Occasional Papers of the Museum of Zoology 1 1 



Morts are large and malleated, those from Fort Totten Lake 

 smaller, very fragile and regularly sculptured. The entire 

 series exhibits a wide range of variation from long spired 

 shells with flaring Up to short stumpy ones with lip regularly 

 curved. 



Lymncca stagnalis appressa Say. Fort Totten Lake, ^lau- 

 vaise Coulee, Lac aux Alorts, Gravel Lake, Lake Metagoshc, 

 Carpenter Lake, Bottineau. \tv\ fragile shells were numer- 

 ous at Fort Totten Lake. One from Gravel Lake may be re- 

 ferred to variety pcrainpla Walker. 



Planorbis altissimns Baker. Devils Lake, Fort Totten Lake, 

 Big ^lission Lake, Wood Lake, Sheyenne River, Upsilon Lake, 

 Gravel Lake. Most of the pan-us-Wko. Planorbes have been 

 referred to this species by Baker. It seems to be the common 

 form found on the shores of lakes now too alkaline for mol- 

 lusks. 



Planorbis antrosns striatus Baker. Gravel Lake, Lake Met- 

 agoshe, Carpenter. Xone were found south of the Turtle 

 Mountains. 



Planorbis circuinstriatus Tryon. Devils Lake. These were 

 named by Walker, "teste Sterki." 



Planorbis dcHectus Say, var. Sweetwater Lake. Walker 

 suggests that they be compared with obliquns De Kay. Xone 

 of the shells taken in 1919 are this species, unless a few im- 

 mature ones may be doubtfully referred to it. 



Planorbis exacuous Say. Fort Totten Lake, ^lauvaise Cou- 

 lee. A\'ood Lake, Lac aux ]\Iorts, Upsilon Lake. These shells, 

 especially the lot from L'psilon Lake, seem to intergrade with 

 the variety niegas Dall. The sculpture of raised revolving 

 lines is particularly conspicuous. 



