REPORT ON THE RADIOLARIA. 



411 



I. Subfamily 



Zonodiscida. 

 Margin of the disk without radial 

 spines. 



II. Subfamily 



Trochodiscida. 



Margin of the disk armed with radial 

 spines (lying in the equatorial plane). 



Synopsis of the Genera of the Cenodiscida. 



Margin quite simple, without equatorial girdle, 175. Cenodiscus. 



Margin surrounded by a solid siliceous equa- 

 torial girdle, .... 



Two spines opposite in one equatorial axis, 

 Three spines on the margin of the disk, 



Four spines opposite in pairs in two perpen- 

 dicularly crossed equatorial axes, 



Ten to twenty or more radial spines (variable in 

 number and commonly irregular indisposi- 

 tion), ..... 



176. Zonodiscus. 



177. Stylodiscus. 



178. Theodiscus. 



179. Crucidiscus. 



180. Trochodiscun. 



Subfamily 1. ZONODISCIDA, Haeckel. 

 Definition. C enodiscida without radial spines on the margin of the disk. 



Genus 175. Cenodiscus, 1 n. gen. 



Definition. C enodiscida with simple margin of the circular disk, without 

 surrounding equatorial girdle and without radial spines. 



The genus Cenodiscus is the most simple and primitive form of all D i s c o i d e a, 

 and represents possibly the common ancestral form of this order. The latticed shell is 

 a simple biconvex lens, and encloses a smaller central capsule of the same form, separated 

 from it by the jelly- veil. Cenodiscus can be derived phylogenetically either from 

 Cenosphcera by lenticular flattening of a simple latticed sphere, or directly from Actissa 

 by formation of a lenticular fenestrated shell around the lentiform central capsule. 

 Possibly also some forms of Cenodiscus can be derived from Sethodiscus by reduction 

 and loss of the medullary shell. 



1. Cenodiscus phacoides, n. sp. (PI. 48, figs. 1, la). 



Disk with smooth surface, without radial ribs or spines. Margin of the lenticular biconvex 

 disk thin, simple. Pores regular, circular ; fifteen to sixteen on the radius of the disk. (Very 

 similar to Sethodiscus phacoides, but without medullary shell.) 



Dimensions.- Diameter of the disk 0'2, of the pores 0'005. 



Habitat. Pacific, central area, Station 271, depth 2425 fathoms. 



1 Cenodiscm = Hollow disk ; xf.i/oy, S/!/.of. 



