Genus 711. Circoporus,[[328]] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 5.

Definition.—Circoporida with a spherical or regularly octahedral shell, composed of eight congruent, triangular plates, with six corners from which arise six radial spines, opposite in pairs in three diameters, perpendicular one to another.

The genus Circoporus, the simplest among the Circoporida, is distinguished by the regular octahedral form of the shell, with the three equal axes of the regular crystalline system perpendicular one to another. Six equal radial spines, arising from the six corners, lie opposite in pairs in those three dimensive axes. The eight equal triangular faces of the octahedron are sometimes plane, sometimes concave or convex, and sometimes the shell becomes spherical. In this case it becomes very similar to the Hexastylida among the Sphæroidea.

1. Circoporus sexfurcus, Haeckel (Pl. [117], fig. 5).

Challengeria sp., John Murray, 1876, Proc. Roy. Soc. Lond., vol. xxiv. pl. xxiv. fig. 5.

Shell spherical, covered with irregular, polygonal plates. Six radial spines shorter than the diameter of the shell, covered with thin curved bristles, in the proximal half cylindrical, in the distal half forked, each with two equal curved fork-branches. Around the ciliated base of each spine a corona of twelve to sixteen pores surrounded by a circle of numerous, curved, longer bristles. Mouth cruciform, with four triangular, convergent teeth.

Dimensions.—Diameter of the shell 0.55, length of the spines 0.4.

Habitat.—South Pacific, Station 289, depth 2550 fathoms.

2. Circoporus hexastylus, n. sp. (Pl. [117], fig. 4).

Shell regularly octahedral, with eight plane, congruent, triangular faces, which are covered with a very delicate network of small, regular, hexagonal plates. Six radial spines as long as the radius of the shell, four-sided pyramidal, simple, in the basal half covered with numerous curved bristles. Around the base of each spine a corona of four equal pores, surrounded by a circle of twelve short teeth. Apex with four crossed, curved branches (like those of Circospathis tetrodon). Mouth cruciform, with four smooth teeth.