52 



it is found, but is not so obtuse in front, and is much less rounded 

 at the hinge margin it is also much thinner, and the beaks ap- 

 proach each other more closely. 



Unio nasutus. — Shell thin, oblong, compressed, rostrated, horn 

 color or fuscous, with fine crowded wrinkles obscurely radiate with 

 green ; within bluish-white ; beak cavity hardly any ; teeth crenate. 

 Length, one inch and one-eighth : breadth, two and three-fifths. 



Very common in the Delaware and Schuylkill. Plate 4, fig. 1. 



Musculus fusctcs, augustior, exaltera parte Cuneatim protensiis. 

 Lister, Conch, tab. 151, Jig. 6. 



Unio alatus. — Shell moderately thick, sub-triangular, gener- 

 ally gaping at the posterior part of the base, fuscous, wrinkled ; 

 beaks not prominent, placed very far back and decorticated ; base 

 almost rectilinear ; hinge margin remarkably oblique, rising near 

 the termination of the cartilage into an alated projection, and form- 

 ing almost a right angle with the inferior slope, which is nearly 

 equal in length ; within red-purple, often with numerous tubercles, 

 which, upon the gaping limb, are confluent ; cicatri(?es very rough ; 

 teeth crenate, the external laminated one obsolete, only one in each 

 valve being very perceptible. Length, including the projection, 

 three inches and four-fifths ; breadth, five inches and a half. Plate 

 4, fig. 2. 



Bnc9/c. Meth. vol. 63, tab. 248, /f/. 1, a, b? 



Mr. Lesueur found this species in Lake Erie, very thin and 

 fragile. 



The specimen from which this description is taken, and also the 

 next species, were purchased by Mr. Joseph Watson, at the sale of 

 the late Professor Barton's collection, and by him presented to the 

 Academy of Natural Sciences of Philadelphia. There is also a 

 specimen in the Museum of Mr. Peale. 



Unio cylindrtcus. — Shell very thick, sub-cylindrical, emargin- 

 ate before, pale horn-color varied with greenish ; hinge margin 

 undulated obliquely across the wrinkles, rough on each side, rec- 

 tilinear and parallel to the base ; beaks broad and prominent, with 

 a deeply impressed posterior lunule ; within porlaceous, teeth thick 

 and crenate ; cavity of the beaks very deep. Length, one inch 

 and three-tenths ; breadth, three inches and one-fifth. Plate 4, 

 fiff. 3. 



