Shell balloon-shaped, subspherical, with twenty smooth meridional ribs, alternating with twenty longitudinal rows of circular pores, of the same breadth as the bars. Peristome constricted, about half as broad as the shell.
Dimensions.—Shell 0.09 long, 0.07 broad; mouth 0.03 broad.
Habitat.—Central Pacific, Station 266, depth 2750 fathoms.
3. Cystophormis spiralis, n. sp. (Pl. [51], fig. 9).
Shell ovate, one and a half times as long as broad, with twenty spirally convoluted, elegantly denticulated ribs, alternating with twenty spiral rows of small circular pores, of about the same breadth as the bars. Peristome constricted, very small, only one-seventh as broad as the shell.
Dimensions.—Shell 0.1 long, 0.07 broad; mouth 0.01 broad.
Habitat.—West Tropical Pacific, Station 225, depth 4475 fathoms.
4. Cystophormis tabulata (Pl. [79], fig. 2).
Shell urceolate and tabulate, twice as long as broad with twenty-five to thirty denticulated longitudinal ribs crossed by twenty to twenty-four transverse rings. Pores therefore regularly disposed in longitudinal and transverse rows; each pore circular, with a square frame. Peristome constricted, scarcely half as broad as the shell.
Dimensions.—Shell 0.2 long, 0.1 broad; mouth 0.04 broad.