Dimensions.—Principal axis 0.16, transverse axis 0.12; length of the medullary shell 0.05, breadth 0.04.
Habitat.—Pacific, central area, Stations 270 to 274, surface; Indian Ocean, Madagascar, Rabbe, surface.
5. Pylonium octacanthum, n. sp.
Cortical shell thorny, with eight long and thin cylindrical radial spines, lying in two crossed diagonal planes, opposite in pairs, and arising from the eight points where the transverse girdle is crossed by the lateral girdle. All three girdles elliptical, one and a half times as long as broad; four gates triangular. (This species is a further developmental stage of Tetrapyle octacantha, with perfect sagittal girdle.)
Dimensions.—Principal axis 0.18, transverse axis 0.13; length of the medullary shell 0.03 to 0.04.
Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.
6. Pylonium stenozonium, n. sp.
Cortical shell thorny, with eight short conical radial spines, lying in two crossed diagonal planes (as in the foregoing species). All three girdles nearly of the same size, subcircular, very narrow, only with one to two rows of pores. Four gates kidney-shaped.
Dimensions.—Principal axis 0.15, transverse axis 0.14; diameter of the quadrangular medullary shell 0.04.
Habitat.—Equatorial Atlantic, Station 347, surface.