6 DESCRIPTION OF FIFTY-TWO SPECIES OF UNIONID^. 



founded with sphcericus (nobis), for that species is nodulous and has higher beaks. 

 The three specimens before me differ very little. In the youngest there are a few 

 indistinct rays near the termination of the beaks : none are exhibited on the others. 

 All these specimens have eroded beaks, and therefore their character as to undula- 

 tion cannot be ascertained. 



Unio validus. pi. 1, fig. 2. 



Testa Igevi, triangulari, inflata, inajquilaterali, antice rotunda, postice obtuse angulata; valvulis crassis, 



antice aliquanto crassioribus ; natibus prominentibus, ad apices undulatis ; epidermide olivacea, 



valde radiata; dentibus cardinalibus crassis, compressis crenulatisque ; lateralibus sublongis, 



crassis subcurvisque ; margarita argentea et iridescente. 



Shell smooth, triangular, inflated, inequilateral, round before, obtusely angular 



behind ; valves thick, somewhat thicker before ; beaks prominent, undulate at the 



tips; epidermis olive color and very radiate; cardinal teeth thick, compressed, 



and crenulate ; lateral teeth rather long, thick and curved ; nacre silver white and 



iridescent. 



Proc. Acad. Nat. Sci., ISU, p. 189. 

 Hab.— Buck River, Tenn., Dr. Powell. 



My cabinet. 

 Diam. 1, Length 1-7, Breadth 2-1 inches. 



Shell smooth, triangular, inflated, inequilateral, round before and obtusely 

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

 prominent and undulate at the tips; ligament rather long and dark brown; epi- 

 dermis olivaceous, with numerous slightly interrupted rays over most of the disks, 

 with distant lines of growth ; umbonial slope obtusely angular ; posterior slope 

 elliptical, very slightly raised, with obscure rays ; cardinal teeth very thick, com- 

 pressed, crenulate, double in the left and disposed to be treble in the right valve ; 

 lateral teeth rather long, thick and disposed to be double in both valves ; anterior 

 cicatrices distinct, rather large and deeply impressed; posterior cicatrices distinct, 

 well impressed; dorsal cicatrices placed above the centre of the cavity of the 

 beaks ; cavity of the shell rather deep and rounded ; cavity of the beaks shallow 

 and obtusely angular ; nacre silver white and iridescent. 



Remarks.— A full grown specimen received from Dr. Powell many years since. 

 It perplexed me as to its specific value, and I was disposed to think it a variety of 

 Bighyensis (nobis), being very nearly of the same outline. It differs in being more 

 inflated and in having an olive epidermis. It is a stouter shell and has thicker 

 teeth. The tips of the beaks of the specimen before me are somewhat eroded, but 

 here remains enough to display several minute subconcentric undulations. 



