IO4 GIDEON S. DODDS. 



largely stenothermic and others euthermic. The outstanding 

 features as seen in the Colorado list are as follows : 



The 16 species of phyllopods in the list are, with two excep- 

 tions, narrowly stenothermic and all but one of the stenothermic 

 species belong to the warm-climate fauna. It is moreover true 

 that nearly all of the known species of the group are stenothermic 

 and have narrow geographic ranges. Among the Cladocera, the 

 Family Daphnidae is represented by n species which are nearly 

 all euthermic in a broad sense, are found at all elevations and in 

 all zones, and are decidedly cosmopolitan, while the Chydoridse 

 has 1 6 species about equally divided between stenothermic and 

 euthermic types. The Copepods include two sharply contrasted 

 genera, Cyclops and Diaptomus, both of which form important 

 components of the entomostracan fauna in all parts of the world. 

 Diaptomus has 13 species in the Colorado list, not one of which 

 is euthermic in any broad sense, and all of which are confined 

 within areas of very limited extent. Cyclops, on the other hand, 

 with only 5 species, is fully as important. Three of these are 

 broadly cosmopolitan and euthermic, a fourth (C. bicuspidatus) 

 is nearly so, being absent only from the warmer waters, and the 

 fifth (C. ater), confined to the United States and not found north 

 of the Transition Zone, has as great a range as the widest spread 

 species of Diaptomus. 



I believe the collections oi Entomostraca described in this 

 paper are the most extensive that have been made in this coun- 

 try from a region where high mountains cause such a decided 

 narrowing of life zones. So far as I know, this is also the first 

 attempt to define the entomostracan fauna of the various zones 

 of such an area and to definitely place them with reference to 

 Merrian's Life Zones. The data from Colorado lend themselves 

 well to such an anaysis. The zonation is definite, even though 

 the present collections do not enable us to discriminate between 

 all of the colder zones. It is equally difficult, on the basis of our 

 present knowledge, to sharply differentiate these same zones in 

 their continental extent in Canada and northern United States. 



Yet it seems well established by these data that the entomos- 

 tracan population of the various life zones as they occur in the 

 mountains of Colorado are but attenuated southern extensions 



