Page:Scientific results HMS Challenger vol 18 part 2.djvu/304

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Definition.—, with the basal mouth of the shell open (vel Monocyrtida eradiata aperta).

Definition.— with conical shell, gradually dilated towards the wide open mouth. Apex armed with a horn.

The genus Cornutella is one of the three oldest genera of Polycystina, described by Ehrenberg, in 1838 (Cornutella, Lithocampe, and Haliomma). He afterwards enumerated, in 1872 and 1875, a large number of fossil and living species, the majority of which, however, belong to other genera of Monocyrtida and Dicyrtida (at least six or seven different genera). We retain here as the true type of the genus the oldest known species:—Cornutella clathrata, and the nearly allied forms Cornutella stylophæna, Cornutella mitra, Cornutella circularis, &c. The simple conical shell exhibits no distinct trace of an original cephalis, excepting the apical horn; it may have originated either independently, or been derived from Sethoconus, by loss of the cephalis.

Definition.—Axis of the conical shell straight. Pores polygonal, or roundish with polygonal frames.

1. Cornutella hexagona, n. sp. (Pl. 54, fig. 9).

Shell slender, conical, with straight outlines. Pores subregular, hexagonal, gradually increasing in size towards the mouth; in about ten to twelve longitudinal series, in the upper part very small. Horn slenderly conical, nearly bristle-shaped, long.

Dimensions.—Shell 0.1 to 0.15 long, 0.04 to 0.06 broad.

Habitat.—Central Pacific, Stations 265 to 274, surface, and at different depths.

2. Cornutella sethoconus, n. sp. (Pl. 54, fig. 10).

Shell slender, conical, with undulate outlines. Pores subregular, hexagonal, gradually increasing in size towards the mouth, in about fifteen to eighteen longitudinal series, in the upper part circular. Horn small, conical, short. The network is not so delicate as in the preceding similar species.

Dimensions.—Shell 0.12 to 0.16 long, 0.06 to 0.08 broad.

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