52 



THE VOYAGE OF H.M.S. CHALLENGER. 



Eegarding the number of the concentric shells which compose the latticed carapace 

 of the S p h se r i d e a, we can distinguish six famihes, viz. : — 

 I. Monosphajrida (with one single shell). 

 II. Dyosphserida (with two concentric shells). 



III. Triosphserida (with three concentric shells). 



IV. Tetrasphserida (with four concentric shells). 



V. Polysphaerida (with five or more concentric shells). 

 VI. Spongosphserida (with spongy shells). 

 On the other hand, regarding the number of the radial spines and their regular 

 disposition on the shell-surface, we can distinguish five families, viz.: — 

 I. Liosphserida (without radial spines). 

 II. Stylosphaerida (with two radial spines, opposite in one axis). 



III. Staurosphserida (with four radial spines, opposite in pairs in two axes, 



perpendicular one to another). 



IV. Cubosphserida (with six radial spines, 



dimensive axes). 

 V. Astrosj)ha3rida {vnth. numerous — eight, 

 spines, often more than a hundred). 

 All five latter groups contain representatives of all six former groups ; therefore we 

 get together not less than thirty diiferent subfamilies of S p h se r o i d e a, already 

 enumerated in mj^ Prodromus, 1881, p. 449. I repeat them here to give a better 

 survey of the system there employed. 



opposite in pairs in the three 

 twelve, twenty, or more — radial 



