78 Natural History Bulletin. 



Unio, Margaritana^ and Anodonta. We have specimens with 

 both cardinal and lateral teeth, others with only the cardinal 

 teeth, and still others with no teeth at all! Individual speci- 

 mens of this species then possess characters \vhich would 

 make it possible for us to divide the species among three 

 genera. This is a much clearer case than that of some 

 Margaritanas and Anodontas which it is difficult to separate. 

 U. triangularis. — Barnes. 



Rare. Found in the Mississippi and Cedar rivers. 



U. trigonus. — Lea. 



Very common. Nacre sometimes salmon-colored. 



U. TUBERCULATUs. — Bames. 



Very common in the rivers of the Mississippi drainage, 

 especially on muddy bottoms. 

 U. undulatus. — Barnes. 



We believe this to be distinct from U. -plicatus. It is found 

 more commonly in smaller streams. We have specimens 

 from Benton, Cerro Gordo, Johnson, Linn and Cedar 

 Counties. 

 U. VENTRicosus. — Bumes. 



Very common and very variable. Often without rays. 

 Sometimes pink-nacred. We believe that U. occidens is 

 synonymous with this. 

 U. VERRUCOSUS. — Barnes. 



Common in the Mississippi at Davenport. Rare at Iowa 

 City. Nacre deep purple. 



Gemis Margaritana. — Schuvi. 

 M. CALCEOLA. — Lea. 



Not common. Reported from Delaware County. The 

 same as M. detoidea. 

 M. coMPLANATA. — Bames. 



Very common and somewhat variable. Young specimens 

 are extremely compressed. Found principally on muddy 

 bottoms. 



