Page:Scientific results HMS Challenger vol 18 part 2.djvu/309

Rh about one-third as long as the shell. Mouth truncate, without peristome, about half as broad as the shell.

Dimensions.—Shell 0.15 long, 0.1 broad; horn 0.05, mouth 0.05.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

3. Archicorys microstoma, n. sp. (Pl. 51, fig. 12).

Shell rough, thick-walled, ovate. Pores large, subregular, circular, twice to four times as broad as the bars. Horn small, conical, not larger than one pore. Mouth very small, truncate, scarcely larger than one pore.

Dimensions.—Shell 0.1 long, 0.07 broad; horn 0.012, mouth 0.015.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

4. Archicorys globosa, n. sp.

Shell nearly spherical, thorny, thick-walled. Pores very large, circular, separated by spinulate frames, smaller towards each pole. Horn conical, large, nearly as long as the radius of the shell; mouth truncate, simple, about one-third as broad as the shell.

Dimensions.—Shell diameter 0.13, horn 0.06, mouth 0.04.

Habitat.—Fossil in Barbados.

5. Archicorys ovata, n. sp. (Pl. 51, fig. 10).

Shell ovate, rough, thick-walled. Pores regular, circular, of equal size, very small and numerous, quincuncially disposed. Horn small, conical, sometimes (as in the figured specimen) rudimentary. When it becomes lost, the species may be called Cyrtocalpis ovata. Mouth truncate, small, simple, one-sixth as broad as the shell.

Dimensions.—Shell 0.2 long, 0.15 broad; horn 0.01 to 0.03 long, mouth 0.03 broad.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

Definition.— with simple urceolate or ovate shell, constricted towards the mouth. Apex without horn.

The genus Cyrtocalpis comprises a large number of common, very primitive Monocyrtida, which in the simple ovate or urceolate form of the shell resemble the well known Gromia among the Thalamophora. Its basal mouth is more or less constricted, as in