Legion IV. PHÆODARIA, (continued 4)

Habitat.—Cosmopolitan; Atlantic, Indian, Pacific, surface.

Genus 689. Aulastrum,^[308] n. gen.

Definition.—Aulosphærida with polygonal meshes in the network, the tangential tubes of which form a simple lattice-sphere. Radial tubes arise at its nodal points.

The genus Aulastrum differs from the preceding Aulonia, its ancestral form, only in the development of radial spines at the nodal points of the simple lattice-sphere. It exhibits therefore to the latter the same relation as Aulosphæra does to Aularia. But the meshes of the spherical network are constantly triangular in the two latter genera, polygonal in the two former. The different species of Aulastrum are much rarer, and are not so differentiated as those of the common Aulosphæra.

1. Aulastrum monoceros, n. sp.

Radial tubes simple, smooth, straight, cylindro-conical, about as long as the smooth tangential tubes or somewhat longer. Meshes of the network irregularly polygonal, the majority usually pentagonal or hexagonal.

Dimensions.—Diameter of the sphere 3.0 to 4.0, of the meshes 0.15; breadth of the tubes 0.012.

Habitat.—Tropical Atlantic, Stations 347, 348, depth 2250 to 2450 fathoms.

2. Aulastrum dichoceros, n. sp.

Radial tubes cylindrical, more or less curved, undulate, smooth, twice as long as the smooth tangential tubes, forked at the distal end, with two divergent curved branches. Meshes of the network subregular, hexagonal (as in Aulonia hexagonia, Pl. 111, fig. 1), intermingled with single pentagonal and square meshes.

Dimensions.—Diameter of the sphere 2.0 to 2.5, of the meshes 0.12 to 0.18; breadth of the tubes 0.01.

Habitat.—Antarctic Ocean, Station 157, depth 1950 fathoms.

3. Aulastrum dendroceros, n. sp. (Pl. 111, figs. 4a, b, c).

Radial tubes cylindrical, straight or slightly curved, thorny, forked at the distal end, two to three times as long as the thorny tangential tubes; the thorns are short and thin, partly simple, partly irregularly branched and scattered, arborescent. Meshes of the network irregularly polygonal, the majority pentagonal or tetragonal.

Dimensions.—Diameter of the sphere 2.4; radial tubes 0.2 to 0.3 long, 0.02 broad.

Habitat.—North Pacific, Station 241 to 244, surface.

4. Aulastrum triceros, n. sp. (Pl. 111, figs. 3, 3a).

Radial tubes cylindrical, straight, smooth, about twice as long as the smooth tangential tubes, armed with three divergent curved teeth at the distal end. Meshes subregular, pentagonal, intermingled with a small number of tetragonal and hexagonal meshes.

Dimensions.—Diameter of the sphere 1.2 to 1.8; radial tubes 0.15 long, 0.01 broad.

Habitat.—Tropical Atlantic, Station 349, depth 2450 fathoms.

5. Aulastrum trichoceros, n. sp.

Radial tubes slender, straight, cylindro-conical, about twice as long as the smooth tangential tubes, armed with six to eight verticils of lateral branches, each of which is composed of three short curved branches (similar to those of Aulophacus lenticularis, Pl. 111, fig. 5a). Meshes irregularly polygonal, the majority tetragonal, intermingled with pentagonal and triangular meshes.

Dimensions.—Diameter of the sphere 2.2; tangential tubes 0.12 long, 0.007 broad.

Habitat.—South Pacific, Station 289, depth 2550 fathoms.

6. Aulastrum tetraceros, n. sp.

Radial tubes straight, cylindrical, about three times as long as the smooth tangential meshes, armed with three to six subregular cruciate verticils of branches, each of which is composed of four short, regularly crossed branches, bearing at the end a spinulate knob (similar to those of Aulatractus fusiformis, Pl. 111, fig, 6b). Meshes subregular, square, intermingled with single pentagonal and hexagonal meshes.

Dimensions.—Diameter of the sphere 1.5, of the meshes 0.12 to 0.16; breadth of the bars 0.008.

Habitat.—South Atlantic, Station 318, depth 2040 fathoms.

7. Aulastrum pentaceros, n. sp.

Radial tubes straight, cylindrical, smooth, about as long as the smooth tangential tubes, armed at the distal end with a corona of five curved teeth (of the same shape as in Cannosphæra atlantica, Pl. 112, fig. 6). Meshes subregular pentagonal (intermingled with single tetragonal, hexagonal, and heptagonal meshes).

Dimensions.—Diameter of the sphere 5.0, of the meshes 0.2; breadth of the bars 0.015.

Habitat.—Indian Ocean, Madagascar (Rabbe), surface.

8. Aulastrum polyceros, n. sp.

Radial tubes spindle-shaped, tapering from the broader middle towards both ends, spiny, twice as long as the spiny tangential tubes, armed at the distal end with a corona of twelve to twenty divergent curved teeth (similar to the radial tubes of Auloscena tentorium, Pl. 110, fig. 6). Meshes irregular, polygonal, very variable in size and form. All tubes of this species are armed with scattered, short, conical spines.

Dimensions.—Diameter of the sphere 4.5, of the meshes 0.1 to 0.2; breadth of the bars 0.006.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

Genus 690. Aulodictyum,^[309] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 6.

Definition.—Aulosphærida with polygonal meshes in the network, the tubes of which are connected in different directions and form the spongy wall of a spherical shell. No radial tubes prominent over the surface.

The genus Aulodictyum differs from Aulonia, its ancestral form, in the development of a spongy framework in the thickened wall of the spherical lattice-shell. It bears therefore to the latter the same relation as Auloplegma does to Aularia. But the outer surface of the hollow sphere is in Aulodictyum completely smooth, as well as the inner, and bears no radial tubes. Only one species of this genus has been observed.

1. Aulodictyum hydrodictyum, n. sp.

Shell spherical, smooth on the outer and inner surfaces, composed of an irregular framework of straight and smooth cylindrical tubes; its meshes very irregular, of unequal size and various forms. The diameter of the sphere is about six or eight times as great as the thickness of its reticular wall.

Dimensions.—Diameter of the sphere 2 to 3, of its meshes 0.1 to 0.2; breadth of the bars 0.01.

Habitat.—Antarctic Ocean, Station 157, depth 1950 fathoms.

Family LXXVII. Cannosphærida, Haeckel (Pl. 112).

Definition.—Phæodaria with two concentric spherical or subspherical shells, which are connected by numerous thin, tubular, radial beams. Inner shell simple, spherical or ovate, solid or latticed, with a peculiar mouth. Outer shell spherical or polyhedral, articulate, composed of hollow tangential tubes, which are separated by astral septa at the stellate nodal points. From the latter arise hollow radial tubes, whilst the inner radial beams, connecting the two shells, are inserted in the middle of the tangential tubes. No peculiar mouth in the outer shell. Central capsule enclosed by the inner shell.

The family Cannosphærida comprises a small number of remarkable Phæodaria which are rare and found only in a few localities. They differ from all the other Phæodaria in the possession of two concentric spherical shells, which are connected by radial beams, and the inner of which is quite simple, like that of the Medusettida, whilst the outer is articulated and composed of hollow tangential tubes, like that of the Aulosphærida. This latter family seems to be most nearly allied to the Cannosphærida, and is perhaps derived from them by loss of the inner shell. The possession of a peculiar mouth in this inner shell brings the Cannosphærida nearer to the Phæogromia. The similar Cœlodrymida, in which also two concentric spherical shells are connected by hollow radial beams, differ essentially in the bivalved shape of the inner shell and the simple, non-articulated, network of the outer shell.

Only a single species of Cannosphærida has been hitherto known, described and figured in 1879 by R. Hertwig as Cœlacantha anchorata (loc. cit., p. 92, Taf. ix. fig. 2). The rich collection of the Challenger has added to it only four other species, one of which is most nearly allied to the former, whilst the others belong to a separate genus, Cannosphæra (Pl. 112). The inner shell is in this latter genus a solid lamella of silica, whilst in the former it is fenestrated. In all other essential points of structure both genera are scarcely different.

The inner shell is either spherical or ovate and has a diameter of 0.1 to 0.4 (usually 0.2 to 0.3 mm.). A distinct main axis is always marked by the large open mouth on its oral pole. The aboral part of the shell-cavity contains the spherical central capsule, the oral part the dark phæodium, a part of which is often prominent through the mouth (figs. 1, 2, 4). The wall of the inner shell is a very thin and transparent lamella of silica, which is structureless and solid in Cannosphæra, distinctly fenestrated in Cœlacantha; the pores of the latter are irregularly rounded and seem to possess a thickened margin.

From the surface of the inner shell arise numerous thin tubular, radial beams (twenty to eighty or more) and connect it with the outer shell. These beams are always very thin and straight cylindrical tubules, about twice to four times as long as the diameter of the inner shell, and usually 0.001 mm. broad, or even less. Their basal end at the surface of the latter appears mammillated (figs. 2, 4). The cavity of the inner shell seems to pass over immediately into the tubular cavities of the radial beams. These latter are sometimes simple, at other times articulated or jointed by a number of transverse septa. The radial beams are covered in all the species observed either with scattered spines (fig. 5) or with verticils of anchor-threads, very thin, filiform, lateral branches which bear a spathilla with three or four recurved teeth on the distal end (figs. 2, 4).

The outer shell is either spherical or an endospherical polyhedron, the prominent nodal points of which fall into a spherical face. Its diameter is usually from 2 to 3 mm., rarely more than 3 or less than 1 mm. Its structure is the same as described for the Aulosphærida, being composed of hollow cylindrical tubes, which form a loose network and are separated at its nodal points by astral septa. The meshes of the network are very large, usually twice to three times as broad as the inner shell, and irregularly polygonal; the usual and prevailing form is pentagonal, but hexagonal meshes are also often intermingled, more rarely meshes with five, seven, or eight sides.

The cylindrical tangential tubes possess in general the same shape as in the similar Aulosphærida, have a thin wall, are filled with jelly, and contain a delicate axial filament in their axis; they differ, however, in a peculiar constant character; in the middle of each tube is inserted an inner radial beam coming from the inner shell, so that both together have the form of a T. The central point of insertion has a somewhat shorter radial distance from the centre of the body than the two nodal points on both ends of the tangential tube, so that the latter is somewhat geniculate (figs. 1-5). The two halves of each tangential tube are usually somewhat thinner on the central end (where the inner radial beam is inserted), thicker on the distal end (where the outer radial tube arises); at both ends they are closed by a thin transverse septum. Often also some other septa are developed, so that each tangential tube seems to be composed of four to six joints or segments. Usually the tangential tubes are armed with spines or anchor threads, similar to those of the inner radial beams. The length of the single tangential tubes is usually between 0.1 and 0.3, their diameter from 0.01 to 0.02.

The nodal points of the outer lattice-sphere, in which the outer radial spines arise, seem to possess the same structure as in the similar Aulosphærida. Since three tangential tubes are connected to each nodal point, in its centre is the union of three small astral septa or sutural partitions. The small nodal cavity on the inside of the nodal point has probably three small pores, which lead into the three tangential tubes between the three astral septa. A fourth pore probably leads from the nodal cavity into the cavity of the hollow radial tube. This structure is difficult to observe, but seems to be demonstrated by the fact, that in the complete and carefully purified skeletons which are treated with hot mineral acids and afterwards dried, all cylinders, the tangential as well as the radial tubes, become easily filled by air (compare the description of the similar structure in the Aulosphærida).

The external radial tubes which arise in the nodal points of the outer shell are either cylindrical or cylindro-conical, straight, and usually about as long as the diameter of the inner shell. Their structure and armature is the same as in the similar Aulosphærida. In the axis of each radial tube runs a delicate axial filament, which is connected with its thin and fragile wall either by filiform transverse branches or by delicate transverse septa. The outside of the radial tubes is either smooth (figs. 3-5) or armed with scattered spines (fig. 4) or with verticils of lateral branches; each verticil is usually composed of three or four branches. The distal end of the radial tubes is rarely simple, pointed; it is usually armed with a spathilla of three or four curved terminal branches (figs. 3, 5) sometimes with an elegant corona composed of twenty to thirty thin radially divergent branches (fig. 4).

The central capsule of the Cannosphærida is small (of 0.1 to 0.15 in diameter) and hidden in the aboral half of the enclosing inner shell, whilst the oral half of the latter is filled up by the phæodium (figs. 2, 4). The structure of the capsule and of its three openings seems to be the same as in the closely allied Aulosphærida. I have, however, not been able to recognise the two parapylæ or secondary openings, and have only observed the astropyle or the main-opening with its radiate operculum surrounded by the phæodium, and directed with its tubular proboscis towards the mouth of the inner shell. As R. Hertwig also could not recognise the two parapylæ, it is not impossible that they are wanting, and that the Cannosphærida possess only one opening, the astropyle, like the Medusettida and Challengerida. The nucleus, enclosed in the central capsule, is spherical, half or one-third as broad as the latter, and contains numerous nucleoli.

Synopsis of the Genera of Cannosphærida.

Internal shell solid, without open pores, 691. Cannosphæra.

Internal shell latticed, with open pores, 692. Cœlacantha.

Genus 691. Cannosphæra,^[310] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 6.

Definition.—Cannosphærida with a solid, not latticed internal shell.

The genus Cannosphæra comprises those Cannosphærida in which the inner shell is formed by a thin solid siliceous-plate and exhibits no pores between the prominent bases of the radial beams.

1. Cannosphæra atlantica, n. sp. (Pl. 112, figs. 5, 6).

Internal shell not mammillate, with fifteen to twenty radial rods, which are loosely studded with single, scattered, simple, lateral spines. External shell with irregular, mostly hexagonal meshes, armed with numerous scattered forks of paired divergent spines, and with twenty to thirty larger simple radial spines, which are about half as long as the internal rods, and bear at the distal end a verticil of three to five curved, simple, terminal branches.

Dimensions.—Diameter of the inner shell 0.1, of the outer 0.5.

Habitat.—Tropical Atlantic, Stations 347 to 349, depth 2250 to 2450 fathoms.

2. Cannosphæra antarctica, n. sp. (Pl. 112, figs. 1-3).

Internal shell mammillate, with sixty to ninety radial rods, which are studded with cruciate verticils of tridentate anchor-threads. External shell with irregular, mostly pentagonal meshes, the bars of which bear on the outside bunches of similar tridentate anchor-threads. At each nodal point arises a simple, smooth, radial spine, which bears at the distal end a verticil of three or four small, curved, terminal branches.

Dimensions.—Diameter of the inner shell 0.2 to 0.3, of the outer 1.5 to 2.0.

Habitat.—Antarctic Ocean, Stations 154 to 157, depth 1300 to 1975 fathoms.

3. Cannosphæra pacifica, n. sp. (Pl. 112, fig. 4).

Internal shell mammillate, with one hundred to one hundred and twenty radial rods, which are studded with cruciate verticils of tridentate anchor-threads. External shell with irregular, mostly hexagonal meshes, the bars of which bear on the outside and on the inside bunches of similar tridentate anchor-threads. At each nodal point arises a simple, thorny, radial spine, which bears at the distal end an elegant verticil of fifteen to twenty flatly expanded, thin, terminal branches.

Dimensions.—Diameter of the inner shell 0.25 to 0.35, of the outer 2.0 to 2.5.

Habitat.—Central Pacific, Stations 270 to 274, depth 2350 to 2925 fathoms.

Genus 692. Cœlacantha,^[311] R. Hertwig, 1879, Organism. d. Radiol., p. 91.

Definition.—Cannosphærida with a latticed internal shell.

The genus Cœlacantha comprises those Cannosphærida in which the inner shell is formed by a fenestrated flint-plate, and exhibits numerous pores between the prominent bases of the radial beams.

1. Cœlacantha anchorata, R. Hertwig.

Cœlacantha anchorata, R. Hertwig, 1879, Organism. d. Radiol., p. 92, Taf. ix. fig. 2.

Internal shell slightly mammillate, with thirty to forty radial rods, which are densely studded with verticils of tridentate anchor-threads. External shell with irregular, mostly pentagonal meshes, the bars of which bear the same verticils, each composed of three thin, tridentate anchor-threads. At each nodal point arises a slender radial spine, which bears six verticils, each composed of three to five lateral branches.

Dimensions.—Diameter of the inner shell 0.5, of the outer 3.0.

Habitat.—Mediterranean, Messina (R. Hertwig), surface.

2. Cœlacantha mammillata, n. sp.

Internal shell strongly mammillate, with sixty to eighty radial rods, which are densely studded with cruciate verticils of quadridentate anchor-threads. External shell with irregular, mostly hexagonal meshes, the bars of which bear the same verticils, each composed of four thin quadridentate anchor-threads. At each nodal point arises a slender, smooth, radial spine, which bears at its distal end a verticil of four large, curved, terminal branches.

Dimensions.—Diameter of the inner shell 0.4, of the outer 3.2.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

Order III. PHÆOGROMIA, Haeckel, 1879.

Definition.—Phæodaria with a simple, not bivalved lattice-shell, which assumes very different forms, but is always provided with a peculiar mouth and peristome on the oral pole of the main axis. Central capsule always excentric, placed in the aboral half of the shell-cavity.

Family LXXVIII. Challengerida, John Murray (Pl. 99).

Definition.—Phæodaria with a monaxonial, usually ovate or lenticular shell, which exhibits a peculiar, fine, regularly hexagonal, diatomaceous structure, and is usually provided with teeth on the mouth, but without articulated feet. Central capsule excentric, placed in the aboral half of the shell-cavity.

The family Challengerida represent a large, peculiar, and interesting group of Phæodaria, which are, for the most part, inhabitants of great depths, and were perfectly unknown before the discoveries of the Challenger. The first note on these remarkable Radiolaria was given in 1876 by John Murray, in his Preliminary Reports on Work done on board the Challenger (Proc. Roy. Soc. Lond., vol. xxiv. pp. 471, 536, pl. xxiv. figs. 1, 2). He described the peculiar exceedingly beautiful tracery of their shell, similar to that of the Diatomaceæ, the enclosed central capsule coloured by carmine, and the surrounding mass of black-brown pigment lumps (the phæodium). "At times these Challengerida come up with a good deal of sarcode outside of the shell, and two specimens have been seen to throw out elongated pseudopodia" (loc. cit., p. 536). He found also the shells in the Radiolarian ooze of the deep sea. The number of different forms found in the collection of the Challenger is so great, that I can describe in the following pages not less than six genera and fifty-eight species. A part of these have already been figured by Dr. John Murray in the Narrative of the Challenger Expedition, vol. i. p. 226, Pl. A, 1885.

In my first preliminary note on the Phæodaria, in 1879, I gave a stricter definition of the Challengerida (Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, 1879, p. 5). But I united at that time the true Challengerida with the Tuscarorida, which, however, are sharply separated by the entirely different structure of their shell. In Plate A given by Dr. John Murray, and mentioned above, figs. 1-14 represent genuine Challengerida, with diatomaceous shell-structure, whilst figs. 15-20 are Tuscarorida, with porcellanous shell-structure. These latter, therefore, are more closely allied to the Circoporida, whilst the Challengerida exhibit a closer affinity to the Medusettida and Castanellida. But the two latter families never possess that peculiar extremely regular and delicate diatomaceous structure which is exhibited only by the Challengerida.

The general form of the Challengerida is rather simple, usually more or less ovate, sometimes nearly triangular, at other times subspherical. In nearly all species, with a few exceptions, the shell is more or less compressed from the two sides, so that its horizontal transverse section is not circular, but elliptical or lanceolate. In many species the shell is more or less lenticular, with a sharp or sometimes keeled margin. This margin lies in the sagittal plane of the body, whilst the two flat sides are right and left. The main axis is always perpendicular, and its oral or anterior pole is marked by the open mouth of the shell; the latter is in the living organism probably the upper pole, whilst the opposite aboral or posterior pole (often marked by large spines) is the lower pole. The dorsal margin of the mouth is usually different from the ventral, and in the majority of species this difference is so striking, that right and left sides of the body may be recognised immediately, the fundamental form being dipleuric or bilaterally-symmetrical. In a few species, however, and mainly in those simplest forms in which the ovate shell has a circular mouth without teeth, and a circular transverse section, that difference is not recognisable, and the ovate shell is monaxonial, as it is in Gromia and Lagena among the Foraminifera (Pl. 99, figs. 19, 20, 22). The size of the shell is in the majority of species between 0.2 and 0.5 mm.; there are, however, some very small species, in which the diameter of the shell is only 0.05 to 0.08, or even less; and some large species, the diameter of which attains 0.8 to 0.9 mm.

The peculiar structure of the siliceous shell-wall, which we call shortly "diatomaceous," and by which the Challengerida differ from all the other Phæodaria, has been already represented very well by Dr. John Murray, in Pl. A. of the Narrative (vol. i. p. 266, figs. 1c-1e, 2a, 4a, 7a, 7b). This elegant diatomaceous structure is extremely similar or nearly identical with that well-known regular structure which we find in the common Diatomaceæ or Bacillariæ. The entire surface of the shell is covered with a very great number of very small pit-like depressions, perfectly regular, circular in form, equal in size, and quincuncial in arrangement. The neighbouring equidistant pits are always surrounded by regular hexagonal frames of equal size, and the prominent fine crests of these frames produce the regular hexagonal tracery, which gives to the shell such a striking similarity to that of the Diatomaceæ. According to the different positions to which the focus of the microscope is brought, the hexagonal tracery exhibits a different appearance; either a regular network of equal hexagonal frames, or a lattice with equal and equidistant circular openings, or a combination of three crossed and equidistant systems of parallel lines (crossed at angles of 120°). All the well-known and often discussed optical phenomena which are observed in the valves of the Diatomaceæ, reappear also on the shell of the Challengerida.

To recognise the true nature of this diatomaceous structure, sections and slides of the shell are required, and also fragments of broken shells, the broken margins of which are of special value for obtaining further explanation. The figures given by Dr. J. Murray (loc. cit., Pl. A) have already demonstrated that the pit-like depressions are regular small cavities in the flinty shell-wall, which possess an inner and an outer opening. These intraparietal cavities are either spherical (fig. 7b) or cylindrical (fig. 1d, 4a) or spindle-shaped, with a constriction (fig. 2a). Further accurate examinations probably will show a greater variety in their shape. But each cavity constantly possesses two small openings, one on the outer, and the other on the inner surface of the shell-wall. Closer examination (especially of broken shells and slides) proves the presence of these two openings, which in the smaller species seem to be absent on the first view. I may, therefore, suppose that also in the similar valves of the Diatomaceæ, which exhibit exactly the same structure, an inner and an outer opening are always present in each hexagonal pit, and that the very small size alone prevents them from being recognised. The regular hexagonally-framed cavities in the shell-wall of the Challengerida (probably also of the Diatomaceæ) are therefore genuine pores, differing from the pores of other Radiolaria only in their smaller size and the dilatation of the middle part, which is much wider than the two openings.

The mouth of the shell, its single larger opening, exhibits in the various Challengerida a great variety in form and structure, and offers the best means for separating genera and species. According to its essential shape two different subfamilies and six genera may be distinguished in this family. In the first subfamily, Lithogromida, the mouth is a simple large opening in the wall of the shell on the oral pole of its main axis (Pl. 99, figs. 1-15). In the second subfamily, Pharyngellida, the mouth is prolonged into a cylindrical hollow tube, which is prominent into the shell-cavity, and comparable to the pharynx of the Metazoa in general form and function (Pl. 99, figs. 16-20). In this case we may distinguish an inner and an outer mouth of the tubular pharynx.

In a few forms of both subfamilies the mouth is toothless, smooth, and not armed with prominent external spines or teeth, as in Lithogromia, the simplest form of all (Pl. 99, fig. 22) and in Entocannula (figs. 19, 20). In the great majority of Challengerida, however, the outer opening of the mouth is armed with one or more teeth, usually strong prominent spines (figs. 1-18). Usually the base of these teeth is semitubular or a half cylinder, forming a more or less prominent peristome or a proboscis; and always in this case the open concave side of the canal-shaped groove is directed towards the ventral side of the shell, the closed convex side towards the dorsal side. When several teeth arise from the two lateral free margins of the groove, they are also directed towards the ventral side (figs. 2, 12, 17, &c.). Often a deep ventral incision or a guttural constriction separates the base of the proboscis from the genuine shell. The structure of this proboscis or peristome is usually the same as in the diatomaceous shell-wall; but sometimes its lattice-work assumes a different shape.

The opening of the mouth itself is rarely circular, usually it is elliptical or even lanceolate, often triangular. Sometimes two prominent opposite lips may be distinguished as right and left, when the fissure of the mouth is prolonged in a sagittal or longitudinal direction; as upper and lower, when it is prolonged in a frontal or transverse direction. The upper or dorsal lip is always more developed than the lower or ventral; and the entire semitubular proboscis may be regarded as a production of the upper lip. Sometimes the latter attains an extraordinary size and development, the greatest in Challengeria murrayi (Pl. 99, fig. 1).

The teeth of the mouth, which arise from the upper lip, are usually hollow, at least on the base; a prolongation of the shell-cavity arising into the base of the teeth. Their form is very variable, conical, lanceolate, triangular, sabre-shaped, &c. Usually they are more or less curved, and shorter than the radius of the shell; rarely they are straight, and longer than the radius (Pl. 99, figs. 5, 6). More important is their different number, which we have employed for the distinction of subgenera; future observations may prove that they are different genera. The most important are the following cases:—(A.) a single odd dorsal tooth (figs. 5, 16); (B.) two paired lateral teeth (figs. 4, 6, 17); (C.) three teeth, an odd dorsal and two paired lateral (figs. 7, 9, 10); (D.) four paired teeth, two dorsal and two ventral (figs. 3, 13); (E.) five teeth, an odd dorsal and two pairs of lateral (figs. 2, 12); (F.) six teeth in three lateral pairs (fig. 1).

The teeth of the peristome are not the only apophyses which arise from the shell of the Challengerida. In the majority other spines appear on the sagittal margin, which separates the right and left halves of the shell. These marginal spines are characteristic of the genera Challengeron and Porcupinia; they are usually radially directed, straight, conical, sometimes solid, at other times hollow. Their number and arrangement is very variable and serves for the distinction of species; the following differences are the most important:—(A.) a single odd spine on the apical pole of the shell, in the principal axis, opposite to the centre of the mouth (Pl. 99, figs. 6, 7); (B.) two aboral spines, a dorsal and a ventral (figs. 8-10); (C.) a bunch or a crowded group of radial spines on the aboral margin of the shell, usually one larger apical spine surrounded by several smaller dorsal and ventral (figs. 11, 12, 16); (D.) numerous radial spines along the whole sagittal margin of the shell (figs. 13-15).

The central capsule of the Challengerida is constantly placed in the aboral half of the shell-cavity, whilst its oral half is occupied by the phæodium; the intervals between them and the inner surface of the shell are filled up by the calymma. Frequently from the outer surface of the capsule arise numerous branched streams of sarcode, which pierce the calymma and are directed towards the inside of the shell-wall, where they are united by a thin continuous layer of protoplasm (Pl. 99, fig. 1). The phæodium is usually more voluminous than the capsule and envelops the latter on its anterior or oral face; more rarely the entire capsule is hidden in the phæodium. The phæodella, constituting the latter, are of very different sizes, of variable colour, olive and greenish-brown, red-brown, black-brown or nearly black. In some preparations, stained with carmine, numerous red coloured granula, similar to nuclei, were scattered in the phæodium (compare Murray, loc. cit., Pl. A, figs. 1-14).

The diameter of the central capsule is usually about one-half or one-third as great as that of the enclosing shell (Pl. 99, figs. 1-20). Its form is either spherical or slightly compressed, spheroidal, or sometimes lenticular. The large nucleus has the same form, is about half as broad as the capsule and contains numerous nucleoli. Sometimes the capsule contained two nuclei of equal size, and in a few specimens the shell contained two central capsules, each with a nucleus, so that the Challengerida seem to propagate also by self-division (Pl. 99, fig. 6).

The astropyle, or the large opening of the central capsule, exhibits the usual radiate operculum of the Phæodaria, and the tubular proboscis arising from it. This is constantly placed on the oral or anterior pole of the capsule and directed towards the mouth of the shell. I was never able to discover any parapyle or secondary opening in the central capsule, though numerous and well-preserved specimens of the Challenger collection were accurately examined. It seems therefore that the Challengerida are not Tripylea (as the majority of Phæodaria), but Monopylea with a single opening (like the closely allied Medusettida and Castanellida).

Synopsis of the Genera of Challengerida.

I. Subfamily Lithogromida. Shell without pharynx or inner prominent tube of the mouth. Shell smooth, without adoral teeth and marginal spines, 693. Lithogromia.

Shell with adoral teeth, but without marginal spines, 694. Challengeria.

Shell with adoral teeth and with marginal spines, 695. Challengeron.

II. Subfamily Pharyngellida. Shell with a pharynx, or an inner cylindrical tube, arising from the mouth and prominent inside. Shell smooth, without adoral teeth and marginal spines, 696. Entocannula.

Shell with adoral teeth, but without marginal spines, 697. Pharyngella.

Shell with adoral teeth and with marginal spines, 698. Porcupinia.

I. Subfamily Lithogromida. Shell without pharynx or inner prominent tube of the mouth.

Shell smooth, without adoral teeth and marginal spines,

693. Lithogromia.

Shell with adoral teeth, but without marginal spines,

694. Challengeria.

Shell with adoral teeth and with marginal spines,

695. Challengeron.

II. Subfamily Pharyngellida. Shell with a pharynx, or an inner cylindrical tube, arising from the mouth and prominent inside.

Shell smooth, without adoral teeth and marginal spines,

696. Entocannula.

Shell with adoral teeth, but without marginal spines,

697. Pharyngella.

Shell with adoral teeth and with marginal spines,

698. Porcupinia.

Subfamily 1. Lithogromida, Haeckel.

Definition.—Challengerida without pharynx, with a simple mouth, not prolonged into an inner prominent tube.

Genus 693. Lithogromia,^[312] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 5.

Definition.—Challengerida without pharynx, without adoral teeth and marginal spines.

The genus Lithogromia and the two following genera represent together the subfamily Lithogromida, comprising those Challengerida in which the mouth of the shell is a simple opening, and not prolonged into a pharynx or an internal prominent tube. Lithogromia may be regarded as the common ancestral form of this family, since it is the simplest of all, and possesses no external apophyses, neither teeth on the mouth, nor spines on the margin of the smooth shell.

1. Lithogromia silicea, n. sp. (Pl. 99, fig. 22).

Shell ovate, one and a half times as long as broad, not compressed. Transverse section circular. Mouth a simple circular opening with smooth edges about one-third as broad as the shell.

Dimensions.—Length of the shell 0.2, breadth 0.15; mouth 0.05.

Habitat.—North Atlantic, Færöe Channel (Gulf Stream), John Murray, depth 600 fathoms.

2. Lithogromia diatomacea, n. sp. (Pl. 99, fig. 21).

Shell ovate, lenticular, one and one-third times as long as broad, strongly compressed. Transverse section elliptical. Mouth a broad fissure, half as broad as the shell.

Dimensions.—Length of the shell 0.27, breadth 0.2; mouth 0.1.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.

3. Lithogromia lenticula, n. sp.

Shell subcircular, lenticular, about as long as broad, strongly compressed. Transverse section lanceolate. Mouth a narrow fissure, one-third as broad as the shell.

Dimensions.—Diameter of the shell 0.15, mouth 0.05.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

Genus 694. Challengeria, John Murray, 1876, Proc. Roy. Soc. Lond., vol. xxiv. p. 536.

Definition.—Challengerida without pharynx, with one or more adoral teeth, but without spines on the sagittal margin.

The genus Challengeria, and the following closely allied Challengeron, differ from the preceding Lithogromia, their ancestral form, in the development of teeth on the mouth of the shell. Challengeron has also radial spines on the sagittal margin, while these are wanting in Challengeria. The latter genus exhibits not less than twenty-one, the former twenty-five species, so that both together make by far the greatest part of the family (containing fifty-eight species). They are also more common and more widely distributed than the four other genera of Challengerida, and many species appear in great numbers in certain localities. With a few exceptions living on the surface, they are all inhabitants of great depths.

Subgenus 1. Challengerantha, Haeckel.

Definition.—Peristome with a single simple tooth, which is neither forked nor branched (Challengeriæ monodontes).

1. Challengeria naresii, John Murray.

Challengeria naresii, John Murray, 1876, Proc. Roy. Soc. Lond., vol. xxiv. pl. xxiv. fig. 1.

Challengeria naresii, John Murray, 1879, in litteris, Narr. Chall. Exp., vol. i. p. 236, pl. A, figs. 1, 1a-1e.

Shell circular or nearly circular, strongly compressed, lenticular. Peristome on the dorsal corner with a single simple vertical tooth, which is nearly straight, conical, with two sharp lateral edges on the base, about half as long as the shell.

Dimensions.—Diameter of the shell 0.5 to 0.6, length of the tooth 0.2 to 0.3.

Habitat.—Cosmopolitan; Atlantic, Indian, Pacific, at depths between 1000 and 3000 fathoms.

2. Challengeria xiphodon, n. sp.

Shell circular, nearly spherical, slightly compressed. Peristome on the dorsal corner with a single simple vertical tooth, which is straight, three-sided prismatic, and as long as the shell.

Dimensions.—Diameter of the shell 0.1 to 0.13, length of the tooth 0.1 to 0.12.

Habitat.—Tropical Atlantic, Stations 349 to 352, surface.

3. Challengeria sigmodon, n. sp.

Shell circular, nearly spherical, slightly compressed. Peristome with a single simple tooth, which is S-shaped, more or less curved, and about one-third as long as the shell.

Dimensions.—Diameter of the shell 0.3 to 0.4, length of the tooth 0.1 to 0.14.

Habitat.—North Pacific, Station 231, depth 2250 fathoms.

4. Challengeria tritonis, n. sp. (Pl. 99, fig. 5).

Shell ovate, slightly compressed. Peristome with a single simple tooth, which is vertical, straight, slenderly conical, and about half as long as the shell.

Dimensions.—Diameter of the shell 0.15 to 0.2, length of the tooth 0.1 to 0.12.

Habitat.—North Atlantic, Færöe Channel, Gulf Stream, in great numbers, in depths from 100 to 600 fathoms. (Expedition of H.M.S. "Triton," 1882), John Murray.

5. Challengeria pyramidalis, n. sp.

Shell slenderly ovate, one and a half times as long as broad, slightly compressed. Peristome with a single, simple, large tooth, which is three-sided pyramidal, vertical, straight, and longer than half the shell.

Dimensions.—Length of the shell 0.6 to 0.8, breadth 0.4 to 0.5; length of the tooth 0.4 to 0.5.

Habitat.—South Atlantic, Station 318, depth 2040 fathoms.

6. Challengeria cyrtodon, n. sp.

Shell ovate, lenticular, strongly compressed. Peristome with a single simple tooth, which is crescent-shaped, curved over the mouth, and about half as long as the shell.

Dimensions.—Length of the shell 0.4 to 0.5, breadth 0.3 to 0.4; length of the tooth 0.2 to 0.25.

Habitat.—South Pacific, Station 289, depth 2550 fathoms.

Subgenus 2. Challengeretta, Haeckel.

Definition.—Peristome with a forked or bifid tooth, or with two parallel lateral teeth (Challengeria diodontes).

7. Challengeria sloggettii, John Murray (Pl. 99, fig. 4).

Challengeria harstoni, John Murray, 1879 (partim), in litteris, Narr. Chall. Exp., vol. i. p. 226, pl. A, fig. 14.

Shell triangular, strongly compressed, with three rounded corners, or nearly semicircular; its aboral margin straight, horizontal, longer than the convex, dorsal, and ventral margins. Peristome with two parallel, triangular pointed teeth, which are obliquely ascending, lamellar, with inflated ovate base, and about as long as the shell-radius.

Dimensions.—Diameter of the shell 0.2 to 0.3, length of the teeth 0.1 to 0.15.

Habitat.—Tropical Atlantic, Stations 347, 348, depth 2250 to 2450 fathoms.

8. Challengeria harstoni, John Murray.

Challengeria harstoni, John Murray, 1879, in litteris, Narr. Chall. Exp., vol. i. p. 226, pl. A, fig. 14a.

Shell subcircular or somewhat triangular, with convex margins. Peristome with two parallel, slender, lanceolate teeth, which are obliquely ascending, and about half as long as the shell-radius.

Dimensions.—Diameter of the shell 0.15 to 0.18, length of the teeth 0.04 to 0.05.

Habitat.—North Pacific, Station 231, depth 2250 fathoms.

9. Challengeria campbelli, John Murray.

Challengeria campbelli, John Murray, 1879, in litteris, Narr. Chall. Exp., vol. i. p. 226, pl. A, fig. 9.

Shell cordate, nearly triangular, compressed, with blunt apex. Peristome in the excavated middle of the broad base, with two short, parallel, triangular teeth. This species is very similar to Porcupinia cordiformis (Pl. 99, fig. 16), but differs from it in the absence of an internal pharynx and of external apical spines.

Dimensions.—Diameter of the shell 0.2 to 0.24; length of the teeth 0.03 to 0.05.

Habitat.—South Atlantic, Stations 332 to 335, depth 1425 to 2200 fathoms.

10. Challengeria thomsoni, John Murray.

Challengeria thomsoni, John Murray, 1879, in litteris, Narr. Chall. Exp., vol. i. p. 226, pl. A, fig. 2.

Shell ovate, slightly compressed, with rounded apical pole. Peristome semitubular, obliquely ascending, nearly straight, in the lower half an open half-cylinder, in the upper half forked, with two parallel, thin, oblique teeth. Sometimes a third small (dorsal) tooth is developed.

Dimensions.—Length of the shell 0.3 to 0.35, breadth 0.2 to 0.25; length of the peristome 0.08 to 0.12.

Habitat.—South Atlantic, Stations 318 to 330, surface, and in depths from 1900 to 2900 fathoms.

11. Challengeria bidens, n. sp.

Shell ovate, strongly compressed, lenticular. Peristome with two curved, long and thin bristle-shaped teeth, which are obliquely inclined over the mouth, and longer than the radius of the shell.

Dimensions.—Length of the shell 0.12 to 0.18, breadth 0.1 to 0.14; length of the teeth 0.08 to 0.1.

Habitat.—Central Pacific, Stations 271 to 274, depth 2350 to 2750 fathoms.

12. Challengeria havergalli, John Murray.

Challengeria havergalli, John Murray, 1879, in litteris, Narr. Chall. Exp., vol. i. p. 226, pl. A, figs. 13, 13a.

Shell subspherical, slightly compressed. Peristome semitubular, slender, somewhat curved, in the lower half a simple half-cylinder, in the upper half forked, with two divergent teeth, nearly as long as the shell.

Dimensions.—Diameter of the shell 0.1 to 0.15, length of the peristome 0.08 to 0.12.

Habitat.—South Pacific, Station 300, depth 1375 fathoms.

13. Challengeria elephas, n. sp.

Shell ellipsoidal, not compressed. Peristome very similar to that of Challengeron diodon (Pl. 99, fig. 6), from which this species differs mainly in the absence of an apical spine, and in a more constricted mouth. The two conical teeth of the mouth are very large, nearly as long as the shell, straight, and almost parallel, each tooth has a large hole on the thickened base.

Dimensions.—Diameter of the shell 0.22, length of the teeth 0.2.

Habitat.—Indian Ocean, Cocos Islands (Rabbe), surface.

Subgenus 3. Challengerilla, Haeckel.

Definition.—Peristome with three teeth or trifid, with an odd dorsal and two paired lateral teeth (Challengeriæ triodontes).

14. Challengeria macleari, John Murray.

Challengeria macleari, John Murray, 1879, in litteris, Narr. Chall. Exp., vol. i. p. 226, pl. A, fig. 3.

Shell subcircular, lenticular, with a sharp marginal edge. Peristome semitubular, an oblique half-cylinder, with three divergent, short, triangular teeth; the dorsal odd tooth nearly vertical, the paired lateral teeth subhorizontal. Length of the peristome about one-third or one-fourth of the diameter of the shell.

Dimensions.—Diameter of the shell 0.25 to 0.35, length of the peristome 0.1 to 0.12.

Habitat.—South Atlantic, Stations 325 to 332, depth 1715 to 2900 fathoms.

15. Challengeria tridens, n. sp.

Shell subspherical, slightly compressed. Peristome about as long as the radius of the shell, with three diverging and obliquely descending teeth; the dorsal odd tooth twice as long as the paired lateral teeth.

Dimensions.—Diameter of the shell 0.08 to 0.12, length of the peristome 0.05 to 0.07.

Habitat.—North Atlantic, Færöe Channel (Gulf Stream), John Murray.

16. Challengeria trigona, Haeckel.

Challengeria macleari, var., John Murray, 1879, in litteris, Narr. Chall. Exp., vol. i. p. 226, pl. A, fig. 3b.

Shell triangular, with three rounded corners; the two lateral sides nearly straight, equal, the aboral side more or less convex and somewhat shorter. Peristome a curved half-tube (often longer than in Murray's figure), one-third to one-half as long as the shell, with three short triangular diverging and ascending teeth of equal length.

Dimensions.—Length of the shell 0.25 to 0.3, breadth 0.2 to 0.25; length of the peristome 0.08 to 0.12.

Habitat.—South Atlantic, Stations 332 to 335, depth 1425 to 2200 fathoms.

17. Challengeria trifida, n. sp.

Shell ovate, more or less compressed, about two-thirds as long as broad. Peristome semitubular, obliquely ascending, about one-third as long as the shell, in the lower half simple, in the upper trifid, with three curved divergent teeth; the dorsal odd tooth shorter than the paired lateral teeth.

Dimensions.—Length of the shell 0.3 to 0.36, breadth 0.24 to 0.28.

Habitat.—South Pacific, Station 289, depth 2550 fathoms.

Subgenus 4. Challengeromma, Haeckel.

Definition.—Peristome with four to six or more teeth.

18. Challengeria quadridens, n. sp.

Shell subglobose, with nearly circular perimeter. Peristome an oblique short and broad tube, the breadth of which is twice as great as its length and equal to the radius of the shell. Margin of the peristome with four divergent, short, triangular teeth, the two dorsal teeth half as long as the two ventral.

Dimensions.—Diameter of the shell 0.22 to 0.24, breadth of the peristome 0.1.

Habitat.—Central Pacific, Stations 265 to 268, depth 2700 to 2900 fathoms.

19. Challengeria bromleyi, n. sp. (Pl. 99, fig. 3).

Shell ovate, lenticular, strongly compressed. Peristome a broad, trapezoidal, horizontal lamella, the breadth of which is twice as great as its length and nearly equal to the diameter of the shell; its margin with four divergent triangular lamellar teeth, the two dorsal teeth three times as long as the two ventral.

Dimensions.—Length of the shell 0.08 to 0.1, breadth 0.05 to 0.07; breadth of the peristome 0.08.

Habitat.—North Pacific, Stations 244 to 253, surface, and in various depths.

20. Challengeria wildi, n. sp. (Pl. 99, fig. 2).

Shell subspherical, slightly compressed. Peristome semitubular, curved, as long as the shell-radius; with five curved lamellar teeth, an odd longer dorsal tooth and two pairs of lateral teeth.

Dimensions.—Diameter of the shell 0.12 to 0.18, length of the peristome 0.08 to 0.12.

Habitat.—Tropical Atlantic, Stations 347 to 348, depth 2250 to 2450 fathoms.

21. Challengeria aldrichi, John Murray, Challengeria aldrichi1876, L. N. 27, pl. 24, fig. 2.

Challengeria aldrichi, John Murray, 1879, in litteris, Narr. Chall. Exp., vol. i. p. 226, pl. A, fig. 4.

Shell subspherical, slightly compressed. Peristome a collar-like curved lamella, the breadth of which is twice as great as its length, and equals the radius of the shell; its margin with six short triangular teeth, two convergent ventral, two external horizontal lateral, and two ascending dorsal.

Dimensions.—Diameter of the shell 0.2, breadth of the peristome 0.1.

Habitat.—North Pacific, Station 244 to 248, depth 2050 to 2900 fathoms.

22. Challengeria murrayi, n. sp. (Pl. 99, fig. 1).

Shell subcircular, lenticular, strongly compressed. Peristome a trapezoidal, curved, collar-like lamella, the breadth of which is three times as great as its length and equal to the diameter of the shell; its margin with six triangular teeth, disposed like the preceding species, but larger.

Dimensions.—Diameter of the shell 0.15, breadth of the peristome 0.15.

Habitat.—North-Western Pacific (south of Japan), Station 231, depth 2250 fathoms.

Genus 695. Challengeron, John Murray, 1879, in litteris et schedulis.

Definition.—Challengerida without pharynx, with one or more teeth on the mouth, and with marginal spines.

The genus Challengeron has in general the same shape as the preceding closely allied Challengeria, but differs from it in the development of radial spines on the sagittal margin of the shell, which in the latter genus is smooth. According to the different number and arrangement of these marginal spines, which give a very singular appearance to them, we divide the twenty-five species of this cosmopolitan genus into four subgenera:—(1) with a single, odd apical spine; (2) with two opposed aboral spines (a dorsal and a ventral); (3) with a bunch of aboral spines; (4) with numerous radial spines along the whole sagittal margin of the shell.

Subgenus 1. Challengeranium, Haeckel.

Definition.—Margin of the shell with a single spine on the apical pole, opposite to the peristome (Challengeriæ caudatæ).

1. Challengeron monodon, n. sp.

Shell subspherical, slightly compressed, with a single straight conical spine on the apical pole, about as long as the radius. Peristome with a single vertical, straight, conical tooth, diametrically opposite to the apical spine and of the same length. (Similar to Challengeria naresii.)

Dimensions.—Diameter of the shell 0.2 to 0.3, length of the two opposite spines 0.1 to 0.15.

Habitat.—Central Pacific, Stations 270 to 274, depth 2350 to 2925 fathoms.

2. Challengeron cochlear, n. sp.

Shell nearly circular, lenticular, strongly compressed, with a single straight conical spine on the apical pole, about half as long as the radius. Peristome spoon-shaped, obliquely curved and inclined over the mouth, with a single terminal tooth, somewhat longer than the radius.

Dimensions.—Diameter of the shell 0.1, length of the peristome 0.06.

Habitat.—Indian Ocean, Cocos Islands, Rabbe, surface.

3. Challengeron diodon, n. sp. (Pl. 99, fig. 6).

Shell ovate, slightly compressed, with a single straight conical spine on the aboral pole, half as long as the radius. Peristome short and broad, collar-shaped, about twice as broad as long, and half as long as the radius, obliquely inclined over the mouth, with two divergent straight teeth, which are conical and longer than the shell-radius; beyond each tooth a large ovate hole in the wall of the peristome.

Dimensions.—Diameter of the shell 0.08 to 0.1, length of the teeth 0.06 to 0.08.

Habitat.—South-Eastern Pacific, Station 298, depth 2225 fathoms.

4. Challengeron pearceyi, n. sp. (Pl. 99, fig. 7).

Shell ellipsoidal or subspherical, scarcely compressed, with a single straight conical spine on the apical pole, about as long as the diameter. Peristome slender, semitubular, nearly as long as the diameter, somewhat obliquely inclined over the mouth, with three divergent triangular or lanceolate teeth; the dorsal odd tooth about twice as large as the paired lateral teeth.

Dimensions.—Diameter of the shell 0.08 to 0.12, length of the peristome 0.08 to 0.1.

Habitat.—Antarctic Ocean, between Kerguelen and Heard Island, Station 157.

5. Challengeron swirei, John Murray.

Challengeria swirei, John Murray, 1879, in litteris, Narr. Chall. Exp., vol. i. p. 226, pl. A, fig. 11.

Shell subspherical or somewhat ovate, with a single straight conical spine on the apical pole, about as long as the radius. Peristome slender, semitubular, straight and vertical, nearly as long as the shell, with three pointed teeth, an odd longer terminal and two paired shorter lateral.

Dimensions.—Diameter of the shell 0.06 to 0.08, length of the peristome 0.05 to 0.06.

Habitat.—Antarctic Ocean, Station 157, surface, common.

6. Challengeron triodon, n. sp.

Shell ovate, one and a half times as long as broad, not compressed, with a single short and stout conical spine on the apical pole, shorter than half the radius. Peristome short and broad, collar-shaped, nearly half as broad and one-third as long as the shell, with three divergent terminal teeth, an odd dorsal and two paired lateral.

Dimensions.—Length of the shell 0.25 to 0.3, breadth 0.15 to 0.2; length and breadth of the peristome 0.1.

Habitat.—North Pacific, Station 245, surface.

Subgenus 2. Challengerebium, Haeckel.

Definition.—Margin of the shell with two widely distant aboral spines, opposite in the sagittal plane, a dorsal and a ventral.

7. Challengeron balfouri, John Murray.

Challengeria balfouri, John Murray, 1879, in litteris, Narr. Chall. Exp., vol. i. p. 226, pl. A, fig. 10.

Shell subcircular, lenticular, strongly compressed, with two short divergent spines on the apical margin (a dorsal and a ventral). Peristome slender, semitubular, as long as the radius, vertical, in the distal half forked, with two parallel teeth.

Dimensions.—Diameter of the shell 0.08 to 0.16, length of the peristome 0.04 to 0.08.

Habitat.—North Atlantic, Stations 353 to 354, Hebrides, surface.

8. Challengeron golfense, n. sp.

Shell ovate, lenticular, compressed, with two short divergent spines on the apical margin (a dorsal and a ventral). Peristome slender, semitubular, half as long as the radius, with three terminal teeth, two short, vertically ascending, paired teeth and a larger odd tooth, which is inclined obliquely over the mouth.

Dimensions.—Diameter of the shell 0.15 to 0.2, peristome 0.05 to 0.07.

Habitat.—North Atlantic, Færöe Channel, Gulf Stream, surface and at various depths, John Murray.

9. Challengeron richardsii, n. sp. (Pl. 99, fig. 8).

Shell subcircular, lenticular, strongly compressed, with two stout, divergent, straight spines on the aboral margin (a dorsal and a ventral) which reach the length of the radius. Peristome slender, semitubular, slightly curved, about as long as the radius, with three short, divergent, terminal teeth. Mouth obliquely truncate. The dorsal odd tooth is nearly vertical, the two lateral paired teeth almost horizontal.

Dimensions.—Diameter of the shell 0.2 to 0.25, length of the spines and the peristome 0.08 to 0.12.

Habitat.—Antarctic Ocean, Station 157, surface, common.

10. Challengeron fergusoni, n. sp. (Pl. 99, fig. 9).

Shell isosceles triangular, with three slightly convex edges and two short, nearly vertically descending spines on the two corners of the aboral margin. Peristome inversely funnel-shaped, with a deep ventral incision on the base, and three broad, ovate, triangular teeth. The dorsal odd tooth is nearly vertical, whilst the two lateral paired teeth are almost horizontal; therefore the angle between the former and the latter is about a right angle.

Dimensions.—Diameter of the shell 0.2 to 0.3, length of the peristome 0.1.

Habitat.—Western Tropical Pacific, Station 224, depth 1850 fathoms.

11. Challengeron tizardi, John Murray.

Challengeria tizardi, John Murray, 1879, in litteris, Narr. Chall. Exp., vol i. p. 226, pl. A, figs. 7-7b.

Shell nearly equilateral triangular, with concave ventral, convex dorsal and aboral edges, on the two corners of the latter two opposite horizontal spines (a dorsal and a ventral). Peristome auriculate and bilobate, with a deep ventral incision on the base, and three pointed triangular teeth, the upper margins of which are nearly horizontal.

Dimensions.—Diameter of the shell 0.22 to 0.3, length and breadth of the peristome 0.01 to 0.12.

Habitat.—South Atlantic, Stations 332 to 335, depth 1425 to 2200 fathoms.

12. Challengeron triangulum, n. sp. (Pl. 99, fig. 10).

Shell nearly equilateral triangular, with three slightly convex or nearly straight sides, and two opposite obliquely descending and diverging spines on the two corners of the aboral margin. Peristome auriculate and bilobate, with a very thin basal neck and a deep incision on its ventral side; its distal margin is obliquely truncate, and exhibits an odd ascending dorsal tooth and two parallel, paired, descending, lateral teeth.

Dimensions.—Diameter of the shell 0.2 to 0.3; length and breadth of the peristome 0.1 to 0.12.

Habitat.—North Pacific, Stations 244 to 253, depth 2050 to 3125 fathoms.

Subgenus 3. Challengeridium, Haeckel.

Definition.—Margin of the shell smooth on the dorsal and the ventral side, but with three to five or more large spines (or a bunch of spines) on the aboral side; the middle spine is placed in the main axis, and larger than the others.

13. Challengeron bisternum, n. sp.

Shell subcircular, lenticular, strongly compressed, with three stout conical spines on the aboral pole; the middle spine is placed in the main axis, as long as the radius and three times as long as the two others. Peristome semitubular, straight, vertical, about as long as the radius, with three divergent teeth, the middle of which is odd and twice as large as the two paired lateral teeth.

Dimensions.—Diameter of the shell 0.22; length of the peristome 0.1.

Habitat.—Indian Ocean, Madagascar (Rabbe), surface.

14. Challengeron heptacanthum, n. sp.

Shell ovate, slightly compressed, with a series of five stout, conical, radial spines on the aboral margin; the middle spine is placed in the main axis and longer than the radius, twice as long as the two next, and three times as long as the more distant spines. Peristome short and broad, collar-shaped, with two large, divergent, straight teeth, each of which is longer than the shell-radius and bears at its base a large hole.

Dimensions.—Length of the shell 0.09 to 0.11, breadth 0.07 to 0.08; length of the teeth 0.07.

Habitat.—Tropical Atlantic, Stations 347, 348, depth 2250 and 2450 fathoms.

15. Challengeron crosbiei, n. sp. (Pl. 99, fig. 11).

Shell ovate, strongly compressed, with a series of seven to nine conical spines on the aboral margin; the middle spine is placed in the main axis, as long as the radius, and much larger than the six or eight other spines. Peristome short and broad, collar-like, with several small spines and two slender, widely distant, conical teeth, which are half as long as the shell, and curved towards one another like a pincer, each with a large hole at its base.

Dimensions.—Length of the shell 0.08 to 0.09, breadth 0.06 to 0.07; length of the two larger teeth 0.04 to 0.05.

Habitat.—Central Pacific, Station 270 to 274, depth 2350 to 2925 fathoms.

16. Challengeron buchanani, n. sp. (Pl. 99, fig. 12).

Shell ovate, slightly compressed, with a terminal comb of nine to twelve conical radial spines, densely crowded on the aboral pole; the middle spine is placed in the main axis, about half as long as the shell and much larger than the others. Peristome subconical, semitubular, recurved, half as long as the shell, with five triangular teeth; the dorsal odd tooth is inclined backwards, the two parallel pairs of lateral teeth directed ventrally.

Dimensions.—Length of the shell 0.15 to 0.18, breadth 0.1 to 0.12; length of the peristome 0.06 to 0.08.

Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.

Subgenus 4. Challengerosium, Haeckel.

Definition.—Margin of the shell dentated or serrated, with a continuous series of numerous short radial spines.

17. Challengeron channeri, John Murray.

Challengeron channeri, John Murray, 1879, in litteris, Narr. Chall. Exp., vol. i. p. 226, pl. A, fig. 12.

Shell subcircular, lenticular, strongly compressed, with fourteen to eighteen slender, straight, radial spines on the margin; the spines are straight, equidistant, cylindrical, and about as long as the radius of the shell. Peristome short, with two parallel, vertical, lateral, straight teeth, which are less than half the length of a spine.

Dimensions.—Diameter of the shell 0.14 to 0.17; length of the spines 0.06 to 0.08.

Habitat.—North Pacific, Station 231, depth 2250 fathoms.

18. Challengeron moseleyi, n. sp. (Pl. 99, fig. 14).

Shell circular, lenticular, strongly compressed, with thirty to forty slender, straight, equidistant, radial spines on the margin, larger and smaller spines alternating; the larger spines are about as long as the radius, the smaller only half as long. Peristome short, tubular, with two divergent ovate or nearly triangular teeth, a dorsal and a ventral, about as long as the shorter marginal spines.

Dimensions.—Diameter of the shell 0.13 to 0.15; length of the larger spines 0.06 to 0.07, of the smaller 0.03 to 0.04.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

19. Challengeron bethelli, John Murray.

Challengeron bethelli, John Murray, 1879, in litteris, Narr. Chall. Exp., vol. i. p. 226, pl. A, fig. 6.

Shell subcircular, lenticular, strongly compressed, with numerous (twenty to thirty) short conical spines on the margin (often wanting in the upper part of the dorsal margin). Peristome with a deep labial incision and two parallel triangular lateral teeth, the upper margin of which is horizontal.

Dimensions.—Diameter of the shell 0.2 to 0.25; length of the spines 0.02 to 0.03.

Habitat.—North Pacific, Stations 238, 241 (off Japan), depth between 2300 and 3950 fathoms.

20. Challengeron bathybium, n. sp.

Shell subcircular, lenticular, slightly compressed, with a corona of numerous (thirty to forty or more) short, conical, radial spines on the margin. Peristome helmet-shaped, nearly as long as the radius, with two widely divergent, conical, curved teeth, a vertical dorsal and a nearly horizontal ventral tooth.

Dimensions.—Diameter of the shell 0.22; length of the peristome 0.1.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

21. Challengeron johannis, n. sp.

Shell ovate, slightly compressed, with a corona of numerous (forty to sixty or more) short radial spines on the margin, ten to fifteen of them (in the aboral half) are pyramidal, and much larger than the others. Peristome helmet-shaped, about one-third as long as the shell, with a deep bosom and two widely divergent teeth on the concave upper margin, a forked dorsal and a conical ventral.

Dimensions.—Length of the shell 0.13, breadth 0.1; length of the peristome 0.04.

Habitat.—North Atlantic, Færöe Channel (Gulf Stream), John Murray.

22. Challengeron carpenterii, John Murray.

Challengeron carpenterii, John Murray, 1877, in litteris, Narr. Chall. Exp., vol. i. p. 226, pl. A, fig. 8.

Shell ovate, with a series of twelve to fifteen short, conical, radial spines on the aboral half of the margin. Peristome slender, semitubular, nearly as long as the shell, in the upper half forked, with two short parallel teeth.

Dimensions.—Length of the shell 0.13 to 0.18, breadth 0.1 to 0.14; length of the peristome 0.1 to 0.12.

Habitat.—Tropical Atlantic, Stations 347 to 348, depth 2250 to 2450 fathoms.

23. Challengeron ciliatum, n. sp.

Shell ovate, slightly compressed, with numerous (forty to fifty or more) short and thin, bristle-shaped, radial spines on the margin. Peristome obliquely truncate, with three curved spines; the dorsal odd spine subvertical, nearly as long as the radius, and much stronger than the two parallel, nearly horizontal, lateral spines.

Dimensions.—Length of the shell 0.15, breadth 0.11; length of the peristome 0.1.

Habitat.—North Pacific, Station 231, depth 2250 fathoms.

24. Challengeron willemoesii, n. sp. (Pl. 99, fig. 13).

Shell broadly-ovate or nearly circular, lenticular, with numerous (fifty to sixty) short and stout, conical, radial spines on the margin, increasing in size towards the aboral pole; the spines are alternately larger and smaller, the largest about half as long as the radius. Peristome helmet-shaped or half conical, longer than the radius of the shell, with two pairs of conical, curved, divergent teeth; the terminal teeth are the halves of a forked dorsal tooth and diverge laterally; the lower teeth are nearly horizontal and directed ventrally.

Dimensions.—Diameter of the shell 0.13 to 0.15; length of the peristome 0.07 to 0.1.

Habitat.—Tropical Pacific, Stations 274 to 276, depth 2350 to 2750 fathoms.

25. Challengeron wyvillei, n. sp. (Pl. 99, fig. 15).

Shell ovate, lenticular, strongly compressed, with numerous (forty to fifty) short, conical, radial spines on the margin; the spines are larger on the aboral side and spinulate. Peristome narrow, with two parallel, lateral, lamellar, forked teeth, about as long as the radius; the upper branch of the forks is sabre-shaped, obliquely truncate, subvertical, ciliate, and much broader than the lower nearly horizontal branch, which is directed towards the ventral side and curved upwards.

Dimensions.—Length of the shell 0.12 to 0.16, breadth 0.1 to 0.14; length of the peristome 0.08 to 0.11.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.

Subfamily 2. Pharyngellida, Haeckel.

Definition.—Challengerida with a pharynx, or an internal prominent mouth tube.

Genus 696. Entocannula,^[313] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 5.

Definition.—Challengerida with a pharynx, without teeth on the mouth, and without marginal spines.

The genus Entocannula and the two following genera represent together the subfamily Pharyngellida, differing from the preceding Lithogromida in the development of a peculiar pharynx, an internal, cylindrical, or funnel-shaped tube, which is conspicuous, leads from the mouth into the shell-cavity, and is provided with an inner and an outer opening. The Pharyngellida are much rarer than the Lithogromida; only ten species have been observed of the former, fifty of the latter. Entocannula is the simplest form of the Pharyngellida, having a smooth shell, without aboral teeth and marginal spines; it differs from Lithogromia only in the possession of the pharynx. One remarkable species is covered entirely with extremely thin, flinty hairs, and may represent therefore a peculiar genus, Trichogromia.

1. Entocannula circularis, n. sp.

Shell circular or nearly circular, lenticular, strongly compressed. Pharynx cylindrical, one-third or one-fourth as broad as the shell, twice as broad as long, its outer and inner apertures of equal breadth. Surface smooth.

Dimensions.—Diameter of the shell 0.20 to 0.32, of the pharynx 0.07 to 0.09.

Habitat.—North Pacific, Station 250, depth 3050 fathoms.

2. Entocannula subglobosa, n. sp.

Challengeria bromleyi, (partim), John Murray, 1879, in schedulis Chall. Coll.

Shell circular, nearly spherical, slightly compressed. Pharynx funnel-shaped, truncate, conical, its outer opening twice as broad as the inner. Surface smooth.

Dimensions.—Diameter of the shell 0.25 to 0.28, of the inner mouth 0.05.

Habitat.—South Pacific, Station 289, depth 2550 fathoms.

3. Entocannula infundibulum, n. sp. (Pl. 99, fig. 19).

Challengeria bromleyi (partim), John Murray, 1879, in litteris, Narr. Chall. Exp., vol. i. p. 226, pl. A, fig. 5.

Shell ovate, truncate at the mouth, slightly compressed. Pharynx funnel-shaped, its outer aperture two to three times as broad as the inner. Surface smooth.

Dimensions.—Length of the shell 0.22 to 0.28, breadth 0.2 to 0.25; inner mouth 0.04 to 0.08.

Habitat.—South Atlantic, Station 318, depth 2040 fathoms.

4. Entocannula hirsuta, n. sp. (Pl. 99, fig. 20).

Trichogromia hirsuta, Haeckel, 1881, Manuscript.

Shell ovate. Pharynx cylindrical, one-fourth as broad as the shell, its inner and outer apertures of equal breadth. The whole surface of the shell, and mainly the outer mouth, is densely covered with thin, curved, siliceous bristles.

Dimensions.—Length of the shell 0.27 to 0.36, breadth 0.2 to 0.3; mouth 0.05 to 0.08.

Habitat.—North Atlantic, Færöe Channel (Gulf Stream), John Murray, depth 600 fathoms.

Genus 697. Pharyngella,^[314] n. gen.

Definition.—Challengerida with a pharynx, and with one or more teeth on the mouth, but without marginal spines.

The genus Pharyngella differs from the preceding Entocannula, its ancestral form, in the development of one or more teeth on the peristome, and exhibits therefore the same relation to it that Challengeria bears to Lithogromia. Only a few species of this genus have been observed, all in the Atlantic.

1. Pharyngella monoceros, n. sp.

Shell ovate, slightly compressed, with a single large tooth on the dorsal corner of the peristome. The tooth is cylindro-conical, half as long as the shell, straight or slightly curved, and lies in the main axis of the shell. Pharynx cylindrical, straight, half as long as the shell-radius. This species is very similar to Challengeria tritonis (Pl. 99, fig. 5), and to the common cosmopolitan Challengeria naresii, but differs generically from them in the possession of the pharynx.

Dimensions.—Diameter of the shell 0.25 to 0.28; length of the tooth 0.14.

Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.

2. Pharyngella gastrula, n. sp. (Pl. 99, fig. 18).

Shell ovate. Peristome with two parallel, vertical, straight, pointed teeth, which are half as long as the shell-radius. Pharynx of the same length, cylindrical or funnel-shaped, its outer aperture scarcely broader than the inner.

Dimensions.—Length of the shell 0.3 to 36, breadth 0.24 to 0.3; teeth and pharynx 0.07 to 0.09.

Habitat.—North Atlantic, Færöe Channel (Gulf Stream), John Murray, depth 600 fathoms.

3. Pharyngella invaginata, n. sp.

Shell circular, slightly compressed or nearly spherical. Peristome with two parallel, vertical, straight, pointed teeth, which are about as long as the shell-radius. Pharynx of the same length, funnel-shaped; its outer aperture twice as broad as the inner.

Dimensions.—Diameter of the shell 0.2 to 0.22, teeth and pharynx 0.05.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.

4. Pharyngella gastræa, n. sp. (Pl. 99, fig. 17).

Shell broad, ovate or nearly circular, lenticular, strongly compressed. Peristome with two parallel, pointed teeth, which are nearly as long as the shell-radius, slightly curved, and obliquely inclined over the mouth. Pharynx half as long, cylindrical, obliquely descending; its outer and inner apertures of equal breadth.

Dimensions.—Diameter of the shell 0.3 to 0.33, teeth 0.12, pharynx 0.06.

Habitat.—South Atlantic, Stations 328 to 334, surface.

Genus 698. Porcupinia,^[315] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 5.

Definition.—Challengerida with a pharynx, with teeth on the mouth and marginal spines.

The genus Porcupinia differs from the preceding Pharyngella in the development of marginal spines, and exhibits therefore the same relation to it that Challengeron bears to Challengeria. Only two species have been observed; the first of these bears, besides the large marginal spines, numerous flinty bristles on the surface of the shell.

1. Porcupinia aculeata, n. sp.

Shell ovate, one and one-third times as long as broad, slightly compressed, covered with short, bristle-shaped spines over the whole surface, similar to Entocannula hirsuta (Pl. 99, fig. 20). The keeled margin is armed with numerous long and stout radial spines, which are alternately larger and smaller, as in Challengeron moseleyi (Pl. 99, fig. 14); the larger about as long as the radius, the smaller half as long. Peristome with two straight, parallel teeth. Pharynx funnel-shaped, half as long as the radius, its outer aperture twice as broad as the inner.

Dimensions.—Length of the shell 0.24, breadth 0.18; peristome 0.05.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.

2. Porcupinia cordiformis, n. sp. (Pl. 99, fig. 16).

Shell heart-shaped, nearly triangular, with a deep, concave bosom at the broad oral base, and a bunch of five to nine divergent spines at the blunt aboral apex, the middle spine (in the main axis) larger than the others. Peristome with two parallel, short, triangular teeth, which are obliquely inclined over the mouth (their upper convex edge nearly horizontal). Pharynx cylindrical, short, curved, and obliquely descending.

Dimensions.—Diameter of the shell 0.2 to 0.25, of the pharynx 0.05 to 0.08.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

Family LXXIX. Medusettida, n. fam. (Pls. 118-120).

Definition.—Phæodaria with a simple, ovate, hemispherical or cap-shaped lattice-shell of peculiar alveolate structure, and with hollow articulate feet surrounding the widely open mouth. Central capsule excentric, placed in the aboral half of the shell-cavity.

The family Medusettida represents a peculiar group of remarkable Phæodaria, which are similar to the Challengerida and Tuscarorida in the general form of the monaxonian shell and its apophyses, but differ from both families in the strange alveolate structure of the shell and of the hollow articulate feet surrounding its mouth. All the forms of this family here described are new, and not a single species was known before the discoveries of the Challenger. The majority seem to be inhabitants of the deep-sea, and occur mainly in those places where other families of Phæodaria (Aulacanthida, Aulosphærida, Cœlodendrida) are also well represented; they are, however, nowhere so common as these latter families. Their long feet and the small delicate shell are extremely fragile, so that complete and well-preserved specimens are rare. Some species are among the most admirable forms of Radiolaria, and are similar to small elegant Medusæ, e.g., Medusetta (Pl. 120, figs. 1-4), Gazelletta (Pl. 118, fig. 1), and Gorgonetta (Pl. 119).

The shell of the Medusettida is usually very small and delicate, in comparison to the long, often exceedingly large, feet, which depend from the margin of its mouth. From the size and the weight of these feet, we must suppose that the shell floats in the water in the same position as in the Nassellaria, so that the main axis is vertical, and the open mouth with the feet on its lower pole. The form of the shell exhibits the same varieties as the similar umbrella of the Medusæ. It is usually more or less hemispherical, sometimes flatter, cap-shaped, at other times more highly vaulted, campanulate or ovate. The similarity with the umbrella of a Medusa is so great, that in many species the large lower opening on the mouth of the shell is surrounded by a prominent ring or diaphragm, comparable to the velum of the Craspedotæ or Hydromedusæ (Pl. 120, figs. 3-4).

The structure of the shell, which we term shortly "alveolate," is very remarkable, and seems to be different from that of the other Phæodaria. Its reticulate appearance seems to indicate at first sight the usual lattice-shell, pierced by numerous very small pores (Pl. 118, figs. 1-3). But as soon as we make the shell dry, air always enters into its thin walls, and each apparent pore is found to be a small alveole or a separate compartment, which contains a small bubble of air (Pl. 120, figs. 11, 16). The thin wall of the shell is therefore double, composed of two parallel, very thin lamellæ of silica, which are little distant from one another, and are connected by a network of small rods or septa. This network is rarely regular, with square meshes (Pl. 118, fig. 3), or with hexagonal or triangular meshes (Pl. 116, fig. 2); it is usually irregular, with polygonal meshes (Pl. 120, figs. 11-16). The size of the meshes or alveoles is usually smallest on the aboral apex of the shell, and increases gradually towards the mouth. The largest alveoles are around the mouth, on the velum-shaped peristome, and here the marginal alveoles of the shell pass directly over into the separate alveoles or hollow compartments of the articulate feet (Pl. 118, fig. 1). Probably each alveole is a separate compartment, filled up by jelly, and has a small opening or pore on its inside; this pore is very distinct in the marginal alveoles of some larger species (Pl. 116, fig. 1a; Pl. 120, fig. 14), but I have not been able to recognise it everywhere. Moreover, it often happens that the alveoles are apparently completely closed. In some smaller species the alveolate structure seems to be present only in the peripheral part of the shell, whilst the central part is solid.

The outer convex surface of the shell is usually smooth, sometimes papillate (Pl. 116, fig. 1), at other times studded with small, conical, radial spines (Pl. 118, fig. 1; Pl. 120, figs. 4-11). Prolonged cylindrical spines or tubes are rarely scattered over the surface (Pl. 116, figs. 1, 2). In some genera a long vertical or oblique spine is developed from the apex of the shell, and is comparable to the "apical horn" of the Nassellaria (Pl. 118, figs. 2, 3; Pl. 120, figs. 1-4).

The mouth of the shell, or the large opening on the lower pole of its vertical main axis, is usually widely open, circular or polygonal, more rarely constricted. In many species the peristome is broadened and its margin developed in the form of a horizontal diaphragm, which constricts the entrance into the shell-cavity, and is comparable to the velum of the Hydromedusæ (Pl. 120, figs. 1-4). Sometimes the margin of the velum is fringed and bears numerous small dependent filaments of silica, comparable to the marginal tentacles of many Medusæ (Pl. 118, figs. 1, 3; Pl. 120, fig. 16). Rarely the mouth is strongly constricted and prolonged into a narrow, long, cylindrical tube, comparable to a proboscis; its opening is usually fringed (Pl. 116, figs. 1, 2).

The hollow articulate feet, or the large radial apophyses of the peristome, are the most remarkable organs of the Medusettida, and occur in the same form in no other family of Radiolaria. Their number is variable from three to twelve or more, and is here employed for the distinction of genera, as it is rather constant; the most frequent number is four (Medusetta) or six (Gazelletta). The feet are usually cylindrical, much longer than the shell, and more or less curved; more rarely they are straight or slightly compressed. They are always articulate, and divided by numerous transverse parallel septa into hollow compartments or alveoles; the transversely striated appearance of the feet is brought about by these septa. The alveoles have usually the form of short discoidal cylinders, and are broader than long (Pl. 120, figs. 5-13); rarely they are longer than broad (fig. 15). The septa between the alveoles are always perforated by a small opening and usually this opening is prolonged into a shorter or longer tubule, comparable to the siphuncle in the septa of the chambered shells of Cephalopoda; as in these latter, the succeeding siphons are arranged in a continuous series, which lies either in the axis of the foot or parallel to it (Pl. 120, figs. 8, 13, 15). The siphons are directed towards the distal end of the foot, so that, e.g., the siphon which arises from the septum between the ninth and tenth alveole, projects into the cavity of the latter. The communicating cavities of all the alveoles are filled up by jelly. In the dry shells, which are cleaned by hot mineral acids or by fire, and in which, therefore, the jelly is destroyed, the cavities become easily filled by air-bubbles (Pl. 120, figs. 8, 11, 15). Whilst the alveoles of each foot always form a long simple series, this series becomes doubled on the base of the larger feet, where they are broadened, and pass over into the compartments of the peristome (Pl. 122, figs. 10, 11, 14). The terminal alveole of each foot is closed.

The feet of the Medusettida are rarely quite simple and smooth (Pl. 120, figs. 1, 5, 7, 10, &c.). Usually they are armed with numerous spines or with elegant pencils of spathillæ. These secondary appendages or branches are also hollow, with a thin wall of silex; but they seem usually not to communicate with the alveoles of the foot directly; the cavities of the foot and its appendages are separated by a thin, solid septum. In Medusetta the convex outer edge of each curved foot is studded with a series of simple alveolate branches (Pl. 120, figs. 2-4). In Gazelletta, the feet are usually armed with verticillate or alternate spines, which are either simple or branched (Pl. 120, figs. 11-15); sometimes each branch is elegantly arborescent (Pl. 118, fig. 1). Sometimes the distal end of each branch is armed with a spathilla or a coronet of recurved teeth. The branches attain their highest development in the admirable Gorgonetta (Pl. 119). The twelve feet of this most interesting genus are differentiated into two different and alternating groups, six descending and six ascending. The six upper or ascending feet are arborescent, and each branch is armed at the distal end with a spathilla (figs. 1, 2). The six lower or descending feet are covered with most elegant arborescent pencils or anchor-bearing trees; each terminal branch of a tree is armed with two spathillæ, a smaller terminal and a larger below it (figs. 3, 4). The distal ends of the feet are rarely simple, usually they are forked or branched, or armed with peculiar spathillæ; and sometimes these terminal branches are very large (Pls. 118, 119).

The central capsule of the Medusettida is usually subspherical or somewhat lenticular, and hidden in the aboral or upper part of the shell-cavity, whilst its oral or lower part is filled up by the phæodium (Pl. 120, figs. 2, 9, 10, 11). Sometimes the phæodium is very large and prominent at the aperture of the mouth (Pl. 118, figs. 2, 3; Pl. 119, fig. 1). The nucleus is usually ellipsoidal, half as large as the central capsule, and includes numerous nucleoli. The membrane of the central capsule seems in all Medusettida to possess only one opening, the astropyle or main-opening with a radiate operculum and proboscis, placed at the lower or oral pole (Pl. 120, fig. 2). I have never been able to observe any secondary opening or parapyle. The free space between the shell wall and the capsule is filled up by the calymma, which also includes the phæodium. The jelly of the calymma is probably in direct continuity with the jelly which fills up the alveoles of the shell-wall and of the articulate feet.

Synopsis of the Genera of Medusettida.

I. Subfamily Euphysettida. Peristome of the shell with a corona of three or four feet. Apex of the shell (usually) with an apical horn. Three equal feet, 699. Cortinetta.

Four equal feet, 700. Medusetta.

One large and three small feet, 701. Euphysetta.

II. Subfamily Gazellettida. Peristome of the shell with six to twelve or more feet. Apex of the shell (usually) without apical horn. Six descending feet, 702. Gazelletta.

Six descending and six ascending alternating feet, 703. Gorgonetta.

Numerous (ten to twenty or more) descending feet, 704. Polypetta.

I. Subfamily Euphysettida. Peristome of the shell with a corona of three or four feet. Apex of the shell (usually) with an apical horn.

Three equal feet,

699. Cortinetta.

Four equal feet,

700. Medusetta.

One large and three small feet,

701. Euphysetta.

II. Subfamily Gazellettida. Peristome of the shell with six to twelve or more feet. Apex of the shell (usually) without apical horn.

Six descending feet,

702. Gazelletta.

Six descending and six ascending alternating feet,

703. Gorgonetta.

Numerous (ten to twenty or more) descending feet,

704. Polypetta.

Genus 699. Cortinetta,^[316] n. gen.

Definition.—Medusettida with three articulate feet on the peristome.

The genus Cortinetta comprises Medusettida which exhibit the minimum number of feet, three, and which therefore may be compared to the tripodal Nassellaria (Cortina, Cortiniscus, Tripodiscus, &c.). This similarity is the greater, as in the few observed species an apical horn is developed (as also in the following genus). The three feet are in the two species observed of equal size and similar form, and equidistant, so that they cannot be distinguished as an odd caudal and two paired lateral feet, as in the similar Nassellaria.

1. Cortinetta tripodiscus, n. sp. (Pl. 117, fig. 7).

Shell campanulate, covered with numerous curved ascending bristles, with a prominent annular velum on the peristome, similar to that of Medusetta craspedota. (Pl. 120, fig. 4). Feet equal, widely divergent and equidistant, somewhat longer than the shell, slightly curved, and covered on their convex outer edge with a series of short lateral branches, the three ramules of which bear a spathilla. Apical horn conical, straight, about as long as the shell, also covered with curved bristles.

Dimensions.—Length of the shell 0.14, breadth 0.11; length of the feet 0.16, of the apical horn 0.11.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

2. Cortinetta cortiniscus, n. sp.

Shell campanulate, subspherical, thorny, with a prominent annular velum on the peristome. Feet equal, very large, widely divergent, about three times as long as the shell and studded with arborescent branches, similar to those of Gazelletta drymonema (Pl. 118, fig. 1). Apical horn slender, conical, straight, thorny, twice as long as the shell.

Dimensions.—Length of the shell 0.18, breadth 0.16; length of the feet 0.5 to 0.6, of the apical horn 0.33.

Habitat.—Central Pacific, Station 274, depth 2750 fathoms.

Genus 700. Medusetta,^[317] n. gen.

Definition.—Medusettida with four equidistant articulate feet of equal size on the peristome.

The genus Medusetta comprises those forms of the family which bear on the peristome four equal radial feet, and therefore exhibit a striking similarity to many small Medusæ (e.g., Codonium, Tiara, Sarsia, &c.). This similarity is the greater, as usually the four feet are elegantly curved and the entrance in the shell-cavity partly closed by a marginal diaphragm, comparable to the velum of the Craspedotæ or Hydromedusæ. In all the species observed the apex of the shell bears a slender vertical or curved spine, comparable to the apical horn of the Nassellaria. In most species the feet bear on their convex outside a series of teeth or branches, which are also alveolate.

1. Medusetta codonium, n. sp. (Pl. 120, fig. 1).

Shell ovate, smooth, twice as broad as the constricted mouth. Apical horn about as long as the shell, nearly straight, smooth. Feet cylindrical, smooth, irregularly curved, about as long as the shell.

Dimensions.—Length of the shell 0.08, breadth 0.05.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.

2. Medusetta tiara, n. sp.

Shell campanulate, smooth, about as long as broad, and three times as broad as the constricted mouth, which is surrounded by a horizontal broad ring, like the velum of a Hydromedusa. Apical horn conical, straight, half as long as the shell. Feet divergent, irregularly curved, twice as long as the shell.

Dimensions.—Length of the shell 0.07, breadth 0.06.

Habitat.—North Atlantic (Færöe Channel), John Murray, surface.

3. Medusetta minima, n. sp.

Shell slenderly ovate, smooth, about twice as long as broad, twice as broad as the constricted mouth. Apical horn straight, vertical, of the same length. Feet somewhat longer, very thin, slightly curved at the base, in the distal half nearly parallel and descending vertically.

Dimensions.—Length of the shell 0.06, breadth 0.03.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

4. Medusetta quadrigata, n. sp. (Pl. 120, fig. 2).

Shell ovate, campanulate, smooth, little broader than the wide open mouth. Apical horn longer than the shell, more or less curved, smooth. Feet cylindrical, about as long as the shell, strongly curved and somewhat spirally revoluted, with a series of short curved teeth on the abaxial margin.

Dimensions.—Length of the shell 0.07 to 0.09, breadth 0.04 to 0.06.

Habitat.—North Pacific (off Japan), Stations 231 to 237, surface.

5. Medusetta tetranema, n. sp. (Pl. 120, fig. 3).

Shell campanulate, conical, smooth, nearly twice as broad as the constricted mouth, without prominent velum. Apical horn somewhat shorter, straight, conical, thorny. Feet strongly curved inwards, convergent, twice as long as the shell, each with four to six strong, ascending, alveolate branches on the abaxial margin.

Dimensions.—Length of the shell 0.07 to 0.09, breadth 0.05 to 0.07.

Habitat.—Tropical Atlantic, Station 352, surface.

6. Medusetta spiralis, n. sp.

Shell hemispherical, thorny, with wide open mouth. Apical horn straight, vertical, thorny, twice as long as the shell; feet cylindrical, three times as long as the shell, spirally convoluted around the vertical axis of the shell, with a series of recurved teeth on the abaxial margin.

Dimensions.—Length of the shell 0.05, breadth 0.08.

Habitat.—Central Pacific, Stations 271 to 272, surface.

7. Medusetta craspedota, n. sp. (Pl. 120, fig. 4).

Shell campanulate or nearly spherical, spiny, twice as broad as the constricted mouth, which is surrounded by a funnel-shaped truncate velum. Apical horn conical, straight, spiny, half as long as the shell. Feet strongly curved, longer than the shell, with a series of short conical spines on the abaxial side.

Dimensions.—Length of the shell 0.06, breadth 0.06.

Habitat.—North Pacific, Station 239, surface.

Genus 701. Euphysetta,^[318] n. gen.

Definition.—Medusettida with four articulate feet on the peristome, one odd very large, and three small or rudimentary feet.

The genus Euphysetta agrees with the preceding Medusetta in the possession of four articulate feet; but whilst these in the latter are of equal size and similar shape, in the former a single odd foot only is developed, and very large, whilst the three others are rudimentary and very small. Euphysetta exhibits therefore the same relation to Medusetta that the Euphysidæ (Euphysa, Steenstrupia, &c.) bear to the Sarsiadæ (Codonium, Sarsia), among the Hydromedusæ (compare my System der Medusen, 1879, vol. i. p. 12).

1. Euphysetta staurocodon, n. sp. (Pl. 118, fig. 2).

Shell ovate, nearly as broad as long, smooth, with an oblique, slender, conical, apical horn of the same length. The larger odd foot cylindrical, curved, somewhat longer than the shell, with three diverging branches at the distal end. The three smaller feet very short, representing the form of a regular rectangular cross.

Dimensions.—Length of the shell 0.15, breadth 0.14.

Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.

2. Euphysetta hybocodon, n. sp.

Shell ovate, one and one-third times as long as broad, smooth, with an oblique, stout, conical horn of half the length. The larger odd foot cylindrical, curved, twice as long as the shell, with a few pairs of short lateral branches and forked distal end. The three smaller feet half as long as the shell, thorny.

Dimensions.—Length of the shell 0.16, breadth 0.12.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.

3. Euphysetta amphicodon, n. sp. (Pl. 118, fig. 3).

Shell subspherical, smooth, with a short, oblique, conical, apical horn. The larger odd foot cylindrical, nearly straight, as long as the shell, with a few short lateral branches, at the distal end forked. The three smaller feet were in one specimen observed forked, in another (the specimen figured) replaced by nine small thorns.

Dimensions.—Length of the shell 0.11, breadth 0.13.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

Genus 702. Gazelletta,^[319] John Murray, 1876 (in litteris).

Definition.—Medusettida with six articulate feet on the peristome.

The genus Gazelletta is by far the most common of all Medusettida, and some species seem to be widely distributed, or even cosmopolitan. The number of species, too, is in this genus much larger than in all the other genera of this family. It differs from the latter in the possession of six feet, which number is very constant in the majority of species; in some species, however, single specimens are not rarely found which possess five or seven feet instead of six. Usually the six feet are rather regularly formed and disposed, and diverge downwards; but sometimes there is more or less irregularity in their shape and arrangement. In the majority of species the feet are very long, curved, and armed in a very various manner, so that four subgenera may be distinguished, according to the armatures.

Subgenus 1. Gazellarium, Haeckel.

Definition.—Feet simple, smooth, without spines and without terminal branches.

1. Gazelletta hexanema, n. sp. (Pl. 120, fig. 5).

Shell hemispherical, smooth. Feet very long, cylindrical, straight, smooth, widely divergent, without terminal branches.

Dimensions.—Length of the shell 0.03 to 0.04, breadth 0.06 to 0.07; length of the feet 0.1 to 0.2.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface.

2. Gazelletta macronema, n. sp. (Pl. 120, figs. 7, 8).

Shell hemispherical, smooth. Feet very long, cylindrical, smooth, in the basal part horizontally expanded, in the distal part strongly curved downwards, without terminal branches.

Dimensions.—Diameter of the shell 0.1 to 0.12, length of the feet 1.2 to 1.6.

Habitat.—Central Pacific, Stations 270 to 274, surface.

3. Gazelletta orthonema, n. sp. (Pl. 120, fig. 10).

Shell hat-shaped, thorny. Feet cylindrical, straight, smooth, widely divergent, without terminal branches.

Dimensions.—Diameter of the shell 0.12 to 0.16, length of the feet 0.3 to 0.5.

Habitat.—Central Pacific, Stations 270 to 274, surface.

4. Gazelletta cyrtonema, n. sp. (Pl. 120, fig. 9).

Shell hat-shaped, thorny. Feet cylindrical, smooth, widely diverging at the base, strongly curved and convergent in the distal part, often semicircular, without terminal branches.

Dimensions.—Diameter of the shell 0.11 to 0.13, length of the feet 0.4 to 0.6.

Habitat.—North Atlantic, Station 354, Canary Islands, surface.

Subgenus 2. Gazellidium, Haeckel.

Definition.—Feet smooth, without lateral spines, but branched at the distal end, or with a bunch of terminal spines.

5. Gazelletta furcata, n. sp.

Shell flat, cap-shaped, smooth. Feet cylindrical, nearly straight, at the distal end forked, with two divergent, spinulate, terminal branches.

Dimensions.—Length of the shell 0.12, breadth 0.3; length of the feet 0.6 to 0.8.

Habitat.—Western Tropical Pacific, Station 224, surface.

6. Gazelletta bifurca, n. sp. (Pl. 120, fig. 6).

Shell cap-shaped, thorny. Feet nearly straight, widely divergent, cylindrical, smooth, at the distal end twice forked, with four divergent, terminal branches, each of which bears a spathillum with six to eight recurved teeth (sometimes, as in the specimen figured, five or six terminal branches instead of four).

Dimensions.—Diameter of the shell 0.1, length of the feet 0.3 to 0.4.

Habitat.—South Pacific, Station 288, surface.

7. Gazelletta penicillata, n. sp.

Shell campanulate, spiny. Feet cylindrical, strongly curved, smooth, with a bunch of twelve to twenty or more curved spines at the distal end.

Dimensions.—Diameter of the shell 0.08, length of the feet 0.6.

Habitat.—Central Pacific, Station 266, surface.

Subgenus 3. Gazellonium, Haeckel.

Definition.—Feet spiny, armed with simple or branched lateral spines, and with terminal branches of the same shape.

8. Gazelletta pectinata, n. sp.

Shell flat, cap-shaped, thorny, three times as broad as high. Feet straight or slightly curved, cylindrical, widely divergent, with four longitudinal rows of short and simple conical spines, which are directed towards the distal end, and about as long as a single joint of the foot.

Dimensions.—Length of the shell 0.16, breadth 0.5; length of the feet 1.5 to 2.0, breadth 0.03 to 0.05.

Habitat.—North Atlantic, Færöe Channel (John Murray), Hebrides (Mœbius).

9. Gazelletta pinnata, n. sp.

Shell hat-shaped, thorny. Feet cylindrical, strongly curved, pinnate, with two opposite longitudinal rows of simple conical spines, which are slightly curved, directed towards the distal end and opposed in pairs on about each third or fourth joint.

Dimensions.—Diameter of the shell 0.3, length of the feet 1.2 to 1.5.

Habitat.—South Atlantic, Station 325, depth 2650 fathoms.

10. Gazelletta studeri, n. sp. (Pl. 120, fig. 15).

Shell flat, cap-shaped, thorny. Feet widely divergent, nearly straight and horizontally expanded, with two alternate longitudinal rows of lateral spines, which arise perpendicularly from the foot, are simple, conical, slightly curved, and alternate on the succeeding joints. Ends of the feet constricted, with four to six spines in one row. Dedicated to Professor Studer.

Dimensions.—Diameter of the shell 0.15, length of the feet 0.6 to 0.8.

Habitat.—South Atlantic (east of Patagonia), Station 318, surface.

11. Gazelletta schleinitzii, n. sp. (Pl. 120, figs. 11, 12).

Shell hat-shaped, thorny. Feet cylindrical, nearly straight and horizontally expanded, with four longitudinal rows of equal lateral spines, which arise perpendicularly from the foot and bear at the end three short divergent teeth. The end of the arms bears three forked spines. I name this elegant species in honour of Captain Schleinitz, commander of the German ship "Gazelle," who conducted the deep-sea soundings during the years 1874 to 1876.

Dimensions.—Diameter of the shell 0.12, length of the feet 0.6 to 0.8.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.

12. Gazelletta trispathilla, n. sp. (Pl. 120, fig. 13).

Shell flat, cap-shaped, smooth. Feet cylindrical, nearly straight, widely divergent, with longitudinal rows of alternate spines, which arise perpendicularly from the foot and bear at the end three short divergent branches, each with a spathilla of six short teeth.

Dimensions.—Diameter of the shell 0.2 to 0.25, length of the feet 1.2 to 1.5.

Habitat.—North Pacific, Station 235 to 238, surface.

13. Gazelletta robusta, n. sp. (Pl. 120, fig. 14).

Shell flat, cap-shaped, thorny. Feet cylindrical, very stout, slightly curved, covered with short irregularly branched spines; their ends with a bunch of similar spines.

Dimensions.—Diameter of the shell 0.6, length of the feet 2.5 to 3.3.

Habitat.—Central Pacific, Stations 263 to 274, surface.

Subgenus 4. Gazellusium, Haeckel.

Definition.—Feet spiny, armed with simple or branched lateral spines, and with larger terminal branches of a different shape.

14. Gazelletta dendronema, n. sp. (Pl. 120, fig. 16).

Shell hemispherical, thorny, with a broad, alveolate velum which bears irregular hollow thorns on the inside and on the free margin (fig. 16). Feet divergent, irregularly curved, with scattered arborescent lateral spines, which are irregularly branched, and bear at the distal end of each branch a small spathilla with four to six teeth. The distal ends of the feet are dichotomously branched, with stouter simple fork-branches.

Dimensions.—Length of the shell 0.17, breadth 0.36; length of the feet 0.5 to 0.7.

Habitat.—North Pacific, Station 252, surface.

15. Gazelletta melusina, n. sp. (Pl. 118, fig. 1).

Shell campanulate, spiny. Feet divergent, strongly curved, with scattered arborescent lateral spines, which are richly and dichotomously branched, with thin, simple, terminal branches. The distal ends of the feet bear three or four much larger and stouter branches, which are again dichotomously branched.

Dimensions.—Length of the shell 0.2, breadth 0.15; length of the feet 0.5 to 0.8.

Habitat.—South Pacific, Station 293, depth 2025 fathoms.

Genus 703. Gorgonetta,^[320] n. gen.

Definition.—Medusettida with twelve articulate feet on the peristome, six ascending and six alternate descending.

The genus Gorgonetta is the most highly developed of all hitherto observed Medusettida, and belongs to the most remarkable forms of Radiolaria. Its general shape is very similar to that of a larva of a Geryonia or Carmarina, in which six interradial larval tentacles are directed upwards, six alternating perradial permanent tentacles downwards. The six ascending feet are in all the four species observed smaller, more or less branched, and armed with spathillæ. The six descending feet are much larger and covered with very elegant pencils, the single threads of which bear a double spathilla. The distal ends of the feet are forked or branched.

1. Gorgonetta mirabilis, n. sp. (Pl. 119, figs. 1-4).

Shell cap-shaped, flatly vaulted, or nearly hemispherical, about twice as broad as long, with smooth surface. Six ascending feet widely divergent, about twice as long as the breadth of the shell, nearly straight, arborescent, with numerous curved branches, each of which bears at the distal end a spathilla with four to six short recurved teeth (fig. 2). Six descending feet about twice as long as the six alternate ascending, nearly straight, covered with numerous elegant pencils. Each pencil is richly branched, with fifty to one hundred or more thread-like ramules, and each terminal ramule has two cruciate spathillæ, a larger proximal and a smaller distal (figs. 3, 4); the four recurved anchor-teeth of the proximal spathilla are twice as large as those of the distal. The distal end of each descending foot bears three or four very stout terminal branches, each of which is about as long as the shell and again trifurcate at the distal end.

Dimensions.—Length of the shell 0.2 to 0.3, breadth 0.4 to 0.5.

Habitat.—Tropical Atlantic, Stations 346 to 348, surface.

2. Gorgonetta geryonia, n. sp.

Shell hemispherical, twice as broad as long, with short scattered thorns on the surface. Twelve feet of similar shape to those in the preceding species, but differing in the following characters:—the six ascending feet are much smaller, about as long as the breadth of the shell, and each bears only six to twelve short branches; the six descending feet are about three times as long as the shell, more or less curved; their pencils much smaller, and the two spathillæ of each pencil-thread bear five anchor-teeth. The distal ends are more richly and irregularly branched.

Dimensions.—Length of the shell 0.4, breadth 0.7.

Habitat.—Indian Ocean (Cocos Islands), Rabbe, surface.

3. Gorgonetta carmarina, n. sp.

Shell flat, cap-shaped, three times as broad as long. Twelve feet similar in shape to those of the two preceding species, but more irregular in form and arrangement, and differing in the following characters:—the six ascending feet are nearly horizontally expanded, one and a half times as long as the breadth of the shell, with few short branches, each of which bears a spathilla with six recurved anchor-teeth. The six descending feet are about five times as long as the shell, irregularly curved, studded with numerous small pencils, each thread of which bears a double spathilla with six teeth. The distal ends are irregularly branched.