54 



compressed, translucent, subovate; epidermis green olive, paler 

 on the disk and greener before ; anterior margin fuscous ; beaks 

 nearer the posterior end ; within bluish-white, edged with whitish. 

 Length, one inch and a half; breadth two inches. Plate 3, fig. 3. 



Resembles the preceding, but is more ovate, and the beaks are 

 placed much further back ; it is very common in our rivers. 



Anodonta undulata. — Shell thin, fragile, convex, olivaceous, 

 obscurely radiate and obtusely wrinkled ; umbo prominent, decor- 

 ticated, with four or five obtuse undulations divsappearing on the 

 disk. In the right valve, immediately under the beak, the margin 

 is curved inwards for the reception of a coiTesponding marginal 

 projection of the opposite valve. Length, nearly half an inch j 

 breadth, nearly seven-tenths of an inch. Plate 3, fig. 6. 



This species is perhaps rare ; it does not exactly agree in all its 

 characters with the genus, but approaches nearer it than to any 

 other ; it resembles Alasviodonta tmdulata, for the young of which 

 it might readily be mistaken. 



Genus Cyclas. — Shell almost orbicular, or a little transverse, 

 without fold on the anterior margin ; two or three primary teeth, 

 and lateral, remote, lamelliform ones on each side. 



Obs. The shells of which this genus is composed were formerly 

 placed with the Cardia and TelUnse ; to the former they are more 

 closely allied ; it was originally established by Seopoli under the 

 name of Sphserhmi, this was changed by Lamarck to Cyclas, which 

 is now adopted by Latreille and other wi'iters, notwithstanding the 

 previous application of the term to a genus of plants. 



Cyclas similis. — Shell suborbicular convex, base a little flat- 

 tened, with nearly equidistant, raised, concentric lines, giving a 

 slightly sulcated appearance to the surface, and generally a more 

 conspicuous elevated darker wave, marking the former year's growth 

 of the shell. Epidermis brown or ferruginous ; beak nearer cen- 

 tral and obtuse ; hinge with minute very oblique teeth, lateral ones 

 very distinct, elongated, and considerably resembling those of the 

 next species. Length, seven-twentieths of an inch ; breadth, two- 

 fifths : a specimen measured in length nearly three-fifths of an inch. 

 Plate 1, fig. 9. 



A'ery much resembles Tellina cornea of authors; is found in 

 plenty in the river Delaware ; animal viviparous ; from one speci- 



