1. Acrocubus octopylus, n. sp. (Pl. 82, fig. 9).
Mitral ring somewhat smaller than the basal ring; both rings rhombic, with curved outlines. Sagittal ring elliptical, with six pairs of nodulate protuberances. Four columellæ curved. Nodal points without radial spines.
Dimensions.—Height of the frontal ring 0.12, breadth 0.18.
Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.
2. Acrocubus tesseralis, n. sp.
Mitral ring of the same size as the basal ring; both rings square, smooth, with straight outlines. Sagittal ring also square, smooth. Four columellæ straight. Nodal points without radial spines. The shell has the form of a regular geometrical cube, the edges of which are represented by the rings.
Dimensions.—Height of the frontal ring 0.1, breadth 0.11.
Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.
Subgenus 2. Dipocubus, Haeckel.
Definition.—Basal ring with two descending feet.
3. Acrocubus brachiatus, n. sp.
Mitral ring smaller than the basal, both rings square, with thick straight rods. Sagittal ring tuberculate, square, equatorial part thinner. Four columellæ curved, the two lateral ones prolonged downwards into two vertical parallel straight feet of half their length.
Dimensions.—Diameter of the cube 0.12; length of the feet 0.06.
Habitat.—North Pacific, Station 244, depth 2900 fathoms.
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
