Chapter XI: Literature and History (20)

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; twenty to twenty-two on the radius of the disk, disposed in radial series. Girdle of the margin nearly as broad as the radius of the medullary shell, in the distal half structureless, in the proximal half with eighty to ninety short radial ribs.

_Dimensions._--Diameter of the disk 0.25, of the medullary shell 0.08, of the pores 0.06.

_Habitat._--Fossil in Barbados.

3. _Periphæna statoblastus_, n. sp.

Disk with smooth surface, five times as broad as the medullary shell. Pores regularly circular; twenty-four to twenty-six on the radius of the disk, disposed in radial series, those in the distal half of the disk being separated by piercing radial beams. Girdle of the margin twice as broad as the radius of the medullary shell, in the whole breadth with one hundred and twenty to one hundred and thirty piercing radial ribs, the prolongations of the beams.

_Dimensions._--Diameter of the disk 0.3, of the medullary shell 0.06, of the pores 0.04.

_Habitat._--South Pacific, Station 300, depth 1375 fathoms.

{427}Genus 184. _Perizona_,[223] Haeckel, 1881, Prodromus, p. 457.

_Definition._--#Phacodiscida# with double medullary shell, without radial spines, but with a solid equatorial girdle around the margin of the lenticular disk.

The genus _Perizona_ differs from its ancestral form _Phacodiscus_ in the development of a thin solid siliceous girdle, lying in the equatorial plane around the margin of the disk. The two genera bear the same relation to each other that _Periphæna_ bears to _Sethodiscus_. But in the two latter genera the spherical medullary shell is simple, in the two former double.

1. _Perizona scutella_, n. sp. (Pl. 32, fig. 7).

Disk with smooth surface, in the distal third radiated, four times as broad as the outer, and ten times is broad as the inner medullary shell. Pores subregular, circular; thirteen to fourteen on the radius of the disk, in the marginal part separated by eighty to ninety prominent radial crests, which are prolonged into the proximal half of the solid girdle. Breadth of the girdle equal to that of the inner medullary shell.

_Dimensions._--Diameter of the disk 0.25, of the outer medullary shell 0.06, of the inner 0.025; pores 0.007.

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

2. _Perizona pterygota_, n. sp. (Pl. 32, figs. 8, 8_a_).

Disk with smooth surface, six times as broad as the outer, and fifteen times as broad as the inner medullary shell. Pores regularly circular; eighteen to twenty on the radius of the disk. Margin much thickened and truncated, abruptly separated in the equatorial circumference from the peripheral sharp margin of the solid girdle; breadth of the girdle equal to that of the outer medullary shell.

_Dimensions._--Diameter of the disk 0.25, of the outer medullary shell 0.04, of the inner 0.015; pores 0.006.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

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).

{428}Genus 185. _Sethostylus_,[224] 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. 31, 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. 31, 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.

{429}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. 34, 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. 34, 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.

{430}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_,[225] 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. 31, 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 {431}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. 32, 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. 34, fig. 1, but much larger, and with a double medullary shell.) {432}_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_,[226] 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. 33, 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. 33, 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 {433}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_,[227] 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. 31, 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. 34, 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.

{434}3. _Sethostaurus rhombostaurus_, n. sp. (Pl. 31, 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. 31, 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. 31, 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 {435}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_,[228] 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. 31, 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.

{436}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. 31, 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_,[229] 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. 34, fig. 6.)

{437}_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.

{438}Genus 191. _Heliosestrum_,[230] 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. 34, 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 {439}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 {440}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. 34, 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.

{441}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_,[231] 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).

{442}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. 32, figs. 4, 4_a_).

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. 32, 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 {443}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.

{444}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.

Subfamily 3. HELIODISCIDA, Haeckel, 1881, Prodromus, p. 457.

_Definition._--#Phacodiscida# with a variable number of radial spines on the margin of the disk (ten to twenty or more), which are commonly more or less irregular (sometimes regularly formed and disposed).

Genus 193. _Heliodiscus_,[232] Haeckel, 1862, Monogr. d. Radiol., p. 436.

_Definition._--#Phacodiscida# with simple 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 _Heliodiscus_, the most common and polymorphic of all #Phacodiscida#, was founded by me in 1862 as the first known type of this family (_loc. cit._). I use {445}here the diagnosis of this genus in a restricted sense, including only the species, in which the number of marginal spines amounts to ten, twenty, or more (sometimes fifty to eighty, rarely more than one hundred). The number of spines is in the different species variable, and their disposition commonly more or less irregular, whilst in the preceding genera (with two, three, four, six, or eight marginal spines) their distance and form are commonly regular.

Subgenus 1. _Heliodiscetta_, Haeckel.

_Definition._--Surface of the disk smooth, without radial spines. Bases of the marginal spines free, without a connecting equatorial girdle.

1. _Heliodiscus asteriscus_, n. sp. (Pl. 33, fig. 8).

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; ten to twelve on the radius of the disk. Marginal spines fifteen to twenty, conical, often double contoured, of variable size and disposition, the largest as long as the radius of the disk, as broad at the base as one pore.

_Dimensions._--Diameter of the disk 0.15, of the medullary shell 0.05; length of the radial spines 0.04 to 0.07, basal breadth 0.01.

_Habitat._--Cosmopolitan; Mediterranean (Corfu), Indian Ocean (Madagascar), Atlantic and Pacific, many Stations, surface and various depths.

2. _Heliodiscus trochiscus_, n. sp. (Pl. 34, figs. 10, 13).

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; fourteen to sixteen on the radius. Marginal spines twelve to sixteen, conical, of variable size and disposition, the largest as long as the diameter of the medullary shell, twice as broad as one pore.

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05; length of the radial spines 0.01 to 0.025, basal breadth 0.005.

_Habitat._--Central Pacific, Stations 272 to 274, surface.

3. _Heliodiscus trigonodon_, n. sp.

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; eighteen to twenty on the radius. Marginal spines sixteen to twenty, equilateral triangular, flat, smooth, about as long and broad as the radius of the medullary shell.

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05; length of the radial spines 0.03, basal breadth 0.03.

_Habitat._--Central Pacific, Stations 266 to 274, depths 2350 to 2925 fathoms.

{446}4. _Heliodiscus glyphodon_, n. sp. (Pl. 35, fig. 2).

_Heliosestrum glyphodon_, Haeckel, 1881, Prodromus et Atlas (pl. xxxv.
fig. 2).

Disk with smooth surface, four times as broad as the medullary shell. Pores subregular, circular; seven to eight on the radius. Marginal spines ten to twelve, equilateral triangular, flat, deeply furrowed, twice as long as broad, and as long as the radius of the disk.

_Dimensions._--Diameter of the disk 0.14, of the medullary shell 0.035; length of the radial spines 0.07, basal breadth 0.035.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

5. _Heliodiscus helianthus_, Haeckel.

_Haliomma helianthus_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 74, Taf. xxvii. fig. 1.

Disk with smooth surface, five times as broad as the medullary shell. Pores regular, oblong, disposed regularly in sixty to eighty radial series; fourteen to sixteen on the radius. Marginal spines sixty to eighty, conical, about as long as the diameter of the medullary shell, twice as broad as one pore.

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.04; length of the radial spines 0.04, basal breadth 0.005.

_Habitat._--Fossil in Barbados.

6. _Heliodiscus sol_, Haeckel.

_Haliomma sol_, Ehrenberg, 1854, Mikrogeol., Taf. xix. fig. 52.

_Heliodiscus sol_, Haeckel, 1862, Monogr. d. Radiol., p. 438.

Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, roundish; eight to ten on the radius. Marginal spines twenty to thirty, conical, the largest as long as the radius of the medullary shell, their bases widely distant. (The species from Barbados figured by Ehrenberg, 1875, as _Haliomma sol_, appertains to _Heliosestrum solare_.)

_Dimensions._--Diameter of the disk 0.2, of the medullary shell 0.05; length of the radial spines 0.02 to 0.025, basal breadth 0.01.

_Habitat._--Fossil in Tertiary rocks of Greece (Ægina), Ehrenberg.

7 _Heliodiscus siculus_, Stöhr.

_Heliodiscus siculus_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 89, Taf.
i. fig. 14.

Disk with smooth surface, three times as broad as the medullary shell. Pores irregular roundish; seven to eight on the radius. Marginal spines forty to fifty, conical, very irregular, the largest as long as the radius of the medullary shell, their bases coming in contact.

_Dimensions._--Diameter of the disk 0.13 to 0.15, of the medullary shell 0.04 to 0.05; length of the radial spines 0.02 to 0.03, basal breadth 0.002 to 0.006.

_Habitat._--Fossil in Tertiary rocks of Sicily, Grotte (Stöhr), Caltanisetta (Teuscher).

{447}8. _Heliodiscus polymorphus_, n. sp. (Pl. 34, figs. 11, 12).

Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, roundish; ten to twelve on the radius. Marginal spines ten to fifteen, pyramidal, angular, very irregular and variable in size and distribution, the largest nearly as long as the diameter of the disk, as broad at the base as the radius of the medullary shell.

_Dimensions._--Diameter of the disk 0.15 to 0.2, of the medullary shell 0.04 to 0.05; length of the radial spines 0.06 to 0.18, basal breadth 0.02 to 0.03.

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

9. _Heliodiscus solaster_, n. sp. (Pl. 34, fig. 4).

Disk with smooth surface, three times as broad as the medullary shell. Pores subregular, roundish; nine to ten on the radius. Marginal spines fifty to sixty, cylindro-conical, flexuose, very variable in size, the largest nearly as long as the diameter of the disk. The spines lie not only in the equatorial plane (as usual), but also in two to four crowded girdles on both sides of it.

_Dimensions._--Diameter of the disk 0.15, of the medullary shell 0.05; length of the radial spines 0.05 to 0.15, basal breadth 0.008.

_Habitat._--Indian Ocean, Madagascar, Rabbe, surface.

Subgenus 2. _Heliodiscilla_, Haeckel.

_Definition._--Surface of the disk covered with radial spines. Bases of the marginal spines free, without a connecting equatorial girdle.

10. _Heliodiscus phacodiscus_, Haeckel.

_Heliodiscus phacodiscus_, Haeckel, 1862, Monogr. d. Radiol., p. 437,
Taf. xvii. figs. 5-7.

_Haliomma phacodiscus_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d.
Wiss. Berlin, p. 815.

Disk with spiny surface, three times as broad as the medullary shell. Pores regular, circular; six to eight on the radius. Marginal spines twelve to sixteen, conical, as long as the radius of the disk, and one-third as broad as the diameter of the medullary shell.

_Dimensions._--Diameter of the disk 0.12 to 0.16, of the medullary shell 0.04 to 0.05; length of the marginal spines 0.06 to 0.08, basal breadth 0.01 to 0.02.

_Habitat._--Mediterranean (Messina), Canary Islands (Lanzerote).

11. _Heliodiscus amphidiscus_, Haeckel.

_Heliodiscus amphidiscus_, Haeckel, 1862, Monogr. d. Radiol., p. 437.

_Haliomma amphidiscus_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 154, Taf. ii. figs. 3-7.

Disk with spiny surface, three times as broad as the medullary shell. Pores regular, circular; eight to ten on the radius. Marginal spines twelve to fifteen, bristle-shaped, not larger than the surface spines, about as long as the radius of the medullary shell.

{448}_Dimensions._--Diameter of the disk 0.16, of the medullary shell 0.05; length of the marginal spines 0.03, basal breadth 0.002.

_Habitat._--Mediterranean (south shore of France), J. Müller.

12. _Heliodiscus echiniscus_, n. sp. (Pl. 34, fig. 5).

Disk with spiny surface, three times as broad as the medullary shell. Pores irregular, roundish or polygonal; eight to ten on the radius. Marginal spines thirty to fifty, pyramidal, angular, of very variable size, number, and disposition, gradually passing into the surface-spines; the largest nearly as long as the diameter of the medullary shell.

_Dimensions._--Diameter of the disk 0.14, of the medullary shell 0.045; length of the radial spines 0.02 to 0.04, basal breadth 0.006.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

13. _Heliodiscus pertusus_, n. sp. (Pl. 35, fig. 1).

_Heliosestrum pertusum_, Haeckel, 1881, Prodromus et Atlas (pl. xxxv.
fig. 1).

Disk with spiny surface, three times as broad as the medullary shell. Pores irregular, circular, hexagonally framed; eight to ten on the radius. Marginal spines ten to thirty, very variable in size and disposition; commonly eight to twelve larger spines, which are pyramidal, about as long as the radius of the disk and perforated by two to four irregular, longish pores. Between these fenestrated large spines are commonly ten to twenty smaller conical spines, gradually passing into those of the surface.

_Dimensions._--Diameter of the disk 0.13 to 0.16, of the medullary shell 0.04 to 0.05; length of the marginal spines 0.04 to 0.08, basal breadth 0.01 to 0.015.

_Habitat._--North Pacific, Stations 241 to 244, depths 2300 to 2900 fathoms.

Subgenus 3. _Heliodiscomma_, Haeckel.

_Definition._--Surface of the disk smooth, without radial spines. Bases of the marginal spines connected by a solid equatorial girdle.

14. _Heliodiscus cingillum_, n. sp. (Pl. 33, fig. 7).

Disk with smooth surface, five times as broad as the medullary shell. Pores regular, circular; twelve to fourteen on the radius. Equatorial girdle about as broad as the medullary shell, in the proximal half radially striped, on the margin with twenty to twenty-four short, flat, triangular spines, which are shorter than the breadth of the girdle.

_Dimensions._--Diameter of the disk 0.25, of the medullary shell 0.05; length of the marginal spines 0.02, basal breadth 0.02.

_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.

{449}15. _Heliodiscus humboldti_, Haeckel.

_Heliodiscus humboldti_, Haeckel, 1862, Monogr. d. Radiol., p. 438.

_Haliomma humboldti_, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 27;
Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Taf. xxvii. fig. 3.

_Haliomma humboldti_, Bury, 1862, Polycystins of Barbados, pl. viii. fig.
3 (at left).

Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular; eighteen to twenty on the radius. Equatorial girdle half as broad as the medullary shell, in the proximal half radially striped, on the margin with sixteen to twenty short, flat, triangular teeth, which are longer than the breadth of the girdle.

_Dimensions._--Diameter of the disk 0.12 to 0.2, of the medullary shell 0.03 to 0.05; length of the marginal spines 0.02 to 0.04, basal breadth 0.02.

_Habitat._--Fossil in Barbados (common and very variable).

16. _Heliodiscus marginatus_, n. sp. (Pl. 34, fig. 9).

Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; nine to ten on the radius. Equatorial girdle one-fourth to one-half as broad as the medullary shell, in the whole breadth radially striped, on the margin with twelve to eighteen very short and broad, triangular, marginal spines.

_Dimensions._--Diameter of the disk 0.15 to 0.2, of the medullary shell 0.05 to 0.06; length of the marginal spines 0.01 to 0.02, basal breadth 0.02.

_Habitat._--Central Pacific, Stations 265 to 268, depth 2900 fathoms.

17. _Heliodiscus sulcatus_, n. sp.

Disk with smooth surface, four times as broad as the medullary shell. Pores subregular, circular; twelve to fifteen on the radius. Equatorial girdle as broad as the medullary shell, in the whole breadth radially striped on the margin with ten to fifteen triangular, deeply sulcated teeth, about as long and broad as the medullary shell. (Similar to _Heliodiscus glyphodon_, Pl. 35, fig. 2, but with broad sulcated girdle and shorter, more numerous spines.)

_Dimensions._--Diameter of the disk 0.15 to 0.2, of the medullary shell 0.04 to 0.05; length of the radial spines 0.05 to 0.06, basal breadth 0.04 to 0.05.

_Habitat._--Atlantic and Pacific, tropical part, many Stations, surface.

18. _Heliodiscus umbonatus_, Haeckel.

_Haliomma umbonatum_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 74, Taf. xxvii. fig. 4.

Disk with smooth surface, three times as broad as the medullary shell. Pores irregular, roundish; eight to ten on the radius. Equatorial girdle half as broad as the medullary shell, hyaline, not radially striped, on the margin with ten to twenty triangular, irregular, smooth teeth, very variable in size and disposition.

{450}_Dimensions._--Diameter of the disk 0.15 to 0.2, of the medullary shell 0.05 to 0.06; length of the marginal spines 0.02 to 0.08, basal breadth 0.01 to 0.03.

_Habitat._--Cosmopolitan; Atlantic, Pacific, in various depths; also fossil in Barbados and Sicily.

Subgenus 4. _Heliodiscura_, Haeckel.

_Definition._--Surface of the disk covered with radial spines. Bases of the marginal spines connected by a solid equatorial girdle.

19. _Heliodiscus apollinis_, n. sp.

Disk with spiny or bristly surface, three times as broad as the medullary shell. Pores regular, circular; eleven to twelve on the radius. Equatorial girdle narrow, on the margin with sixteen to twenty broad, flat, triangular teeth, which are half as long and one-fourth as broad as the medullary shell. (Very similar to _Astrophacus apollinis_, Pl. 32, fig. 2, but with simple medullary shell.)

_Dimensions._--Diameter of the disk 0.18, of the medullary shell 0.06; length of the marginal spines 0.03, basal breadth 0.015.

_Habitat._--Mediterranean (Corfu), Haeckel, surface.

20. _Heliodiscus zoroaster_, n. sp.

Disk with spiny surface, four times as broad as the medullary shell. Pores subregular, circular; fourteen to sixteen on the radius. Equatorial girdle broad, radially striped, on the margin with ten to twelve pyramidal, deeply sulcated radial spines, which are nearly as long as the radius of the disk, and one-fourth as broad at the base.

_Dimensions._--Diameter of the disk 0.24, of the medullary shell 0.06; length of the marginal spines 0.11, basal breadth 0.03.

_Habitat._--Indian Ocean, between Aden and Ceylon, Haeckel, surface.

Genus 194. _Heliodrymus_,[233] Haeckel, 1881, Prodromus, p. 457.