84 



CLASSIFICATION OF THE 



A. Tubercles crenulated and perforated. 



a. Ambulacral areas subflexuou?, provided witb large tubercles at the 



ambitus aud inferior surface .... 



b. Ambulacra straight, provided witb tubercles in all their extent. 



X. Ambulacral and inter-ambulacral plates -without angular impressions. 

 X. Inter-ambulacral areas subgranular as they approach the summit. 

 y. Apical disc subpentagonal, peristome large. 

 r. Each of the ovarial plates of the apical disc carry a large tubercle 

 zz. Apical disc, without a large tubercle on its ovarial plates. 



1 . Poriferous plates unequal and irregular. 



If. Spines solid, aciculated, striated 

 ifiip. Spines tubular, verticillated 



2. Poriferous plates straight, equal, regular 



)jy. Apical disc narrow, annular, peristome reentrant 



yyy- Apical disc elongated, prolonged into the middle of the single inter- 

 ambulacral area ; peristome narrow 



xx. Inter-ambulacra smooth near the summit, and presenting a stellate 

 appearance ..... 



XX. Ambulacral aud inter-ambulacral plates marked with angular impressions 



Hemicidauis. 



.\CROCIDAKIS. 



PSEUDODIADEMA. 

 DiADEMA. 



HiBERTIA. 



MiCRODIADF.MA. 



IIeterodiadema. 



asteeiocibaeis. 

 Glypiiocyphus. 



15. Tubercles perforated and not crenulated. 



(I. Ambulacra subflexuous, provided with tubercles only towards the 



ambitus and inferior surface .... Cidakopsis. 



//. Ambulacra straight, provided with tubercles in all their extent. 



X. Pores simple near to the summit. 



X. Ambulacral plates unequal, irregular. 



//. Apical disc largely developed, peristome wide. 



:. Miliary zone extended; principal inter-ambulacral tubercles very large, 



placed on the external border of the plates . . . Diadl.moi'SIS. 



t.-. Miliary zone narrower, tubercles tolerably large and placed in the middle 



of the plates. ..... Hemipedina. 



yy. Apical disc narrow, peristome slightly developed, tubercles very small . Echi.nopsis. 

 XX. Ambulacral plates, straight, regular, sutures very apparent . . Orthopsis. 



.\x. Pores in double series at the superior surface and towards the ambitus 



Pedinopsis. 



