Occasional Papers of the Mnscuui of Zoology 15 



Biological Station. It is interesting to note that in 1920 no 

 live snails were found in the ditch where they were so numer- 

 ous in 1919. 



Perrisskb parallcla (Hald.). Cottrt Lake, Carpenter Lake. 

 A few dead specimens only. One from Court Lake is a curi- 

 ous "double-decked'' shell. 



Fcrrissia tarda (Say). Sheyenne River. This seems to in- 

 tergrade wuth the following Ferrissia sp. 



Fcrrissia riinilaris (Say). Sheyenne River. 



Ferrissia sp. Sheyenne River. "]\Iay be a depressed form 

 of tarda." (Walker.) 



Valvata tricarinata Say. Wood Lake, Upsilon Lake. Found 

 in quantity in debris of Upsilon Lake. No live ones taken. 



Amnicola cincinnaticusis (Anth.). Sheyenne River. 



Auinicola cuiarginata Kiister. Sheyenne River. 



Amnicola liniosa porata (Say). Wood Lake. 



Anodonta grandis Say. Some :are of a curious truncated 

 form, rather heavy, and in outward appearance not unlike 

 StropJiitus cdcntulus. 



Anodonia pcpiniana Lea. Gravel Lake. Dead shells only.' 



? Anodonta keiniicotti Lea. Gravel Lake. W^alker sug- 

 gests that this may be a large form of pcpiniana and that the 

 two intergrade. 



Laiiipsilis hit cola Lam. Sheyenne River. 



Lasmigona coinprcssa (Lea). Sheyenne River. 



SpJiccriuin (aurcnin) dcclive Sterki. Sheyenne River. 

 "Same, apparently, as 'aurciiin dcclire of the Preliminary Cat- 

 alog, from Illinois and westward. They were referred to 

 ourciini with doubts, and to judge from the good Sheyenne 



