74 Natural History Bulletin. 



sandy bottoms in the Iowa river. It varies in color from ai 

 deep brown to a very light straw color. 

 U. ALATUS. — Say. 



Very common, particularly on muddy bottoms. The young 

 shells are often distinctly rayed. Nacre usually purple, some- 

 times white. 



U. ANODONTOIDES. I^Cd. 



Very common on sandy bottoms. Both the rayed and the 

 uniform light yellow forms occur. The rays become less 

 distinct with age. 

 U. CAPAx. — Green. 



Not common. Found in the larger eastern streams. 

 U. COCCINEUS. — Hild. 



Very common in the Iowa river and occurs in most of the 

 larger eastern streams. Beautifully rayed specimens are 

 common near Iowa City. Sometimes pink-nacred. 

 U. CORNUTUS. — Barnes. 



Not rare, particularly on mud-covered rock bottoms. 

 Specimens are sometimes found which are almost perfectly 

 smooth. Varies in color from a deep greenish-brown to a 

 straw color. 



U. CRAssiDENS. — Lam. 



Found sparingly in the larger eastern streams. 

 U. DOXACiFORMis. — Lea. 



Very common rn the larger streams on both sandy and 

 muddy bottoms. Those which are found on sandy bottoms 

 are usually beautifully marked, sometimes pink-nacred, and 

 occasionally uniform in color. This species is commonly 

 known as U. zigzag. 

 U. DORFEUiLLiANUs. — Lea. 



Specimens referable to this species were received by us 

 from the northwestern part of the state. Reported from the- 

 Cedar river doubtfully by Prof. Witter. 



