10 



the mutability of colour, and presents every shade 

 of salmon colour and purple, whilst other specimens 

 are pure white; others again bluish and highly irri- 

 descent. Amongst those hitherto found only white 

 in the nacre, I can show examples of Unio rejiexus, 

 Raf. ( U. cornutus, Barnes,) and U. verrucosus, Raf. 

 ( U. tuberculatus, Barnes,) which are purple. I found 

 five specimens of the former in the Black Warrior 

 river, near Erie, and three in the Alabama river, all 

 purple; four of them a deep shade of that colour. 

 They accompanied others of the same species, per- 

 fectly white. I found at Erie only one specimen of 

 U. verrucosus, which is purple, and the tint is pale. 

 The colour of most species is apt to vary in the dif- 

 ferent rivers. Thus most of the Unios of Bayol" 

 Teche are distinguished by a pearly lustre, approach- 

 ing more than is usual in the American Naiades to 

 the peculiar brilliancy of the pearl oyster. 



Some of the small streams in Alabama contain 

 shells that I have not found in the rivers to which 

 they are tributary. Thus Unio declivis, Say, U. 

 flavus, Raf. {U.ruhiginosus, Lea,) U. stratnineu^, 

 nob. U. perovatits, nob. appear to inhabit only the 



years since, found it in the Schuylkill of a purple colour, 

 but the finest specimens of this variety were found in 

 Chester riverj Md. by Mr. Thomas Fisher. 



