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. JAm/ broad, with two vertical 
rows of tubercles similar to those of the Amb, but 
FIG. 365. much larger. Peristome large, with well-developed 
Hemicidaris crenularis, Lam. )ranchial incisions. Permian to Cretaceous. 
sp. Coral Rag; Chatel Censoire, - . 
Yonne. 1). 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. stramoniwm, Ag. 

Fic. 366. 
_ Acrocidaris nobilis, Ag. Upper Jura; St. Sulpice, near Locle, Neuchatel. A, Dorsal view. 3B, Ventral 
view. C, Spine, 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, Ktall. 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 ares of from four to seven pairs near the larger tubercles, 
crowded and polyserial actinally. dmb with two vertical 
rows of primary tubercles; only the largest perforate and 
crenulate. Spines cylindrical, often tricarinate. Upper 
Jura and Cretaceous. 
he Rae Goniopygus, Ag. Apical disk large, plates more or less 
ion eelte, ‘Con fae ornamented ; basal plates punctured on adoral margin. Peri- 
Sipaeets i stome very large, with small branchial incisions. Cretaceous 
and Kocene. 
Glypticus, Ag. (Fig. 367). Amb straight, and narrow except at the peri- 
stome, where the poriferous zones are expanded; with two vertical rows of 

a 
