42 
It is interesting to note the distribution of the several families repre- 
sented in this fauna, some groups increasing in species northward and 
others decreasing in this respect. The table below indicates this geographic 
distribution. 
Southern fauna 
Northern fauna 
— 
Known 
Probable 
— 
Known 
Probable 
Unionidae 
6 
7 
Sphaeriidae 
38 
61 
Viviparidae.. 
1 
1 
Valvatidae 
5 
10 
A m n i eol i d an. 
6 
7 
Lymnaeidae 
15 
2o 
Physidae. 
3 
9 
Planorbidae 
13 
19 
Ancylidae 
2 
5 
It is also probable that species and varieties not at present known 
will be found in some of the lakes and streams, especially in the groups 
Sphaeriidae, Lymnaeidae, Planorbiclae, and Physidae. The area as a whole 
may almost be considered virgin territory as far as the aquatic fauna is 
concerned. It is especially desirable that more material with the animal 
be collected, and that the habitat relations be accurately described, for it 
is now appreciated by biologists that differences in the animals are often 
coincident with differences in the physiographic relationships of the environ- 
ment. The study of the fauna of the Canadian region is of great value in 
connexion with the geological history of North America, comparisons 
between the present fauna and that of the interglacial intervals showing 
clearly that great changes have taken place in the nature of the aquatic 
fauna since the last ice-sheet retreated to the north. 
In the present paper comparative notes on each species represented 
are given more fully than is usual in local faunal papers, and in view of the 
inherent tendency to vary that is found in all organisms this becomes 
necessary to adequately understand the relationships of this fauna to that 
of other areas. Under each group other published records are included 
and comparisons are made with adjacent territory, Manitoba, Mackenzie 
river, etc., thus bringing together all of the information at present known 
concerning the fauna of central Canada. The nomenclature is brought 
down to date and is essentially that used by the senior author in his “Fresh 
Water Mollusca of Wisconsin,” Bulletin 70 of the Wisconsin Geological 
and Natural History Survey. 
ACKNOWLEDGMENTS 
Dr. Victor Sterki has examined all of the Sphaeriidae and has made 
valuable notes on many species, these being indicated under each species. 
Mr. William J. Clench has examined the only species of Physa found by 
the party. The hearty co-operation of Mr. Jack T. Kemp is to be especi- 
ally noted. 
