ECHINODERMATA. 39 



all species belonging to that zone of the Inferior Oolite which contains Ammonites 

 Parkinsoni, Sow., and Ammonites subradiatus, Sow. Some separate plates of an urchin 

 collected with spines from the Bradford Clay, near Tetbury-road Station, Great Western 

 Railway (PI. V, fig. 7 a, b), closely resemble this form ; but no entire test of this Cidaris 

 has been found, and it is doubtful whether or not it is distinct from Cidaris Bouchardii. 



We dedicate this urchin to our friend M. Bouchard Chantereaux, of Boulogne-sur-Mer, 

 to whom we are indebted for some beautiful and rare Jurassic Echinoderms and other 

 fossils, sent by him in the kindest manner to aid us in the production of this Monograph. 



Cidaris Wrightii, Besor. PL I, fig. 3 a, b, c, d, <?,/. 



Cidaris propinqua. Wright, Annals and Magazine of Natural History, 2d series, vol. viii, 

 p. 250, pi. 11, fig. 6. 

 — Wrightii. Desor's Synopsis des Echinides Fossiles, p. 7. 



Test thick, circular, inflated, not much depressed at the poles ; ambulacral areas very 

 narrow, sinuous, and furnished with two rows of close-set marginal granules through- 

 out ; the inter-ambulacral areas have six tubercles in each column of plates ; the tubercles 

 are large, and slightly perforated ; the upper mammillary bosses only are crenulated j 

 the areolas are surrounded by complete scrobicular circles of small, prominent, well- 

 spaced-out granules ; apical disc unknown ; spines never found attached to the test. 



Dimensions. — Height, six tenths of an inch ; transverse diameter, 1 inch. 



Description. — When this urchin was found, five years ago, we were then unable to 

 compare it with a type specimen of Cidaris prqpinqua, Minister. A subsequent com- 

 parison with the German species has convinced us that we were mistaken in our deter- 

 mination, and it has long lain marked as a new species in the trays of our cabinet. M. 

 Desor, in his ' Synopsis des Echinides Fossiles,' has likewise detected the difference 

 between this species and Cidaris propingua, and justly observes — " Petite espece voisine 

 du Cid. propinqua, mais plus renflee ; les tubercules paraissent aussi etre moins gros. 

 Ambulacres tres etroits, composes de deux rangees seulement de granules."* This 

 rectification removes another of those apparent exceptions to the law which regulates 

 the distribution of species in time and space, for it is now evident that no species of 

 Echinoderm is common to the Inferior Oolite and Coral Rag of England ; but, on the 

 contrary, that both these formations are characterised by distinct and well-defined species 

 of this class. 



The test of Cidaris Wrightii is very thick for so small a species. It is inflated at the 



* ' Synopsis des Echinides Fossiles,' p. 7. 



