THE LIFE OF DEVILS LAKE 63 



Clathrocystis aeruginosa. Reported by Dr. Moore as "abundant 

 in towings and associated with filamentous algae." In the quan- 

 titative plancton samples it has not been possible to distinguish this 

 species. The cells are very small and the indefinite form of the 

 colony renders it difficult, in preserved material and with low 

 magnifications, to differentiate it from masses of zooglea, so that 

 some of it may be included under "Micrococcus" in the counts. 



Microcystis incerta. Taken in Lake P only. 



Coelosphaerium kuetzingianum. This is one of the most abun- 

 dant forms in the lake. With low magnifications it is very difficult 

 to distinguish it from the following species, so that both have been 

 listed together in the counts. Reported from Main Lake and Lake 

 C. 



Gomphosphaeria aponina. A common and widely distributed 

 species. Var. cordiformis has been found in Lake P. The seasona\ 

 distribution of this species is shown, together with that of the pre- 

 ceding, in the chart (pi. 12), which shows that they first appear in 

 March or early April, and are present until after the freeze-up in 

 December. The record for 1913-14 shows their presence thru the 

 winter until March 1, followed by a brief absence and re-appearance 

 about April 1. In 1911 a marked drop occurred in August parallel 

 to that of Nodularia, Merismopedia and Chaetoceros, but not parallel- 

 ed by Chroococeus or Oocystis. This behavior does not correspond 

 to the record of subsequent years. In 1912-14 there is apparently 

 but a single maximum for each year, but this occurs at different 

 times in 1912 (Aut. 25-Sept. 1), 1913 (Oct. 20) and 1914 (May 20- 

 30). In the latter year a poorly marked minimum occurred July 25 

 to August 1, followed by a slight increase in August and September. 



Coelosphaerium and Gomphosphaeria are much less common in 

 East than in Main Lake (fig. 19). 



The occurrence of Coelosphaerium in Lake Mendota (Birge and 

 Juday, 1922) is less regular than in Devils Lake, for in the former, 

 in 1915 it was absent or rare until June, developing in considerable 

 numbers from July onward. 



Merismopedia convuluta, elegans, glauca and tenuissima. Of 

 these the latter "is by far the most abundant." No attempt has 

 been made to differentiate between them in the counts, the results 

 of which are shown in plate 13. 



The curve corresponds rather closely to that of Chroococeus, 

 with a distinct drop in mid-August in 1911 and a maximum at the 

 same time in 1912 and 1913. In the 1914 collections probably most 

 of the material had disintegrated before the counting was done, so 

 no definite conclusions can be drawn for that year. In 1912 a small 

 maximum is apparent about the end of May, and this is also indi- 

 cated in the 1913 curve, altho the collections here are rather too 

 scanty to admit of any definite conclusions. Merismopedia sp. oc- 



