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.
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.
Cannosphærida, Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 6.
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.
| Internal shell solid, without open pores, | 691. Cannosphæra. |
| Internal shell latticed, with open pores, | 692. Cœlacantha. |
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.
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.
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.
Challengerida, John Murray, 1876, Proc. Roy. Soc. Lond., vol. xxiv. p. 471, pl. xxiv. figs. 1, 2.
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).
|
I. Subfamily Lithogromida. Shell without pharynx or inner prominent tube of the mouth. |
brace | 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. |
brace | 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. | ||||
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II. Subfamily Pharyngellida. Shell with a pharynx, or an inner cylindrical tube, arising from the mouth and prominent inside. |
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| 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. | ||||
Definition.—Challengerida without pharynx, with a simple mouth, not prolonged into an inner prominent tube.
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.