17. Aulographis tetrancistra, n. sp. (Pl. 103, fig. 22).
Radial tubes slender, cylindrical, straight. Terminal branches four to six (usually four), eight to ten times as long as the tube is broad, slightly curved and widely divergent, with a terminal spathilla of four crossed recurved teeth.
Dimensions.—Length of the tubes 0.5 to 0.7, breadth 0.01; branches 0.08 to 0.1.
Habitat.—South Pacific, Station 285, depth 2375 fathoms.
18. Aulographis hexancistra, n. sp. (Pl. 103, figs. 18, 19).
Radial tubes club-shaped, slightly curved, gradually thickened from the proximal to the distal end. Terminal branches four to eight (usually six in the majority of tubes), widely divergent, nearly straight, three to four times as long as the tube is broad, with a terminal spathilla of six (rarely five) recurved teeth.
Dimensions.—Length of the tubes 0.4 to 0.6, breadth 0.01 to 0.02; branches 0.04 to 0.08.
Habitat.—North Pacific, Stations 244 to 253, depth 2050 to 3125 fathoms.
19. Aulographis polyancistra, n. sp.
Radial tubes club-shaped, straight, thickened towards the distal end. Terminal branches ten to twenty, smooth, strongly curved, disposed in a corona, six to eight times as long as the tube is broad, each with a terminal spathilla of eight to twelve radial teeth.
Dimensions.—Length of the tubes 0.6 to 0.8, distal breadth 0.02; branches 0.12 to 0.16.
Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.
20. Aulographis asteriscus, n. sp. (Pl. 103, fig. 24).
Radial tubes slender, cylindrical, straight, equally broad. Terminal branches six to nine, widely divergent, disposed in a radiate corona, around a central branch, which is the distal prolongation of the tube itself. Each branch bears a stellate terminal spathilla, composed of ten to twenty conical teeth, which radiate in all directions.
Dimensions.—Length of the tubes 0.5 to 0.8, breadth 0.02; branches 0.06 to 0.09.
Habitat.—South Atlantic, Station 318, depth 2040 fathoms.
Definition.—Terminal branches of the radial tubes armed with numerous lateral denticles, and with terminal spathillæ (or whorls of small radial teeth).
21. Aulographis dentata, n. sp. (Pl. 103, fig. 20).
Radial tubes slender, cylindrical, equally broad, scarcely inflated at the distal end. Terminal branches six to eight, curved, disposed in a corona around a straight central branch, eight to ten times as long as the tube is broad, armed with numerous stout recurved lateral denticles and with a terminal spathilla of five or six recurved teeth.
Dimensions.—Length of the tubes 1.5 to 2.5, breadth 0.03; branches 0.15 to 0.2 long.
Habitat.—North Atlantic, Station 354, depth 1675 fathoms.
22. Aulographis pulvinata, n. sp. (Pl. 103, fig. 26).
Radial tubes club-shaped, straight, gradually thickened towards the distal end, which bears a broad, circular, biconvex cushion. The margin of this cushion bears two alternating verticils of radially divergent, straight, terminal branches, which are twice to three times as long as the tube is broad. Each branch is armed with two opposite lateral rows of numerous small denticles, and bears a terminal spathilla with six to eight recurved radial teeth.
Dimensions.—Length of the tubes 2.0 to 2.4, distal breadth 0.03 to 0.07; branches 0.05 to 0.08 long.
Habitat.—South-east Pacific (off Valparaiso), Station 298, depth 2225 fathoms.
23. Aulographis tripentas, n. sp. (Pl. 105, fig. 13, 13a).
Radial tubes club-shaped, straight, thickened towards the inflated distal end, which bears three alternating verticils of terminal branches, each with five radial branches. The ten branches of the inner and outer verticils are perradial, smooth; the alternating five branches of the middle verticil are armed with recurved lateral denticles. Each of the fifteen branches bears a terminal spathilla with five to seven recurved teeth.
Dimensions.—Length of the spines 2.0 to 2.5, distal breadth 0.03 to 0.06; branches 0.1 long.
Habitat.—South-east Pacific (off Juan Fernandez), Station 299, depth 2160 fathoms.
24. Aulographis verticillata, n. sp. (Pl. 105, fig. 12, 12a).
Radial tubes cylindrical, equally broad, with an inflated ellipsoidal knob at the distal end. This knob bears twenty to thirty slender, slightly curved, terminal branches, which are regularly arranged in five radial or meridional rows, and in four to six concentric verticils. The branches are five to ten times as long as the tube is broad, and armed with two opposite rows of lateral denticles, and with a terminal spathilla of six to eight recurved teeth.
Dimensions.—Length of the tubes 1.5 to 1.8, breadth 0.01 to 0.02; branches 0.5 to 1.0 long.
Habitat.—South Pacific, Station 293, depth 2025 fathoms.
25. Aulographis serrulata, n. sp. (Pl. 103, fig. 27).
Radial tubes club-shaped, curved, thickened towards the inflated ellipsoidal distal end, which bears a bunch of fifteen to twenty-five terminal branches, arranged more or less regularly in radial or meridional rows and concentric horizontal verticils. The branches are irregularly curved, twice to four times as long as the distal end of the tube, armed with two opposite rows of lateral denticles, and at the distal end with a spathilla of six radial teeth.
Dimensions.—Length of the tubes 1.5 to 1.8, breadth 0.02 to 0.04; branches 0.1 to 0.15 long.
Habitat.—North Pacific, Stations 253 and 254, depth 3025 to 3125 fathoms.
26. Aulographis candelabrum, n. sp. (Pl. 103, fig. 1).
Radial tubes club-shaped, straight, thickened towards the distal end and constricted beyond the ovate, inflated, terminal knob. This knob is similar to a candelabrum and bears a corona of six to nine strongly curved terminal branches, which are eight to ten times as long as the tube is broad, armed with scattered lateral denticles, and with a spathilla of five to seven radial teeth.
Dimensions.—Length of the tubes 1.6 to 2.4, breadth 0.03 to 0.05; branches 0.2 to 0.3 long.
Habitat.—South-east Pacific (off Juan Fernandez), Station 300, depth 1375 fathoms.
Definition.—Aulacanthida with a veil of tangential needles, and with radial tubes, which bear no lateral branches, but at the distal end a verticil of ramified or forked terminal branches.
The genus Auloceros differs from the preceding closely allied Aulographis, its ancestral form, in the ramification of the verticillate terminal branches. They are either simply forked or again ramified, and their distal ends are either simply pointed or armed with a terminal spathilla, or a little crown of recurved teeth. Some forms of this genus belong to the most elegant and graceful Phæodaria, as the Auloceros elegans figured, which I observed living in the Indian Ocean.
Definition.—Distal ends of the terminal branches pointed, smooth, without spathilla (or corona of radiate denticles).
1. Auloceros furcosus, n. sp. (Pl. 102, figs. 2-6).
Radial tubes slender, spindle-shaped or nearly cylindrical, more or less tapering towards the two ends. Terminal branches slender, curved, twice to four times as long as the tube is broad, very variable in number (usually two or three, rarely four, five, or six; compare figs. 2-6), once or twice forked; the secondary branches are short, irregular, and pointed. No terminal spathillæ. In some specimens of this species all the tubes bear two or three terminal branches, whilst in others there are tubes with four, five, or six branches intermingled. When the number of the terminal branches is constant in single localities, this transformistic or "Darwinian" species may be divided into the following "subspecies:" (1) Auloceros pandora (with variable numbers); (2) Auloceros bifurca (fig. 2); (3) Auloceros trifurca (fig. 3); (4) Auloceros quadrifurca (fig. 4); (5) Auloceros quinquefurca (fig. 5); (6) Auloceros sexfurca (fig. 6).
Dimensions.—Length of the tubes 1.5 to 2.5, breadth 0.02 to 0.03; branches 0.05 to 0.15 long.
Habitat.—North Pacific, Stations 231 to 253, surface and at various depths.
2. Auloceros trigeminus, n. sp. (Pl. 102, fig. 7).
Radial tubes club-shaped, gradually thickened towards the inflated distal end. Terminal branches short, scarcely longer than the tube is broad, two constantly opposite, each with three equal, conical, short secondary branches. No terminal spathillæ.
Dimensions.—Length of the tubes 0.6 to 0.8, breadth 0.02 to 0.03; branches 0.04 to 0.08.
Habitat.—North Atlantic, Station 353, depth 2965 fathoms.
3. Auloceros capreolus, n. sp. (Pl. 102, fig. 8).
Radial tubes cylindrical, equally broad. Terminal branches in two opposite clustered bunches, each with sixteen to eighteen unequal secondary branches. The total length and breadth of each cluster is about four times as great as the tube is broad. No terminal spathillæ.
Dimensions.—Length of the tube 1.5 to 2.0, breadth 0.03; branches 0.07 to 0.1.
Habitat.—South Pacific, Station 295, depth 1500 fathoms.
4. Auloceros cervinus, n. sp. (Pl. 102, figs. 9, 10).
Radial tubes slender, spindle-shaped, slightly curved, tapering gradually from the middle towards the two ends. Terminal branches constantly three, obliquely ascending, each twice or three times forked (often more or less irregularly), with slender, curved, secondary and tertiary branches (twenty to twenty-four on each tube); the latter are scarcely half as broad as the three main branches of each tube. No terminal spathillæ.
Dimensions.—Length of the tubes 2.0 to 3.5, breadth 0.03 to 0.04; branches 0.12 to 0.15 long.
Habitat.—South Atlantic, Station 325, depth 2650 fathoms.
5. Auloceros elegans, n. sp. (Pl. 102, fig. 1).
Radial tubes slender, cylindrical, straight, equally broad. Terminal branches two or three, more or less irregularly branched, each with twelve to eighteen curved and pointed secondary branches. No terminal spathillæ. Differs from the preceding Auloceros cervinus in the cylindrical form of the thinner straight tubes, and the more irregular ramification; the branches are nearly tangentially expanded, The specimen figured, with expanded pseudopodia, red central capsule, and green phæodium, was observed living by me in 1882 in Ceylon.
Dimensions.—length of the tubes 1.0 to 2.0, breadth 0.02 to 0.03; branches 0.15 to 0.3.
Habitat.—Indian Ocean, Ceylon (south of Matura), Haeckel, surface.
Definition.—Distal ends of the terminal branches with a spathilla, or a small corona of radial, usually recurved teeth.
6. Auloceros dicranaster, n. sp. (Pl. 105, figs. 14, 15).
Radial tubes cylindrical, straight, equally broad. Terminal branches tangential, forked, expanded horizontally, five to six times as long as the tube is broad; their number is usually five (more rarely four or six), and each is divided into two short, equal, divergent, secondary branches, armed at the distal end with a spathilla of five or six unequal recurved teeth.
Dimensions.—Length of the tubes 1.0 to 1.5, breadth 0.01 to 0.02; branches 0.05 to 0.08.
Habitat.—North Pacific, Stations 244 to 252, depth 2050 to 3050 fathoms.
7. Auloceros spathillaster, n. sp. (Pl. 102, fig. 12).
Radial tubes club-shaped or nearly cylindrical, straight, often thickened towards the distal end. Terminal branches ascending, three to six, usually four, partly simple, partly forked, slightly curved. The branches are from twice to three times as long as the tube is broad, and much thinner; at the distal end they are armed with a spathilla of five or six recurved teeth.
Dimensions.—Length of the tubes 2.0 to 2.5, breadth 0.02 to 0.03; branches 0.08 to 0.12.
Habitat.—South Atlantic, Station 319, depth 2425 fathoms.
8. Auloceros arborescens, n. sp, (Pl. 102, figs. 11, 13).
Radial tubes club-shaped, irregularly curved, thickened towards the distal end. Terminal branches two opposite (rarely three or four), forked near the base, and either dichotomously or more irregularly branched; each tube bears fifteen to thirty, usually twenty to twenty-four, secondary branches, which are irregularly curved, and armed at the distal end with a spathilla of four to eight recurved teeth. The tubes are more richly branched than in the preceding, smaller, closely allied species, and the branches are more flatly expanded.
Dimensions.—Length of the tubes 2.6 to 3.3, breadth 0.03 to 0.04; branches 0.1 to 0.2.
Habitat.—South Pacific, Stations 288 to 295, depth 1500 to 3000 fathoms.
Definition.—Aulacanthida with a veil of tangential needles, and with radial tubes, which bear two verticils of branches, a distal verticil of terminal branches, and a proximal verticil of lateral branches.
The genus Aulospathis and the following Aulodendron differ from the preceding Aulacanthida in the possession of lateral branches; these are usually similar to the terminal branches, and irregularly scattered along the distal half of the tubes in Aulodendron. In Aulospathis, however, the largest form in the family, each tube bears two whorls or verticils only, a verticil of terminal branches at the distal end, and a verticil of lateral branches beyond the latter, between the middle and distal third of the tube. The number of branches in each verticil is usually from two to four, rarely more; it is, however, very variable, so that the ten species described in the sequel are "Darwinian species," derived either from Aulospathis polymorpha, or from Aulospathis variabilis. Each branch bears at the distal end a spathilla, the teeth of which are very variable in form, number and arrangement.
Definition.—Distal ends of the radial tubes inflated, usually in the form of an ovate or pyriform terminal knob.
1. Aulospathis bifurca, n. sp. (Pl. 104, figs. 1-5).
Radial tubes with an inflated ovate terminal knob at the distal end, which bears two divergent, curved, terminal branches (often a few tubes bear three or four branches instead of the usual two). Proximal whorl usually cruciate, with four irregularly crossed lateral branches (but often with five or six, more rarely with two or three).
Dimensions.—Length of the tubes 0.15 to 25 mm., breadth 0.04 to 0.06; branches 0.1 to 0.15.
Habitat.—South Pacific, Stations 293 to 295, depth 1500 to 2270 fathoms.
2. Aulospathis trifurca, n. sp. (Pl. 104, figs. 6, 7, 7a).
Radial tubes with an inflated ovate terminal knob at the distal end, which bears three divergent, straight, or slightly curved terminal branches (often a few tubes bear two or four branches instead of the usual three). Proximal whorl irregular, usually with six divergent, straight, lateral branches.
Dimensions.—Length of the tubes 2.2 to 3.4, breadth 0.03 to 0.05; branches 0.1 to 0.15.
Habitat.—South Pacific (off Valparaiso), Stations 298 to 300, depth 1375 to 2225 fathoms.
3. Aulospathis quadrifurca, n. sp.
Radial tubes with an inflated ovate terminal knob at the distal end, which bears four crossed, divergent, curved terminal branches. Proximal whorl also rather regular, with a cross of four straight lateral branches.
Dimensions.—Length of the tubes 3.0 to 4.0, breadth 0.04 to 0.08; branches 0.2 to 0.3.
Habitat.—South Pacific, Station 291, depth 2250 fathoms.
4. Aulospathis polymorpha, n. sp. (Pl. 104, figs. 10-13).
Radial tubes with an inflated ovate terminal knob at the distal end, which bears a variable number of divergent, curved, irregular, terminal branches. Usually the majority of the tubes bear three branches, whilst others exhibit two or four, sometimes also five or six. Proximal whorl also very variable and irregular, with two to six, usually three or four unequal branches.
Dimensions.—Length of the tubes 2.0 to 4.0, breadth 0.04 to 0.06; branches 0.1 to 0.3.
Habitat.—South Pacific, Station 289, depth 2550 fathoms.
Definition.—Distal ends of the radial tubes of equal breadth or tapering gradually, not inflated, without terminal knobs.
5. Aulospathis diodon, n. sp.
Radial tubes without inflated terminal knob, forked at the tapering distal end, with two divergent curved branches of equal size. Proximal whorl cruciate, with four rather equal, crossed, straight, lateral branches (sometimes three or five instead of four in single tubes).
Dimensions.—Length of the tubes 2.0 to 2.5, breadth 0.03 to 0.04; branches 0.1 to 0.3.
Habitat.—North Pacific, Station 231, depth 2250 fathoms.
6. Aulospathis triodon, n. sp. (Pl. 104, fig. 8).
Radial tubes without inflated terminal knob, with three divergent, slightly curved, terminal branches. Proximal whorl with a variable number of curved lateral branches, usually also three (often two or four, rarely more).
Dimensions.—Length of the tubes 2 to 3, breadth 0.03 to 0.05; branches 0.2 to 0.3.
Habitat.—North Pacific, Stations 250 to 253, depth 2740 to 3125 fathoms.
7. Aulospathis tetrodon, n. sp. (Pl. 104, fig. 9).
Radial tubes without inflated terminal knob, with four crossed, divergent, slightly curved terminal branches. Proximal whorl usually with an irregular cross of four lateral branches (often five or six, rarely two or three instead of the usual four).
Dimensions.—Length of the tubes 2.0 to 2.5, breadth 0.03 to 0.04; branches 0.2 to 0.3.
Habitat.—North Pacific, Stations 244 to 245, depth 2775 to 2900 fathoms.
8. Aulospathis hexodon, n. sp.
Radial tubes without inflated terminal knob, with three forked, curved branches at the distal end, so that each tube usually bears six terminal branches; but other tubes of the same specimen bear only three simple or a few irregularly forked branches. Proximal whorl usually with six curved, irregular, lateral branches.
Dimensions.—Length of the tubes 2.0 to 3.0, breadth 0.03 to 0.06; branches 0.2 to 0.5.
Habitat.—Western Tropical Pacific, Station 224, depth 1850 fathoms.
9. Aulospathis furcata, n. sp.
Radial tubes without inflated terminal knob, with a variable number of unequal terminal branches, which are partly simple, partly irregularly forked or branched; the usual number of terminal branches is three or four, more rarely two or five or six. Proximal whorl very irregular, usually with four to six unequal, lateral branches.
Dimensions.—Length of the tubes 2.0 to 2.5, breadth 0.03 to 0.05; branches 0.1 to 0.3.
Habitat.—Stations 265 to 268, depth 2700 to 2900 fathoms.
10. Aulospathis variabilis, n. sp. (Pl. 104, figs. 14-17).
Radial tubes without inflated terminal knob, with a variable number of unequal terminal branches, which are constantly simple, never forked; the usual number is in the majority of the tubes three or four, often also two, rarely five to eight. Proximal whorl irregular, with a variable number of lateral branches (usually four to six).
Dimensions.—Length of the tubes 2.0 to 3.0, breadth 0.03 to 0.06; branches 0.1 to 0.3.
Habitat.—Central Pacific, Stations 271 to 274, depth 2350 to 2750 fathoms.
Definition.—Aulacanthida with a veil of tangential needles, and with radial tubes, which bear numerous, irregularly scattered, lateral and terminal branches.
The genus Aulodendron differs from the other Aulacanthida in the possession of lateral and terminal branches, which are irregularly scattered on the radial tubes and not arranged in regular verticils. The branches are usually short, simple or forked, rarely longer and again irregularly ramified.
1. Aulodendron antarcticum, n. sp. (Pl. 105, fig. 5).
Radial tubes cylindrical, more or less curved, in the inner proximal half smooth and half as broad as in the outer distal half, which is studded with irregularly curved, partly branched spines, arising usually perpendicularly from the tube. The majority of the spines usually simple, the minority forked, with two to four short branches, the largest spines scarcely twice as long as the breadth of the tube.
Dimensions.—Length of the tubes 0.7 to 0.9, breadth 0.01 to 0.02; length of the branches 0.02 to 0.04.
Habitat.—Antarctic Ocean (Kerguelen), Stations 156 to 159, surface.
2. Aulodendron pacificum, n. sp. (Pl. 105, fig. 2).
Radial tubes cylindrical, slightly curved, in the proximal half smooth, in the distal half with scattered lateral branches, which are partly simple, partly forked, about twice as long as the breadth of the tube, and bear at the distal end a spathilla with five to six recurved teeth. The distal end of the tubes bears a spherical knob, which is separated by a deep stricture and armed with a bunch of six to twelve strong conical teeth.
Dimensions.—Length of the tubes 1 to 1.2, breadth 0.015 to 0.02; branches 0.03 to 0.04.
Habitat.—South Pacific, Station 293, depth 2025 fathoms.
3. Aulodendron australe, n. sp. (Pl. 105, fig. 3).
Radial tubes cylindrical, straight, thin, smooth in the proximal half, armed with numerous lateral branches in the distal half; the majority of the branches forked, about as long as the breadth of the tube, with two or three short ramules, each of which bears a spinulate terminal knob. The distal end of the tubes also forked, with two or three divergent branches.
Dimensions.—Length of the tubes 1.2 to 1.6, breadth 0.01 to 0.012.
Habitat.—South Pacific, Station 289; New Zealand, Station 169, surface.
4. Aulodendron atlanticum, n. sp.
Radial tubes cylindrical, tapering gradually towards the two ends; smooth and straight in the proximal half, irregularly curved and branched in the distal half, with ten to twenty (rarely more) branches, which arise almost perpendicularly from the tube. The proximal branches are from four to eight times as long as the greatest breadth of the tube, forked, with two or three short ramules; the distal branches are much smaller and simple. The distal end of each branch bears a spathilla with four to six short teeth.
Dimensions.—Length of the tubes 2.4 to 3.6, breadth 0.06 to 0.08.
Habitat.—South Atlantic, Station 332, depth 2200 fathoms.
5. Aulodendron indicum, n. sp. (Pl. 105, fig. 1).
Radial tubes cylindrical, irregularly curved, tapering gradually towards the two ends; smooth in the proximal half, irregularly branched in the distal half, with ten to twenty or more curved branches. The proximal branches are very large, one-sixth to one-fourth as long as the tube and irregularly ramified; the distal branches are much shorter, also ramified or simple. All the branches are more or less curved and bear a spinulate knob at the distal end.
Dimensions.—Length of the tubes 1.2 to 1.8, breadth 0.02 to 0.03; length of the branches 0.1 to 0.3.
Habitat.—Indian Ocean; Cocos Islands (Rabbe), surface.
Definition.—Phæodaria with a simple or double, usually spherical lattice-shell, which is not bivalved and has no peculiar mouth or peristome. Central capsule placed in the centre of the shell.
Definition.—Phæodaria with a big spherical (sometimes polyhedral or ellipsoidal), very coarse shell, which is composed of thick bars containing an axial canal. Nodal points of the coarse network without astral septa. Meshes of moderate size, irregularly polygonal. Surface of the shell usually with radial spines and pyramidal elevations. No peculiar mouth in the shell. Central capsule tripylean, in the centre of the shell.
The family Orosphærida comprises those Phæodaria which possess a simple spherical or polyhedral lattice-shell, composed of hollow, very thick, non-articulate rods, without a peculiar shell-mouth. They agree in the considerable size of the spherical lattice-shell and the absence of a peculiar shell-mouth with the other Phæosphæria, but differ from them in the coarse and irregular shape of the massive network, which is composed of irregular polygonal meshes, separated by very thick concentrically stratified rods, containing a fine axial canal. The closely allied Sagosphærida differ from them in the delicate shape of the solid and very thin, filiform rods of the network, and its subregular triangular meshes. The Aulosphærida differ in the development of the peculiar nodal cavities and astral septa, by which the thin-walled cylindrical tubes of the articulated network are separated in the stellate nodal points. The Cannosphærida, closely allied to these latter, also differ in the articulated network, and further in the possession of an internal concentric shell. The Castanellida are sometimes similar to the Orosphærida, but distinguished by a peculiar large shell-mouth and a network of different shape.
The Orosphærida belong to the biggest Radiolaria, and the lattice-work of their spherical shell is of a ruder and coarser shape than in any of the other families of this class. Nevertheless they have been hitherto perfectly unknown, and were first discovered by the Challenger. We have been able to distinguish in the collection four genera and twenty-seven species. This strange fact may be explained by the circumstance, that they are in general rare, and restricted to a few localities, and that probably all the species are inhabitants of great depths. Complete shells also are rarely found, whilst broken fragments of their big shells, easily recognisable by the coarse irregular meshes and the thick stratified bars, are met with frequently in the Radiolarian ooze of some Pacific Stations, especially at Stations 265 and 268, at a depth of 2900 fathoms.
The lattice-shell of the Orosphærida is usually spherical, or an endospherical polyhedron (Pl. 106, fig. 4); rarely one axis is somewhat prolonged, so that the shell becomes slightly ellipsoidal (Pl. 106, fig. 1). Its diameter is usually between 2 and 3, often also between 2 and 1 mm., rarely more than 3, or less than 1 mm. The largest shells observed attained 5 to 6, the smallest 0.5 to 0.6 mm. Their general habit is very characteristic, so that they may be easily distinguished from all other spherical lattice-shells, especially from the Castanellida and from the simple Monosphærida (Cenosphæra, Acanthosphæra), with which I confounded them in the beginning (hence the first shell observed, figured in 1878, was placed among the Monosphærida in Pl. 12). A closer examination of the coarse network and of the peculiar structure of its thick bars always enables one to recognise even small isolated fragments of broken shells.
The meshes of the coarse network exhibit in all observed Orosphærida a very irregular form and unequal size; the majority are usually more or less quadrangular, more rarely they are triangular, pentagonal or hexagonal, very rarely rounded. They are often arranged in parallel rows, which seem to be determined by prominent crests, connecting the bases of the radial spines (Pl. 12, fig. 1; Pl. 106, fig. 4, &c.). The diameter of the meshes is usually between 0.05 and 0.1, often 0.1 to 0.2, rarely more than 0.25, or less than 0.025 mm. In Oroplegma, which develops an outer loose, spongy shell around the inner primary shell, the big meshes of the former become much larger and very irregular (Pl. 107, fig. 1).
The coarse bars which separate the large meshes of the irregular network are very thick and massive, cylindrical, usually of unequal thickness, straight or slightly curved, never angular or prismatic. Their diameter is usually between 0.01 and 0.02, rarely more than 0.03 or less than 0.005 mm. Their surface is either smooth or slightly spinulate. Examined in the dry state and by strong lenses, they constantly exhibit a fine, but distinct longitudinal striation, as the expression of concentric stratification. A fine axial canal or central tubule is usually visible in the axis of each rod, and often this axial canal is studded with numerous short lateral branches (Pl. 107, figs. 2, 4, 8). But very often the axial canals become rudimentary or lost, or are developed only in a part of the bars (Pl. 12, fig. 1). When they are completely developed, the entire network of the shell is drained by a reticulate system of communicating axial canals; they are probably filled by jelly in the living body. This tubular system never attains that regularity and high development which is constantly found in the Aulosphærida; and the characteristic stellate nodal points of the latter, with their astral septa, are never found in any of the Orosphærida. Moreover the wall of the tubular bars is very thin and structureless in the Aulosphærida, very thick and stratified in the Orosphærida, the enclosed canal very wide in the former, very narrow in the latter. The stratification of the concentric cylindrical lamellæ, which surround the narrow axial canal, is effected by the gradual deposition of the concentric layers, and is very similar to that which is found in the thick spicula of many sponges. The peculiar structure of the bars in the Orosphærida becomes very distinct if the skeleton be burned, or acted upon by fire for some time; it then assumes a brown colour and its surface often appears dimpled. Sometimes the concave dimples on the surface of the bars are rather deep and separated by prominent crests (Pl. 107, figs. 4, 7). The few genera of Orosphærida which are here distinguished have all the same structure, are closely allied, and differ mainly in the shape of the outer surface of the lattice-sphere. The latter is quite simple and smooth only in Orona. In the common Orosphæra (Pl. 106, figs. 1-3) it is studded with radial spines. In the most frequent form, Oroscena, the shell has a pyramidal or tent-shaped elevation on the base of each radial spine, and usually the bases of the neighbouring spines are connected by strong prominent crests, the edges of the three-sided or four-sided pyramids (Pl. 12, fig. 1; Pl. 106, fig. 4). This remarkable form is more or less polyhedral, with concave sides, and is similar to the characteristic shells which are represented by Auloscena among the Aulosphærida, by Sagoscena and Sagoplegma among the Sagosphærida (compare Pls. 108 and 110). The pyramids or tents, however, are in these latter more regularly and distinctly developed than in the Orosphærida. The radial spines which arise form the top of the pyramids are often branched, and the branches become connected to form an outer enveloping secondary shell or a loose spongy framework in Oroplegma (Pl. 107, fig. 1).
The radial spines of the Orosphærida never exhibit a constant number or disposition in the individual species; their usual number is from twenty to sixty. Their form exhibits two different types, which, however, are not sharply separated; robust club-shaped and slender rod-shaped spines. The robust club-shaped spines are usually about as long as the diameter of the shell; they are longitudinally striped in the basal part, spinulate or reticulately dimpled in the distal part; sometimes they are straight, at other times curved or undulate (Pl. 106, figs. 1-4; Pl. 107, figs. 4-6). The slender rod-shaped spines are usually longer than the diameter of the shell, cylindrical, more or less curved or even undulate, smooth or thorny, sometimes irregularly branched, and often the branches are all or partly connected (Pl. 106, fig. 3; Pl. 107, fig. 1). In the majority of the shells observed the radial spines were found to be partly broken off. Their structure is the same as that of the bars of the network; but the central axial canal and the surrounding concentric lamellæ are usually more distinct than in the latter.
The central capsule of the Orosphærida lies in the centre of the spherical lattice-shell, surrounded by the voluminous calymma, which fills up its cavity. The form, structure, and size of the central capsule are the same as in the closely allied Aulosphærida (Pl. 111, fig. 2). Its diameter is usually about 0.2, or between 0.15 and 0.25, rarely more than 0.3 or less than 0.12. The dark phæodium is of about the same volume as the central capsule, and envelops its oral half with the radiate operculum and the proboscis of the astropyle. The two opposite parapylæ are small.
| I. Subfamily Oronida. Surface of the shell without pyramidal or tent-shaped elevations. | brace | Surface smooth, without radial spines, | 671. Orona. |
| Surface studded with simple or branched radial spines, | 672. Orosphæra. | ||
| II. Subfamily Oroscenida. Surface of the shell with numerous pyramidal or tent-shaped elevations. | brace | Pyramids of the surface free, without spongy envelope, | 673. Oroscena. |
| Pyramids of the surface connected by a spongy envelope or an external lattice-shell, | 674. Oroplegma. |
| I. Subfamily Oronida. Surface of the shell without pyramidal or tent-shaped elevations. | ||||
| Surface smooth, without radial spines, | ||||
| 671. Orona. | ||||
| Surface studded with simple or branched radial spines, | ||||
| 672. Orosphæra. | ||||
| II. Subfamily Oroscenida. Surface of the shell with numerous pyramidal or tent-shaped elevations. | ||||
| Pyramids of the surface free, without spongy envelope, | ||||
| 673. Oroscena. | ||||
| Pyramids of the surface connected by a spongy envelope or an external lattice-shell, | ||||
| 674. Oroplegma. | ||||
Definition.—Orosphærida with a simple spherical or slightly ellipsoidal shell, without pyramidal elevations and radial spines.
The genus Orona is the simplest of the Orosphærida, and probably the common ancestral form of this family. The lattice-shell is a simple fenestrated sphere, sometimes slightly ellipsoidal, with prolonged main axis, and bears on its surface neither tent-shaped elevations nor radial spines. It may be confounded with some big forms of Cenosphæra; it differs, however, in the possession of hollow central canals in the thick bars of the very coarse lattice-plate.