216 MYA. 



S&J.U Ji X A 



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, 

 margaritiferci) (false pearl oyster,) shell ovate, a 

 little contracted in the middle of the thinner mar- 

 gin ; primary tooth of the hinge conic ; protu- 

 berant part near the hinge decorticated. 



Sec. B. Shell with three deep cicatrices. Shell 

 transverse ; hinge with a strong irregular tooth 

 and two lateral ones. UNIO of JBruguieres. 



cornutd) (horned muscle,) shell sub-spheroidal, di- 

 vided longitudinally by a regular row of large 

 distant tubercles. Shell thick, rounded behind j 

 cardinal teeth furrowed ; pearly-white and irri- 

 descent within. Dimensions an inch and three- 

 fourths by an inch and a half. 



verrucosd, (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, shell subquadrangular, emarginate before, 

 knotted, ri^gy, corrugated ; lateral tooth ter- 

 minating abruptly ; shell thick and heavy ; 

 beaks distant, eroded ; hinge margin straitish 5 



