12 University of Michigan 



rianorbis parvus Say- Lac aux Morts, pond south of Stump 

 Lake, Williston. Those from Stump Lake pond are small and 

 rather flat. 



Planorbis parvus Say, var. Devils Lake, ^lauvaise Coulee, 

 Wood Lake, Lac aux Morts. Sweetwater Lake, Bottin?au. 

 "\'ery much larger than typical parvus and the aperture is 

 somewhat differently shaped." (Baker.) 



Planorbis pari'us i\.'alkcri A'anatta. Lac aux ]\Iorts. Some 

 of the shells from debris at the edge of the lake have the heavy 

 lip characteristic of the variety, but they occur with the Plan- 

 orbis pari'us var. listed above, and seem in all respects to be 

 only an ecological form due perhaps to an increase in the alka- 

 linity of the water. [Modifications in the shells of P. trivolvis 

 from the same habitat may be due to the same cause. 



Planorbis triz'oli'is Say. Mauvaise Coulee, Wood Lake, 

 vSheyenne River, Upsilon Lake. Gravel Lake. 



Planorbis trirohis Say, var. Fort Totten Lake, Wood 

 Lake, Gravel Lake, Carpenter Lake. Several varieties are 

 included under this head. The shells from Fort Totten Lake 

 have the flaring lip, covered with callus, that is characteristic 

 of the variety juacrostoiuus ^^'hiteaves. Those from Lac aux 

 Morts are small forms, a depauperate, misshapen race, closely 

 coiled. Li Gravel and Carpenter Lakes the upper whorls of 

 the shells are rounded rather than carinated above. 



Planorbis umbilicatcUus Cockerell. Devils Lake, ditch north 

 of Lac aux ]\Iorts. Typical shells were taken from meadows 

 once a part of Devils Lake. The present localities are not far 

 south of the original locality, Brandon, Manitoba." 



Scgmcntiiia cliristyi Dall. T^Iauvaise Coulee, ditch north of 



' See Vanatta, E. G., The Geographic Distribution of Planorbis 

 umbiUcatellus. Nautilus, XXIV, 191 1, pp. 136-138. 



