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thickness ; and, of necessity, of a considerable weight : the cavity 
which had been left for the dwelling of the animal being, in propor- 
tion, but small. The shells appear evidently to be formed of laminae, 
so placed on each other, that their several projecting edges terminate 
with much irregularity, 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 re- 
moved. 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. ccinalis 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 
fossil, 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 theterminations 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. 
I am happy in being able to place before you an account of the 
situation 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. 
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