Pleistocene Shells from Milwaukee, Wis. 



177 



being somewhat depressed and the whorls swollen. All of 

 the specimens are small, not exceeding four and one half 

 mm. in length. 



13. Valvata sincera Say. Not common. The speci- 

 mens before the writer show some variation, particularly in 

 the height of the spire and the deflection of the aperture. 

 The sutures are all deeply channeled. 



14. Valvata tricarinata Say. Very common and va- 

 riable. The individuals may be ecarinate, bicarinate or tri- 

 carinate. A search for quadri-carinate specimens (as men- 

 tioned by Mr. Bryant Walker*) was not successful. The 

 ratio of ecarinate specimens, about two in five, was greater 

 than among recent tricarinata. Bicarinate forms were about 

 one in five. 



*The Nautilus, Vol. XI, p. 121, 1898. 



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