Page:Scientific results HMS Challenger vol 18 part 2.djvu/771

Rh

Definition.— without pharynx, with a simple mouth, not prolonged into an inner prominent tube.

Definition.— without pharynx, without adoral teeth and marginal spines.

The genus Lithogromia and the two following genera represent together the subfamily Lithogromida, comprising those Challengerida in which the mouth of the shell is a simple opening, and not prolonged into a pharynx or an internal prominent tube. Lithogromia may be regarded as the common ancestral form of this family, since it is the simplest of all, and possesses no external apophyses, neither teeth on the mouth, nor spines on the margin of the smooth shell.

1. Lithogromia silicea, n. sp. (Pl. 99, fig. 22).

Shell ovate, one and a half times as long as broad, not compressed. Transverse section circular. Mouth a simple circular opening with smooth edges about one-third as broad as the shell.

Dimensions.—Length of the shell 0.2, breadth 0.15; mouth 0.05.

Habitat.—North Atlantic, Færöe Channel (Gulf Stream), John Murray, depth 600 fathoms.

2. Lithogromia diatomacea, n. sp. (Pl. 99, fig. 21).

Shell ovate, lenticular, one and one-third times as long as broad, strongly compressed. Transverse section elliptical. Mouth a broad fissure, half as broad as the shell.

Dimensions.—Length of the shell 0.27, breadth 0.2; mouth 0.1.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.

3. Lithogromia lenticula, n. sp.

Shell subcircular, lenticular, about as long as broad, strongly compressed. Transverse section lanceolate. Mouth a narrow fissure, one-third as broad as the shell.

Dimensions.—Diameter of the shell 0.15, mouth 0.05.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.