GENERAL, DISCUSSION 3 



Hudson Bay. — This system, the largest of all, comprises the 

 entire area draining into Hudson Bay, including Keewatin, the 

 southeastern corner of the Mackenzie district, eastern Atha- 

 baska, the whole of Saskatchewan, the southeastern two thirds 

 of Alberta, Assiniboia and Manitoba, the drainage area of the 

 Red River of the North in the Dakotas and northeastern Minne- 

 sota, all of Ontario, Quebec, and Ungava north and west of the 

 ' Height of Land.' 



Canada. — This system comprises the drainage of the St. 

 Lawrence and the Great Lakes south and east from the Height 

 of Land, including the island of Anticosti. 



Labrador. — This comprises the area draining into Ungava 

 Bay and the Atlantic north of the Straits of Belle Isle and the 

 Height of Land, being the Labrador coast and the northeastern 

 part of the Ungava district of the Dominion of Canada. 



A few species are noted from Greenland ; when peculiar to 

 Greenland, or found in Greenland and also on the continent, 

 the species have been entered in the Labrador column but dis- 

 tinguished by an asterisk. 



The vast territories included in these drainage systems are, 

 it is true, only partially and imperfectly explored for mollusks. 

 Yet certain portions of them are tolerably well known, and the 

 uniformity imposed on the fauna by its high northern position 

 and unvaried conditions leads to the belief that while much is 

 yet to be known in tracing out the details of distribution, little 

 is to be expected in the way of absolutely new species, even 

 from this immense territory still to be explored. It would be 

 rash to conclude that nothing new remains to be found ; but it 

 certainly behooves us to be moderate in our expectations. 



It is probable that new additions will be made from among 

 the ranks of the smaller species, such as Corneocyclas (or Pi- 

 sidium). Vertigo, and the more minute Helicidai. Perhaps a 

 considerable number of the more southern forms which are 

 known to approach the boundary will eventually be found to 

 pass beyond it ; and other additions to the list will result from 

 the more careful discrimination of similar or closely allied 

 species. 



