ENTOMOSTRACA AND LIFE ZONES. IO3 



regions. I have one record, however, from a collection dated 

 May 30, 1912, sent me by Professor Max M. Ellis from St. 

 Vrain, Colorado, at an elevation of about 5,100 feet and well 

 within the Upper Sonoran. It seems improbable that there can 

 be any mistake about the label of this collection, and I have re- 

 peatedly looked at the material in an attempt to detect differences 

 which would relieve me of the necessity of referring it to this 

 species. This record places it at once in the Upper Sonoran and 

 calls for a revision of our notions of its distribution. 



IV. SUMMARY AND DISCUSSION. 



The zonal distribution, local and general, of the 71 species in- 

 cluded in this report affords good material for the study of cer- 

 tain characteristics of euthermic and stenothermic species belong- 

 ing to closely related families and genera. It is at once apparent 

 that the total entomostracan population of this region is readily 

 divisible into these two components. The euthermic species not 

 only range through several zones in their local and general dis- 

 tribution, but a large proportion of them are essentially cosmo- 

 politan, being reported from all parts of the world where collec- 

 tions have been made. The stenothermic species are divisible 

 into two groups, one belonging to the colder, the other to the 

 warmer zones. The stenothermic species of the colder zones 

 may in turn be resolved into two groups, one of which includes 

 species that range over a considerable area from Colorado north- 

 ward into the corresponding zones of our northern states, Canada, 

 and even into Greenland, Iceland, and northern Europe, while 

 the other includes species with very narrow ranges, confined to 

 the higher parts of the Rocky mountains. The stenothermic 

 species of the warmer lakes (the Upper Sonoran of Colorado) 

 may likewise be divided into two groups, one, of species ranging 

 over the Sonoran, and through the Austral in general, and into 

 the Tropical Zone, the other, of those with a narrow range in the 

 Upper Sonoran of a few states. 



It is further evident from a scrutiny of the facts presented in 

 Table I., where the species are arranged on the basis of tem- 

 perature toleration, that such a grouping bears a certain relation 

 to taxonomic groups, inasmuch as some of these groups are 



