THE LIFE OF DEVIDS LAKE 83 



D. megalocephala. One record only, a single specimen in a 

 collection from Creel Bay (8/31/14). 



Brachionns plicatilis. A very common and widely distributed 

 species but not usually as numerous as either Pcdalia or Brachionns 

 satanicus; occurring in Main, East, Mission, Lamoreau, Spring and 

 Stump Lakes, Lakes A, C, and 0, and in certain fresh water 

 lakes of the complex as well. Owing to the close similarity between 

 this species and its variety spatiosus no attempt has been made tr> 

 distinguish them in the plancton counts. Typical spatiosus is 

 sufficiently distinct, but intergradations render it impossible to 

 determine where every specimen belongs. Accordingly I have? 

 included both the species and variety in the chart (pi. 18), which 

 illustrates the seasonal distribution. This shows its presence thru 

 a comparatively short period. In 1911 a few were present up to the 

 end of September. In 1912 the records show their practical absence 

 prior to June 26, one or two records being all that I have before 

 this date. A few were present later in the season, but the records 

 are too scanty to represent as a curve. In 1913 they were absent 

 prior to June 24, when the spring collections ended, occurring in 

 small numbers from August 1 to September 6. The 1914 records 

 cover a longer period (May 15 to September 14) but even here 

 they were present in considerable numbers during July only. In 

 1918 on August 7 a rough comparison of the numbers of various 

 species of rotifers taken in a tow showed 63 Brachionns p. spa- 

 tiosus and 1 plicatilis? to 36 Pedalia and 3 Brachionns satanicus. 

 August 12, 1918, a similar comparison showed 103 B. p. spatiosus, 

 47 Pedalion, 2 B. satanicus and 1 Colurella? With remarkable 

 suddenness, however, the plicatilis disappeared, for on August 21, 

 I found but one specimen, as compared with 86 Pedalia and 9 B. 

 satanicus.* Usually two maxima with an intervening minimum 

 occur in a season. In 1913 there is a very definite minimum on 

 August 11 folloAved by a definite maximum on the 20th and pre- 

 ceded by a maximum sometime in July or early August. In 1914 

 there was a distinct maximum on July 20, and another, less well 

 defined, between August 17 and 26, with a verv^ distinct minimum 

 on August 2. In 1911 the records are not adequate for inter- 

 pretation. The records for East Lake are too scattering to have 

 much value. 



Brachioniis plicatilis spatiosus. The spatial distribution of the 

 variety described by Rousselet (1912) is similar to that of the 

 parent species, altho there is no record from Lake P. from whicfi 

 the parent species is recorded. In the main lake, where the most 

 extensive collecting has been done, spatiosus is much commoner than 

 plicatilis. In his description of this form Rousselet says (p. 374) 



*See p. 45. 



