Page:Scientific results HMS Challenger vol 18 part 1.djvu/410

202 3. Hexacromyum arachnoides, n. sp.

Hexacromidium arachnoides, Haeckel, 1881, Prodromus, p. 453.

Shell composed of four concentric shells, with radial proportion = 1 : 2 : 3 : 4. Innermost shell with regular, hexagonal meshes; the three other shells with irregular, polygonal meshes; bars between the large meshes in all four shells very thin, cobweb-like. Surface covered with thin bristle-shaped by-spines, as long as the radius. Six radial main spines three-sided prismatic, longer than the diameter of the whole shell.

Dimensions.—Diameter of the four shells—(A) 0.08, (B) 0.16, (C) 0.24, (D) 0.32; length of the spines 0.4, breadth 0.01.

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

4. Hexacromyum octahedrum, n. sp. (Pl. 23, fig. 2).

Shell composed of four concentric shells which are not spherical (as in the three preceding species), but regular octahedral. Radial proportion = 1 : 2.5 : 6 : 9. Network in all four shells delicate, with irregular polygonal meshes and thin bars; the thickness of the bars and size of the meshes increasing from the innermost to the outermost shell. Six radial spines three-sided prismatic, increasing slowly in breadth towards the distal end, much longer than the shell diameter.

Dimensions.—Diameter of the four shells—(A) 0.02, (B) 0.05, (C) 0.12, (D) 0.18; length of the radial spines 0.2 to 0.3 and more, breadth 0.01.

Habitat.—Central Pacific, Station 263, depth 2650 fathoms.

Definition.— with five or more concentric lattice-shells.

Definition.— with five to six or more concentric lattice-shells and six simple spines of equal size.

The genus Cubosphæra is developed from the preceding Hexacromyum by further addition of the concentric lattice-shells, their number amounting to five, six, or more. The innermost two of these are medullary shells, the others being cortical shells. All are connected by six radial beams, prolonged outside into six simple spines of equal size; these lie opposite in pairs in three dimensive axes, corresponding to the three axes of a cube.