56 i in. CHICAGO ACADEMY OF SCIENCES. 



for dividing this large area into a number of smaller ones. Thus, 

 Binney 1 divides North America into three major regions, I — The Pa- 

 cific Province; 11 — The Central Province; and 111 — 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 Palaearctic 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 3 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 Lymnasas, 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 4 "Transcontinental 'life- 

 zones' have no necessary connection with the larger facts of faunal 

 distribution, but define secondary divisions, parallel, so to speak, all 

 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 Lymnseid fauna of North 

 America strongly substantiates Dr. Pilsbry's statement. 



The geographic study of the Lymnaeas 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. 5 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 l). 6 



1. Labradorian. 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. 



'Man. Amer. Land Shells, Bull. U. S. Nat. Mus. No. 28, p. 18. 

 J Proc. Nat. Mus., XVIII, pi. 9; XXII, pi. 18. 



8 See 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. 



"Alaska Mollusks, p. 1; Popular Science Monthly, Vol. LXVI, p. 362. 



6 The majority of the northern regions are the same as those proposed by 

 Dr. Dall, op. cit. 



