476 Bivge — 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 Lejrfodora 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 Gorethra 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 larvae 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 Kyalodaphnia, 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 



