The Mollusca of Eastern Iowa. 79 



M. coNFRA(iOSA. — Say. 



Rare. Reported from Muscatine by Prof. Witter. 



M. HILDRETHIANA. Lea. 



Exceedingly abundant in the Iowa river at Iowa City. We 

 do not know of its occurence in other portions of the state 

 excepting in the Cedar river near Cedar Rapids, and in the 

 Des Moines. In 1887 we found it very abundant in mud 

 under large slabs of limestone in the Iowa river. Some con- 

 ception of its abundance may be formed from the fact that we 

 found J2^ specimens under a single slab measuring 16x18 

 inches. We collected several thousand specimens of all sizes. 

 The young are light brown, the adults dark brown. 



M. MARGINATA. Say. 



Not common. We have seen specimens from the Missis- 

 sippi, Des Moines, Skunk, Iowa, Cedar and Shell Rock rivers. 



M. MONODONTA. — Say. 



Rare in the Mississippi river at Davenport, Muscatine, etc. 

 Commonly called a Unio. 

 M. RUGOSA. — Barnes. 



Locally very common in the Cedar and Iowa '•ivers, 

 especially in mud among stones. This in common with 

 several other species of the same habits is often considered 

 rare where it is quite common. Being found among stones 

 neither dredging nor wading will suffice to reveal their 

 abundance. It is often only when the water is unusually low 

 and they are fully exposed that we ascertain their occurrence 

 in great numbers. 



M. UNDULATA. Say. 



Specimens probably of this species were received from 

 Davenport. 



Genus Anodonta. — Cuvier. 



A. CORPULENTA. CoOp. 



Found in the Mississippi. 



