56 THE CHICAGO ACADEMY OF SCIENCES. 
for dividing this large area into a number of smaller ones. Thus, 
Binney! divides North America into three major regions, I—The Pa- 
cific Province ; [I—The Central Province; and I1I—The Eastern Pro- 
vince, the latter being subdivided into (a) The Northern Region, (b) 
The Interior Region, and (c) The Southern Region. Simpson? divides 
the area under consideration into the Palzarctic Region, west of the 
Rocky Mountains, the Mississippi Region, including the whole of the 
continent between the Rocky Mountains and the 80° of longitude, the 
Atlantic Region, lying east of the 80° of longitude and the Central 
American Region, including Mexico and Central America east of the 
Sierra Madre range. 
Dr. C. Hart Merriam’ has divided the North American continent 
into life zones and this seems to be one of the best attempts which has 
thus far been made to divide this region into subregions. While this 
subdivision is admirably adapted for the mapping of some land forms, 
it is totally inadequate for the proper study of such aquatic forms as 
the Lymnezas, a single species of which may be equally distributed 
throughout the Boreal, Transition, Upper Austral and Lower Austral 
life zones. As Pilsbry has recently stated* “Transcontinental ‘life- 
zones’ have no necessary connection with the larger facts of faunal 
distribution, but define secondary divisions, parallel, so to speak, ali 
over the world. For instance equal zones in the southern Alleghanies 
and Rocky Mountains might be spoken of as “physically homologous,’ 
but not faunally so.” The distribution of the Lymnzid fauna of North 
America strongly substantiates Dr. Pilsbry’s statement. 
The geographic study of the Lymnzas has shown that an adequate 
and understandable division can be obtained only by a comparison of 
the different river systems, as has been suggested by Dr. Dall. The 
area under consideration has, therefore, been divided into regions em- 
bracing the natural drainage areas separated by divides. These may 
be characterized as follows (figure 1).° 
1. LapraportAn. This region includes all of the drainage areas 
emptying into Ungava Bay and the Atlantic Ocean north of the Strait 
of Belle Isle. It includes the eastern part of Ungava, the extreme 
eastern end of Quebec, and the whole of Labrador. 
41Man. Amer. Land Shells, Bull. U. S. Nat. Mus. No. 28, p. 18. 
2Proc: Nat. Mus. OVE eply 9s) nextel. diss 
3See North American Fauna No. 3, 1890; Bull. No. 10, Division Biol. Surv., 
1898; A. O. U. check-list, 1910. 
*Proc. Phil. Acad., 1906, p. 530. 
SAlaska Mollusks, p. 1; Popular Science Monthly, Vol. LXVI, p. 362. 
‘The majority of the northern regions are the same as those proposed by 
Dr. Dall, op. cit. : 
