THE 



GEOLOGICAL MAGAZINE 



NEW SERIES. DECADE V. VOL. IX. 



No. XII.— DECEMBER, 1912. 



I- — The Species of Cidaris from the Lowek Greensand 

 OF Faringdon. 



By Herbert L. Hawkins, M.Sc, F.G.S., Lecturer in Geology, University 

 College, Beading. 



(PLATES XXV AND XXVI.) 



1. iNTRODUCTIOIir. 



OF the varied Echinoid fauna from the well-known ' Sponge- 

 gravels ' of Faringdon, Berkshire, tliere are no constituent forms 

 of which the remains are more abundant than those of Cidaris. It is 

 no exaggeration to say that every handful of the ' gravel ' will include 

 many fragments of radicles, and some portions of test, which can be 

 ascribed to that comprehensive genus. 



The radioles seem to have been known to Llhwyd, although his 

 mention of a " spine from Faringdon " may possibly refer to Paracidaris 

 jiorigemma from the Corallian of the neighbourhood. It is, however, 

 curious to find that, apart from references in lists of fossils found at 

 the locality, these remains have been systematically discussed only by 

 Wright (1868) in the monograph of British Cretaceous Echinoidea. 

 In that work the species C. faring doiunsis was first described, but the 

 description and figures given were quite inadequate. This paper is 

 an amplification of his description, based on very large quantities of 

 material. 



2. The name C. faringdonebsis. 



Wright spelt the specific name with a double r. It is true that on 

 some old maps of Berkshire the name had this spelling, but long 

 before 1864 it became usual to write it with the single r. I therefore 

 prefer to follow Phillips, who in 1871 first changed the spelling to 

 correspond with that of the name of the town. 



As early as 1854 Sharpe (Q.J.G.S., vol. x, p. 194) remarked on 

 the existence of more than one species of Cidaris in the Faringdon 

 deposits, but until recently C. faring donensis has been the only one 

 recognized by name. In the report of an excursion of the Geologists' 

 Association in 1909, Treacher gives a provisional identification of the 

 radioles of the second type to C. pretiosa, Desor. Radioles of the 

 same type are similarly labelled in the South Kensington Museum, 

 but up to the present time no test fragments have been associated 

 with them. 



decade v. — VOL. IX. — NO. XH. 34 



