87 



out most of the summer, attending only approximately the sup- 

 pressed and interrupted pulses of Melosira in that year of disturbed 

 hydrograph. It has been recorded from the latter part of April 

 till the middle of September, and, as a rule, above 60. This beau- 

 tiful little choano flagellate is sessile upon the filaments of Melosira, 

 principally upon the variety spinosa, and but rarely upon M. varians 

 or other planktonts such as Pediastrum. It is often associated 

 with Bicosceca lacustris and is usually found upon the sides of the 

 filaments, the bowl of the transparent brownish lorica being closely 

 sessile upon the diatom. In one instance a lorica was found upon 

 the corner at the end of the filament. The lorica had adapted 

 itself to this novel situation by an angular indentation fitted upon 

 the corner of the diatom. 



Syncrypta volvox Ehrbg. Average number, 625. This species 

 has a definite and somewhat unusual seasonal distribution. In 

 1898 it was found from March 1 to April 12, and reappeared Novem- 

 ber 8, attaining a maximum of 13,500 on December 6, and of 43,000 

 on January 1, declining then to 800 and rising on February 14 to 

 4,800, and subsequently disappearing in the flood waters of March. 

 It was not recorded in 1897. In 1895 it appeared September 27 and 

 continued for a month, reappearing in February and March, and 

 not occurring after April 10. It has attained its largest develop- 

 'ment at minimum temperatures under the ice 43,000 January 3, 

 1899, at 32.7. The greater part of its occurrences in 1898-1899 

 lie very near this temperature, and but three in all the years lie 

 above 50. It is par excellence a winter planktont, or at least a 

 cold-water one. 



Its occurrences in 1895-1896 lie near the beginning and the 

 close of the seasonal pulse of Synura. In 1898-1899 the pulses of 

 Syncrypta coincide in location with or immediately follow those of 

 Synura. The resemblance of Syncrypta to small colonies of 

 Synura is striking, and this fact combined with the relation of their 

 seasonal fluctuations raises the query if Syncrypta may not be an 

 encysting stage of the Synura colony. Its life history should be 

 fully worked out. 



Synura uvella Ehrbg. Average number of colonies, 8,463. 

 The seasonal distribution of this chrysomonad flagellate is some- 

 what similar to that of its near relative Syncrypta. It is a 

 perennial, though predominantly cold-water, planktont. It appears 



