Page:Scientific results HMS Challenger vol 18 part 2.djvu/846

1722 3. Conchidium rhynchonella, n. sp. (Pl. 124, fig. 3).

Shell with three different dimensive axes in the proportion = 6 : 5 : 4. Ventral valve semi-ovate, larger than the humpbacked dorsal valve. Margins of the valves dentate almost in the whole periphery; on each side of one valve twelve or thirteen strong conical teeth. Aboral hinge with two very unequal horns, the dorsal much smaller than the pyramidal ventral. Under lip of the mouth emarginate, much larger than the acute upper lip. Pores subregular, circular, twice as broad as the bars.

Dimensions.—Length of the shell 0.3, height 0.25, breadth 0.2.

Habitat.—North Pacific, Stations 244 to 253, surface, and at various depths.

4. Conchidium dimerella, n. sp.

Shell laterally compressed, very similar to the preceding, but differing in the following characters:—Proportion of the three axes = 7 : 5 : 4. Ventral valve hemispherical, larger than the humpbacked dorsal. Margins of the valves dentate in the middle half only, whilst the anterior and posterior quarters are smooth; on each side of one valve six or seven strong conical teeth. Ventral horn of the aboral hinge very large, pyramidal, one-third as long as the shell and three times as long as the dorsal.

Dimensions.—Length of the shell 0.35, height 0.25, breadth 0.2.

Habitat.—North Pacific, Station 236, surface.

5. Conchidium leptæna, n. sp. (Pl. 124, figs. 4, 5).

Shell laterally compressed, with three different dimensive axes of the proportions = 4 : 3 : 2. Ventral valve larger than the dorsal, both semi-ovate. Margins of the valves dentate along the lateral sides; on each side of one valve nine or ten conical teeth, the middle of which are smaller. Aboral hinge with two unequal short horns; the dorsal rudimentary. Under lip of the mouth pointed, much larger than the truncate upper lip. Pores circular, about twice as broad as the bars.

Dimensions.—Length of the shell 0.2, height 0.15, breadth 0.1.

Habitat.—Central Pacific, Stations 271 and 272, surface, and at various depths.

6. Conchidium argiope, n. sp. (Pl. 124, figs. 7-9).

Shell laterally compressed, with three different dimensive axes of the proportion = 6 : 5 : 3. Both valves nearly equal. Margins of the shell dentate along the lateral fissure, on each side of one valve thirteen or fourteen thin conical teeth. Aboral hinge with two equal, short, pyramidal horns. Mouth with two equal short lips. Pores subregular, circular, twice as broad as the bars.

Dimensions.—Length of the shell 0.2, height 0.17, breadth 0.1.

Habitat.—Tropical Atlantic, Stations 341 to 349, surface, and at various depths.