Definition.—Astrosphærida with a single, spherical, latticed medullary shell, immediately enveloped by the spongy framework of the cortical shell; on the surface of the latter are numerous radial spines.
The genus Spongopila is a Spongoplegma with radial spines. On the other hand it may be derived either from Elaphococcus, by communication of the branched spines, or from Arachnosphæra, by development of spongy branches between the concentric spheres.
1. Spongopila dichotoma, n. sp.
Medullary shell with regular, hexagonal meshes, six times as broad as the bars. From each nodal-point (between every three meshes) arises a bristle-shaped radial spine, which is dichotomously branched. By communication of the neighbouring branches the loose spongy framework of the spherical cortical shell is formed, which is four times as broad as the medullary shell. On the surface occur very numerous bristle-shaped radial spines, as long as the diameter of the medullary shell. (May be derived from Elaphococcus.)
Dimensions.—Diameter of the spongy cortical shell 0.3, of the medullary shell 0.08.
Habitat.—Tropical Atlantic, Station 347, surface.
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.