ALTITUDINAL DISTRIBUTION OF ENTOMOSTRACA IN 



COLORADO. 



By Gideon S. Dodds, 



Of the Department of Zoology, University of Missouri, Columbia, Missouri. 



INTRODUCTION. 



During the summers of 1908, 1912, and 1913 I made collections 

 of plankton Crustacea from 124 lakes and ponds in Colorado, at 

 elevations from 4,100 to 12,188 feet. I have also received material 

 from Prof. Max M. Ellis and Mr. L. C. Bragg. These collections have 

 yielded 55 species of Entomostraca, wliich form the basis of this 

 report. I have also made use of all other available records of species 

 previously reported from the State, giving a total of 71 species 

 (Phyllopoda, 16; Cladocera, 34; Copepoda, 21).^ 



The following list includes the localities where fairly complete col- 

 lections have been made in the State. 



On the plains: Feet. 



La Junta (Dodds), 11 lakes at about 4, 100 



Boulder (Dodds), 7 lakes at about 5, 300 



Greeley (Beardsley), several lakes at about 4, 600 



In the mountains: 



Tolland region (Dodds), 106 lakes 8, 100-12, 188 



Twin Lakes region (Juday), several at about 9, 200 



Pikes Peak region (Ward), 5 lakes at about 11, 000 



Besides these, there are a number of localities from which one or 

 two species have been reported — scattered records in mountains and 

 plains by various men, including some records by early naturalists, 

 chiefly with the Hayden survey. 



The interest of this study lies in the fact that here, within a rela- 

 tively small area, we find a wide range of environmental conditions, 

 physiographic and climatic, with a corresponding diversity of ani- 

 mal and plant life. The eastern two-fifths of the State of Colorado 

 is included within the area of the Great Plains, with a climate, except 

 for its arid nature, essentially like that of the Mississippi Valley 

 generally, while the remainder includes the highest area of the Rocky 

 Mountain region, parts of which have a climate almost arctic. 



I For list of these lakes, their elevations, and the species collected in each, see Table 8, printed as a foUo 

 at the end of the text. 



Proceedings U. S. National Museum, Vol. 54— No. 2226. 



59 



