62 PBOP. p. M. Duncan's revision op the 



of triplets slightly crowded near the peristome ; primary tubercles in two 

 rows, perforate and crenulate, fairly developed. 



Interradia wide, with two or more vertical rows of primary tubercles, 

 larger than those of the ambulacra, and otherwise similar; secondary 

 tubercles may exist with or without a distinct and often crowded granu- 

 lation. Some diminution in the size of the tubercles and of the number of 

 vertical rows may occur dorsally. 



Peristome moderate, nearly flush or incurved, decagonal, with large 

 branchial incisions, having a raised edge. Jaws well developed, with a 

 large foramen, without epiphyses ; teeth grooved ; perignathic girdle conti- 

 nuous. Spines variable in size, short, or longer than the diameter of the 

 test, striated longitudinally, finely tapering, cylindrical pointed (solid, and 

 this condition is due to fossilization). 



Fossil. Lias, Oolites, Cretaceous : England, Europe, N. Africa, Egypt, 

 Asia, N. America; probably Eocene, Europe (Hebertia). 



The alliance of Microdiadema, Diademopsis, Hemipedina, and Echino- 

 diadema (Cott.) with the old genus Pseudodiadema is evident. The im- 

 perforation and non-crenulation, or the reverse conditions, of primary 

 tubercles are insufficient to define and limit genera. Now all these "genera" 

 are placed as subgenera with Pseudodiadema, which is synonymous with 

 Diadema. 



Subgenus Miceodiabema, Cotteau, 1863 (geuus), Bev. et Mag. 

 de Zool. ser. 2, vol. xv. p. 225. 



Test small, swollen and hemispherical abactinally, re-entering 

 actinally. 



Apical system solid, narrow, projecting, granular. 



Ambulacra with the pairs of pores in simple vertical series ; 

 arrangement of plates " diadematoid." Interporiferous areas 

 with small, almost uniform, perforate and crenulate, scrobiculate 

 primary tubercles in several vertical rows. 



Interradia with, primary tubercles resembling those of the 

 ambulacra in several vertical rows. 



Peristome large, subcircular or decagonal, with well-developed 

 branchial incisions. 



Fossil. Lias : Europe. 



Subgenus Diademopsis, Desor, 1858 (genus), Synopsis, p. 79. 

 Cotteau, 1864, Bev. et Mag. de Zool. ser. 2, vol. xvi. p. 212. 



Test moderate and small, depressed, but subconical above the 

 tumid ambital outline. Coronal plates low and numerous. 



Apical system large ; madreporite and the basals large ; radial 

 plates between the basals, but excluded from the periproct. 



