386 



THE CHICAGO ACADEMY OF SCIENCES. 



Catasc opium occupies a large part of the Boreal (Canadian) and 

 Transition life zones and enters the Upper Austral life zone on the 

 south. In the United States it does not extend west of the humid 

 division of the Transition and Upper Austral life zones. In British 

 America it occupies the larger part of the Boreal (Canadian) life 

 zone, east of the 115th degree of latitude and south and wst of Hud- 

 son Bay, extending south into North Dakota. Its northern limit seems 



Distribution of 

 CATASCOPIUM \ 



FIG. 45. 



to be Great Slave Lake at about the 60th parallel. It probably in- 

 habits some of the country to the east of Hudson Bay, but no speci- 

 mens or authentic records have been seen ; Ball reports it from Ungava 

 and Labrador. Its center of distribution appears to be the Great 

 Lake region lying to the southwest of Hudson Bay. It has not been 

 found in the great plains area, but is common in the prairie regions 

 of the central west. It is a common mollusk in the Canadian, Hud- 



