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-J-. 
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-J-. 
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. 
