Page:Scientific results HMS Challenger vol 18 part 1.djvu/779

Rh 3. Pylodiscus cardiopylus, n. sp.

Cortical shell hexangular, equilateral, five times as broad as the triangular, Triopyle-shaped medullary shell. Surface smooth. Three arms triangular, at the distal end as broad as the three heart-shaped gates. On the margin six strong pyramidal spines in the equatorial plane (adradial, as prolongations of the lateral arm-edges).

Dimensions.—Diameter of the disk 0.15, of the gates 0.05.

Habitat.—Indian Ocean, Sunda Strait, Rabbe.

4. Pylodiscus nephropylus, n. sp.

Cortical shell circular, three times as broad as the circular, Triopyle-shaped medullary shell. Surface spiny. Three arms trapezoidal, half as broad as the three kidney-shaped gates. On the margin twelve stronger, conical, radial spines, opposite in pairs on both sides of the disk, disposed in six pairs at the distal end of the arms.

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.06.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

Definition.— with Triopyle-shaped medullary shell and Pylodiscus-shaped cortical shell, which is surrounded by a marginal chambered equatorial girdle.

Definition.— with Triopyle-shaped medullary shell and Pylodiscus-shaped cortical shell, which is surrounded by an equatorial chambered girdle. No peculiar osculum on the margin of the disk.

The genus Discozonium and the following Discopyle make up together the small group of the Discopylida, or those Pylodiscida in which a discoidal shell like Pylodiscus is surrounded by a marginal equatorial girdle; this girdle is divided into twelve to twenty-four or more chambers by radial beams, which are the external prolongations of the radial marginal spines of Pylodiscus. The latter genus bears therefore to Discozonium the same relation as Sethodiscus in the other does to Lithocyclia, or Phacodiscus to Coccodiscus.

1. Discozonium cyclonium, n. sp.

Disk circular, lenticular, with smooth margin, three times as broad as the triangular, Triopyle-shaped medullary shell. Three gates of the cortical shell kidney-shaped, twice as broad as the three