3. Hexapyle circularis, n. sp.
Cortical shell circular, four times as broad as the triangular, Triopyle-shaped medullary shell. Surface smooth. Three arms half as broad as the three kidney-shaped gates on each side of the shell.
Dimensions.—Diameter of the cortical shell 0.2, of the medullary shell 0.05; breadth of the gates 0.08, of the bridges between them 0.04.
Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.
4. Hexapyle triacantha, n. sp.
Cortical shell triangular, thorny, with three pointed corners, prolonged into three strong conical radial spines; its diameter four times as great as that of the medullary shell. Three arms of the same breadth as the three egg-shaped gates of each side.
Dimensions.—Diameter of the cortical shell (or length of one side of the triangle, without spines) 0.2, of the medullary shell 0.05; breadth of the gates and of the bridges between them 0.06.
Habitat.—Indian Ocean, surface; Madagascar, Rabbe.
5. Hexapyle hexacantha, n. sp.
Cortical shell hexagonal, thorny, three times as broad as the medullary shell. Six stronger conical radial spines on the six corners at equal distances, lying in the equatorial plane of the disk. Three half girdles half as broad as the three triangular gates of each side.