Marsh — Limnetic Crustacea of Green Lake. 187 



The surface temperature varied from the freezing point of 

 water in winter to eighty degrees in August, 1896. In general 

 the rise of surface temperature in the spring, and the fall in 

 autumn, were both uniform and rapid, but there were some ex- 

 ceptions. Very noticeable is the jog in the curve in May, 1895. 

 In this month there was a period of unusually warm weather, 

 followed by severe frosts. 



There was a curious rise in the bottom temperature in the 

 fall of both 1894 and 1895. On November 11, 1894, I found 

 the bottom temperature 45, while the highest point reached 

 previous to that time was 42^-. 



On October 24, and November 3, 1894, I found the bottom 

 temperature 44, while the highest point reached previous to 

 that time was 43. On November 11, 1895, the bottom temper- 

 ature was 45, while the highest previously recorded was 42^-. 

 My first impression on seeing these temperatures was that there 

 must have been a mistake in the observation. I felt the more 

 certain of this probability in one case, as the observation had 

 been made by my assistant without my direct supervision. 

 But a repetition of the work showed that there was no mis- 

 take. 



A similar rise in bottom temperature in November has 

 been noticed in Lake Cochituate (Whipple, '95, p. 205, and 

 Fitzgerald, '95, p. 74), and these authors have also noticed a 

 fall in bottom temperature in the spring. These apparent ab- 

 normalities in temperature have been explained by the above 

 mentioned authors on the supposition that as the top and bot- 

 tom temperatures approached each other, the water, being of 

 nearly equal density from top to bottom, would be in a state of 

 unstable equilibrium, and currents would be set in motion, which 

 would effect the whole depth, especially under the influence of 

 high winds. Whipple has shown ('95, p. 208), that under some 

 circumstances an overturning and mingling of the whole mass 

 of water in a lake may take place with almost incredible sud- 

 denness. 



Although no attempt was made to keep a systematic record 

 of other organisms than Crustacea, some notes were kept of the 

 appearance of other animals and of plants. 



