part 1, p. 226, Pl. A; viz., fourteen species of _Challengeria_ and six

species of _Tuscarora_.

The most important advance in the knowledge which we had of the peculiar organisation of the PHÆODARIA, was made by the accurate description which Richard Hertwig published, in 1879, of the intimate structure of their central capsule, and mainly of its peculiar openings. He examined living at Messina the following three forms, described in my Monograph; (1) _Aulacantha scolymantha_, (2) _Aulosphæra elegantissima_, and (3) _Coelodendrum ramosissimum_. Besides, he described an interesting new genus, _Coelacantha anchorata_; and another new form, which he placed in the Aulosphærida, as _Aulosphæra gracilis_, but which really was a new genus of Sagosphærida, here described as _Sagoscena gracilis_. Finally, Hertwig first discovered that the peculiar bodies, described by Ehrenberg as _Dictyocha_ and placed by him in the _Diatomea_ (_Polygastrica_), were the isolated pieces of the skeleton of a true _Phæodarium_, and that they were scattered loosely in great numbers over the surface of the jelly-sphere, just as are the hollow spicula of _Thalassoplancta_ or _Cannobelos_.

The six species mentioned, of which Hertwig gave a very accurate description and very instructive figures, belong to six different genera, and these represent six different families of PHÆODARIA, viz.; Aulacanthida, Aulosphærida, Coelodendrida, Cannosphærida, Sagosphærida and Cannorrhaphida. He found that all these six forms, in spite of great differences in the form and structure of their skeleton, were identical in the structure of the central capsule; and since he observed constantly three openings in its double wall (a large main-opening on the oral pole, and a pair of lateral accessory openings on the aboral pole of its main axis) he called them TRIPYLEA (_loc. cit._, p. 87, 94). But he also pointed out the remarkable shape of their voluminous extracapsular body, and especially the characteristic position, size, colour and composition of the large pigment body, which I had called the phæodium.

The accurate description of the gigantic and elegant skeleton of a new _Phæodarium_, surpassing all other known Radiolaria in its extraordinary size (15 mm.), was published in 1882 by O. Bütschli (in Zeitschr. f. wiss. Zool., vol. xxxvi. p. 486, Taf. xxxi.). He called it _Coelothamnus davidoffii_, in honour of its discoverer, who had found it floating on the surface of the Gulf of Villafranca, near Nice. He placed it among the Coelodendrida; it belongs, however, to that part of this group which possesses a nasal tube, and which I afterwards separated under the name Coelographida.

{1524}The total number of PHÆODARIA, hitherto described and illustrated by figures, amounts therefore to seventeen species, viz., the seven species first described by myself (in 1862); the six new species figured by Dr. John Murray (in 1876); the three new species discovered by Hertwig (in 1879) and the single species last-mentioned described by Bütschli (in 1882). The rich collection of the Challenger has added to this small number such an astonishing wealth of new and remarkable forms, that I can describe in the following system of PHÆODARIA not less than eighty-four genera and four hundred and sixty-five species. These belong to fifteen different families and four different orders. But this great number is probably only a small part of the numerous interesting PHÆODARIA, which are abundantly distributed over all the oceans; those (_e.g._) of the Indian and of the Arctic Oceans are almost unknown.

The great majority of these wonderful PHÆODARIA are inhabitants of the deep-sea, mainly of the southern hemisphere, and are so common in many stations explored by the Challenger, that its collection contains many thousands (or rather hundreds of thousands) of well-preserved specimens. A smaller part of the legion is found on the surface, widely distributed over all oceans; some of these are very common (as, _e.g._, _Aulacantha_, _Aulosphæra_, _Sagosphæra_, _Coelodendrum_, _Castanella_, &c.) and it is difficult to explain how they could entirely escape the eyes of all former observers.

The three general characters which distinguish the PHÆODARIA easily and constantly from all the other Radiolaria are the following:--(1) the double membrane, a thick outer and a thin inner envelope, of the big central capsule; (2) its typical main-opening or astropyle, placed on the oral pole of the main axis, and distinguished by a peculiar radiate operculum, with tubular proboscis; (3) the phæodium, or the peculiar voluminous pigment-body, which constantly lies in the oral half of the calymma, surrounds the oral part of the central capsule, and is composed of numerous phæodella, or singular pigment-granules of green, olive, brown or black colour.

Besides these three general and never failing marks of the PHÆODARIA, the majority of this legion (but by no means all) possess the three following peculiarities; (1) two parapylæ or accessory openings of the central capsule, placed laterally (at the right and left) on the aboral pole of the main axis (wanting in the Challengerida, Medusettida, Castanellida, and perhaps in some other families); (2) a characteristic skeleton which is always extracapsular, wanting only in the Phæodinida, incomplete in the Cannorrhaphida and Aulacanthida, but perfectly developed and of very various shapes in the twelve other families; usually this silicated skeleton is composed of hollow tubules, which are filled up by jelly (PANSOLENIA); but in some families it is composed of ordinary solid network, not different from that of the other Radiolaria, _e.g._, especially in the Castanellida and Sagosphærida; (3) an extraordinary size of the body, as well of the central capsule and its nucleus, as of the extracapsular skeleton; the majority of PHÆODARIA have a diameter of 1 to 2 mm., and are therefore from ten to twenty times as large as the {1525}majority of the other Radiolaria; in some gigantic forms the diameter of the unicellular body reaches 20 or even 30 mm.

_The Central Capsule_ of the PHÆODARIA is the most important part of their body and preserves in all families of this legion the same essential structure, and nearly the same form, in striking contrast to the extraordinary variety and complication of the skeleton. As already mentioned, it differs from the central capsule of all the other Radiolaria in two most important peculiarities; firstly, the double membrane of the spheroidal capsule, and secondly, the singular structure of its constant main-opening, the astropyle. A third constant character is the considerable size of the enclosed nucleus, the diameter of which usually equals about half of that of the capsule itself.

The diameter of the capsule is, in the majority of PHÆODARIA, 0.1 to 0.2 mm., often also 0.3 to 0.4, rarely more than 0.5, or less than 0.05 mm.

The position of the central capsule is somewhat different in the four orders into which we have divided the PHÆODARIA. It lies in the centre of the spherical, concentric calymma in all the #Phæocystina#, or in those PHÆODARIA which possess no complete lattice-shell--Phæodinida, Cannorrhaphida, and Aulacanthida (Pls. 101-105). The #Phæosphæria# (comprising the Orosphærida, Sagosphærida, Aulosphærida, and Cannosphærida, Pls. 106-112) all possess a very big, usually spherical lattice-shell, and here the central capsule is much smaller than the latter and lies in its centre. Another position is constantly occupied by the central capsule in all #Phæogromia# (Pls. 99, 100, 113-120; the families Challengerida, Medusettida, Castanellida, Circoporida, Tuscarorida), which have a peculiar mouth on the lattice-shell, placed on the oral pole of its main axis; the central capsule lies in the opposite aboral half of the shell cavity. The #Phæoconchia# finally (Pls. 121-128, the families Concharida, Coelodendrida, and Coelographida) all possess a bivalved shell, and the capsule is here enclosed between the two valves of the shell.

The form of the central capsule is constantly spheroidal, slightly depressed in the direction of the main axis, and therefore comparable to the spheroidal form of our globe. The depression is generally very slight, so that the proportion of the minor vertical main axis to the major horizontal or equatorial axis is about 4 : 5 or 5 : 6, often even 8 : 9 or less; but sometimes the proportion becomes 3 : 4, or even 2 : 3, so that the capsule becomes nearly lenticular; very rarely its form becomes almost perfectly spherical (Pl. 101, fig. 1). The main axis stands always vertically, and is distinctly marked by the peculiar shape of the astropyle, placed on its oral pole. Usually this pole, in the living and freely floating PHÆODARIA seems to be the lower pole, directed downwards (as also in the NASSELLARIA); but in some families it seems to be inversely directed upwards, as in the Challengerida and Tuscarorida, (Pls. 99, 100).

The two _membranes of the central capsule_ possess in all PHÆODARIA a very different shape, and were in all preparations which I could accurately examine (some hundreds {1526}belonging to all families) separated by a clear, rather wide interval, filled up either by a colourless fluid or by a structureless jelly (Pl. 103, fig. 1; Pl. 123, figs. 8, 9, &c.). They are in direct connection only at the openings. In the living PHÆODARIA, however, their distance is very small, or they are in immediate contact without any interval (Pl. 101, fig. 10; Pl. 102, fig. 1). According to the observations of Hertwig, the two membranes are always in close contact, and without interspace, in the living PHÆODARIA; and the space between them is an artificial product due to the influence of the preserving fluid or of certain chemical agents. In every case it is very easy to separate both membranes completely, except at the openings, where they are in direct connection. We distinguish both membranes shortly as ectocapsa and endocapsa.

The ectocapsa, or the outer membrane of the central capsule, is rather firm and durable, double-contoured, elastic and difficult to destroy. Its physical and chemical qualities seem to approach those of chitin. It becomes, however, stained red by carmine, and yellow by nitric acid. Usually it appears structureless and refracts the light strongly. In a few cases, however, it exhibits, when examined by strong lenses, a fine punctation; and in some Aulacanthida (especially in some big forms of _Aulographis_ and _Aulospathis_) the entire ectocapsa was densely covered with peculiar curved, or S-shaped dark corpuscles (Pl. 114, fig. 13). They were all of the same length, about 0.01, and seemed to lie on its inner face.

The endocapsa, or the inner membrane of the central capsule, is much thinner than the outer, with which it is in immediate connection only at the openings. It encloses the entire contents of the capsule, and becomes very distinct, as soon as the latter are dissolved by chemical agents, or stained by carmine. In the majority of well-preserved preparations it is irregularly plicated, and resembles a thin, but firm, crumpled paper. Isolated pieces of the endocapsa are completely structureless, but exhibit also a considerable resistance, in spite of their minute thickness.

The openings of the central capsule exhibit in the PHÆODARIA a greater variety than their discoverer, R. Hertwig, supposed. The majority of the legion, certainly, possess the three openings described by him, and are therefore true TRIPYLEA. Some families, however, have only one opening, the astropyle, which is generally present (Challengerida, Medusettida, Castanellida, and _Phæocolla_ among the Phæodinida, Pl. 101, fig. 1). In some other families there is a variable number of accessory openings or parapylæ, one, three, or more, _e.g._, especially in the Circoporida and Tuscarorida. The former may be called Astropylea, the latter Sporopylea. Thus only a single opening to the central capsule is constant in all PHÆODARIA without exception, and that is the astropyle, or the large main-opening with its peculiar structure.

The astropyle, or the single constant main-opening of the central capsule, is distinguished by a very remarkable structure, and is sufficient of itself to separate the {1527}PHÆODARIA from all the other Radiolaria, and from the other Rhizopoda in general. It is always placed on the oral pole of the main axis, forming here a peculiar cap-shaped or flatly conical elevation, the centre of which is prolonged into a short, cylindrical tubule; we call the latter shortly a proboscis, and the former an operculum. To understand better the different forms which these important parts assume in the different families, compare Pl. 101, figs. 1-6; Pl. 102, fig. 1; Pl. 103, fig. 1; Pl. 104, figs. 1-3; Pl. 111, fig. 2; Pl. 123, figs. 1-9; Pl. 127, figs. 4-6; Pl. 128, fig. 2, &c. Compare also the first very accurate figures which R. Hertwig has given in 1879 (_loc. cit._) in his Taf. x.

The operculum of the astropyle, the most important part of this main opening ("der Oeffnungshof der Hauptöffnung," in the description of Hertwig), is a circular convex plate, always more strongly vaulted than the surrounding part of the capsule membrane, and is sharply separated from it by a circular, often thickened and double-contoured margin. The operculum covers the main-opening like the lid of a tea-kettle, and the proboscis arising from its centre is comparable to the handle of that lid. The diameter of the circular operculum is usually about half as long (rarely as long) as the radius of the central capsule, therefore in the majority of PHÆODARIA 0.03 to 0.06, sometimes 0.1 and more. Its form is sometimes more conical, sometimes more like a mamma. Its height is usually about equal to half its diameter. It always exhibits a very distinct radial striation, produced by numerous prominent radial ribs, which arise in the centre and end at the circular sharply truncated margin. The usual number of these radial ribs may be, in the operculum of smaller capsules, from thirty to fifty, in those of medium size from sixty to ninety, and in the largest two hundred to three hundred or more. Usually the ribs are simple (Pl. 101, figs. 1, 2, 6, 10; Pl. 127, figs. 4-6; also in all figures given by Hertwig); but sometimes, mainly in the biggest Aulacanthida, they are distinctly branched in a centrifugal direction (Pl. 114, fig. 13; Pl. 115, fig. 3). Hertwig is of the opinion that the radial ribs are thickened ridges of the endocapsa ("leistenartige Verdickungen der inneren Membran"), and that the ectocapsa covering it is structureless (compare his figs. 1 and 1_a_, in Taf. x.). But I am convinced now, by numerous experiments and observations, that the radiate operculum is a part of the outer, not of the inner membrane. That part of the latter which lies immediately beyond the former, and which may be called the "inner operculum," also exhibits usually a fine radial striation; but this is probably only the cast of the stronger and much more prominent radial ribbing of the "outer operculum" belonging to the ectocapsa. The latter exhibits a large circular opening with thickened margin, when the radiate operculum is taken from it. The operculum becomes stained intensely red by carmine, yellow by nitric acid, corresponding to the ectocapsa, the main-opening of which is closed by it.

The proboscis, or the cylindrical tubule, which arises in the centre of the {1528}operculum, is often rather short, and bears the same relation to it as the nipple does to the human breast (Pl. 104, fig. 2). But usually it is more or less prolonged and often about as long as the radius of the capsule, rarely nearly as long as its diameter (Pl. 101, fig. 1). Its form is usually a slender cylinder, sometimes somewhat conical and tapering towards the distal end. It is more or less curved or S-shaped in the majority of preparations (Pl. 115, fig. 3; Pl. 127, fig. 6, &c.). Its thin wall is a direct prolongation of the outer membrane of the capsule, therefore it appears as a direct apophysis of the operculum, when this is detached from the latter. The opening at the distal end of the proboscis, through which the endosarc is thrown out, is circular.

The parapylæ, or the accessory openings of the central capsule, exhibit in all PHÆODARIA the same form and structure, but vary in number and disposition. They are recognised with difficulty in the smaller species, since they are always of small size, and may be easily overlooked. They seem to be completely wanting in the following families:--Challengerida (Pl. 99), Medusettida (Pls. 118-120), Castanellida (Pl. 113), and in single genera of other families, as in _Phæocolla_ (Pl. 101, fig. 1). The majority of PHÆODARIA seem to possess the two lateral parapylæ, first described by Hertwig, placed at a variable distance on each side of the aboral pole, to the right and left (Pl. 101, figs. 2, 6, 10; Pl. 103, fig. 1_a_; Pl. 104, figs. 1, 2_a_; Pl. 123, figs. 1, 8_a_ &c.). The horizontal axis, on which the two parapylæ lie, is the the frontal or lateral axis; and the plane, which passes through the three openings of these "Tripylea," is the frontal or lateral plane. The number of the parapylæ seems to be variable in the two families, Circoporida and Tuscarorida, which also differ from the other PHÆODARIA in the peculiar (porcellanous) structure of their shell-wall. The number seems to vary even in the single species of one genus; and the following cases may be found: (A) a single parapyle, placed on the aboral pole of the main axis and directly opposed to the astropyle (on the oral pole), as in _Tuscaridium_ (Pl. 100, fig. 8); (B) three equidistant parapylæ, one of which is placed in the sagittal plane, and the two others one on each side of it, to the right and left, is in _Tuscarora_ (Pl. 100, figs. 1-6); the three parapylæ seem to correspond here to the three long feet, or the tubular aboral apophyses of the shell, which are arranged in a similar manner to the three cortinar feet of the NASSELLARIA; (C) four equidistant parapylæ, placed in pairs on the poles of the diagonal axes of a horizontal plane, as in _Tuscarora_ (Pl. 100, fig. 7); they seem here to correspond to the four crossed aboral feet; (D) six to eight or more parapylæ probably in the different genera of Circoporida (Pls. 114-117); perhaps each radial tube, which is surrounded on its base by a circle of pores, here corresponds to a separate parapyle. The number of well-preserved central capsules belonging to the two latter families, however, which I could examine was relatively small and their examination very difficult; therefore these numbers are not stated with satisfactory certainty and require a further more accurate examination. {1529}The minute structure of the parapylæ (or "Neben-Oeffnungen") has been described already very accurately by Hertwig (_loc. cit._, p. 95, Taf. x. figs. 1-11_b_). The two membranes of the capsule are in direct and immediate connection on each parapyle. The strong outer membrane arises in the form of a ring or of a short cylindrical tubule (collare paraboscidis or "Oeffnungshals"), is then reflected inwards, and connected at the bottom of the cylindrical cavity with the delicate inner membrane. From this connective ring arises a short conical or cylindrical tubule, which we call shortly the "paraboscis." According to Hertwig (who calls it "Oeffnungskegel") the paraboscis is a direct prolongation of the inner membrane only. My own observations have led me to the opinion, that the paraboscis of each parapyle is a direct prolongation of the outer membrane (similarly to the larger proboscis of the astropyle), and that the basal connective ring is, therefore, the inner opening of the paraboscis, through which the entosarc enters, being protruded through its outer circular opening. Usually the paraboscis of each parapyle is only a short cylinder, arising by a conical base; but sometimes, especially in some Aulosphærida and Sagosphærida, it is prolonged into a slender tubule, nearly as long as the radius of the central capsule. It has been already figured by Hertwig (_loc. cit._, Taf. x. figs. 6-8). It seems, therefore, that the paraboscis of the accessory openings is developed in a way similar to the proboscis of the main-opening, and that the chief difference between the two is indicated by the large radiate operculum of the latter.

The cavity of the endocapsa, or the spheroidal space enclosed by the inner membrane of the central capsule, is filled up in its central part by the big nucleus, in its peripheral part by the endoplasm, or by the internal protoplasm, which is in communication with the outer or extracapsular protoplasm by the openings of that capsule. The endoplasm, or the intracapsular sarcode, is rather opaque, finely granulated, and usually filled up by numerous small clear spherules of equal size, which are more or less regularly arranged and equidistant. These spherules have usually a diameter of 0.01 to 0.015, rarely more than 0.02 or less than 0.005 mm.; their size is generally equal in each capsule. They have been already described and figured in my Monograph, as "wasserhelle kugelige Bläschen," and are probably vacuoles or small vesicles filled up by jelly or by a clear fluid. Usually each vesicle contains a small dark granule of fat, or a group of such granules connected together; and in these Hertwig observed a vibrating molecular motion. The central capsule of many PHÆODARIA contains, besides the vacuoles, often granules of pigment (usually red or yellow) and sometimes numerous groups of small crystals, placed mainly beyond the operculum of the astropyle (Pl. 127, figs. 4-7). The outer layer of the endoplasm, placed immediately beyond the endocapsa, often exhibits a fine striation, as if composed of delicate fibrillæ. This fibrillar striation is usually most distinct on the base of the openings, where also the endoplasm becomes stained very intensely by carmine. The astropyle as well as {1530}the parapylæ often exhibit here, when observed from the face, a distinct radial striation (compare Hertwig, _loc. cit._, p. 98, Taf. x. figs. 6-14) Perhaps the radiate shape of the operculum is only produced by radial folds of the endocapsa placed beyond it, and these folds may be in turn the product of the radial fibrillæ, which are prominent beyond the astropyle. On the other hand, these fibrillæ may be compared to the muscular fibrillæ or "myophane filaments" in the ectosarc of the Infusoria, and may perhaps effect by their contraction a dilatation of the openings of the capsule.

The nucleus of the PHÆODARIA is always very large, usually about half or two thirds as broad as the central capsule and placed either in its centre, or sometimes nearer to one pole of the main axis, which is common to the capsule and its nucleus. Therefore the diameter of the latter is usually half or even two thirds of that of the capsule, and may be in the majority 0.05 to 0.15, often 0.2 to 0.3, rarely more than 0.4 or less than 0.01 mm. The form of the nucleus is rarely spherical, usually spheroidal, and it is more depressed in the direction of the main axis than the capsule itself. In my Monograph, where I gave the first description of it, I called it "Binnenbläschen." The membrane of the vesicular nucleus is thin but rather firm, and contains a rather clear, finely granulated substance, in which numerous nucleoli are usually scattered. (Compare Pl. 101, figs. 1-10; Pl. 102-104; Pl. 123; Pl.127, &c.; the nucleus is marked by _n_, the nucleoli by _l_.)

The nucleoli are very different in respect to their form, size, number and arrangement. Since these differences are very great even in different specimens of a single species (as, _e.g._, in the common cosmopolitan _Aulacantha scolymantha_, _Aulosphæra trigonopa_, _Coelodendrum ramosissimum_, &c.), it is probable that they represent different stages of development and multiplication, and that the smallest fragments of the nucleoli, or the final results of their repeated division, become the nuclei of the flagellate spores, which are developed in the PHÆODARIA just as in the other Radiolaria. In the majority of nuclei examined, the number of the enclosed nucleoli proved to be very great, fifty to eighty or more, often some hundreds, the greater their number the smaller their size. Their form is usually irregular, roundish, or even amoeboid--probably the result of amoebiform motions (Pl. 101, fig. 1). Sometimes the nucleoli were regularly spherical, equidistant, and connected apparently by a delicate network (Pl. 101, fig. 2). (Compare Pl. 102-104, 111, 123, and also Taf. x. of Hertwig, _loc. cit._).

The calymma, or the extracapsular jelly-veil, is in the PHÆODARIA always well developed and usually much larger than the enclosed central capsule. The entire volume of the calymma may be three to six times as great as that of the capsule in the majority of this legion; but in the large Aulacanthida, Aulosphærida, Coelodendrida, Coelographida, &c., the volume of the former is twenty to fifty as great as that of the latter, or even more. The jelly substance is rather firm and consistent, clear, structureless, and becomes more or less intensely stained by carmine. In the {1531}larger forms it is often filled by numerous large alveoles, which are usually absent in the smaller forms. These extracapsular alveoles are most strongly developed in the calymma of the #Phæocystina#, or the PHÆODARIA with incomplete skeleton, embracing the three families Phæodinida, Cannorrhaphida and Aulacanthida (Pls. 101-104). Usually the calymma is here very voluminous and entirely filled up by large alveoles, which are either spherical, irregularly roundish, or polyhedral by mutual compression. These alveoles or vacuoles have no peculiar wall, but are only cavities in the homogeneous substance of the jelly, and are filled by a clear aqueous fluid. Between these the network of the anastomosing pseudopodia is expanded. They exhibit, therefore, the same shape, as was first observed in _Thalassicolla_ and in the #Polycyttaria# (Collozoida, Sphærozoida and Collosphærida).

The relation of the calymma to the skeleton is in the PHÆODARIA of the same importance as in the other Radiolaria, and we may also here distinguish a primary and a secondary calymma. The primary calymma is that on the surface of which at a certain period of life (in the "shell-building period") the fenestrated shell is secreted in the majority of PHÆODARIA. The secondary calymma, however, is formed after this period, and envelops the shell itself as well as its apophyses externally. Usually the entire skeleton seems to be enveloped by the secondary calymma.

The parts of the extracapsular body, which are enclosed in the gelatinous calymma possess a peculiar importance in the PHÆODARIA; these are firstly the sarcomatrix and the pseudopodia arising from it, and secondly the phæodium. The sarcomatrix, or the layer of extracapsular sarcode (ectoplasm), which immediately surrounds the central capsule is very thick and more strongly developed in all PHÆODARIA than in all other Radiolaria. Its extraordinary size has been already mentioned by Hertwig (1879, _loc. cit._, p. 99). It is in direct connection with the intracapsular sarcode (or the endoplasm) only by the openings of the central capsule, and mainly by the astropyle. Very numerous radial pseudopodia arise everywhere from the sarcomatrix and run to the surface of the calymma, usually forming a rich network in it by means of numerous branches and anastomoses (compare Pl. 101-104). On the surface of the calymma the meshes of this network are very numerous, and there arise from its nodal points the terminal pseudopodia, which float freely in the surrounding water. The metamorphoses of this network of sarcode, the perpetual changes in the number and size of its meshes, and the movements of the sarcode streams as well as of the small granules running in it, are always very manifest in the PHÆODARIA and in the big forms of this legion (mainly in the Aulacanthida) they are better observed than in the majority of other Radiolaria. In many PHÆODARIA (and perhaps in all) a part of the pseudopodia seems to have undergone a local differentiation, for special physiological purposes; and Hertwig has described a peculiar conical contractile body, which arises in _Coelodendrum_ between the two parapylæ (_loc. cit._, p. 100, fig. 3). Further examination {1532}of these interesting organs in living PHÆODARIA is required. Usually the sarcode, issuing from the openings of the capsule, forms a stronger cylinder, with peculiar movements.

The phæodium, or the peculiar dark extracapsular pigment-body of the PHÆODARIA, is one of the most important and most characteristic parts of their organisation, and has induced me to derive their name from it; it is not less typical for the whole legion, than the astropyle with its radiate operculum and the proboscis; and both these important parts are always in direct topographical and physiological connection. Whilst I have missed the phæodium in no _Phæodarium_ in which the soft body was well preserved, I have not found it in any other Radiolaria; for the similar extracapsular pigment bodies, which are found in some species of _Thalassicolla_ and some other #Sphærellaria#, have a composition and signification different from that of the phæodium--an exclusive peculiarity of the PHÆODARIA.

The typical importance of the phæodium for all members of this legion is proved by the following five facts:--(1) its constant presence in all PHÆODARIA; (2) its constant excentric position in the oral half of the calymma; (3) its constant relation to the astropyle, the operculum and the proboscis of which is always surrounded by it; (4) its constant considerable size, its volume being usually greater than that of the central capsule, the aboral half of which is covered by it; (5) its constant colour and morphological as well as chemical composition. These five facts together demonstrate by their absolute constancy the high morphological and physiological importance of the phæodium for this peculiar subclass of Radiolaria, although its true nature is difficult to make out, and its main function is not yet sufficiently known.

The first remarks that have been made on the phæodium were published in 1862 in my Monograph, where I noticed the peculiar dark brown extracapsular pigment body and its excentric position covering only one-half of the central capsule, in _Aulacantha_ (p. 263, Taf. ii. figs. 1, 2), in _Thalassoplancta_ (p. 262, Taf. iii. fig. 10), and in _Coelodendrum_ (p. 361, Taf. xxxii. fig. 1). Its general presence and peculiar composition were first recognised by Dr. John Murray, who had, during the Challenger Expedition, the first opportunity of examining many big living PHÆODARIA brought up from great depths. He gives in his first Report (1876, _loc. cit._, p. 536), the following important notice:--"The sarcode of all these deep-sea Rhizopods has many large black-brown pigment-cells. Small bioplasts are scattered through the sarcode. These collect into capsular-like clumps when the animal is at rest, and are quickly coloured by carmine." In 1877 Dr. John Murray sent me the wonderful collection of PHÆODARIA brought home by the Challenger, and I had now the best opportunity for examining the phæodium in hundreds of well-preserved specimens. Supported by these extensive observations, I gave, in 1879, in a preliminary paper,[273] a fuller description of the {1533}phæodium, and of the phæodella (or the peculiar dark pigment-granules composing it). At the same time R. Hertwig published his observations on the big living TRIPYLEA examined by him at Messina, and pointed out particularly that the constant presence, composition, and arrangement of this excentric extracapsular pigment-body was most characteristic, and sufficient in itself to distinguish this group from all the other Radiolaria (1879, _loc. cit._, p. 99).

The most striking peculiarity of the phæodium, and the most important on account of its absolute constancy, is its excentric position, covering only the oral hemisphere of the central capsule, and wholly or partly wanting on the aboral hemisphere. This constant topographical relation to the capsule never fails, and may be always observed at the first glance, when the body is seen from the side (the main axis of the capsule being perpendicular to the axis of the eye of the observer), (compare Pl. 101, figs. 6, 10; Pl. 102, fig. 1; Pl. 103, fig. 1, &c.). The phæodium envelops, therefore, the oral half of the capsule completely, and especially the astropyle in its centre; hence, the radiate operculum and the proboscis arising from the latter cannot be seen usually before the former is removed. The general form of the entire phæodium, in consequence of this excentric position, is concavo-convex (or crescentic in longitudinal section), its concave face embracing the oral or anterior face of the capsule, and its convex face being turned to the surface of the calymma.

The topographical relation of the phæodium to the surrounding shell is also very characteristic in the suborder #Phæogromia#, or in those PHÆODARIA which possess a peculiar shell-mouth placed on the oral pole of its main axis. Here the capsule is always placed in the aboral half of the shell-cavity, the phæodium in its oral half, separating the astropyle from the mouth of the shell, both of which lie in the main axis; as in the Challengerida (Pl. 99), Tuscarorida (Pl. 100), Castanellida (Pl. 113), Circoporida (Pl. 115), and Medusettida (Pl. 118-120). In this suborder (the #Phæogromia#), the volume of the phæodium may be, on an average, about as great as that of the central capsule, whilst in the majority of other PHÆODARIA it is much greater than the latter.

A similar topographical relation between the phæodium and the enclosing shell, as in the #Phæogromia#, also exists in the suborder #Phæoconchia#, or in those PHÆODARIA, which are distinguished from all the others by the possession of a bivalved shell (Pl. 121-128). The two valves of this curious shell, which resembles that of the Brachiopoda, are dorsal and ventral, and the tripylean central capsule is always so placed between them that its two lateral parapylæ (right and left) lie in the frontal plane of the shell, where a large frontal fissure opens between the opposed margins of the two hemispherical or cap-shaped valves. The phæodium is also placed here on the oral half of the capsule and surrounds its astropyle; but it exhibits some differences in the three families of #Phæoconchia#.

{1534}The Concharida, the bivalved shell of which is simple, and without tubular apophyses (Pl. 123-125), possess a relatively small central capsule, which usually fills up only the third or fourth part of the shell-cavity. This is the aboral or posterior part, on the apex of which both valves are united by a ligament in some Concharida (Pl. 123, figs. 8, 9). The oral or anterior part of the shell-cavity (usually two-thirds or more) is filled up by the phæodium, and this is usually bifid, being divided by a frontal constriction into two wings or lobes; the dorsal wing is hidden in the upper valve of the shell, the ventral wing in the lower valve; both wings are usually united only by a small central bridge, and this bridge of the phæodium is pierced in its centre by the proboscis of the astropyle (Pl. 124, figs. 6, 10; Pl. 123, figs. 8, 9).

The Coelodendrida have a different shape (Pl. 121). Their bivalved shell is relatively small and tiny, and bears on the two poles of the sagittal axis two conical apophyses or galeæ, from each of which three or four very large, dichotomously branched tubes arise. The central capsule fills up the cavity of the bivalved shell almost entirely, and the voluminous dark phæodium envelops both to such an extent that the shell and the enclosed capsule are often hidden in it completely. Therefore I arrived in my first description of _Coelodendrum_ (1862, _loc. cit._) at the erroneous conclusion that the capsule lies outside, not inside the shell. The first accurate figure and description of its structure was given in 1879, by Hertwig (_loc. cit._, p. 99, Taf. x. fig. 3). The central capsule (_v_) is here separated from the bivalved shell (_m_) only by a very small distance, and the oral part of both is hidden in the phæodium. I find, however, in the majority of the numerous preparations of the Challenger collection, the volume of the phæodium much greater, and it often envelops the entire shell.

The Coelographida, finally, have a phæodium of the most remarkable shape, since in their bivalved shell a peculiar reserve store or magazine of phæodella, which we call the "phæocapsa" is developed for it (Pl. 126-128, _g.t.m._). The bivalved shell has in these most perfect PHÆODARIA a structure similar to that in the Coelodendrida; but they differ from the latter in the stronger development, and greater differentiation of the two apical galeæ, and the large hollow tubes arising from them. These two helmet-shaped cupolæ, the galeæ (_g_), which arise from the two valves on the poles of the sagittal axis, are in the Coelographida usually larger than the valves themselves, and are not closed, as in the Coelodendrida, but open by a tubular apophysis at their base, the nasal tube or rhinocanna (_t_). The apex of the galea is connected with the open mouth of the rhinocanna by a single or double frenulum (_b_). The two nasal tubes or rhinocannæ (a dorsal and a ventral) lie in the sagittal plane of the body and run from the base of each galea along the anterior convexity of the valve to its oral margin. Here is placed the proboscis of the astropyle, between the two opposed mouths of the rhinocannæ (Pl. 128, fig. 2). The phæodium is usually hidden entirely {1535}in the two phæocapsæ, which are composed of the two galeæ (_g_), and the two rhinocannæ arising from them (Pl. 127, figs. 4-9). A part of the phæodella is usually thrown out by the mouth of the latter (_m_).

The characteristic colour of the phæodium exhibits numerous different tints between green, brown, and black. It seems to be in the majority blackish-brown or greenish-brown, very often olive, more rarely almost quite green or red-brown. Usually the colour is so dark, intense and opaque, that the parts enclosed by the phæodium, mainly the oral hemisphere of the central capsule and the astropyle, are completely hidden in it. The chemical composition of the phæodium demands further accurate researches; unfortunately I have not been able to make out its true nature, since numerous different experiments furnished no certain general results.

The phæodella, or the pigment-corpuscles, which compose the phæodium, aggregated in hundreds, and in the bigger species in thousands, are usually spherical, sometimes somewhat ellipsoidal, at other times spheroidal or lenticular; but usually numerous smaller, irregular, roundish particles are intermingled between the larger and more regular corpuscles, and often the main mass forms a very fine black powder. The size of the phæodella is very variable, not only in the different species, but also in one and the same individual. The larger phæodella have a diameter of 0.01 to 0.02, the smaller of 0.004 to 0.008 mm.; but there also occur very big forms of 0.04 to 0.05 mm., or even more, and very small ones of 0.001 mm. or less. Usually the phæodium appears as an aggregate of numerous larger and smaller phæodella, which are very different in size as well as in the intensity and tint of their colour, and are irregularly crowded in a black, powder-like substance.

The morphological nature of the phæodella is also difficult to make out. I have already pointed out in my first description of _Aulacantha_, _Thalassoplancta_ and _Coelodendrum_ (1862, _loc. cit._), that a great part of these pigment-corpuscles are true cells, composed of a nucleus and protoplasm, which contains granules of pigment, and is enveloped by a membrane. Dr. John Murray, who had during the Challenger voyage the opportunity of examining numerous different living PHÆODARIA, and staining them by carmine, also asserts that a great part of those dark corpuscles are "large black-brown pigment-cells" (1876, _loc. cit._, p. 536). Numerous preparations of the Challenger collection, well preserved in glycerine, and stained by carmine, contain PHÆODARIA belonging to different families, the phæodium of which contains numerous such "pigment-cells," with a dark red nucleus, and so similar are these cells, that every histologist should recognise them. But in strange contrast to this is the fact, that in numerous other mountings, prepared in the same manner, not a single cell of this kind is found in the phæodium, and that the latter is composed only of irregular pigment-granules. In many PHÆODARIA belonging to different families I, like Hertwig, could not find a single true nucleated cell in the phæodium.

{1536}A great part of the PHÆODARIA, and usually the bigger forms of Aulacanthida, Cannorrhaphida, Coelodendrida, Coelographida, &c., exhibit a peculiar structure of the larger phæodella, viz., a fine parallel striation (Pl. 101, figs. 3, 6; Pl. 102, fig. 1; Pl. 103, fig. 1; Pl. 104, figs. 1-3, &c.). In each phæodellum may be counted about ten to twenty such fine parallel stripes (more in the greater, less in the smaller forms); and in the ellipsoidal phæodella the stripes are either transverse rings, perpendicular to their main axis, or ascending obliquely; they often resemble the convoluted spiral filament of a thread-cell or nettle-cell of an Acaleph. Sometimes these parallel transverse stripes are very striking. Another structure is seen in larger phæodella, namely an aggregate or cluster of smaller globules, often of equal size, resembling a small morula. All these minute structures of the phæodella as well as their changes in the living PHÆODARIA, require a far more extensive examination (by means of strong lenses and different chemical reagents), than I could, unfortunately, devote to them.

The physiological signification of the phæodella, therefore, is at present not yet known; but the general facts quoted above, their constant presence, position, volume, and composition, make it probable that their physiological value in the PHÆODARIAN organism is very great. The following hypotheses may be taken provisionally into consideration:--A. The phæodella are peculiar symbiontes, or unicellular algæ, comparable to the xanthellæ or zooxanthellæ of the other Radiolaria. This hypothesis is probably correct for those phæodella which are true nucleated cells; and the more so, as the majority of PHÆODARIA do not exhibit those common yellow xanthellæ, which are usually found in the SPUMELLARIA and NASSELLARIA. It is even possible that the latter are absent in all PHÆODARIA. B. The phæodella are dark pigment-bodies, which absorb light and heat in a manner similar to the simple "pigment-eyes" of many lower animals, and may therefore be optical sense-organs of the PHÆODARIA. This hypothesis may be supported by a comparison with the large-eyed unicellular Protist, _Erythropsis agilis_, described by R. Hertwig. C. The phæodella are organs of nutrition of the PHÆODARIA and active in their metastasis ("Stoffwechsel"). Regarding them from this point of view, we may suppose that the phæodella are secreted products which serve for digestion, acting like the bile or the saliva of higher animals. Perhaps they too act like the venomous matter produced in the thread-capsules of the Acalephæ. The suggestion that they are mere excretions, or half-digested matters, as Hertwig supposes ("halb assimilirte Nahrungs-bestandtheile," 1879, _loc. cit._, p. 99) seems less probable. The most important fact illustrating their high signification for the processes of nutrition, digestion and for effecting changes on matter, seems to be the close relation of the phæodium to the astropyle; the radiate operculum of the latter, and the proboscis arising from it, being constantly covered and completely hidden by the central main mass of the phæodium.

{1537}The skeleton of the PHÆODARIA is always extracapsular, and exhibits in the majority of this legion such a characteristic shape, form, and structure, that these organisms may be easily recognised by it, even apart from the central capsule and the phæodium. In a few cases, however, the skeleton is so similar to that of some NASSELLARIA and SPUMELLARIA, that it may be accidentally confounded with it. In general the skeleton of the PHÆODARIA is much larger, and much more highly developed, than that of most other Radiolaria, and exhibits the most wonderful appearances, and the most marvellous complications, which are found in the whole world of Protists, or of unicellular organisms. The varied composition and differentiation of the skeleton alone distinguishes the numerous families, genera, and species of PHÆODARIA described in the sequel; all the fifteen families, however, agree so completely in the structure of the central capsule and the phæodium described, that we may derive them all phylogenetically from a small skeletonless family, the Phæodinida.

The chemical composition of the skeleton seems to be, in the majority of PHÆODARIA, somewhat different from that of the other Radiolaria. In a few groups only, especially in the Cannobelida (_Dictyocha_, _Mesocena_, &c.), and in a part of the Castanellida and Concharida, the substance of the skeleton seems to be of pure silica, as in the NASSELLARIA and SPUMELLARIA; these flinty skeletons, therefore, may be also found fossil. In the majority of PHÆODARIA, however, the skeleton does not consist of pure silica, but of an organic silicate; it becomes more or less intensely stained by carmine, and browned or blacked by fire; in many cases it even becomes completely burned and destroyed by the prolonged action of heat. This circumstance explains why PHÆODARIA in general are rare in deep-sea deposits, as in the common Radiolarian ooze of the Pacific, and why they are generally absent in fossil deposits. Even the pure Radiolarian rocks of the Barbados, &c., contain only a few PHÆODARIA, mainly Dictyochida.

According to the different forms of the skeleton, we may divide the legion or subclass of PHÆODARIA into two sublegions, four orders, and fifteen families. Firstly, we may distinguish as two groups the #Phæocystina#, without a lattice-shell, and the #Phæocoscina#, with a lattice-shell (compare above, p. 5). The #Phæocystina# comprise three different families, viz., (1) Phæodinida, without any skeleton (Pl. 101, figs. 1, 2); (2) Cannorrhaphida, with an incomplete skeleton, composed of numerous separate, not radial pieces, which are scattered around the capsule in the calymma (Pl. 101, figs. 3-14; Pl. 114, figs. 7-13), and (3) Aulacanthida (Pl. 102-105), with an incomplete skeleton, composed of numerous hollow radial tubes, which pierce the calymma and come in contact by their proximal ends with the surface of the central capsule.

The #Phæocoscina#, or the PHÆODARIA with a lattice-shell (embracing the great majority of the whole legion) exhibit three principal differences in the shape of their shell, and from these we distinguish the three following orders; (A) #Phæosphæria#, with a spherical, not bivalved shell (rarely of an ellipsoidal or lenticular, or another {1538}modified form), without a shell-mouth or a peculiar constant large opening on the lattice-shell; (B) #Phæogromia#, with an ovate or polyhedral, not bivalved shell (often also of a subspherical, ellipsoidal, or another modified form), constantly provided with a shell-mouth or a peculiar large opening on one pole of the main axis of the lattice-shell; (C) #Phæoconchia#, with a bivalved shell, composed of two completely separated, hemispherical, cap-shaped or boat-shaped valves (a dorsal and a ventral), comparable to that of the Brachiopoda.

The #Phæosphæria#, or those PHÆODARIA the big shell of which is usually spherical, never bivalved and never provided with a peculiar shell-mouth, comprise a great number of common and large-sized PHÆODARIA, which may be arranged into four different families, according to the different structure of the shell--(1) Orosphærida (Pl. 106, 107), spherical shell extremely big and robust, composed of single piece of coarse lattice-work, the thick bars of which are stratified and contain partly a fine axial-canal, meshes of the network usually irregularly polygonal, no astral septa in the nodal points; (2) Sagosphærida (Pl. 108), spherical shell large-sized, but extremely delicate and fragile, composed of a single piece of arachnoidal lattice-work, the thin bars of which are simple solid threads, without axial-canal, meshes of the network always large and triangular, no astral septa in the nodal points; (3) Aulosphærida (Pl. 109-111), spherical shell large-sized, but very fragile, composed of numerous hollow cylindrical tubes, which are connected (and at the same time separated) by peculiar astral septa in the nodal points, meshes either triangular or polygonal; (4) Cannosphærida (Pl. 112), spherical shell double, composed of two concentric shells which are connected by thin hollow radial tubes, the inner shell simple, solid or fenestrated, with a shell-mouth on the basal pole, the outer shell composed of hollow cylindrical tubes which are connected by astral septa in the nodal points. The structure of this outer shell is the same as in the Aulosphærida, while the basal mouth of the inner shell brings this family in closer relationship to the #Phæogromia#.

The #Phæogromia#, or those PHÆODARIA the shell of which is not bivalved, but provided with a peculiar constant mouth on the oral pole of the main axis, are in general similar to the NASSELLARIA (Monocyrtida), and may be divided into five different families, viz., (1) Challengerida (Pl. 99), shell ovate or subspherical, also often triangular or lenticular, distinguished by a peculiar diatomaceous structure, an exceedingly fine tracery of regular hexagonal, very delicate network; (2) Medusettida (Pl. 118-120), shell ovate, campanulate or cap-shaped, distinguished by a peculiar alveolar structure, with a corona of peculiar hollow, large, articulated feet around the mouth; (3) Castanellida (Pl. 113), shell spherical or subspherical, of ordinary simple lattice-work, usually with a corona of simple solid teeth around the mouth; (4) Circoporida (Pl. 114-117), shell spherical or polyhedral, with panelled or dimpled surface, distinguished by a peculiar porcellanous structure (numerous thin needles being {1539}embedded in a punctulate cement-substance), with hollow radial spines and with a corona of simple solid teeth around the mouth; (5) Tuscarorida (Pl. 100), shell ovate or subspherical, with smooth surface, of the same peculiar porcellanous structure as the Circoporida, but with hollow, very long tubular teeth around the mouth.

The #Phæoconchia# are the peculiar and most interesting "PHÆODARIA bivalva," differing from all other PHÆODARIA, and from all known Radiolaria in general, in the possession of a bivalved lattice-shell, composed of a dorsal and a ventral valve. They may be divided into three families: (1) Concharida (Pl. 123-125), shell with two thick and firm, regularly latticed valves, which bear no hollow tubes and no cupola or galea on their apex or sagittal pole; (2) Coelodendrida (Pl. 121), shell with two thin and fragile, scarcely latticed valves, which bear a conical cupola or a helmet-shaped galea on their apex, and hollow branched tubes arising from it (without rhinocanna and frenula); (3) Coelographida (Pl. 122, 126-128), shell with two thin and fragile, scarcely latticed valves, similar to those of the Coelodendrida, but differing from them in the development of a peculiar rhinocanna or nasal tube upon each valve; this tube is connected by an odd or paired frenulum with the apex of the galea, and both together contain the phæodium.

The phylogenetic affinity of the fifteen families enumerated, and the morphological relationship based upon it, form a very difficult problem. The whole legion of PHÆODARIA is probably monophyletic, in as much as all the families may be derived from a single ancestral group, the skeletonless Phæodinida (_Phæodina_ and _Phæocolla_); but at the same time polyphyletic, in as much as probably many families have been derived, independently one from another, from different branches of Phæodinida; or in other words, the characteristic malacoma of the PHÆODARIA (the cannopylean central capsule and the calymma with the phæodium) may be a monophyletic product, inherited from a single ancestral form; the manifold skeleton, however, is certainly a polyphyletic product, originating from different skeletonless Phæodinida.

Among the independent families of PHÆODARIA, derived directly from skeletonless Phæodinida by production of a peculiar skeleton, may be the following: Cannorrhaphida (Pl. 101, probably polyphyletic), Aulacanthida (Pl. 102-105), Castanellida (Pl. 113), Challengerida (Pl. 99), Concharida (Pl. 123-125), Circoporida (Pl. 114-117) and Tuscarorida (Pl. 100). The four families of #Phæosphæria# (the Orosphærida, Sagosphærida, Aulosphærida and Cannosphærida (Pl. 106-112), may be derived perhaps from the Castanellida; and the Medusettida (Pl. 118-120), have been perhaps derived from the Challengerida. The complicated affinities of these groups are however difficult to explain. The Coelodendrida (Pl. 121) are probably derived from the Concharida, and the Coelographida (Pl. 126-128) from the Coelodendrida.

The geometrical fundamental form of the shell is in the majority of PHÆODARIA monaxonial, corresponding to the main axis of the enclosed central capsule; the {1540}astropyle of the latter, placed on the oral pole of the main axis, corresponds to the mouth of the shell in all #Phæogromia#. In the #Phæosphæria#, where no peculiar shell mouth is developed, the general fundamental form of the shell is usually homaxonial or spherical, often an endospherical polyhedron, rarely ellipsoidal or spindle-shaped (with prolonged main axis), or lenticular (with shortened main axis). The bivalved #Phæoconchia# have usually either an amphithect shell (with the same fundamental form as the Ctenophora), or a dipleuric, bilaterally symmetrical shell (with a dorsal and a ventral valve, a right and a left parapyle). A small number of PHÆODARIA (mainly Circoporida) are remarkable on account of the regular polyhedral form of their shell, the geometrical axes of which resemble crystalline axes and are defined by regular radial tubes; as the octahedral _Circoporus_ (Pl. 117, fig. 6), the dodecahedral _Circorrhegma_ (fig. 2), and the icosahedral _Circogonia_ (fig. 1).

The siliceous or silicate bars, which compose the skeleton of the PHÆODARIA, are in the majority hollow tubes, filled up by jelly; in some other families, however, they are solid rods, as in the NASSELLARIA and SPUMELLARIA. Such usual lattice-work, composed of solid rods, occurs only in the families Sagosphærida (Pl. 108), Castanellida (Pl. 113), and Concharida (Pls. 123-125). A quite peculiar structure, a diatomaceous tracery of extremely fine and regular hexagonal frames, distinguishes the Challengerida (Pl. 99). The hollow cylindrical tubes, which are found in the other families, appear in three different forms, simple, articulate, and provided with an axial thread. Simple hollow tubes, which are neither articulate nor provided with an axial thread, occur in the Cannorrhaphida (Pl. 101), Aulacanthida (Pl. 102-105), Coelodendrida (Pl. 121, 122), and Coelographida (Pl. 126-128). In all these families the hollow cylindrical tubes have a very thin wall and contain a wide cavity, filled only by jelly. The Orosphærida (Pl. 106, 107), differ in the reduction of the cavity, which becomes very narrow (often rudimentary or lost), whilst the walls of the tubes become extremely thickened and stratified, numerous concentric layers of silica being disposed one over the other. The hollow cylindrical tubes contain an axial filament, or a thin thread of silica, placed in its axis, in the families Aulosphærida (Pl. 109-111), Cannosphærida (Pl. 112), Circoporida (Pl. 114-117), and Tuscarorida (Pl. 100). Usually the axial filament is connected with the thin wall of the tube by numerous horizontal branches. A quite peculiar structure distinguishes the Medusettida (Pl. 118-120); their hollow tubes, extremely prolonged, are articulate owing to the presence of numerous, regular, equidistant transverse septa; these are pierced by a short tubule, similar to the siphon of the shells of _Nautilus_; this remarkable alveolar structure also occurs in the peripheral part of their shell-wall (and sometimes in the whole shell), numerous small polyhedral chambers or alveoles which communicate by small openings, being developed; they become easily filled with air in the dry shell (Pl. 120, figs. 11-16).

{1541}The substance of the siliceous or silicated shell-wall is, in the majority of PHÆODARIA, homogeneous and structureless, as in the SPUMELLARIA and NASSELLARIA; but sometimes it acquires a peculiar structure. The thickened wall of the hollow tubes in the Orosphærida and in several Aulacanthida (Pl. 105, figs. 6-10) becomes distinctly stratified, concentric strata being disposed one over the other. A very remarkable structure, differing from that in all other Radiolaria, is found in the porcellanous shell of the Circoporida (Pl. 114-117), and Tuscarorida (Pl. 100). The thickened wall of the opaque shell is here composed of a peculiar silicated cement, which encloses numerous very thin and irregularly scattered needles (Pl. 115, figs. 6-9; Pl. 116, fig. 3). Dry fragments of these shells, observed by a strong lens, appear finely punctulate, and probably air, entering into these fine porules of the cement, causes the white colour and the calcareous or porcellanous appearance of the opaque dry shell. Its surface is smooth in the Tuscarorida (Pl. 100), panelled in the Circoporida (Pl. 114-117).

The hollow or solid spines, which arise from the shell of the PHÆODARIA, exhibit an extraordinary variety and elegance in the production of different branches, bristles, hairs, secondary spine, and thorns, hooks, anchor-threads, pencils, spathillæ, &c. These appendages are developed similarly to those of many SPUMELLARIA, but exhibit a far greater variety and richness in form. They are organs partly for protection, partly for retention of food. They are much more interesting than in other Radiolaria.

_Synopsis of the Orders and Families of_ PHÆODARIA.

------------------------------------------------------------------------- I. Order PHÆOCYSTINA. Skeleton absent or incomplete, composed of numerous single scattered pieces, without connection. Central capsule placed in the centre of the calymma. ------------------------------------------------------------------------- Skeleton completely absent, 1. PHÆODINIDA.

Skeleton composed of numerous scattered pieces, not of radial tubes, 2. CANNORRHAPHIDA.

Skeleton composed of numerous hollow radial tubes, the proximal ends of which are in contact with the central capsule, 3. AULACANTHIDA. ------------------------------------------------------------------------- II. Order PHÆOSPHÆRIA. Skeleton a simple or double lattice-shell, not bivalved, without a peculiar shell-mouth (shell usually spherical, rarely of a modified form, always without peristome). Central capsule placed in the centre of the shell-cavity. ------------------------------------------------------------------------- { Network very robust and Shell composed { coarse, with irregular of a simple { polygonal meshes; bars non-articulated { very thick, partly hollow, 4. OROSPHÆRIDA. lattice-plate, { without astral { Network very delicate and septa in the { fragile, with subregular, nodal points. { triangular meshes; rods { very thin, filiform, always { solid, 5. SAGOSPHÆRIDA.

Shell composed { Shell articulated, with of numerous { astral septa, without a hollow, tangential { simple central shell, 6. AULOSPHÆRIDA. cylindrical tubes, { which are { Shell double, composed of separated by { two concentric shells; astral septa in { the outer articulated, the the nodal points. { inner simple, 7. CANNOSPHÆRIDA. ------------------------------------------------------------------------- III. Order PHÆOGROMIA. Skeleton a simple lattice-shell, not bivalved, constantly provided with a peculiar large shell-mouth placed on the oral pole of the main axis; peristome usually surrounded by peculiar feet or teeth. (Shell either spherical or ovate, or of another form). Central capsule excentric, placed in the aboral half of the shell-cavity. ------------------------------------------------------------------------- { Structure of the shell { diatomaceous, with very { delicate and regular { hexagonal pores. No { articulate feet, 8. CHALLENGERIDA. Structure of the { shell not { Structure of the shell porcellanous { alveolar, with hollow (without needles { alveoles between a double imbedded in { plate. A corona of a punctulate { articulated feet around cement-substance). { the mouth, 9. MEDUSETTIDA. { { Structure of the shell of { simple lattice-work, neither { diatomaceous nor alveolar. { No articulate feet, 10. CASTANELLIDA.

Structure of the { Surface of the shell shell porcellanous, { (sphericalpanelled or with peculiar fine { dimpled or polyhedral). needles imbedded { Peristome flat, 11. CIRCOPORIDA. in a punctulate { cement-substance { Surface of the shell (a circle of { smooth, even (ovate or pores around the { subspherical). Peristome base of each tube). { prominent, 12. TUSCARORIDA. ------------------------------------------------------------------------- IV. Order PHÆOCONCHIA. Skeleton a bivalved lattice-shell, composed of a dorsal and a ventral valve which are completely separated (rarely connected by a ligament on the aboral pole). Central capsule enclosed between the two valves. ------------------------------------------------------------------------- The two valves of the bivalved shell thick and firm, regularly latticed, without a galea or cupola on their apex, and without hollow tubes, 13. CONCHARIDA.

The two valves { Galea without rhinocanna of the bivalved { or nasal tube, without shell very thin { frenula, 14. COELODENDRIDA. and fragile, { scarcely latticed, { Galea with a rhinocanna or each with a conical { nasal tube, both connected cupola or a { by an odd or helmet-shaped galea { paired frenulum, 15. COELOGRAPHIDA. on its sagittal { pole or apex, and { with hollow tubes. {

Order I. PHÆOCYSTINA, Haeckel (1879).

_Definition._--PHÆODARIA without lattice-shell, either without any skeleton, or with an incomplete skeleton, composed of numerous single pieces, which are scattered in the calymma without connection. Central capsule placed in the centre of the spherical calymma.

{1543}Family LXXI. #Phæodinida#, Haeckel (Pl. 101, figs. 1, 2).

_Phæodinida_, Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 4.

_Definition._--PHÆODARIA without skeleton. Central capsule with one to three (or more) openings, placed in the centre of the spherical naked calymma.

The family #Phæodinida# is the simplest and most primitive of the PHÆODARIA, and differs from all the other families of this legion in the complete absence of a skeleton. It bears, therefore, the same relation to the latter as the Thalassicollida do to the other SPUMELLARIA. The soft body is only composed of the central capsule with the nucleus, and the calymma with the phæodium.

Of course it is quite possible that the skeletonless PHÆODARIA, which we regard here as the ancestral family of that legion, may be either members of other families which have lost their skeleton accidentally, or young PHÆODARIA which have not yet developed a skeleton. But in some preparations of the Challenger certain large, well-preserved PHÆODARIA, without any trace of skeleton, are not rare; and since I myself have observed a complete living _Phæodina_, I have no doubt that they are independent, primordial forms (like _Actissa_, _Thalassicolla_, _Cystidium_, _Nassella_, &c.). Probably also two skeletonless PHÆODARIA belong to this family which are figured by R. Hertwig, in 1879, in his Organismus d. Radiol. (Taf. x. fig. 1, 11); this author, however, supposed that they had lost their original skeleton.

The three species of Phæodinida which are described in the sequel represent two different genera, _Phæodina_ and _Phæocolla_, already distinguished in my first note on the PHÆODARIA (Sitzungsb. med.-nat. Gesellsch. Jena, 1879, Dec. 12, p. 4). _Phæodina_ is a true TRIPYLEA, and has the usual three openings which occur in the majority of PHÆODARIA, a large astropyle or main-opening on the oral pole of the main axis, and a pair of lateral accessory openings, or parapylæ, on the aboral pole. _Phæocolla_, however, has only a single opening, the astropyle, and agrees therefore with those PHÆODARIA which possess no parapylæ (Challengerida, Medusettida, Castanellida, &c.).

The complete body is in all observed Phæodinida a small jelly sphere of 1 to 3 mm. in diameter, with a transparent cortical layer and an opaque dark central part. This latter is the phæodium, in which the central capsule is hidden, surrounded on all sides by the gelatinous spherical calymma; the smooth surface of the latter is spherical.

The _central capsule_ of the Phæodinida (Pl. 101, figs. 1, 2), is either spherical or spheroidal, somewhat lenticular, slightly depressed in the direction of the main axis. Its diameter is between 0.15 and 0.25. Its double membrane exhibits the same structure as in the other PHÆODARIA. The thick, double-contoured outer membrane is separated from the thin and delicate inner membrane by a clear space, filled up by jelly or by a fluid; the two are connected in _Phæocolla_ (fig. 1) only at the astropyle, in _Phæodina_ (fig. 2), {1544}they are also connected at the two parapylæ. The radiate operculum of the astropyle opens by a tubular prolongation or proboscis, which is very long in the former, shorter in the latter. The two parapylæ of the latter also bear short tubules. The protoplasm, enclosed in the inner membrane, contains numerous small circular vacuoles. The large central nucleus is sometimes spherical or ellipsoidal, at other times spheroidal or lenticular; it always contains numerous nucleoli. One specimen observed, with two nuclei, was apparently engaged in self-division (fig. 2).

The spherical gelatinous calymma, in the centre of which the central capsule is placed, has a diameter of 1 to 2 mm. In the specimen of _Phæodina tripylea_, which I observed living, it exhibited exactly the same shape as the figure of _Dictyocha stapedia_ in Pl. 101, fig. 10; the only distinction in this latter being indicated by the pileated pieces of the skeleton on the surface. The jelly-sphere contained numerous roundish or globular alveoles of very different sizes, and between them an areolated network of protoplasm; the latter has arisen from the outer surface of the calymma in the form of very numerous, radiating, partly branched and anastomosing pseudopodia. The dark and opaque centre of the jelly-sphere is filled up by the granular, blackish-brown phæodium, which envelops the oral half of the central capsule completely; it exhibits the same characters as in all the other PHÆODARIA.

_Synopsis of the Genera of Phæodinida._

Central capsule with a single opening (an astropyle on the oral pole), 656. _Phæocolla_.

Central capsule with three openings (an oral astropyle and two aboral parapylæ), 657. _Phæodina_.

Genus 656. _Phæocolla_,[274] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 4.

_Definition._--#Phæodinida# with a single aperture to the central capsule (an astropyle with radiate operculum, placed on the oral pole of the main axis).

The genus _Phæocolla_ may be regarded as the simplest form of all PHÆODARIA, and perhaps as the common ancestral form of this legion. It has no skeleton, and the central capsule exhibits only a single aperture on one pole of the main axis. In this it agrees with the Challengerida, Medusettida, and Castanellida, which have also no parapylæ or secondary openings.

1. _Phæocolla primordialis_, n. sp. (Pl. 101, fig. 1).

Central capsule subspherical, or somewhat depressed in the direction of the main axis. The oral pole of the latter exhibits a large astropyle, or a radiate operculum, about as broad as the {1545}nucleus. From its centre arises a conical mammilla, prolonged into a thin, cylindrical, S-like tubulus, the proboscis, which is about as long as the diameter of the capsule. The outer membrane of the capsule is thick and double-contoured; the inner is very thin, but distinct, and includes finely granulated protoplasm, and numerous spherical, clear vacuoles, each with some small granules. Nucleus spheroidal, depressed in the direction of the main axis, containing numerous dark, irregularly amoebiform nucleoli. The diameter of the nucleus is about equal to the radius of the central capsule. The extracapsular calymma is an alveolated sphere, the diameter of which is six to eight times that of the capsule. The inner part of it contains an irregular, blackish phæodium, which surrounds and hides the oral half of the central capsule.

_Dimensions._--Diameter of the central capsule 0.16, of the nucleus 0.08, of the calymma 1.0 to 1.2.

_Habitat._--Central Pacific, Station 271 to 274, surface.

Genus 657. _Phæodina_,[275] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 4.

_Definition._--#Phæodinida# with three apertures to the central capsule (an astropyle on the oral pole of the main axis, and two lateral parapylæ on both sides of the aboral pole).

The genus _Phæodina_ has the same structure of the central capsule as the majority of PHÆODARIA; one large main-opening or astropyle on the oral pole of the main axis, and two smaller lateral accessory openings or parapylæ on each side of the aboral pole: it is therefore a true Tripylean genus, like the majority of PHÆODARIA.

1. _Phæodina tripylea_, Haeckel (Pl. 101, fig. 2).

? _Tripylea_ sp., R. Hertwig, 1879, Organismus d. Radiol., Taf. x. figs. 1, 11.

Central capsule spheroidal or lenticular, somewhat depressed in the direction of the main axis. Astropyle with a strongly ribbed, radiate operculum, scarcely one-third as broad as the diameter of the capsule, and prolonged into a short tubular proboscis. Parapylæ also with short tubular openings. The outer strong (double-contoured) membrane of the central capsule is separated from the inner thin (simple-contoured) membrane by a wide interval, filled up by a clear fluid or jelly; only at the three apertures both membranes are in direct connection. The granulated protoplasm contains numerous vacuoles, and surrounds a large spheroidal nucleus, with numerous small nucleoli. The voluminous calymma in a specimen, observed living, was alveolar, and the ramification of the pseudopodia, as well as the formation of the dark brown phæodium, very similar to that of _Dictyocha stapedia_ (Pl. 101, fig. 10). Another specimen, figured in Pl. 101, fig. 2, exhibited the first stages of self-division; the reticulated nucleus and the radiate operculum of the astropyle were already doubled, and the two membranes of the capsule between them constricted in the median plane. To this species belong probably the central capsules figured by R. Hertwig, _loc. cit._

{1546}_Dimensions._--Diameter of the central capsule 0.15 to 0.25, of the nucleus 0.06 to 0.1, of the calymma 0.8 to 1.2.

_Habitat._--Mediterranean; Portofino, near Genoa (Haeckel); Messina (Hertwig).

2. _Phæodina cannopylea_, n. sp.

Central capsule subspherical, scarcely depressed in the direction of the main axis. Astropyle with a finely ribbed radiate operculum, about as broad as the radius of the capsule, prolonged into a slender, tubular proboscis which is S-shaped, about as long as the radius, and similar to that of _Phæocolla primordialis_, Pl. 101, fig. 1. Parapylæ also tubular, with two slender prolongations, half as long and broad as the proboscis of the parapyle. Nucleus spheroidal, about half as broad as the capsule. This species differs from the preceding mainly in the cylindrical slender prolongations of the three apertures, which are similar to those of _Aulosphæra_ and _Aularia_ (Pl. 111, fig. 2).

_Dimensions._--Diameter of the central capsule 0.2, of the nucleus 0.1, of the calymma 1.2 to 1.5.

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

Family LXXII. #CANNORRHAPHIDA#, Haeckel, 1879 (Pl. 101, figs. 3-14; Pl. 114, figs. 7-13).

_Cannorrhaphida_, Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 4.

_Definition._--PHÆODARIA with an incomplete skeleton, composed of numerous separate, not radially arranged pieces, which are either hollow tangential spicula or cap-shaped dishes, or fenestrated rings, scattered loosely in the calymma. Central capsule placed in the centre of the spherical calymma.

The family #Cannorrhaphida# comprises those PHÆODARIA in which the incomplete skeleton is represented by numerous separate pieces of silica, which exhibit very different forms, and are scattered tangentially on the surface of the spherical calymma, sometimes also throughout its jelly-mass. They agree in this peculiar character with the Thalassosphærida (among the SPUMELLARIA) and bear the same relation to the skeletonless Phæodinida as the Thalassosphærida do to the Thalassicollida (compare pp. 10 and 29). The Cannorrhaphida represent the former group among the PHÆODARIA. They differ from the following family, the Aulacanthida, in the arrangement and position of the hollow spicula, which are never directed radially and never touch the central capsule, as is constantly the case in the latter.

Two genera of Cannorrhaphida have been hitherto known. The first species observed in a complete and living state (at Messina in 1859) was _Cannobelos cavispicula_, described in 1862 in my Monograph as _Thalassoplancta cavispicula_ (_loc. cit._, p. 261, Taf. iii. figs. 10-13). I there figured a complete living specimen with expanded pseudopodia and a double central capsule (in the stage of self-division). The latter was surrounded by an {1547}alveolar calymma and by a voluminous mass of blackish-brown pigment, the phæodium; numerous, long, hollow, cylindrical tubes were scattered on the surface of the calymma. At that time I did not know the tripylean character of the central capsule and the peculiar radiate operculum in the PHÆODARIA, and therefore placed _Thalassoplancta cavispicula_ among the Thalassosphærida.

The second description of a complete form of Cannorrhaphida was given in 1879 by R. Hertwig, under the name _Dictyocha fibula_ (Organismus d. Radiol., p. 89, Taf. ix. fig. 5). The genus _Dictyocha_ had been already founded by Ehrenberg in 1838, with the following definition:--"Lorica simplex, univalvis, silicea, laxe reticulata aut stellata" (Abhandl. d. k. Akad. d. Wiss. Berlin, 1838, p. 128). Ehrenberg had found only scattered pieces of the skeleton, fossil in Tertiary rocks. He placed them among the _Bacillaria_ (= _Diatomaceæ_), but added, that they may be possibly scattered spicula of Sponges ("forsan Spongiarum ossicula").

In 1859 I myself observed similar forms of _Dictyocha_ at Messina, and first recognised them as true Radiolaria. But I placed them at that time among the Acanthodesmida, beside _Prismatium_, supposing that a small spherical body which I had sometimes seen in the cavity of the pileated pieces (probably a phæodellum) was the small central capsule (Monogr. d. Radiol., 1862, p. 271, Taf. xii. figs. 3-6). The complete body of _Dictyocha_ was not described till 1879, when R. Hertwig gave a full description of its peculiar structure, and especially of the great central capsule, which resembles that of the other PHÆODARIA. He first stated that the singular pileated pieces described by Ehrenberg were not complete shells, but isolated pieces of the skeleton, which are scattered in the jelly-envelope around the central capsule in a mode similar to the spicula of _Thalassoplancta_, _Thalassosphæra_ and _Sphærozoum_. Hertwig also first recognised that the thin rods, which compose the reticular pileated pieces of the skeleton in _Dictyocha_, are not solid bars, but thin hollow tubules, similar to the hollow rods of _Aulacantha_ and of other PHÆODARIA.

Numerous complete and well-preserved specimens of _Dictyocha_, which I found in the collection of the Challenger, have convinced me that the accurate description of R. Hertwig is correct in every respect, and that these remarkable bodies are true PHÆODARIA, most closely allied to _Cannobelos_ (= _Thalassoplancta_) and to _Aulacantha_ (compare Pl. 101, fig. 10). I now regard them as representatives of a peculiar subfamily of Cannorrhaphida, which I call Dictyochida. To the same subfamily also belong the small annular bodies which Ehrenberg described in 1841 as _Mesocena_ (_loc. cit._, p. 401), and the elegant, more complicated, reticular and pileated bodies, which Stöhr figured in 1880 under the name _Distephanus_ (Palæontogr., vol. xxvi. p. 121). These peculiar bodies are also only isolated pieces of the siliceous skeleton, and are scattered tangentially in great numbers in the calymma, around the tripylean central capsule. A still higher degree of development is attained by the interesting forms {1548}which I describe here as _Cannopilus_ (Pl. 114, figs. 7-13). All these peculiar forms may be derived from the simple annular pieces of skeleton, which are aggregated in great numbers in the calymma of _Mesocena_. The pieces of the skeleton of these Dictyochida never assume the form of slender, cylindrical, tangential tubules which is characteristic of the Cannobelida.

A third subfamily of Cannorrhaphida, the Catinulida, is represented by the remarkable new genus _Catinulus_ (Pl. 117, fig. 8). The single pieces of the skeleton, scattered in hundreds or thousands throughout the calymma, are here not composed of hollow rods, as in the two former subfamilies, but are solid hemispherical caps, or small, more flatly vaulted dishes, with a peculiar radial striation. All the complete specimens of _Catinulus_ which I could examine possessed four equal central capsules, united in one spherical calymma.

The common character which unites the three rather different subfamilies, the Cannobelida, Dictyochida and Catinulida into a single family, and which separates this family, the Cannorrhaphida, from the other PHÆODARIA, is to be found in the composition of the rudimentary skeleton from numerous single pieces, which are loosely scattered either on the surface of the calymma, or throughout its jelly-mass, and which are never arranged radially and never touch the central capsule as is always the case in the closely allied Aulacanthida.

The slender spicula of the Cannobelida are cylindrical or spindle-shaped, tubular, scattered in variable numbers, but always in a tangential direction on the surface of the calymma. Usually they are 0.2 to 0.5 long, and 0.005 to 0.03 broad; either straight or slightly curved; smooth and simple in _Cannobelos_, spiny or branched in _Cannorrhaphis_ (Pl. 101, figs. 3-5). Their wall is thin and fragile, their diameter sometimes equal throughout their whole length, at other times tapering towards both ends. Their cavity is filled by jelly, and seems to be open at both ends, since the purified and dried spicula constantly become filled by air.

The peculiar pieces of silica which compose the skeleton of the Catinulida are not hollow, like the rods of the other Cannorrhaphida, but concave hemispherical cups or more flatly vaulted little dishes, the thin flinty wall of which is slightly thickened at the circular margin, and radially striped above it. In all three species of _Catinulus_ observed they were scattered throughout the calymma in hundreds or thousands (Pl. 117, fig. 8). Their relation to the Dictyochida is doubtful. Perhaps the small cups of _Catinulus_ may be derived from the simple rings of _Mesocena_, by development of an operculum on one side of the ring.

The skeleton of the Dictyochida is much more developed and possesses a higher morphological interest; the numerous different forms, however, which its pieces here assume, may be all derived from the simple circular ring of _Mesocena_. This ring is formed by a thin, hollow, cylindrical, or prismatic rod, sometimes circular or elliptical, at {1549}other times polygonal. From its margin small, hollow, radial spines often proceed (Pl. 101, fig. 9). In _Dictyocha_ there arise from the ring two, three, four or more siliceous bars or arches, which form one or more bulges over one side of the ring; usually the little fenestrated shell thus produced assumes the form of a three-sided or four-sided pyramid, or of a little hat with three or four meshes (Pl. 101, figs. 10-14). From this _Dictyocha_ (in a restricted sense) we separate the genus _Distephanus_, in which the little pyramids become truncated, so that one central apical mesh (the apical or upper ring) is surrounded by four, five, six or eight lateral meshes, the sides of the pyramid (Pl. 114, figs. 7-9). The edges of the small pyramid are formed by the same number of siliceous bars arising from the ring and alternating with the meshes. Radial spines in different numbers and arrangements arise from the corners of the two parallel rings, as well from the smaller apical as from the larger basal ring. The simple apical ring of _Distephanus_ becomes divided or fenestrated in the highest developed genus of this subfamily, in _Cannopilus_ (Pl. 114, figs. 10-13); each pileated piece of the skeleton exhibits here two rows of alternating lateral meshes, an upper row of smaller and a lower row of larger meshes.

The majority of Dictyochida are armed with spines or thorns, which arise in a regular manner from different points of the annular or pileated pieces. In the ancestral genus, _Mesocena_, radial spines start from the corners of the simple ring in centrifugal direction, and lie horizontally in its plane. As these primary corner-spines determine the radial composition of the more highly developed genera we call them perradial (lying in rays of the first order). In _Dictyocha_ and _Distephanus_ commonly (but not quite constantly) these perradial spines alternate with the ascending bars which bisect the sides of the basal ring; these bars are therefore interradial (lying in rays of the second order); consequently also the corners of the apical ring of _Distephanus_ are interradial. The latter also often bear small thorns or teeth. Other teeth frequently start in centripetal direction from the lower or basal ring, on the side of the perradial spines, and frequently they are directed obliquely downwards.

In _Dictyocha_ and _Distephanus_ are frequently found remarkable twin pieces, composed of two pileated and reticulated skeleton pieces. These are united by their basal rings loosely in such a way that they form together a small fenestrated subspherical body; the union is strengthened by those small teeth of the basal rings, which are directed downwards and catch one into the other (Pl. 101, fig. 12; Pl. 114, fig. 8). A similar twin piece has been already observed by Stöhr in the fossil _Distephanus rotundus_, and upon this was founded this genus. Since the teeth of the two opposed basal rings, catching one into the other, seem to be specially adapted for the composition of those small double pyramids, it is probable that the latter possess a special protective function in these PHÆODARIA, and perhaps envelop their phæodella or their flagellate spores (?). In every case these formations are very remarkable.

{1550}_The Central Capsule_ of the Cannorrhaphida seems to possess the same shape in the three subfamilies, and to agree in general with that of the Aulacanthida. In a living specimen of _Dictyocha stapedia_, which I observed at Ceylon (Pl. 101, fig. 10), the three openings of the TRIPYLEA were distinct; the radiate operculum of the astropyle (on the oral pole) was surrounded by the granules of the dark phæodium, whilst on the opposite aboral side, two parapylæ or conical secondary openings were visible. The voluminous spherical calymma (about four times as broad as the central capsule) contained numerous large alveoles (as in _Aulosphæra_) and its surface was protected by numerous pileated pieces of the skeleton; the basal ring of the latter was placed tangentially in the spherical surface of the calymma, their apical spine being directed outwards. The pseudopodia, arising from the central capsule and forming a network between the alveoles of the calymma, radiated outwards in great number from its surface (Pl. 101, fig. 10).

The propagation by self-division seems to be very frequent in the Cannorrhaphida. I frequently found two equal central capsules in one calymma, as in the first observed species, _Cannobelos cavispicula_, and in _Cannorrhaphis spinulosa_ (Pl. 101, fig. 3), sometimes also in _Dictyocha_ and _Distephanus_. As already mentioned, _Catinulus_ constantly exhibited four central capsules united in each calymma.

_Synopsis of the Genera of Cannorrhaphida._

------------------------------------------------------------------------- I. Subfamily Cannobelida. Pieces of the skeleton cylindrical or spindle-shaped tangential tubules. ------------------------------------------------------------------------- Tubules simple, smooth, 658. _Cannobelos_.

Tubules spiny or branched, 659. _Cannorrhaphis_. ------------------------------------------------------------------------- II. Subfamily Catinulida. Pieces of the skeleton hemispherical or cap-shaped, solid. ------------------------------------------------------------------------- Caps or hemispherical pieces of the skeleton solid, with radiate margin and circular opening, 660. _Catinulus_. ------------------------------------------------------------------------- III. Subfamily Dictyochida. Pieces of the skeleton either simple rings or pileated or pyramidal bodies, composed of thin hollow rods and reticular meshes. ------------------------------------------------------------------------- Flinty pieces simple { Basal ring simple, not or arched rings, not { arched or fenestrated, 661. _Mesocena_. truncated pyramids, { with a basal ring, { Basal ring fenestrated, but without apical { with two or more arches, ring. { vaulted over one side, 662. _Dictyocha_.

Flinty pieces of the { Apical ring simple, not skeleton resembling { fenestrated (one girdle a truncated pyramid, { of meshes on each piece), 663. _Distephanus_. with an upper smaller { apical ring, and a { Apical ring fenestrated lower larger basal { (two girdles of meshes ring. { on each piece), 664. _Cannopilus_.

{1551}Subfamily 1. CANNOBELIDA, Haeckel.

_Definition._--#Cannorrhaphida# with numerous hollow cylindrical or spindle-shaped tubes, which lie tangentially scattered on the surface of the spherical calymma.

Genus 658. _Cannobelos_,[276] n. gen.

_Definition._--#Cannorrhaphida# with a skeleton composed of tubular acicular pieces, which are smooth, cylindrical or spindle-shaped tangential needles, without spines and branches.

The genus _Cannobelos_, and the following closely allied _Cannorrhaphis_, represent the peculiar subfamily Cannobelida, differing from the other Cannorrhaphida in the acicular form of the pieces of the skeleton, which are tangentially scattered on the surface of the spherical calymma. The cylindrical or spindle-shaped hollow needles are smooth in _Cannobelos_, whilst in _Cannorrhaphis_ they are studded with lateral spines or branches.

1. _Cannobelos cavispicula_, Haeckel.

_Thalassoplancta cavispicula_, Haeckel, 1862, Monogr. d. Radiol., p. 261, Taf. iii. figs. 10-13.

_Thalassicolla cavispicula_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wis. Berlin, p. 798.

_Cannorrhaphis cavispicula_, Haeckel, 1881, Prodromus, p. 470.

Tangential tubes cylindrical, more or less curved, gradually tapering towards the two pointed ends. Calymma with a voluminous phæodium.

_Dimensions._--Length of the tubular spicule 0.25, breadth 0.003.

_Habitat._--Mediterranean, Messina, surface.

2. _Cannobelos calymmata_, n. sp.

Tangential tubes cylindrical, straight, of equal breadth throughout their whole length, closed by a hemispherical cap on the two rounded ends. Calymma very voluminous, with a small phæodium.

_Dimensions._--Length of the tubular spicula 0.3 to 0.5, breadth 0.004 to 0.008.

_Habitat._--Central Pacific, Stations 263 to 274, surface.

3. _Cannobelos thalassoplancta_, n. sp.

Tangential tubes spindle-shaped, straight, gradually tapering towards the two pointed ends. Calymma and the included phæodium rather voluminous.

_Dimensions._--Length of the tubular spicula 0.15 to 0.2, breadth in the middle part 0.02.

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

{1552}Genus 659. _Cannorrhaphis_,[277] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 4.

_Definition._--#Cannorrhaphida# with a skeleton composed of tubular acicular pieces, which are spiny, cylindrical or spindle-shaped tangential needles, either with lateral spines or branches.

The genus _Cannorrhaphis_ differs from the preceding closely allied _Cannobelos_ in the spiny shape of the tangential acicular spicula, which are studded either with short spines or with longer lateral branches.

1. _Cannorrhaphis spinulosa_, n. sp. (Pl. 101, figs. 3, 4).

Tangential tubes cylindrical, straight, gradually tapering towards the two pointed ends, densely studded with conical spines, arising perpendicularly. (The specimen figured, fig. 3, exhibited two ovate central capsules, each of which contained two large nuclei, with numerous nucleoli.)

_Dimensions._--Length of the tubular spicula 0.3 to 0.5, breadth 0.01 to 0.015.

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

2. _Cannorrhaphis lampoxanthium_, n. sp.

Tangential tubes cylindrical, more or less curved, suddenly tapering towards the two pointed ends, densely studded with irregular conical spines of unequal length, which arise obliquely from their surface.

_Dimensions._--Length of the tubular spicula 0.4 to 0.5, breadth 0.005 to 0.008.

_Habitat._--South Pacific, Station 289, depth 2550 fathoms.

3. _Cannorrhaphis lappacea_, n. sp.

Tangential tubes spindle-shaped, gradually tapering towards the two pointed ends, densely studded with irregular lateral branches, which are partly simply, partly forked, more or less curved, and arise obliquely from their surface.

_Dimensions._--Length of the tubular spicula 0.2 to 0.3, breadth 0.015 to 0.025.

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

4. _Cannorrhaphis spathillata_, n. sp. (Pl. 101, fig. 5).

Tangential tubes cylindrical, thin and straight, regularly zigzag, with pointed, regularly alternating lateral spines, with an elegant spathilla, or a cap-shaped verticil of eight to ten recurved spines on the two ends.

_Dimensions._--Length of the tubular spicula 0.3, breadth 0.003.

_Habitat._--Indian Ocean, Cocos Islands (Rabbe), surface.

{1553}Subfamily 2. CATINULIDA, Haeckel.

_Definition._--#Cannorrhaphida# with a skeleton composed of numerous cap-shaped pieces, which lie tangentially scattered on the surface of the spherical calymma. Each piece is a hemispherical or flatly cap-shaped siliceous body, often with radial striations, and with a thin solid wall.

Genus 660. _Catinulus_,[278] n. gen.

_Definition._--#Cannorrhaphida# with a skeleton composed of solid, cap-shaped or hemispherical, not fenestrated, pieces.

The genus _Catinulus_ differs from all the other Cannorrhaphida in the peculiar shape of the numerous siliceous pieces, which are scattered on the surface of the calymma and compose their rudimentary skeleton. These pieces are neither hollow rings (as in the Dictyochida), nor hollow tubes (as in the Cannobelida), but solid hemispherical caps or more flatly vaulted small dishes. All the complete specimens of this genus which I observed exhibited four equal central capsules in the spherical calymma.

1. _Catinulus quadrifidus_, n. sp. (Pl. 117, figs. 8, 8_a_).

Cap-shaped pieces of the skeleton flatly vaulted, three times as broad as high, smooth; the marginal ring with fine radial ribs and with smooth margin.

_Dimensions._--Diameter of the calymma 0.6 to 0.8, of the four central capsules 0.12 to 0.2; breadth of the concave caps 0.024, height 0.008.

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

2. _Catinulus catillum_, n. sp.

Cap-shaped pieces of the skeleton flatly vaulted, three times as broad as high, rough, covered with numerous small spinules; the marginal ring with stout radial ribs and a corona of denticles on the margin.

_Dimensions._--Breadth of the concave caps 0.03, height 0.01.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

3. _Catinulus lopadium_, n. sp.

Cap-shaped pieces of the skeleton hemispherical, twice as broad as high, smooth; the marginal ring smooth, slightly radiate, with thickened smooth margin.

_Dimensions._--Diameter of the calymma 1.2, of the central capsule 0.22; breadth of the concave caps 0.024, height 0.012.

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

{1554}Subfamily 3. DICTYOCHIDA, Haeckel.

_Definition._--#Cannorrhaphida# with a skeleton composed of numerous annular pieces, which lie tangentially scattered on the surface of the calymma. Each piece is either a simple hollow ring or a pileate and reticulate cap, composed of a ring and several connected bars.

Genus 661. _Mesocena_,[279] Ehrenberg, 1841, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 401.

_Definition._--#Cannorrhaphida# with a skeleton composed of simple annular pieces, each of which is a circular, elliptical or polygonal, not fenestrated, ring, with or without radial spines.

The genus _Mesocena_ is the simplest form of the Dictyochida, and no doubt the common ancestral form of this subfamily. The siliceous pieces, which are scattered in variable and indefinite number in the calymma, are simple hollow rings, with or without spines on the periphery. Ehrenberg, who first described and figured such rings (found fossil in different Tertiary rocks) has mistaken them for Diatoms. Some species, which I found in the Challenger preparations, leave no doubt that these rings are the siliceous pieces of the skeleton of the simplest Dictyochida. They are scattered in great numbers in the spherical calymma, which surrounds a tripylean central capsule with all the characters of the PHÆODARIA. In the living body the rings probably always lie in the spherical periphery of the extracapsular jelly-veil, in tangential planes, whilst in some of the Challenger preparations the rings were scattered in hundreds throughout the whole jelly-mass. In a few species the rings are quite simple, circular or elliptical, smooth, and without teeth or spines. In the majority of species some teeth or radial spines, regularly disposed, arise from the periphery of each ring (two, three, four to eight; sometimes sixteen, eight smaller alternating with eight larger spines). In some species small teeth occur on the inner margin of the rings. The number of radial spines seems to be rather constant in all the rings of one and the same individual, with the exception of a few variations. Thus in _Mesocena octogona_ I found here and there single rings with seven or nine teeth, instead of the usual number eight. Ehrenberg enumerated sixteen different species of _Mesocena_; many, however, of these are synonymous, being founded on slight variations in the number of the teeth; of others he has given only the name, but neither a figure nor a description (_e.g._, _Mesocena stephanolithis_, _Mesocena spongolithis_, &c.).

{1555}1. _Mesocena circulus_, Ehrenberg.

_Mesocena circulus_, Ehrenberg, 1840, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 208.

_Mesocena circulus_, Ehrenberg, 1854, Mikrogeol., Taf. xix. fig. 44.

Rings of the skeleton circular, smooth or slightly denticulate on the outer margin, without spines. This simple form is probably the ancestral form of the Dictyochida.

_Dimensions._--Diameter of the rings 0.02 to 0.03, thickness of the hollow rod 0.001 or less.

_Habitat._--Fossil in Tertiary rocks of Barbados and of the Mediterranean (Ægina, Greece; Caltanisetta, Sicily).

2. _Mesocena annulus_, n. sp.

? _Mesocena crenulata_, Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 822.

Rings of the skeleton elliptical, smooth or slightly denticulate on the outer margin, without spines. This species is possibly identical with _Mesocena crenulata_ of Ehrenberg, of which, however, no figure is given. The major axis of the ellipse is one and a half times as long as the minor.

_Dimensions._--Diameter of the rings in the major axis 0.03, in the minor 0.02; thickness of the bars 0.002.

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

3. _Mesocena diodon_, Ehrenberg.

_Mesocena diodon_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 84.

_Mesocena diodon_, Ehrenberg, 1854, Mikrogeol., Taf. xxxiii., Nr. xv. fig. 18.

Rings of the skeleton elliptical, smooth, with two opposite spines on the poles of the major axis, which is about one and one-third as long as the minor axis.

_Dimensions._--Diameter of the rings in the major axis 0.04, in the minor 0.03; length of the spines 0.01.

_Habitat._--Fossil in Barbados, and in North America (Virginia).

4. _Mesocena triangula_, Ehrenberg.

_Mesocena triangula_, Ehrenberg, 1840, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 208.

_Mesocena triangula_, Ehrenberg, 1854, Mikrogeol., Taf. xxii. fig. 41.

_Dictyocha triangula_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 46.

_Lithocircus triangularis_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 121, Taf. vii. fig. 10.

Rings triangular, with small peripheral thorns, and three larger teeth on the corners of the equilateral triangle.

_Dimensions._--Diameter of the rings 0.03 to 0.05, length of the spines 0.01.

_Habitat._--Fossil in Tertiary deposits of the Mediterranean; Caltanisetta, Sicily (Ehrenberg, Stöhr).

{1556}5. _Mesocena quadrangula_, Ehrenberg.

? _Mesocena quadrangula_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, pp. 145, 273.

? _Mesocena quaternaria_, Ehrenberg, 1855, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 302.

Rings square, with four radial spines on the corners of the square. Ehrenberg has given only the name of this species, but neither diagnosis nor figure. I think it may be identical with the species described, which I found in the North Atlantic.

_Dimensions._--Diameter of the rings 0.02 to 0.025, length of the spines 0.007 to 0.01.

_Habitat._--North Atlantic, Færöe Channel, Gulf Stream (John Murray), depth 600 fathoms.

6. _Mesocena elliptica_, Ehrenberg.

_Mesocena elliptica_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 84.

_Mesocena elliptica_, Ehrenberg, 1854, Mikrogeol., vol. i. Taf. xx. fig. 44.

_Dictyocha elliptica_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 44.

Rings elliptical or ovate, with four peripheral spines which lie in two diameters, perpendicular to one another, two opposite in the major, the two others in the minor axis of the ellipse.

_Dimensions._--Diameter of the rings 0.015 to 0.03, length of the spines 0.005.

_Habitat._--Fossil in Tertiary rocks of the Mediterranean (Placca di furni, from Zante, Greece); Caltanisetta, Sicily.

7. _Mesocena pentagona_, n. sp.

Rings regularly pentagonal, with smooth straight bars, and with five short and straight radial spines on the five corners.

_Dimensions._--Diameter of the rings 0.02, length of the spines 0.005.

_Habitat._--Fossil in Barbados.

8. _Mesocena hexagona_, Haeckel.

? _Mesocena senaria_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, pp. 163, 273.

? _Mesocena septenaria_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, pp. 163, 273.

Rings regular, hexagonal, with six radial spines on the six corners (sometimes between the usual six-radiate rings of one and the same individual are intermingled single rings with five or seven spines).

_Dimensions._--Diameter of the rings 0.025 to 0.03, length of the spines 0.007 to 0.01.

_Habitat._--Mediterranean, Krim (Ehrenberg), Corfu (Haeckel).

{1557}9. _Mesocena octogona_, Ehrenberg.

_Mesocena octogona_, Ehrenberg, 1841, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 417, Taf. i., Nr. iii. fig. 27.

? _Mesocena heptagona_, Ehrenberg, 1841, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 417, Taf. i., Nr. iii. fig. 26.

? _Mesocena heptagona_, Ehrenberg, 1854, Mikrogeol., Taf. xx. fig. 49.

? _Mesocena octoradiata_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, pp. 163, 273.

? _Mesocena nonaria_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, pp. 163, 273.

Rings regular, octagonal, with eight radial spines on the eight corners of the ring (sometimes between the common octoradiate rings single rings with seven or nine teeth are intermingled in one and the same calymma).

_Dimensions._--Diameter of the rings 0.02, length of the spines 0.005.

_Habitat._--Tropical Pacific; Peru, Ehrenberg; Station 272 to 274, surface.

10. _Mesocena bisoctona_, Ehrenberg.

_Mesocena bisoctona_, Ehrenberg, 1845, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 78; Mikrogeol., Taf. xxxv., Nr. xviii. figs. 9, 10.

_Mesocena binonaria_, Ehrenberg, 1845, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 78, _loc. cit._

Rings circular, with sixteen teeth; eight stronger teeth regularly disposed on the outer margin, alternating with these eight smaller teeth on the inner margin.

_Dimensions._--Diameter of the rings 0.02, length of the outer spines 0.005.

_Habitat._--Fossil in Guano from Peru and South Africa, also in Barbados.

11. _Mesocena stellata_, n. sp. (Pl. 101, fig. 9).

Rings circular, with sixteen teeth regularly disposed on the outer margin of the rings, eight stronger teeth alternating with eight smaller.

_Dimensions._--Diameter of the rings 0.03, length of the larger spines 0.01.

_Habitat._--Central area of the Pacific, Station 270, depth 2925 fathoms.

Genus 662. _Dictyocha_,[280] Ehrenberg, 1838, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 128.

_Definition._--#Cannorrhaphida# with a skeleton composed of annular pieces, which are fenestrated by one or more arches, arising on one side of the simple ring, but do not form a truncated pyramid (therefore no apical ring).

The genus _Dictyocha_ is a very remarkable and interesting form of PHÆODARIA, which has had a curious history. Ehrenberg, who first observed single pieces of it fossil in Tertiary rocks, supposed it to be the siliceous carapace of a Diatom, and gave it the following {1558}diagnosis: "Dictyocha, e familia Bacillariorum. Lorica simplex univalvis silicea, laxe reticulata aut stellulata" (_loc. cit._). In my Monograph (1862, p. 271), I placed it in the class Radiolaria, supposing that it might be a simple form of Acanthodesmida, having found only isolated siliceous pieces. Afterwards (in 1879) Richard Hertwig observed the entire living body, and demonstrated that the hollow siliceous pieces are scattered in great numbers around a tripylean central capsule, which exhibits all the essential characters of PHÆODARIA (Organismus d. Radiol., 1879, p. 89). Hertwig describes the position of the numerous siliceous pieces in the surface of the extracapsular jelly-sphere so densely aggregated, that they touch one another and produce the appearance of a reticulated sphere. In two specimens, which I observed living (Pl. 101, fig. 10), and in numerous complete specimens which I found in the collection of the Challenger, the number of the siliceous pieces was much smaller, and they were scattered irregularly in the surface of the alveolate jelly-sphere, being separated by wide and unequal intervals. The regular position seems to be that the basal rings lie tangentially in the spherical surface of the calymma, whilst the bars of the reticulum are directed outwards, and the apical spine radially in centrifugal direction. Very often two pieces are united by their basal rings in such a manner that they form a little spheroidal fenestrated body (as in _Distephanus_, Stöhr; compare p. 1550). The characteristic reticular skeleton-pieces of _Dictyocha_ must be derived from _Mesocena_; from its simple siliceous ring (on one side of its plane), arise two, three, or four (rarely more) bars, which become united to a loose framework (with two, three, or four meshes). When this network assumes the form of a truncated pyramid (with a central mesh on the apex), _Dictyocha_ passes over into _Distephanus_. From the corners of the original basal ring several radial spines usually arise in a centrifugal direction, and on the sides of these sometimes small teeth or thorns also run in a centripetal direction. The number of the meshes and the separating rods is usually four, more rarely two or three. The hollow rods are very thin, either cylindrical or prismatic. As the ascending rods alternate regularly with the corner-spines of the basal ring, we may call the latter perradial, the former interradial. Ehrenberg has distinguished in his genus _Dictyocha_ not less than fifty species, thirty-five living and twenty-five fossil (ten species both living and fossil). The greater part of these cannot be retained, as they are only slight varieties or abnormalities of single pieces of the skeleton, such as very frequently occur associated with the common regular forms in one and the same individual. Such abnormal species are, _e.g._, _Dictyocha abnormis_, _Dictyocha binoculus_, _Dictyocha bipartita_, _Dictyocha haliomma_, _Dictyocha hexathyra_, _Dictyocha septenaria_, &c. One species (_Dictyocha splendens_), is the fenestrated calcareous body of a Holothurian. Of some other species Ehrenberg has only given the name, but neither a description nor a figure (e.g., _Dictyocha borealis_, _Dictyocha cenostephania_, _Dictyocha compos_, _Dictyocha coronata_, _Dictyocha socialis_, _Dictyocha specillum_). A number of other species must be placed in the genera _Distephanus_ and _Cannopilus_, so that only eight of his species of true _Dictyocha_ remain.

{1559}1. _Dictyocha navicula_, Ehrenberg.

_Dictyocha navicula_, Ehrenberg, 1838, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 129; Mikrogeol., Taf. xx., Nr. i. fig. 43.

_Dictyocha ponticulus_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 267.

Each individual ring elliptical or oblong, with one transverse arch in the shorter axis, which bisects it into two meshes. No spines or teeth.

_Dimensions._--Diameter of the ring 0.02, of the bars 0.001.

_Habitat._--Fossil in Tertiary deposits, Barbados, Sicily, &c.; living in the Atlantic, Stations 352, 354, and off Bermuda, surface.

2. _Dictyocha quadrata_, Ehrenberg.

_Dictyocha quadrata_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 267.

Each individual ring square or rhomboid, with one transverse arch in the shorter axis, forming two meshes. Two peripheral opposite spines on the poles of one axis.

_Dimensions._--Diameter of the ring 0.015.

_Habitat._--Atlantic, Bermuda Islands; fossil in Barbados.

3. _Dictyocha pons_, Ehrenberg.

_Dictyocha pons_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 80; Mikrogeol., Taf. xxi. fig. 40.

_Dictyocha tripyla_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 80; Mikrogeol., Taf. xxi. fig. 41.

Each individual ring elliptical or oblong, with one transverse arch in the shorter axis, forming two meshes. Four peripheral spines, on the poles of the longer and of the shorter axis. (The individual abnormality, figured as _Dictyocha tripyla_, _loc. cit._, Taf. xxi. fig. 41, has the transverse arch bifid at one end, therefore three meshes result; this forms an interesting transition to _Dictyocha fibula_.)

_Dimensions._--Diameter of the ring 0.01, of the bars 0.001.

_Habitat._--Fossil in Tertiary rocks, Oran, Africa.

4. _Dictyocha triommata_, Ehrenberg.

_Dictyocha triommata_, Ehrenberg, 1845, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 76; Mikrogeol., Taf. xxxiii., Nr. xv. fig. 11.

_Dictyocha triactis_ (= _triacantha_), Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 80.

_Dictyocha trifenestrata_, Ehrenberg, 1841, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 410; Mikrogeol., Taf. xix. fig. 38.

_Dictyocha abyssorum_, Ehrenberg, 1854, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 38.

Each pileated piece of the skeleton is a small three-sided pyramid, the sides of which form three triangular meshes; the three edges between them are three curved interradial beams, united in the {1560}centre (the apex of the pyramid). Alternating with these, three horizontal, perradial, centrifugal spines start from the base.

_Dictyocha trigona_, Zittel, 1876 (L. N. 29, p. 83, Taf. ii. fig. 6), is an interesting Cretaceous species, perhaps a variety of _Dictyocha triommata_.

_Dimensions._--Diameter of the basal triangle 0.01, of the three meshes 0.005.

_Habitat._--Fossil in different Tertiary deposits (of Sicily, Greece, North America); living in the Central Pacific, Stations 270 to 272, depth 2600 to 2925 fathoms.

5. _Dictyocha tripyla,_ Ehrenberg.

_Dictyocha tripyla,_ Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 80.

_Dictyocha tripyla,_ Ehrenberg, 1854, Mikrogeol., Taf. xix. fig. 38 (et Taf. xxi. fig. 41?).

Each pileate piece of the skeleton is a small three-sided pyramid, similar to that of _Dictyocha triommata_, but differs from it in the possession of three small perpendicular teeth, which are directed downwards and start from the basal ring near the origin of the three horizontal spines.

_Dimensions._--Diameter of the triangular basal ring 0.015, of the three meshes 0.007.

_Habitat._--Fossil in Tertiary deposits. North Africa (Oran), Sicily (Caltanisetta).

6. _Dictyocha medusa_, n. sp. (Pl. 101, figs. 13, 14).

Each pileated piece of the skeleton has four equal, cruciate, triangular meshes. From the four corners of the square basal ring proceed four perradial horizontal spines, and between these four interradial curved bars, which correspond to the edges of a four-sided pyramid, arise from the centre of the four sides and become united in the centre (on the apex of the pyramid). No apical spine.

_Dimensions._--Diameter of the basal ring 0.02, of the four meshes 0.01.

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

7. _Dictyocha staurodon_, Ehrenberg.

_Dictyocha staurodon,_ Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 80.

_Dictyocha staurodon,_ Ehrenberg, 1854, Mikrogeol., Taf. xviii. fig. 58.

Each pileated piece of the skeleton is a small, regular, four-sided pyramid, similar to the foregoing species. It differs from _Dictyocha medusa_ in the development of a vertical apical spine, and of four small centripetal teeth, which start from the inside of the basal square, between the four perradial spines and the four ascending interradial beams.

_Dimensions._--Diameter of the basal ring 0.025, of the meshes 0.01.

_Habitat._--Fossil in Tertiary rocks; Tripel of Richmond, Virginia (Ehrenberg); Barbados, (Haeckel); living in the Tropical Atlantic, Station 347, surface.

{1561}8. _Dictyocha fibula_, Ehrenberg.

_Dictyocha fibula_, Ehrenberg, 1839, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 149; Mikrogeol., Taf. xviii. fig. 54, _a_, _b_, _c_, Taf. xix. fig. 43, Taf. xx. fig. 45, Taf. xxi. fig. 42, &c.

_Dictyocha abnormis_, Ehrenberg, 1845, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 76; Mikrogeol., 1854, Taf. xxxvA., Nr. xvii. fig. 9.

_Dictyocha bipartita_, Ehrenberg, 1854, Mikrogeol., Taf. xxii. fig. 44.

_Dictyocha tenella_, Ehrenberg, 1841, Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. ii. fig. 11.

Each pileated piece of the skeleton stirrup-shaped, with two pairs of meshes, and a square basal ring, the four corners of which are prolonged into four perradial spines. Between the latter four interradial beams arise from the sides in pairs, and the two pairs are connected by a diagonal arch. Therefore the two opposite meshes are larger and pentagonal, the other two meshes (alternating with these) are smaller and square. No vertical spine on the apex.

_Dimensions._--Diameter of the basal square ring (diagonal) 0.01 to 0.02, of the meshes 0.005.

_Habitat._--Fossil in different Tertiary rocks (Barbados, Oran, Greece, Sicily, &c.), Ehrenberg.

9. _Dictyocha messanensis_, Haeckel.

_Dictyocha messanensis_, Haeckel, 1862, Monogr. d. Radiol., p. 272, Taf. xii. figs. 3-6.

_Dictyocha fibula_, R. Hertwig (not Ehrenberg), 1879, Organismus d. Radiol., p. 89, Taf. ix. fig. 5.

Each pileated piece of the skeleton stirrup-shaped, very similar to _Dictyocha fibula_, but distinguished by a vertical apical spine in the centre of the transverse arch, which connects the two pairs of ascending bars.

_Dimensions._--Diameter of the basal ring 0.02 to 0.03, of the meshes 0.01 to 0.016.

_Habitat._--Mediterranean (Messina), North Atlantic (Canary Islands), Station 354, surface.

10. _Dictyocha epiodon_, Ehrenberg.

_Dictyocha epiodon_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 79; Mikrogeol., Taf. xviii. fig. 55.

Each pileated piece of the skeleton stirrup-shaped, with four paired meshes similar to the hats of _Dictyocha fibula_, but distinguished by four small centripetal thorns, which start from the inside of the basal ring, at the side of the four ascending beams. No apical spine.

_Dimensions._--Diameter of the basal ring 0.03, of the meshes 0.01.

_Habitat._--Fossil in Tertiary rocks of North America (Miocene Tripel of Richmond, Virginia, &c.).

11. _Dictyocha stapedia_, n. sp. (Pl. 101, figs. 10-12).

Each pileated piece of the skeleton stirrup-shaped, with four paired meshes, similar to the hats of _Dictyocha fibula_ and _Dictyocha messanensis_, but distinguished by four small centripetal teeth, which start from the inside of the basal ring, at the side of the four ascending beams. In the centre of the diagonal arch arises a vertical apical spine (differing from _Dictyocha epiodon_). This species seems {1562}to be the most common of the living forms and widely distributed over all warmer seas. I observed in Ceylon, taken on the surface, the living specimen figured in Pl. 101, fig. 10, the numerous spicula were irregularly scattered over the spherical surface of the alveolate calymma. Other specimens occur in various preparations of the Challenger collection, from the Atlantic and the Pacific. The majority of the siliceous little hats exhibited the stirrup-form shown in fig. 11, and many were united in pairs, forming a twin-piece (fig. 12). Intermingled with these are found some irregular forms, representing the specific form of some allied species, viz., _Dictyocha speculum_, _Dictyocha staurodon_, _Dictyocha epiodon_ and _Dictyocha messanensis_.

_Dimensions._--Diameter of the basal ring 0.015 to 0.03, of the meshes 0.005 to 0.012.

_Habitat._--Cosmopolitan; Atlantic, Pacific, Indian Ocean, in the Tropical and warmer regions; Stations 159, 244, 266-272, 318, 352, &c.

12. _Dictyocha rhombus_, n. sp.

Each pileated piece of the skeleton stirrup-shaped, similar to _Dictyocha stapedia_, with four paired meshes. It differs from the latter in the rhomboid form of the basal ring and the larger size of the two opposite meshes, which are two to three times as large as the two others. Therefore the four centripetal teeth of the basal ring do not stand in the four single meshes, but in pairs only in the two larger meshes.

_Dimensions._--Diameter of the basal ring 0.02, of the meshes 0.005 to 0.01.

_Habitat._--North Atlantic; Færöe Channel, Gulf Stream, depth 50 to 600 fathoms, John Murray.

Genus 663. _Distephanus_,[281] Stöhr, 1880, Palæontogr., vol. xxvi. Taf. ii. p. 121.

_Definition._--#Cannorrhaphida# with a skeleton composed of pileated pieces, each of which is a small truncated pyramid with one girdle of meshes (the apical ring being simple).

The genus _Distephanus_ was founded in 1880 by Stöhr (_loc. cit._) for a single twin-piece of the skeleton of _Dictyocha speculum_. Among the common fossil forms of this species he once found in the Tertiary rocks of Caltanisetta, Sicily, a single piece (_loc. cit._, Taf. vi. fig. 9), which seemed to be composed of two equal pieces so united that they formed a little sphere with fourteen meshes; on each pole of the sphere lies a central hexagonal mesh surrounded by six pentagonal meshes, and from the six corners of the equatorial ring arise six centrifugal spines. No doubt this was a mistake, and the apparent little sphere was one of the above mentioned twin-forms, composed of two separate hexagonal truncated pyramids, which were loosely connected by their basal rings. I have often seen such twin-pieces of _Dictyocha speculum_ and of other species (Pl. 101, fig. 12, Pl. 114, fig. 8), and was always able to separate the two loosely connected halves of the bivalve shell by slight compression.

{1563}The genus _Distephanus_ of Stöhr, therefore, is nothing other than the _Dictyocha_ of Ehrenberg. But I think it is more convenient to retain the name _Distephanus_ for those forms of _Dictyocha_ which possess a simple apical mesh surrounded by a ring of lateral meshes, and in which each piece of the skeleton forms a small truncated pyramid. The basal plane of this pyramid is marked by the original basal ring (_Mesocena_), the truncated upper plane by the parallel apical ring, and the edges of the pyramid by the rising bars which connect both rings. In this sense, so far as the two rings lying in parallel planes are concerned, the term _Distephanus_ is correct (but not in the original sense of Stöhr). The number of the rising bars between the two rings varies from four, five, six to eight or more. It seems rather constant in each species, so that all the pieces of the skeleton of one specimen possess either four or six or eight lateral meshes, &c. But sometimes individual irregularities occur. In the majority of species each skeleton-piece is armed with spines. Usually a radial horizontal spine starts centrifugally from each corner of the basal ring, and on the side of this a small tooth or thorn often starts centripetally or downwards. In the twin-pieces, where the two basal rings are united, these teeth catch into one another. In some species upper spines also occur, starting from the corners of the apical ring. The perradial spines of the corners of the basal ring alternate regularly with the interradial ascending bars, which bisect the sides of the ring, as in _Dictyocha_.

1. _Distephanus crux_, Haeckel.

_Dictyocha crux_, Ehrenberg, 1840, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 207; Mikrogeol., 1854, Taf. xviii. fig. 56, Taf. xx. fig. 46, Taf. xxxiii. Nr. xv. fig. 9.

_Dictyocha bipartita_, Ehrenberg, 1844, _loc. cit._, p. 79, Taf. xxii. fig. 44.

Each pileated piece of the skeleton exhibits four pentagonal lateral meshes around one square central mesh, and is composed of two horizontal square rings; the smaller upper square is connected with the larger lower square by four ascending interradial beams, which start from the corners of the former and bisect the sides of the latter; from the corners of the basal ring arise four short perradial spines.

_Dimensions._---Diameter of the basal ring 0.02 to 0.03, of the apical ring 0.008.

_Habitat._---Tropical Atlantic, Station 347, surface; fossil in Tertiary deposits of the Mediterranean (Sicily, Oran).

2. _Distephanus mesophthalmus_, Haeckel.

_Dictyocha mesophthalma_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 80; Mikrogeol., 1854, Taf. xxii. fig. 43.

Each pileated piece of the skeleton exhibits four lateral meshes around the central mesh, and is composed of two parallel horizontal square rings, like those of _Distephanus crux_, but distinguished {1564}from this by eight short teeth, four centripetal on the larger lower ring and four perradial centrifugal on the smaller upper ring.

_Dimensions._--Diameter of the basal ring 0.03, of the apical ring 0.015.

_Habitat._--Fossil in Tertiary rocks of Sicily, Caltanisetta (Ehrenberg); living in the Central Pacific, Station 270 to 272, surface.

3. _Distephanus stauracanthus_, Haeckel.

_Dictyocha stauracanthus_, Ehrenberg, 1845, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 76; Mikrogeol., 1854, Taf. xxxiii., Nr. xv. fig. 10.

Each pileated piece of the skeleton exhibits four lateral meshes around the central mesh, and is composed of two horizontal rings, which are connected by four perradial beams arising from the corners of the upper and smaller square ring. Lower ring octagonal, with eight peripheral adradial spines, and with four interradial centripetal teeth on the inside.

_Dimensions._--Diameter of the basal ring 0.03, of the apical ring 0.004.

_Habitat._--Fossil in Tertiary rocks of North America (Hollis Cliff, Virginia; Norwich, Connecticut).

4. _Distephanus asteroides_, n. sp.

_Dictyocha asteroides_, Haeckel, 1881, Prodromus.

Each pileated piece of the skeleton exhibits five lateral meshes around the central mesh (or the upper ring). Five peripheral spines (on the corners of the lower ring) simple, not articulated.

_Dimensions._--Diameter of the basal ring 0.02, of the apical ring, 0.007.

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

5. _Distephanus pentasterias_, Haeckel.

_Dictyocha pentasterias_, Ehrenberg, 1839, Mikrogeol., Taf. xviii. fig. 61.

? _Dictyocha quinaria_, Ehrenberg, 1842, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 265.

? _Dictyocha elegans_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 80; Mikrogeol., 1854, Taf. xxii. fig. 51.

_Actiniscus elegans_, Ehrenberg, 1854, Mikrogeol., Taf. xxii. fig. 51.

Each pileated piece of the skeleton exhibits five lateral meshes around the central mesh (or the upper ring). Five peripheral spines (on the corners of the lower ring) articulated, triangular, with three distinct joints (tapering towards the distal end).

_Dimensions._--Diameter of the basal ring 0.012 to 0.018, of the apical ring 0.002 to 0.003.

_Habitat._--Cosmopolitan; living in the depths of the Atlantic and Central Pacific, Stations 247, 270 to 272, depths 2530 and 2600 to 2925 fathoms; fossil in Tertiary deposits (Tripel of Caltanisetta, Sicily; Richmond, Virginia).

{1565}6. _Distephanus speculum_, Haeckel.

_Dictyocha speculum_, Ehrenberg, 1837, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 150; Mikrogeol., 1854, Taf. xviii. fig. 57, Taf. xix. fig. 41, Taf. xxi. fig. 44, Taf. xxii. fig. 47, &c.

_Dictyocha speculum_, Stöhr, 1880, Palæontogr., vol. xxvi., Taf. vii. fig. 8.

_Dictyocha anacantha_, Ehrenberg, 1854, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 238.

_Dictyocha diommata_, Ehrenberg, 1854, Mikrogeol., Taf. xxxiii., Nr. xvii. fig. 6.

_Dictyocha erebi_, Ehrenberg, 1854, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 238.

_Dictyocha haliomma_, Ehrenberg, 1844, Mikrogeol., 1854. Taf. xxi. fig. 46.

_Dictyocha hexathyra_, Ehrenberg, 1844, Mikrogeol., 1854, Taf. xxii. fig. 46.

_Dictyocha ubera_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 80.

_Dictyocha stella_, Ehrenberg, 1854, Mikrogeol., Taf. xxii. fig. 52.

_Dictyocha rotundus_, Stöhr, 1880, Palæontogr., vol. xxvi., Taf. vii. fig. 9.

Each pileated piece of the skeleton is a truncated, six-sided pyramid, and composed of two regular hexagonal rings which lie in parallel plains, and are connected by six ascending interradial beams; these start from the corners of the upper smaller ring and bisect the sides of the lower larger ring; from the corners of the latter start six perradial centrifugal spines.

_Dimensions._--Diameter of the basal ring 0.03, of the apical ring 0.01.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific; fossil in Barbados, Sicily, &c.

7. _Distephanus ornamentum_, Haeckel.

_Dictyocha ornamentum,_ Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 80; Mikrogeol., 1854, Taf. xxii. fig. 49.

_Dictyocha binoculus_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 79; Mikrogeol., 1854, Taf. xix. fig. 42.

Each pileated piece of the skeleton is a truncated, six-sided pyramid, similar to that of _Distephanus speculum_, but distinguished by six small (probably vertical) teeth, which start from the inside of the lower (larger) ring, on the sides of the ascending beams.

_Dimensions._--Diameter of the basal ring 0.03, of the apical ring 0.015.

_Habitat._--Fossil in Tertiary deposits of Sicily, Caltanisetta (Ehrenberg).

8. _Distephanus aculeatus_, Haeckel.

_Dictyocha aculeata_, Ehrenberg, 1839, Abhandl. d. k. preuss. Akad. d. Wiss. Berlin, p. 149; Mikrogeol., 1854, Taf. xxii. Fig. 48, Taf. xix. fig. 40.

_Dictyocha aculeata_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 120, Taf. vii. fig. 7.

_Dictyocha bisternaria_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 201.

Each pileated piece of the skeleton is a truncated, six-sided pyramid, similar to that of _Distephanus speculum_, but distinguished by six small perradial, horizontal teeth, which start from the sides of the upper (smaller) ring.

_Dimensions._--Diameter of the basal ring 0.02, of the apical ring 0.008.

_Habitat._--Fossil in Tertiary deposits of the Mediterranean; plastic clay of Greece and Sicily; living in the Mediterranean and the Atlantic, Station 352, surface.

{1566}9. _Distephanus sirius_, Haeckel.

_Actiniscus sirius_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 68.

_Dictyocha sirius_, Ehrenberg, 1854, Mikrogeol., Taf. xviii. fig. 59.

Each pileated piece of the skeleton is a truncated six-sided pyramid, similar to that of _Distephanus speculum_, but distinguished by the six broad, triangular, peripheral spines, which are articulated and connected by a thin siliceous membrane (like a web-membrane); each spine has three articulations (as in _Dictyocha pentasterias_).

_Dimensions._--Diameter of the basal ring 0.02, of the apical ring 0.005.

_Habitat._--Fossil in Tertiary rocks (Richmond, Virginia), but also living in the Atlantic Ocean, Gulf Stream, Færöe Channel, John Murray, 1880.

10. _Distephanus corona_, n. sp. (Pl. 114, figs. 7-9).

_Dictyocha corona_, Haeckel, 1881, Prodromus.

Each pileated piece of the skeleton is a truncate six-sided pyramid like that of _Distephanus speculum_, but differing in the number (twenty-four) of teeth or spines. Six interradial ascending beams connect the two horizontal rings between these, and six nearly vertical spines arise from the perradial corners of the upper hexagonal ring. In the same meridional (perradial) plains six larger spines descend downwards from the corners of the lower larger ring. Between these six descending spines and the six ascending beams arise from the upper edge of the lower ring twelve shorter teeth of unequal size (the right tooth in each pentagonal lateral mesh being smaller and directed upwards, the left tooth being larger and directed nearly horizontally outwards). The lower ring is nearly dodecagonal.

_Dimensions._--Diameter of the basal ring 0.025 to 0.03, of the apical ring 0.012 to 0.02.

_Habitat._--North-west Pacific, Sea of Japan, Station 231, depth 2250 fathoms.

11. _Distephanus octonarius_, Haeckel.

_Dictyocha octonaria_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 201.

_Dictyocha polyactis_, Ehrenberg, 1844, _loc. cit._, p. 80; Mikrogeol., 1854, Taf. xxii. fig. 50.

_Dictyocha septenaria_, Ehrenberg, 1844, _loc. cit._, p. 80; Mikrogeol., 1854, Taf. xxi. fig. 45.

Each pileate piece of the skeleton is a truncated eight-sided pyramid, composed of two regular octagonal rings, which lie in parallel plains, and are connected by eight radial beams. From the eight outer corners of the lower ring (or from the eight interradial meshes, between the eight perradial beams) start eight basal centrifugal spines. (This species is similar to _Distephanus speculum_, but has eight beams instead of six. In single pieces the number of the beams and meshes varies between seven and nine, the constant number being eight.) A seven-rayed variety is _Dictyocha septenaria_ (_loc. cit._), a nine-rayed _Dictyocha polyactis_.

_Dimensions._--Diameter of the basal ring 0.02 to 0.03, of the apical ring 0.01 to 0.015.

_Habitat._--Fossil in Tertiary rocks (Tripel and Marne from Caltanisetta, Sicily; Oran, Africa); living in the depths of the Atlantic, Station 348, and Pacific, Station 270, &c.

{1567}12. _Distephanus octogonius_, n. sp.

_Dictyocha septenaria_, Ehrenberg, 1854, Mikrogeol., Taf. xxxvA., Nr. xxi. fig. 8.

Each pileated piece of the skeleton is a truncated eight-sided pyramid, like that of _Distephanus octonarius_, but differs from it by having eight short erect teeth, which arise from the corners of the upper smaller ring and lie in the same perradial plains as the eight horizontal spines starting from the corners of the lower larger ring. Ehrenberg has figured only an individual abnormality with seven beams instead of eight, taken from the Antarctic ice; but I found the same form frequent in deep-sea soundings from the Antarctic, almost constantly with eight beams, isolated hats with six, seven, or nine beams being intermingled.

_Dimensions._--Diameter of the basal ring 0.02, of the apical ring 0.012.

_Habitat._--Antarctic Ocean; in smolten "Pancake-Ice," taken by Sir James Clark Ross in lat. 78° 10' S., long. 162° W. (Ehrenberg); Station 156, depth 1975 fathoms.

13. _Distephanus diadema_, n. sp.

_Dictyocha diadema_, Haeckel, 1881, Prodromus.

Each pileated piece of the skeleton is an eight-sided pyramid, like that of the two foregoing species, but differing in the number and distribution of the teeth or spines, which are thirty-two. From the eight corners of the basal ring start eight long, nearly horizontal perradial spines, which bear on each side a smaller, nearly vertically descending spine. From the eight corners of the upper ring ascend also eight perradial spines, alternating with the eight interradial beams, which connect the two rings.

_Dimensions._--Diameter of the basal ring 0.04, of the apical ring 0.02.

_Habitat._--South Pacific, Station 293, depth 2025 fathoms.

Genus 664. _Cannopilus_,[282] n. gen.

_Definition._--#Cannorrhaphida# with a skeleton composed of pileated pieces, each of which is a small truncated pyramid with two girdles of meshes (the apical ring being fenestrated).

The genus _Cannopilus_ represents the most highly developed form of Dictyochida. Each piece of the skeleton is a little fenestrated hat or topped pyramid, as in _Distephanus_. But the apical mesh is simple in the latter, in the former it is divided into several meshes by bars which start in a centripetal direction from the upper ring. Therefore we find two annular rows of meshes, one above the other; an apical or upper row of smaller meshes and a basal or lower row of larger meshes. In the apex of the little {1568}hat is either a central mesh or an apical spine. Other spines arise from the basal ring, as in the former genera. The number of corner-spines on the basal ring is either four, six, or eight (in individual abnormalities also five or seven).

1. _Cannopilus superstructus_, Haeckel.

_Dictyocha superstructa_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 80; Mikrogeol., Taf. xxii. fig. 45.

Each pileated piece of the skeleton is a reticulated four-sided pyramid. The base of it (or the lower ring) is a square, from the four perradial corners of which start four centrifugal horizontal spines. In the centres of the four basal bars (or the sides of the square) arise four interradial beams, which unite in the second (or upper) square ring. This latter forms a second (but much smaller) four-sided pyramid, the apex of which is truncated. Therefore the little hat bears nine meshes; around the large central opening four upper smaller and four lower larger quadrangular meshes.

_Dimensions._--Diameter of the basal ring 0.03, of the apical ring 0.01.

_Habitat._--Fossil in Tertiary rocks of Sicily (Caltanisetta).

2. _Cannopilus diplostaurus_, n. sp. (Pl. 114, fig. 10).

Each pileated piece of the skeleton is a truncated quadrangular pyramid. From the corners of the square basal ring start four perradial, nearly horizontal, spines. Between these arise four interradial beams, which are united above by an upper square ring. This latter is divided into four small square meshes by a regular cross of perradial bars, the distal ends of which are prolonged into four short ascending spines. In the centre of the cross arises a vertical apical spine.

_Dimensions._--Diameter of the basal ring 0.04, of the apical ring 0.016.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

3. _Cannopilus calyptra_, Haeckel.

_Dictyocha heptacanthus_, Ehrenberg, 1840, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 208; Mikrogeol., 1854, Taf. xix. fig. 39 (?).

Each pileated piece of the skeleton is a truncated six-sided pyramid, like that of _Dictyocha speculum_, but distinguished by the reticulation of the upper (smaller) ring, which is divided by six beams into six meshes, lying in the horizontal plane of the upper ring. Six peripheral spines on the corners of the lower ring. (The irregular form, figured by Ehrenberg as _Dictyocha heptacanthus_, _loc. cit._, is probably only an individual abnormality with seven peripheral spines, instead of six; similar abnormalities occur also among the regular hexagonal forms which I found in the Tertiary rocks of Caltanisetta (Sicily).

_Dimensions._--Diameter of the basal ring 0.05, of the apical ring 0.02.

_Habitat._--Fossil in Tertiary deposits of Greece and Sicily.

{1569}4. _Cannopilus hemisphæricus_ (Haeckel).

_Dictyocha hemisphærica_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 266.

Each pileated piece of the skeleton is nearly hemispherical, with thirteen meshes; six lower and larger meshes in the sides of the truncated six-sided pyramid, seven others in the convex surface of the upper ring (one central with six surrounding it). From the six corners of the lower ring arise six horizontal perradial spines. From the inside of the same ring (probably on the side of the six ascending interradial beams) spring six centripetal teeth.

_Dimensions._--Diameter of the basal ring 0.02, of the apical ring 0.01.

_Habitat._--North Atlantic; Bermuda (Bailey).

5. _Cannopilus cyrtoides_, n. sp. (Pl. 114, figs. 11, 12).

_Dictyocha cyrtoides_, Haeckel, 1881, Prodromus.

Each pileated piece of the skeleton is an eight-sided truncated pyramid, or nearly hemispherical. From the basal ring arise twenty-four thorns or teeth, eight longer perradial centrifugal teeth placed almost horizontally, and between these sixteen shorter adradial teeth, directed downwards and somewhat centripetally. The network of the small hat is composed of seventeen meshes, arranged in two rows. The eight lower meshes are hexagonal, separated by six interradial ascending beams, and twice as large as the eight upper pentagonal meshes, which are separated by eight perradial beams, and enclose an apical central mesh.

_Dimensions._--Diameter of the basal ring 0.04, of the apical ring 0.005.

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

Family LXXIII. #AULACANTHIDA#, Haeckel (Pls. 102-105).

_Aulacanthida_, Haeckel, 1862, Monogr. d. Radiol., p. 262.

_Definition._--PHÆODARIA with an incomplete skeleton, composed of numerous hollow radial tubes, which pierce the spherical calymma and touch with their proximal ends the surface of the tripylean central capsule.

The family #Aulacanthida# represents a large and interesting group of PHÆODARIA, differing from all other families of this legion in the possession of numerous large radial tubes, which pierce the gelatinous and alveolated calymma in a radial direction, and come in contact with the outer surface of the central capsule by their inner or proximal ends, whilst their outer or distal ends project over the surface of the spherical calymma, and develop a great variety of manifold branches and terminal appendages. Usually (with the exception of a single genus only) the surface of the calymma is covered by an {1570}arachnoidal veil or mantle, composed of thousands of very fine, hollow, tangential needles. The skeleton therefore is incomplete, without any direct connection between the isolated pieces, just as in the preceding Cannorrhaphida, but the latter never possess the large, hollow, cylindrical, radial tubes, which are characteristic of all Aulacanthida.

The spherical body of the Aulacanthida has usually a diameter of 1 to 2 mm., and including the radial tubes, of 4 to 5 mm. or more. Some species are very common and cosmopolitan, and some genera contain numerous species, distributed widely over all oceans. In spite of their considerable size and wide distribution, only one species of this great family has been hitherto known, having been discovered by me at Messina in 1859, and described in my Monograph as _Aulacantha scolymantha_ (1862, p. 263, Taf. ii. figs. 1, 2, and Taf. iv. figs. 1-5). I there founded for it the peculiar subfamily Aulacanthida, and annexed it to the Thalassicollida. The same cosmopolitan species has been subsequently observed at Messina by R. Hertwig, who first recognised the three openings in its central capsule, and therefore united it with his TRIPYLEA (Organism. d. Radiol., 1879, p. 88, Taf. ix. figs. 3, 4; Taf. x. figs. 7, 10). The rich collection of the Challenger has added an astonishing number of new and interesting forms of Aulacanthida, so that I can describe here not less than six genera and fifty-eight species. The majority are inhabitants of the colder parts of the South Pacific and South Atlantic, at great depths, whilst a few species only are found in the tropics.

The structure of the body in all Aulacanthida seems to be similar in all important points, and the differences by which we are enabled to separate this great number of species are mainly produced by differences in the development of the radial tubes, their form and their polymorphous apophyses. The entire body represents a rather firm jelly-sphere of 1 to 2 mm. diameter (rarely less or more); the peripheral layer of the spherical calymma is rather clear and transparent, whilst its central part is dark and opaque, containing the big phæodium and the enclosed central capsule. The diameter of the latter is usually between 0.1 and 0.3, often 0.4 to 0.5, or even more. The gelatinous calymma, in the centre of which the capsule is placed, always contains numerous, large, spherical or roundish alveoles, similar to those of _Thalassicolla_, and between them a delicate network of sarcode (Pl. 102, fig. 1; Pl. 103, fig. 1; Pl. 104, fig. 1).

The spherical surface of the calymma is nearly always protected by that characteristic arachnoidal veil or mantle, which is composed of thousands of very fine tangential needles, densely interwoven in all tangential directions but never directly connected. They are wanting in a single genus only, in _Aulactinium_ (Pl. 101, figs. 6-8). This genus, therefore, may represent a separate subfamily, the Aulactinida, whilst all other genera protected by that mantle constitute the subfamily Aulographida. The tangential needles always seem to have the same shape as I have accurately described, in 1862, of _Aulacantha scolymantha_. They are constantly smooth, very thin and fragile, but also very elastic cylinders of silica, of equal breadth throughout their whole length, and seem {1571}to be open at both ends, since they are easily and constantly filled by air when dried. Their length is usually between 0.2 and 0.3 mm., rarely less than 0.15 or more than 0.5; their diameter is always less than 0.001, usually less than 0.0005.

The large radial tubes of the Aulacanthida constitute the most characteristic structures of this family, and are always so placed that their inner or proximal ends are in loose contact with the outer surface of their central capsule (upon which they rest), whilst their outer or distal ends are more or less prominent over the spherical surface of the calymma. Their position, therefore, is rather loose and movable, since they are fixed only by the consistence of the jelly of the surrounding calymma, and on the surface of the latter by the covering veil or the mantle of tangential needles (compare Pl. 102, fig. 1; Pl. 103, fig. 1; Pl. 104, fig. 1). Their number seems never to be fixed, and is probably very variable in different species. I found, in 1859, in the common _Aulacantha scolymantha_, the number varying from thirty to one hundred and fifty (_loc. cit._, p. 264). So also in _Aulographis pandora_, _Aulospathis variabilis_, and some other common species, numerous specimens of which I could compare, I found their number very variable, being in one and the same species sometimes only from ten to twenty, at other times from fifty to eighty, and sometimes even from one hundred to one hundred and fifty or more. Perhaps the number increases with the age and the increasing size of the calymma.

The radial tubes are always cylindrical (circular in transverse section), never angular or prismatic. Usually they are straight, more rarely slightly curved (Pl. 105, figs. 1, 2; Pl. 101, fig. 6). The cylinders are usually more or less tapering towards both ends, sometimes even spindle-shaped; the inner or proximal end is always simple and rounded, often slightly swollen or inflated, and ovate; the outer or distal end is often thickened, club-shaped, and exhibits the greatest variety in form and ramification. The length of the radial tubes is usually from 1 to 3 mm., rarely less than 0.8, or more than 3.2; their diameter is usually between 0.02 and 0.03, rarely less than 0.01 or more than 0.05. The smallest radial tubes are found in _Aulactinium_, the largest in _Aulospathis_.

The siliceous wall of the cylindrical radial tubes is usually very thin, fragile, and perfectly structureless. Only in a few species, mainly of _Aulographis_, does the wall become very thick and composed of concentric cylindrical layers (Pl. 105, figs. 6-11). Their cavity is wide and simple, and filled up by jelly (not by sarcode, as I supposed in my first description). The simple cavity of the tubes, though not smaller than in the radial tubes of the Aulosphærida, Circoporida and Tuscarorida, never contains the characteristic axial filament with its branches, which is constantly found in the latter families. According to the description of R. Hertwig, the tubes are perfectly closed and have no opening. I suppose, however, that a small opening always exists in the centre of the rounded base, and perhaps a second on the distal apex. Otherwise the circumstance that the entire and well-preserved tubes become easily and constantly filled {1572}up by air, when purified by hot mineral acids and afterwards dried, cannot be explained. I suppose that the jelly contained in the cavity of the tubes remains in constant connection by these openings with the jelly of the surrounding calymma.

The distal ends of the radial tubes exhibit in the Aulacanthida the greatest variety in the production of different branches and capturing apparatus, and this serves for the distinction of the genera and subgenera here described. In two genera only (in _Aulactinium_ Pl. 101, figs. 6-8; and in _Aulacantha_, Pl. 105, fig. 16), the distal ends are simple, not branched. In the four other genera they are armed with terminal branches, which are usually arranged in elegant verticils. The greatest variety in the formation of these verticils is developed in _Aulographis_ (Pl. 103). The single branches of the terminal verticils are here simple, whilst in the closely allied _Auloceros_ they are forked or elegantly ramified (Pl. 102). _Aulospathis_, the biggest of all Aulacanthida, is distinguished by the possession of a verticil of lateral branches, placed beyond the terminal verticil, immediately above the veil of tangential needles (Pl. 104). _Aulodendron_, finally, possesses lateral and terminal branches, which are irregularly scattered.

The branches of the radial tubes are rarely straight, usually more or less curved, either simple or again ramified. Their surface is either smooth or armed with small spines or recurved teeth, often elegantly dentated or serrated (Pl. 103, figs. 20-27; Pl. 105, figs. 7-13). Their distal ends are either simply pointed or armed with a spathilla, or a small crown of verticillate, usually recurved teeth (Pl. 104, figs. 4-17). The variety and elegance of these minute armatures are very interesting, the more so as they occur in very similar and analogous forms among the Aulosphærida, the Coelographida, and other PHÆODARIA.

The _central capsule_ of the Aulosphærida and its large nucleus ("Binnenbläschen"), as well as the surrounding alveolate calymma ("Alveolen-Hülle"), and the enclosed dark phæodium ("dunkels Pigment") were first described in my Monograph (1862, _loc. cit._, p. 362). Their minute structure has been examined afterwards very accurately by R. Hertwig (1879, _loc. cit._, p. 95). The numerous well-preserved preparations of the Challenger (stained with carmine and preserved in glycerine) which I could examine, confirmed in all respects the detailed description of Hertwig (compare Pl. 102, fig. 1; Pl. 103, fig. 1; Pl. 104, fig. 1).

The spherical or subspherical central capsule is usually slightly depressed in the shortened main axis. Its diameter is usually between 0.1 and 0.3, rarely less than 0.08 or more than 0.4 mm. Its outer membrane (_e_) is thick and double-contoured, separated by a clear interval from the very thin but firm inner membrane (_i_). The large astropyle, or the main-opening on the oral pole of the main axis, is closed by a large, convex, radiate operculum (_o_), from which arises a short tubular proboscis. On both sides of the opposite aboral pole (to the right and left) are two conical parapylæ or secondary openings (_u, u_). The space between the inner membrane of the capsule and {1573}the nucleus is filled up by protoplasm, containing numerous spherical vacuoles of equal size (_v_); each vacuole encloses a small, dark, fat-granule. The large nucleus (_n_) is either spherical or lenticular, and more or less depressed in the main axis; its diameter is usually about half as great as that of the enclosing capsule, 0.05 to 0.15, rarely less or more; it contains, enclosed in a clear mass, numerous dark, roundish or oblongish nucleoli (_l_).

Numerous preparations of Aulacanthida exhibited a central capsule with two nuclei (Pl. 101, fig. 6), or a calymma with two central capsules (Pl. 104, figs. 1, 3); so that the process of propagation by self-division, observed already in many different PHÆODARIA, seems to happen very frequently in the Aulacanthida. The voluminous phæodium is usually about twice or three times as large as the central capsule, and covers its oral or anterior half; the colour of the roundish phæodella composing it is sometimes more green or brown, at other times more blackish. The roundish alveoles, which fill up the rather firm jelly of the calymma, exhibit nearly the same shape as in the common _Thalassicolla nucleata_. The surface of the calymma is usually protected by the dense veil of tangential needles, and often forms conical or tent-shaped elevations around the bases of the piercing radial tubes (Pl. 102, fig. 1).

_Synopsis of the Genera of Aulacanthida._

{ Surface of the calymma { naked, without tangential { needles, 665. _Aulactinium_. Radial tubes simple, { without lateral and { Surface of the calymma terminal branches. { covered by a veil of { tangential needles, 666. _Aulacantha_.

Radial tubes without { Terminal branches simple, 667. _Aulographis_. lateral branches, but { with a verticil of { Terminal branches forked terminal branches. { or again ramified, 668. _Auloceros_.

{ Lateral branches Radial tubes with { verticillate, 669. _Aulospathis_. lateral and with { terminal branches. { Lateral branches { irregularly scattered, { not verticillate, 670. _Aulodendron_.

Subfamily 1. AULACTINIDA, Haeckel.

_Definition._--#Aulacanthida# without external veil of tangential needles on the surface of the calymma.

Genus 665. _Aulactinium_,[283] n. gen.

_Definition._--#Aulacanthida# without a veil of tangential needles, with simple radial tubes, which bear neither lateral nor terminal branches.

{1574}The genus _Aulactinium_ differs from all the other Aulacanthida in the complete absence of the characteristic fine tangential needles, which constitute in the latter an arachnoidal veil or mantle around the spherical calymma. We accordingly divide the whole family into two subfamilies, the Aulactinida with a naked calymma, and the Aulographida with a veil of tangential needles. The radial tubes possess in the few species of _Aulactinium_ observed a very simple shape, as in the closely allied _Aulacantha_.

1. _Aulactinium actinastrum_, n. sp. (Pl. 101, figs. 6, 7).

Radial tubes slenderly spindle-shaped, slightly curved, gradually tapering from the middle towards both ends. The proximal two-thirds of the tubes enclosed in the calymma are smooth; the distal freely prominent third is armed with six to eight equidistant verticils of small conical teeth (ten to fifteen in each verticil).

_Dimensions._--Length of the tubes 0.5 to 1.5, breadth 0.02.

_Habitat._--South Pacific, Station 289, depth 2550 fathoms.

2. _Aulactinium actinelium_, n. sp. (Pl. 101, fig. 8).

Radial tubes cylindrical, straight, slightly tapering towards both ends. Proximal two-thirds smooth, the distal third studded with numerous small recurved thorns.

_Dimensions._--Length of the tubes 0.6 to 0.9, breadth 0.02.

_Habitat._--South Pacific, Station 293, depth 2025 fathoms.

3. _Aulactinium actinosphærium_, n. sp.

Radial tubes cylindrical, straight, smooth, of nearly equal breadth throughout their whole length, without thorns and spathillæ, pointed at both ends.

_Dimensions._--Length of the tubes 1.6 to 2.2, breadth 0.02 to 0.03.

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

Subfamily 2. AULOGRAPHIDA, Haeckel.

_Definition._--#Aulacanthida# with an external veil of interwoven, very numerous and thin, hollow, tangential needles, entirely covering the surface of the calymma.

Genus 666. _Aulacantha_,[284] Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 799.

_Definition._--#Aulacanthida# with a veil of tangential needles, and with simple radial tubes, which bear neither lateral nor terminal branches.

{1575}The genus _Aulacantha_, hitherto the only representative of this family, was founded by me in 1860 for the cosmopolitan _Aulacantha scolymantha_, the most common and most widely distributed of all the members of the family. It is the simplest form of the Aulographida, or of those Aulacanthida in which the spherical surface of the calymma is densely covered with interwoven tangential needles. The large radial tubes of _Aulacantha_ possess a very simple shape, as in the preceding _Aulactinium_, and have neither lateral nor terminal branches.

1. _Aulacantha scolymantha_, Haeckel.

_Aulacantha scolymantha_, Haeckel, 1862, Monogr. d. Radiol., p. 263, Taf. ii. figs. 1, 2, Taf. iv. figs. 1-5.

_Aulacantha scolymantha_, R. Hertwig, 1879, Organism. d. Radiol., p. 88, Taf. ix. fig. 3, Taf. x. figs. 7-10.

Radial tubes cylindrical, straight, of nearly equal breadth throughout their whole length, somewhat inflated on the proximal basal end, smooth throughout the greater part of their length, but in the distal third dentate, with numerous (ten to forty) small pointed teeth, which are curved outwards, and shorter than the thickness of the tube.

_Dimensions._--Length of the tubes 0.5 to 2.0, breadth 0.01 to 0.02.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific; at many Stations; surface and at various depths; the most common of all Aulacanthida.

2. _Aulacantha tubulosa_, n. sp.

Radial tubes cylindrical or nearly spindle-shaped, straight, gradually tapering towards the two pointed ends, twice as broad in the middle third as in the outer and inner third, smooth in the inner half, dentate in the outer half, with very numerous (one hundred to two hundred) short conical teeth, which are scarcely one-fourth as large as the greatest breadth of the tube.

_Dimensions._--Length of the tubes 0.4 to 0.5, breadth in the middle part 0.02 to 0.03.

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

3. _Aulacantha spinosa_, n. sp. (Pl. 105, fig. 4).

Radial tubes cylindrical, straight, of equal breadth throughout their whole length, rounded on the proximal base, smooth in the inner proximal half, dentate or spinescent in the outer distal half, with numerous (fifty to eighty) slender conical teeth, which are curved forwards, increasing in size towards the distal end, and somewhat longer than the breadth of the tube.

_Dimensions._--Length of the tubes 0.8 to 1.2, breadth 0.015 to 0.02.

_Habitat._--North Pacific, Stations 241 to 253, surface.

{1576}4. _Aulacantha cannulata_, n. sp. (Pl. 105, fig. 16).

Radial tubes cylindrical in the inner proximal half, prismatic in the outer distal half, with from three to six, usually four, prominent, thick, parallel edges, which are dentate towards the thicker distal end; their teeth short, conical, directed outwards, scarcely one-fourth as long as the thickness of the tube. The edges are separated in the distal third by more or less deep furrows, like a channelled column.

_Dimensions._--Length of the tubes 1.2 to 2.5, breadth 0.03 to 0.04.

_Habitat._--South Pacific, Stations 291 to 293, surface.

5. _Aulacantha clavata_, n. sp.

Radial tubes more or less irregularly curved, in the inner proximal half slenderly conical, and gradually tapering towards the inflated base, in the outer distal half club-shaped, armed with a few (five to twenty) short conical teeth.

_Dimensions._--Length of the tubes 1.0 to 1.2, breadth in the middle pact 0.01, in the distal part 0.04.

_Habitat._--South Atlantic, Station 318, depth 2040 fathoms.

6. _Aulacantha lævissima_, n. sp.

Radial tubes cylindrical, straight, of nearly equal breadth throughout their whole length; the inner proximal end rounded, the outer distal end pointed. Surface of the tubes perfectly smooth, without any teeth. The thickness and length of the simple spicula, as well as the thickness of their wall, are very variable in this species.

_Dimensions._--Length of the tubes 0.5 to 4.2, breadth 0.003 to 0.02.

_Habitat._--North Atlantic, Station 253, Færöe Channel, surface, John Murray.

Genus 667. _Aulographis_,[285] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 5.

_Definition._--#Aulacanthida# with a veil of tangential needles, and with radial tubes, which bear no lateral branches, but at the distal end a verticil of simple terminal branches.

The genus _Aulographis_, the richest in the number of species among all Aulacanthida, differs from the preceding _Aulacantha_, its ancestral form, in the development of simple terminal branches, which form either a fork or a verticil. The branches are either smooth or spiny, but not ramified as in the following genus, _Auloceros_. Their distal {1577}ends are either simply pointed or bear a terminal spathilla, or a little crown of recurved teeth. According to these differences we may dispose the twenty-six species described into four subgenera.

Subgenus 1. _Aulographantha_, Haeckel.

_Definition._--Terminal branches of the radial tubes simple, smooth, without lateral teeth and terminal spathillæ. Tubes usually thin and fragile.

1. _Aulographis pandora_, n. sp. (Pl. 103, figs. 2-9).

Radial tubes cylindrical, slender, straight or slightly curved, of equal breadth. Terminal branches of the tubes very variable in size and number (two to six, usually three or four), without lateral teeth and terminal spathillæ, slender, conical, slightly curved, directed outwards, twice to four times (rarely five to eight times) as long as the breadth of the tubes. This species is extraordinarily variable in the number and size of the simple terminal branches; the eight tubes, shown in figs. 2 to 9, are all found in one and the same specimen.

_Dimensions._--Length of the tubes 0.5 to 1.5, breadth 0.01 to 0.03; branches 0.02 to 0.12.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific; surface and in various depths.

2. _Aulographis bovicornis_, n. sp. (Pl. 103, figs. 12-14).

Radial tubes cylindrical, slender, straight, of equal breadth. Terminal branches usually two (rarely three), smooth, without lateral teeth and terminal spathillæ, eight to ten times as long as the breadth of the tube, pointed, S-shaped, or curved like the horns of an ox.

_Dimensions._--Length of the tubes 0.6 to 0.8, breadth 0.015 to 0.02; branches 0.1 to 0.2.

_Habitat._--South Atlantic (east of Buenos Ayres), Stations 323 to 325, surface.

3. _Aulographis taumorpha_, n. sp. (Pl. 103, fig. 16).

Radial tubes cylindrical, slender, straight, gradually tapering towards the pointed proximal end. Terminal branches constantly two, opposite in a tangential, slightly concave or nearly straight line, ten to twelve times as long as the breadth of the tube, smooth, straight in the proximal part, recurved in the distal part.

_Dimensions._--Length of the tubes 0.7 to 0.8, breadth 0.01 to 0.015; branches 0.1 to 0.15.

_Habitat._--North Pacific, Station 231, depth 2250 fathoms.

{1578}4. _Aulographis triglochin_, n. sp. (Pl. 103, fig. 17).

Radial tubes robust, club-shaped at the distal end. Terminal branches three (rarely two or four), widely divergent, geniculated and recurved, smooth, without lateral teeth and terminal spathillæ.

_Dimensions._--Length of the tubes 1.2 to 1.8, breadth 0.02; branches 0.12 to 0.15.

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

5. _Aulographis cruciata_, n. sp. (Pl. 103, fig. 25).

Radial tubes slender, cylindrical, of equal breadth. Terminal branches almost constantly four, equal, regularly crossed (very rarely three or five), slender, straight or slightly curved, smooth, divergent outwards, six to eight times as long as the breadth of the tube.

_Dimensions._--Length of the tubes 1.0 to 1.5, breadth 0.02; branches 0.12 to 0.15.

_Habitat._--South Atlantic, Stations 325 to 332, surface.

6. _Aulographis ancorata_, n. sp. (Pl. 103, fig. 21).

Radial tubes slender, cylindrical, straight. Terminal branches constantly four, equal, regularly crossed, arcuato-recurved or nearly semicircular, smooth, six to eight times as long as the breadth of the tube. Resembling an anchor with four teeth.

_Dimensions._--Length of the tubes 0.5 to 0.7, breadth 0.012 to 0.015; branches 0.07 to 0.09.

_Habitat._--South-west Atlantic, Station 318, depth 2040 fathoms.

7. _Aulographis stellata_, n. sp. (Pl. 103, figs. 23, _a_-_c_).

Radial tubes club-shaped, gradually thickened towards the distal end. Terminal branches stellate, numerous (five to ten or more), diverging in all directions, smooth, straight or slightly curved, slenderly conical, three to five times as long as the distal breadth of the tube. The branches are very variable in size, sometimes very small (figs. _a_, _b_).

_Dimensions._--Length of the tubes 0.4 to 0.8, breadth 0.02; branches 0.01 to 0.02.

_Habitat._--Indian Ocean, Madagascar (Rabbe), surface.

8. _Aulographis penicillata_, n. sp.

Radial tubes slender, cylindrical, of equal breadth. Terminal branches pencil-shaped, smooth, very numerous (twenty to thirty or more), diverging outwards, curved, eight to ten times as long as the breadth of the tube, very thin and fragile, resembling a brush.

_Dimensions._--Length of the tubes 1.0 to 1.5, breadth 0.02; branches 0.15 to 0.2.

_Habitat._--North Atlantic (Antilles), Weber, surface.

{1579}9. _Aulographis pistillum_, n. sp. (Pl. 105, fig. 6).

Radial tubes club-shaped, robust, straight, gradually thickened towards the distal end. Terminal branches eight to ten (usually nine), conical, smooth, slightly curved, divergent outwards like a regular corona.

_Dimensions._--Length of the tubes 0.5 to 0.6, distal breadth 0.04; branches 0.08.

_Habitat._--North Atlantic, Station 354, depth 1675 fathoms.

Subgenus 2. _Aulographella_, Haeckel.

_Definition._--Terminal branches of the radial tubes without terminal spathillæ, but with lateral teeth or secondary spines. (Tubes usually very stout and robust, club-shaped.)

10. _Aulographis triæna_, n. sp. (Pl. 105, fig. 8).

Radial tubes club-shaped, straight, tapering gradually towards the rounded proximal end. Terminal branches constantly three, divergent, very stout, eight to ten times as long as the breadth of the tube, each studded with three to six irregular, conical, secondary spines. Sometimes the branches become forked, the species passing over into _Auloceros cervinus_.

_Dimensions._--Length of the tubes 1.2 to 1.5, breadth 0.004 to 0.06; branches 0.3 to 0.5.

_Habitat._--South Pacific, Station 299, depth 2160 fathoms.

11. _Aulographis martagon_, n. sp. (Pl. 105, fig. 7).

Radial tubes club-shaped or slenderly conical, strongly thickened towards the distal end. Terminal branches six to nine, conical, slightly curved, divergent outwards, studded outside with small, conical, secondary spines, twice to three times as long as the breadth of the tube.

_Dimensions._--Length of the tubes 1.0 to 1.2, breadth 0.04 to 0.05; branches 0.1 to 0.15.

_Habitat._--South Atlantic, Station 318, depth 2040 fathoms.

12. _Aulographis flammabunda_, n. sp. (Pl. 105, fig. 9).

Radial tubes club-shaped, more or less curved, with thickened distal ends. Terminal branches three to six, conical, very stout, three to four times as long as the breadth of the tube, densely studded with numerous, crowded, conical, secondary spines, which are very irregular and more or less curved, resembling the flames of a fire.

_Dimensions._--Length of the tubes 1.0 to 1.2, distal breadth 0.08 to 0.1; branches 0.2 to 0.4.

_Habitat._--South Pacific, Station 302, depth 1450 fathoms.

{1580}13. _Aulographis gemmascens_, n. sp. (Pl. 105, fig. 11).

Radial tubes club-shaped, more or less curved, with thickened distal end. Terminal branches three to nine (usually three larger and six smaller) stout, conical, studded with irregular, straight, conical, secondary spines, crowded and densely aggregated, like the leaves in a bud.

_Dimensions._--Length of the spines 1.5 to 1.8, distal breadth 0.07 to 0.1; branches 0.2 to 0.6.

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

14. _Aulographis flosculus_, n. sp. (Pl. 105, fig. 10).

Radial tubes club-shaped, straight, tapering gradually towards the rounded proximal end. Terminal branches nine to twelve, stout, conical, twice to three times as long as the breadth of the tube, studded with irregular secondary spines, connected in the proximal half by a solid, cap-shaped, flinty lamella, so that the terminal corona resembles a flower. The hollow canal of the tube sends a thin branch into each branch of the crown.

_Dimensions._--Length of the tubes 1.2 to 1.8, distal breadth 0.04 to 0.05; branches 0.1 to 0.2.

_Habitat._--North Atlantic, Færöe Channel (Gulf Stream), John Murray, depth 600 fathoms.

Subgenus 3. _Aulographidium_, Haeckel.

_Definition._--Terminal branches of the radial tubes armed with terminal spathillæ (or whorls of small radial teeth), but without lateral denticles or spines.

15. _Aulographis furcula_, n. sp. (Pl. 103, figs. 10, 11).

Radial tubes cylindrical, slender, slightly curved. Terminal branches usually two, sometimes on single tubes three, eight to ten times as long as the tube is broad, strongly curved, ascending vertically from a horizontal base, with a terminal spathilla of four crossed teeth at the distal end.

_Dimensions._--Length of the tubes 0.6 to 0.8, breadth 0.006 to 0.008; branches 0.06 to 0.08.

_Habitat._--North-west Pacific (off Japan), Station 231, depth 2250 fathoms.

16. _Aulographis triangulum_, n. sp. (Pl. 103, fig. 15).

Radial tubes cylindrical, slender, straight. Terminal branches constantly three, slender, slightly curved, nearly horizontally (tangentially) expanded, eight to ten times as long as the tube is broad, with a terminal spathilla of four recurved teeth which are opposite in pairs. Since the angles between the three branches are equal (= 120°) they correspond to the axes of an equilateral triangle.

_Dimensions._--Length of the tubes 1.2, breadth 0.015 to 0.02; branches 0.1 to 0.12.

_Habitat._--South Pacific, Station 289, depth 2550 fathoms.

{1581}17. _Aulographis tetrancistra_, n. sp. (Pl. 103, fig. 22).

Radial tubes slender, cylindrical, straight. Terminal branches four to six (usually four), eight to ten times as long as the tube is broad, slightly curved and widely divergent, with a terminal spathilla of four crossed recurved teeth.

_Dimensions._--Length of the tubes 0.5 to 0.7, breadth 0.01; branches 0.08 to 0.1.

_Habitat._--South Pacific, Station 285, depth 2375 fathoms.

18. _Aulographis hexancistra_, n. sp. (Pl. 103, figs. 18, 19).

Radial tubes club-shaped, slightly curved, gradually thickened from the proximal to the distal end. Terminal branches four to eight (usually six in the majority of tubes), widely divergent, nearly straight, three to four times as long as the tube is broad, with a terminal spathilla of six (rarely five) recurved teeth.

_Dimensions._--Length of the tubes 0.4 to 0.6, breadth 0.01 to 0.02; branches 0.04 to 0.08.

_Habitat._--North Pacific, Stations 244 to 253, depth 2050 to 3125 fathoms.

19. _Aulographis polyancistra_, n. sp.

Radial tubes club-shaped, straight, thickened towards the distal end. Terminal branches ten to twenty, smooth, strongly curved, disposed in a corona, six to eight times as long as the tube is broad, each with a terminal spathilla of eight to twelve radial teeth.

_Dimensions._--Length of the tubes 0.6 to 0.8, distal breadth 0.02; branches 0.12 to 0.16.

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

20. _Aulographis asteriscus_, n. sp. (Pl. 103, fig. 24).

Radial tubes slender, cylindrical, straight, equally broad. Terminal branches six to nine, widely divergent, disposed in a radiate corona, around a central branch, which is the distal prolongation of the tube itself. Each branch bears a stellate terminal spathilla, composed of ten to twenty conical teeth, which radiate in all directions.

_Dimensions._--Length of the tubes 0.5 to 0.8, breadth 0.02; branches 0.06 to 0.09.

_Habitat._--South Atlantic, Station 318, depth 2040 fathoms.

Subgenus 4. _Aulographonium_, Haeckel.

_Definition._--Terminal branches of the radial tubes armed with numerous lateral denticles, and with terminal spathillæ (or whorls of small radial teeth).

{1582}21. _Aulographis dentata_, n. sp. (Pl. 103, fig. 20).

Radial tubes slender, cylindrical, equally broad, scarcely inflated at the distal end. Terminal branches six to eight, curved, disposed in a corona around a straight central branch, eight to ten times as long as the tube is broad, armed with numerous stout recurved lateral denticles and with a terminal spathilla of five or six recurved teeth.

_Dimensions._--Length of the tubes 1.5 to 2.5, breadth 0.03; branches 0.15 to 0.2 long.

_Habitat._--North Atlantic, Station 354, depth 1675 fathoms.

22. _Aulographis pulvinata_, n. sp. (Pl. 103, fig. 26).

Radial tubes club-shaped, straight, gradually thickened towards the distal end, which bears a broad, circular, biconvex cushion. The margin of this cushion bears two alternating verticils of radially divergent, straight, terminal branches, which are twice to three times as long as the tube is broad. Each branch is armed with two opposite lateral rows of numerous small denticles, and bears a terminal spathilla with six to eight recurved radial teeth.

_Dimensions._--Length of the tubes 2.0 to 2.4, distal breadth 0.03 to 0.07; branches 0.05 to 0.08 long.

_Habitat._--South-east Pacific (off Valparaiso), Station 298, depth 2225 fathoms.

23. _Aulographis tripentas_, n. sp. (Pl. 105, fig. 13, 13_a_).

Radial tubes club-shaped, straight, thickened towards the inflated distal end, which bears three alternating verticils of terminal branches, each with five radial branches. The ten branches of the inner and outer verticils are perradial, smooth; the alternating five branches of the middle verticil are armed with recurved lateral denticles. Each of the fifteen branches bears a terminal spathilla with five to seven recurved teeth.

_Dimensions._--Length of the spines 2.0 to 2.5, distal breadth 0.03 to 0.06; branches 0.1 long.

_Habitat._--South-east Pacific (off Juan Fernandez), Station 299, depth 2160 fathoms.

24. _Aulographis verticillata_, n. sp. (Pl. 105, fig. 12, 12_a_).

Radial tubes cylindrical, equally broad, with an inflated ellipsoidal knob at the distal end. This knob bears twenty to thirty slender, slightly curved, terminal branches, which are regularly arranged in five radial or meridional rows, and in four to six concentric verticils. The branches are five to ten times as long as the tube is broad, and armed with two opposite rows of lateral denticles, and with a terminal spathilla of six to eight recurved teeth.

_Dimensions._--Length of the tubes 1.5 to 1.8, breadth 0.01 to 0.02; branches 0.5 to 1.0 long.

_Habitat._--South Pacific, Station 293, depth 2025 fathoms.

25. _Aulographis serrulata_, n. sp. (Pl. 103, fig. 27).

Radial tubes club-shaped, curved, thickened towards the inflated ellipsoidal distal end, which bears a bunch of fifteen to twenty-five terminal branches, arranged more or less regularly in radial {1583}or meridional rows and concentric horizontal verticils. The branches are irregularly curved, twice to four times as long as the distal end of the tube, armed with two opposite rows of lateral denticles, and at the distal end with a spathilla of six radial teeth.

_Dimensions._--Length of the tubes 1.5 to 1.8, breadth 0.02 to 0.04; branches 0.1 to 0.15 long.

_Habitat._--North Pacific, Stations 253 and 254, depth 3025 to 3125 fathoms.

26. _Aulographis candelabrum_, n. sp. (Pl. 103, fig. 1).

Radial tubes club-shaped, straight, thickened towards the distal end and constricted beyond the ovate, inflated, terminal knob. This knob is similar to a candelabrum and bears a corona of six to nine strongly curved terminal branches, which are eight to ten times as long as the tube is broad, armed with scattered lateral denticles, and with a spathilla of five to seven radial teeth.

_Dimensions._--Length of the tubes 1.6 to 2.4, breadth 0.03 to 0.05; branches 0.2 to 0.3 long.

_Habitat._--South-east Pacific (off Juan Fernandez), Station 300, depth 1375 fathoms.

Genus 668. _Auloceros_,[286] n. gen.

_Definition._--#Aulacanthida# with a veil of tangential needles, and with radial tubes, which bear no lateral branches, but at the distal end a verticil of ramified or forked terminal branches.

The genus _Auloceros_ differs from the preceding closely allied _Aulographis_, its ancestral form, in the ramification of the verticillate terminal branches. They are either simply forked or again ramified, and their distal ends are either simply pointed or armed with a terminal spathilla, or a little crown of recurved teeth. Some forms of this genus belong to the most elegant and graceful PHÆODARIA, as the _Auloceros elegans_ figured, which I observed living in the Indian Ocean.

Subgenus 1. _Auloceræa_, Haeckel.

_Definition._--Distal ends of the terminal branches pointed, smooth, without spathilla (or corona of radiate denticles).

1. _Auloceros furcosus_, n. sp. (Pl. 102, figs. 2-6).

Radial tubes slender, spindle-shaped or nearly cylindrical, more or less tapering towards the two ends. Terminal branches slender, curved, twice to four times as long as the tube is broad, very variable in number (usually two or three, rarely four, five, or six; compare figs. 2-6), once or twice forked; the secondary branches are short, irregular, and pointed. No terminal spathillæ. {1584}In some specimens of this species all the tubes bear two or three terminal branches, whilst in others there are tubes with four, five, or six branches intermingled. When the number of the terminal branches is constant in single localities, this transformistic or "Darwinian" species may be divided into the following "subspecies:" (1) _Auloceros pandora_ (with variable numbers); (2) _Auloceros bifurca_ (fig. 2); (3) _Auloceros trifurca_ (fig. 3); (4) _Auloceros quadrifurca_ (fig. 4); (5) _Auloceros quinquefurca_ (fig. 5); (6) _Auloceros sexfurca_ (fig. 6).

_Dimensions._--Length of the tubes 1.5 to 2.5, breadth 0.02 to 0.03; branches 0.05 to 0.15 long.

_Habitat._--North Pacific, Stations 231 to 253, surface and at various depths.

2. _Auloceros trigeminus_, n. sp. (Pl. 102, fig. 7).

Radial tubes club-shaped, gradually thickened towards the inflated distal end. Terminal branches short, scarcely longer than the tube is broad, two constantly opposite, each with three equal, conical, short secondary branches. No terminal spathillæ.

_Dimensions._--Length of the tubes 0.6 to 0.8, breadth 0.02 to 0.03; branches 0.04 to 0.08.

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

3. _Auloceros capreolus_, n. sp. (Pl. 102, fig. 8).

Radial tubes cylindrical, equally broad. Terminal branches in two opposite clustered bunches, each with sixteen to eighteen unequal secondary branches. The total length and breadth of each cluster is about four times as great as the tube is broad. No terminal spathillæ.

_Dimensions._--Length of the tube 1.5 to 2.0, breadth 0.03; branches 0.07 to 0.1.

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

4. _Auloceros cervinus_, n. sp. (Pl. 102, figs. 9, 10).

Radial tubes slender, spindle-shaped, slightly curved, tapering gradually from the middle towards the two ends. Terminal branches constantly three, obliquely ascending, each twice or three times forked (often more or less irregularly), with slender, curved, secondary and tertiary branches (twenty to twenty-four on each tube); the latter are scarcely half as broad as the three main branches of each tube. No terminal spathillæ.

_Dimensions._--Length of the tubes 2.0 to 3.5, breadth 0.03 to 0.04; branches 0.12 to 0.15 long.

_Habitat._--South Atlantic, Station 325, depth 2650 fathoms.

5. _Auloceros elegans_, n. sp. (Pl. 102, fig. 1).

Radial tubes slender, cylindrical, straight, equally broad. Terminal branches two or three, more or less irregularly branched, each with twelve to eighteen curved and pointed secondary branches. No terminal spathillæ. Differs from the preceding _Auloceros cervinus_ in the cylindrical form of the thinner straight tubes, and the more irregular ramification; the branches are nearly {1585}tangentially expanded, The specimen figured, with expanded pseudopodia, red central capsule, and green phæodium, was observed living by me in 1882 in Ceylon.

_Dimensions._--length of the tubes 1.0 to 2.0, breadth 0.02 to 0.03; branches 0.15 to 0.3.

_Habitat._--Indian Ocean, Ceylon (south of Matura), Haeckel, surface.

Subgenus 2. _Auloceratium_, Haeckel.

_Definition._--Distal ends of the terminal branches with a spathilla, or a small corona of radial, usually recurved teeth.

6. _Auloceros dicranaster_, n. sp. (Pl. 105, figs. 14, 15).

Radial tubes cylindrical, straight, equally broad. Terminal branches tangential, forked, expanded horizontally, five to six times as long as the tube is broad; their number is usually five (more rarely four or six), and each is divided into two short, equal, divergent, secondary branches, armed at the distal end with a spathilla of five or six unequal recurved teeth.

_Dimensions._--Length of the tubes 1.0 to 1.5, breadth 0.01 to 0.02; branches 0.05 to 0.08.

_Habitat._--North Pacific, Stations 244 to 252, depth 2050 to 3050 fathoms.

7. _Auloceros spathillaster_, n. sp. (Pl. 102, fig. 12).

Radial tubes club-shaped or nearly cylindrical, straight, often thickened towards the distal end. Terminal branches ascending, three to six, usually four, partly simple, partly forked, slightly curved. The branches are from twice to three times as long as the tube is broad, and much thinner; at the distal end they are armed with a spathilla of five or six recurved teeth.

_Dimensions._--Length of the tubes 2.0 to 2.5, breadth 0.02 to 0.03; branches 0.08 to 0.12.

_Habitat._--South Atlantic, Station 319, depth 2425 fathoms.

8. _Auloceros arborescens_, n. sp, (Pl. 102, figs. 11, 13).

Radial tubes club-shaped, irregularly curved, thickened towards the distal end. Terminal branches two opposite (rarely three or four), forked near the base, and either dichotomously or more irregularly branched; each tube bears fifteen to thirty, usually twenty to twenty-four, secondary branches, which are irregularly curved, and armed at the distal end with a spathilla of four to eight recurved teeth. The tubes are more richly branched than in the preceding, smaller, closely allied species, and the branches are more flatly expanded.

_Dimensions._--Length of the tubes 2.6 to 3.3, breadth 0.03 to 0.04; branches 0.1 to 0.2.

_Habitat._--South Pacific, Stations 288 to 295, depth 1500 to 3000 fathoms.

{1586}Genus 669. _Aulospathis_,[287] n. gen.

_Definition._--#Aulacanthida# with a veil of tangential needles, and with radial tubes, which bear two verticils of branches, a distal verticil of terminal branches, and a proximal verticil of lateral branches.

The genus _Aulospathis_ and the following _Aulodendron_ differ from the preceding Aulacanthida in the possession of lateral branches; these are usually similar to the terminal branches, and irregularly scattered along the distal half of the tubes in _Aulodendron_. In _Aulospathis_, however, the largest form in the family, each tube bears two whorls or verticils only, a verticil of terminal branches at the distal end, and a verticil of lateral branches beyond the latter, between the middle and distal third of the tube. The number of branches in each verticil is usually from two to four, rarely more; it is, however, very variable, so that the ten species described in the sequel are "Darwinian species," derived either from _Aulospathis polymorpha_, or from _Aulospathis variabilis_. Each branch bears at the distal end a spathilla, the teeth of which are very variable in form, number and arrangement.

Subgenus 1. _Aulospathessa_, Haeckel.

_Definition._--Distal ends of the radial tubes inflated, usually in the form of an ovate or pyriform terminal knob.

1. _Aulospathis bifurca_, n. sp. (Pl. 104, figs. 1-5).

Radial tubes with an inflated ovate terminal knob at the distal end, which bears two divergent, curved, terminal branches (often a few tubes bear three or four branches instead of the usual two). Proximal whorl usually cruciate, with four irregularly crossed lateral branches (but often with five or six, more rarely with two or three).

_Dimensions._--Length of the tubes 0.15 to 25 mm., breadth 0.04 to 0.06; branches 0.1 to 0.15.

_Habitat._--South Pacific, Stations 293 to 295, depth 1500 to 2270 fathoms.

2. _Aulospathis trifurca_, n. sp. (Pl. 104, figs. 6, 7, 7_a_).

Radial tubes with an inflated ovate terminal knob at the distal end, which bears three divergent, straight, or slightly curved terminal branches (often a few tubes bear two or four branches instead of the usual three). Proximal whorl irregular, usually with six divergent, straight, lateral branches.

_Dimensions._--Length of the tubes 2.2 to 3.4, breadth 0.03 to 0.05; branches 0.1 to 0.15.

_Habitat._--South Pacific (off Valparaiso), Stations 298 to 300, depth 1375 to 2225 fathoms.

{1587}3. _Aulospathis quadrifurca_, n. sp.

Radial tubes with an inflated ovate terminal knob at the distal end, which bears four crossed, divergent, curved terminal branches. Proximal whorl also rather regular, with a cross of four straight lateral branches.

_Dimensions._--Length of the tubes 3.0 to 4.0, breadth 0.04 to 0.08; branches 0.2 to 0.3.

_Habitat._--South Pacific, Station 291, depth 2250 fathoms.

4. _Aulospathis polymorpha_, n. sp. (Pl. 104, figs. 10-13).

Radial tubes with an inflated ovate terminal knob at the distal end, which bears a variable number of divergent, curved, irregular, terminal branches. Usually the majority of the tubes bear three branches, whilst others exhibit two or four, sometimes also five or six. Proximal whorl also very variable and irregular, with two to six, usually three or four unequal branches.

_Dimensions._--Length of the tubes 2.0 to 4.0, breadth 0.04 to 0.06; branches 0.1 to 0.3.

_Habitat._--South Pacific, Station 289, depth 2550 fathoms.

Subgenus 2. _Aulospathilla_, Haeckel.

_Definition._--Distal ends of the radial tubes of equal breadth or tapering gradually, not inflated, without terminal knobs.

5. _Aulospathis diodon_, n. sp.

Radial tubes without inflated terminal knob, forked at the tapering distal end, with two divergent curved branches of equal size. Proximal whorl cruciate, with four rather equal, crossed, straight, lateral branches (sometimes three or five instead of four in single tubes).

_Dimensions._--Length of the tubes 2.0 to 2.5, breadth 0.03 to 0.04; branches 0.1 to 0.3.

_Habitat._--North Pacific, Station 231, depth 2250 fathoms.

6. _Aulospathis triodon_, n. sp. (Pl. 104, fig. 8).

Radial tubes without inflated terminal knob, with three divergent, slightly curved, terminal branches. Proximal whorl with a variable number of curved lateral branches, usually also three (often two or four, rarely more).

_Dimensions._--Length of the tubes 2 to 3, breadth 0.03 to 0.05; branches 0.2 to 0.3.

_Habitat._--North Pacific, Stations 250 to 253, depth 2740 to 3125 fathoms.

{1588}7. _Aulospathis tetrodon_, n. sp. (Pl. 104, fig. 9).

Radial tubes without inflated terminal knob, with four crossed, divergent, slightly curved terminal branches. Proximal whorl usually with an irregular cross of four lateral branches (often five or six, rarely two or three instead of the usual four).

_Dimensions._--Length of the tubes 2.0 to 2.5, breadth 0.03 to 0.04; branches 0.2 to 0.3.

_Habitat._--North Pacific, Stations 244 to 245, depth 2775 to 2900 fathoms.

8. _Aulospathis hexodon_, n. sp.

Radial tubes without inflated terminal knob, with three forked, curved branches at the distal end, so that each tube usually bears six terminal branches; but other tubes of the same specimen bear only three simple or a few irregularly forked branches. Proximal whorl usually with six curved, irregular, lateral branches.

_Dimensions._--Length of the tubes 2.0 to 3.0, breadth 0.03 to 0.06; branches 0.2 to 0.5.

_Habitat._--Western Tropical Pacific, Station 224, depth 1850 fathoms.

9. _Aulospathis furcata_, n. sp.

Radial tubes without inflated terminal knob, with a variable number of unequal terminal branches, which are partly simple, partly irregularly forked or branched; the usual number of terminal branches is three or four, more rarely two or five or six. Proximal whorl very irregular, usually with four to six unequal, lateral branches.

_Dimensions._--Length of the tubes 2.0 to 2.5, breadth 0.03 to 0.05; branches 0.1 to 0.3.

_Habitat._--Stations 265 to 268, depth 2700 to 2900 fathoms.

10. _Aulospathis variabilis_, n. sp. (Pl. 104, figs. 14-17).

Radial tubes without inflated terminal knob, with a variable number of unequal terminal branches, which are constantly simple, never forked; the usual number is in the majority of the tubes three or four, often also two, rarely five to eight. Proximal whorl irregular, with a variable number of lateral branches (usually four to six).

_Dimensions._--Length of the tubes 2.0 to 3.0, breadth 0.03 to 0.06; branches 0.1 to 0.3.

_Habitat._--Central Pacific, Stations 271 to 274, depth 2350 to 2750 fathoms.

Genus 670. _Aulodendron_,[288] n. gen.

_Definition._--#Aulacanthida# with a veil of tangential needles, and with radial tubes, which bear numerous, irregularly scattered, lateral and terminal branches.

{1589}The genus _Aulodendron_ differs from the other Aulacanthida in the possession of lateral and terminal branches, which are irregularly scattered on the radial tubes and not arranged in regular verticils. The branches are usually short, simple or forked, rarely longer and again irregularly ramified.

1. _Aulodendron antarcticum_, n. sp. (Pl. 105, fig. 5).

Radial tubes cylindrical, more or less curved, in the inner proximal half smooth and half as broad as in the outer distal half, which is studded with irregularly curved, partly branched spines, arising usually perpendicularly from the tube. The majority of the spines usually simple, the minority forked, with two to four short branches, the largest spines scarcely twice as long as the breadth of the tube.

_Dimensions._--Length of the tubes 0.7 to 0.9, breadth 0.01 to 0.02; length of the branches 0.02 to 0.04.

_Habitat._--Antarctic Ocean (Kerguelen), Stations 156 to 159, surface.

2. _Aulodendron pacificum_, n. sp. (Pl. 105, fig. 2).

Radial tubes cylindrical, slightly curved, in the proximal half smooth, in the distal half with scattered lateral branches, which are partly simple, partly forked, about twice as long as the breadth of the tube, and bear at the distal end a spathilla with five to six recurved teeth. The distal end of the tubes bears a spherical knob, which is separated by a deep stricture and armed with a bunch of six to twelve strong conical teeth.

_Dimensions._--Length of the tubes 1 to 1.2, breadth 0.015 to 0.02; branches 0.03 to 0.04.

_Habitat._--South Pacific, Station 293, depth 2025 fathoms.

3. _Aulodendron australe_, n. sp. (Pl. 105, fig. 3).

Radial tubes cylindrical, straight, thin, smooth in the proximal half, armed with numerous lateral branches in the distal half; the majority of the branches forked, about as long as the breadth of the tube, with two or three short ramules, each of which bears a spinulate terminal knob. The distal end of the tubes also forked, with two or three divergent branches.

_Dimensions._--Length of the tubes 1.2 to 1.6, breadth 0.01 to 0.012.

_Habitat._--South Pacific, Station 289; New Zealand, Station 169, surface.

4. _Aulodendron atlanticum_, n. sp.

Radial tubes cylindrical, tapering gradually towards the two ends; smooth and straight in the proximal half, irregularly curved and branched in the distal half, with ten to twenty (rarely more) branches, which arise almost perpendicularly from the tube. The proximal branches are from four to eight times as long as the greatest breadth of the tube, forked, with two or three short ramules; {1590}the distal branches are much smaller and simple. The distal end of each branch bears a spathilla with four to six short teeth.

_Dimensions._--Length of the tubes 2.4 to 3.6, breadth 0.06 to 0.08.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

5. _Aulodendron indicum_, n. sp. (Pl. 105, fig. 1).

Radial tubes cylindrical, irregularly curved, tapering gradually towards the two ends; smooth in the proximal half, irregularly branched in the distal half, with ten to twenty or more curved branches. The proximal branches are very large, one-sixth to one-fourth as long as the tube and irregularly ramified; the distal branches are much shorter, also ramified or simple. All the branches are more or less curved and bear a spinulate knob at the distal end.

_Dimensions._--Length of the tubes 1.2 to 1.8, breadth 0.02 to 0.03; length of the branches 0.1 to 0.3.

_Habitat._--Indian Ocean; Cocos Islands (Rabbe), surface.

----

Order II. PHÆOSPHÆRIA, Haeckel, 1879.

_Definition._--PHÆODARIA with a simple or double, usually spherical lattice-shell, which is not bivalved and has no peculiar mouth or peristome. Central capsule placed in the centre of the shell.

Family LXXIV. #OROSPHÆRIDA#, n. fam. (Pls. 106, 107).

_Definition._--PHÆODARIA with a big spherical (sometimes polyhedral or ellipsoidal), very coarse shell, which is composed of thick bars containing an axial canal. Nodal points of the coarse network without astral septa. Meshes of moderate size, irregularly polygonal. Surface of the shell usually with radial spines and pyramidal elevations. No peculiar mouth in the shell. Central capsule tripylean, in the centre of the shell.

The family #Orosphærida# comprises those PHÆODARIA which possess a simple spherical or polyhedral lattice-shell, composed of hollow, very thick, non-articulate rods, without a peculiar shell-mouth. They agree in the considerable size of the spherical lattice-shell and the absence of a peculiar shell-mouth with the other #Phæosphæria#, but differ from them in the coarse and irregular shape of the massive network, which is composed of irregular polygonal meshes, separated by very thick concentrically stratified rods, containing a fine axial canal. The closely allied Sagosphærida differ from them in the delicate shape of the solid and very thin, filiform rods of the network, and its subregular {1591}triangular meshes. The Aulosphærida differ in the development of the peculiar nodal cavities and astral septa, by which the thin-walled cylindrical tubes of the articulated network are separated in the stellate nodal points. The Cannosphærida, closely allied to these latter, also differ in the articulated network, and further in the possession of an internal concentric shell. The Castanellida are sometimes similar to the Orosphærida, but distinguished by a peculiar large shell-mouth and a network of different shape.

The Orosphærida belong to the biggest Radiolaria, and the lattice-work of their spherical shell is of a ruder and coarser shape than in any of the other families of this class. Nevertheless they have been hitherto perfectly unknown, and were first discovered by the Challenger. We have been able to distinguish in the collection four genera and twenty-seven species. This strange fact may be explained by the circumstance, that they are in general rare, and restricted to a few localities, and that probably all the species are inhabitants of great depths. Complete shells also are rarely found, whilst broken fragments of their big shells, easily recognisable by the coarse irregular meshes and the thick stratified bars, are met with frequently in the Radiolarian ooze of some Pacific Stations, especially at Stations 265 and 268, at a depth of 2900 fathoms.

The lattice-shell of the Orosphærida is usually spherical, or an endospherical polyhedron (Pl. 106, fig. 4); rarely one axis is somewhat prolonged, so that the shell becomes slightly ellipsoidal (Pl. 106, fig. 1). Its diameter is usually between 2 and 3, often also between 2 and 1 mm., rarely more than 3, or less than 1 mm. The largest shells observed attained 5 to 6, the smallest 0.5 to 0.6 mm. Their general habit is very characteristic, so that they may be easily distinguished from all other spherical lattice-shells, especially from the Castanellida and from the simple Monosphærida (_Cenosphæra_, _Acanthosphæra_), with which I confounded them in the beginning (hence the first shell observed, figured in 1878, was placed among the Monosphærida in Pl. 12). A closer examination of the coarse network and of the peculiar structure of its thick bars always enables one to recognise even small isolated fragments of broken shells.

The meshes of the coarse network exhibit in all observed Orosphærida a very irregular form and unequal size; the majority are usually more or less quadrangular, more rarely they are triangular, pentagonal or hexagonal, very rarely rounded. They are often arranged in parallel rows, which seem to be determined by prominent crests, connecting the bases of the radial spines (Pl. 12, fig. 1; Pl. 106, fig. 4, &c.). The diameter of the meshes is usually between 0.05 and 0.1, often 0.1 to 0.2, rarely more than 0.25, or less than 0.025 mm. In _Oroplegma_, which develops an outer loose, spongy shell around the inner primary shell, the big meshes of the former become much larger and very irregular (Pl. 107, fig. 1).

The coarse bars which separate the large meshes of the irregular network are very thick and massive, cylindrical, usually of unequal thickness, straight or slightly curved, never angular or prismatic. Their diameter is usually between 0.01 and 0.02, rarely {1592}more than 0.03 or less than 0.005 mm. Their surface is either smooth or slightly spinulate. Examined in the dry state and by strong lenses, they constantly exhibit a fine, but distinct longitudinal striation, as the expression of concentric stratification. A fine axial canal or central tubule is usually visible in the axis of each rod, and often this axial canal is studded with numerous short lateral branches (Pl. 107, figs. 2, 4, 8). But very often the axial canals become rudimentary or lost, or are developed only in a part of the bars (Pl. 12, fig. 1). When they are completely developed, the entire network of the shell is drained by a reticulate system of communicating axial canals; they are probably filled by jelly in the living body. This tubular system never attains that regularity and high development which is constantly found in the Aulosphærida; and the characteristic stellate nodal points of the latter, with their astral septa, are never found in any of the Orosphærida. Moreover the wall of the tubular bars is very thin and structureless in the Aulosphærida, very thick and stratified in the Orosphærida, the enclosed canal very wide in the former, very narrow in the latter. The stratification of the concentric cylindrical lamellæ, which surround the narrow axial canal, is effected by the gradual deposition of the concentric layers, and is very similar to that which is found in the thick spicula of many sponges. The peculiar structure of the bars in the Orosphærida becomes very distinct if the skeleton be burned, or acted upon by fire for some time; it then assumes a brown colour and its surface often appears dimpled. Sometimes the concave dimples on the surface of the bars are rather deep and separated by prominent crests (Pl. 107, figs. 4, 7). The few genera of Orosphærida which are here distinguished have all the same structure, are closely allied, and differ mainly in the shape of the outer surface of the lattice-sphere. The latter is quite simple and smooth only in _Orona_. In the common _Orosphæra_ (Pl. 106, figs. 1-3) it is studded with radial spines. In the most frequent form, _Oroscena_, the shell has a pyramidal or tent-shaped elevation on the base of each radial spine, and usually the bases of the neighbouring spines are connected by strong prominent crests, the edges of the three-sided or four-sided pyramids (Pl. 12, fig. 1; Pl. 106, fig. 4). This remarkable form is more or less polyhedral, with concave sides, and is similar to the characteristic shells which are represented by _Auloscena_ among the Aulosphærida, by _Sagoscena_ and _Sagoplegma_ among the Sagosphærida (compare Pls. 108 and 110). The pyramids or tents, however, are in these latter more regularly and distinctly developed than in the Orosphærida. The radial spines which arise form the top of the pyramids are often branched, and the branches become connected to form an outer enveloping secondary shell or a loose spongy framework in _Oroplegma_ (Pl. 107, fig. 1).

The radial spines of the Orosphærida never exhibit a constant number or disposition in the individual species; their usual number is from twenty to sixty. Their form exhibits two different types, which, however, are not sharply separated; robust club-shaped and slender rod-shaped spines. The robust club-shaped spines are usually about as long as {1593}the diameter of the shell; they are longitudinally striped in the basal part, spinulate or reticulately dimpled in the distal part; sometimes they are straight, at other times curved or undulate (Pl. 106, figs. 1-4; Pl. 107, figs. 4-6). The slender rod-shaped spines are usually longer than the diameter of the shell, cylindrical, more or less curved or even undulate, smooth or thorny, sometimes irregularly branched, and often the branches are all or partly connected (Pl. 106, fig. 3; Pl. 107, fig. 1). In the majority of the shells observed the radial spines were found to be partly broken off. Their structure is the same as that of the bars of the network; but the central axial canal and the surrounding concentric lamellæ are usually more distinct than in the latter.

The central capsule of the Orosphærida lies in the centre of the spherical lattice-shell, surrounded by the voluminous calymma, which fills up its cavity. The form, structure, and size of the central capsule are the same as in the closely allied Aulosphærida (Pl. 111, fig. 2). Its diameter is usually about 0.2, or between 0.15 and 0.25, rarely more than 0.3 or less than 0.12. The dark phæodium is of about the same volume as the central capsule, and envelops its oral half with the radiate operculum and the proboscis of the astropyle. The two opposite parapylæ are small.

_Synopsis of the Genera of Orosphærida._

I. Subfamily { Surface smooth, without Oronida. { radial spines, 671. _Orona_. Surface of the shell { without pyramidal { Surface studded with simple or or tent-shaped { branched radial spines, 672. _Orosphæra_. elevations. {

II. Subfamily { Pyramids of the surface free, Oroscenida. { without spongy envelope, 673. _Oroscena_. Surface of the shell { with numerous { Pyramids of the surface pyramidal or tent- { connected by a spongy shaped elevations. { envelope or an external { lattice-shell, 674. _Oroplegma_.

Genus 671. _Orona_,[289] n. gen.

_Definition._--#Orosphærida# with a simple spherical or slightly ellipsoidal shell, without pyramidal elevations and radial spines.

The genus _Orona_ is the simplest of the Orosphærida, and probably the common ancestral form of this family. The lattice-shell is a simple fenestrated sphere, sometimes slightly ellipsoidal, with prolonged main axis, and bears on its surface neither tent-shaped elevations nor radial spines. It may be confounded with some big forms of _Cenosphæra_; it differs, however, in the possession of hollow central canals in the thick bars of the very coarse lattice-plate.

{1594}1. _Orona maxima_, n. sp. (Pl. 107, fig. 5).

Shell spherical, with very irregular polygonal meshes. Bars of the loose network smooth or slightly spinulate, very thick, with a pinnulate axial canal.

_Dimensions._--Diameter of the sphere 5.0 to 5.5, of the meshes 0.2 to 0.4, of the bars 0.01.

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

2. _Orona robusta_, n. sp.

Shell spherical, with irregular quadrangular meshes (intermingled with single triangular, pentagonal, and hexagonal meshes). Bars of the coarse network very thick, spinulate.

_Dimensions._--Diameter of the sphere 3.0 to 3.6, of the meshes 0.05, of the bars 0.012.

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

3. _Orona crassissima_, n. sp. (Pl. 107, fig. 7).

Shell ellipsoidal, slightly prolonged in the main axis, with irregular polygonal meshes of very different sizes and unequal forms. Bars of the coarse network very thick, thorny and dimpled, their surface being covered with a network of prominent polygonal crests.

_Dimensions._--Diameter of the sphere 3.0 to 4.0, of the meshes 0.2 to 0.5, of the bars 0.02 to 0.06.

_Habitat._--South Pacific, Station 289, depth 2550 fathoms.

Genus 672. _Orosphæra_,[290] n. gen.

_Definition._--#Orosphærida# with a simple, spherical (sometimes slightly ellipsoidal or polyhedral) lattice-shell without pyramidal elevations, but with numerous radial spines.

The genus _Orosphæra_ differs from the preceding _Orona_, its ancestral form, in the development of simple or branched radial spines. It bears, therefore, the same relation to the latter that _Acanthosphæra_ has to _Cenosphæra_. In the two latter genera, however, the bars of the network are solid, in the two former hollow. The species referred to _Orosphæra_ are closely allied and require a further accurate examination.

Subgenus 1. _Oronium_, Haeckel.

_Definition._--Radial spines simple, smooth or spiny, but neither branched nor arborescent.

{1595}1. _Orosphæra hastigera_, n. sp.

Radial spines cylindrical, straight, smooth, simple, about as long as the diameter of the spherical shell, and as broad as its smooth bars. Meshes of the network irregularly polygonal, the majority quadrangular, of different sizes.

_Dimensions._--Diameter of the sphere 1.0 to 1.2, length of the radial spines 1.1 to 1.5, middle breadth 0.004.

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

2. _Orosphæra spinigera_, n. sp.

Radial spines cylindrical, irregularly curved, thorny, simple, two to three times as long as the diameter of the spherical shell, and as broad as its spiny bars. Meshes of the network irregularly polygonal, the majority pentagonal.

_Dimensions._--Diameter of the sphere 1.5 to 1.8, length of the spines 3.0 to 5.0, breadth 0.006.

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

3. _Orosphæra fusigera_, n. sp.

Radial spines slender, spindle-shaped, straight, smooth, about as long as the diameter of the spherical or slightly ellipsoidal shell, in the thicker middle part five times as broad as the bars, and tapering equally towards both ends. Meshes of the network irregularly polygonal, the majority quadrangular, separated by smooth bars.

_Dimensions._--Diameter of the shell 1.0 to 1.2, length of the spines 1.2 to 1.6, basal breadth 0.02, middle breadth 0.1.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

4. _Orosphæra foveolata_, n. sp.

Radial spines spindle-shaped, straight, dimpled, half as long as the radius of the spherical shell and three to five times as thick as the bars. Meshes irregular, polygonal, of very different shapes, separated by dimpled bars. (Similar to _Oroscena gegenbauri_, Pl. 106, fig. 4, but with spherical dimpled shell, without pyramidal elevations.)

_Dimensions._--Diameter of the shell 2.0 to 2.4, length of the spines 0.5, breadth 0.15.

_Habitat._--Central Pacific, Station 267, depth 2700 fathoms.

5. _Orosphæra serpentina_, n. sp. (Pl. 106, fig. 1).

Radial spines cylindrical, dimpled, undulate or curved in a snake-like manner, about as long as the diameter of the ellipsoidal or spherical shell and four to six times as broad as its smooth bars. Meshes very irregular, polygonal.

_Dimensions._--Diameter of the shell 1.0 to 1.2, length of the spines 0.12 to 0.15, breadth 0.12.

_Habitat._--South Pacific, Station 289, depth 2550 fathoms.

{1596}6. _Orosphæra horrida_, n. sp. (Pl. 106, fig. 2).

Radial spines club-shaped, very strong, straight, about as long as the diameter of the polyhedral shell, ovate and smooth in the distal half, slenderly conical, and armed with recurved spines in the proximal half; their outer third is the thickest, and five times as broad as the smooth bars of the coarse network. Meshes of the latter irregularly quadrangular.

_Dimensions._--Diameter of the shell 1.2 to 1.6, length of the spines 1.2 to 2.0, breadth 0.2.

_Habitat._--South Pacific, Station 291, depth 2250 fathoms.

7. _Orosphæra clavigera_, n. sp.

Radial spines club-shaped, thickened towards the distal end, more or less curved, spinulate, about as long as the diameter of the spherical shell; in the distal third four to six times as broad as the spinulate bars. Meshes irregularly polygonal, the majority pentagonal.

_Dimensions._--Diameter of the shell 2.0 to 2.5, length of the spines 1.8 to 2.2, breadth 0.16.

_Habitat._--Central Pacific, Station 263, depth 2650 fathoms.

Subgenus 2. _Orothamnus_, Haeckel.

_Definition._--Radial spines branched or arborescent.

8. _Orosphæra ramigera_, n. sp.

Radial spines cylindrical, spinulate, straight, about twice as long as the diameter of the spherical shell and as thick as its spinulate bars. Numerous simple spinulate branches, straight or slightly curved, and two to four times as long as the meshes, are irregularly scattered, and arise nearly perpendicularly from the bars.

_Dimensions._--Diameter of the shell 2.0 to 2.2, length of the spines 4 to 5, breadth 0.05.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

9. _Orosphæra furcata_, n. sp.

Radial spines cylindrical, smooth, irregularly curved, about as long as the radius of the spherical shell and as thick as its smooth bars, forked at the distal end, with two or three terminal branches of various lengths. Meshes irregularly polygonal (the majority hexagonal).

_Dimensions._--Diameter of the shell 1.2, length of the spines 0.7, breadth 0.03.

_Habitat._--Indian Ocean, Madagascar (Rabbe), surface (?).

10. _Orosphæra confluens_, n. sp.

Radial spines cylindrical, smooth, irregularly curved, two to three times as long as the diameter of the polyhedral shell, twice as broad as its smooth bars, bearing numerous irregular, lateral {1597}branches, which are partly confluent and fenestrated (similarly as in Pl. 107, fig. 1), but not forming an outer lattice-shell. Meshes irregularly polygonal.

_Dimensions._--Diameter of the shell 3.3, length of the spines 6 to 9, breadth 0.03.

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

11. _Orosphæra arborescens_, n. sp. (Pl. 106, fig. 3).

_Orothamnus arborescens_, Haeckel, 1881, Atlas, loc. cit.

Radial spines cylindrical, rough, more or less curved, somewhat longer than the diameter of the subspherical or slightly ellipsoidal shell, and at the thicker base three times as broad as its smooth bars, bearing numerous irregularly branched and curved, sometimes confluent, lateral branches. Meshes irregularly quadrangular.

_Dimensions._--Diameter of the shell 1.2 to 1.6, length of the spines 1.5 to 2.2, breadth 0.06.

_Habitat._--South Atlantic, Station 335, depth 1425 fathoms.

Genus 673. _Oroscena_,[291] n. gen.

_Definition._--#Orosphærida# with a simple, polyhedral or subspherical lattice-shell, and with numerous pyramidal elevations on its surface, the top of which bears a radial spine.

The genus _Oroscena_ differs from the preceding _Orosphæra_ in the possession of numerous pyramidal or tent-shaped elevations, each of which bears on its top a radial spine. It exhibits therefore the same relation to the latter that _Sagoscena_ does to _Sagosphæra_ and _Auloscena_ to _Aulosphæra_. The bases of the radial spines are usually connected by prominent concave crests, the edges of the pyramids. The species described of _Oroscena_ seem to be very variable and transformistic.

Subgenus 1. _Oroscenium_, Haeckel.

_Definition._--Radial spines simple, smooth or spiny, but neither branched nor forked.

1. _Oroscena gegenbauri_, n. sp. (Pl. 106, fig. 4).

Radial spines club-shaped, about half as long as the radius of the shell, cylindrical and finely sulcate in the basal third, ovate and elegantly dimpled in the distal two-thirds. The bases of the radial spines are connected by prominent concave crests, which form the edges of the polyhedral shell. Meshes irregularly polygonal, the majority quadrangular, separated by denticulate bars.

{1598}_Dimensions._--Diameter of the shell (without spines) 1.2 to 1.8, of the meshes 0.04 to 0.1; length of the spines 0.3 to 0.5.

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

2. _Oroscena mülleri_, n. sp. (Pl. 107, fig. 8).[292]

Radial spines club-shaped, very similar to that of the preceding species, but much larger, about as long as the radius of the shell. Meshes irregularly polygonal, the majority pentagonal, separated by smooth bars.

_Dimensions._--Diameter of the shell 2.0 to 2.4, length of the spines 1.0 to 1.2.

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

3. _Oroscena cuvieri_, n. sp. (Pl. 107, fig. 6).

Radial spines club-shaped, compressed and smooth in the proximal half, spindle-shaped and dimpled in the distal half, about as long as the radius of the shell. Meshes irregularly polygonal, the majority hexagonal, separated by denticulate bars.

_Dimensions._--Diameter of the shell 1.5, length of the spines 0.8.

_Habitat._--South Pacific, Station 289, depth 2550 fathoms.

4. _Oroscena bærii_, n. sp. (Pl. 107, fig. 4).

Radial spines nearly spindle-shaped, undulate, tapering from the thicker middle towards both ends, coarsely dimpled, about one-third as long as the radius of the shell. Meshes irregularly polygonal, the majority pentagonal, separated by spinulate bars.

_Dimensions._--Diameter of the shell 3.2, length of the spines 1.0 to 1.2, breadth 0.1.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

5. _Oroscena wolffii_, n. sp.

Radial spines cylindrical, spinulate, more or less curved, longer than the diameter of the shell and about twice as broad as its bars. Meshes irregularly polygonal, of very variable form and unequal size, separated by smooth bars.

_Dimensions._--Diameter of the shell 2.5, length of the spines 3.0 to 3.5, breadth 0.02.

_Habitat._--Indian Ocean, Zanzibar (Pullen), depth 2200 fathoms.

Subgenus 2. _Orodendrum_, Haeckel.

_Definition._--Radial spines branched or arborescent.

{1599}6. _Oroscena huxleyi_, n. sp. (Pl. 12, figs. 1, 1_a_).

Radial spines cylindrical, obliquely ascending and irregularly curved, about as long as the diameter of the shell and somewhat thicker than its thorny bars. A variable number of short, irregular, partly simple, partly forked, lateral branches arises from the spines. Meshes of the network very irregular, partly solid, partly hollow (fig. 1_a_*), the majority quadrangular. This species, the first observed form of Orosphærida (captured the 21st February 1873 at Station 5), was at the beginning of my observations, in 1876, and when I had no knowledge of the central capsule, erroneously regarded by me as a gigantic Sphæroid (of the Monosphærida) and therefore placed in Pl. 12. The long branched spines, afterwards observed complete in another specimen, were broken off in the specimen first figured.

_Dimensions._--Diameter of the shell 2.0 to 2.5, length of the spines 2 to 3 mm., breadth 0.03.

_Habitat._--North Atlantic (west of Canary Islands), Station 5, depth 2740 fathoms.

7. _Oroscena darwinii_, n. sp.

Radial spines cylindrical, irregularly curved and branched, about twice as long as the diameter of the shell; the branches are all again ramified and partly confluent (as in Pl. 107, fig. 1). The branches and the bars of the network are of equal breadth, smooth (not thorny as in the similar preceding species). Meshes rather subregular, quadrangular.

_Dimensions._--Diameter of the shell 2.4 to 2.8, length of the spines 4 to 5 mm., breadth 0.015.

_Habitat._--Tropical Atlantic, Station 348, depth 2450 fathoms.

8. _Oroscena duncanii_, n. sp.

? _Hexactinellida dictyonina_, Martin Duncan, 1881, Journ. Roy. Micr. Soc., p. 175, pl. iii. figs. 4, 6.

Radial spines cylindrical, thorny, arborescent, somewhat shorter than the diameter of the shell, with irregular ramified branches (similar to _Orosphæra arborescens_, Pl. 106, fig. 3). The size and ramification of the arborescent spinulate branches decrease towards the apex. The thicker branches are from two to three times as broad as the spinulate bars of the network. Meshes of the latter irregular, the majority quadrangular.

_Dimensions._--Diameter of the shell 3.2, length of the spines 3.5 to 4.5, breadth 0.02 to 0.3.

_Habitat._--South Atlantic, Station 318, depth 2040 fathoms; coast of Portugal, 1095 fathoms.

Genus 674. _Oroplegma_,[293] n. gen.

_Definition._--#Orosphærida# with a spongy, spherical or slightly polyhedral lattice-shell, which is enveloped by a loose spongy framework and bears numerous radial spines.

The genus _Oroplegma_ differs from the other Orosphærida in the development of an external lattice-work enveloping the internal primary shell, and produced by the union {1600}of the branches of the radial spines. This outer shell is either a simple lattice-plate (comparable to the cortical shell of _Diplosphæra_), or a spongy framework (as in _Rhizoplegma_).

Subgenus 1. _Oroplegmium_, Haeckel.

_Definition._--External shell a simple fenestrated lamella, forming an outer concentric lattice-sphere around the inner primary shell.

1. _Oroplegma diplosphæra_, n. sp. (Pl. 107, fig. 1).

Radial spines slender, cylindrical, smooth, more or less curved, about twice as broad as the smooth bars of the network. External shell a simple irregular lattice-sphere, with loose polygonal meshes, which are on an average three to four times as broad as the irregular meshes of the internal shell. The free prominent parts of the radial spines are irregularly branched, very long, with partly confluent branches.

_Dimensions._--Diameter of the inner sphere 1.5 to 2.0, of the outer 2.5 to 3.0; length of the free spines 1.2, breadth 0.04.

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

2. _Oroplegma spinulosum_, n. sp.

Radial spines slender, cylindrical, thorny, more or less curved, very similar to those of the preceding species; the shell also much resembles that of _Oroplegma perplexum_. It differs from the latter in the more regular fenestration of both shells, and mainly in the shape of the bars and the spine-branches, which are all spinulate and densely studded with small conical thorns.

_Dimensions._--Diameter of the inner sphere 1.5 to 2.0, of the outer 2.5 to 3.0; length of the spines 1.2, breadth 0.03.

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

3. _Oroplegma velatum_, n. sp.

Radial spines stout, cylindrical, somewhat club-shaped, spiny, slightly curved, about three to four times as broad as the thorny bars of the network. External shell a simple lattice-sphere with irregular polygonal meshes, which are for the most part pentagonal and about four times as broad as the polygonal meshes of the inner shell. The free prominent parts of the radial spines are thickened, club-shaped, and about as long as the radius.

_Dimensions._--Diameter of the inner sphere 2.0 to 2.4, of the outer 2.8 to 3.6; length of the free spines 0.5 to 0.7, breadth 0.12 to 0.15.

_Habitat._--Tropical Atlantic, Station 338, depth 1990 fathoms.

{1601}Subgenus 2. _Orodictyum_, Haeckel.

_Definition._--External shell a complex framework, forming an outer spongy envelope around the inner primary shell.

4. _Oroplegma spongiosum_, n. sp. (Pl. 107, fig. 3).

Radial spines stout, cylindrical, spinulate, slightly curved, three to five times as broad as the inner rough bars. External shell with pyramidal elevations, forming a loose spongy framework, the irregular polygonal meshes of which are two to five times as broad as those of the enclosed internal shell; the thickness of the spongy envelope equals about half the radius of the inner shell. External free prolongations of the radial spines about equal to the radius.

_Dimensions._--Diameter of the inner sphere 2 to 2.5, of the outer 3 to 3.5; length of the free radial spines 0.5 to 2.0, breadth 0.1.

_Habitat._--North Pacific, Station 241, depth 2300 fathoms.

5. _Oroplegma giganteum_, n. sp. (Pl. 107, fig. 2).

Radial spines slender, cylindrical, spinulate, irregularly curved, about twice as broad as the spinulate tubular bars of the network (fig. 2). External shell an irregular, loose, spongy framework, the polygonal meshes of which are three to six times as broad as the rounded irregular meshes of the inner shell; the thickness of the spongy envelope about equals the radius of the inner shell. External free prolongation of the radial spines irregularly branched.

_Dimensions._--Diameter of the inner sphere 3.2 to 3.5, of the outer 5.4 to 6.6; length of the free spines 1.4 to 1.5, breadth 0.03.

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

Family LXXV. #SAGOSPHÆRIDA#, n. fam. (Pl. 108).

_Definition._--PHÆODARIA with a large spherical (or sometimes polyhedral), very delicate shell, which is composed of solid, very thin and long threads. Nodal points of the arachnoidal network without astral septa. Meshes large, triangular. Surface of the shell usually armed with radial spines and often studded with pyramidal elevations. No peculiar mouth in the shell. Central capsule tripylean, in the centre of the shell.

The family #Sagosphærida# comprises a rather large number of common and widely distributed PHÆODARIA, which in respect of the special form and differentiation of the shell exhibit the greatest similarity to the common Aulosphærida, but differ essentially from them in the peculiar structure of the network. This is not composed of stout hollow cylindrical tubes, but of solid, very thin threads; and these fine arachnoidal {1602}threads are simply united or confluent at the nodal points, and are not connected by a radial or stellate septal junction, as in the Aulosphærida. There are, therefore, neither astral septa nor a nodal cavity in each nodal point. The delicate shape of the thin and fragile threads separates the Sagosphærida from the closely allied Orosphærida, the thick bars of which contain a central axial canal and exhibit a concentric structure. Another difference between these two similar families is indicated by the form of the meshes of the network, which are constantly triangular in the Sagosphærida, but irregularly polygonal or quadrangular in the Orosphærida. The general habit of these two families, however, is very different, since the big and stout spheres of the Orosphærida are the coarsest and rudest spherical shells of all Radiolaria, whilst the fragile and delicate spheres of the Sagosphærida represent the finest and most tender in the whole class.

The spherical lattice-shell of the Sagosphærida has a considerable size, its diameter being usually between one and three millimetres, rarely less or more. Some species are very common and widely distributed, usually accompanying the common Aulosphærida; very frequently the similar shells of the two are found interwoven. But in spite of this frequency and visible size, the Sagosphærida have hitherto almost completely escaped the attention of observers. The main cause of this strange fact may be their extreme delicacy and fragibility, so that complete and intact shells occur very rarely, the majority being more or less broken and incomplete. It seems that only two species of Sagosphærida have been hitherto observed.

The first form described is _Sagmarium trigonizon_, observed by me in 1859 living at Messina, and figured in 1862 in my Monograph as _Dictyosoma trigonizon_ (Taf. xxvi. figs. 4-6), but afterwards called _Spongodictyum trigonizon_ (_loc. cit._, p. 459). I supposed at that time (now twenty-five years ago), that this remarkable and in many respects distinct form might belong to the Spongosphærida, and that an internal, triple, spherical lattice-shell, found entangled in its spongy framework, might be its central "medullary shell." But at present, having found many shells of different Radiolaria accidentally entangled in the arachnoidal framework of various Sagosphærida, I think it much more probable, that that "triple medullary shell," composed of three simple concentric lattice-spheres, was really a species of _Plegmosphæra_ or _Actinomma_, accidentally entangled in the arachnoidal spongy framework of _Sagmarium_. This is the more probable, as I had observed very frequently at Messina, in 1859, fragments of that framework, but only once the triple lattice-shell which I supposed to be the "triple medullary shell" of the former. The peculiar structure of the loose framework, its very large triangular meshes and thin arachnoidal bars, partly provided with cruciate verticils (_loc. cit._, Taf. xxvi. figs. 4, 5) have been very frequently observed by me during the last ten years in various Sagosphærida (PHÆODARIA), but never in any true #Sphæroidea# (SPUMELLARIA).

The second species of Sagosphærida hitherto observed, is _Sagoscena gracilis_, described and figured in 1879 by Richard Hertwig as _Aulosphæra gracilis_ (Organism. {1603}d. Radiol., p. 91, Taf. ix. fig. 4). He too observed only fragments of destroyed and incomplete shells, and was led by their striking similarity to fragments of _Aulosphæra elegantissima_ to unite it with the genus _Aulosphæra_. But the accurate description and the figure given by him of the fragments observed leaves no doubt that it was a true _Sagoscena_.

In the collection of the Challenger the Sagosphærida are so common and so richly represented, that we may describe here not less than seven genera and thirty-three species, but this may be a small part only of the numerous species of this family, which seems to be widely distributed over all oceans, in the Arctic and Antarctic as well as in temperate and tropical zones. The majority are inhabitants of the surface, but a few species have been found only in deep-sea soundings. A striking fact is their usual association with the similar Aulosphærida. The majority of shells of both families were found entangled in one another.

The shell of all Sagosphærida seems to be spherical or nearly spherical in the complete state; but complete spheres can be observed only very rarely, and it is not impossible that deviations from the spherical form exist just as in some Aulosphærida (_e.g._, the lenticular _Aulophacus_ and the spindle-shaped _Aulatractus_). The diameter of the spheres usually seems to be between 1 and 2, often also 3 millimetres; very rarely shells occur which are less than 1 or more than 3 (4 or 5) millimetres.

The siliceous network or lattice-work of the Sagosphærida exhibits a very characteristic shape, and this enables one to distinguish it at first sight from all the other Radiolaria. It is constantly composed of triangular, very large meshes, which are separated by very thin and delicate, flexible and elastic bars. With respect to the arrangement of these meshes we distinguish two different subfamilies; in the Sagenida the wall of the spherical shell is very thin and composed only of a simple lattice-plate; in the Sagmarida the wall is thickened and spongy, with a complete wicker-work of threads, interwoven in different directions.

The typical triangular form of the large meshes is usually regular or subregular in the fenestrated Sagenida, more or less irregular in the spongy Sagmarida. In many cases, however, irregular triangles also occur in the former, and regular triangles in the latter subfamily. Very rarely irregular polygonal meshes are found in a part of the network, small connecting bars being developed accidentally between two neighbouring sides of the triangles. The diameter of the meshes is usually between 0.1 and 0.2 mm., often also greater, between 0.2 and 0.3, rarely smaller, 0.05 to 0.09