107 



OBSERVATIONS. 



This shell may readily be distinguished from U. 

 cariosus by its darker, less polished, more wrinkled 

 epidermis, more regular convexity of the disks, and 

 by the rays extending over the whole surface, which 

 is very rarely the case with the former; the plicated 

 beaks constitute another point of difference. Two 

 specimens were sent me from Illinois by Dr. Fussel, 

 who found them in the upper part of White river. 



UNIO HEROS. 



Plate LIX. 

 DESCRIPTION. 



Shell oval, somewhat oblong, with large distinct 

 undulations, three or four in number, directed to- 

 wards the posterior margin, and not proceeding di- 

 rectly from the umbo; surface with a few abbreviated 

 transverse lines, placed without any regularity; umbo 

 placed far forward, not prominent, hardly elevated 

 above the general curvature, more or less literate 

 with short irregular lines or slight elevations; hinge 

 margin compressed, nearly rectilinear, prominently 

 angulated or subalated at tip; in the more perfect 

 specimens with numerous connected regular lines, 

 curved to the edge and undulating it; posterior mar- 

 gin rectilinear from the extremity of the hinge margin 

 to the rounded inferior half, and undulated by the tip 

 of the grooves of the disk; anterior margin very 

 short, regularly rounded; base very obtusely rounded, 



