Chapter XI: Literature and History (21)

_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. {451}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.

Subgenus 1. _Heliocladus_, Haeckel, 1881, Prodromus, p. 457.

_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.

{452}Subgenus 2. _Heliodendrum_, Haeckel.

_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.

Genus 195. _Astrophacus_,[234] Haeckel, 1881, Prodromus, p. 457.

_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 {453}(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.

Subgenus 1. _Astrophacetta_, Haeckel.

_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.

{454}Subgenus 2. _Astrophacilla_, Haeckel.

_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.

Subgenus 3. _Astrophacomma_, Haeckel.

_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 {455}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.

Subgenus 4. _Astrophacura_, Haeckel.

_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.

Family XX. #COCCODISCIDA#, Haeckel (Pls. 36-38).

_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 {456}#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 {457}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 {458}(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.

_Synopsis of the Genera of Coccodiscida_.

-------------------------------------------------------------------------
I. Subfamily Lithocyclida.
Margin of the disk simple, circular, without radial appendages.
-------------------------------------------------------------------------
Neither radial spines nor {Medullary shell simple, 196. _Lithocyclia_.
chambered arms on the {
circular margin. {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 {Medullary shell simple, 202. _Astrocyclia_.
radial spines. {
{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 {Without patagium, 204. _Diplactura_.
one axis. {
{With patagium, 205. _Amphiactura_.

Three radial arms (at {Without patagium, 206. _Trigonactura_.
equal distances). {
{With patagium, 207. _Hymenactura_.

Four arms (in two {Without patagium, 208. _Astractura_.
crossed diameters). {
{With patagium, 209. _Stauractura_.

Five radial arms (at {Without patagium, 210. _Pentactura_.
variable distances). {
{With patagium, 211. _Echinactura_.

{459}Subfamily 1. LITHOCYCLIDA, Haeckel, 1881, Prodromus, p. 458.

_Definition._--#Coccodiscida# with simple circular disk, without any radial appendages of the margin (either solid radial spines or chambered arms).

Genus 196. _Lithocyclia_,[235] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

_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.

{460}3. _Lithocyclia ocellus_, Ehrenberg.

_Lithocyclia ocellus_, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 30;
Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Taf. xxix. fig. 3.

Phacoid shell three times as broad as the medullary shell, surrounded by numerous (seven to eleven) chambered rings, which are divided by piercing radial beams each into sixty to ninety chambers. Margin of the disk smooth. Pores regular, circular; nine on the radius of the phacoid shell, one single pore on each chamber.

_Dimensions._--Diameter of the disk (with eleven rings) 0.22, of the phacoid shell 0.1, of the medullary shell 0.035.

_Habitat._--Fossil in the rocks of Barbados.

4. _Lithocyclia monococcus_, n. sp.

_Stephanopyxis dubiosa_ (?), Bury, 1862, Polycystins of Barbados, pl.
xiii. figs. 1, 2.

Phacoid shell four times as broad as the medullary shell, surrounded by numerous (five to eight) chambered rings, which are divided by piercing radial beams each into fifty to seventy chambers. Margin of the disk thickened, thorny. Pores regular, circular; seven on the radius of the phacoid shell, one single pore on each chamber.

_Dimensions._--Diameter of the disk (with eight rings) 0.18, of the phacoid shell 0.12, of the medullary shell 0.03.

_Habitat._--Pacific, central area, Station 267, depth 2700 fathoms; also fossil in the rocks of Barbados.

5. _Lithocyclia heteropora_, n. sp.

Phacoid shell two and a third times as broad as the medullary shell, surrounded by five to nine chambered rings, which are divided by piercing radial beams each into fifty to seventy chambers. Margin of the disk smooth. Pores very different in the inner and outer part of the surface; in the phacoid shell larger, regular, circular, eight on its radius, in the chambered periphery very small and irregular, somewhat spongy.

_Dimensions._--Diameter of the disk (with nine rings) 0.2, of the phacoid shell 0.13, of the medullary shell 0.055.

_Habitat._--Pacific, central area, Station 263, depth 2650 fathoms.

Genus 197. _Coccodiscus_,[236] Haeckel, 1862, Monogr. d. Radiol., p. 485.

_Definition._--#Coccodiscida# with simple circular margin of the disk, without radial appendages. Medullary shell double.

The genus _Coccodiscus_ has quite the same form and structure as the preceding _Lithocyclia_, and differs from it only in the double medullary shell, composed of two concentric latticed spheres; sometimes the inner medullary shell is spherical, the outer {461}lenticular; the latter is connected with the lenticular phacoid shell (or cortical shell) by radial beams.

1. _Coccodiscus lamarckii_, n. sp. (Pl. 36, fig. 1).

Phacoid shell (or lenticular porous cortical shell) very thick walled (as thick as one ring), three times as broad as the outer and seven times as broad as the inner medullary shell, surrounded by two to three chambered rings of equal breadth, each of which is divided by piercing radial beams into thirty-six to forty square chambers. Margin of the disk circular, smooth. Pores regular, circular, of equal size; ten on the radius of the phacoid shell, two on the breadth of each chamber.

_Dimensions._--Diameter of the disk (with two rings) 0.2, of the phacoid shell 0.14, outer medullary shell 0.05, inner 0.02.

_Habitat._--Western Tropical Pacific, Station 220, depth 1100 fathoms.

2. _Coccodiscus darwinii_, Haeckel.

_Coccodiscus darwinii_, Haeckel, 1862, Monogr. d. Radiol., p. 486, Taf.
xxviii. figs. 11, 12.

Phacoid shell three times as broad as the outer and nine times as broad as the inner medullary shell, surrounded by five to eight chambered rings of equal breadth, each of which is divided by forty piercing radial beams into forty square chambers of equal size. Margin of the disk smooth, circular. Pores irregular, roundish, of unequal size; eleven on the radius of the phacoid shell, one to two on each chamber.

_Dimensions._--Diameter of the disk (with eight rings) 0.32, of the phacoid shell 0.11, outer medullary shell 0.036, inner 0.012.

_Habitat._--Mediterranean, Messina, surface.

3. _Coccodiscus goethei_, n. sp. (Pl. 36, fig. 2).

Phacoid shell two and a half times as broad as the outer and five times as broad as the inner medullary shell, surrounded by three to seven chambered rings of equal breadth, each of which is divided by piercing radial beams into sixty to eighty chambers. Margin of the disk thorny. Pores regular, circular; eight on the radius of the phacoid shell, a single one on the breadth of each chamber.

_Dimensions._--Diameter of the disk (with seven rings) 0.25, of the phacoid shell 0.1, of the medullary shell 0.04, inner 0.02.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

Subfamily 2. STYLOCYCLIDA, Haeckel, 1881, Prodromus, p. 458.

_Definition._--#Coccodiscida# with solid radial spines on the margin of the circular disk, situated in its equatorial plane (without chambered arms).

{462}Genus 198. _Stylocyclia_,[237] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

_Definition._--#Coccodiscida# with two opposite solid radial spines on the margin of the circular disk. Medullary shell simple.

The genus _Stylocyclia_ opens the series of the Stylocyclida or of those Coccodiscida in which the margin of the chambered disk is armed with solid radial spines, situated in its equatorial plane, but without chambered arms. _Stylocyclia_ is the most simple form of this subfamily, and bears only two marginal spines, opposite in one equatorial axis of the disk. The medullary shell is simple. This genus corresponds to _Xiphodictya_ in the family Porodiscida. The genus was previously known only by one single species described by Ehrenberg.

1. _Stylocyclia dimidiata_, Ehrenberg.

_Stylocyclia dimidiata_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 84, Taf. xxix. fig. 4.

Phacoid shell three times as broad as the medullary shell, surrounded by five to eight chambered rings of equal breadth, divided by eighty to ninety piercing radial beams into square chambers. Pores subregular, circular; six to seven on the radius of the phacoid shell, a single one on each chamber. Both opposite marginal spines strong, club-shaped, their thickness decreasing from the margin towards the centre of the disk. (The figure of Ehrenberg is very incomplete.)

_Dimensions._--Diameter of the disk (with eight rings) 0.25, of the phacoid shell 0.11, of the medullary shell 0.035.

_Habitat._--Fossil in the Tertiary rocks of Barbados; living in the depths of the Equatorial Atlantic, Station 348, depth (2450) fathoms.

2. _Stylocyclia prionacantha_, n. sp. (Pl. 37, fig. 6).

Phacoid shell two and a half times as broad as the medullary shell, surrounded by five to six chambered rings, which are divided by fifty to sixty piercing radial beams into square chambers. Pores in the thick-walled phacoid shell regularly circular, increasing in size from the centre; eight to nine on its radius. Pores on the surface of the chambered girdle smaller, very irregular, two to three on each ring. Both marginal spines longer than the diameter of the disk, with broad serrated edges.

_Dimensions._--Diameter of the disk (with five rings) 0.23, of the phacoid shell 0.12, of the medullary 0.05.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

{463}3. _Stylocyclia excavata_, n. sp. (Pl. 37, fig. 8).

Phacoid shell four times as broad as the medullary shell, surrounded by four chambered rings, which are divided by twenty to thirty radial beams into broad chambers. The height of the rings increases strongly from the centre, so that the fourth ring is two and a half times as high as the first. Pores irregular, roundish; five to six on the radius of the phacoid shell, one to two on the breadth of each ring. Margin of the disk smooth. Both marginal spines thin and long, cylindrical, arising from the medullary shell, longer than the diameter of the disk.

_Dimensions._--Diameter of the disk (with four rings) 0.25, of the phacoid shell 0.1, of the medullary shell 0.025.

_Habitat._--Fossil in the rocks of Barbados. Indian Ocean, Cocos Islands, Rabbe.

4. _Stylocyclia amphacantha_, n. sp.

Phacoid shell twice as broad as the medullary shell, surrounded by five chambered rings, divided by piercing beams each into forty to fifty chambers. Pores regular, circular; eight to nine on the radius of the phacoid shell, one on each chamber. Margin of the disk thorny. Both marginal spines strong, conical, as long as its radius.

_Dimensions._--Diameter of the disk (with five rings) 0.24, of the phacoid shell 0.1, of the medullary shell 0.05.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

Genus 199. _Amphicyclia_,[238] Haeckel, 1881, Prodromus, p. 458.

_Definition._--#Coccodiscida# with two opposite solid radial spines on the margin of the circular disk. Medullary shell double.

The genus _Amphicyclia_ has the same form and structure as _Stylocyclia_, and differs from it only in the double concentric medullary shell. It bears therefore to the latter the same relation that _Coccodiscus_ does to _Lithocyclia_.

1. _Amphicyclia chronometra_, n. sp. (Pl. 38, fig. 1).

Phacoid shell three times as broad as the outer and nine times as broad as the inner medullary shell, surrounded by two broad chambered rings, which are divided into irregular chambers by fifty to sixty radial beams of different distance. Margin of the disk thorny, lacerated. Pores irregular, roundish; twelve to sixteen on the radius of the phacoid shell, two to three on the breadth of each ring. The two opposite marginal spines strong, prismatic, with prominent edges, about as long as the diameter of the disk.

_Dimensions._--Diameter of the disk (with two rings) 0.24, of the phacoid shell 0.15, outer medullary shell 0.05, inner 0.017.

_Habitat._--Pacific, central area, Stations 265 to 268, depths 2700 to 2900 fathoms.

{464}2. _Amphicyclia amphistyla_, n. sp. (Pl. 37, fig. 7).

_Stylocyclia amphistyla_, Haeckel, 1879, MS. et Atlas (pl. xxxvii. fig.
7).

Phacoid shell thin walled, two and a half times as broad as the outer and seven times as broad as the inner medullary shell, divided by eighty to ninety radial beams into irregular chambers, which are stratified in four to five floors. Pores regular, circular; eight to nine on the radius of the phacoid shell, two on the breadth of each chamber. Both marginal spines cylindrical.

_Dimensions._--Diameter of the disk (with seven rings) 0.27, of the phacoid shell 0.1, outer medullary shell 0.04, inner 0.014.

_Habitat._--North Atlantic, Canary Islands, Station 354, surface.

3. _Amphicyclia pachydiscus_, n. sp. (Pl. 38, fig. 2).

Phacoid shell very thick, spongy, twice as broad as the outer and five times as broad as the inner medullary shell, divided by fifty to seventy radial beams into subregular chambers, which are stratified in five to six floors. Pores irregular, roundish; ten to twelve on the radius of the phacoid shell, two to three on the breadth of each chamber. The two opposite marginal spines quadrangular prismatic, very long, as broad as the radius of the inner medullary shell. Fig. 2 exhibits a vertical section (slide) through the centre.

_Dimensions._--Diameter of the disk (with five rings) 0.22, of the phacoid shell 0.1, outer medullary shell 0.05, inner 0.02.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms; fossil in Barbados.

Genus 200. _Trigonocyclia_,[239] Haeckel, 1881, Prodromus, p. 458.

_Definition._--#Coccodiscida# with three solid radial spines on the margin of the circular disk. Medullary shell simple.

The genus _Trigonocyclia_ (only known by one single species, once observed) bears on the margin of the chambered disk three solid radial spines, at equal distances one from another. It corresponds to the genus _Tripodictya_ amongst the Porodiscida.

1. _Trigonocyclia triangularis_, n. sp. (Pl. 37, fig. 5).

Phacoid shell three times as broad as the medullary shell, connected with it by six equidistant radial beams, three of which are prolonged into marginal spines. In the equatorial plane only one single chambered ring, divided by forty-four radial beams into narrow chambers. Pores large, irregular, roundish; five on the radius of the phacoid shell, two on each chamber. Surface and margin of the disk spiny. Three strong conical marginal spines, divergent at equal angles, as long as the radius of the disk.

_Dimensions._--Diameter of the disk 0.16, of the phacoid shell 0.12, of the medullary shell 0.04.

_Habitat._--Indian Ocean, Zanzibar, depth 2200 fathoms, Pullen.

{465}Genus 201. _Staurocyclia_,[240] Haeckel, 1881, Prodromus, p. 458.

_Definition._--#Coccodiscida# with four solid radial spines on the margin of the disk, crossed in two equatorial diameters perpendicular one to another. Medullary shell simple.

The genus _Staurocyclia_ is characterised by four radial spines on the margin of the disk, which are opposite in pairs and situated in two equatorial diameters, commonly perpendicular one to another. They form therefore a rectangular cross (rarely more or less irregular). The genus corresponds exactly to _Staurodictya_ in the family Porodiscida. The medullary shell is simple.

1. _Staurocyclia cruciata_, n. sp. (Pl. 37, fig. 1).

Phacoid shell two and a half times as broad as the medullary shell, surrounded by six to eight regular rings, which are divided by fifty to seventy piercing beams into square chambers. Pores regular, circular; six on the radius of the phacoid shell, one single pore on each chamber. Four crossed radial spines, arising from the medullary shell by thin bases, prolonged over the dentated margin as four strong quadrangular swords, as long as the radius of the disk.

_Dimensions._--Diameter of the disk (with eight rings) 0.23, of the phacoid shell 0.09, of the medullary shell 0.035.

_Habitat_--Pacific, central area, Station 267, depth 2700 fathoms.

2. _Staurocyclia serrata_, n. sp.

? _Haliomma_ sp., Bury, 1862, Polycystins of Barbados, pl. xxii. fig. 2.

Phacoid shell twice as broad as the medullary shell, surrounded by three to four spongy rings, which are divided by thirty to forty radial beams into irregular chambers. Pores in the phacoid shell regular, circular, five on its radius; in the chambered spongy girdle much smaller and irregular. Margin dentated, with four crossed, very large, quadrangular spines, as long as the radius of the disk, with wing-shaped, serrated edges.

_Dimensions._--Diameter of the disk (with four rings) 0.2, of the phacoid shell 0.1, of the medullary shell 0.05.

_Habitat._--Fossil in the rocks of Barbados.

3. _Staurocyclia phacostaurus_, n. sp. (Pl. 37, figs. 2, 3).

_Phacostaurus pyramidalis_, Haeckel, 1879, MS. (as a separate genus).

Phacoid shell two and a quarter times as broad as the medullary shell, connected with it by twelve radial beams (four equatorial and eight divergent) and surrounded by one single ring, which is divided by forty radial beams into regular chambers. Pores regular, honeycomb-like in the {466}phacoid shell, seven on its radius; smaller on the equatorial ring, three on its breadth. Four marginal spines pyramidal four-sided, as long and as broad at the base as the ring.

_Dimensions._--Diameter of the disk (with one ring) 0.14, of the phacoid shell 0.11, of the medullary shell 0.048.

_Habitat._--South Atlantic, Station 335, depth 1425 fathoms.

4. _Staurocyclia magniducis_, n. sp. (Pl. 37, fig. 4).

_Coccostaurus magniducis_, Haeckel, 1881, MS. et Atlas (pl. xxxvii. fig.
4).

Phacoid shell twice as broad as the medullary shell, connected with it by numerous radial beams and surrounded by eight chambered rings, which are divided by one hundred to one hundred and twenty piercing radial beams into small chambers. Pores subregular, circular; ten on the radius of the phacoid shell, two on the breadth of each chamber. Margin of the disk armed with numerous bristle-shaped radial spines, as long as the breadth of the chambered girdle. Four very large crossed spines, nearly as long as the diameter of the disk, quadrangular, with four dentated edges; at the club-shaped distal end thorny, as broad as the medullary shell and three times as broad as at the narrow base. I name this splendid species in the honour of H.R.H. the Grand Duke of Saxe-Weimar, Carl Alexander, the magnanimous protector of arts and sciences, the rector magnificentissimus of the University of Jena.

_Dimensions._--Diameter of the disk (with eight rings) 0.27, of the phacoid shell 0.11, of the medullary shell 0.05; length of the four crossed club-spines 0.2, basal breadth 0.02, distal breadth 0.06.

_Habitat._--Indian Ocean, Ceylon, Belligemma, surface (Haeckel).

Genus 202. _Astrocyclia_,[241] Haeckel, 1881, Prodromus, p. 458.

_Definition._--#Coccodiscida# with numerous (five or more, commonly thirty to sixty) solid radial spines on the margin of the circular disk. Medullary shell simple.

The genus _Astrocyclia_ exhibits on the margin of the circular chambered disk a large but variable number of solid radial spines, commonly between thirty and sixty. They are the external prolongations of the inner piercing radial beams, which divide the concentric rings of the disk into chambers. All the spines lie in the equatorial plane of the disk. The genus corresponds to _Stylodictya_ in the family Porodiscida.

1. _Astrocyclia solaster_, n. sp. (Pl. 36, fig. 7).

Phacoid shell two and a half times as broad as the medullary shell, surrounded by four to six regular rings of equal breadth, which are divided by thirty to forty piercing radial beams into broad {467}chambers. Pores regular, circular; seven on the radius of the phacoid shell, one single pore on each chamber (the size increasing from the centre). Margin with thirty to forty angular, broad, dentate spines, the prolongations of the inner radial beams.

_Dimensions._--Diameter of the disk (with six rings) 0.22, of the phacoid shell 0.1, of the medullary shell 0.04.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

2. _Astrocyclia stella_, Haeckel.

_Lithocyclia stella_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 78, Taf. xxix. fig. 2.

Phacoid shell three times as broad as the medullary shell, surrounded by four to eight rings of increasing breadth from the centre, the outer of which are more or less spongy. Each ring is divided by forty to fifty piercing radial beams into chambers of increasing size. Pores regular, circular; a single one on each chamber, ten on the radius of the phacoid shell. On the margin are scattered ten to twenty thick and short spines, four-sided pyramidal, about as long and as broad at the base as the diameter of the medullary shell.

_Dimensions._--Diameter of the disk (with eight rings) 0.25, of the phacoid shell 0.09, of the medullary shell 0.03.

_Habitat._--Fossil in the rocks of Barbados.

3. _Astrocyclia rotula_, n. sp.

Phacoid shell four times as broad as the medullary shell, surrounded by one single ring, which is divided by forty radial beams into equal chambers. Pores regular, circular; two on the breadth of the ring, six on the radius of the phacoid shell. Margin with forty short, conical spines, the prolongations of the inner radial beams, twice as long as the breadth of the ring.

_Dimensions._--Diameter of the disk 0.13, of the phacoid shell 0.1, of the medullary shell 0.025.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

4. _Astrocyclia arachnia_, n. sp.

Phacoid shell twice as broad as the medullary shell, surrounded by four to six rings of equal breadth, which are divided by twelve to twenty radial beams into broad chambers. Pores regular, circular; two on the breadth of each ring, eight on the radius of the phacoid shell. Margin with twelve to twenty very long and thin, bristle-shaped, radial spines, the prolongations of the inner beams, longer than the diameter of the disk. (Resembles _Stylodictya arachnia_, but differs in the possession of a phacoid shell.)

_Dimensions._--Diameter of the disk (with six rings) 0.22, of the phacoid shell 0.09, of the medullary shell 0.045.

_Habitat._--North Atlantic, Canary Islands.

{468}5. _Astrocyclia heterocycla_, n. sp. (Pl. 36, fig. 8). Phacoid shell two and a half times as broad as the medullary shell, surrounded by three rings of unequal breadth, the first ring as broad as the second and third together. They are divided by fifty to sixty piercing radial beams into chambers, which are square in the second and third rings, and half as large as in the first. The radial beams are alternately thicker and thinner, prolonged into short marginal spines. Pores subregular, circular; eight on the radius of the phacoid shell, two on the breadth of the first ring, a single one on each chamber of the second and third rings.

_Dimensions._--Diameter of the disk (with three rings) 0.2, of the phacoid shell 0.12, of the medullary shell 0.05.

_Habitat._--Equatorial Atlantic, Station 348, depth (2450) fathoms; also fossil in Barbados.

Genus 203. _Coccocyclia_,[242] Haeckel, 1881, Prodromus, p. 458.

_Definition._--#Coccodiscida# with numerous (five or more) solid radial spines on the margin of the circular disk. Medullary shell double.

The genus _Coccocyclia_ has the same form and structure as the foregoing _Astrocyclia_, and differs from it only in the double concentric medullary shell. It bears therefore to the latter the same relation as _Coccodiscus_ to _Lithocyclia_.

1. _Coccocyclia liriantha_, n. sp.

Phacoid shell three times as broad as the outer and ten times as broad as the inner medullary shell, connected with both by six equidistant piercing radial beams. The margin of the phacoid shell is surrounded by one or two equatorial rings, each as broad as the outer medullary shell, and divided by thirty to forty radial beams into narrow chambers. Pores subregular, circular, about nine to ten on the radius of the phacoid shell, three to four on the breadth of each ring. Margin of the disk ciliated, with six regularly disposed radial spines as prolongations of the inner six piercing beams. Each spine cylindrical, delicately crenulated, about as broad as the inner medullary shell, and once to twice as long as the diameter of the whole disk, elegantly undulated, with a conical terminal point.

_Dimensions._--Diameter of the disk (with two rings) 0.32, of the phacoid shell 0.2, of the outer medullary shell 0.06, of the inner 0.02.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

2. _Coccocyclia heliantha_, n. sp. (Pl. 36, figs. 5, 6).

Phacoid shell two and a half times as broad as the outer and six times as broad as the inner medullary shell, surrounded by six to eight rings of nearly equal breadth, the outer somewhat smaller. They are divided by fifty to sixty piercing radial beams into irregular chambers. Pores {469}irregular, roundish; ten on the radius of the phacoid shell, a single one on each chamber of the equatorial girdle. Margin of the disk with numerous strong conical radial spines of different breadths, arranged in several circles, the strongest in the equatorial plane, about as broad as one ring and twice as long. Surface thorny.

_Dimensions._--Diameter of the disk (with seven rings) 0.3, of the phacoid shell 0.12, of the outer medullary shell 0.05, of the inner 0.02.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms; also fossil in Barbados.

Subfamily 3. ASTRACTURIDA, Haeckel, 1881, Prodromus, p. 458.

_Definition._--#Coccodiscida# with two or more (commonly three or four) chambered radial arms on the margin of the disk, situated in its equatorial plane (with or without a connecting patagium between the arms).

Genus 204. _Diplactura_,[243] Haeckel, 1881, Prodromus, p. 458.

_Definition._--#Coccodiscida# with two opposite chambered arms on the margin of the circular disk, without a connecting patagium.

The genus _Diplactura_ is the simplest form of the Astracturida, or of those Coccodiscida in which the margin of the disk bears chambered arms, situated in its equatorial plane. This subfamily corresponds to the Euchitonida among the Porodiscida, to the Spongobrachida among the Spongodiscida. In _Diplactura_ there are only two free arms, opposite in one equatorial diameter (corresponding to _Amphibrachium_ among the former, to _Spongolena_ among the latter).

Subgenus 1. _Diplacturium_, Haeckel.

_Definition._--Arms blunt at the distal end, without radial spines.

1. _Diplactura diplobrachia_, n. sp.

Phacoid shell twice as broad as the medullary shell, with six pores on its radius, without a perfect chambered ring around it. Arms club-shaped, one and a half times as long as the diameter of the phacoid shell, at the distal end rounded, blunt, as broad as the latter, at the base only half as broad.

_Dimensions._--Diameter of the phacoid shell 0.08, of the medullary shell 0.04; length of the arms 0.12, basal breadth 0.04, distal breadth 0.08.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

{470}Subgenus 2. _Diplactinium_, Haeckel.

_Definition._--Arms on the distal end armed with a radial terminal spine.

2. _Diplactura diploconus_, n. sp. (Pl. 38, fig. 5).

_Amphiactura diploconus_, Haeckel, 1877, MS. et Atlas (pl. xxxviii. fig.
5).

Phacoid shell three times as broad as the medullary shell, with eight pores on its radius, surrounded by a single chambered ring. Arms club-shaped, twice as long as the diameter of the phacoid shell, at the distal end as broad as the latter, at the base only half as broad. Both poles of the common axis of the arms are armed with a strong spindle-shaped terminal spine.

_Dimensions._--Diameter of the phacoid shell 0.09, of the medullary shell 0.03; length of the arms (without terminal spines) 0.17, basal breadth 0.05, distal breadth 0.09.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

Genus 205. _Amphiactura_,[244] Haeckel, 1881, Prodromus, p. 458.

_Definition._--#Coccodiscida# with two opposite chambered arms on the margin of the circular disk, connected by a spongy patagium.

The genus _Amphiactura_ differs from the foregoing _Diplactura_ in the development of a patagium between the arms, and therefore bears the same relation to it as _Amphymenium_ in the Porodiscida does to _Amphibrachium_, or _Spongobrachium_ in the Spongodiscida does to _Spongolene_. In this and in the following #Discoidea# provided with a patagium, this connecting web constantly exhibits a different texture of its framework, which is sometimes more regularly chambered, at other times more irregularly spongy.

1. _Amphiactura amphibrachia_, n. sp. (Pl. 38, figs. 3, 4).

Phacoid shell three times as broad as the medullary shell, with eight pores on its radius. Arms nearly equilateral triangular, twice as long as the diameter of the phacoid shell, at the truncated distal end as broad as the latter, at the base only one-third as broad. Patagium a circular lenticular disk, enveloping only the basal third of the arms, with three to four concentric circular rings, divided into chambers by about forty radial beams, which are prolonged beyond the margin of the patagium into radial spines. The vertical section (fig. 4) shows that the chambers of each arm (eleven to twelve transverse rows in the radius) are disposed in two layers.

_Dimensions._--Diameter of the phacoid shell 0.09, of the medullary shell 0.03; length of the arms 0.18, basal breadth 0.03, distal breadth 0.09.

_Habitat._--Pacific, central area, Station 263, depth 2650 fathoms.

{471}Genus 206. _Trigonactura_,[245] Haeckel, 1881, Prodromus, p. 459.

_Definition._--#Coccodiscida# with three chambered arms on the margin of the circular or triangular disk, without a connecting patagium.

The genus _Trigonactura_ exhibits three radial arms, which in all known species are separated by three equal angles. The terminal points of the arm-axes are the corners of an equilateral triangle. It corresponds therefore to _Dictyastrum_ among the Porodiscida.

Subgenus 1. _Trigonacturium_, Haeckel.

_Definition._--Distal end of the arms blunt or truncated, without a terminal spine.

1. _Trigonactura pythagoræ_, Haeckel.

_Astromma pythagoræ_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 66, Taf. xxx. fig. 2.

Phacoid shell circular, twice as broad as the medullary shell, with five pores on its radius, without a completely surrounding chambered girdle. Arms nearly square, at the truncated distal end as broad as long, and scarcely broader than at the base, two-thirds as long as the diameter of the central disk.

_Dimensions._--Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.07, distal breadth 0.07.

_Habitat._--Cosmopolitan; Atlantic, Indian, Pacific, in various depths; also fossil in Tertiary rocks of Barbados and Nicobar.

2. _Trigonactura rhopalastrella_, n. sp.

_Stephanastrum_ sp., Bury, 1862, Polycystins of Barbados, pl. xv. fig. 7.

Phacoid shell twice as broad as the medullary shell, with five pores on its radius, without a perfect chambered ring around it. Arms club-shaped, at the blunt distal end rounded, as long as the diameter of the phacoid shell; their basal breadth is one-fourth, their distal breadth one-half of its length.

_Dimensions._--Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.1, basal breadth 0.025, distal breadth 0.05.

_Habitat._--Pacific, central area, Stations 270 to 274, depths 2400 to 2800 fathoms; also fossil in Tertiary rocks of Barbados.

{472}3. _Trigonactura trigonobrachia_, n. sp.

Phacoid shell two and a half times as broad as the medullary shell, with six pores on its radius, without a perfect chambered girdle. Arms nearly equilateral triangular, twice as long as the diameter of the phacoid shell, at the truncated distal end as broad as its diameter and three times as broad as at the narrow base. (Resembles _Hymenactura hexagona_, but without a patagium.)

_Dimensions._--Diameter of the phacoid shell 0.11, of the medullary shell 0.045; length of the arms 0.2, basal breadth 0.035, distal breadth 0.1.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

4. _Trigonactura lanceolata_, n. sp.

Phacoid shell three times as broad as the medullary shell, with eight pores on its radius, surrounded by one perfect chambered ring. Arms lanceolate, three times as long as the diameter of the phacoid shell, and four times as long as broad in the middle part, at both ends very narrow, blunt.

_Dimensions._--Diameter of the phacoid shell 0.09, of the medullary shell 0.03; length of the arms 0.25, breadth in the midst 0.06.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

Subgenus 2. _Trigonactinium_, Haeckel.

_Definition._--Distal end of the arms armed with a radial spine.

5. _Trigonactura triacantha_, n. sp. (Pl. 38, figs. 6, 7).

Phacoid shell two and a half times as broad as the medullary shell, with eight pores on its radius, surrounded by one perfect chambered ring. Arms nearly lanceolate, in the middle part one and a half times as broad as at both ends, twice as long as the phacoid shell, at the distal end with a strong pyramidal terminal spine. Through the spongy framework of each arm shine sixteen to eighteen transverse bars (as septa of the joints) and six to eight longitudinal piercing beams.

_Dimensions._--Diameter of the phacoid shell 0.09, of the medullary shell 0.038; length of the arms 0.2, greatest breadth 0.08.

_Habitat._--Pacific, central area, Station 265, depth 2900 fathoms.

6. _Trigonactura trigonodiscus_, n. sp.

? _Astromma_ sp., Bury, 1862, Polycystins of Barbados, Taf. xv. fig. 2.

Phacoid shell triangular, twice as broad as the spherical medullary shell, with six to seven pores on its radius, surrounded by one chambered ring. Arms equilateral triangular, as long as {473}the diameter of the central disk and at the base half as broad, slowly decreasing in breadth towards the distal end, which is armed with a strong pyramidal spine.

_Dimensions._--Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.12, basal breadth 0.07.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms; also fossil in Barbados.

7. _Trigonactura trixiphos_, n. sp.

Phacoid shell circular, twice as broad as the medullary shell, without a completely surrounding chambered ring, with four pores on its radius. Arms club-shaped, about as long as the diameter of the central disk, at the base half as broad as long, at the rounded distal end broader, and armed with a strong pyramidal terminal spine, nearly as long as the arm itself.

_Dimensions._--Diameter of the phacoid shell 0.08, of the medullary shell 0.04; length of the arms (without terminal spine) 0.08, basal breadth 0.04, distal breadth 0.06.

_Habitat._--Fossil in the rocks of Barbados.

Genus 207. _Hymenactura_,[246] Haeckel, 1881, Prodromus, p. 459.

_Definition._--#Coccodiscida# with three chambered arms on the margin of the circular or triangular disk, connected by a spongy patagium.