Subfamily 3. Discopylida, Haeckel

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

Genus 251. Discozonium, n. gen.

Definition.—Pylodiscida 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 Discoidea 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 arms. Chambered equatorial girdle with twenty to twenty-four subregular chambers (similar to Discopyle osculata, Pl. , fig. 19, but without any marginal osculum).

Dimensions.—Diameter of the disk 0.2, of the cortical shell 0.14, of the medullary shell 0.07.

Habitat.—Central Pacific, Station 265, depth 2900 fathoms.

2. Discozonium trigonium, n. sp.

Disk triangular, with thorny margin, four times as broad as the triangular, Triopyle-shaped medullary shell. Three gates of the cortical shell egg-shaped, scarcely as broad as the three arms. Chambered equatorial girdle with twenty-four to thirty irregular chambers.

Dimensions.—Diameter of the disk 0.24, of the cortical shell 0.2, of the medullary shell 0.06.

Habitat.—Central Pacific, Station 274, depth 2750 fathoms.

3. Discozonium hexagonium, n. sp. (Pl. , fig. 18).

Disk hexagonal, with spiny margin, four times as broad as the triangular, Triopyle-shaped medullary shell. Three gates of the cortical shell kidney-shaped, one and a half times as broad as the arms. Chambered equatorial girdle with twelve large regular chambers; the radial beams between them are prolonged into twelve strong pyramidal marginal spines (three perradial on the ends of the arms, three interradial on the radii of the gates, six adradial between the former and latter).

Dimensions.—Diameter of the disk 0.2, of the cortical shell 0.12, of the medullary shell 0.05.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

Genus 252. Discopyle, n. gen.

Definition.—Pylodiscida with Triopyle-shaped medullary shell and Pylodiscus-shaped cortical shell, which is surrounded by an equatorial chambered girdle. One peculiar osculum, surrounded by a corona of spines, on the margin of the disk.

The genus Discopyle differs from the preceding genus Discozonium in the development of a peculiar marginal osculum, and bears therefore to it the same relation as, in the Porodiscida, Ommatodiscus does to Porodiscus (compare above, p. ). This peculiar osculum is here also surrounded by a corona of spines, and serves probably for the exit or outlet of a bunch of pseudopodia or a "sarcode-flagellum." Only two species of Discopyle have been observed, which represent perhaps better two different genera; in one species the disk is circular, in the other elliptical. In this latter the osculum lies on one pole of the main axis.

1. Discopyle osculata, n. sp. (Pl. , fig. 19).

Disk circular with spiny margin, three times as broad as the triangular, Triopyle-shaped medullary shell. Three gates of the cortical shell kidney-shaped, on the inside with an interradial spine, twice as broad as the three pentagonal arms. Chambered equatorial girdle with twenty-four subregular chambers, in the radius of one odd gate with a large marginal osculum, which is as broad as the medullary shell, and surrounded by a dense corona of twenty to thirty strong conical spines.

Dimensions.—Diameter of the disk 0.15, of the cortical shell 0.1, of the medullary shell 0.05, of the marginal osculum 0.06.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

2. Discopyle elliptica, n. sp. (Pl. , fig. 20).

Disk elliptical, four-fifths as broad as long, with spiny margin, three times as broad as the triangular, Triopyle-shaped medullary shell. Three gates of the cortical shell roundish, on the inside with an interradial spine, little broader than the quadrangular arms. Chambered equatorial girdle with twenty to thirty irregular chambers, on one pole of the main axis with a large marginal osculum, which is one-third as broad as the length of the main axis, and armed with a corona of twenty to thirty short conical spines. The osculum does not correspond to a certain radius.

Dimensions.—Diameter of the disk 0.15, of the cortical shell 0.08, of the medullary shell 0.04, of the marginal osculum 0.05.

Habitat.—Central Pacific, Station 267, depth 2700 fathoms.