THE LIFE OF DEVILS LAKE 87 



present. Prior to its discovery in the Devils Lake complex it had 

 only been reported from Chile, which is doubtless due to incomplete 

 study of our waters. 



Testudinella patina. One record only for Main Lake (10/18/14), 

 Reported also from Spring Lake, and there are several records from 

 fresh water lakes of the region. 



Ptygura sp. Two specimens in a collection from Mission Lake 

 (8/18/14). 



Collotheca cornuta. Infrequent. Reported only from Main 

 Lake. 



GASTROTRICHA 



Chaetonotus maximns. Occasionally noted in collections from 

 the Ruppia zone in Main Lake. 



CRUSTACEA 

 In plate 17 is shoAvn the annual records of the Crustacea for 

 Main Lake, from 2/6. 1911 to 9/14, 1914 and 12/3, 1922 to 

 7/23, 1923, and in figure 23 those for East Lake for 1913-14. 

 There are gaps in the records for 1912 (6/25-8/6. 8/28-10/7), 1913 

 (6/24-8/12) and 1923 (1/27-3/11). The curves represent the aver- 

 age of all collections from different depths on a given day or for a 

 period of successive days. The shore collections have not, however, 



Figure 23. Seasonal distribution of Crustacea in East Lake. 



been included until 9/3/13 because of their scarcity prior thereto. 

 The number of collections have varied from time to time, so that 

 the probable accuracy of the record is not the same thruout. Es- 

 pecially is this true of 1911, in which year comparatively few col- 

 lections were made. In spite of these defects the records are fairly 

 consistent thruout, except for 7/13/23 when great numbers of 

 nauplii appeared, averaging over 1000 per 1., to disappear again as 

 quickly as they came. Furthermore, the 1923 records in general 

 are very much higher than for former years. What the explana- 

 tion for this is I cannot say. There was a marked development of 

 Coelosphaerium about the end of June in this year, but not con- 

 spicuously more than in 1914, while the diatoms and other algae 

 showed no unusual development. Lyngbya, however, was greatly 

 reduced in 1923 as compared with former years. Birge (1897) con- 

 siders an abundance of this genus prejudicial to the Crustacea 

 since the latter do not feed on it. I doubt very much whether this 

 hypothesis holds good for Devils Lake because the filaments of the 



