Dimensions.—Breadth of the shell 0.14, length 0.09.
Habitat.—North Pacific, Station 244, depth 2900 fathoms.
3. Tympaniscus dipodiscus, n. sp. (Pl. [94], figs. 5, 6).
Basal ring smaller than the mitral ring, with two lateral descending feet, which are nearly parallel and vertical, obtuse, about as long as the sagittal ring, and which bear on the outside a horizontal spur. Sagittal ring hexagonal, very stout, with a caudal appendix at the base, and with a small sagittal arch, bearing a stout spinulate double knob at the apex. The two subfrontal rings depressed, twice as broad as high, on the outside thorny, connected at each side in the lower half by a double transverse arch.
Dimensions.—Breadth of the shell 0.18, length 0.08 (with spines 0.18).
Habitat.—Central Pacific, Station 268, depth 2900 fathoms.
4. Tympaniscus tripodiscus, n. sp. (Pl. [94], fig. 7).
Basal ring of about the same size as the mitral ring, with three large and stout divergent feet (two lateral and one caudal). Sagittal ring stout, broader than the two spiny subsagittal rings; the upper part of the latter bears two ascending arches, which are united with the large apical horn arising from the apex of the sagittal ring. Six columellæ nearly vertical, slightly curved on the outside; their lateral edges armed with numerous simple or forked spines.
Dimensions.—Breadth of the shell 0.1, total length 0.12.
Habitat.—Central Pacific, Station 265, depth 2900 fathoms.