uc 
* i . : 
LE x. k í se. 
142 Couthouy's Monograph on 
species, neither. is it noticed by Mr. Montagu; and 
Dr. Dillwyn has considered it merely as a convex 
variety of Mr. Pennants Mya declivis. It may be 
reasonably doubted, whether either of these authors 
ever had the true convéxa before them, as they must 
otherwise have perceived it to be very distinct from 
- M. declivis, Pennant, not only in its external charac- 
ters, (being much more convex, shorter in proportion, 
thinner, and in a great measure destitute of the aspe- 
rities so conspicuous in that species), but in the more 
. important character of the form of the ligamentary 
supports, which, instead of being broad and spoon- 
shaped, projecting boldly inward, as in M. declivis, are 
formed rather by an internal thickening of the cardinal 
edge, as in T. corbuloides, and are moreover without 
the dividing ridge, observable in Mr. Pennant's species. 
Dr. Turton, p. 44 of his British Bivalves, expresses a 
belief, that the large and very convex light shell de- 
scribed by Mr. Montagu, p. 166 of his Supplement, as 
Licvra distérta, was this species. This is very pro- 
 bable ; ; indeed, Mr. Montagu himself speaks of his L. 
distórta, as having been usually confounded with M. 
declivis, Penn. It was first described under the name 
of Mya convéra, by Mr. Wood, P 92 of his General 
i Conchology, where he states that it was evidently this 
A species which Donovan figured under the name of Mya 
declivis, from which he: difine Mr. Pennant’s shell of 
the same name to be very distinct. Not having seen 
Donovan’s figure, I cannot determine how far Mr. Wood 
is Correct in regard to that, but think there can be no 
doubt that he is quite so in considering the shell figured — 
by himself to be distinct. There is "but a slight dif 
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