Page:Scientific results HMS Challenger vol 18 part 1.djvu/895

Rh 3. Zoniscus tetracanthus, n. sp. (Pl. 50, fig. 10).

Cortical shell nearly quadrangular, one and a half times as long as broad, with four prominent corners, from which arise in the lateral plane four strong, three-sided pyramidal radial spines (opposite in pairs in two crossed diagonal axes). Surface thorny, with exception of the concave lateral sides. Sagittal constriction two and a half times as long as the hexagonal medullary shell. Both equatorial cupolas scarcely half as large as the four corner cupolas.

Dimensions.—Length of the cortical shell 0.18, breadth 0.12; length of the medullary shell 0.07, breadth 0.04.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.

4. Zoniscus octacanthus, n. sp.

Cortical shell nearly four-sided, prismatic, one and a third times as long as broad, with spiny surface. Eight longer thin radial spines opposite in pairs in two crossed diagonal planes (as in Tetrapyle octacantha). Sagittal constriction two and a half times as long as the hexagonal medullary shell. Both equatorial cupolas somewhat larger than the four corner cupolas.

Dimensions.—Length of the cortical shell 0.16, breadth 0.12; length of the medullary shell 0.055, breadth 0.04.

Habitat.—Pacific, central area, Station 263, depth 2650 fathoms.

5. Zoniscus hexatholius, n. sp. (Pl. 50, fig 11).

Cortical shell nearly rectangular, with four rounded corners and deep sagittal constriction, one and a fourth times as long as broad with thorny surface. Twelve longer edged radial spines; eight opposite in pairs in two crossed diagonal planes (as in the foregoing species), four others in the lateral plane, opposite in pairs on both sides of the sagittal constriction, which is scarcely twice as long as the hexagonal, in the equatorial plane constricted medullary shell. Both equatorial cupolas nearly of the same size as the four corner cupolas.

Dimensions.—Length of the cortical shell 0.16, breadth 0.13; length of the medullary shell 0.07, breadth 0.04.

Habitat.—South Pacific, Station 300, depth 1375 fathoms.

Definition.— with eight dome-shaped chambers of the cortical shell, separated by four annular constrictions (one sagittal, one transverse, and two others parallel to the latter).

The genus Zonidium must be regarded as a Zonarium, in which the four cupolas (in the quadrants of the lateral plane) are halved by diagonal beams or latticed septa,