Page:Scientific results HMS Challenger vol 18 part 2.djvu/848

1724 horn. Aboral hinge with two pyramidal, horizontal, caudal horns of different sizes, the dorsal smaller than the ventral. Lateral margin of each valve on one side with twelve to fourteen strong conical teeth (fig. 12). Lips of the narrow mouth thickened (fig. 11).

Dimensions.—Length of the shell 0.3, height 0.27, breadth 0.21.

Habitat.—Tropical Atlantic, Station 342, depth 1445 fathoms.

2. Conchonia triodon, n. sp. (Pl. 124, figs. 13, 14).

Shell laterally compressed, with two very unequal valves. Dorsal valve (fig. 14) larger, hat-shaped, on the apex with a large pyramidal horn which is half as long as the shell, curved and directed backwards. Ventral valve (fig. 13) smaller, boat-shaped, without apical horn. Aboral hinge with two pyramidal caudal horns of different sizes, the dorsal horn twice as long as the ventral. Lateral margin of each valve on one side with twelve to fifteen conical teeth. Perhaps the larger horned valve (fig. 14) may be the ventral, and the opposite smaller hornless (seen from above in fig. 13) the dorsal valve.

Dimensions.—Length of the shell 0.21, height 0.17, breadth 0.12.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

3. Conchonia tetrodon, n. sp.

Conchura tetrodon, Haeckel, 1882, Manuscript.

Shell subspherical, with two nearly equal hemispherical valves, which are very thin-walled and similar in structure to those of the Cœlodendrida, with very irregular roundish pores of different shapes and sizes (compare Pl. 121, fig. 3). Lateral margins of the valves with very numerous and irregular, thin, bristle-shaped teeth, similar to those of some Cœlographida (compare Pl. 127, fig. 8). Aboral hinge with two equal, conical, caudal horns, which are straight, parallel, and half as long as the shell. Two similar straight conical horns are opposed on the poles of the sagittal axis, and arise from the apex of the two valves. This remarkable species may perhaps better represent a separate genus, Conchura, forming a direct transition to the ancestral form of the Cœlodendrida, Cœlodoras; it differs from the latter in the absence of a galea or hollow conical cupola on the apex of each valve, and in the solid, not hollow structure of the horns.

Dimensions.—Diameter of the shell 0.24, length of the two sagittal horns 0.1, of the two caudal horns 0.12.

Habitat.—Indian Ocean, Cocos Islands (Rabbe), surface.

Definition.— with dentate lateral margins and a sharp sagittal keel of the compressed valves, without horns on the hinge.