62 
Presented to the Academy by Mr. L’Hermeriier of Charleston^ 
an intelligent and zealous naturalist ; he assured me that this species 
inhabits near Charleston. It somewhat resembles large specimens 
of the P. trivolvis of the American edition of Nicholson’s Encyc.^ 
but differs in the total absence of carina^ and in '-having a more 
smooth and polished surface^ as well as a declining and more 
oblique aperture^ and a more profound and much more regularly 
concave umbilicus. 
[J. A. N. S. vol. i. p. 459, 460, Dec., 1818.] 
Genus Alasmidonta. — ^Shell transverse, equivalve ; inequila- 
teral, hinge with a primary tooth in each valve ; cicatrices three. 
Animal resembling that of Unio ? 
Alasmidonta marginata. — Shell transversely oblong-suboval, 
Y/hite, covered with an olive brown epidermis, obsoletely radiate 
with green numerous concentric wrinkles ; umbo, with about three 
concentric undulations ; ligament slope abruptly depressed, with 
numerous, obtuse, oblique rugae, decussating the concentric ones, 
which are obsolete in that part ; within bluish-white, margin white ; 
cavity of the umbo not distinctly impressed by the external undu- 
lations ; tooth compressed, oblique, nearly parallel with the poste- 
rior slope, and terminating abruptly behind. 
Length, exclusive of the umbo, one inch and a quarter, breadth 
two inches and a half. Cabinet of the Academy. 
The inner margin is of a chalky whiteness, in this respect re- 
sembling Anadonta marginata. It was communicated to me by 
Mr. Isaac Lea, who found it in the Scioto river. 
Unio undidata of the first and second American editions of 
Nicholson’s Encyclopaedia, is a species of this genus, but it is very 
distinct from the marginata. 
This genus will be properly placed between Unio and Anodonta^ 
and in conjunction with Pispas of Leach, it will complete the 
chain of connection between those two genera. Alasmidonta 
corresponds with those genera in the number of its cicatrices, but 
is separable from Anodonta by its primary tooth ; from Unio by 
being destitute of the lamelliform teeth : and from Dispas also by 
the last mentioned character, as well as by the presence of a pri- 
mary tooth, which is wanting in that genus. 
