ENTOMOSTRACA AND LIFE ZONES. 99 



When we search for distinctive faunal characters of the higher 

 zones we are confronted with a problem somewhat different than 

 in the Sonoran. In no other zone is there even a single species 

 confined to it and at the same time abundant enough to be used 

 as a zone indicator. In certain respects the zones of the moun- 

 tain region, Transition to Arctic-Alpine, form a unit group, 

 which, as a whole, may be contrasted with the Sonoran. There 

 are 23 species which have been collected exclusively in the moun- 

 tains, many of them in considerable abundance, which clearly 

 belong to the colder zones. Yet when we attempt to apportion 

 them among the zones it is found that most of them range 

 through two or more zones. There are, however, certain pretty 

 definite faunal characters of each zone, a description of which 

 follows. 



TJie Transition Zone. 



In the foothill region of the mountains there are but few lakes 

 or ponds and accordingly few collections have been made and a 

 small number of species recorded from this zone. This leaves 

 sOme doubt as to the nature of the transition between the fauna 

 of the plains and that of the mountains. We cannot determine 

 whether this is truly a transition zone or if it is one having special 

 and striking characters of its own, though the former view seems 

 more probable. It is further probable that the fauna of this zone 

 partakes more of the nature of the higher than of the lower zones. 

 While there are 23 species which make the Transition Zone their 

 lower limit, there is not one which finds its upper limit in this 

 zone, though from the records of general range, there are some 

 which may be expected to do so when more extensive collections 

 have been made here. Twenty-eight species have been recorded 

 in this zone, but a total of 50 might be expected because certain 

 others of the Colorado list are present in the Transition of our 

 northern states. 



The Canadian Zone. 



In the belt assigned to this zone there are many small lakes, 

 nearly all of morainal origin, mostly shallow, often without outlet, 

 and commonly surrounded by forest. Their fauna is rich in in- 

 dividuals and species. Trie-re have been collected in the lakes of 

 this zone 37 species, and about 8 others might be expected. This 



