Genus 116. Rhizoplegma,[[155]] Haeckel, 1881, Prodromus, p. 456.
Definition.—Astrosphærida 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.
Subgenus 1. Rhizoplegmarium, Haeckel.
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.