46 Greenes new species of TJnio. 
mud or clay along the shores of the Monongahela and Ohio : 
few of them occur in the gravelly banks of the Alleghany, 
The Jilatus and Ovatus, owing to their large and muscular 
foot, adhere so firmly to the bottom that it is quite difficult 
to remove them — so far from withdrawing the foot into the 
shell, as most other Unios, on being grasped by the hand, 
they seem to exert all their power to adhere more firmly 
to the bottom. When captured after such an effort, the foot 
always projects an inch or two beyond the shell, and often 
remains exposed till the death of the animal. 
Notwithstanding the difficulties and discouragements ia 
settling what ought to be considered true specific charac- 
ters in the genus Unio, I shall now describe a supposed 
new species, found in some abundance during my late ex- 
amination of this rich locality. 
UNIO ^sopus. 
Testa ovafa, antice undato angulafa, compressa, postice 
orbiculata, transversem suliata et rugosa; rugis prope 
margines obsoletis, serie nodulorum a natibus versus 
margines, inferiorem decurrenie, instructis; natibus 
decorticalis et leviter erosis; periostracha nitida, luteo 
fusca; intus alba indescente; dentibus, crassis, striatis. 
Plate 3. 
Hunched Unio — Shell oval — compressed, thin and slight- 
ly angular at the anterior end or margin — regularly round- 
ed — convex and thick at the posterior margin — beaks near 
the posterior margin slightly incurved and but a little ero- 
ded — from the beaks over the disk and near the middle of 
the shell there is a remarkable gibbosity or nodulous ridge, 
produced by the striae becoming in this place remarkably 
thick and tuberculated. There appears also in some speci- 
