90 THE NAUTILUS. 



Endodontidce. 

 Helicodiscus paraUelus Say. Alt. 1.4 mm., diam. 4.7 mm. 



Succinida. 

 Svccinea avara Say. Alt. 12.1 mm., diam. 6.4 mm. 

 Succinea grosveaor Lea. 



Lm,nceid(B. 

 Lyvincea mbensis Pfr. Alt. 11.8 mm., diam 6.6 mm. 

 Planorbis antrosus Conr. (bicarinatus Say). Alt. 4.9 mm., 

 diam. 9.9 mm. 



Planorbis pan-vs Say. Alt. 1.0 mm., diam. 4.0 mm. 

 Planorbis trivolvis Say. Alt. 7.3 mm., diam. 19.5 mm. 



Physidce. 

 Physa gyrina Say. Alt. 14.7 mm. diam. 7.6 mm. 



Amri'lcolidce. 

 Avmicola cincinnatiensis Anth. Alt. 4.7 mm., diam. 3.2 mm. 

 In this connection it may be mentioned that while gastropods 

 are abundant in the ponds, small creeks and the larger streams 

 tributary to the Cimarron, not a single form of molluscan life 

 was found in the Cimarron River, in Payne county, although 

 the dredge was used at frequent intervals along a stretch of 

 fifteen miles. 



MOLLTJSCA OF SOUTH DAKOTA. 



BY W. H. OVER. 



(Concluded frora page 81). 



All species listed were collected by me and are in my private 

 collection of land and freshwater Mollusca now on exhibition 

 in the Museum of the University of South Dakota. 



For the determination of species I am grateful to Messrs H. 

 A. Pilsbry, jE. G. Vanatta, Bryant Walker, Dr. Sterki, L. S. 

 Frierson, F. C. Baker and A. A. Hinkley. But for the latter 

 I probably never would have become interested in the study 

 and collecting of shells. 



Vallonia costata Miill. Deuel Co. 



Vallonia pulchella Miill. Deuel Co. 



