THE LIFE OF DEVIDS LAKE 91 



DiaptouiKs leptopus piscinae. Reported in one collection from 

 Lake A (9/23/17). 



Diaptomns siciloides. This species has been recorded from 

 Main and Stump Lakes and Lake A ; in Stump Lake since 1922 

 only. Prior to this time D. sicilis was common as elsewhere in the 

 complex, but appears to have given place to siciloides at this time. 

 That this is a case of seasonal succession is unlikely, since the 

 1922 and '23 collections were made at times (8/25/22 and 

 7/21/23) when sicilis was formerly common. In 1922-23 siciloides 

 was apparently" as common as sicilis had been formerly. 



Cyclops viridis americanus, (pi. 20 and 22). Cyclops is gener- 

 ally present in much smaller numbers than Diaptomns, and, with 

 the exception of the shore records, which are erratic, for reasons 

 already noted, shows little evidence of waves of abundance thru 

 the season. It is almost wholh'- absent in winter, appears first in the 

 collections in April or May, the time of its appearance varying in dif- 

 ferent years, and disappears again in November. In 1914 it 

 appeared much later than usual, the earliest record being May 30. 

 The reason for this is not evident. There was no corresponding 

 scarcity of other zooplancton this spring and the temperature was 

 similar to that of preceding years. Cyclops is seldom abundant 

 and the number present in the spring months is always so few as 

 to have little significance. Their total absence in the early spring of 

 1914 is nevertheless notable. 



It is difficult to locate the time of maximum production of 

 Cyclops, because of its general scarcity and the influence of the 

 erratic shore collections. The curves are fairly regular from May 

 to November, with the crest about August 1. In Lake Mendota 

 Birge (1. c.) found Cyclops brevispinosus reproducing under the ice. 

 This I have not observed in C. v. americanus in Devils Lake. He 

 traces the decline of the former from its spring maximum to lack 

 of food. In Devils Lake there is no evident relation between food 

 supply and abundance of Crustacea, and I suggest as one possible 

 factor in determining the summer maxima and minima, a brief life 

 cycle accompanying rapid metabolism, which in turn is depcn(!'ent 

 on temperature.* 



It is similar in its spatial distribution to Diaptomns. 



Cyclops leuckarti. I have one record of this species from Lake 

 A, 9/23/17. 



Cyclops serrulatus. There is only one record for this .species 

 in the complex — Main Lake, 10/2/17. It has also been taken in a 

 neighboring fresh water coulee. 



Moina macrocopa (pi. 20 and fig. 25). Appears in the plancton 

 samples about August 1, rises to a maximum about four weeks later, 



*See pp. 45 and 90. 



