Page:Scientific results HMS Challenger vol 18 part 1.djvu/483

Rh 2. Spongopila verticillata, n. sp.

Medullary shell with regular, hexagonal meshes, four times as broad as the bars. From its surface arise forty to sixty, three-sided prismatic radial spines, bearing eight to ten verticils of lateral branches, each verticil with six forked branches (two from each edge). By irregular ramification of these branches, and communication in all directions, the loose spongy framework of the cortical shell originates, which is six times as broad as the medullary shell. The free distal ends of the spines are as long as the shell radius. (May be derived from Arachnosphæra.)

Dimensions.—Diameter of the spongy cortical shell 0.6, of the medullary shell 0.1.

Habitat.—Tropical Pacific, Station 200, surface.

Definition.— with a single, spherical, latticed medullary shell, which is not armed with by-spines, but connected by stout radial main spines with the spongy cortical shell.

The genus Rhizoplegma is immediately allied to the foregoing Spongopila, but differs from it in the large interval separating both shells. In this interval lies the wall of the central capsule, which is only pierced by the radial spines connecting both shells.

Definition.—No free lateral branches of the radial spines between the two shells.

1. Rhizoplegma polyacanthum, n. sp.

Spongy cortical shell with a very fine dense framework and nearly smooth surface (without superficial by-spines). Its inner cavity is four times as broad as the medullary shell, which exhibits regular, hexagonal meshes. Radial spines sixty to eighty, three-sided prismatic, with three smooth edges, without lateral branches between both shells; their free outer part as long as the shell radius.

Dimensions.—Diameter of the spongy cortical shell 0.3, of its inner cavity 0.2, of the medullary shell 0.05.

Habitat.—Central Pacific, Station 274, surface.

2. Rhizoplegma spirale, n. sp.

Spongy cortical shell with a very delicate loose framework and bristly surface. Its inner cavity three times as broad as the medullary shell, which exhibits regular, hexagonal meshes.