Page:Scientific results HMS Challenger vol 18 part 1.djvu/408

200 2. Hexadendron bipinnatum, n. sp. (Pl. 23, fig. 1).

All three shells regular octahedral, with very delicate network of irregular polygonal meshes, and very thin, thread-like bars between them; their radial proportion = 1 : 2.5 : 7.5. Surface of the cortical shell covered with numerous bristle-shaped by-spines, as long as the radius. Six main spines very large, three-sided prismatic, with three rows of pinnate, lateral branches, on the three wing-like, spirally twisted edges (similar to those of Hexancistra mirabilis, p. 189, Pl. 23, fig. 3).

Dimensions.—Diameter of the outer shell 0.12, middle 0.04, inner 0.016.

Habitat.—Central Pacific, Station 272, surface.

Definition.— with three concentric lattice-spheres and six simple spines of different size; one opposite pair larger than the two others.

The genus Hexacontarium exhibits to its ancestral form Hexacontium the same relation that Hexaloncharium bears to Hexalonche; the former is developed from the latter by duplication of the medullary shell. As two opposite spines of one pair are larger than the four others, they correspond to the three axes of a quadratic crystal.

1. Hexacontarium dentatum, n. sp.

Cortical shell with regular circular, hexagonally framed pores, twice as broad as the bars, with smooth surface. Radial proportion of the three spheres = 1 : 2 : 5. Six radial spines three-sided prismatic, half as broad as the inner medullary shell, with three dentated edges. Two opposite major spines longer than the shell diameter; four other minor spines only half as long as the radius. (Similar to Hexacontium clavigerum, Pl. 23, fig. 5, but distinct by the prolongation of the spines of one axis.)

Dimensions.—Diameter of the outer shell 0.15, middle 0.06, inner 0.03; length of the major spines 0.2, minor 0.04.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

2. Hexacontarium clavatum, n. sp.

Cortical shell covered with short conical by-spines and irregular roundish pores, three to four times as broad as the bars. Radial proportion of the three spheres = 1 : 3 : 8. Six radial spines three-sided prismatic, at the distal end club-shaped; two major spines three times as long as the four others, which are equal to the shell radius.

Dimensions.—Diameter of the outer shell 0.16, middle 0.06, inner 0.02.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.