178 



CLYPEASTERlyn:. 



ECHINIDJE. 



CLYPEASTERIJE. 



Genus Echinarachnius. Leske. 



Generic Character. — Body circular, very much depressed, with the margin sub- 

 acute and entire ; ambulacra dorsal, five, short ; the ambulacral spaces broader 

 than the inter-ambulacral ; anus marginal, superior ; mouth central. 



THE CAKE-URCHIN. 



Echinarachnius placenta. Gmelin. 



Specific Character. — Body orbicular, very flat ; ambulacral spaces between the 

 avenues prominent ; base slightly concave. 



Echinarachnius, Leskk, ap. Klein, t. xx. f. a, b. Encyc. Meth. 



pi. cxliii. figs. 11, 12. 



