3. Castanissa richardsi, n. sp.
Pores subregular, circular, about as broad as the bars. Bristles twice as long as one pore. Radial main-spines (about twenty) slender, cylindrical, irregularly curved, with dimpled surface (like those in Pl. 113, fig. 5a). Mouth with a corona of six stout, parallel, triangular teeth.
Dimensions.—Diameter of the shell 0.3 to 0.35, of the pores 0.015.
Habitat.—North Atlantic, Station 354, surface.
4. Castanissa crosbiei, n. sp.
Pores irregular, roundish, two to three times as broad as the bars. Bristles one-third as long as the radius. Radial main-spines very numerous, straight, cylindrical, smooth, about as long as the diameter of the shell. Mouth with ten or twelve irregular, conical, parallel teeth.
Dimensions.—Diameter of the shell 0.28, of the pores 0.01 to 0.015.
Habitat.—North Pacific, Stations 231 to 235, surface.
5. Castanissa macleani, n. sp.
Pores irregular, roundish or polygonal, two to four times as broad as the bars. Bristles about one-fourth as long as the radius. Radial main-spines numerous, straight, conical, stout, with dimpled surface, shorter than the radius. Mouth with six to eight irregular conical teeth.
Dimensions.—Diameter of the shell 0.32, of the pores 0.012 to 0.024.
Habitat.—Tropical Pacific, Station 268, depth 2900 fathoms.
6. Castanissa hoylei, n. sp.
Pores irregular, polygonal, two to three times as broad as the bars. Bristles nearly half as long as the radius. Radial main-spines (about thirty) very long and thin, cylindrical, irregularly curved, at the conical base inflated and fenestrated; shell therefore slightly polyhedral. Mouth with five strong conical teeth.
Dimensions.—Diameter of the shell 0.35 to 0.4, of the pores 0.02 to 0.03.
Habitat.—North Pacific, Station 245 to 250, surface.
Definition.—Castanellida with branched radial main-spines and a simple smooth mouth.
The genus Castanopsis differs from its ancestral form Castanidium in the ramification of the radial main-spines; the branches are usually very irregular and often partly confluent. The shell is very similar to the Astrosphæride Cladococcus (compare above p. 223, Pl. 27), but differs from it in the possession of the shell-mouth, absent in all Sphæroidea.
1. Castanopsis naresi, n. sp. (Pl. 113, fig. 3).
Pores subregular, circular, about twice as broad as the bars. Bristles twice as long as one pore. Radial main-spines somewhat shorter than the diameter of the shell, straight, cylindrical, in the proximal half simple, in the distal half irregularly branched, each with ten to twelve partly confluent branches.
Dimensions.—Diameter of the shell 0.6 to 0.7, of the pores 0.02 to 0.03.
Habitat.—Tropical Atlantic, Station 347 to 349, surface.
2. Castanopsis macleari, n. sp.
Pores irregular, roundish, two to four times as broad as bars. Bristles half as long as the radius. Radial main-spines about as long as the radius, stout and straight, cylindrical, forked at the distal end, with two or three unequal fork-branches.
Dimensions.—Diameter of the shell 0.42, of the pores 0.015 to 0.03.
Habitat.—South Atlantic, Station 332, depth 2200 fathoms.
3. Castanopsis fergusoni, n. sp.
Pores irregular, roundish or polygonal, about as broad as the bars. Bristles three times as long as one pore. Radial main-spines somewhat longer than the diameter of the shell, cylindrical, with irregular and partly confluent lateral branches (similar to Pl. 113, fig. 4a).
Dimensions.—Diameter of the shell 0.55, of the pores 0.012 to 0.016.
Habitat.—North Atlantic, Station 354, surface.
Definition.—Castanellida with branched radial main-spines and a dentate mouth.
The genus Castanura differs from the preceding Castanopsis in the possession of a corona of teeth surrounding the mouth, similar to that of Castanissa. It differs from the latter in the ramification of the radial main-spines, wherein it agrees with the former. Castanura may therefore be derived either from Castanissa by ramification of the main-spines, or from Castanopsis by development of teeth around the mouth.
1. Castanura tizardi, n. sp. (Pl. 113, fig. 4, 4a).
Pores regular, circular, without hexagonal frames, twice as broad as the bars. Bristles twice as long as one pore. Radial main-spines somewhat longer than the radius, straight, very stout, with irregular lateral branches, which are partly confluent. Mouth with six strong conical teeth.
Dimensions.—Diameter of the shell 0.6, of the pores 0.03.
Habitat.—Tropical Atlantic, Station 346, surface.
2. Castanura havergali, n. sp.
Pores regular, circular, hexagonally framed, as broad as the bars. Bristles three times as long as one pore. Radial main-spines as long as the shell-diameter, in the basal half simple, in the distal half with irregular, not confluent, lateral branches. Mouth with ten to twelve irregular, parallel, conical teeth of different sizes.
Dimensions.—Diameter of the shell 0.5, of the pores 0.045.
Habitat.—Indian Ocean, Madagascar (Rabbe), surface.
3. Castanura swirei, n. sp.
Pores regular, circular, hexagonally framed, as broad as the bars. Bristles half as long as the radius. Radial main-spines straight, longer than the shell-diameter; on the distal end with a few irregular, confluent, lateral branches. Mouth with six larger and six alternate smaller, parallel, conical teeth.
Dimensions.—Diameter of the shell 0.28, of the pores 0.015.
Habitat.—North Pacific, Station 253, surface.
4. Castanura carpenteri, n. sp.
Pores irregular, roundish, twice to four times as broad as the bars. Bristles about as long as the largest pores. Radial main-spines irregularly curved, longer than the shell-diameter, with inflated and fenestrated conical base; in the distal half irregularly branched, with simple, not confluent, lateral branches. Mouth with six to nine irregular, strong, conical teeth.
Dimensions.—Diameter of the shell 0.3, of the pores 0.012 to 0.025.
Habitat.—South Atlantic, Station 331, depth 1715 fathoms.
Circoporida, Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 5.
Definition.—Phæodaria with a spherical or polyhedral shell, exhibiting a peculiar solid porcellanous structure, with a stellate circle of radial pores around the base of the hollow radial spines. Mouth usually with teeth. Surface of the shell tabulate, panelled or dimpled. Central capsule excentric, placed in the aboral half of the shell-cavity.
The family Circoporida comprises those Phæodaria in which the simple spherical or polyhedral shell exhibits a peculiar porcellanous structure, possesses a simple mouth, and is particularly distinguished by the constant character denoted by their name, viz., by circles of pores surrounding the base of the radial spines. It agrees in these striking peculiarities with the following family, the Tuscarorida, but differs from them essentially by the spherical or polyhedral form of the shell, which is never ovate, with the main axis prolonged. The radial spines, variable in number, are regularly or symmetrically disposed in all Circoporida, whilst they are arranged around the poles of the main axis in all Tuscarorida. Whilst the latter are always extremely large, more than a millimeter in size, the former are much smaller and never reach the diameter of a millimeter. The number of genera and species in this family is not large, and the majority are very rare, but they belong to the most remarkable Radiolaria by the peculiar structure, as well as by the geometrical regularity of the polyhedral shell.
The Circoporida may be divided into two different subfamilies, the Circogonida and the Haeckelinida. The latter are represented by the single genus Haeckeliana (Pl. 114), and possess a spherical shell with numerous small dimples between the circles of pores, and numerous simple radial spines which do not exhibit a regular arrangement. The Circogonida, on the other hand, comprise all other genera (Pls. 115-117) and possess a panelled shell with polygonal plates, and a certain number of radial spines, which are regularly disposed on the corners of the polyhedral shell, and usually armed with verticillate bristles and terminal forks or spathillæ. Perhaps the Circogonida and Haeckelinida may be better considered as two separate families.
The geometrical fundamental form of the shell is in the Circoporida of the highest interest, since it exhibits regular proportions, which are very rare in other organic forms, generally some rare forms of regular polyhedrons. The shell in all members of this family belongs to that group of geometrical forms which I have called in my General Morphology "Polyaxonia" (vol. i., 1866, pp. 406-416). The shell therefore is constantly an "endospherical polyhedron," i.e., a polyhedron, all the corners of which lie in a spherical surface. The corners are always indicated by the bases of the radial spines arising from the surface of the shell and marking its axes, and it is immaterial whether the shell itself is a true polyhedron or a sphere; for in the latter case also the radial spines mark the axes of the polyhedron.
The six genera which we here distinguish among the Circoporida, represent six different fundamental forms. Circoporus (Pl. 115, figs. 1-3; Pl. 117, figs. 5, 6) possesses six radial spines, opposite in pairs in three diameters, perpendicular one to another; it agrees therefore with the Cubosphærida (p. 169, Pls. 21-25) and represents the regular octahedron, with eight congruent triangular faces and six corners. It has the same form as the well-known antheridia of Chara (Gener. Morphol., vol. i. p. 412). Circogonia (Pl. 115, figs. 8-10; Pl. 117, fig. 1) exhibits twelve radial spines, opposite in pairs in six equidistant diameters. The surface of the shell is divided into twenty equal and equilateral triangles, and agrees therefore with the regular icosahedron. The same form appears also in some forms of Aulosphæra, and in several Astrosphærida (Gener. Morphol., vol. i. p. 411). Circorrhegma (Pl. 117, fig. 2) possesses a regular shell with twelve equal pentagonal faces and twenty equidistant corners, from which arise twenty regularly disposed radial spines. It represents therefore the regular "pentagonal dodecahedron," the same remarkable form which is found in some Astrosphærida, and in the pollen-grains of some plants, e.g., Bucholzia maritima, Fumaria spicata, Polygonum amphibium, &c. (Gener. Morphol., vol. i. p. 412, Taf. ii. fig. 18).
The three genera of Circoporida mentioned therefore represent three different forms of regular polyhedrons, in the exact mathematical sense, viz., Circoporus, the regular octahedron, Circogonia, the regular icosahedron, and Circorrhegma, the regular dodecahedron. In each of these three regular forms all the faces, edges, and corners are equal. The remaining three genera of Circoporida represent, however, three forms of subregular or irregular endospherical polyhedra, which are not perfectly regular. Circospathis (Pl. 115, figs. 4-7; Pl. 117, fig. 3) is a rather common form, and constantly possesses nine symmetrically disposed radial spines; the shell is either spherical or polyhedral, with fourteen triangular faces and thirty edges; the nine spines lie in three meridional planes, which are crossed at equal angles (three equidistant spines in each plane). We call this remarkable form the tetradecahedron; it appears also in some Astrosphærida (e.g., in Haliomma echinaster, figured in my Monograph, Taf. xxiv. fig. 1). Circostephanus (Pl. 116, fig. 3) exhibits a subregular polyhedral shell with a variable number of triangular faces and of radial spines (twenty-four to forty or more). Circostephanus sexagenarius possesses sixty triangular equilateral faces, which are disposed in twelve pentagonal groups (each with five faces), so that the shell seems to be derived from a regular pentagonal dodecahedron, the twelve regular faces of which are divided each into five congruent triangles. From its corners arise thirty-two radial spines (twelve from the central points of the pentagons, twenty from the meeting corners of every three pentagons). In other cases the number of faces and radial spines seems to be larger and their arrangement more irregular. The same may be said of Haeckeliana, in which the dimpled shell is constantly spherical, and possesses a variable number of radial spines, from sixteen to fifty-five (usually between thirty and forty).
The structure of the shell in the Circoporida is the same as in the Tuscarorida, of a peculiar porcellanous nature. The shell-wall is very thick, more or less opaque, and in direct light whitish or yellowish. Its surface is dimpled, with numerous small, circular, roundish or polygonal dimples in Haeckeliana (Pl. 114, figs. 1-6). In the Circogonida, however, the surface is panelled, with regular or irregular polygonal plates, often separated by high prominent crests (Pl. 115, figs. 4-9, &c.). Numerous simple thin needles of silica lie tangentially disposed and irregularly scattered in the porcellanous or cement-like substance of the thick shell-wall. Under a strong lens this substance appears finely punctate, being probably pierced by numerous very fine pores. The surface of the shell is therefore minutely roughened, and often appears quite black under the microscope, by the adhesion of innumerable fine air-bubbles. In all Circoporida, as well is in the Tuscarorida, the porcellanous shell has not the perfect transparency of the purely siliceous shells of other Radiolaria; its refractive power is somewhat different from the latter; it becomes deeply stained by carmine and browned by fire, and seems therefore to consist of a peculiar carbonic silicate.
The shell in all Circoporida exhibits a simple, excentric mouth, which corresponds to the main osculum of the central capsule. The excentric position of this shell-mouth has no influence on the regular form of the shell. The mouth is either circular or polygonal, usually about as large as a basal circle of pores. It is always armed with prominent conical or pyramidal teeth, the number of which is variable and seems to depend partly upon the number of the shell-faces or the radial spines. Circoporus has usually four cruciate teeth (Pl. 115, fig. 1; Pl. 117, figs. 4, 5). Circorrhegma exhibits a pentagonal mouth with five teeth (Pl. 117, fig. 2). Circogonia possesses a hexagonal mouth with six teeth (Pl. 115, fig. 8; Pl. 117, fig. 1). Circospathis has no constant number; some species have five teeth (Pl. 115, fig. 4), others four (Pl. 115, fig. 10), others nine (Pl. 117, fig. 3a). Circostephanus is also variable; one species exhibits eight teeth (Pl. 116, fig. 3a), another ten, another twelve. In Haeckeliana (Pl. 114, fig. 3) the teeth are smaller and more numerous. Usually the teeth arise vertically from the surface of the shell and are spinulate; more rarely their points are directed towards the centre of the mouth. Sometimes numerous thin needles arise between the teeth (Pl. 115, fig. 10).
The radial spines of the Circoporida are tubular, usually cylindrical and conical at the thickened base, more rarely prismatic or slenderly pyramidal, with three or more edges; sometimes the edges are spirally wound around the axis (Pl. 115, fig. 6). In the majority of species their length is about equal to the diameter of the shell; often they are somewhat shorter, more rarely longer. Their tubular structure is always the same as in the Tuscarorida; the wall of the tube is thick, and in the axis of its cavity lies an axial cord or funicle, which is connected with the wall by numerous horizontal, simple, or branched threads (Pl. 115, figs. 6, 7). The axial funicle itself is either a simple thread of silica, or a strand, composed of three to fifteen or more filaments, which are closely twisted like a rope around the axis of the spine, and arise separately from the bridges between the pores of the basal circle (Pl. 115, figs. 7, 9). The number of pores in these circles is very variable, commonly from three to nine, sometimes twelve to fifteen or more; their form is usually irregularly ovate (Pl. 115, figs. 7, 9). The bridges between the pores usually bear numerous siliceous threads or bristles, which are curved downwards or upwards (Pl. 115, figs. 4-6). Sometimes the spines are entirely covered with similar bristles or cilia (Pl. 117, figs. 2-5), more rarely with regular verticils of lateral branches (Pl. 117, fig. 6).
The distal ends of the radial spines are simple in Haeckeliana (Pl. 114), whilst in the other Circoporida they are usually (or perhaps constantly) either forked or armed with a verticil of terminal branches. When the spines are simply forked, their two terminal branches lie in certain meridional planes (Pl. 117, fig. 5). The same is probably the case when they bear three divergent branches (Pl. 115, figs. 1, 2), or four crossed branches (Pl. 117, figs. 4, 6). The larger species usually bear a corona of five curved branches disposed around the distal apex of each spine (Pl. 116, fig. 3; Pl. 117, figs. 1, 2). Sometimes the formation of these coronas is twice or more often repeated, so that the spines appear verticillate.
The central capsule of the Circoporida (Pl. 115, fig. 8; Pl. 117, fig. 6) is usually about half as large as the enclosing shell, and lies excentrically in that half of its cavity which is remote from the shell-mouth (Pl. 115, fig. 8). The other half (near the mouth) is filled up by the cap-shaped, dark phæodium. The proboscis, or the central tubule of the astropyle, is hidden in the axis of the blackish phæodium, and is directed towards the mouth of the shell; it is often S-shaped, more or less curved. The circular radiate operculum of the astropyle, placed on the base of the proboscis, exhibits numerous branched radial ribs, and closes the main-opening like the lid of a tea-kettle (Pl. 115, fig. 3). The number of the parapylæ, or the accessory openings of the capsule, which in the majority of Phæodaria is two, seems to be usually increased in the Circoporida. In Circoporus the capsule seems to posses six and in Circospathis nine secondary openings, and therefore there is some probability that each circle of pores on the base of a radial spine corresponds to a secondary opening of the capsule. In Haeckeliana, however (Pl. 114), I could observe no parapylæ at all. These accessory openings are always very small in the Circoporida, and may be easily overlooked. Furthermore, the number of observations respecting this difficult point is too small, and their certainty not satisfactory; it requires therefore further accurate examination, as also does the whole central capsule of the Circoporida.
The numerous and remarkable characters of shape and structure, which we have described above as occurring in the Circoporida, are also found in the following closely allied family, the Tuscarorida; all the species are inhabitants of great depths. Perhaps it may therefore be more convenient to separate these two families from the other Phæogromia as a peculiar order, under the name Phæocalpia.
|
I. Subfamily Circogonida. Shell spherical or polyhedral with panelled structure and polygonal plates. A certain number of radial spines are geometrically disposed. |
brace | Shell octahedral (or spherical), | Six radial spines, | 711. Circoporus. | |
| Shell tetradecahedral, | Nine radial spines, | 712. Circospathis. | |||
| Shell icosahedral, | Twelve radial spines, | 713. Circogonia. | |||
| Shell dodecahedral, | Twenty radial spines, | 714. Circorrhegma. | |||
| Shell polyhedral, | Twenty-four to forty or more radial spines, | 715. Circostephanus. | |||
| II. Subfamily Haeckelinida. | brace | Shell spherical, with dimpled structure, and a variable number of radial spines (without polygonal plates), | 716. Haeckeliana. | ||
|
I. Subfamily Circogonida. Shell spherical or polyhedral with panelled structure and polygonal plates. A certain number of radial spines are geometrically disposed. |
||||||
| Shell octahedral (or spherical), | ||||||
| Six radial spines, | ||||||
| 711. Circoporus. | ||||||
| Shell tetradecahedral, | ||||||
| Nine radial spines, | ||||||
| 712. Circospathis. | ||||||
| Shell icosahedral, | ||||||
| Twelve radial spines, | ||||||
| 713. Circogonia. | ||||||
| Shell dodecahedral, | ||||||
| Twenty radial spines, | ||||||
| 714. Circorrhegma. | ||||||
| Shell polyhedral, | ||||||
| Twenty-four to forty or more radial spines, | ||||||
| 715. Circostephanus. | ||||||
| II. Subfamily Haeckelinida. | ||||||
| Shell spherical, with dimpled structure, and a variable number of radial spines (without polygonal plates), | ||||||
| 716. Haeckeliana. | ||||||
Definition.—Circoporida with panelled shell, composed of polygonal plates. The shell is usually polyhedral, more rarely spherical, and the radial spines are usually (or perhaps constantly) branched and regularly arranged.
Definition.—Circoporida with a spherical or regularly octahedral shell, composed of eight congruent, triangular plates, with six corners from which arise six radial spines, opposite in pairs in three diameters, perpendicular one to another.
The genus Circoporus, the simplest among the Circoporida, is distinguished by the regular octahedral form of the shell, with the three equal axes of the regular crystalline system perpendicular one to another. Six equal radial spines, arising from the six corners, lie opposite in pairs in those three dimensive axes. The eight equal triangular faces of the octahedron are sometimes plane, sometimes concave or convex, and sometimes the shell becomes spherical. In this case it becomes very similar to the Hexastylida among the Sphæroidea.
1. Circoporus sexfurcus, Haeckel (Pl. 117, fig. 5).
Challengeria sp., John Murray, 1876, Proc. Roy. Soc. Lond., vol. xxiv. pl. xxiv. fig. 5.
Shell spherical, covered with irregular, polygonal plates. Six radial spines shorter than the diameter of the shell, covered with thin curved bristles, in the proximal half cylindrical, in the distal half forked, each with two equal curved fork-branches. Around the ciliated base of each spine a corona of twelve to sixteen pores surrounded by a circle of numerous, curved, longer bristles. Mouth cruciform, with four triangular, convergent teeth.
Dimensions.—Diameter of the shell 0.55, length of the spines 0.4.
Habitat.—South Pacific, Station 289, depth 2550 fathoms.
2. Circoporus hexastylus, n. sp. (Pl. 117, fig. 4).
Shell regularly octahedral, with eight plane, congruent, triangular faces, which are covered with a very delicate network of small, regular, hexagonal plates. Six radial spines as long as the radius of the shell, four-sided pyramidal, simple, in the basal half covered with numerous curved bristles. Around the base of each spine a corona of four equal pores, surrounded by a circle of twelve short teeth. Apex with four crossed, curved branches (like those of Circospathis tetrodon). Mouth cruciform, with four smooth teeth.
Dimensions.—Diameter of the shell 0.24, length of the spines 0.12.
Habitat.—Central Pacific, Station 271, depth 2425 fathoms.
3. Circoporus characeus, n. sp.
Shell spherical, covered with a delicate network of irregular polygonal plates. Six radial spines longer than the diameter of the shell, cylindrical, covered with numerous curved bristles, each with eight pores at the base surrounded by a circle of long bristles. Apex of each spine with a trident or fuscina, similar to that of the following species. Similar to an antheridium of Chara.
Dimensions.—Diameter of the shell 0.32, length of the spines 0.4.
Habitat.—South Pacific, Station 285, depth 2375 fathoms.
4. Circoporus sexfuscinus, n. sp. (Pl. 115, figs. 1-3).
Shell subregular, octahedral, with eight triangular, concave, somewhat unequal faces, which are covered with an extremely delicate network of small square dimples, and furrowed by radial crests arising from the bases of the spines (fig. 2). Six radial spines about as long as the diameter of the shell, four-sided, prismatic, with rounded edges; each in the basal half with a verticil of four crossed, curved bristles (fig. 1), sometimes with two verticils (fig. 2); on the distal apex inflated, armed with a trident or fuscina. Around the base of each spine four crossed elliptical pores. Mouth cruciform, with four small teeth (fig. 1).
Dimensions.—Diameter of the shell 0.2 to 0.25, length of the spines 0.2 to 0.25.
Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.
5. Circoporus octahedrus, n. sp. (Pl. 117, fig. 6).
Shell regularly octahedral, with eight plane, or slightly convex, congruent, triangular faces, which are covered with very small, regular, triangular plates (like those of Polypetta tabulata, Pl. 116, fig. 2). Six stout radial spines, about as long as the diameter of the shell, four-sided prismatic, covered with three or four verticils of four long curved bristles; at the distal apex inflated, with four crossed, divergent, stout, curved horns. Around the pyramidal base of each spine a corona of eight pores (two on each of the four faces). Mouth cruciform, with four triangular, convergent teeth.
Dimensions.—Diameter of the shell 0.16, length of the spines 0.18.
Habitat.—South Pacific, Station 298, depth 2225 fathoms.
Definition.—Circoporida with a subregular, spherical, or polyhedral shell, composed of fourteen triangular, nearly equal plates, with nine corners, from, which arise nine radial spines, symmetrically disposed.
The genus Circospathis exhibits the remarkable and peculiar form of a "Tetradecahedron," or a subregular polyhedron with fourteen triangular faces, thirty edges, and nine corners, from which arise nine radial spines. These lie in three meridional planes, which are crossed at equal angles (three equidistant spines in each plane). The same interesting form occurs also in some Astrosphærida, which bear nine regularly disposed radial spines, as Haliomma echinaster. All four observed species of Circospathis are South Atlantic.
1. Circospathis furcata, n. sp. (Pl. 115, figs. 4-6).
Shell polyhedral or nearly spherical, with nine prominent corners, from which arise nine radial spines, about as long as the diameter of the shell. The polygonal plates of the shell are separated by high crests, usually hexagonal or pentagonal, irregular, about twelve to fifteen on the half meridian. Radial spines cylindrical, straight, about as long as the diameter of the shell, with spirally turned edges, covered with numerous curved bristles, at the distal end forked; the two fork branches curved, one-third as long as the simple basal part. The inflated base of each spine is surrounded by a corona of nine to twelve ovate basal pores. Mouth pentagonal, with five thick, mammillate and spinulate, somewhat convergent teeth (fig. 5).
Dimensions.—Diameter of the shell 0.6, length of the spines 0.5.
Habitat.—South Atlantic (east of Buenos Ayres), Station 325, depth 2650 fathoms.
2. Circospathis novena, n. sp. (Pl. 117, figs. 3, 3a).
Shell polyhedral (tetradecahedral), with fourteen triangular, plane, or slightly convex faces, covered with small, irregular, polygonal (usually hexagonal) plates, and nine prominent corners, from which arise nine radial spines, shorter than the diameter of the shell. Each spine is surrounded at the broader base by a circle of twelve to sixteen pores and a corona of bristles, and bears at the inflated distal apex a trident or fuscina, similar to that of Circoporus sexfuscinus (Pl. 115, fig. 2). Mouth with nine convergent, conical, denticulate teeth (fig. 3a).
Dimensions.—Diameter of the shell 0.6, length of the spines 0.4.
Habitat.—South Atlantic, Station 318 (east of Patagonia), depth 2040 fathoms.
3. Circospathis tetradeca, n. sp.
Shell spherical, covered with irregular, polygonal plates. Nine radial spines, cylindrical, as long as the radius of the shell, bristly, armed at the distal apex with a trident. (In one specimen six spines possessed three terminal branches, two spines two branches, and one spine four branches.) The broader base of each spine is surrounded by a corona of nine pores and a circle of curved bristles. Mouth with nine smooth conical teeth.
Dimensions.—Diameter of the shell 0.55, length of the spines 0.3.
Habitat.—South Atlantic, Station 332 (west of Tristan da Cunha), depth 2200 fathoms.
4. Circospathis tetrodonta, n. sp. (Pl. 115, fig. 10).
Shell subspherical or polyhedral, with fourteen triangular, convex faces, covered with irregular polygonal plates. Nine radial spines cylindrical, nearly smooth, about as long as the diameter of the shell; at the distal apex with four strong curved horns, like those of Circoporus hexastylus, Pl. 117, fig. 4. Each spine is surrounded at the base by a corona of nine irregular pores. Mouth with four large, prominent, conical teeth, which are spinulate, with vertical inner edge (fig. 10).
Dimensions.—Diameter of the shell 0.5, length of the spines 0.45.
Habitat.—South Atlantic, Station 323 (east of Buenos Ayres), depth 1900 fathoms.
Definition.—Circoporida with a regular icosahedral shell, composed of twenty congruent, triangular plates, with twelve corners, from which arise twelve radial spines.
The genus Circogonia is remarkable for the regular icosahedral form of its shell, a geometrical fundamental form, which occurs very rarely in organised bodies (as in Aulacantha icosahedra, and in some Astrosphærida with twelve regularly disposed radial spines). The shell is composed of twenty triangular, equilateral and congruent plates, which are sometimes separated by prominent crests; their surface is panelled by smaller hexagonal or polygonal secondary plates. The thirty edges between the plates are sometimes thickened. From the twelve corners of the regular icosahedron (where every five triangular plates meet), twelve equal radial spines arise, each of which is surrounded at the base by a corona of nine to sixteen pores. Two species only of Circogonia have been observed; the one has smooth spines, forked at the distal end, the other bears numerous curved bristles around each spine, and at the distal end a verticil of five curved branches. The mouth of the shell (placed in the centre of one of the triangular plates) is in both species armed with six teeth. Both species are found in the Tropical Atlantic.
1. Circogonia icosahedra, n. sp. (Pl. 117, figs. 1, 1a).
Shell regularly icosahedral, with twenty equal, triangular, nearly plane faces, which are separated by thirty prominent, crest-like edges, and covered by a delicate network of small, subregular, hexagonal plates. Twelve radial spines nearly conical, one and a half times as long as the radius of the shell, with five prominent edges. The campanulate base of each spine is covered with numerous long, curved bristles, surrounded by a circle of twelve to sixteen ovate, irregular pores, and separated from the slender distal part by a constriction. The distal apex of the spine is surrounded by a verticil of five conical, curved branches (corresponding to the five edges of the spines, and to the five faces, which meet in the corners where the spine arises). Mouth hexagonal, with six conical, spinulate teeth, convergent towards its centre (fig. 1a).
Dimensions.—Diameter of the shell 0.75, length of the spines 0.5.
Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.
2. Circogonia dodecacantha, n. sp. (Pl. 115, figs. 8, 9).
Shell subregularly icosahedral, with twenty equal, triangular, slightly convex faces, which are not separated by prominent crests, but covered with a network of irregular polygonal plates. Twelve radial spines, cylindrical, smooth, about as long as the diameter of the shell, forked at the distal end with two divergent, slightly curved branches (similar to Circospathis furcata, Pl. 115, figs. 4-6). The conical base of each spine is surrounded by a circle of nine to twelve irregular, ovate pores (fig. 9). Mouth circular, with a corona of six conical, smooth teeth which arise perpendicularly from the shell (in the upper part of fig. 8, at left).
Dimensions.—Diameter of the shell 0.6, length of the spines 0.7.
Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.
Definition.—Circoporida with a regular dodecahedral shell, composed of twelve congruent, pentagonal plates, with twenty corners, from which arise twenty radial spines.
The genus Circorrhegma is remarkable for the geometrical regularity of its shell, which represents a pentagonal dodecahedron. The shell is therefore composed of twelve equal and regular pentagonal plates, and these are separated in the only known species by thirty prominent crest-like edges. From the corners of the dodecahedron, at which every three pentagons meet, arise twenty radial spines, opposite in pairs in ten equidistant axes.
1. Circorrhegma dodecahedra, n. sp. (Pl. 117, figs. 2, 2a).
Shell dodecahedral, with twelve equal and regular, plane, pentagonal plates, which are separated by thirty prominent crests, and bear a network of numerous polygonal (usually also pentagonal), smaller plates. Twenty radial spines about as long as the radius of the shell, three-sided prismatic, covered with numerous bristles; each surrounded at the thickened base by a circle of twelve to sixteen pores, and at the distal apex by a corona of five curved, terminal branches. Mouth pentagonal, with five conical, subvertical, spinulate teeth (fig. 2a).
Dimensions.—Diameter of the shell 0.8, length of the spines 0.5.
Habitat.—Indian Ocean, Madagascar (Rabbe).
Definition.—Circoporida with a subregular, polyhedral or nearly spherical shell, composed of thirty to sixty or more triangular plates, with twenty-four to thirty-two or more corners, from which arise radial spines, symmetrically disposed.
The genus Circostephanus comprises those Circoporida in which the porcellanous shell is an endospherical polyhedron, with numerous (thirty to sixty or more) triangular faces, and has a variable number of radial spines (twenty-four to forty or more), arising from its corners. The number of faces and corners seems to be variable in this genus, but may perhaps be typical in some species. Circostephanus sexagenarius has the typical form of a "Sexagenal-Polyhedron," with sixty equal triangular faces and thirty-two corners, and may be derived from the "Pentagonal-Dodecahedron" (Circorrhegma) by dividing its twelve pentagonal faces each into five congruent triangles.
1. Circostephanus coronarius, n. sp. (Pl. 116, figs. 3, 3a, 3b).
Shell polyhedral, with thirty-two to forty triangular, concave faces of nearly equal size, which are separated by high prominent crests. From the elevated corners of the polyhedron arise twenty-four to thirty radial spines, which are three-sided prismatic or nearly cylindrical, about as long as the radius of the shell, and covered with long curved bristles. The distal end of each spine is surrounded by a verticil of five stout, curved branches, its pyramidal base by a corona of five (or sometimes six) ovate, basal pores (fig. 3b). Mouth armed with a corona of eight short, conical, vertical, spinulate teeth (fig. 3a).
Dimensions.—Diameter of the shell 0.4 to 0.5, length of the spines 0.2 to 0.25.
Habitat.—South-Eastern Pacific (off Valparaiso), Station 298, depth 2225 fathoms.
2. Circostephanus sexagenarius, n. sp.
Shell polyhedral, with sixty triangular, equilateral congruent faces which are nearly plane, and separated by high prominent crests. They are disposed in twelve pentagonal groups, each with five faces, so that they appear as if derived from a regular pentagonal dodecahedron, the twelve regular faces of which are each divided into five congruent triangles, meeting in its centre. From the elevated corners of the polyhedron arise thirty-two radial spines (twelve in the central points of the pentagons, twenty in the meeting corners of every three pentagons). The radial spines are nearly as long as the diameter of the shell, cylindrical, spinulate, and surrounded at the distal end by a verticil of five stout, curved branches, and at the pyramidal base by a corona of twelve to sixteen basal pores. Mouth armed with a corona of twelve conical, vertical, spinulate teeth.
Dimensions.—Diameter of the shell 0.75, length of the spines 0.6.
Habitat.—South Pacific, Station 295, depth 1500 fathoms.
3. Circostephanus polygonarius, n. sp.
Shell polyhedral, with sixty to eighty subregular, triangular, concave faces, which are separated by prominent crests. From the elevated corners of the polyhedron arise thirty to forty radial spines, which are longer than the diameter of the shell, densely covered with curved bristles and three-sided prismatic, with three spirally convoluted edges. Their distal end is surrounded by a verticil of eight or nine curved branches, and their pyramidal base by a corona of eight or nine basal pores. Mouth armed with a corona of ten conical, vertical, spinulate teeth.
Dimensions.—Diameter of the shell 0.8, length of the spines 0.9.
Habitat.—South Pacific, Station 288, depth 2600 fathoms.
Definition.—Circoporida with dimpled spherical shell, not composed of polygonal plates. The shell is covered with small roundish dimples, never polyhedral, and the radial spines are simple, not branched, and usually not regularly arranged.
Definition.—Circoporida with spherical shell of a peculiar dimpled, porcellanous structure, and with a variable number of simple radial main-spines which are usually not regularly arranged.