The Mollusca of Eastern Iowa. 5^ 



common in portions of the Iowa river, especially near Eldora 

 in Ha'-din county. We also have specimens which are said to 

 have come from some of the small lakes in the north-western 

 part of the state. This species is generally called S. defrcs- 

 siis. — Try. 



S UB-FAMIL r—POMA TIOPSIN^^. 



Genus Pomatiopsis. — Try on. 

 P. lapidaria. — Say. 



Common under leaves and logs on low creek and river bot- 

 toms. 



FAMILY— VALV ATI DiE. 

 Genus Valvata. — Muell. 



V. TRIG ARIN ATA. Say. 



Common on muddy bottoms in ponds. 



V. BICARINATA. Lca. 



> 



This is usually regarded as a mere variety of the preceding 

 but we believe it to be distinct. It is much larger than V. 

 tricarinatcB, Say, has a much broader umbilicus, and the apex 

 is fiat, in fact usually concave. In a series of several hundred 

 specimens, these characters were found to be very constant. 

 Both forms occur in the Same ponds near Iowa City. 



FAMILY— VIVIPARIDiE. 



Genus Vivipava. — Montf. 

 V. SUBPURPUREA. — Say. 



Found in ponds in the eastern part of the state. 



V. INTERTEXTA. Say. 



Common in ponds in the eastern part of the state, especially 

 along the Missis-^'opi. 



V. CONTECTOIDES. W. G. B. 



Dead specimens have been found on the Cedar river both 

 by Prof. Witter and by the writer. The species occurs in the 

 Mississippi. Was it introduced? 



