126 MOLLUSC A FROM THE GREAT OOLITE. 



Pholas oolitica. Tab. IX, fig. 21. 



Testa parvd ovatd, antice convexd, postice compressd, dorso in medio sulco pro/undo ; 

 costulis radiantibus acutis, anticis magnis distantibus, posticis crebris ; plicis longitudinalibus 

 regularibus imbricatis. 



Shell small, ovate, anterior side convex, posterior side rather compressed and attenuated ; 

 the dorsal surface with a deep mesial depressed line, which extends from the umbo to the 

 inferior border ; radiating costse acute, elevated, and distant upon the anterior side, less 

 elevated and more numerous posteriorly ; they are indented by longitudinal plications, or 

 lamella?, which are regular and imbricated. 



The test of this small species is very delicate ; in adult specimens the umbones are 

 placed one third from the anterior extremity ; the convexity at that part is equal to the 

 height, or about half of the length ; young examples are shorter in proportion, and the 

 mesial furrow is more strongly marked. The Pholas crassa, of Deslongchamps, ' Mem. 

 Soc. Linn, de Normandie,' 1839, pi. ix, figs. 1, 3, 5, 7, has a similar or perhaps shorter figure ; 

 it has prominent but fewer imbricated folds, and it would appear to be destitute of the 

 radiating costae which ornament our species. 



Length of our largest specimen, 10 lines; height and diameter through both the 

 valves, 5 1 lines. 



Localities. — Minchinhampton and Bisley Commons, Gloucestershire. 



YORKSHIRE SHELLS. 



Ostrea Marshii, Sow. Tab. XIV, fig. 2, 2 a. 



Ostrea diluviana, Park. Org. Rem., 3, t. 15, f. 1. 



— — Zeiten. Petref., t. 46, f. 1. 



— Marshii, Gold/. Petref., t. 73. 



— — Roemer. Verst. Ool., p. 58. 



— sulcifera, Phil. Geol. York., 1, t. 9, f. 35, junior. 



Testa subsolitarid subaquivalvi, ovato-trigond, convexo-pland, crassd, plicis radiantibus, 

 magnis incecpialibus acutis subimbricatis. (Roemer.) 



Shell subequivalve, either ovately oblong or fan-shaped ; umbones small, terminal ; the 

 dorsal surface near to the umbones, has a mesial elevated smooth longitudinal ridge fringed 

 upon each side with acute radiating plications, towards the lower border. 



