34 PLANKTON OF WINNEBAGO AND GREEN LAKES. 



followed by a rapid rise in the fall, which, may come as early 

 as September, but more commonly occurs in October or Govern- , 

 ber. In 1900, by far the largest number of the year occurred 

 in July. Nothing like this appeared in the other years, al- 

 though there was an increase in July, 1899. 



I think it can be said safely that Bosmina has two annual 

 maxima, one in the late spring or early summer, and one late 

 in the fall. In comparing the two lakes under consideration 

 we find that the spring maximum occurs earlier in Lake Win- 

 nebago than in Green lake, probably due to the fact of the more 

 rapid warming of the water in the shallow Lake Winnebago. 

 In some years the spring maximum fails to appear in Green 

 lake. The fall maximum seems, on the whole, to appear in 

 Green lake somewhat later than in Lake Winnebago. If this 

 maximum is dependent on some conditions following the fall 

 cooling of the water, this later appearance in Green lake is 

 easily explained. But so little is known of the life history of 

 Bosmina that one would hardly feel safe in hazarding an ex- 

 planation. 



In comparing my results of the annual distribution of Bos- 

 mina, there seems to be a good deal of discrepancy, but prob- 

 ably the differences can be explained either by differences in 

 local conditions or by the fact that most of the statements have 

 been based on observations carried on for only a comparatively 

 short time. Eo other observations, so far as I know, have been 

 published in America, and the statements of European authors 

 would indicate that in some cases there were tw T o distinct max- 

 ima, but not in others. 



Eurycercus lamellatus O. F. Miiller. 



Eurycercus lamellatus does not occur in the limnetic plank- 

 ton of Green lake, but in Lake Winnebago (Plate XVIII) it 

 was an important element of the summer plankton in 1899 and 

 1900. Curiously enough I found it in only one collection in 

 1901, — that of June 8. In the summer of 1899 it was found 

 in great numbers about the middle of July, but had almost dis- 



