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ness ; and, of necessity, of a considerable weight : the cavity which had 

 been left for the dwelling of the animal being, in proportion, but small. 

 The shells appear evidently to be formed of laminae, so placed on each 

 other, that their several projecting edges terminate with much irregula- 

 rity, and give a considerable degree of asperity to their external surfaces. 

 Their size varies considerably ; some being hardly five inches in length, 

 and about an inch and a half in width ; whilst others attain to the length 

 of twenty inches. 



In the mountain of Heutlingen there existed a considerable stratum of 

 these fossils, the uppermost of which had both their valves united; but 

 these were in so fragile a state, that very few indeed could be removed. 

 An under valve which I possess, which is more than thirteen inches in 

 length, and three in thickness, weighs four pounds. To this species may 

 be perhaps referred, O. canalis of Lamarck. 



The broad flat oyster, from Shotover Hill, Oxfordshire, is a very 

 remarkable fossil. It differs in its form, even admitting that it may 

 have suffered some degree of compression, from any oyster, recent or fos- 

 sil, which has been hitherto described. 



Both valves are equally flat ; their form subtrigonal, but very irre- 

 gular. The external surface is smooth, with the exception of the fine 

 transverse striae resulting from the terminations of the different laminae, 

 which do not prevent its resembling a plate of roofing slate. On the 

 internal surface, the very shallow cavity for the oyster, the muscular 

 impression, and the broad pit of the hinge, are very accurately pre- 

 served. They differ considerably in size, having been found from two 

 to more than six inches in diameter. 



1 am happy in being able to place before you an account of the situa- 

 tion in which these fossils were found, about forty years ago, as given in 

 a letter from that assiduous inquirer in this department of natural history. 

 Mr. Joshua Platt, of Oxford, to Mr. Strange. 



The depth of the pit, from the surface to. stone, is about twenty- 

 seven feet. 



