1698 THE VOYAGE OF H.M.S. CHALLENGES. 



the other bears numerous curved bristles around each spine, and at the distal end a 

 verticil of five curved branches. The mouth of the shell (placed in the centre of one of 

 the triangular plates) is in both species armed with six teeth. Both species are found 

 in the Tropical Atlantic. 



1. Circogonia icosahedra, n. sp. (PL 117, figs. 1, la). 



Shell regularly icosakedral, with twenty equal, triangular, nearly plane faces, which are separated 

 by thirty prominent, crest-like edges, and covered by a delicate network of small, subregular, hexagonal 

 plates. Twelve radial spines nearly conical, one and a half times as long as the radius of the shell, 

 with five prominent edges. The campanulate base of each spine is covered with numerous long, 

 curved bristles, surrounded by a circle of twelve to sixteen ovate, irregular pores, and separated from 

 the slender distal part by a constriction. The distal apex of the spine is surrounded by a verticil 

 of five conical, curved branches (corresponding to the five edges of the spines, and to the five faces, 

 which meet in the corners where the spine arises). Mouth hexagonal, with six conical, spinulate 

 teeth, convergent towards its centre (fig. la). 



Dimensions. Diameter of the shell - 75, length of the spines 0'5. 



Habitat. Tropical Atlantic, Station 347, depth 2250 fathoms. 



2. Circogonia dodecacantha, n. sp. (PL 115, figs. 8, 9). 



Shell subregularly icosahedral, with twenty equal, triangular, slightly convex faces, which are 

 not separated by prominent crests, but covered with a network of irregular polygonal plates. 

 Twelve radial spines, cylindrical, smooth, about as long as the diameter of the shell, forked at the 

 distal end, with two divergent, slightly curved branches (similar to Circospatliis furcata, PI. 115, 

 figs. 46). The conical base of each spine is surrounded by a circle of nine to twelve irregular, 

 ovate pores (fig. 9). Mouth circular, with a corona of six conical, smooth teeth which arise per- 

 pendicularly from the shell (in the upper part of fig. 8, at left). 



Dimensions. Diameter of the shell 0'6, length of the spines -I 7. 



Habitat. Tropical Atlantic, Station 348, depth 2450 fathoms. 



Genus 714. Circorrhegma, 1 n. gen. 



Definition. C ircoporida with a regular dodecahedral shell, composed of twelve 

 congruent, pentagonal plates, with twenty corners, from which arise twenty radial 

 spines. 



The genus Circorrhegma is remarkable for the geometrical regularity of its shell, 

 which represents a pentagonal dodecahedron. The shell is therefore composed of twelve 

 equal and regular pentagonal plates, and these are separated" in the only known 



1 Circorrhegma = Shell with circles of fissures ; x/jxoj, 



