Subfamily 2. Heliosestrida, Haeckel
Definition.—Phacodiscida with a constant number of radial spines on the margin of the disk (two, three, four, six, or eight), which are commonly regularly disposed (sometimes more or less irregularly).
Genus 185. Sethostylus, Haeckel, 1881, Prodromus, p. 457.
Definition.—Phacodiscida with simple medullary shell and with two radial spines on the margin of the disk, opposite in the equatorial axis.
The genus Sethostylus opens the series of the Heliosestrida or of those Phacodiscida in which a constant number of radial spines (two to eight) is more or less regularly disposed on the margin of the disk. All these marginal spines lie in the equatorial plane of the lens, and have in the same species a rather constant number and similar size, a certain form and disposition. Sometimes they incline more or less to irregular variations. In Sethostylus there are only two spines, opposite in the equatorial diameter of the lens; it corresponds to Stylocyclia among the Coccodiscida, and to Xiphodictya among the Porodiscida.
Subgenus 1. Sethostylium, Haeckel.
Definition.—Margin of the disk simple, smooth, without equatorial girdle and without a corona of marginal spines.
1. Sethostylus distyliscus, n. sp. (Pl. , fig. 9).
Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; nine to ten on the radius of the disk, in the outer rows cylindrical. Margin of the disk simple, smooth, thin, without peculiar equatorial girdle, radially striped by the prominent beams of the peripheral series of pores. Both marginal spines of equal size, pyramidal, sulcated, about as long as the radius of the disk and as broad at the base as the medullary shell.
Dimensions.—Diameter of the disk 0.13 to 0.16, of the medullary shell 0.04 to 0.05; length of both opposite spines 0.06 to 0.08, basal breadth 0.03 to 0.04.
Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.
2. Sethostylus dicylindrus, n. sp. (Pl. , fig. 10).
Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; sixteen to eighteen on the radius of the disk. Margin of the disk simple, smooth, thick, without peculiar equatorial girdle. Both marginal spines cylindrical, about as long as the diameter of the disk, about twice as broad as a single pore. (Walls of the disk in the central part twice to three times as thick as in the peripheral part.)
Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of both spines 0.2 to 0.3, breadth 0.008.
Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.
Subgenus 2. Heliostylus, Haeckel, 1881, Prodromus, p. 457.
Definition.—Margin of the disk with a solid equatorial girdle or a corona of radial spines.
3. Sethostylus dentatus, n. sp. (Pl. , fig. 1).
Heliostylus dentatus, Haeckel, 1881, Prodromus et Atlas (pl. xxxiv. fig. 1).
Disk with smooth surface, six times as broad as the medullary shell. Pores regular, circular; eighteen to twenty on the radius of the disk. Margin of the disk with a broad solid equatorial girdle, which bears fifty to sixty strong conical teeth on the periphery; teeth about as long as the diameter of the medullary shell. Both opposite marginal spines cylindro-conical, about as long as the diameter of the disk, and as broad as the girdle.
Dimensions.—Diameter of the disk 0.3, of the medullary shell 0.05; length of both main spines 0.2 to 0.3, breadth 0.02.
Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.
4. Sethostylus serratus, n. sp. (Pl. , fig. 2).
Heliostylus serratus, Haeckel, 1881, Prodromus et Atlas (pl. xxxiv. fig. 2).
Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; fourteen to sixteen on the radius of the disk. Margin with a broad solid equatorial girdle, which bears forty to fifty strong conical teeth on the periphery; teeth about as long as the radius of the medullary shell. Both opposite marginal spines spindle-shaped, about as long as the diameter of the disk, and as broad as the girdle.
Dimensions.—Diameter of the disk 0.3, of the medullary shell 0.075; length of both main spines 0.2 to 0.3, breadth 0.03.
Habitat.—South Atlantic, Station 332, depth 2200 fathoms.
5. Sethostylus hastatus, n. sp.
Disk with smooth surface, two and a half times as broad as the medullary shell. Pores irregular, roundish; ten to twelve on the radius of the disk. Margin with a broad solid equatorial girdle, which bears on the periphery six conical teeth, three on each half between the two main spines, which are cylindrical, longer than the diameter of the disk, and half as broad as the girdle. (This species can be derived from Heliosestrum, two opposite spines of the eight marginal spines being much stronger developed than the other six.)
Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.06; length of both main spines 0.2, breadth 0.01.
Habitat.—North Atlantic, Station 354, surface.
6. Sethostylus spicatus, n. sp.
Disk with spiny surface, four times as broad as the medullary shell. Pores irregular roundish, with many unequal conical spines between them. Margin with an equatorial girdle, composed of three to four concentric series of conical radial spines, about as long as the radius of the medullary shell. Both main spines very large, cylindrical, longer than the diameter of the disk, and as broad as the radius of the medullary shell.
Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the main spines 0.3 or more, breadth 0.025.
Habitat.—Fossil in the rocks of Barbados, Haeckel; living in the depths of the Equatorial Atlantic, Station 348, depth (2450) fathoms.
Genus 186. Phacostylus, Haeckel, 1881, Prodromus, p. 457.
Definition.—Phacodiscida with double medullary shell and with two radial spines on the margin of the disk, opposite in the equatorial axis.
The genus Phacostylus differs from the foregoing Sethostylus by the duplication of the medullary shell, and bears the same relation to it as Phacodiscus does to Sethodiscus, or as Amphicyclia in the Coccodiscida does to Stylocyclia.
Subgenus 1. Phacostylium, Haeckel.
Definition.—Margin of the disk simple, smooth, without equatorial girdle, and without a corona of marginal spines.
1. Phacostylus amphistylus, n. sp. (Pl. , fig. 12).
Disk with smooth surface, four times as broad as the outer, and twelve times as broad as the inner medullary shell. Pores regular, circular; twelve to fourteen on the radius of the disk. Margin of the disk simple, smooth, without spines and equatorial girdle. Both polar spines conical, longer than the diameter of the disk, furrowed at the base, and twice as broad as the inner medullary shell.
Dimensions.—Diameter of the disk 0.16 to 0.18, of the outer medullary shell 0.045, of the inner 0.015; length of the polar spines 0.2, basal breadth 0.03.
Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.
2. Phacostylus amphixiphus, n. sp.
Disk with smooth surface, three times as broad as the outer, and eight times as broad as the inner medullary shell. Pores irregular, roundish; ten to eleven on the radius. Margin of the disk simple, smooth, without spines and equatorial girdle. Both polar spines sword-shaped triangular, two-edged, about as long as the radius of the disk, and as broad at the base as the inner medullary shell.
Dimensions.—Diameter of the disk 0.15, of the outer medullary shell 0.05, of the inner 0.02; length of the polar spines 0.08, basal breadth 0.02.
Habitat.—Indian Ocean, Madagascar, Rabbe, surface.
Subgenus 2. Astrostylus, Haeckel.
Definition.—Margin of the disk with a solid equatorial girdle or a corona of radial spines.
3. Phacostylus amphipyramis, n. sp.
Disk with spiny surface, four and a half times as broad as the outer, and fourteen times as broad as the inner medullary shell. Pores irregular, roundish; eight to ten on the radius. Margin of the disk with a corona of irregular, radial spines. Both opposite polar spines pyramidal, twice as long as broad, and nearly as long as the radius of the disk.
Dimensions.—Diameter of the disk 0.22, of the outer medullary shell 0.05, of the inner 0.016; length of the polar spines 0.1, basal breadth 0.05.
Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.
4. Phacostylus caudatus, n. sp. (Pl. , fig. 6).
Astrosestrum caudatum, Haeckel, 1881, Prodromus et Atlas (pl. xxxii. fig. 6).
Disk with smooth surface, two and a half times as broad as the outer, and six times as broad as the inner medullary shell. Pores regular, circular; six to seven on the radius of the disk. Margin with a solid equatorial girdle, and irregularly bordered with eight to ten conical spines; two opposite of these are much longer than the others. (This species can be derived from Astrosestrum, two opposite marginal spines being much more strongly developed than the six to eight others.)
Dimensions.—Diameter of disk 0.12, of the outer medullary shell 0.05, of the inner 0.02; length of the polar spines 0.1 to 0.25, basal breadth 0.025.
Habitat.—North Pacific, Station 244, depth 2900 fathoms.
5. Phacostylus maximus, n. sp.
Disk with smooth surface, five times as broad as the outer, and ten times as broad as the inner medullary shell. Pores regular, circular; twenty to twenty-two on the radius. Margin with a solid equatorial girdle, bearing on the periphery one hundred to one hundred and twenty plain teeth, and two very large polar spines, which are cylindrical, longer than the diameter of the disk, and as broad at the furrowed base as the radius of the outer medullary shell. (Similar to Sethostylus dentatus, Pl. , fig. 1, but much larger, and with a double medullary shell.) Dimensions.—Diameter of the disk 0.4, of the outer medullary shell 0.08, of the inner 0.04; length of the polar spines 0.5, basal breadth 0.04.
Habitat.—Fossil in the rocks of Barbados.
Genus 187. Triactiscus, Haeckel, 1881, Prodromus, p. 457.
Definition.—Phacodiscida with simple medullary shell, and with three radial spines on the margin of the disk, placed in the equatorial plane.
The genus Triactiscus exhibits on the margin of the lenticular phacoid shell three radial solid spines, the distance between which is sometimes equal, at other times unequal. Either all the three spines are of equal size and similar form, or one odd arm is smaller than the two paired arms. The triradial form of this genus is repeated in Tripodocyclia among the Coccodiscida, and in Tripodictya among the Porodiscida. The medullary shell of Triactiscus is simple.
1. Triactiscus tripyramis, n. sp. (Pl. , fig. 6).
Disk with smooth surface and smooth margin, three times as broad as the medullary shell. Pores regular, circular; twelve to thirteen on the radius of the disk. Three radial spines of nearly equal size and equidistant, or one odd spine a little smaller, and the opposite angle (between the paired spines) also smaller. Spines pyramidal, with broad prominent edges, one to one and a half times as long as the radius of the disk, as broad at the base as the radius of the medullary shell.
Dimensions.—Diameter of the disk 0.15; of the medullary shell 0.05, pores 0.006.
Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.
2. Triactiscus tricuspis, n. sp. (Pl. , fig. 5).
Disk with smooth surface and smooth margin, five times as broad as the medullary shell. Pores irregular, roundish; ten to eleven on the radius of the disk. Three radial spines of unequal size and at unequal distances, very short, conical, not longer than the radius of the medullary shell.
Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.03; pores 0.004 to 0.008.
Habitat.—Central Pacific, Station 268, depth 2900 fathoms.
3. Triactiscus tripodiscus, Haeckel.
Haliomma triactis, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 236, Taf. xxviii. fig, 4.
Disk with thorny surface and spiny margin, three times as broad as the medullary shell. Pores regular, circular; eight to nine on the radius of the disk. Three radial spines of different size and at unequal distances, one odd spine as long as the radius, both paired spines as long as the diameter of the disk; the odd angle between the latter is smaller. Spines pyramidal, with broad edges.
Dimensions.—Diameter of the disk 0.16, of the medullary shell 0.05, pores 0.008.
Habitat.—Fossil in the rocks of Barbados.
Genus 188. Sethostaurus, Haeckel, 1881, Prodromus, p. 457.
Definition.—Phacodiscida with simple medullary shell and with four radial spines on the margin of the disk, crossed in the equatorial plane.
The genus Sethostaurus exhibits four marginal spines, which form commonly a more or less regular cross in the equatorial plane. Sometimes the size and disposition of the four spines become more or less different, and also the angles between them vary; the regular rectangular cross passes over into a bilateral or irregular form. The medullary shell is simple. The same cross-form of the disk is seen in Staurocyclia among the Coccodiscida, and in Staurodictya among the Porodiscida.
Subgenus 1. Sethostaurium, Haeckel.
Definition.—Margin of the disk without a solid equatorial girdle or a corona of spines.
1. Sethostaurus orthostaurus, n. sp. (Pl. , figs. 1, 2).
Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; thirteen to fourteen on the radius of the disk. Margin simple, smooth, without girdle. Four crossed spines equal, pommel-shaped, angular, contracted at the base, scarcely as long as the diameter of the medullary shell.
Dimensions.—Diameter of the disk 0.16, of the medullary shell 0.05; length of the crossed spines 0.04, breadth 0.02.
Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.
2. Sethostaurus conostaurus, n. sp. (Pl. , figs. 7, 8).
Disk with spiny surface, three times as broad as the medullary shell. Pores irregular, roundish; seven to eight on the radius. Margin simple, smooth, without girdle. Four crossed spines subregular, equal, conical, about as long as the diameter and as broad at the base as the radius of the medullary shell. (Fig. 7 exhibits the normal form, fig. 8 an abnormality with five spines.)
Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.06; length of the crossed spines 0.05, basal breadth 0.03.
Habitat.—South Atlantic, Station 333, surface.
3. Sethostaurus rhombostaurus, n. sp. (Pl. , fig. 4).
Disk with smooth surface, two and a half times as broad as the medullary shell. Pores regular, circular; ten to eleven on the radius. Margin simple, smooth, without girdle. Two opposite spines longer than the diameter of the disk, four times as long as the two others, which only equal its radius. Spines sword-shaped, angular.
Dimensions.—Diameter of the disk 0.14, of the medullary shell 0.06; length of the major spines 0.2, of the minor 0.05, breadth 0.025.
Habitat.—North Atlantic, Station 353, depth 2965 fathoms.
4. Sethostaurus recurvatus, n. sp. (Pl. , fig. 3).
Disk with smooth surface, three times as broad as the medullary shell. Pores irregular, roundish; eight to nine on the radius. Margin simple, smooth, without girdle. Four spines cylindrical, irregularly curved, of different sizes; one single very large, much longer than the three others; two opposite lateral spines recurved, hook-shaped.
Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.05; length of the major spine 0.32, of the opposite spine 0.16, of both lateral spines 0.08.
Habitat.—South Pacific, Station 295, depth 1500 fathoms.
Subgenus 2. Heliostaurus, Haeckel 1881, Prodromus, p. 457.
Definition.—Margin of the disk with a solid equatorial girdle or a corona of spines.
5. Sethostaurus cruciatus, n. sp. (Pl. , fig. 5).
Heliostaurus cruciatus, Haeckel, 1881, Prodromus et Atlas (pl. xxxi. fig. 5).
Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; eleven to twelve on the radius. Margin with a solid, radially striped girdle, which bears on the periphery forty to fifty triangular pointed teeth of unequal length. Four crossed spines of equal size and similar form, pyramidal, sulcated, about as long as the radius of the disk, as broad at the base as the girdle.
Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.06; length of the crossed spines 0.1, basal breadth 0.02.
Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.
6. Sethostaurus coronatus, n. sp.
Disk with spiny surface, twice as broad as the medullary shell. Pores irregular, roundish; nine to ten on the radius. Margin of the disk with a solid broad girdle, bearing on the periphery a corona of thirty to forty flat tongue-shaped teeth of different length. Four crossed spines prismatic with prominent edges, about as long as the diameter of the disk, and as broad as the girdle.
Dimensions.—Diameter of the disk 0.16, of the medullary shell 0.08, length of the crossed spines 0.18, breadth 0.02.
Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.
7. Sethostaurus gigas, n. sp.
Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; twenty to twenty-two on the radius. Margin of the disk with a narrow solid girdle, bearing on the periphery one hundred to one hundred and twenty slender flat pointed teeth. Four crossed spines equal, conical, about as long as the radius of the disk, as broad at their furrowed base as the radius of the medullary shell.
Dimensions.—Diameter of the disk 0.4, of the medullary shell 0.1; length of the crossed spines 0.5, basal breadth 0.05.
Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.
Genus 189. Phacostaurus, Haeckel, 1881, Prodromus, p. 457.
Definition.—Phacodiscida with double medullary shell and with four radial spines on the margin of the disk, crossed in the equatorial plane.
The genus Phacostaurus differs from the foregoing Sethostaurus by the duplication of the medullary shell, and bears to it the same relation as Phacodiscus does to Sethodiscus. Also in this genus the cross of the shell is commonly regular, rectangular, sometimes more or less irregular.
Subgenus 1. Phacostaurium, Haeckel.
Definition.—Margin of the disk without a solid equatorial girdle or a corona of spines.
1. Phacostaurus oceanidum, n. sp. (Pl. , fig. 6).
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 twelve on the diameter of the disk. Margin smooth. Four crossed spines pyramidal, deeply sulcate, about as long as the diameter of the outer medullary shell, and two-thirds as broad at the base.
Dimensions.—Diameter of the disk 0.15, of the outer medullary shell 0.05, of the inner 0.02; length of the spines 0.05, basal breadth 0.03.
Habitat.—Central Pacific, Station 266, depth 2750 fathoms.
Subgenus 2. Astrostaurus, Haeckel, 1881, Prodromus, p. 457.
Definition.—Margin of the disk with a solid equatorial girdle, or a corona of spines.
2. Phacostaurus quadrigatus, n. sp.
Disk with smooth surface, four times as broad as the outer and ten times as broad as the inner medullary shell. Pores irregular, roundish; fifteen to sixteen on the diameter of the disk. Margin with a broad solid equatorial girdle, from which arise four crossed spines, conical, as long as the radius of the disk.
Dimensions.—Diameter of the disk 0.2, of the outer medullary shell 0.05, of the inner 0.02; length of the spines 0.1, basal breadth 0.03.
Habitat.—South Pacific, Station 300, depth 1375 fathoms.
3. Phacostaurus magnificus, n. sp. (Pl. , figs. 7, 8).
Astrostaurus magnificus, Haeckel, 1881, Prodromus et Atlas (pl. xxxi. figs.7, 8).
Disk with smooth surface, three times as broad as the outer and nine times as broad as the inner medullary shell. Pores regular, circular; thirteen to fourteen on the diameter of the disk. Margin with a corona of fifty to sixty conical spines of unequal length. Four spines of the cross very large pyramidal, deeply sulcated, longer than the radius of the disk, and as broad at the base as the radius of the medullary shell.
Dimensions.—Diameter of the disk 0.22, of the outer medullary shell 0.07, of the inner 0.025; length of the four spines 0.16, basal breadth 0.04.
Habitat.—Indian Ocean, Madagascar, Rabbe, surface.
Genus 190. Distriactis, n. gen.
Definition.—Phacodiscida with simple medullary shell and with six radial spines on the margin of the disk placed in the equatorial plane.
The genus Distriactis exhibits on the margin of the lenticular phacoid shell six radial solid spines. Their distance is commonly equal, rarely unequal. Either all six spines are of equal size and similar form, or three larger (perradial) alternating with three smaller (interradial), so that Distriactis appears to be derived from Triactiscus by development of three secondary between three primary spines.
1. Distriactis liriantha, n. sp.
Disk smooth, four times as broad as the medullary shell, with regular, circular pores (about ten on the radius). Six marginal spines of equal size and at equal distances, triangular, sulcate, half as long as the radius. (Similar to Heliosestrum medusinum, Pl. , fig. 6.)
Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the spines 0.05, basal breadth 0.04.
Habitat.—Central Pacific, Station 265, depth 2900 fathoms.
2. Distriactis corallantha, n. sp.
Disk thorny, three times as broad as the medullary shell, with regular, circular pores, about eight on the radius. Six marginal spines of equal size and equidistant, conical, nearly as long as the diameter of the disk, half as broad at the base as the medullary shell.
Dimensions.—Diameter of the disk 0.12, of the medullary shell 0.04; length of the spines 0.1, breadth 0.02.
Habitat.—South Pacific, Station 300, surface.
3. Distriactis alterna, n. sp.
Disk smooth, five times as broad as the medullary shell, about twelve pores on the radius. Six marginal spines pyramidal, at equal distances, but unequal alternating size; three larger (perradial) spines as long as the shell radius, three smaller between them (interradial) half as long and broad.
Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.03; length of the three major spines 0.08, of the three minor 0.05.
Habitat.—North Atlantic, Station 353, surface.
4. Distriactis palmantha, n. sp.
Disk rough, four times as broad as the medullary shell, about ten pores on the radius. Six marginal spines conical, at equal distances, but unequal alternating size; three larger (perradial) spines as long as the shell diameter, three smaller between them (interradial) as long as the radius.
Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the three major spines 0.2, of the three minor 0.1,
Habitat.—South Atlantic, Station 325, surface.
5. Distriactis amphithecta, n. sp.
Disk thorny, three times as broad as the medullary shell. Six marginal spines conical, of very different size; one single (anterior) much larger than the five others, the opposite (posterior) much smaller. The other four spines are paired, the anterior pair larger than the posterior.
Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.05; length of the longest spine 0.2, of the shortest 0.04, of the anterior pair 0.1, of the posterior 0.07.
Habitat.—Indian Ocean, Cocos Islands, surface, Rabbe.
Genus 191. Heliosestrum, Haeckel, 1881, Prodromus, p. 457.
Definition.—Phacodiscida with simple medullary shell and with eight radial spines on the margin of the disk (more or less regularly disposed, sometimes seven or nine).
The genus Heliosestrum (with simple medullary shell) and the following Astrosestrum (with double medullary shell) contain those Phacodiscida in which the margin of the lenticular disk bears eight radial spines, commonly more or less regularly disposed in the equatorial plane, so that the equal angles between them amount to 45°. There are, however, many exceptions to this regular eight-rayed form, either the angles between the eight spines becoming unequal or the number of the spines amounting to seven or nine (sometimes also six or ten) in one and the same species. But the regular form is as prevalent, and also in the abnormal forms indicated by the position of the spines, that we separate the genus Heliosestrum from Heliodiscus. Both genera are rich in common species, and in some of the former four perradial (larger) spines alternate regularly with four interradial (smaller) spines.
Subgenus 1. Heliosestantha, Haeckel.
Definition.—Surface of the disk smooth, without radial spines. Bases of the marginal spines free, not connected by an equatorial girdle.
1. Heliosestrum medusinum, n. sp. (Pl. , fig. 6).
Heliodiscus medusinus, Haeckel, 1881, Atlas (pl. xxxiv. fig. 6).
Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; about ten on the radius of the disk. Eight marginal spines regularly distributed (sometimes seven or nine, more or less irregular), angular, nearly pyramidal (with equilateral triangular outline), about as long and broad as the diameter of the medullary shell, without connecting equatorial girdle. From the broad base of each spine run eight to ten deep furrows convergent to its apex.
Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the radial spines 0.05, basal breadth 0.05.
Habitat.—North Pacific, Station 266, surface.
2. Heliosestrum octastrum, n. sp.
Disk with smooth surface, three times as broad as the medullary shell. Pores irregular, roundish; eight to nine on the radius. Eight marginal spines regularly distributed (sometimes seven or nine, more or less irregular), conical, about as long as the diameter of the disk, without a connecting equatorial girdle.
Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.05; length of the radial spines 0.16, basal breadth 0.01.
Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.
3. Heliosestrum solarium, Haeckel.
Haliomma sol (partim), Ehrenberg, 1875 (non 1844), Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxviii. fig. 1.
Surface of the disk smooth; its diameter six times as large as that of the medullary shell. Pores regular, circular; nine to ten on the radius. Eight marginal spines regularly distributed (sometimes seven or nine, more or less irregular), conical, about as long as the diameter of the medullary shell, without a connecting equatorial girdle.
Dimensions.—Diameter of the disk 0.18, of the medullary shell 0.03; length of the radial spines 0.03, basal breadth 0.01.
Habitat.—Fossil in the Tertiary rocks of Barbados.
4. Heliosestrum liriope, n. sp.
Surface of the disk smooth; its diameter four times as large as that of the medullary shell. Pores subregular, circular; seven to eight on the radius. Eight marginal spines regularly distributed, conical, compressed, alternating longer and shorter; the longer equal to the diameter of the disk, the shorter to the radius.
Dimensions.—Diameter of the disk 0.16, of the medullary shell 0.4; length of the major radial spines 0.15, of the minor 0.09.
Habitat.—North Pacific, Station 236, surface.
5. Heliosestrum quadrigeminum, n. sp.
Surface of the disk smooth; its diameter four times as large as that of the medullary shell. Pores irregular, roundish; six to seven on the radius. Eight marginal spines triangular, flat, regularly disposed, alternating longer and shorter, the major as long as the radius of the shell, and half as broad at the base, with three to four deep furrows on both sides, without a connecting equatorial girdle.
Dimensions.—Diameter of the disk 0.16, of the medullary shell 0.04; length of the larger radial spines 0.08, of the smaller 0.04, basal breadth 0.04.
Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.
6. Heliosestrum contiguum, Haeckel.
Haliomma contiguum, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxvii. fig. 5.
Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, roundish, touching, with very thin bars; nine to ten on the radius. Eight marginal spines (often seven or nine) conical, half as long as the radius, twice as long as broad, without a connecting equatorial girdle.
Dimensions.—Diameter of the disk 0.17, of the medullary shell 0.04; length of the radial spines 0.04, basal breadth 0.02.
Habitat.—Fossil in Barbados.
7. Heliosestrum irregulare, n. sp.
Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, roundish; nine to eleven on the radius. Eight conical radial spines of irregular size and distribution, often seven or nine, about as long as the radius of the disk (in some cases longer, in others shorter). No connecting equatorial girdle.
Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the radial spines 0.1, basal breadth 0.02.
Habitat.—Central Pacific, Stations 270 to 272, depth 2425 to 2925 fathoms.
Subgenus 2. Heliosestilla, Haeckel.
Definition.—Surface of the disk armed with radial spines. Bases of the marginal spines free, without a connecting equatorial girdle.
8. Heliosestrum octonum, n. sp. (Pl. , fig. 3).
Disk with spiny surface, three times as broad as the medullary shell. Pores circular, of very different sizes; eight to ten on the radius. Eight conical marginal spines of equal size and equidistant, as long as the radius of the disk, and one-third as broad at the base as the medullary shell. Numerous spines on the surface bristle-shaped, on the margin half as long as the eight main spines, in the central part shorter.
Dimensions.—Diameter of the disk 0.18, of the medullary shell 0.06; length of the marginal spines 0.1, basal breadth 0.02.
Habitat.—Central Pacific, Station 271, surface.
9. Heliosestrum ægineta, n. sp.
Disk with spiny surface, four times as broad as the medullary shell. Pores irregular, roundish, of different sizes; twelve to fourteen on the radius. Eight pyramidal marginal spines regularly disposed, four larger (perradial) alternating with four smaller (interradial); the former as long as the radius of the disk, the latter half as long.
Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the marginal spines 0.05 to 0.1, basal breadth 0.03.
Habitat.—South Atlantic, Station 330, surface.
Subgenus 3. Heliosestomma, Haeckel.
Definition.—Surface of the disk smooth, without radial spines. Bases of the marginal spines connected by a solid equatorial girdle.
10. Heliosestrum octangulum, n. sp.
Disk with smooth surface, octagonal, twice as broad as the medullary shell. Pores regular, circular; nine to ten on the radius. Equatorial girdle narrow, radially striped, connecting the points of the eight short, regularly disposed, marginal spines in such a manner that the whole shell forms a regular octagon with rectilinear sides.
Dimensions.—Diameter of the disk 0.11 to 0.12, of the medullary shell 0.05 to 0.06; length of the sides of the octagon 0.06.
Habitat.—Central Pacific, Station 268, depth 2900 fathoms.
11. Heliosestrum octogonium, n. sp.
Disk with smooth surface, octagonal, four times as broad as the medullary shell. Pores irregular, roundish; eight to nine on the radius. Equatorial girdle broad, smooth, connecting the points of the eight short, triangular, flat marginal spines in such a manner that the whole shell forms a subregular octagon with concave, nearly equal sides. (Sometimes seven or nine spines instead of eight are developed.)
Dimensions.—Diameter of the disk 0.16 to 0.18, of the medullary shell 0.04 to 0.05; length of the radial spines 0.02 to 0.04, basal breadth 0.03.
Habitat.—Central Pacific, Station 266, depth 2750 fathoms.
12. Heliosestrum craspedotum, n. sp.
Haliomma humboldti, var., Bury, 1862, Polycystins of Barbados, pl. viii. fig. 4 (below).
Disk with smooth surface, three times as broad as the medullary shell. Pores subregular, circular; ten to twelve on the radius. Eight marginal spines (sometimes seven or nine) triangular, deeply sulcated, half as long and one-third as broad as the radius of the disk, connected by a narrow, radially striped equatorial girdle.
Dimensions.—Diameter of the disk 0.18, of the medullary shell 0.06; length of the radial spines 0.05, basal breadth 0.03.
Habitat.—Central Pacific, Stations 271 to 274, at various depths, also fossil in Barbados.
Genus 192. Astrosestrum, Haeckel, 1881, Prodromus, p. 457.
Definition.—Phacodiscida with double medullary shell and with eight radial spines on the margin of the disk (more or less regularly disposed, sometimes seven or nine).
The genus Astrosestrum differs from the foregoing Heliosestrum by the duplication of the medullary shell. The eight marginal spines in the majority of individuals are regularly formed and disposed, of equal size and equidistant. But there are frequent exceptions to this rule, either the angles between the eight spines being more or less different, or the number amounting to seven or nine, instead of eight. Here also in some species four larger (perradial) spines alternate regularly with four smaller (interradial spines), after the same law of symmetry, which is common in the Medusæ.
Subgenus 1. Astrosestantha, Haeckel.
Definition.—Surface of the disk smooth, without radial spines. Bases of the marginal spines free, not connected by an equatorial girdle.
1. Astrosestrum ephyra, n. sp. (Pl. , figs. 4, 4a).
Disk with smooth surface, three times as broad as the outer and nine times as broad as the inner medullary shell. Pores subregular, circular; seven to eight on the radius of the disk. Eight marginal spines (sometimes seven or nine) more or less irregularly disposed, of variable size, commonly as long as the radius of the disk, twice as long as broad, pyramidal, sulcate, without a connecting equatorial girdle.
Dimensions.—Diameter of the disk 0.12, of outer medullary shell 0.04, of the inner 0.014; length of the marginal spines 0.05 to 0.07, basal breadth 0.03.
Habitat.—Central Pacific, Stations 270 to 274, depths 2350 to 2925 fathoms.
2. Astrosestrum nauphanta, n. sp. (Pl. , fig. 5).
Disk with smooth surface, two and a half times as broad as the outer and five times as broad as the inner medullary shell. Pores regular, circular; eight to nine on the radius of the disk. Eight marginal spines (often seven or nine) more or less regularly disposed, of equal size, half as long as the radius of the disk, and quite as broad at the base, compressed triangular, sulcate, without a connecting equatorial girdle.
Dimensions.—Diameter of the disk 0.15, of the outer medullary shell 0.06, of the inner 0.03; length of the marginal spines 0.04, basal breadth 0.04.
Habitat.—Pacific, central area, Stations 266 to 268, depth 2700 to 2900 fathoms.
3. Astrosestrum octacanthum, Haeckel.
Haliomma octacanthum, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 295, Taf. viii. fig. 11.
Disk with smooth surface, twice as broad as the outer and six times as broad as the inner medullary shell. Pores regular, circular; six to seven on the radius of the disk. Eight marginal spines regularly disposed, of variable size, the longest as long as the radius, pyramidal, not broader at the base than one pore, without a connecting equatorial girdle.
Dimensions.—Diameter of the disk 0.12, of the outer medullary shell 0.06, inner 0.02; length of the marginal spines 0.03 to 0.06, basal breadth 0.01.
Habitat.—Western Pacific, Philippine Sea, 3300 fathoms, Ehrenberg; Station 225, depth 4475 fathoms.
4. Astrosestrum acraspedum, n. sp.
Disk with smooth surface, three times as broad as the outer and six times as broad as the inner medullary shell. Pores regular, circular; nine to ten on the radius of the disk. Eight marginal spines regularly disposed, of alternating size; four major (perradial) spines as long as the diameter of the disk, four minor (interradial) half as long; spines cylindrical, not broader at the base than one pore, without a connecting equatorial girdle.
Dimensions.—Diameter of the disk 0.2, of the outer medullary shell 0.07, of the inner 0.035; length of the larger spines 0.2, of the smaller 0.1, basal breadth 0.01.
Habitat.—South Atlantic, Station 332, depth 2200 fathoms.
Subgenus 2. Astrosestilla, Haeckel.
Definition.—Surface of the disk covered with radial spines. Bases of the marginal spines free, not connected by an equatorial girdle.
5. Astrosestrum acanthastrum, n. sp.
Disk with spiny surface, three times as broad as the outer and nine times as broad as the inner medullary shell. Pores subregular, circular; ten to eleven on the radius. Eight marginal spines (sometimes seven or nine) regularly disposed, triangular, about half as long as the radius of the disk, and one-third as broad at the base, without a connecting equatorial girdle.
Dimensions.—Diameter of the disk 0.18, of the outer medullary shell 0.06, of the inner 0.02; length of the radial spines 0.05, basal breadth 0.03.
Habitat.—North Atlantic, Gulf Stream, Færöe Channel, surface, John Murray.
6. Astrosestrum echinastrum, n. sp.
Disk with spiny surface, twice as broad as the outer and four times as broad as the inner medullary shell. Pores irregular, roundish; eight to nine on the radius. Eight marginal spines more or less regularly disposed, pyramidal, nearly as long as the radius of the disk, and not broader at the base than one large pore, without a connecting equatorial girdle.
Dimensions.—Diameter of the disk 0.15, of the outer medullary shell 0.07, of the inner 0.04; length of the radial spines 0.07, basal breadth 0.01.
Habitat.—Fossil in the Tertiary rocks of Sicily, Caltanisetta, Teuscher.
Subgenus 3. Astrosestomma, Haeckel.
Definition.—Surface of the disk smooth, without radial spines. Bases of the marginal spines connected by a solid equatorial girdle.
7. Astrosestrum pelagia, 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; eight to nine on the radius. Eight marginal spines conical, about as long as the radius of the disk, of nearly equal length, one-third as broad at the base, connected by a radially striped equatorial girdle.
Dimensions.—Diameter of the disk 0.18, of the outer medullary shell 0.06, of the inner 0.023; length of the radial spines 0.09, basal breadth 0.03.
Habitat.—Indian Ocean, Ceylon, Haeckel, surface.
8. Astrosestrum floscula, n. sp.
Disk with smooth surface, two and a half times as broad as the outer and five times as broad as the inner medullary shell. Pores irregular, roundish; ten to eleven on the radius. Eight marginal spines triangular, plain, scarcely half as long as the radius of the disk, nearly as broad at the base, connected by an even equatorial girdle.
Dimensions.—Diameter of the disk 0.2, of the outer medullary shell 0.08, of the inner 0.04; length of the radial spines 0.09, basal breadth 0.07.
Habitat.—South Atlantic, Station 325, surface.