212 ON THE NAIADES, 



dorsal cicatrices in the centre of the cavity of the beaks ; palleal im- 

 pression small and distant from the margin ; cavity of the shell very 

 shallow ; cavity of the beaks small, subangular ; nacre pearly white and 

 iridescent. 



Remarks. — I am indebted to the kindness of Dr Burrough for the 

 advantage of examining and describing this interesting species. It was 

 procured by him, during his late voyage round the world, at Buenos 

 Ayres, having been brought from the river Parana. It is remarkable 

 for its outline, its expanded basal margin and folded beaks. 



Unio Nashvillianus. Plate XIV. fig. 43. 



Tesld ellipticd, transversd, msequilaterali ; valvuUs subcrassis ; natibus promi- 

 nulis et minute undulatis ; dentibiis cardinalibus laminatis et in valvuld utraque 

 duplicibus, lateralibiis subrectis ; margaritd alba. 



Shell elliptical, transverse, inequilateral ; valves somewhat thick ; beaks slightly ele- 

 vated and minutely undulated ; cardinal teeth lamelliform and double in both valves ; 



lateral teeth nearly straight ; nacre pearly white. 



« 



Hab. Cumberland River. Professor Troost. 

 Ohio, at Louisville. Dr Fitch. 

 My Cabinet. 

 Cabinet of Professor Troost. 

 Diam. -9, Length 1-4, Breadth 2-5 inches. 



Shell elliptical, sometimes truncate behind, transverse, inequilateral; 

 substance of the shell somewhat thick; beaks slightly elevated and 

 minutely imdulated at the tip ; ligament rather short and straight ; 

 epidermis dark brown, obscurely rayed; cardinal teeth lamelliform, 

 disposed to be crenulate, double in both valves ; lateral teeth nearly 

 straight, the inferior section in the left valve being enlarged towards the 

 posterior end ; anterior cicatrices distinct ; posterior cicatrices confluent ; 

 dorsal cicatrices in the centre of the cavity of the beaks ; cavity of the 

 beaks angular, rather shallow ; nacre beautifully pearly white, disposed 

 in many individuals to be pinkish on the posterior part of the shell. 



