Vol. XXXIX. August, 1920. No. 2. 



BIOLOGICAL BULLETIN 



ENTOMOSTRACA AND LIFE ZONES. 

 A STUDY OF DISTRIBUTION IN THE COLORADO ROCKIES. 



GIDEON S. DODDS, 

 WEST VIRGINIA UNIVERSITY. 



I. THE REGION COVERED. 



In a former paper ('17) I described the altitudinal distribu- 

 tion of the 71 species of Entomostraca known to occur within the 

 limits of the state of Colorado. Fifty-five of these species are 

 from my own collections made in a definite attempt to gather a 

 reasonable amount of information about the nature of the ento- 

 mostracan fauna at different elevations in this part of the Rocky 

 Mountains. The material included 280 vials of plankton from 

 124 lakes and ponds at elevations ranging from 4,100 to 12,188 

 feet above sea level. By far the greater number of these collec- 

 tions are from an area covering adjacent parts of the counties of 

 Boulder, Jefferson, Gilpin, Clear Creek, and Grand, and includes, 

 within a distance of 25 miles, portions of all the life zones from 

 the Upper Sonoran to the Arctic-Alpine. A full description of 

 the topography and climate of this region is included in my 

 former paper. In addition to my own collections from this 

 region, together with a few from other parts of the plains of the 

 state, I have made use of all available records of species collected 

 by others within the state. 



The state of Colorado affords an area for study which is not 

 wholly an arbitrary or unnatural one. Its higher portions include 

 the greatest elevations of the Rocky Mountains, with their south- 

 ern extension of climatic and biotic characters from the north, 

 and its lower portions are typical of the arid and hot conditions 

 of the southwestern portion of the United States, while its posi- 

 tion astride the Continental Divide makes it the meeting place of 



89 



