20 

 UNIO PARVUS. 



Plate IX.— Fig. 1. 

 DESCRIPTION. 



Shell oblong or elliptical, with prominent concen- 

 tric lines, and slightly contracted from beak to base; 

 inflated posteriorly and the basal margin dilated and 

 rather abruptly ascending to the extremity, which is 

 narrow, obtuse, and much above the line of the base; 

 umbo when not decorticated, profoundly sulcated; 

 umbonial slope undefined; posterior slope with a sub- 

 marginal, slightly prominent line; ligament margin 

 not oblique; posterior margin obliquely truncated 

 above; within white; cardinal teeth very erect. 



SYNONYMES. 



U. parvus, Barnes. Silliman's Journal, vol. vi. p. 174. 

 Cab. A. N. S. No. 1872. 



OBSERVATIONS. 



A small species, without any prominent character, 

 yet very distinct. It approaches nearest to U. lieno- 

 sus, nob. but that species is always more or less 

 radiated and generally pink or purple in the interior; 

 the parvus is white within and rarely rayed. Inhabits 

 western rivers generally from Bayou Teche in Louisi- 

 ana to Fox river in the North Western Territory. 



An elegant specimen from the Scioto river is dark 

 olive-green and distinctly rayed; and the acutely an- 

 gulated ridges on the beaks are very perfect. 



