Page:Scientific results HMS Challenger vol 18 part 2.djvu/772

1648 Genus 694. Challengeria, John Murray, 1876, Proc. Roy. Soc. Lond., vol. xxiv. p. 536.}}

Definition.— without pharynx, with one or more adoral teeth, but without spines on the sagittal margin.

The genus Challengeria, and the following closely allied Challengeron, differ from the preceding Lithogromia, their ancestral form, in the development of teeth on the mouth of the shell. Challengeron has also radial spines on the sagittal margin, while these are wanting in Challengeria. The latter genus exhibits not less than twenty-one, the former twenty-five species, so that both together make by far the greatest part of the family (containing fifty-eight species). They are also more common and more widely distributed than the four other genera of Challengerida, and many species appear in great numbers in certain localities. With a few exceptions living on the surface, they are all inhabitants of great depths.

Definition.—Peristome with a single simple tooth, which is neither forked nor branched (Challengeriæ monodontes).

1. Challengeria naresii, John Murray.

Challengeria naresii, John Murray, 1876, Proc. Roy. Soc. Lond., vol. xxiv. pl. xxiv. fig. 1.

Challengeria naresii, John Murray, 1879, in litteris, Narr. Chall. Exp., vol. i. p. 236, pl. A, figs. 1, 1a-1e.

Shell circular or nearly circular, strongly compressed, lenticular. Peristome on the dorsal corner with a single simple vertical tooth, which is nearly straight, conical, with two sharp lateral edges on the base, about half as long as the shell.

Dimensions.—Diameter of the shell 0.5 to 0.6, length of the tooth 0.2 to 0.3.

Habitat.—Cosmopolitan; Atlantic, Indian, Pacific, at depths between 1000 and 3000 fathoms.

2. Challengeria xiphodon, n. sp.

Shell circular, nearly spherical, slightly compressed. Peristome on the dorsal corner with a single simple vertical tooth, which is straight, three-sided prismatic, and as long as the shell.

Dimensions.—Diameter of the shell 0.1 to 0.13, length of the tooth 0.1 to 0.12.

Habitat.—Tropical Atlantic, Stations 349 to 352, surface.