ECHINOIDEA. 31 



Family 1. CLYPEASTRIDiE. 



Clypeastrida, Haeckel, Gen. Morph. ii. (1866) p. lxxxv. 



Irregular gnathostomatous Euechinoidea with a depressed and 

 more or less oval test. The ambulacra petaloid or subpetaloid. 

 Apical area almost entirely occupied by the madreporite, and the 

 genital pores sometimes external to it. Anus ordinarily marginal 

 or inframarginal. 



One genus : Echinocyamus . 



Grade B. NODOSTOMATA. 



Spatangidee, Gray, Ann. Phil. x. (1825) p. 430; id. Cat. Ech, B. M. 



(1855) p. 38. ' 

 Echinides exocycliques atelostomes, de Loriol, Echinol. helvet. 2 e partie, 



in Pal. Suisse (Pictet), 1873, p, 198. 

 Atelostomata, Zittel, Hdbuch. Pal. i. (1879) p. 523. 

 Spatangoida, Duncan, J. Linn. Soc. xxiii. (1889) p. 25. 



Irregular Euechinoidea in which the mouth is central, and more 

 often pushed forwards, and is devoid of teeth and auricles. The 

 anterior odd ambulacrum often divides the test into two well-marked 

 bilaterally symmetrical halves. 



Only one family. 



Family 2. SPATANGID^E. 



Subfamily 1. CASSIDULINA. 



Peristome nearly central. 

 One genus : Neolampas . 



Subfamily 2. SPATANGINA. 

 Peristome excentric, with a hinder lip (labrum). 



Group i. PRYMNADETES. 



Prymnadetes, Loven, K. Svensha Vet.-Akad. Hdly. xi. 7. (1874) p. 16. 



Spatangina without a subanal fasciole. 

 One genus : Schizasler. 



Group ii. PRYMNODESMIA. 



Prymnodesmia, Loven, K. Svensha Vet.-Ahad. Edlg. xi. 7. (1874) p. 15. 

 Prymnodesmia, Duncan, J. Linn. Soc. xxiii. (1889) p. 239. 



Spatangina with a subanal fasciole. 



Three genera : Spatangus, Echinocarclium, Brissopsis. 



