OBSERVATIONS. 



The anterior emarginations, above mentioned, are obvi- 

 ous in many species, but are more particularly remarkable 

 in the present shell ; they mark the situation of the tubes 

 of the animal. 



The form and arrangement of the teeth are very much 

 like those of the monodonfa, Nob. but the outline and 

 other characters of this shell, as expressed in the above 

 description and exhibited in the plate, are w idely different. 



It is certainly an inosculating species between Unio 

 and Anodonta, but traces of the primary and lamelliform 

 teeth are, I believe always discoverable. It is an inhabit- 

 ant of the Wabash river, and is not uncommon. 



The largest individual that has occurred, is in length one 

 inch and three tenths, and in breadth three inches and two 

 fifths ; but the plate exhibits the usual magnitude. The 

 cavity of the beaks is often more or less tinted with purple. 



REFERENCE TO THE PLATE. 



The ;;'late represents tho exterior, dorsal, and inner views of the shell. 

 PLATE XXIV. 



