14 University of Michigan 



marsh ditch north of Lac aux ]\Iorts, some of the larger ones 

 resembhng at first glance a small /-*. trvvolvis. Dead shells 

 were abundant in the ^lauvaise Coulee and in the pond two 

 miles west of Garske, but no live ones were taken at either 

 of those places. The largest specimen measures: greater di- 

 ameter. 12.5 mm., lesser diameter, 11 mm., altitude, 3.5 mm. 

 The lamellae were compared with those of Scgmentina ar- 

 rnigera and S. crassilabi is. The teeth of all three are figured, 

 for comparison, drawn from camera lucida outlines. Only 

 the young shells of christyi retain the lamellae, and none of 

 them show an upper (4th) palatal. Even in very young shells 

 it is absent. The lower palatal is bilobed as in crassilabris. 

 The shells may also be distinguished in ever}' case from aniii- 

 gera by the angle of the aperture, for whereas it is deflected 

 downward in arniigcra it continues in the plane of the pre- 

 ceding whorls in christyi. 



Physa auipnllacca Gould. Devils Lake, Court Lake, Big 

 ]\Iission Lake, Wood Lake, Sheyenne River, Upsilon Lake, 

 Gravel Lake, Carpenter Lake, Bottineau. The height of the 

 spire varies somewhat, but most of the shells correspond es- 

 sentially to the species as recently described and figured by 

 Baker.'' 



Physa intcgra Hald. Sheyenne River. A few specimens 

 only. 



Aplcxa hypiiontm tryoni Currier. Mauvaise Coulee, ditch 

 north of Lac aux ]\Iorts. Beautiful specimens were taken in 

 quantity from the ditch. Many are of large size, measuring 

 in altitude 24, 24.5, 25.5 mm. The shells are of a rich brown 

 color, with a decided rose tint on the columella. The smaller 

 form, A. hypnoruni, occurred in the meadows north of the 



" Baker, F. C, Freshwater Mollusca from Colorado and Alberta. 



