Mollusca of Lower Canada. 455 • 



to be really indigenous to America. Now, with one exception, 

 all the shells of both Upper and Lower Canada also inhabit the 

 Atlantic region. The little group of fresh water bivalves, to which 

 I endeavoured previously to draw some attention, forms this excep- 

 tion. Eight species of Cyclas and three of Pisidiura are, so far as 

 we know at present, peculiar to Canada, and have never been found 

 elsewhere. But these little shells require to be carefully searched 

 for, and are very similar one to an other ; hence they may have 

 been overlooked in the New England states. 



When we turn to the sister science of botany, we shall find that 

 somewhat different views of geographical distribution have been 

 entertained. If we compare our knowledge of Canadian plants 

 with Prof. Schouw's theories respecting the general geographical 

 distribution of the vegetable kingdom we shall see that in Canada 

 two botanical provinces meet. The first is the well-known Arctic 

 flora, which is characterized by the abundance of mosses, Saxi- 

 frages, Gentians, species of Silene, Arenaria, and Dianthus ; and 

 also by the presence of many species of willow and sedges. 



As defined by Prof. Schouw, the total absence of tropical fa- 

 milies, a notable decrease of the forms peculiar to the temperate 

 zone, and the prevalence of forests of firs and birches, form addi- 

 tional characteristics of this region. Geographically, it includes 

 all the countries within the polar circle, with some parts of Eu- 

 rope, Asia and America to the south of it ; as for example, the 

 mountains of Scotland and Wales, Labrador, Greenland, and the 

 northern part of Canada. Next we have what Prof. Schouw calls 

 the region of Asters and Solidagos, characterized by the great 

 variety of oaks and firs, the small number of Umbelliferae and 

 Cruciferse, by the almost total absence of true heaths, which are 

 here replaced by Vacciniums, and by the abundance of the said 

 Asters and Solidagos. Geographically it includes Mr. Wood- 

 ward's Atlantic region, and the southern part of Canada. Thus, 

 judging from the distribution of Mollusca, Mr. Woodward thinks 

 that Canada should rank as a distinct natural-history region, 

 -while on the contrary, judging from the evidence afforded by the 

 vegetable kingdom, — according to Prof. Schouw's theory, part of 

 Canada belongs to an Arctic, and part to an Atlantic region. 

 But here again we must not neglect to inquire what light the 

 geology throws upon this question, and turning to the geologic 

 record, we shall find that since the first appearance of these ani- 

 mals ancf plants on the surface of our globe, great alterations in 

 the relative distribution of land and water and a general subsi- 



