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 disappearing on the 
disk. In the right valve, immediately under the beak, the margin 
is curved inwards for the reception of a corresponding marginal 
projection of the opposite valve. Length, nearly half an inch; 
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 Alasmodonta undulata, for the young of which 
it might readily be mistaken. 
Grenus 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. 
Ohs. The shells of which this genus is composed were formerly 
placed with the Gardia and Tellinm ; to the former they are more 
closely allied ; it was originally established by Scopoli under the 
name of Spliseriiim, this was changed by Lamarck to Gyclas, which 
is now adopted by Latreille and other writers, 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. 
Yery much resembles Tellina cornea of authors; is found in 
plenty in the river Delaware ; animal viviparous ; from one speci- 
