53 
From tlie collection of the late Professor Barton ; it is said to be 
found in the river Wabash. 
XJnio 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 Dipas of Leach, will complete 
the chain of connection between the two genera JJnio and Ano- 
donta. It corresponds with these genera, in the number of its 
cicatrices, but is separable from Anodonta^ by its primary tooth • 
from TJnio by being destitute of the lamelliform teeth ) and from 
Dvpsas, 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. 
Grenus Anodonta. — Shell transverse, with three obsolete mus- 
cular impressions ; hinge simple, destitute of teeth. 
Ohs. 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 
