45 



UNIO DECLIVIS. 



Plate XXIII. Fig. 1. 



DESCRIPTION. 



Shell trapezoidal, moderately thick; anterior mar- 

 gin obtusely rounded; beaks slightly elevated, with 

 oblique undulations; hinge margin rather elevated 

 and compressed, angulated at tip; posterior margin 

 rectilinear, descending obliquely to a prominent ros- 

 trum of the posterior basal margin at the extremity of 

 the umbonial slope; umbonial slope abruptly rounded, 

 and bounded on its posterior side by two slightly im- 

 pressed lines; basal margin arcuate; surface deeply 

 wrinkled; within tinged with purplish; cardinal teeth 

 oblique; lateral teeth distant from the cardinal teeth. 



SYNONYMES. 



U. declivis, Say. Trans. Journ. vol. iv. p. 527, Amer. Conch. 



pi. 35. 

 U. geometricus, Lea. Trans. Amer. Philos. Soc. new series, 



vol. v. p. 38, pi. 4, fig. 10. 

 Cab. A. N. S. No. 1875. 



OBSERVATIONS. 



This species resembles a variety of the complanatus 

 in its general form, and its teeth and posterior angle 

 are somewhat similar to those ofnasutus. It is very 

 distinct from either. The figure is from a fine speci- 

 men which I found in a small creek in Greene county, 

 Alabama, where the species is abundant, but usually 

 more compressed than the one I have selected for 

 representation. I was unable to find a specimen in 



