206 
angle witli tlie base, obtusely emarginate in tbe middle by tbe 
termination of tbe groove; umbonial slope carinated, in conse- 
quence of tbe depression of tbe anterior side ; lunule very short ; 
posterior margin very short, rounded ; color light brownish, obso- 
letely radiated ; within white ; cardinal teeth direct ; lateral teeth 
rectilinear, short, with but little obliquity ; posterior accessory ci- 
catrix obliquely elongated, slender; anterior accessory cicatrix 
confluent. 
TJnio nexusy noh. Transylvania Journal, vol. 4, 527, 1831. 
Unio arcseformis. Trans. Amer. Philos. Soc., vol. 4,iV". S. 1832. 
The shell which we have designated by the above name is 
closely related to triqueter, Raf, but differs in the greater promi- 
nence of the superior portion of the anterior margin, the shorter 
posterior margin and lunule, the direct cardinal teeth, and the little 
obliquity of the lateral ones. It was sent to me from Nashville 
by Dr. Troost. I may remark that some of the shells of Cumber- 
land river vary much from their corresponding species of other 
streams, if I may judge by several specimens which I have seen 
from that river. 
In stating the generic character, the number of muscular im- 
pressions is said to be two, by which is understood, two principal 
ones, for that there are many smaller ones is familiar to all those 
who have examined these shells. Dr. J. Gf. Klees in his Disser- 
tio Inauguralis,^^ (for which work I am indebted to Dr. L. D. 
Schweinitz,) says, musculis duobus binis majoribus clausoribus 
accessoriis.’^ Ferussac, in his Notice sur les Etheries,^’ says, 
Presque toutes les muUttes et les Anodontes ofirent quartre im- 
pressions separees, et Ion n’a point encore distingue d’une maniere 
comparative celui des muscles d^attache que dans leur position 
varie acquiert une predominance sur les autres, selon la forme 
de Tanimale, la grosseur, ou la figure des valves.^^ The four prin- 
cipal cicatrices of course exist in all the species of this family, but 
the}?’ are sometimes so approximated in pairs as to form but two or 
three separate impressions. The several smaller cicatrices in the 
cavity of the beaks indicate points of the attachment of small dor- 
sal muscles, for the secure support of that part of the animal. The 
palleal impression is also very distinct. These dorsal cicatrices, 
were, no doubt, taken into acccount by Mery, Mem. Acad. Royale 
des Sci. for 1710, p. 409, who says that there are eight muscles 
attached to the inner surface of the shell. PI. 51. 
