92 GIDEON S. DODDS. 



The approximate altitudinal limits and outstanding floral char- 

 acters of these zones in this part of the state as given by Gary 

 and verified by my own observations, are as follows : 



1. Upper Sonoran (arid, western portion of Upper Austral) : 

 Western edge of the Great Plains as far as the base of the foot- 

 hills (about 5,300 feet). Grassland with deciduous trees along 

 watercourses only. 



2. Transition: The foothill region up to about 8,000 feet: Char- 

 acterized by an open growth of rock pine (Pinus scopulorum) . 



3. Canadian: Includes the intermediate mountain elevations 

 up to about 10,500 feet. Lower portion characterized by a dense 

 growth of lodge-pole pine (Pinus murrayana) which gives place 

 at about 10,000 feet to a close forest of Engelmann spruce (Picea 

 engelmanni) and balsam fir (Abies lasiocarpa}. 



4. Hudsonian: A rather narrow strip characterized by a dwarf- 

 ing of the spruces and firs of the Canadian Zone and bounded 

 above by timberline, a sharply defined but jagged division line 

 occurring roughly at about 11,000 feet. 



5. Arctic-Alpine: An area without trees or woody plants ex- 

 cept some scrub willows. Huge snowdrifts last far into the sum- 

 mer or do not entirely melt. Summer temperatures are accord- 

 ingly low and the season is short. 



II. THE SPECIES OF ENTOMOSTRACA. 



Table I. gives the list of species recorded for this area, and 

 indicates for each the zones within which it has been collected. 

 Of course it must be recognized that to make these data of final 

 importance, very much more extensive collections are needed. It 

 is apparent, however, that even the incomplete records here pre- 

 sented are sufficient to bring out facts of interest. The records 

 for the more abundant species are sufficient to give wholly de- 

 pendable results while the scattered records of the rarer ones are 

 accurate as far as they go, but leave deficiencies and blanks to be 

 filled by subsequent collections. 



I have also included in Table I. the zones inhabited by each 

 of these species throughout the Continent as a whole. These 

 data are in many cases incomplete and in others uncertain because 

 I have not had access to literature where I might find detailed ac- 



