62 CIDARIS 



general inflated and sub-conical, its superior inter- ambulacral plates are entirely deprived 

 of tubercles, the structure of its periproct and apical disc impart a peculiar physiognomy 

 to it, and clearly distinguish it from its congeners. It is distinguished from C. sub- 

 vesiculosa by its greater size, its inflated sub-conoidal form, its straighter ambulacra, and 

 smaller and less regular granules. Its inter-ambulacral plates are more numerous, and 

 the three uppermost plates in each column are entirely deprived of tubercles in the 

 specimen figured by M. Cotteau, and they are small and rudimentary in the urchin figured 

 in our PI. VIII, fig. 2. 



Locality and Stratigraphical position. — Collected from the White Chalk, where it is 

 very rare. The fine specimen figured by Mr. Bone belongs to Dr. Bowerbank's collection. 

 That figured by M. Humbert for M. Cotteau was collected at La Faloise pres Breteuil 

 (Somme) ; in the Etage Senonien, where it is very rare. It belongs to M. Tombeck's 

 collection. 



Cidaris perornata, Forbes, 1850. PI. VII a, fig. 2. 



Cidaris perornata, Forbes, in Dixon's Geol. of Sussex, p. 339, pi. xxv, fig. 8. 



1850. 



— longispinosa, Sorignet. Ours. Foss. de l'Eure, p. 19, 1850. 



— Sarthacensis, oVOrbiyny. Prod, de Pal. Strat, t. ii, p. 2/4, 1850. 



— perornata, Forbes, in Morris's Catal. of Brit. Fossils, 2nd edit., p. "4, 



1854. 



— — Cotteau. Paleontologie Franchise, t. vii, p. 274, pi. 1065, 



figs. 3—14, 1862. 



Test elevated, melon-shaped. Ambulacra nearly straight, narrow, depressed. Six 

 rows of small granules, the marginal the largest and most regular, the inner small, with 

 intermediate smaller ones. Inter-ambulacra wide, seven or eight large plates in each 

 column ; areolae wide, circular, with a marginal circle of very small granules ; boss smooth 

 or slightly crenulated ; tubercles small and perforate; sutures well marked, depressed. 

 Spines long, cylindrical, several-ridged ; ridges irregular towards the base, and serrated, 

 the interstices granulated. 



Dimensions. — Height, one inch and eight tenths ; transverse diameter, two inches. 



Description. — The test of this fine urchin is high and melon-shaped, and reminds me 

 of C. mcrnmus, from the Coral-rag of Germany. The ambulacral areas are narrow, 



