216 MYA. 
grounds ; it will then be early enough to adopt 
them. I have retained the original name, and 
made sections of the genera, which appear to be 
unsettled. 
All the species, here described, are found in 
our fresh waters, excepting the first. Taken 
from Say in Nicholson, and Barns in Silliman. 
Sec. A. Shell without cicatrices. 
margaritifera, (false pearl oyster,) shell ovate, a 
little contracted in the middle of the thinner mar- 
*sin 5 primary tooth of the hinge conic 3 protu- 
berant part near the hinge decorticated. 
Sec. B. Shell with three deep cicatrices. Shel 
transverse ; hinge with a strong irregular tooth 
and two lateral ones. Unio of Bruguieres. 
cornuta, (horned muscle,) shell sub-sphercidal, di- 
vided longitudinally by a regular row of large 
distant tubercles. Shell thick, rounded behind ; 
cardinal teeth furrowed ; pearly-white and irri- 
descent within. Dimensions an inch and three- 
fourths by an inch and a half. 
verrucosa, (warted muscle,) shell subtruncate be- 
fore, irregularly tubercled ; the tubercles trans- 
versely compressed ; brownish-red within. Sub- 
quadrangular, thick, rounded behind; beaks 
elevated and recurved ; cardinal teeth crenate 
or furrowed ; cavity of the beaks deep. Di- 
mensions about two inches by one and two 
* thirds, 
nodosa, sheil subquadrangular, emarginate before, 
knotted, ri gy, corrugated ; lateral tooth ter- 
minating abruptly ; shell thick and heavy ; 
beaks distant, eroded ; hinge margin straitish ; 
