ECHINOIDBA. on 
Family 1. CLYPEASTRIDA. 
Clypeastrida, Haeckel, Gen. Morph. ii. (1866) p. Ixxxv. 
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. 
Spatangide, Gray, Ann. Phil. x. (1825) p. 480; id. Cat. Ech. B. M. 
(1855) p. 38. 
Kchinides exocycliques atélostomes, de Loriol, Echinol. helvét. 2° 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. SPATANGIDA. 
Subfamily 1. CASSIDULINA. 
Peristome nearly central. 
One genus: Neolampas. 
Subfamily 2. SPATANGINA. 
Peristome excentric, with a hinder lip (labrum). 
Group i. PRYMNADETES. 
Prymnadetes, Lovén, K. Svenska Vet.-Akad. Hdlg. xi. 7. (1874) p. 16. 
Spatangina without a subanal fasciole. 
One genus: Schizaster. 
Group ii. PRY MNODESMIA. 
Prymnodesmia, Lovén, K. Svenska Vet.-Akad. Hadlg. xi. 7. (1874) p. 15. 
Prymnodesmia, Duncan, J. Linn. Soc. xxiii. (1889) p. 239. 
Spatangina with a subanal fasciole. 
Three genera: Spatangus, Echinocardium, Brissopsis. 
