Page:Scientific results HMS Challenger vol 18 part 2.djvu/179

Rh cylindrical, S-shaped curved, strongly divergent, with few short branches, the two pectoral feet twice as long as the shell and the two tergal feet; odd caudal foot shorter.

Dimensions.—Shell 0.08 long, 0.13 broad; pectoral feet 0.2 long, tergal feet 0.1, caudal foot 0.06.

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

2. Pentaspyris isacantha, n. sp.

Shell subspherical, smooth, with slight sagittal stricture. Pores small, regular circular. Basal plate with six large pores (?). All five feet equal, cylindrical, C-shaped curved, slightly divergent, about as long as the shell.

Dimensions.—Shell 0.08 long, 0.09 broad; feet 0.07 long.

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

Definition.— tetrapoda with two pairs of descending basal feet, one pair corresponding to the anterior or pectoral, the other pair to the posterior or tergal feet of the Hexaspyrida.

Definition.— with two pairs of lateral feet and an apical horn.

The genus Zygospyris and the following three genera represent together the peculiar subfamily of Therospyrida. These always possess four basal feet, like the Tetraspyrida; but whilst in the latter group two feet are sagittal, and two lateral, in the Therospyrida there are no sagittal feet at all, but the four feet are opposed in two lateral pairs; the anterior pair corresponds to the pectoral, the posterior to the tergal feet of the Hexaspyrida and Pentaspyrida; from these latter the Therospyrida have been derived by loss of the sagittal feet.

1. Zygospyris quadrupes, n. sp.

Shell nut-shaped, tuberculate, with deep sagittal stricture. Pores irregular roundish, on each side of the ring two pairs of larger pores. Apical horn conical, straight. Four feet equal, straight, divergent, conical, about as long as the shell and the horn.

Dimensions.—Shell 0.08 long, 0.11 broad; horn and feet 0.1 long.

Habitat.—South Atlantic, Station 335, depth 1425 fathoms.