PLATE CI. 



doubted whether they are not In general indebted to age, accident, rtr 

 the peculiar qualities of the waters they inhabit, for those variation* 

 |n general appearance that have been too frequently mistaken for cha- 

 racteristic differences of species. 



As the Myas will fall under consideration more fully hereafter, we 

 shall for the present confine our remarks to the shell before us, and 

 its very analogous kind, the Mya ovata of Dr. Solander. 



This has been considered by some as a mere variety of ovata, and 

 we confess our opinion is still wavering in assigning it a name and 

 character as a hew species. The Mya ovata has been lately found 

 in the river Froome in Somersetshire, and likewise in the New River 

 near London. What are usually deemed its varieties are numerous, 

 but none of them can, we believe, be considered as distinct species, 

 except the present, which is certainly the most remote of any, if it is 

 really a variety of that species. The Mya ovata, in all its gradations, 

 seems somewhat more ventricose and ovate in its contour, than this 

 Shell ; and though the variations of the latter are considerable, we 

 have generally observed a slight depression, across the middle, 

 which causes the narrowest end to be rather flattened throughout, 

 and it is also rather more cuneiform or wedge-shaped at this end 

 than Mya ovata : to this we might perhaps add, with some propriety, 

 that the gaping beyond the binge at the broadest end, is wider than 

 in Mya ovata. 



Whether this difference is actually sufficient to form a distinct specific 

 character, and whether it is constant in other shells of this kind, still 

 remains in some degree of uncertainty. Both this and the Mya ovata 

 inhabit the same waters, for we have seen several specimens from the 



