Page:Scientific results HMS Challenger vol 18 part 2.djvu/823

Rh species by thirty prominent crest-like edges. From the corners of the dodecahedron, at which every three pentagons meet, arise twenty radial spines, opposite in pairs in ten equidistant axes.

1. Circorrhegma dodecahedra, n. sp. (Pl. 117, figs. 2, 2a).

Shell dodecahedral, with twelve equal and regular, plane, pentagonal plates, which are separated by thirty prominent crests, and bear a network of numerous polygonal (usually also pentagonal), smaller plates. Twenty radial spines about as long as the radius of the shell, three-sided prismatic, covered with numerous bristles; each surrounded at the thickened base by a circle of twelve to sixteen pores, and at the distal apex by a corona of five curved, terminal branches. Mouth pentagonal, with five conical, subvertical, spinulate teeth (fig. 2a).

Dimensions.—Diameter of the shell 0.8, length of the spines 0.5.

Habitat.—Indian Ocean, Madagascar (Rabbe).

Definition.— with a subregular, polyhedral or nearly spherical shell, composed of thirty to sixty or more triangular plates, with twenty-four to thirty-two or more corners, from which arise radial spines, symmetrically disposed.

The genus Circostephanus comprises those Circoporida in which the porcellanous shell is an endospherical polyhedron, with numerous (thirty to sixty or more) triangular faces, and has a variable number of radial spines (twenty-four to forty or more), arising from its corners. The number of faces and corners seems to be variable in this genus, but may perhaps be typical in some species. Circostephanus sexagenarius has the typical form of a "Sexagenal-Polyhedron," with sixty equal triangular faces and thirty-two corners, and may be derived from the "Pentagonal-Dodecahedron" (Circorrhegma) by dividing its twelve pentagonal faces each into five congruent triangles.

1. Circostephanus coronarius, n. sp. (Pl. 116, figs. 3, 3a, 3b).

Shell polyhedral, with thirty-two to forty triangular, concave faces of nearly equal size, which are separated by high prominent crests. From the elevated corners of the polyhedron arise twenty-four to thirty radial spines, which are three-sided prismatic or nearly cylindrical, about as long as the radius of the shell, and covered with long curved bristles. The distal end of each spine is surrounded by a verticil of five stout, curved branches, its pyramidal base by a corona of five (or