Page:Scientific results HMS Challenger vol 18 part 1.djvu/1008

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Definition.— with twenty radial spines shorter than the radius of the shell; therefore their distal ends not connected with the twenty perspinal holes, which are simple, not prolonged into radial tubes.

The genus Porocapsa and the following Cannocapsa form together the small sub-family of Porocapsida, distinguished by the peculiar reduction or retrograde development of the twenty radial spines; all these twenty are present and disposed according to the Müllerian law of the Icosacantha, but they are shorter than the radius of the shell and therefore do not reach it. In the ideal prolongation of the spines the shell is pierced by twenty simple quadrangular or circular perspinal holes.

1. Porocapsa murrayana, n. sp. (Pl. 133, fig 7).

Perspinal holes cruciform, with smooth thickened margin or with four short teeth between the four lobes. Porules of the shell simple, without ring and dimple. Four edges of the spines smooth. (Differs from Sphærocapsa cruciata, Pl. 135, figs. 6, 7, living in the same locality, mainly in the reduction of the radial spines, which do not reach the shell.)

Dimensions.—Diameter of the shell 0.28; length of the spines 0.2.

Habitat.—North Atlantic, Færöe Channel, Gulf Stream (expedition of H.M.S. "Triton," August 1882), John Murray, surface and in depths from 40 to 640 fathoms.

2. Porocapsa tetrodon, n. sp.

Perspinal holes cruciform, with four triangular prominent teeth between the four lobes of the cross. Porules of the shell with an elevated polygonal ring, in the bottom of a dimple. Four edges of the spines elegantly denticulate.

Dimensions.—Diameter of the shell 0.36; length of the spines 0.12.

Habitat.—North Pacific, Station 253, surface.

3. Porocapsa octodon, n. sp.

Perspinal holes square, with four larger prominent teeth on the sides of the square, and four smaller teeth on its corners. Porules of the shell surrounded by an elevated ring with elegantly crenated irregular margin. Four edges of the spines smooth.

Dimensions.—Diameter of the shell 0.48; length of the spines 0.18.

Habitat.—Arctic Ocean (Greenland), in the contents of the stomach of the Peromedusa, Periphylla hyacinthina.