480 Wisconsin Academy of Sciences, Arts, and Letters. 
Corethra punctipennis. The average number of Corethra larvae 
is shown for the different months of the year in table 11. The win¬ 
ter population of this form at station I was much smaller than at 
the other stations. In 20 samples obtained from October to April, 
inclusive, at station I, the average number of these larvae is 9,605 
individuals per square meter. During these same months 30 sam¬ 
ples taken at station II yielded an average of 21,170 larvae per 
square meter, while, in the same period, 74 samples from the five 
regular stations in the deep water gave an average of 17,425 Cor- 
thra larvae. In general, then, it may be said that the population 
of Corethra larvae at station I was about half as large from Octo¬ 
ber to April as it was at the stations in the deeper water. The 
August population at station I was also lower than the general 
average of the other stations combined, but it was larger than the 
August population of station II in 1917 and smaller than the 
August population of 1918. 
Protenthes choreus. These larvae were much more abundant at 
station I than at the deep water stations (table 13). These larvae 
were not counted in the January sample from station I, but in the 
other months the averages were distinctly larger at station I than 
at the other stations, except in April. 
The live weight and dry weight of the various forms found at 
station I are shown in the second part of table 15. The amounts 
have been calculated on the same basis as those for the five stations 
in the deeper water, that is, on the general average of Oligochaeta, 
Pisidium, and Chironomus, and on the April crops of Corethra 
and Protenthes. The results for the two regions are thus directly 
comparable. The dry weight of Pisidium and Protenthes was sub¬ 
stantially the same at station I as at the five stations in the deeper 
water, but that of the Corethra larvae was very much smaller and 
that of Limnodrilus and Tubifex was smaller. Chironomus, on the 
other hand, gave a larger amount of dry material at station I than 
the average for the other stations. The total quantity of dry mat¬ 
ter in the bottom population at station I amounted to 53.8 kilo¬ 
grams per hectare, while the other stations yielded an average of 
76.6 kilograms per hectare. The former is only about 70 per cent, 
as large as the latter. 
