ENTOMOSTRACA AND LIFE ZONES. IOI 



their bottoms. Lakes of the former type in this zone have a 

 fauna of much the same nature as in the Canadian, while those 

 of the latter kind have their affinities, though less decidedly so, 

 with the Arctic-Alpine. A few species make this zone their upper 

 limit and it seems probable that it may have some importance in 

 this respect. In the main, it seems to be a transition zone, one 

 having no important distinctive characters and it might well be 

 included within the Canadian. 



The Arctic-Alpine Zone. 



This zone is an interesting one partly because of a type not 

 familiar to us, and partly because its fauna is distinctive and 

 striking. The lakes of this zone lie in the deep cirques at the 

 heads of the streams and on the stream courses not far below, 

 and are all just at or above timberline. Most of them are deep 

 and clean and are bordered by steep, rocky slopes. Ice remains 

 till June or July or even later, and the snowdrifts on the sur- 

 rounding walls furnish cold water throughout the greater part 

 of the summer so that the highest temperatures reached range 

 from 45 to 55 F. Shallow pools of this region have about the 

 same type of fauna and must clearly be classed along with the 

 lakes of this zone. 



Fifteen species have been collected here, nine of which are 

 widely euthermic and range through all the zones, not only to the 

 Upper Sonoran of Colorado, but into the Lower Sonoran and 

 Austral, and in some cases into the Tropical. Nearly all of the 

 more abundant species of the zone belong to this group, as Daph- 

 nia pule.v, Chydorus sphaericus, Alona rectangula, and four 

 species of Cyclops. Species of more restricted zonal range are, 

 however, important and abundant, though none of great impor- 

 tance is confined to the zone. Most of the northern species listed 

 as of importance in the Canadian fail to reach this zone, but find 

 their highest range in the Hudsonian, though it appears from 

 records of their presence in Greenland and other high northern 

 regions that they might be expected here. An abundance of col- 

 lections in this region has not, however, found them in the Arctic- 

 Alpine of this region, and we must omit them from its list. 



The two most conspicuous and abundant species are Diaptomus 



