Page:Scientific results HMS Challenger vol 18 part 1.djvu/413

Rh pyramidal, longer than the diameter of the octahedron, arising from its six corners, as broad at the base as one mesh.

Dimensions.—Diameter of the shell 0.15, meshes 0.01 to 0.012, bars 0.001; length of the spines 0.2, basal breadth 0.01.

Habitat.—South Pacific, Station 300, surface.

Definition.— with spongy spherical shell and one simple latticed medullary shell in its centre, having six simple spines of equal size.

The genus Hexadoras exhibits the same structure of the spongy shell as Spongoplegma, but differs from it in the production of six dimensive spines. In the centre lies one simple, latticed, medullary shell, which is either spherical or octahedral. In the latter case the six spines arise from the six corners of the octahedron.

1. Hexadoras axophæna, n. sp.

Medullary shell spherical, with regular hexagonal meshes, twice as broad as the bars. Cortical shell entirely enclosing it, with loose irregular framework and thorny surface. Diameter of the outer shell three times as large as that of the inner. Six radial spines arising from the medullary shell, four to five times as long as the radius of the cortical shell, three-sided prismatic, with straight dentated edges.

Dimensions.—Diameter of the outer shell 0.15, inner 0.05; length of the spines 0.3 to 0.4.

Habitat.—Central Pacific, Station 265, depth 2900 fathoms.

2. Hexadoras lychnosphæra, n. sp.

Medullary shell spherical, with regular, circular, hexagonally framed pores, three times as broad as the bars. Cortical shell enveloping it, with loose irregular framework and spiny surface. Diameter of the outer shell eight times as large as that of the inner. Six radial spines arising from the inner shell, three-sided prismatic, with dentated, spirally contorted edges, seven times as long as the diameter of the medullary shell, with three lateral branches at the distal end (similar to Lychnosphæra, Pl. 11, fig. 1).

Dimensions.—Diameter of the outer shell 0.5, inner 0.06; total length of the spines 0.4, breadth 0.01.

Habitat.—Central Pacific, Station 270, depth 2925 fathoms.

3. Hexadoras octahedrum, n. sp.

Medullary shell regular octahedral, with irregular polygonal meshes, five times as broad as the bars. Cortical shell enveloping it, with dense spongy framework, also octahedral with rough surface.