GENEBA AND GROUPS OF THE ECHIKOIDEA. 31 



II. DiTisiON. Syn. Grenus BJialdocidaris, Desor, 1848, Synopsis, 



p. 39. 

 Large swollen tests, often as high as broad ; remarkable on 

 account of the particular structure of the poriferous zones, 

 which are broader than in true Gidaris, the two pores of a pair 

 being distant, and linked by a groove which is small and hori- 

 zontal. Ambulacra in general straight or slightly llexuous. 

 Tubercles large, always strongly crenulated (at least in the 

 fossil species), and proportionally more numerous than in true 

 Gidaris. Scrobicules large, often elliptical. Miliary zone 

 broad. Spines very stout, some cylindrical or prismatic, and 

 furnished with dentations or spines, and others in the shape 

 of oars, either simple or with spines at the base. Articular 

 facette very large and strongly crenulated. N^eck little or not 

 constricted. — (Type, Gidaris copeoides, Cott., and G. guttata, 

 Cott.) 



III. DiYisiOK. Syn. G-enus Leiocidaris, Desor, op. cit. p. 48. 

 Large tests, with smooth tubercles ; but they differ from 



Gidaris because the pores of a pair are linked by a small groove, 

 as in BJialdocidaris. Miliary zones very broad. Spines as 

 large smooth cylinders, resembling those of Seterocentrotus. 

 Desor defines Leiocidaris as Shahdocidaris with uncrenulated 

 tubercles. — {Gidaris canaliculata, Dune. & Sladen, Foss. Ech. 

 Sind, Pal. Ind. ser. xiv. p. 109, 1884, is a good type.) 



lY. DiYisiON. Syn. Subgenus JDorocidaris, A. Agassiz, 1872, 

 Kevision, p. 254. 

 ' Ambulacral median area narrow ; a small number of inter- 

 radial plates ; scrobicules sunken, and median space also. 

 Tubercles without crenulations, and the pores of a pair without 

 an intermediate groove. It will be observed that the spines 

 are very variable in this division. 



Dorocidaris is a true Gidaris, with no crenulation on the 

 tubercles. — {Gidaris papiUata, Leske, is the type.) 



Y. Division. Syn. Genus Stephanocidaris, A. Agassiz, 1872, 



Kevision, p. 393. 



Test thin. Apical system larger than the peristome, the 



plates feebly united, and the whole flexible ; the polygonal 



basal plates separated by large radial plates. — (Gidaris bispi- 



nosa, Lmk., is the type.) 



