90 THE NAUTILUS. 



Endodontida. 

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



Sucdnidee. 



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

 Succinea grosvenor Lea. 



Lymncea cubensis Pfr. Alt. 11.8 mm., diam 6.6 mm. 

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

 diam. 9.9 mm. 



Planorbis parvits Say. Alt. 1.0mm., diam. 4.0mm. 

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



Physidce. 

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



AmnicolidiE. 

 Amnicola 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 from pfige 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 Mull. Deuel Co. 



Vallonia pidchella Mu'll. Deuel Co. 



