twenty, commonly twelve to sixteen, four-sided prismatic, with smooth thin edges, of equal breadth in their whole length or a little thinner towards the proximal end.

_Dimensions._--Length of the spines 0.3, breadth 0.005.

_Habitat._--Mediterranean (Nice); Central Pacific, Station 274, surface.

6. _Litholophus rhipidium_, Haeckel.

_Litholophus rhipidium_, Haeckel, 1862, Monogr. d. Radiol., p. 402, Taf. xix. fig. 6.

Spines of variable number, from eleven to twenty, commonly twelve to sixteen, four-sided prismatic, with distantly denticulated edges, of equal breadth in their whole length or a little thinner towards both ends.

_Dimensions._--Length of the spines 0.3, breadth 0.006.

_Habitat._--Mediterranean (Messina); North Atlantic, Station 352, surface.

Subgenus 3. _Litholophonium_, Haeckel.

_Definition._--Number of the radial spines twenty (or more?).

7. _Litholophus fasciculus_, n. sp.

Spines constantly (?) twenty, four-sided prismatic, with smooth prominent edges, nearly of equal breadth throughout their whole length.

_Dimensions._--Length of the spines 0.3 to 0.5, breadth 0.008.

_Habitat._--South Pacific, Station 291, surface.

8. _Litholophus penicillus_, n. sp.

Spines constantly twenty (or more?), four-sided prismatic, with distantly denticulated edges, gradually thickened from the small pyramidal base to the middle part, of equal breadth in the distal half.

_Dimensions._--Length of the spines 0.3 to 0.4, breadth 0.005 to 0.007.

_Habitat._--North Pacific, Station 252, surface.

Family XXXV. #CHIASTOLIDA#, Haeckel.

_Acanthochiasmida_, Haeckel, 1862, Monogr. d. Radiol., p. 402.

_Definition._--ACANTHARIA with a variable number of simple radial spines, which are grown together in pairs (two opposite spines of each pair representing together a single diametral spine). Diametral spines crossed loosely in the centre of the spherical or irregular roundish central capsule. No lattice-shell.

{737}The family #Chiastolida# (or Acanthochiasmida) differs from all other ACANTHARIA in the peculiar mode of the radial spines; these grown together in pairs in the centre of the body, so that every two spines opposite in one axis of the body form together one single diametral spine. All diametral spines are loosely crossed in the middle of the central capsule, or connected by a peculiar screw-like winding, but not united firmly.

I established the family Acanthochiasmida in my Monograph (1862, p. 402) upon the single genus _Acanthochiasma_ (with three species), in which only ten diametral spines are constantly found; I derived these from the twenty radial spines of the common #Acanthometra#, supposing that every two opposite spines of the latter (lying in one axis) were grown together in the centre, whilst the intimate connection of the twenty radial spines in the common centre was dissolved. This opinion was afterwards confirmed by Richard Hertwig, who observed _Acanthochiasma_ intact in the living state. Although two species of this genus are cosmopolitan and very common, the number of species is very small; I could add to those three older known forms only a single new species.

Another genus of this family, _Chiastolus_, was observed by me only in a single specimen but it is extremely interesting. It has sixteen diametral spines, disposed quite regularly after the same law of the thirty-two spines of _Actinastrum_ which we described above (compare above, p. 729). Therefore we cannot doubt that the former is derived from the latter in the same way, every two opposite radial spines (of one axis) being grown together to form a single diametral spine. As we place _Acanthometron_ (with twenty spines) and _Actinastrum_ (with thirty-two spines) in two different families, it would perhaps be more convenient to separate also _Acanthochiasma_ and _Chiastolus_ as representatives of two different families--Acanthochiasmida (with ten diametral spines) and Chiastolida (with sixteen diametral spines).

As we derive _Acanthochiasma_ from _Acanthometron_ by concrescence in pairs of the twenty radial spines, the Müllerian law of Icosacantha must be employed also to the ten diametral spines of the former, therefore two of them are equatorial, four tropical, and four polar spines. In the same way we may employ the new law of disposition found in the thirty-two radial spines of _Actinastrum_ equally to the sixteen diametral spines of _Chiastolus_, which we derive from the former, four of them are equatorial, eight tropical, and four polar spines (compare above, p. 732).

_The Central Capsule_ of the Chiastolida is spherical, and exhibits in general the same shape as in the #Acanthonida#, and specially in the Astrolonchida. Of course every diametral spine pierces the capsule twice, at two points diametrically opposed. In some species of _Acanthochiasma_ the central capsule is formed very late, so that it seems often to be absent. A very accurate description of the capsule and its nucleus, as well as of the calymma and the pseudopodia, is given by Richard Hertwig in his Organismus der Radiolarien (1879, pp. 10-18). The pseudopodia are very numerous, and sometimes bear reddish granules.

{738}_Synopsis of the Genera of Chiastolida._

I. Subfamily Chiastolidina. Sixteen diametral spines, derived by concrescence of thirty-two radial spines, 321. _Chiastolus_.

II. Subfamily Acanthochiasmida. Ten diametral spines, derived by concrescence of twenty radial spines, 322. _Acanthochiasma_.

Genus 321. _Chiastolus_,[361] n. gen.

_Definition._--#Chiastolida# with sixteen diametral spines, derived from thirty-two radial spines opposite and grown together in pairs.

The genus _Chiastolus_, hitherto known only by a single observed specimen, comprises the Chiastolida with sixteen diametral spines, which are loosely crossed in the centre of the body. Four of these spines are equatorial, four polar, and eight tropical. We derive _Chiastolus_ from _Actinastrum_ by concrescence of every two opposite spines in one axis of the body (compare above, pp. 729, 732).

1. _Chiastolus amphicopium_, n. sp. (Pl. 129, figs. 3, 3_a_, 3_b_).

Spines in the central part cylindrical, spirally convoluted in a very peculiar manner, broadened towards both ends, strongly compressed, two-edged; the broadest parts are the two truncated distal ends, five to seven times as broad as the thinnest central part, which is placed between two spindle-shaped intumescences. These cochleary central parts of the sixteen spines seem to be resting one upon another. Each spine (composed of two opposite equal radial spines) has nearly the form of a double oar. The single observed specimen (preserved in glycerine) exhibited a most regular disposition of the thirty-two spines (grown together in pairs in the centre). The diameter of the dark non-transparent spherical central capsule equalled one-fifth to one-fourth of the total length of the double spines. When the soft parts of the body were destroyed by sulphuric acid, the sixteen single spines were suddenly dispersed.

_Dimensions._--Length of the sixteen double spines 0.5, distal breadth (of the truncated ends) 0.05, central breadth 0.01; diameter of the central capsule 0.12.

_Habitat._--South-east Pacific (near Juan Fernandez), Station 297, surface.

Genus 322. _Acanthochiasma_,[362] Krohn, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 810.

_Definition._--#Chiastolida# with ten diametral spines, derived from twenty radial spines opposite and grown together in pairs.

{739}The genus _Acanthochiasma_ with a small number of common species, comprises the Chiastolida with ten diametral spines, which are loosely crossed in the centre of the body. I could distinguish only four species, two of which are cosmopolitan and very widely distributed. In all four species the diametral spines are quite simple, cylindrical; only in one species distinguished by a spiral winding or torsion in the middle part, where they are crossed one to another. We derive _Acanthochiasma_ from _Acanthometron_ by concrescence of every two spines opposite in one axis of the body.

1. _Acanthochiasma krohnii_, Haeckel.

_Acanthochiasma krohnii_, Haeckel, 1862, Monogr. d. Radiol., p.403, Taf. xix. fig. 7.

_Acanthochiasma krohnii_, R. Hertwig, 1879, Organismus d. Radiol., Taf. ii. fig. 6.

Spines needle-shaped, cylindrical, very thin and long, of equal breadth in their whole length, distinguished by a high degree of elasticity. Central capsule colourless or yellowish-white, transparent. Granules of the sarcode colourless.

_Dimensions._--Length of the spines 0.5 to 1.0, breadth 0.001 to 0.002.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, very common.

2. _Acanthochiasma rubescens_, Krohn.

_Acanthochiasma rubescens_, Haeckel, 1862, Monogr. d. Radiol., p. 403.

Spines cylindrical, of equal breadth in their whole length, not very elastic, pointed at the two ends. Central capsule intransparent, reddish, with violin-shaped concretions. Granules of the sarcode red coloured.

_Dimensions._--Length of the spines 0.2 to 0.6, breadth 0.004 to 0.006.

_Habitat._--North Atlantic, Madeira, Krohn; Lanzerote, Haeckel.

3. _Acanthochiasma fusiforme_, Haeckel.

_Acanthochiasma fusiforme_, Haeckel, 1862, Monogr. d. Radiol., p. 404, Taf. xix. fig. 8.

Spines spindle-shaped, from the thicker central part thinned towards the two thin conical ends, perfectly straight and smooth, rigid, inelastic. Central capsule non-transparent, brown.

_Dimensions._--Length of the spines 0.3 to 0.5, breadth in the central part 0.006 to 0.009.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific.

4. _Acanthochiasma spirale_, n. sp.

Spines spindle-shaped, tapering from the thicker central part towards the two thin conical ends, rigid, inelastic; their central part is spirally convoluted in a very peculiar cochlea-like manner, as in _Chiastolus amphicopium_ (Pl. 129, figs. 3_a_, 3_b_). The ten spines are propped one upon another by the central screw. Central capsule dark, opaque.

_Dimensions._--Length of the spines 0.2 to 0.3, breadth of the central spiral part 0.01.

_Habitat._--Central Pacific, Station 266, surface.

{740}----

Suborder II. ACANTHONIDA, Haeckel (Pls. 130-132).

_Acanthonida_, Haeckel, 1881, Prodromus, p. 465.

_Definition._--#Acanthometra# with twenty radial spines, disposed according to the Müllerian or Icosacanthan law in five zones each of four spines.

Family XXXVI. #ASTROLONCHIDA#, Haeckel (Pl. 130).

_Astrolonchida_, Haeckel, 1881, Prodromus, p. 465.

_Definition._--#Acanthometra# with twenty radial spines of nearly equal size and similar form, disposed according to the law of the Icosacantha. No lattice-shell.

The family #Astrolonchida#, the first and oldest of the #Acanthonida#, is no doubt the ancestral stock not only of this suborder but also all #Acanthophracta#, _i.e._, of all Icosacantha or all ACANTHARIA in which twenty radial spines are regularly disposed according to the Müllerian law, forming five zones each of four alternating spines (compare above, p. 717). The Astrolonchida differ from the #Acanthophracta# in the absence of a complete lattice-shell, from the other two families of #Acanthonida# (the Quadrilonchida and Amphilonchida) in the equal size and similar form of all the spines. Probably this equality is nowhere quite perfect, since in all Icosacantha the central bases of the twenty spines exhibit originally certain slight differences of form and junction, effected by the regular disposition itself. But setting aside this slight difference, only recognisable by means of a very accurate investigation of the central junction (and in thinner spines often not at all recognisable), the twenty spines of the Astrolonchida appear perfectly equal. Therefore the four equatorial spines are not distinguished from the sixteen other spines, as is constantly the case in the two following families.

The number of genera (eleven) and of species (seventy-six) in the Astrolonchida is far larger than in the five other families of #Acanthometra#, and requires a distinction into three different subfamilies. (A) In the Zygacanthida the form of the radial spines is quite simple, without apophyses or transverse processes; (B) in the Phractacanthida each spine bears two opposite apophyses (rarely two longitudinal rows of these opposite apophyses); (C) in the Stauracanthida each spine bears a cross of four apophyses, opposite in pairs (rarely four longitudinal crossed rows of apophyses, opposite in pairs). The Phractacanthida and Stauracanthida appear as two divergent branches of the pedigree, derived independently from the common ancestral stock of Zygacanthida.

In the Zygacanthida, constantly devoid of apophyses, we can distinguish only three genera, characterised by the different fundamental form of the radial spines; these are:--(1) _Acanthometron_, with cylindrical or conical spines (without edges); (2) _Zygacantha_, with compressed and two-edged spines; (3) _Acanthonia_, with four-edged, prismatic or pyramidal spines. The transverse section of the spines is in the first case {741}circular, in the second elliptical or lanceolate, in the third square. All the different forms of spines, which we find in the numerous ACANTHARIA, may be reduced to these three forms, and among these the second and third are derived from the first.

The development of apophyses or of lateral transverse processes (wanting in the Zygacanthida) is of the greatest value for the further differentiation of the ACANTHARIA. For from the Phractacanthida (with two opposite apophyses on each spine) we must derive the Phrastaspida, the common ancestral stock of the Diporaspida (and therefore also the Belonaspida, Hexalaspida, Diploconida, and Phractopeltida). On the other hand the Stauracanthida (with four crossed apophyses on each spine) have produced the Stauraspida, or the ancestral group of the Tessaraspida and Sphærocapsida. From all these #Acanthophracta#, possessing a complete lattice-shell, the Astrolonchida differ in the absence of such a complete shell. Also in the few cases in which the apophyses become latticed (_Doracantha_ among the Phractacanthida, and _Phatnacantha_ among the Stauracanthida), the lattice-plates of the neighbouring spines never meet with their edges, as is the case in all #Acanthophracta#. But in a phylogenetic as well as in an ontogenetic sense the former are the ancestral stock of the latter.

_The Central Capsule_ in the Astrolonchida is commonly spherical, sometimes with twenty roundish elevations or conical papillæ, extending radially to the basal half of the radial spines. The calymma is voluminous, and forms around the radial spines conical or cylindrical "jelly-sheaths," which are connected with the spines by coronas of Myophrisca (or of the bodies formerly called "Gallert-cilien," afterwards recognised as "contractile Filamente").

_Synopsis of the Genera of Astrolonchida._

------------------------------------------------------------------------- I. Subfamily Zygacanthida. Twenty radial spines simple, without apophyses or lateral transverse processes. ------------------------------------------------------------------------- Spines cylindrical, with circular transverse section, 323. _Acanthometron_.

Spines compressed, two-edged or lamellar, with elliptical or rhomboidal transverse section, 324. _Zygacantha_.

Spines quadrangular (prismatic or pyramidal), with four edges, with square transverse section, 325. _Acanthonia_.

------------------------------------------------------------------------- II. Subfamily Phractacanthida. Twenty radial spines provided each with two opposite apophyses (or two longitudinal rows of apophyses). ------------------------------------------------------------------------- { Apophyses simple, 326. _Lithophyllium_. { Two apophyses opposite on { Apophyses branched, 327. _Phractacantha_. each spine. { { Apophyses latticed, 328. _Doracantha_.

Two opposite longitudinal rows of apophyses (four to eight or more apophyses on each spine, opposite in pairs), 329. _Astrolonche_. ------------------------------------------------------------------------- III. Subfamily Stauracanthida. Twenty radial spines provided each with four crossed apophyses (or four crossed longitudinal rows of apophyses). ------------------------------------------------------------------------- { Apophyses simple, 330. _Xiphacantha_. Four apophyses (in cross { form) opposite in pairs { Apophyses branched, 331. _Stauracantha_. on each spine. { { Apophyses latticed, 332. _Phatnacantha_.

Four longitudinal rows of apophyses, opposite in pairs in cross form on each spine, 333. _Pristacantha_.

{742}Subfamily 1. ZYGACANTHIDA, Haeckel.

_Definition._--#Astrolonchida# with twenty simple radial spines, without apophyses or lateral transverse processes.

Genus 323. _Acanthometron_,[363] J. Müller, 1855, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 229.

_Definition._--#Astrolonchida# with simple cylindrical or needle-shaped radial spines, without edges and without apophyses; their transverse section is circular.

The genus _Acanthometron_, with the restricted definition here given, is the most simple form of all #Acanthonida#, and may be regarded as the common ancestral form not only of this suborder but also of all #Acanthophracta#, in general of all Icosacantha, or all ACANTHARIA in which twenty radial spines are regularly disposed after the Müllerian law (p. 717). In the wider sense, given originally to #Acanthometra# by Johannes Müller, its discoverer, this genus comprised all ACANTHARIA constituting here our order "#Acanthometra#" (Radiolaria without lattice-shell, with radial spines united in the centre). In my Monograph (1862, p. 375) I restricted this genus to those "Acanthometrida" in which twenty simple spines of equal size (and without apophyses) are supported one upon another in the centre, and I separated as _Astrolithium_ those forms in which they are grown together in the centre. But this difference now appears not so important, and I restrict here the genus _Acanthometron_ (not #Acanthometra#) to those most simple forms in which the simple radial spines are cylindrical or conical, without edges.

Subgenus 1. _Acanthometrella_, Haeckel.

_Definition._--Spines at the central base without leaf-cross, united by the opposed triangular faces of their pyramidal bases, resting one upon another.

1. _Acanthometron elasticum_, Haeckel.

_Acanthometra elastica_, Haeckel, 1862, Monogr. d. Radiol., p. 376, Taf. xv. fig. 1, Taf. xviii. fig. 1.

_Acanthometra elastica_, R. Hertwig, 1879, Organismus d. Radiol., Taf. i. figs. 2, 2_a_, 2_b_.

Spines cylindrical, very thin and long, needle-shaped, at the central base four-sided pyramidal, without leaf-cross. Distal apex conical. The spines are very elastic, of nearly equal thickness in their whole length. Central capsule quite pellucid, colourless, with a variable number of yellow pigment-bodies (xanthellæ?).

_Dimensions._--Length of the spines 0.3 to 0.6, breadth 0.001 to 0.002.

_Habitat._--Cosmopolitan, very common in all warmer seas; Mediterranean, Atlantic, Indian, Pacific, surface.

{743}2. _Acanthometron cylindricum_, n. sp. (Pl. 130, fig. 2).

Spines cylindrical, thick and long, at the central base thickened with a pear-shaped knob, and with very small central fulcral pyramid, without leaf-cross. Distal apex rounded or truncated. Central capsule opaque, filled with red pigment-bodies.

_Dimensions._--Length of the spines 0.4 to 0.8, breadth 0.01 to 0.015.

_Habitat._--Central Pacific, Stations 266 to 274, surface.

3. _Acanthometron fuscum_, J. Müller.

_Acanthometra fusca_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 47, Taf. xi. fig. 4.

_Acanthometra fusca_, Haeckel, 1862, Monogr. d. Radiol, p. 377.

Spines very thin and long, in the proximal half cylindrical, in the distal half conical, gradually thinned towards the simple conical apex. Central base a small four-sided pyramid, without leaf-cross. Central capsule opaque, filled with brown pigment-bodies.

_Dimensions._--Length of the spines 0.2 to 0.4, breadth 0.002 to 0.004.

_Habitat._--Mediterranean (Cette, Portofino, Messina).

4. _Acanthometron bulbosum_, Haeckel.

_Acanthometra bulbosa_, Haeckel, 1862, Monogr. d. Radiol., p. 377, Taf. xv. fig. 2, Taf. xviii fig. 2.

Spines very thin and long, cylindrical, with simple needle-shaped apex; in the basal part conical, towards the centre much thickened, with a short four-sided fulcral pyramid, without leaf-cross. Central capsule opaque, filled with brown pigment-bodies.

_Dimensions._--Length of the spines 0.3 to 0.5, breadth in the middle and outer part 0.001, in the basal part 0.008 to 0.012.

_Habitat._--Mediterranean; Atlantic, Station 354, surface.

5. _Acanthometron dolichoscion_, Haeckel (Pl. 129, figs. 6-8).

_Acanthometra dolichoscia_, Haeckel, 1862, Monogr. d. Radiol., p. 377, Taf. xviii. figs. 3_a_, 3_b_.

Spines very long and thin, cylindrical, in the thickened outer half about twice as thick as in the thin inner half, at the simple apex compressed, two-edged. Central base little thickened, with a small four-sided pyramid, without leaf-cross. Central capsule transparent, whitish or yellowish.

_Dimensions._--Length of the spines 0.6 to 0.8, breadth in the proximal