Basal ring larger than the mitral ring, with numerous irregular short spines but without descending feet. Six columellæ strongly curved, in the lower half thicker and thorny; the four lateral much thinner than the two sagittal. Apex of the jointed sagittal ring with a conical horn. _Dimensions._--Length of the shell 0.08, breadth 0.11. _Habitat._--Central Pacific, Station 272, depth 2600 fathoms. 2. _Tympaniscus bipes_, n. sp. Basal ring of about the same size as the mitral ring, with two lateral descending feet, which are parallel and vertical, simple, without spur, half as long as the sagittal ring. The latter is ovate, twice as long and broad as the two circular frontal rings. _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. {1002}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. 5. _Tympaniscus quadrupes_, n. sp. (Pl. 94, fig. 4). Basal ring larger than the mitral ring, with four short vertical three-sided pyramidal feet of equal size (two lateral and two sagittal); the feet are three-sided pyramidal, with finely denticulate median edges, and bear at the base a horizontal thorny spur. Sagittal ring at the apex with a very large cross-shaped horn, bearing two horizontal thorny lateral branches; the horn is supported by an anterior and a posterior arch. Six columellæ strongly curved and dentate. _Dimensions._--Breadth of the shell 0.15, length 0.12. _Habitat._--South Pacific, Station 298, depth 2225 fathoms. 6. _Tympaniscus fibula_, Haeckel. _Ceratospyris fibula_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xx. fig. 3.