Page:Scientific results HMS Challenger vol 18 part 1.djvu/863

Rh 2. Pylonium hexazonium, n. sp.

Cortical shell smooth, without symmetrical radial spines. Transverse girdle elliptical, one and a half times as long as broad. Lateral and sagittal girdles nearly circular. Four gates egg-shaped.

Dimensions.—Principal axis 0.16, transverse axis 0.15; diameter of the subspherical medullary shell 0.04.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

3. Pylonium nephropylium, n. sp.

Cortical shell thorny, without radial spines. All its three girdles elliptical, one and a third times as long as broad. Four gates kidney-shaped, nearly twice as broad as high.

Dimensions.—Principal axis 0.17, transverse axis 0.13; length of the lentelliptical medullary shell 0.04, breadth 0.03.

Habitat.—Pacific, central area, Station 273, depth 2350 fathoms.

Definition.—Cortical shell armed with large, symmetrically disposed spines.

4. Pylonium quadricorne, n. sp. (Pl. 9, fig. 14).

Cortical shell thorny, with four strong horn-like curved spines in the lateral plane. All its three girdles elliptical, one and a third times as long as broad. Four gates kidney-shaped, twice as broad as high. (This species is a further developmental stage of Tetrapyle quadricornis, with perfect sagittal girdle.)

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.