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Fig. 3, seems to agree with O. deformis, of Lamarck. Its irregular and 

 deformed figure is not capable of being described. It is from one to two 

 inches in length, and half as broad. The under valve is much more 

 ventricose than the upper. 



The oyster, the lower valve of which is represented Plate XIV. Fig. 5, 

 is very remarkable. It is rather more than an inch and a quarter in 

 length, and nearly an inch in breadth. Its base is transversely extended 

 and truncated, so as to form a straight line: the cartilaginal pit, which is 

 trigonal and very obliquely disposed, somewhat resembles that of a Pec- 

 ten : at the same time, that an obtuse, tooth-like ridge, lying obliquely 

 across the hinge-pit, gives it much of the appearance of a Chama. This 

 shell very much accords with O. biauriculata, Lam. 



The fossil oyster represented Plate XIV. Fig. 14, is highly interesting. 

 This minute shell, of which I possess two valves, one only of which is 

 perfect at the hinge, is from Verona. It but little exceeds half an inch in 

 length, and three eighths of an inch in width. The cartilaginal pit extends 

 high up into the shell, and is very finely striated. The circumstance which 

 most particularly claims attention, in this curious little fossil, is, that its 

 thickness is nearly a third of its length, and that its substance is composed 

 of a striated spar, the columnar crystals forming which are disposed per- 

 pendicularly to the plane of the shell. Other instances of this striated 

 structure, in fossil shells, have been already shown. 



A fossil oyster before me, from the neighbourhood of Maidstone, in 

 Kent, is remarkable for the great depth of its under valve, which is 

 nearly as deep as the shell is long ; being two inches in depth, and only 

 three in length. 



Having now placed before you such of the fossil oysters, with either 

 a smooth or irregularly rough surface, as appeared to me to be the 

 most interesting, I shall now call your attention to those fossil oysters, 

 the surfaces of which are regularly plicated. These I shall divide into, 

 1st, those which have somewhat of a roundish form, and in which the 

 plicae radiate from the beak to the circumference of the shell ; and, 2dly, 



