6 Wisconsin Academy of Sciences , Arts and Letters . 
ber of individuals thus hatched were raised to maturity and 
sent to Dr. C. Dwight Marsh for identification. He identified 
them as C. bicuspiclatus Clans. This is the same species which 
Dr. Marsh formerly called C. pulchellus Koch and so reported 
in his paper on the plankton of Lake Winnebago and Green 
Lake, and in other publications. He now agrees with Schmeil 
in rejecting Koch’s name for the species. 
Marsh (’03, p. 27) reports that C. pulcheHlus ( bicuspidatus ) 
is found as a summer limnetic form in the Chain of Lakes, 
Lakes Geneva, Elkhart, Cedar, Birch, Stone, Sand, Michigamme 
and Long (Bond du Lac County). It is the common limnetic 
form in the Great Lakes, and is found in Lake Winnebago 
from October to June only, being absent in summer. Eromthis 
statement, and from the facts as ascertained in Lake Mendota, 
it would appear that the species prefers cool water, that it 
might live in an active state throughout the year in any lake 
whose deeper and cooler water was such as to afford it a refuge 
during the summer, and that it would become encysted in lakes 
where the oxygen disappeared from the lower water in the 
summer. The facts, however, are much more complex and 
puzzling. 
This Survey has determined the amount of oxygen in the 
Chain of Lakes, Lakes Geneva, Elkhart, Stone and Sand. It 
is abundant throughout the summer, except in Kainbow Lake 
(one of the Chain of Lakes), where it almost disappears in 
September, and even in this lake there remains a cool stratum 
of water with sufficient oxygen. Sand Lake is shallow, only 
9.5 meters deep, with a bottom temperature of 18.7° C. on 
August 22, 1907; only slightly below that of the surface. It 
is, therefore, of a type wholly different from the other lakes 
and more closely resembles Lake Winnebago, which is a very 
large, shallow lake and is nearly homothermous. In one of 
these lakes, however, the species disappears during the sum¬ 
mer, while in the other (Sand Lake) it remains active and no 
cocoons could be found in mud from the bottom. Ho cocoons 
were found in mud from Stone Lake, while mud taken in Bain- 
bow Lake on June 29, 1907, contained them. 
