4 PROCEEDINGS OF THE NATIONAL. MUSEUM. vor. .65. 



more apparent when we remember that these two groups of lakes 

 are separated by but a few miles, the extremes of the two being 

 separated by not more than 10 miles. Yet the two groups support 

 entomostracan faunas quite distinct from each other, as distinct 

 as if separated by hundreds of miles in a north and south direction, 

 a fact which emphasizes the importance of an altitudinal difference of 

 a little more than a thousand meters. It is commonly recognized 

 that the entomostraca are a group in which dispersal is easy, as indi- 

 cated by the cosmopolitan distribution of some species and the wide 

 range of nearly all genera. Yet here, close together, we find two 

 groups of lakes in each of which there are several species which are 

 not found in the other. The several species common to the two 

 groups stand in strong contrast to the others and serve to emphasize 

 the fact that temperature may be an effective barrier for some species 

 but not for others. 



The zonal distribution of the species in these collections agrees 

 well with that of the same species as found in the Tolland region. 

 In a few instances the Shantz collections have served to extend the 

 range of species into altitudes in which they had not previously been 

 collected in the Colorado region, and in others they fail to give certain 

 species as wide a range as assigned to them on the basis of collections 

 in various other parts of the State. This, however, is not sur- 

 prising. The gratifying thing is the large extent of the agreement, 

 and the few differences are not surprising in view of the relatively 

 small amount of the work that has been done in this as well as in 

 other parts of the State. It is of interest to remember, also, that the 

 lakes on the plains are artificial, that the oldest was only 28 years old 

 at the time Shantz made his collections, and that most of them are 

 far younger than that, and that even the youngest of them had an 

 abundant entomostracan fauna (as Mesa No. 3, which was only 1 

 year old and yet yielded eight species) . 



The lakes of the higher group fall into two divisions on the basis 

 of their fauna, and these two divisions have an altitudinal significance. 

 Dead Lake, which falls within the Husdonian or upper part of the 

 Canadian zone, typifies the highest division and agrees well with 

 the 43 lakes and ponds in the Tolland region assigned to the Alpine 

 Zone (Dodds '17). In the 22 vials of material from this lake there 

 were 11 species. By far the most abundant among them were 

 Da'phnia pulex and Diaptomus shoshone, the two species which 

 characterize the highest lakes of the Tolland region. BrancMnecta 

 coloradensis, another typically alpine form,* is also present. Certain 



* Shant7,, H. L. Notes on the North American Species of BrancMnecta and their Habits, Biol. Bull., 

 vol.0, pp.249-2r)4, 1905. 



BrancMnecta coloradenns has been considered an exclusively alpine species, but if the record as deter- 

 mined by the author from a collection sent him from St. Vrain, Colorado, at 1,525 meters (5,000 feet) , 

 May 30, 1912, be correct, our notions on this must be revised. The author invites comment on this and 

 would be glad cf additional material bearing on this point. (See Dodds '17, p. 77.) 



