CLASS I 



ECHINOIDEA 



27' 



The Amh are 





primordial amhulacral, also non-amhulacral plates. Lantern erect, or (Astropyga) 

 inclined. Stewart's organs slight, or absent. Lias to Recent. 



Centrechimis Jackson (Diadema Schynvoet) (Fig. 368, D). 

 narrow, often projecting; two vertical ^ 



rows of small, primary, crenulate and 

 perforate tubercles extending from 

 peristome to apex. lAml with two 

 or more vertical rows of primary 

 tubercles resembling those of the 

 Amh, but larger. Secondary tubercles 

 and granules surrounding the scrobi- 

 cules. Spines long, hollow, longitu- 

 dinally striated. Lias to Recent. 



Hemipedina AVright. Jura, Creta- 

 ceous and Recent. Differs from Centre- 

 chimis in having simple AmJi plates 

 near the apex, and perforate, but 

 not crenulate tubercles. 



Pseiidodiadema Desor (Fig. 388). 

 Includes small species having wide 

 Amh, tubercles of uijiform size in 

 Amh and lAmb areas, and oculars 

 typically all exsert. Jura to Ter- 

 tiary. 



Heterodiadema Cotteau. Like 

 Centrechinus, but Avith the apical 



system greatly extended into the depressed posterior lAmh 

 H. lilnjcmn Cotteau. 



Codiopsis Ag. (Fig. 389). Primary tubercles of both areas small, smooth. 



Fii5. 38S. 



Pseudodiadema neglectum Thunii. From the Bernese 

 Jura. -I, B, Profile and ventral aspect of test, l/i. 

 C, Ambulacrum, enlarged. ' D, Spine, Vi- 



Cretaceous. 



Fic. 3811. ■ 



Codiopsis doma (Desm.). Cenomanian (Tourtia) ; Tournay, Belgium. ^, Side-view of test, i/i- 5, Ventral 



aspect of same. C, Apical system, enlarged. 



nearly equal in size, and only occurring actinally and for a short distance 

 toward the ambitus. Pore-pairs uniserial. Cretaceous. 



Cottaldia Desor. Cretaceous and (?) Recent. Pleurodiadema de Loriol. 

 Jura. Magnosia Michelin. Jura and Cretaceous. 



Diplopodia M'Coy. Amh narrow, with two vertical rows of perforate and 

 crenulate primary tubercles. Pore-pairs in double vertical series near the 

 poles, uniserial at the ambitus. Jura and Cretaceous. 



Pedinopsis Cotteau. Cretaceous. Phymechinus Desor. Jura. 



