GENERA AND GROUPS OF THE ECHINOIDEA. 81 



perignathic girdle with ridges and processes which unite and 

 form a small arch. 



Fossil. Oolite : England, Europe. Cretaceous : Europe, 

 N. Africa, Hindustan. Eocene : Egypt. 



De Loriol has shown that Hemipedina Scsmmmi, Wright, 1855, 

 is an Ortliopsis. 



Grenus Eodiabema, gen. nov. 



Test small, thin, circular in tumid marginal outline, subcorneal 

 dorsally, tumid and re-entering actinally, broader than high. 



Apical system moderate in size, ovoid or elliptical in the out- 

 line of the periproct ; five large basal plates, four in contact and 

 the fifth or posterior separated from its fellows, on either side, 

 by a radial plate. 



Ambulacra narrow, 'straight, wider than the interradia at the 

 peristomial margin, narrower elsewhere ; poriferous zones narrow ; 

 the pairs of pores numerous, in simple vertical series, barely 

 any crowding near the peristome ; plates all low, broad primaries ; 

 interporiferous areas rather broad, crowded with blunt granules 

 dorsally, some larger granules near the poriferous zones, and 

 giving place at the ambitus to some very small crenulate and 

 perforate tubercles which diminish actinally. 



Interradia broad ; plates not numerous, broader than high ; 

 two vertical rows of perforate, crenulate and scrohiculate pri- 

 mary tubercles in each area, a few large at the ambitus and 

 becoming rapidly very small dorsally, or replaced by distinct, 

 large, crowded granulation, diminishing also actinally. Scro- 

 bicules large at the ambitus, and usually coalescing. A large, 

 blunt, very marked granulation occurs beyond the scrobicules on 

 each plate, and also on all the plates up to the apex, except at an 

 angular space contiguous with each basal plate, and extending 

 downwards, variously, along each median line, where there are 

 no granules, but a plain surface. Peristomial edge small and 

 pointed. 



Peristome sunken, decagonal, small, and with well-marked 

 branchial incisions. 



Fossil. Middle Lias : England. 



This is a most interesting genus ; and the species Eodiadema 

 granulata was discovered by E. Wilson, Esq., E.Gr.S., of the Bristol 

 Museum. The alliance is very close to the Orthopsidse, although 



LINN. JOTJRN. — ZOOLOGY, TOL. XXIII. 6 



