53 



From the collection of the late Professor Barton ; it is said to be 

 found in the river Wabash. 



Unio undulata. — Shell thin, convex, suboval, greenish or 

 olivaceous, with obtuse concentric wrinkles and radiate with green, 

 a little uneven before ; beaks prominent, acute, approximate, decor- 

 ticated, and with four or five large obtuse, distant undulations, dis- 

 appearing towards the basal margin ; within bluish-white, cavity 

 deep ; teeth one in each valve, think and strong ; that of the left 

 valve crenated, of the right valve somewhat bifid, and gradually 

 sloping to the hinge margin. Length, three-fifths of an inch : 

 breadth, nine-tenths of an inch. Plate 3, fig. 3. 



Found in the Delaware and Schuylkill rivers, but is rather rare, 

 and resembles Anodonta undulata. 



This genus, in conjunction with Dlpas of Leach, will complete 

 the chain of connection between the two genera Unio and Ano- 

 donta. It corresponds with these 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 

 Dipsas, also, by the last mentioned character, as well as by the 

 presence of a primary tooth, which is wanting in that genus. 



This new genus we proposed in the former editions of this work, 

 when describing the Undulata, under the name of Monodonta ; 

 but as the same term has been applied to a genus of univalves, I 

 have substituted that of Alasmodonta. 



Genus Anodonta. — Shell transverse, with three obsolete mus- 

 cular impressions ; hinge simple, destitute of teeth. 



Obs. The shells which constitute this genus were arranged by 

 Linnaeus and many other writers, under the genus Mytillus. 



Anodonta cataracta. — Shell thin, fragile, translucent, ob- 

 long-oval, convex, covered with a green olive, radiated, epidermis, 

 within perlaceous; beaks nearer central, frontal margin brown. 

 Length, two inches and two-fifths : breadth, four inches and a half 

 concavity of one valve nearly.seven-eighths of an inch. Plate 3, 

 fig. 4. 



This large muscle occurs in lakes, milldams, &c., and bears some 

 resemblance to the A. anatinus, of Europe. 



Found by Mr. I. Lukens, in the deep part of a mill-dam. 



Anodonta marginata. — Shell very thin, fragile, somewhat 



