Habitat.—Indian Ocean, Madagascar (Rabbe).
Genus 715. Circostephanus,[[332]] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 5.
Definition.—Circoporida 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 sometimes six) ovate, basal pores (fig. 3b). Mouth armed with a corona of eight short, conical, vertical, spinulate teeth (fig. 3a).
Dimensions.—Diameter of the shell 0.4 to 0.5, length of the spines 0.2 to 0.25.
Habitat.—South-Eastern Pacific (off Valparaiso), Station 298, depth 2225 fathoms.
2. Circostephanus sexagenarius, n. sp.
Shell polyhedral, with sixty triangular, equilateral congruent faces which are nearly plane, and separated by high prominent crests. They are disposed in twelve pentagonal groups, each with five faces, so that they appear as if derived from a regular pentagonal dodecahedron, the twelve regular faces of which are each divided into five congruent triangles, meeting in its centre. From the elevated corners of the polyhedron arise thirty-two radial spines (twelve in the central points of the pentagons, twenty in the meeting corners of every three pentagons). The radial spines are nearly as long as the diameter of the shell, cylindrical, spinulate, and surrounded at the distal end by a verticil of five stout, curved branches, and at the pyramidal base by a corona of twelve to sixteen basal pores. Mouth armed with a corona of twelve conical, vertical, spinulate teeth.