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.
2. Zygospyris equus, n. sp. (Pl. [83], fig. 16).
Shell subspherical, rough, with slight sagittal stricture. Pores small and numerous, subregular circular; no larger annular pores. Apical horn cylindrical, half as long as the shell. Two pectoral feet somewhat smaller than the two tergal feet, about as long as the shell, slightly divergent, cylindrical. The distal ends of the feet and of the horn form an ovate, dimpled and spinulate cone.
Dimensions.—Shell 0.06 long, 0.09 broad; horn 0.04 long, feet 0.06 long.
Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.