PA 
158 Couthouy' s Monograph on 
or ochraceous epidermis, not existing in T. Conrádi, 
and its basal margin, instead of curving outwardly near 
the middle, a constant peculiarity of our shell, has al- 
ways an inward curve at that part. From T. pubéscens, 
ours differs in every essential particular, and could not, 
with any figure of that shell, be mistaken for it. 
From having observed several specimens which yet 
contained the animal, either in a state of partial decom- 
position, or dried in the shell, I am enabled to state with 
certainty, that- the cardinal ossiculum, mentioned by 
Deshayes as found upon some species, has no existence 
in ours, which nevertheless possesses all the other char- 
acters of the genus as expressed by him. 
The size here given is about an average one, though 
specimens have been found measuring a third more. 
Besides the species of "Thracia here described, there 
are several shells classed by Dr. Turton among the 
Anatine, and by Mr. Montagu, included im his genus 
Licura, which may possibly bereafter be found to be- 
long to the Thracia. | ANaTINA declivis, 'Turton, is one 
of these. He states, p. 45, of his Bivalves, that it had 
usually been confounded with the young of Mya declivis, 
Penn., but that he had been enabled, by obtaining the 
intermediate sizes, to clear up all difficulties relative to 
the young of that shell and M. declivis, Montagu. 
Now, as Mr. Montagu has no species of that name, the 
difficulties arè increased instead of cleared up, by Dr. 
Turton, wlio has added still more to the confusion, by 
giving, in his Conchological Dict. p. 98, Mya pretémus, 
Penn., as a synonym of this species, when it is also, p. 
101, given as a synonym of his and Mr. Montagu’s Mya 
