OBSERVATIONS. 



This large and handsomely sculptured shell, was found 

 in the Fox river of the Wabash, by Mr. Lesueur and Dr. 

 Troost. 



It resembles U. plicafus, Nob., but on comparison it will 

 be observed to differ very essentially from that common 

 species. The umbo and beaks of the plicatus are very 

 prominent and altogether destitute of any small literations 

 or divaricating lines, having only the origin of one or two 

 of the large undulations grooved upon it. The primary 

 teeth of the plicatus also are much thicker than those of 

 this species. 



I formerly considered this species, with much doubt, as 

 distinct from the undulatus of Barnes, and gave to it the 

 name of heros^ but notwithstanding some differences, I 

 have concluded, after a more mature examination and 

 comparison, that it may be with propriety referred to that 

 species. Barnes drew his description and figure from a spe- 

 cimen then unique, belonging to the cabinet of Mr. S. B. 

 Collins, which was so eroded as not to exhibit the orna- 

 mental tubercles of the umbo and beak. 



The dimensions of a fine specimen found by Mr. O. 

 Evans are, length five inches, breadth over seven, and con- 

 vexity two inches and seven-tenths. 



It is not uncommon in Fox river, an arm of the Wa- 

 bash, in muddy and sluggish parts of the stream. 



REFERENCE TO THE PLATE. 



Upper figure, exterior view. 

 Lower figure, inner view. 

 PLATE XVI. 



