Page:Scientific results HMS Challenger vol 18 part 1.djvu/1038

830 on the base, with two divergent straight branches (similar to those of Hystrichaspis furcata, Pl. 138, fig. 9). Radial main spines two-edged, sword-like, nearly as long as the diameter of the shell.

Dimensions.—Diameter of the shell 0.13, of the pores 0.008.

Habitat.—Central Pacific, Station 272, surface.

4. Acontaspis capillata, n. sp.

Shell very dark and thick walled, non-transparent, with very numerous (three hundred to four hundred or more?) deep funnel-shaped dimples, each of which is perforated by a small circular pore (forty aspinal, two hundred to three hundred coronal, and fifty to one hundred sutural pores?). The high crests between the dimples bear very numerous simple by-spines, nearly half as long as the radius, so that the shell appears covered with hairs. Radial main spines very long and thin, cylindrical, longer than the diameter of the shell.

Dimensions.—Diameter of the shell 0.2, of the pores 0.012.

Habitat.—North Pacific, Station 244, surface.

Definition.— with twenty radial spines, each of which bears four crossed apophyses (opposite in pairs). The spherical shell is composed either of the meeting branches of these apophyses (Stauraspida), or of twenty perforated plates, produced by concrescence of their branches (Lychnaspida).

Definition.— with spherical shell, which is composed either of the meeting branches of the four crossed apophyses only, or exhibits four to twelve perforated plates which are produced by the crossed apophyses of four to twelve radial spines (but never of all twenty spines). Each plate bears four crossed pores.

Definition.— without perforated plates; shell composed only of the meeting branches of the four crossed apophyses, which arise (opposite in pairs) from each radial spine. Condyles of the branch-ends without by-spines.

The genus Stauraspis is the most simple and primitive form among all Tessaraspida, or that subfamily of Dorataspida, in which the shell is composed of twenty