103 



very slightly contracted anterior to the middle; car- 

 dinal teeth compressed and oblique; within bluish- 

 white. 



SYNONYMES. 



U. sayi, Ward, Silliman's Journal, vol. xxxv. , pi. 3. fig. 1. 

 U. declivis, nob., p. 45, pi. xxiii. fig. 1 of this work. 



OBSERVATIONS. 



This shell I found several years since in a small 

 stream in Greene county, Alabama, and supposed it 

 to be a perfect specimen of the declivis of Say, but 

 it differs from that species in having a narrower 

 umbo, plicated obliquely on the summit, a lighter 

 coloured and smoother epidermis, and especially in 

 wanting the "rostrum or prominent angle" of Say's 

 description of U^ declivis. It inhabits the canal near 

 Savannah, where it was found by Mrs. Say; also the 

 canal at Louisville, Kentucky. The name was in- 

 advertently given as Sayanus instead of Sayi. 



UNIO PLANILATERIS. 



Plate L VII.— Fig. 1. 



DESCRIPTION. 



Shell oblong-subovate, rather thin; disks flattened, 

 compressed anteriorly; ligament margin elevated, 

 parallel with the base, rounded at tip; umbonial slope 

 inflated and angulated; posterior slope flattened, and 

 having on its upper part short, slightly prominent 



