4. Acrocubus amphistylus, n. sp.
Mitral and basal rings of nearly equal size, square, with thick curved rods. Sagittal ring elliptical, in the equatorial part thinner. Frontal ring tuberculate. Four columellæ curved, the two lateral ones prolonged downwards into two vertical, tuberculate feet of half their length.
Dimensions.—Diameter of the cube 0.13; length of the feet 0.07.
Habitat.—Central Pacific, Station 268, depth 2900 fathoms.
5. Acrocubus arcuatus, n. sp. (Pl. [93], fig. 15).
Mitral and basal rings, as well as the sagittal ring, of the same form as in the preceding nearly allied species. The two lateral columellæ are prolonged not only downwards into two short vertical feet, but also upwards into two curved bows, which are united in a vertical ascending horn, arising from the apical pole of the sagittal ring.
Dimensions.—Diameter of the cube 0.14; total height 0.21.
Habitat.—Central Pacific, Station 265, depth 2900 fathoms.
Subgenus 3. Tripocubus, Haeckel.
Definition.—Basal ring with three descending feet (one odd caudal and two paired lateral).