476 Birge—Vertical Distribution of Pelagic Crustacea. 
mens to each series of observations, but the number was very 
irregularly distributed. The irregularity, however, was of a 
somewhat uniform nature, comparatively large numbers being 
obtained at occasional intervals throughout the month. The 
largest individual numbers were taken in the upper level. One 
of these catches yielded as many as 25 individuals, another 21, 
and a third 15. The lower levels were practically without this 
form. All of the single catches containing more than 6 speci¬ 
mens in the upper levels were made at night. This would indi¬ 
cate a rise of Leptoclora by night, were it not for the fact that 
none of the day catches show any corresponding numbers of the 
species at greater depths. 
The larva of a species of Chironomus was found in very 
small numbers, the total number counted in the 59 sets of ob¬ 
servations being only 105. The largest individual catches were 
obtained in the upper 6 m. The largest number caught was 12 
•on July 27. 
The larva of a species of Corethra was the most abundant animal 
except those which have been regularly tabulated. Nearly 2000 
were obtained during all our observations, an average of 33 ani¬ 
mals per series. The average number per series in Period I 
was about 13; in Period II, 18; in Period III, 80, and in Pe¬ 
riod IV, 22. An enormous number of this species was obtained 
in a few catches on the 28th of July, where the larvse were 
found in comparatively large numbers throughout the entire 
vertical distance. The largest number was 148, 85 of which 
came from the 6-9 m. level. The numbers taken are too small 
and too irregularly distributed to say anything definite regard¬ 
ing the vertical distribution, beyond the general fact that a 
large number of this species proportionately was found in the 
lower levels of the lake. It was not at all uncommon for the 
dredge to contain perhaps a dozen Crustacea from the lower 
levels, and one or two specimens of Corethra. 
Daphnia Kahlbergiensis , var. retrocurva , Forbes, our represen¬ 
tative of the section Hyalodaphnia, was found very sparingly. 
Only two or three specimens were seen during the entire 
month. 
Chydorus sphaericus O. F. M., one of the most abundant of 
