Page:Scientific results HMS Challenger vol 18 part 1.djvu/637

Rh

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.