56 THE LIFE OF UEVILH LAKE 



The chemical character of the water is indicated iii table 3. 



Spring Lake possesses several species of rotifers, not as yet re- 

 ported elsewhere in complex, but in other respects, its characteristics 

 are chiefly negative. 



LAKE P (pi. 10). 



This small pond was separated from Devils Lake about 1906. 

 It is probably spring fed, as it maintains a fairly constant level from 

 year to year, in spite of the lack of supply, apart from run-off and 

 possible springs. Its maximum depth is between one third and half 

 a metre. 



The chemical analysis and osmotic pressure are given in table 

 3. 



Lake P has several species of algae not reported elsewhere in 

 the complex, which are of interest, coupled with the absence of 

 Nodularia noted above. 



One of the most interesting inhabitants of this lake is the larva 

 of the dragon fl.y Sympetrum. This has not been found in any 

 other of the brackish lakes of the complex, and is probably to be 

 considered as a typically fresh water animal. 



Triaenodes flavescens is another species occurring only in Lakes 

 C and P and in neighboring fresh water ponds; all of these facts 

 seem to relate Lake P rather more closely to fresh than brackish 

 waters, and j'et the analysis (table 3) shows the water to be highly 

 brackish. I cannot at present reconcile these apparently irrecon- 

 cilable facts. 



LAKES N AND O 



Both of these are shallow pools in spring and continue as such 

 during wet seasons. They occupy parts of the old lake basin, from 

 which they were separated about 1886-87. Like other pools they 

 freeze solid in winter, when water is present, w^hile in summer their 

 temperatures must occasionally run to 30° or over. 



Conditions in these lakes are too variable, and their study is 

 as ,yet too incomplete, to justify any conclusions regarding their 

 characteristics. 



Besides the lakes already enumerated there are several fresh 

 water ponds which at one time were a part of Devils or Stump 

 Lake. These I have omitted from the discussion, because, being 

 fresh water, they are very different, both chemically and biological- 

 ly, from most of the cut-off lakes forming part of the Devils-Stump 

 Lake complex. 



Another lake has only recently (1923) been separated from 

 Devils Lake by the construction of a highway, but its recent separa- 

 tion renders its consideration unnecessarv here. 



