The genus Oroscena differs from the preceding Orosphæra in the possession of numerous pyramidal or tent-shaped elevations, each of which bears on its top a radial spine. It exhibits therefore the same relation to the latter that Sagoscena does to Sagosphæra and Auloscena to Aulosphæra. The bases of the radial spines are usually connected by prominent concave crests, the edges of the pyramids. The species described of Oroscena seem to be very variable and transformistic.
Subgenus 1. Oroscenium, Haeckel.
Definition.—Radial spines simple, smooth or spiny, but neither branched nor forked.
1. Oroscena gegenbauri, n. sp. (Pl. [106], fig. 4).
Radial spines club-shaped, about half as long as the radius of the shell, cylindrical and finely sulcate in the basal third, ovate and elegantly dimpled in the distal two-thirds. The bases of the radial spines are connected by prominent concave crests, which form the edges of the polyhedral shell. Meshes irregularly polygonal, the majority quadrangular, separated by denticulate bars.
Dimensions.—Diameter of the shell (without spines) 1.2 to 1.8, of the meshes 0.04 to 0.1; length of the spines 0.3 to 0.5.
Habitat.—Central Pacific, Station 268, depth 2900 fathoms.
2. Oroscena mülleri, n. sp. (Pl. [107], fig. 8).[[292]]
Radial spines club-shaped, very similar to that of the preceding species, but much larger, about as long as the radius of the shell. Meshes irregularly polygonal, the majority pentagonal, separated by smooth bars.
Dimensions.—Diameter of the shell 2.0 to 2.4, length of the spines 1.0 to 1.2.