BIVALVIA. 97 



Shell ovately oblong, compressed ; umbones small, mesial, compressed, rather pointed ; 

 shell with the sides anteriorly rounded, posteriorly compressed, truncated, and forming an 

 obtuse angle, which slopes obliquely downwards to the infero-posterior extremity ; the 

 posterior side has some irregular longitudinal plications, which disappear towards the 

 middle of the shell. 



The Great Oolite variety of this species is many times smaller than that of the Inferior 

 Oolite, and it is rather more elongated, but it presents no real specific difference. The 

 test is delicate. 



This shell was referred to Pullastra, by Professor Phillips, from its external form only, 

 and we believe that only one or two specimens were at his disposal. The figure in the 

 ' Geology of Yorkshire,' unaccompanied by any description, appears to have misled 

 Professor Quenstedt, who has figured the hinge of Tancredia donaciformis, Lye., for his 

 exemplification of Q. oblita. The Panopcea Lebruncsa, Buvig. ' Paleont. de la Meuse,' 

 Atlas, pi. 7, fig. 6, 7, is nearly allied to our species, but is more elongated and less trun- 

 cated posteriorly. The arrangement of the longitudinal ridges is very similar. 



Localities and position. Quenstedtia oblita has occurred in the Inferior Oolite of Blue 

 Wick, Yorkshire, and in the upper portion of the same formation at Rodborough Hill, 

 Cotteswolds. The shelly Great Oolite of Minchinhampton Common has afforded our 

 smaller variety ; but the species appears to be rare at each locality. 



Dimensions. Our largest Inferior Oolite specimen has a length of 2i inches, and is 

 12 inch in height, the greater number of specimens being about 2 inches in length; but 

 the Great Oolite variety is only 6 lines in length, and 3 in height. 



CORBULA, Bruff. 1791. 



Shell ovately trigonal, convex, inequivalve, the left valve being the smaller ; a single 

 cardinal tooth in each valve projecting, that of the left valve being compressed ; there is 

 likewise a pit in each valve contiguous to the tooth, which is destined to receive the 

 ligament ; the ligament is internal, inserted in the pit of the right valve, and in the cavity 

 of the tooth of the left valve ; depression of the mantle posteriorly angulated. 



CORBULA INVOLUTA, Goldf. Tab. IX, fig. 6. 



CORBULA INVOLCTA, Goldfuss. Petref., t. 151, f. 14. 



STRIATA, Buckman. Geol. of Cheltenham, 2d edit. p. 97, pi. 3, f. 4. 



Testa parvd convexd, conccntrice striatd; umbonibus submedianis ; latere postico rostrato, 

 carinato, excavato ; latere antico rotundato. 



Shell small, convex, concentrically striated ; umbones nearly mesial ; posterior side 

 rostrated and slightly excavated ; anterior side rounded. 



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