1694 THE VOYAGE OF H.M.S. CHALLENGER. 



Synopsis of the Genera of Circoporida. 



' Shell octahedral (or spherical), Six radial spines, . . 711. Circoporus. 



Shell tetradecahedral, . Nine radial spines, . ,712. Circoqjathis. 



I. Subfamily 



Circogonida. 

 Shell spherical or poly- 

 hedral with panelled 

 structure and poly- J Shell icosahedral, . . Twelve radial spines, . 713. Circogonia. 



gonal plates. A 

 certain number of 

 radial sjjines are 

 geometrically dis- 

 posed. 



Shell dodecahedral, . . Twenty radial spine.s, . 714. Ciirorrheijma. 



Shell polyhedral, . . Twenty-four to forty or more 



radial spines, . . 715. CircosteplMnus. 



II. Subfamily J Shell spherical, with dimpled structure, and a variable number 



Haeckelinida. ( of radial spines (without polygonal plates), . .716. Haeckdiana. 



Subfamily 1. Circogonida, Haeckel. 



Definition. — i r c o p o r i d a with panelled shell, composed of polygomil plates. 

 The shell is usually polyhedral, more rarely spherical, and the radial spines are usually 

 (or perhaps constantly) branched and regularly arranged. 



Genus 711. Circoporus} Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. 



Jena, Dec. 12, p. 5. 



Definition. — C i r c o p o r i d a with a spherical or regularly octahedral shell, com- 

 posed 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 iinother. 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 S p h se r o i d e a. 



1. Circoporus sexfurcus, Haeckel (PI. 117, fig. 5). 



Challengeria sp,, John Murray, 1876, Proc. Eoy. Soc. Lond.j vol. xxiv. pi. xxiv. fig. .5. 



Shell spherical, covered with irregular, polygonal plates. Six radial spines shorter than the 

 cUameter of the shell, covered with thin curved bristles, in the proximal half cyhndrical, m the 

 distal half forked, each with two equal curved fork-branches. Around the cihated base of each spine a 



1 Circoporus = Shell with circles of pores ; x/jkoj, a-o'go;. 



