Page:Scientific results HMS Challenger vol 18 part 1.djvu/638

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.

Definition.— 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.

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