46 Green's 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 Matus and Ovutus, 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 arr 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 in 

 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 JEsopus. 



Testa ovale/, antice undato angulata, compressa, postice 

 orbiculata, transversem suliata et rugosa; rugis prope 

 margines obsoletis, serie nodulorum a nalibus versus 

 margines, inferiorem decurrenle, instructis; natibus" 

 decorticalis et leviter erosis; periostracha nitida, luteo 

 fiisca; intus alba indescente; dentibus, crassis, slriatis. 

 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- 



