10 DESCRIPTION OF FIFTY-TWO SPECIES OF UNIONID^. 



by its being rather more compressed, having higher beaks, a greener looking epi- 

 dermis, and in being more pyramidal. In outline it reminds one of the pyramidal 

 form of the young of pyramidatus (nobis). Neither of the specimens was perfect 

 enough at the beaks to observe the undulations. 



Unio recurvatus. pi. 2, fig. 6. 



Testa Isevi, rotundata, valde inflata, valde insequilaterali, antice rotundata, postice obtuse angulata; 

 valvuliscrassis, antice crassioribus ; natibus valde prominentibus et recurvatis; epidermide fusca, 

 eradiata ; dentibus cardinalibus parvis, crassis sulcatisqne ; lateralibus percrassis, curtis, sub- 

 curvis corrugatisque ; margarita argentea et irideseente. 



Shell smooth, rounded, very much inflated, very inequilateral, rounded before, 



obtusely angular behind; valves thick, thicker before; beaks very prominent and 



recurved ; epidermis brown and rayless ; cardinal teeth small, thick and sulcate ; 



lateral teeth very thick, short, somewhat curved, and roughened; nacre silver white 



and iridescent, 



Proc. Acad. Nat. Sci., 1871, p. 192. 



jlab. — Tennessee Kiver, J. G. Anthony ; Holston River, E. Tenn., Miss Law. 



My cabinet, and cabinets of Mr. Anthony, Mr. Wheatley, and Dr. Lewis. 

 Diam. 1, Length 1-5, Breadth 1-6 inch. 



Shell smooth, rounded, very much inflated, very inequilateral, round before and 

 obtusely angular behind ; substance of the shell thick, thicker before ; beaks very 

 prominent and much recurved ; ligament short, thick and brown; epidermis brown, 

 without rays, and with very close marks of growth ; umbonial slope very much 

 raised and obtusely angular; posterior slope cordate; cardinal teeth small, thick, 

 sulcate, and disposed to be treble in the right valve; lateral teeth very thick, short, 

 somewhat curved and corrugate ; anterior cicatrices distinct, rather small and 

 deeply impressed; posterior cicatrices distinct and well impressed; dorsal cicatrices 

 placed over the centre of the cavity of the beaks ; cavity of the shell deep and 

 rounded ; cavity of the beaks deep and obtusely angular ; nacre silvery white and 

 iridescent. 



Remarks. — There are three specimens before me. One of them, belonging to 

 Mr. Anthony, has been in my possession for many years. I was never satisfied 

 that it was not a variety of ehenus (nobis) until lately, when I received two other 

 specimens, which were sent by Miss Law to Dr. Lewis and Mr. Wheatley. Com- 

 paring the three specimens with the allied species, I became entirely satisfied that 

 the species was distinct. In the above description of the epidermis it is said to 

 be without rays. It is very likely that young and perfect specimens may be found 

 with some rays. Two of these specimens have three or four spots immediately 



