part 0.02 to 0.025.

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

7. _Acanthonia concava_, n. sp.

Spines quadrangular, with four broad lamellar, concave, prominent edges, which from the smaller middle part are broadened towards the two emarginated ends; each end with a small {751}quadrangular pyramid, without leaf-cross. All the twenty spines of this species exhibit nearly the same form, which is seen in the frontal or anterior (hydrotomical) spine of _Amphilonche anomala_ (Monogr. d. Radiol., Taf. xviii. fig. 23, _a_).

_Dimensions._--Length of the spines 0.15, breadth in the middle part 0.012, on both ends 0.025.

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

8. _Acanthonia quadrangula_, n. sp.

Spines quadrangular prismatic, with smooth prominent straight edges, but of very different breadth in both halves; the inner or proximal half (inside the central capsule) twice to four times as broad as the outer or distal half (outside the central capsule); both ends suddenly separated by a constriction, in which is inserted the membrane of the capsule. The latter is pellucid, with a number of yellow bodies. Apex of the spines simple, base pyramidal, without leaf-cross.

_Dimensions._--Length of the spines 0.2 to 0.4, breadth of the basal half 0.01, of the distal half 0.002 to 0.004.

_Habitat._--Atlantic, Canary Islands, Azores, Station 354, surface.

Subgenus 2. _Acanthonidium_, Haeckel.

_Definition._--Spines at the central base with a broad leaf-cross, composed of four prominent triangular lamellæ; the meeting edges of these crossed lamellæ between every three or four neighbouring spines so rest one upon another that twenty-two hollow pyramidal compartments are formed (compare p. 721).

9. _Acanthonia echinoides_, Haeckel.

_Acanthometra echinoides_, Claparède et Lachmann, 1858, Études sur les Infusoires et les Rhizopodes, &c., p. 459, pl. xxiii. figs. 1-5.

_Acanthometra echinoides_, Haeckel, 1862, Monogr. d. Radiol., p. 383.

Spines quadrangular prismatic without prominent edges, with four plane lateral faces, of equal breadth throughout their whole length. Central base three to four times as broad, with large leaf-cross. Apex truncated or bifid (sometimes with four short teeth).

_Dimensions._--Length of the spines 0.3 to 0.5, breadth 0.004 to 0.008; leaf-cross 0.02 to 0.03.

_Habitat._--North Atlantic, west coast of Norway (Claparède et Lachmann); Færöe Channel (Gulf Stream), John Murray, surface.

10. _Acanthonia claparedei_, Haeckel.

_Acanthometra claparedei_, Haeckel, 1862, Monogr. d. Radiol., p. 383, Taf. xviii. fig. 12.

Spines quadrangular prismatic, with four prominent lamellar edges, of equal breadth throughout their whole length. Apex bifid. Central base twice as broad, with large leaf-cross. Central capsule opaque, reddish-brown.

_Dimensions._--Length of the spines 0.6, breadth 0.016; leaf-cross 0.032.

_Habitat._--Mediterranean (Messina); Atlantic, Station 347, surface.

{752}11. _Acanthonia cuspidata_, Haeckel.

_Acanthometra cuspidata_, Haeckel, 1862, Monogr. d. Radiol., p. 383, Taf. xviii. fig. 11.

Spines quadrangular pyramidal, with four prominent lamellar edges, tapering gradually from the broad base towards the simple distal apex. Basal leaf-cross as broad, with a small central pyramid.

_Dimensions._--Length of the spines 0.5, basal breadth 0.012; leaf-cross 0.025.

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

12. _Acanthonia quadrifolia_, Haeckel.

_Acanthometra quadrifolia_, Haeckel, 1862, Monogr. d. Radiol., p. 382, Taf. xviii. fig. 10.

Spines in the basal part quadrangular pyramidal, with four prominent lamellar edges and a large basal leaf-cross; in the distal part three to six times as long, cylindrical, of equal breadth. Apex simple, conical, or bifid. Central capsule yellow or whitish. This common species differs from the nearly allied _Acanthometron catervatum_ mainly by the strong development of the large basal leaves or wings.

_Dimensions._--Length of the spines 0.3 to 0.5, breadth in the distal half 0.002, in the basal part 0.02.

_Habitat._--Mediterranean; North Atlantic, Stations 252 to 254; Færöe Channel, Gulf Stream, in enormous numbers, John Murray, surface and at various depths.

13. _Acanthonia diplopyramis_, n. sp.

Spines formed like a quadrangular double pyramid or an irregular octahedron; the basal leaf-cross being extremely developed, with four very large and thin lamellar leaves; the basal halves of the twenty double pyramids are united by the meeting edges of those leaves, while their distal halves are free, with simple apices. Therefore the four triangular leaves of each spine are equally thinned from the middle towards the two ends.

_Dimensions._--Length of the spines 0.1 to 0.2, greatest breadth 0.04 to 0.08.

_Habitat._--Central Pacific, Stations 266 to 274, surface.

14. _Acanthonia multispina_, Haeckel.

_Acanthometra multispina_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 47, Taf. vii. figs. 6-9.

_Acanthometra multispina_, Haeckel, 1862, Monogr. d. Radiol., p. 384.

Spines quadrangular, with four lamellar prominent edges, in the proximal half nearly prismatic, in the distal half pyramidal; both halves separated by a prominent short tooth on each edge. Here in the middle part the breadth (including the four teeth) is equal to the basal leaf-cross. Central capsule opaque, brown.

_Dimensions._--Length of the spines 0.2 to 0.3, greatest breadth 0.01 to 0.02.

_Habitat._--Mediterranean (Messina); Tropical Atlantic, Station 348.

{753}15. _Acanthonia serrulata_, n. sp.

Spines quadrangular pyramidal, with simple apex; the large basal leaf-cross nearly half as long as the prolonged distal part. The four prominent triangular edges of the latter are very thin and broad lamellæ, finely dentate or serrate.

_Dimensions._--Length of the spines 0.2 to 0.3, greatest breadth 0.05 to 0.06.

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

Subgenus 3. _Acantholithium_, Haeckel.

_Definition._--Spines in the basal part grown together, so that the whole skeleton is not composed of twenty separated pieces, but represents a single piece of acanthin--a star with twenty equal rays.

16. _Acanthonia stellata_, n. sp.

Spines quadrangular pyramidal, with simple distal apex, in the basal part grown perfectly together, so that the whole skeleton forms a single piece of acanthin--a starlet with twenty equal rays. The free pyramidal part of each spine is twice to four times as long as the basal part.

_Dimensions._--Length of the spines 0.1 to 0.15, greatest breadth (on the surface of the central solid sphere) 0.02 to 0.04.

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

Subfamily 2. PHRACTACANTHIDA, Haeckel.

_Definition._--#Astrolonchida# with twenty radial spines, each of which bears two opposite apophyses or lateral transverse processes; sometimes two longitudinal rows of opposite apophyses.

Genus 326. _Lithophyllium_,[366] J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 52.

_Definition._--#Astrolonchida# with two simple, not branched, opposite apophyses on each radial spine.

The genus _Lithophyllium_ was founded by J. Müller for a single species (_Lithophyllium foliosum_), which we also here retain as the type of the genus. It is the first observed Astrolonchid, which bears two opposite lateral apophyses on each spine, and may therefore be regarded as the ancestral form of the subfamily Phractacanthida. The two opposite apophyses are here simple, whilst in the other genera of the subfamily they are branched or multiplied.

{754}1. _Lithophyllium cruciatum_, Haeckel.

_Acanthometra cruciata_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 49, Taf xi. fig. 11.

_Xiphacantha cruciata_, Haeckel, 1862, Monogr. d. Radiol., p. 385, Taf. xviii. fig. 13.

Spines cylindrical, very thin, crossed perpendicularly in the distal third by a thin transverse beam; both lateral rods of the cross have the same length as the distal end. Apex simple. Base pyramidal, without leaf-cross.

_Dimensions._--Length of the spines 0.05 to 0.15, breadth 0.001 to 0.002.

_Habitat._--Mediterranean, Atlantic, Stations 352 to 354, &c., surface.

2. _Lithophyllium gladiatum_, n. sp. (Pl. 130, fig. 3).

Spines compressed, sword-shaped, two-edged, crossed perpendicularly in the middle part by a broad, somewhat curved transverse beam; both lateral rods of the cross are triangular compressed, and have the same length as the proximal end. Apex simple. Base pyramidal, without leaf-cross.

_Dimensions_.--Length of the spines 0.2 to 0.25, breadth 0.01.

_Habitat_.--North Pacific, Station 241, surface.

3. _Lithophyllium condylatum_, n. sp.

Spines compressed quadrangular, tapering from the broader middle towards the two ends; from the middle part arise two opposite perpendicular apophyses, which bear on the rounded end a thickened condyle. Apex simple. Base pyramidal, with a small leaf-cross.

_Dimensions._--Length of the spines 0.1 to 0.12, breadth in the middle part 0.02.

_Habitat._--Central Pacific, Station 266 to 272, surface.

4. _Lithophyllium foliosum_, J. Müller.

_Lithophyllium foliosum_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 52, Taf. xi. figs. 6-10.

_Xiphacantha foliosa_, Haeckel, 1862, Monogr. d. Radiol., p. 385.

Spines lanceolate, tapering from the broader middle towards the two ends. From the middle part or from the outer third arise two opposite triangular apophyses, which are not perpendicular to the axis of the spine, but form an acute angle with its distal part. Therefore each spine represents a broad leaf with a middle rib and with three lobes or truncated teeth. The distal apex is distinguished by a violet colour. Base pyramidal, without leaf-cross. Central capsule yellow.

_Dimensions._--Length of the spines 0.05 to 0.1, breadth 0.02 to 0.03.

_Habitat._--Mediterranean, French shore, Saint Tropez, J. Müller.

{755}Genus 327. _Phractacantha_,[367] Haeckel, 1881, Prodromus, p. 465.

_Definition_.--#Astrolonchida# with two branched, but not latticed, opposite apophyses on each radial spine.

The genus _Phractacantha_ differs from its ancestral form, the preceding _Lithophyllium_ by the ramification of the apophyses, which are either forked or bear lateral branches. If the prolonged fork-branches of the neighbouring spines meet and form a lattice-shell, this genus passes over into _Phractaspis_, the common ancestral form of the Diporaspida.

1. _Phractacantha_ bifurca, n. sp.

Spines cylindrical, thin, of equal breadth throughout their whole length. Apex simple. Base pyramidal, without leaf-cross. From the outer third arise two opposite, thin, forked apophyses; ends of the fork branches acute.

_Dimensions._--Length of the spines 0.1, breadth 0.006.

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

2. _Phractacantha bipennis_, n. sp.

Spines compressed, two-edged, tapering from the broader middle towards the two ends. Apex simple. Base pyramidal, without leaf-cross. From the middle arise two opposite broad, forked apophyses; ends of the fork-branches broad and obtuse.

_Dimensions._--Length of the spines 0.15, breadth in the middle 0.012.

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

Genus 328. _Doracantha_,[368] Haeckel, 1881, Prodromus, p. 465.

_Definition_.--#Astrolonchida# with two latticed or fenestrated apophyses on each radial spine.

The genus _Doracantha_ arises from the foregoing _Phractacantha_ by union of the fork-branches of the apophyses on each spine. By this concrescence is formed a polygonal or roundish plate with two pores, pierced by the radial spine between them. _Doracantha_ may be regarded as a _Dorataspis_, in which the twenty small fenestrated plates have not become united.

{756}1. _Doracantha dorataspis_, n. sp.

Spines compressed, two-edged, tapering from the broader middle towards the two ends. Apex simple. Base pyramidal, without leaf-cross. From the middle part of each spine arise two opposite forked apophyses; the neighbouring fork-branches are recurved and united in the tangential plane; so that each spine bears a plate or shield with two elliptical pores; the margin of the roundish plate bears a variable number of short teeth.

_Dimensions._--Length of the spines 0.2, breadth 0.02.

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

Genus 329. _Astrolonche_,[369] Haeckel, 1881, Prodromus, p. 465.

_Definition._--#Astrolonchida# with numerous simple apophyses (four to eight or more on each radial spine), which are arranged in two opposite longitudinal rows (rarely in six such rows, opposite in three parallel planes).

The genus _Astrolonche_ differs from the preceding Phractacanthida in the multiplication of the simple apophyses. Commonly these are opposite in pairs in two longitudinal rows (on the two edges of the compressed spine, at least two on each side). But sometimes (in the subgenus _Astrolonchidium_) there are six instead of two longitudinal rows of teeth, and these are placed in three parallel planes.

Subgenus 1. _Astroloncharium_, Haeckel.

_Definition._--Each spine with two longitudinal rows of apophyses, opposite in one meridian plane.

1. _Astrolonche bicruciata_, n. sp.

Spines compressed, two-edged, almost of equal breadth throughout their whole length, with simple apex and small leaf-cross at the base. From the two edges of the middle part of each spine arise two pairs of opposite apophyses, which are compressed and a little curved (convex on the distal, concave on the proximal margin). All four apophyses are of the same size and form; the radial distance of each pair much smaller than their common distance from the centre.

_Dimensions._--Length of the spines 0.25, breadth 0.02.

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

2. _Astrolonche mucronata_, Haeckel.

_Acanthometra mucronata_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 49, Taf. x. fig. 9.

_Aspidomma mucronatum_, Haeckel, 1862, Monogr. d. Radiol., p. 424.

Spines conical, little compressed, with simple apex and small leaf-cross at the base. From the basal half of each spine arise two pairs of opposite apophyses, which exhibit a very different form. {757}The upper or distal apophyses (nearly in the middle of the spine) are flat, leaf-shaped, broadened in the periphery, often lobed, and sometimes branched or even fenestrated. (Transition to _Phractaspis_ and _Dorataspis_, or to _Phractopelta_?) The lower or proximal apophyses are thick, simple, all slightly curved; they are equidistant from the former and from the centre.

_Dimensions._--Length of the spines 0.2 to 0.3, greatest breadth 0.01.

_Habitat._--Mediterranean (Cette on the French shore), surface, J. Müller.

3. _Astrolonche pectinata_, Haeckel.

_Acanthometra pectinata_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 48, Taf. x. figs. 1, 2.

_Xiphacantha pectinata_, Haeckel, 1862, Monogr. d. Radiol., p. 386.

Spines compressed quadrangular, with short, simple or bifid apex, pyramidal on the base, without leaf-cross. From the two broader edges of the proximal half arise two longitudinal rows of opposite apophyses; three to four slender teeth in each row.

_Dimensions._--Length of the spines 0.2, breadth 0.08.

_Habitat._--Mediterranean, Cette (French shore), surface, J. Müller.

4. _Astrolonche pinnata_, n. sp.

Spines in the distal half compressed, linear, two-edged, with bifid apex; in the proximal half three times as broad lanceolate, at the base pyramidal, without leaf-cross. From the two broader edges of the proximal half arise two longitudinal rows of opposite apophyses; four to six broad triangular teeth in each row.

_Dimensions._--Length of the spines 0.3 to 0.4, breadth in the outer half 0.012, in the inner half 0.03 to 0.04.

_Habitat._--South Atlantic, Station 332, surface.

Subgenus 2. _Astrolonchidium_, Haeckel.

_Definition._--Each spine with three parallel double rows of opposite apophyses.

5. _Astrolonche serrata_, Haeckel.

_Xiphacantha serrata_, Haeckel, 1862, Monogr. d. Radiol., p. 386, Taf. xvii. fig. 3, Taf. xviii. figs. 14_a_, 14_b_.

_Xiphacantha serrata_, R. Hertwig, 1879, Organismus d. Radiol., p. 11, Taf. ii. fig. 4.

_Acanthometra serrata_, Haeckel, 1860, Monogr. d. Radiol., p. 807.

Spines in the distal half thin, nearly cylindrical or a little compressed, thinned towards the short simple or bifid apex; in the proximal half three to six times as broad, four-winged, with six longitudinal rows of opposite apophyses. From the edges of the two broader (lateral) wings arise three {758}to four pairs of strong conical teeth; from the edges of the two smaller (sagittal) wings arise also three to four pairs of teeth, but very short and broad, triangular; each of these teeth bears on both its (lateral) sides two opposite slender conical teeth, which are parallel to the large conical teeth of the lateral wings. Therefore all teeth (eighteen to twenty-four) are placed opposite in pairs in three parallel planes. Base of the spines pyramidal, with a small leaf-cross. The central capsule of this large and very remarkable species commonly entirely includes the apophyses of the spines, and is opaque, whitish.

_Dimensions._--Length of the spines 0.2 to 0.3, breadth of the distal half 0.002 to 0.004, of the proximal half 0.01 to 0.02.

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

Subfamily 3. STAURACANTHIDA, Haeckel.

_Definition._--#Astrolonchida# with a cross of four free apophyses (or four crossed longitudinal rows of apophyses) on each radial spine.

Genus 330. _Xiphacantha_,[370] Haeckel, 1862, Monogr. d. Radiol., p. 384.

_Definition._--#Astrolonchida# with four simple apophyses on each radial spine, opposite in pairs in the form of a cross.

The genus _Xiphacantha_ was founded by me in 1862 for all those _Acanthometrida_ which bear simple or branched apophyses on their twenty equal spines. I restrict here the genus to those Astrolonchida which bear on each spine a cross of four simple, not branched, apophyses. These are either conical teeth or broad wings, sometimes extremely thin leaves. _Xiphacantha_ may be regarded as the ancestral form not only of the subfamily Stauracanthida, but also of the Tessaraspida, derived from the latter.

Subgenus 1. _Xiphacanthonia_, Haeckel.

_Definition._--Apophyses of the radial spines small, formed like a tooth or a hook, not wing-shaped. Edges of the spines commonly narrow, little prominent.

1. _Xiphacantha quadridentata_, Haeckel.

_Xiphacantha quadridentata_, Haeckel, 1862, Monogr. d. Radiol., p. 387, Taf. xviii. figs. 15_a_, 15_b_.

_Acanthometra quadridentata_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 48, Taf. x. fig. 3.

Spines slender, four-sided prismatic, gradually thinner towards the simple pyramidal apex. Base with large wing-cross. Four apophyses about in the middle of each spine, conical, straight, smooth, about as long as the basal breadth of the spine. Central capsule opaque, reddish-brown.

{759}_Dimensions._--Length of the spines 0.2 to 0.3, breadth in the middle