90 HEMICIDARIS. 



spherical miliary granules ; the areas, however, are more prominent and convex, and want 

 the defined rows of marginal granules which characterise the Swiss specimen. It very 

 much resembles Hemicidaris Luciensis, d'Orbigny ; but the four rows of nearly equal- 

 sized granules filling the ambulacral areas serve to distinguish it from that species. 



Locality and Stratigraphical position. — This species was collected from the Bradford 

 Clay of Pickwick, Wilts. A valve of Terehratula digona was attached to the test, and 

 the specimen is firmly adherent to the surface of Rhynclionella concinna. In Mr. Lowe's 

 cabinet there is a fine specimen of this urchin, which was collected at Pickwick ; and in 

 the British Museum there is another good specimen, likewise from Wiltshire. Separate 

 plates of this Hemicidaris have been found in the Bradford Clay at the Tetbury-road Station 

 of the Great Western Railway. It is, however, a rare species. 



History. — First figured and described in my ' Memoir on the Cidaridae of the Oolites,' 

 afterwards included in Professor Porbes's descriptions of Jurassic Hemicidaris, in the 

 ' Memoirs of the Geological Survey of Great Britain,' Decade III ; entered in the second 

 edition of Professor Morris's ' Catalogue ;' lastly, separated from Hemicidaris alyina by 

 M. Desor in his ' Synopsis des Echinides Possiles.' 



Hemicidaris icaunensis, Cotteau. PI. HI, fig. 4 a, b. 



Hemicidaris icaunensis. Cotteau, Etudes sur les Echinides Fossiles, p. ,56, pi. 3, figs. 1 — 3. 



— — Forbes, Memoirs of the Geological Survey, Decade III. Notes 



on Hemicidaris. 

 — Wright, on the Cidaridse of the Oolites, Annals and Blagazine of 



Natural History, 2d series, vol. viii, p. 256, pi. 11, fig. 3 a, b. 



— — Morris, Catalogue of British Fossils, p. 82, 2d edit. 



— — Desor, Synopsis des Echinides Fossiles, p. 53. 



Test hemisperical, inflated, and slightly depressed ; ambulacral areas with two rows of 

 small marginal tubercles, and with three or four pairs of semi-tubercles at the base ; 

 inter-ambulacral areas with two ranges of primary tubercles ; mouth large and decagonal ; 

 margin deeply notched. 



Dimensions. — Height, four fifths of an inch ; transverse diameter, one inch and one 

 fifth. 



Description. — This species is hemispherical and inflated at the sides, and its transverse 

 diameter is one half more than its height. The inter-ambulacral areas are furnished with 

 two rows of large primary tubercles ; in each range there are from six to seven tubercles, 



