146 



THE CHICAGO ACADEMY OF SCIENCES. 



a portion of the Arctic, the Hudsonian, Canadian, Transition and the 

 extreme northern portion of the Upper Austral life zones. 



GEOLOGICAL RANGE (Figure 10) : Pleistocene. The records of 

 fossil stagnalis show that the species extended from eastern Ontario 

 west to Nevada. The records are few in number and, being mostly 

 post-glacial, no generalizations are nossihle. Stagnalis doubtless lived 

 in Pliocene or earlier times, and Lymncea stcarnsi, a Middle Miocene 

 fossil found in the Mascall beds of Grant County, John Day Valley, 

 Oregon, is probably an ancestor of appressa. The specimens thus far 

 obtained, however, are too imperfect to afford a basis for comnarison 

 with the recent species. 



Geological 

 Distribution 

 Loess 



l beds ' 

 f Sand'X 



FIG. 10. 

 RECORDS. 



LOESS. 



ILLINOIS : Base of Loess in bluff of Mill Creek, about five miles north of 

 Milan, Rock Island Co. (Leverett; Shimek; Udden). 

 NEBRASKA: Washington Co. (Aughey). 

 SOUTH DAKOTA: Otis Mill, Union Co. (Darton coll., Smith. Inst.). 



MARL BEDS. 



ILLINOIS: Clay and marl, Cook Co., various localities (Baker); marl 

 beds, Clyde Ave. near Austin Ave., Chicago (Scharf). 



MICHIGAN: Crooked Lake, Oden, Emmet Co. (Slocum). 



UTAH: White njarl, Lake Bonneville (Gilbert). 



ONTARIO, CANADA: Hemlock Lake, near Edinburgh, east of Ottawa, in 

 soft white calcareo-argillaceous matrix (Ami. Ottawa Nat., XI, p. 20, 1897). 



SAND AND GRAVEL PITS, CLAY, ETC. 



ILLINOIS: Bowmanville, Cook Co. (Baker). 



MICHIGAN : Found with mastodon remains in Niles, Berrien Co., from 

 muck beneath the mastodon (Walker, Nautilus, XI, p. 121, 1898). 



