Dimensions.—Diameter of the disk 0.15 to 0.2, of the medullary shell 0.05 to 0.06; length of the marginal spines 0.02 to 0.08, basal breadth 0.01 to 0.03.
Habitat.—Cosmopolitan; Atlantic, Pacific, in various depths; also fossil in Barbados and Sicily.
Definition.—Surface of the disk covered with radial spines. Bases of the marginal spines connected by a solid equatorial girdle.
19. Heliodiscus apollinis, n. sp.
Disk with spiny or bristly surface, three times as broad as the medullary shell. Pores regular, circular; eleven to twelve on the radius. Equatorial girdle narrow, on the margin with sixteen to twenty broad, flat, triangular teeth, which are half as long and one-fourth as broad as the medullary shell. (Very similar to Astrophacus apollinis, Pl. 32, fig. 2, but with simple medullary shell.)
Dimensions.—Diameter of the disk 0.18, of the medullary shell 0.06; length of the marginal spines 0.03, basal breadth 0.015.
Habitat.—Mediterranean (Corfu), Haeckel, surface.
20. Heliodiscus zoroaster, n. sp.
Disk with spiny surface, four times as broad as the medullary shell. Pores subregular, circular; fourteen to sixteen on the radius. Equatorial girdle broad, radially striped, on the margin with ten to twelve pyramidal, deeply sulcated radial spines, which are nearly as long as the radius of the disk, and one-fourth as broad at the base.
Dimensions.—Diameter of the disk 0.24, of the medullary shell 0.06; length of the marginal spines 0.11, basal breadth 0.03.
Habitat.—Indian Ocean, between Aden and Ceylon, Haeckel, surface.
Definition.—Phacodiscida with simple medullary shell and with numerous (ten to twenty or more) branched radial spines on the margin of the disk (commonly with a variable number and an irregular disposition of the ramified spines).
The genus Heliodrymus differs from the nearly allied Heliodiscus by the ramification of the marginal spines, a character hitherto observed in no other genus of Phacodiscida. The branching is more or less irregular, either a simple bifurcation or a repeated fissure; the spines and their branches are commonly more or less flexuose. We can distinguish two subgenera: in Heliocladus the surface of the disk is smooth, in Heliodendrum covered with bristle-shaped radial spines, which are either simple or also branched, sometimes longer than the thick marginal spines.
Definition.—Surface of the disk smooth, without radial spines.
1. Heliodrymus dendrocyclus, n. sp. (Pl. 33, fig. 9).
Heliocladus dendrocyclus, Haeckel, 1881, Prodromus et Atlas (pl. xxxiii. fig. 9).
Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular, hexagonally framed; eight to nine on the radius. Marginal spines sixteen to twenty, cylindrical, very strong, flexuose, irregularly branched, nearly as long as the diameter of the disk. Between these main spines, each of which bears two to six irregular branches, are scattered on the margin numerous smaller simple spines.
Dimensions.—Diameter of the disk 0.16, of the medullary shell 0.05; length of the main spines 0.1 to 0.14, breadth 0.01 to 0.02.
Habitat.—Central Pacific, Station 271, surface.
2. Heliodrymus furcatus, n. sp.
Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, roundish; ten to twelve on the radius. Marginal spines twenty to twenty-five, cylindrical, flexuose, forked, about as long as the radius of the disk; fork-branches irregular, of unequal size. Some smaller simple spines are scattered between the forked ones.
Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.04; length of the radial spines 0.07 to 0.09, breadth 0.01.
Habitat.—Central Pacific, Station 265, surface.
3. Heliodrymus grottensis, Haeckel.
Heliodiscus grottensis, Stöhr, 1880, Palæontogr., vol. xxvi. p. 89, Taf. i. fig. 13.
Disk with smooth surface, two and a half times as broad as the medullary shell. Pores irregular, roundish; eight to nine on the radius. Marginal spines twenty to thirty, conical, very irregular in form, size, and disposition; the smaller simple, the larger irregularly branched and half as long as the radius of the disk.
Dimensions.—Diameter of the disk 0.17, of the medullary shell 0.07; length of the marginal spines 0.02 to 0.04, basal breadth 0.01 to 0.02.
Habitat.—Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.
Definition.—Surface of the disk armed with simple or branched radial spines.
4. Heliodrymus setosus, n. sp.
Disk with spiny surface, four times as broad as the medullary shell. Pores regular, circular; twelve to thirteen on the radius. Marginal spines ten to twelve, cylindrical, irregularly branched, each with two to eight flexuose branches of different sizes; the largest as long as the diameter of the disk. Spines of the surface bristle-shaped, half as long, not branched.
Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the marginal spines 0.12 to 0.18, breadth 0.025.
Habitat.—North Pacific, Station 254, surface.
5. Heliodrymus ramosus, n. sp. (Pl. 35, figs. 3, 4).
Disk with spiny surface, three times as broad as the medullary shell. Pores regular, circular, hexagonally framed; eleven to twelve on the radius. Marginal spines sixteen to twenty, cylindrical, about as long as the radius, irregularly forked or branched, with unequal flexuose branches. Spines of the surface nearly as long, bristle-shaped, also irregularly branched.
Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.05; length of the spines 0.06 to 0.08, basal breadth 0.01 to 0.015.
Habitat.—South Pacific, Station 288, surface.
6. Heliodrymus viminalis, n. sp. (Pl. 35, fig. 5).
Disk with spiny surface, two and a half times as broad as the medullary shell. Pores irregular, roundish; ten to twelve on the radius. Marginal spines fifteen to twenty, cylindro-conical, strong, partly simple, partly forked, about as long as the diameter of the disk. Spines of the surface very numerous, bristle-shaped, longer than the marginal spines, and more branched.
Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.06; length of the marginal spines 0.11 to 0.14, basal breadth 0.01 to 0.015; length of the surface spines 0.2 to 0.03.
Habitat.—Central Pacific, Station 271, surface.
Definition.—Phacodiscida with double medullary shell and with numerous (ten to twenty or more) simple radial spines on the margin of the disk (commonly with a variable number and an irregular disposition of the undivided spines).
The genus Astrophacus differs from the similar Heliodiscus in the duplication of the medullary shell. The number and disposition of the radial spines of the margin (commonly between ten and twenty) is also here variable in one and the same species. The greater number of observed species of Astrophacus resemble in a very remarkable manner the corresponding species of Heliodiscus, and differ only in the double medullary shell.
Definition.—Surface of the disk smooth, without radial spines. Bases of the marginal spines free, without a connecting equatorial girdle.
1. Astrophacus asteriscus, n. sp.
Disk with smooth surface, three times as broad as the outer and eight times as broad as the inner medullary shell. Pores regular, circular; twelve to fourteen on the radius. Marginal spines fifteen to twenty, of variable size and disposition; the largest as long as the radius of the disk, as broad at the base as one pore. (Very similar to Heliodiscus asteriscus, Pl. 33, fig. 8, but differing in the double medullary shell.)
Dimensions.—Diameter of the disk 0.2, of the outer medullary shell 0.07, of the inner 0.025; length of the marginal spines 0.05 to 0.1, basal breadth 0.01.
Habitat.—Central Pacific, Station 265, depth 2900 fathoms.
2. Astrophacus trochiscus, n. sp. (Pl. 34, fig. 14).
Disk with smooth surface, three times as broad as the outer and seven times as broad as the inner medullary shell. Pores irregular, roundish; twelve to thirteen on the radius. Marginal spines sixteen to twenty, conical, of irregular variable size and disposition; the largest as long as the inner medullary shell. (Differs from Heliodiscus trochiscus in the double medullary shell.)
Dimensions.—Diameter of the disk 0.22, of the outer medullary shell 0.08, of the inner 0.03.
Habitat.—North Atlantic, Station 354, surface.
3. Astrophacus solaris, n. sp. (Pl. 32, fig. 1).
Disk with smooth surface, three times as broad as the outer and seven times as broad as the inner medullary shell. Pores subregular, roundish; twelve to fourteen on the radius. Marginal spines one hundred to one hundred and twenty, conical, flexuose, of irregular size and form; the largest one-third as long as the diameter of the disk. The spines lie not only in the equatorial plane (as is usual) but also in two to four crowded girdles on both sides of it. (Very similar to Heliodiscus solaster, Pl. 34, fig. 4, but of double the size, with double the number of spines and with a double medullary shell.)
Dimensions.—Diameter of the disk 0.3, of the outer medullary shell 0.11, of the inner 0.045; length of the spines 0.03 to 0.1, basal breadth 0.01 to 0.02.
Habitat.—Indian Ocean, Sunda Strait, Rabbe, surface.
Definition.—Surface of the disk covered with radial spines. Bases of the marginal spines free, without a connecting equatorial girdle.
4. Astrophacus phacodiscus, n. sp. (Pl. 32, fig. 3).
Disk with spiny surface, two and a half times as broad as the outer and seven times as broad as the inner medullary shell. Pores subregular, circular; ten to twelve on the radius. Marginal spines twelve to sixteen, conical, stout, nearly as long as the radius of the disk, and as broad at the base as the inner medullary shell. The numerous bristle-shaped spines of the surface are scarcely half as long. (Similar to Heliodiscus phacodiscus, Haeckel, Monogr. d. Radiol., Taf. xvii. figs. 5-7, but differing in the double medullary shell.)
Dimensions.—Diameter of the disk 0.18, of the outer medullary shell 0.07, of the inner 0.025; length of the marginal spines 0.08 to 0.09, basal breadth 0.03.
Habitat.—South Pacific, Station 300, surface.
Definition.—Surface of the disk smooth, without radial spines. Bases of the marginal spines connected by a solid equatorial girdle. (Perhaps = Chilomma(?) Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.)
5. Astrophacus cingillum, n. sp.
Haliomma humboldti, var., Bury, 1862, Polycystins of Barbados, pl. viii. fig. 3 (at right).
Disk with smooth surface, three times as broad as the outer and eight times as broad as the inner medullary shell. Pores regular, circular; eleven to thirteen on the radius. Equatorial girdle about as broad as the inner medullary shell, in the proximal half radially striped, on the margin with eighteen to twenty-four short, flat, triangular spines, about as long as the breadth of the girdle. (Similar to Heliodiscus cingillum, but with double medullary shell.)
Dimensions.—Diameter of the disk 0.2, of the outer medullary shell 0.07, of the inner 0.025; length of the spines 0.02, basal breadth 0.02.
Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms; also fossil in Barbados.
6. Astrophacus saturnus, Haeckel.
? Chilomma saturnus, Ehrenberg, 1861, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 297; 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 286, Taf. ii. fig. 5.
? Chilomma saturnus, Haeckel, 1862, Monogr. d. Radiol., p. 447.
Disk with smooth surface, two and a half times as broad as the outer, six times as broad as the inner medullary shell. Pores large, irregular, roundish; five to seven on the radius (?). Equatorial girdle very broad, radially striped, nearly as broad as the outer medullary shell, perforated by twenty to thirty (or more?) radial spines. (The position of this species, and the identity of Chilomma with Astrophacomma, remains doubtful, as the imperfect figure given by Ehrenberg of Chilomma saturnus, the only species of the genus, is in contradiction with his vague description, as is very often the case.)
Dimensions.—Diameter of the disk 0.12 (with girdle 0.22) of the outer medullary shell 0.05, of the inner 0.02.
Habitat.—Arctic Ocean (Greenland, depth 1000 fathoms), Ehrenberg.
Definition.—Surface of the disk covered with radial spines. Bases of the marginal spines connected by a solid equatorial girdle.
7. Astrophacus apollinis, n. sp. (Pl. 32, fig. 2).
Disk with spiny surface, three times as broad as the outer, eight times as broad as the inner medullary shell. Pores regular, circular; eleven to twelve on the radius of the disk. Equatorial girdle narrow, smooth, on the margin with twelve to sixteen broad, flat, triangular spines, of the same length as the numerous bristle-shaped spines of the surface, which reach half the radius of the disk. (Very similar to Heliodiscus apollinis, but differing in the double medullary shell.)
Dimensions.—Diameter of the disk 0.24, of the outer medullary shell 0.08, of the inner 0.03; length of the radial spines 0.06, basal breadth 0.03.
Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.
Coccodiscida, Haeckel, 1862, Monogr. d. Radiol., p. 485.
Coccodiscida, Haeckel, 1881, Prodromus, p. 458.
Lithocyclidina, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad.
d. Wiss. Berlin, p. 214 (partim).
Definition.—Discoidea with extracapsular phacoid shell (or lenticular latticed cortical shell), connected by radial beams with an intracapsular, simple or double, concentric medullary shell, and surrounded by one or more concentric chambered equatorial girdles on the margin.
The family Coccodiscida was founded by me in 1862 for those Discoidea which agree with the Phacodiscida in the formation of the lenticular "phacoid shell" (including a simple or double medullary shell), but differ from them in the development of peculiar concentric chambered rings or girdles around the equatorial margin of the disk, similar to those of the Porodiscida.
The Coccodiscida represent a polymorphic family, in which we here distinguish sixteen genera with fifty-seven species; it comprises the greater part of those Discoidea which Ehrenberg united in his group Lithocyclidina (1875, represented by four genera and eight species); several of these, however, appertain to quite different families, as his Astromma entomocora, Lithocyclia amphitrites, &c. His knowledge of the structure was very imperfect. The peculiar differentiation of the genera and species exhibits the greatest analogy to that of the following family, Porodiscida, though the structure of the central disk in both families is quite different.
The Phacoid Shell, or the circular, lenticular cortical shell exhibits in the Coccodiscida quite the same structure and composition as in the Phacodiscida, described above (p. 420), so that there can be no doubt as to the phylogenetic origin of the former from the latter. Quite in the same way in both families, the lenticular "phacoid shell" is connected by numerous, short, radial beams with the intracapsular, simple or double, medullary shell; and also here these beams are commonly disposed in two groups around the poles of the shortened main axis of the lens, so that their distal ends are implanted in both circumpolar areas (Pl. 36, figs. 2-6; Pl. 37, figs. 3, 7; Pl. 38, figs. 2, 7). The medullary shell is commonly simple, spherical, sometimes a little lenticularly compressed; more rarely it is double, composed of two concentric lattice-shells, which are connected by radial beams; in this case either both concentric medullary shells are spherical, or the inner is spherical, and the outer lenticular, very rarely the inner is lenticular also. In average size and structure they agree perfectly with those of the Phacodiscida.
The Chamber Girdles or "chambered rings" around the equatorial margin of the disk, which constitute the only difference between the Coccodiscida and the Phacodiscida, seem to exhibit a considerable degree of difference of structure in the numerous species of this family; but I regret that I cannot explain them here satisfactorily. The study of these structures is extremely difficult because of the thickness and darkness of the massive opaque shells; to get a perfect knowledge of them, it is indispensable to compare slides made in different directions (horizontal slides through the equatorial and parallel planes, vertical slides through radial and parallel planes, oblique slides in different directions). But this requires a long time and a most careful study of the slides, which are very difficult to get in satisfactory condition. Therefore the following remarks can have only a provisional value.
In all Coccodiscida we can distinguish on the equatorial chamber-girdle of the lens-margin (even on superficial inspection) three different elements of structure, viz.:—(A) concentric circular rings in the equatorial plane; (B) numerous radial beams piercing the former and dividing them into imperfect chambers; (C) porous plates or sieve-plates on both convex faces of the disk. The probable morphological significance of these three elements is the following:—Each ring or girdle corresponds to an outer lenticular cortical shell, which is only developed on the marginal part, whilst its central part is represented by the phacoid shell. Therefore the radial beams (separating the imperfect chambers) are the same as in the concentric Polysphærida, and the sieve-plates of the surface are the porous walls of the cortical shell itself. The correctness of this explanation seems to be proved by such forms as figured in Pl. 38, figs. 2, 4, where the whole surface of the phacoid shell is covered by a concentric chamber-work, as a central continuation of the marginal concentric rings. If we imagine a system of perfect concentric lenticular phacoid shells, compressed strongly from both poles of the shortened main axis, we get the same figure.
Rarely one single girdle only is developed on the equatorial margin of the lenticular disk (Pl. 37, figs. 2, 3, 5). Commonly the number of concentric girdles amounts to three to six, often to ten to twelve or more. Some of these largest Coccodiscida reach a considerable size. Commonly all girdles are of the same breadth, which is about equal to the radius or to the diameter of the inner medullary shell. Rarely the first (or innermost) girdle differs by its greater breadth from the succeeding ones (Pl. 36, fig. 8).
Only in few Coccodiscida the girdle-building remains restricted to the equatorial planes, so that all the chambers lie in it. Commonly on both sides of this plane become developed several layers, and often the number of these (three to six or more) increases towards the periphery; in other cases not their number, but their height increases. Therefore very often the margin of the discoidal shell is much thickened, as thick as the centre of the lenticular phacoid shell (or even more); whilst between the latter and the former (on the proximal girdles) the disk is considerably thinner (Pl. 36, figs. 2, 4; Pl. 37, figs. 7, 8; Pl. 38, figs. 2, 4). The stratified layers communicate by large openings between their chambers. The radial beams are commonly more or less regular and piercing, but also frequently irregular and interrupted; often their number increases towards the margin by intercalation of new beams.
The Pores of the sieve-plates, which cover both sides of the chambered disk, appear on the margin of the phacoid shell as direct continuations of the pores of the latter, and sometimes they are so regularly disposed that one single circular pore is situated on the surface of each chamber (Pl. 36, fig. 7; Pl. 37, fig. 1). But commonly the pores are of variable size and number, two to three on each chamber, and often quite irregularly scattered.
The Margin of the chambered disk exhibits many differences, which afford characters for the distinction of genera. In the first subfamily, the Lithocyclida, the margin is quite simple without radial appendages. In the second subfamily, the Stylocyclida, it is armed with solid radial spines lying in the equatorial plane, and often regularly disposed in the same manner as in the Phacodiscida (compare above, p. 421). In the third subfamily, the Astracturida, the margin bears two or more (commonly three or four) chambered arms, also situated in the plane of the disk, and of the same structure as the circular chambered girdles (Pl. 38). In some cases even the whole system of chamber-girdles is represented only by the radial arms, which are inserted immediately on the margin of the phacoid shell. We may regard therefore these formations as imperfect chambered disks, which are developed only in the direction of certain rays (perradii), and reduced in the direction of the alternating rays (interradii). In some Astracturida the chambered arms exhibit a structure different from the more irregular chamber-work between them, so that we can distinguish the latter, connecting the arms like a web-membrane, as a peculiar "patagium" (as in many Porodiscida) (Pl. 38, figs. 8, 9). Often the distal ends of the chambered arms are armed with a radial spine (Pl. 38, figs. 5, 6, 9).
The Central Capsule of the Coccodiscida is originally always of the same form and shape as in their ancestral group, the Phacodiscida; a circular lenticular disk, which envelops the simple or double medullary shell and is enclosed by the cortical phacoid shell. But whilst in the Phacodiscida the phacoid shell envelops the central capsule perfectly, in the Coccodiscida it envelops only the capsule from the two flat sides (by the upper and lower sieve-plates); the marginal part of the lenticular capsule overgrows the margin of the phacoid shell by peripheral extension, and fills out the chambered cavity of the concentric girdles. In the Lithocyclida and the Stylocyclida, where there are no chambered arms, the central capsule remains a simple circular lens or disk; in the Astracturida, where chambered radial arms surround the margin of the circular central disk, the capsule enters also into these arms and fills out the greatest part of their chambered cavities.
|
I. Subfamily Lithocyclida. Margin of the disk simple, circular, without radial appendages. |
brace | Neither radial spines nor chambered arms on the circular margin. | brace | Medullary shell simple, | 196. Lithocyclia. |
| Medullary shell double, | 197. Coccodiscus. | ||||
|
II. Subfamily Stylocyclida. Margin of the disk armed with solid radial spines. |
brace | Two opposite spines. | brace | Medullary shell simple, | 198. Stylocyclia. |
| Medullary shell double, | 199. Amphicyclia. | ||||
| Three radial spines. | Medullary shell simple, | 200. Trigonocyclia. | |||
| Four crossed spines. | Medullary shell simple, | 201. Staurocyclia. | |||
| Five to ten or more radial spines. | brace | Medullary shell simple, | 202. Astrocyclia. | ||
| Medullary shell double, | 203. Coccocyclia. | ||||
|
III. Subfamily Astracturida. Margin of the disk with two to five or more (commonly three or four) hollow radial chambered arms (with or without a connecting patagium). (Medullary shell commonly simple.) |
brace | Two arms, opposite in one axis. | brace | Without patagium, | 204. Diplactura. |
| With patagium, | 205. Amphiactura. | ||||
| Three radial arms (at equal distances). | brace | Without patagium, | 206. Trigonactura. | ||
| With patagium, | 207. Hymenactura. | ||||
| Four arms (in two crossed diameters). | brace | Without patagium, | 208. Astractura. | ||
| With patagium, | 209. Stauractura. | ||||
| Five radial arms (at variable distances). | brace | Without patagium, | 210. Pentactura. | ||
| With patagium, | 211. Echinactura. |
| I. Subfamily Lithocyclida. Margin of the disk simple, circular, without radial appendages. | ||||||
| Neither radial spines nor chambered arms on the circular margin. | ||||||
| Medullary shell simple, | ||||||
| 196. Lithocyclia. | ||||||
| Medullary shell double, | ||||||
| 197. Coccodiscus. | ||||||
| II. Subfamily Stylocyclida. Margin of the disk armed with solid radial spines. | ||||||
| Two opposite spines. | ||||||
| Medullary shell simple, | ||||||
| 198. Stylocyclia. | ||||||
| Medullary shell double, | ||||||
| 199. Amphicyclia. | ||||||
| Three radial spines. | ||||||
| Medullary shell simple, | ||||||
| 200. Trigonocyclia. | ||||||
| Four crossed spines. | ||||||
| Medullary shell simple, | ||||||
| 201. Staurocyclia. | ||||||
| Five to ten or more radial spines. | ||||||
| Medullary shell simple, | ||||||
| 202. Astrocyclia. | ||||||
| Medullary shell double, | ||||||
| 203. Coccocyclia. | ||||||
| III. Subfamily Astracturida. Margin of the disk with two to five or more (commonly three or four) hollow radial chambered arms (with or without a connecting patagium). (Medullary shell commonly simple.) | ||||||
| Two arms, opposite in one axis. | ||||||
| Without patagium, | ||||||
| 204. Diplactura. | ||||||
| With patagium, | ||||||
| 205. Amphiactura. | ||||||
| Three radial arms (at equal distances). | ||||||
| Without patagium, | ||||||
| 206. Trigonactura. | ||||||
| With patagium, | ||||||
| 207. Hymenactura. | ||||||
| Four arms (in two crossed diameters). | ||||||
| Without patagium, | ||||||
| 208. Astractura. | ||||||
| With patagium, | ||||||
| 209. Stauractura. | ||||||
| Five radial arms (at variable distances). | ||||||
| Without patagium, | ||||||
| 210. Pentactura. | ||||||
| With patagium, | ||||||
| 211. Echinactura. | ||||||
Definition.—Coccodiscida with simple circular disk, without any radial appendages of the margin (either solid radial spines or chambered arms).
Definition.—Coccodiscida with simple circular margin of the disk, without radial appendages. Medullary shell simple.
The genus Lithocyclia is the most simple form of Coccodiscida, and represents the common ancestral form of this family, from which all other genera of it can be derived. The lenticular, biconvex disk is quite simple, composed of a variable number of concentric, circular, chambered rings, which are pierced by radial beams, and which surround the circular lenticular cortical shell or "phacoid shell." The latter contains a simple spherical medullary shell in its centre, and is connected with it by radial beams. The margin of the disk is circular, quite simple, without radial spines or chambered arms.
1. Lithocyclia cingulata, n. sp.
Phacoid shell (or lenticular porous cortical shell) three times as broad as the spherical enclosed medullary shell, surrounded by one single chambered girdle or ring (with about forty chambers of equal size, separated by radial beams). Margin of the disk circular, smooth. Pores of the convex covering plates regular, circular; eight on the radius of the phacoid shell, two on the breadth of the ring.
Dimensions.—Diameter of the disk (with one ring) 0.13, of the phacoid shell 0.1, of the medullary shell 0.033.
Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.
2. Lithocyclia lenticula, n. sp. (Pl. 36, figs. 3, 4).
Phacoid shell two and a half times as broad as the enclosed medullary shell, surrounded by three chambered girdles of equal size, which are divided by piercing radial beams each into about fifty chambers. Margin of the disk thorny. Pores irregular, roundish; seven on the radius of the phacoid shell, two on the breadth of each girdle.
Dimensions.—Diameter of the disk (with three girdles) 0.2, of the phacoid shell 0.11, of the medullary shell 0.045.
Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.