228 



ECHINODERMATA ECHINOIDEA 



SUB-BRANCH III 



primary tubercles well developed. Interambulacral plates few ; their primary tubercles 

 very large at the ambitus, but decreasing in size or obsolescent toward the poles ; 

 scrobicules often coalescing. Permian to Cretaceous. 



Hemicidaris, Ag. (Fig. 365). Amb narrow ; plates 

 near the apical system very numerous, small, low 

 primaries, succeeded by plates formed of from two 

 to four components, together with additional primary 

 or demi-plates. Tubercles in two vertical rows, per- 

 forate and crenulate. I Ami) broad, with two vertical 

 rows of tubercles similar to those of the Anib, but 

 much larger. Peristome large, with well-developed 

 , ^ Lam. branchial incisions. Permian to Cretaceous. 



sp. Coral Rag; Chatel Censoire, mi .. ,, . , 



Yonne. ty. The following sub-genera are recognised : 



(a) Hemidiadema, Ag. Amb tubercles large, and few in number below the ambitus, 

 alternating distinctly. Jura and Cretaceous. H. stramonium, Ag. 



FIG. 365. 



Is CTenuh'ris. 



FIG. 366. 



Acrocidaris nobllis, Ag. Upper Jura ; St. Sulpice, near Locle, Neuchatel. A. Dorsal view. B, Ventral 

 view. C, Spine, 1/1- D, Three compound Amb plates, enlarged. 



' (b) Hypodiadema, Desor. Amb narrow, straight ; their tubercles of nearly the same size 

 throughout. Peristome and branchial incisions small. Trias to Cretaceous. 



(c) Pseudocidaris, ]tall. Amb very undulating abactinally, with 

 primary tubercles near the peristome, granules elsewhere. Jura and 

 Cretaceous. 



Acrocidaris, Ag. (Fig. 366). Test large, spheroidal 

 dorsally, flat actinally. Amb straight, broad at the ambitus ; 

 pairs of pores uniserial and in simple series near the apex, 

 in arcs of from four to seven pairs near the larger tubercles, 

 crowded and polyserial actinally. lAmb with two vertical 

 rows of primary tubercles; only the largest perforate and 

 crenulate. Spines cylindrical, often tricarinate. Upper 

 Jura and Cretaceous. 



Goniopygus, Ag. Apical disk large, plates more or less 

 ornamented ; basal plates punctured on adoral margin. Peri- 

 stome very large, with small branchial incisions. Cretaceous 

 and Eocene. 



Glypticus, Ag. (Fig. 367). Amb straight, and narrow except at the peri- 

 stome, where the poriferous zones are expanded ; with two vertical rows of 



Fid. 367. 



Glypticus hierogl 

 icus, Goldf. Coral Rag 

 (Glyptician) ; Fringeli, 

 Switzerland. 1/1- 



lyph- 

 IRae 



