6. Acrocubus lasanum, n. sp.
Mitral ring smaller than the basal, both rings square, with curved rods. Sagittal ring ovate, prolonged upwards into an occipital simple horn, downwards into a caudal foot. Two lateral columellæ prolonged downwards into two pectoral feet. All three feet conical, about as long as the height of the cube.
Dimensions.—Diameter of the cube 0.08; length of the feet 0.07.
Habitat.—North Pacific, Station 241, depth 2300 fathoms.
7. Acrocubus cortina, n. sp. (Pl. [93], fig. 16).
Mitral ring smaller than the basal, both rings elliptical, with curved rods. Sagittal ring ovate, prolonged upwards into an occipital horn, downwards into a caudal foot, as in the preceding species. As in the latter, also, the two lateral columellæ are prolonged downwards into two pectoral feet, but also upwards into two convergent horns, which are united with the occipital horn (commencing the formation of a galea). Rings and feet somewhat thorny.
Dimensions.—Diameter of the cube 0.16; total height 0.2.
Habitat.—Central Pacific, Station 266, depth 2750 fathoms.
Subgenus 4. Tetracubus, Haeckel.
Definition.—Basal ring with four descending feet (two sagittal and two lateral).