NO. 2226. DISTRIBUTION OF ENTOMOSTRACA—DODDS. 83 



fauna, it is very unusual for so large a proportion of a fauna to fall 

 within this group. Of the 42 North American species of Phyllopods, 

 16 have been found m Colorado (12 confined strictl}^ to the plains) 

 and 25 are confined to the area west of the meridian of Kansas City. 

 These species are the part of the fauna which differentiates it from 

 that of most lowlands in temperate regions. This type of fauna finds 

 a suitable home in the transient pools of the arid plains, from which 

 the species unable to endure these conditions are excluded. Because 

 other types of lakes and ponds were almost unknown here until the 

 development of irrigation produced them, the more generalized por- 

 tion of the fauna has not had the same chance to develop, and it is 

 probable that even with the facility of dispersal which characterizes 

 plankton organisms, an equilibrium has not yet been reached, so that 

 we may expect the next period of years to produce considerable changes. 

 Though the exploration in no part of the area studied has been 

 anything like complete (especially deficient in the plams area) it is 

 pretty evident that three well-defined zones exist, and while farther 

 investigations may change many details, it seems safe to assume that 

 what has been presented here expresses fairly well the main facts. 

 Table 4, page 76, expresses briefly the facts about zonation. It would 

 be of interest to learn how far this zonation may be applicable to 

 other portions of the Rocky Mountain region, and to what extent the 

 dommant species may be the same in other localities, but up to the 

 present, in other mountain areas in this country, insufficient work has 

 been done to give a very definite notion of its plankton Crustacea. 



COMPARISON WITH OTHER MOUNTAIN FAUNAS. 



Though no extensive work on mountain plankton Crustacea has 

 been done m this country, there has been accomplished in Europe 

 some work of considerable importance, notably in two regions, the 

 Alps and the mountains of the Scandinavian Penmsula. 



Important among work in the Alps is that of Zschokke (1900) 

 treatmg other European mountains as well. Much of his descriptive 

 matter dealing with the nature of lakes and streams, and his photo- 

 graphs of lakes in the Alps, might well be used to illustrate conditions 

 in the higher part of the mountains of the ToUand region. His 

 description of a typical alpme lake essentially describes lakes of our 

 own alpine zone, so that we are justified in making a direct compari- 

 son of the fauna. The only conspicuous difference is that in the Alps 

 correspondmg conditions are reached at a lower elevation than m the 

 Colorado Rockies. A comparison of the plankton Crustacea beings 

 out a striking similarity also, for though so far separated geographi- 

 cally, a comparison of the 63 species from the Alps with the 44 

 reported from our own mountains shows 19 species in common 

 (Table 6). Zschokke's data are not presented in such a wa}^ as to 



