202 
Marsh—Limnetic Crustacea of Green Lake. 
Birge a set of serial temperatures was taken with the thermo¬ 
phone September 3, 1896, which seemed to show that at that 
time the “sprungschicht ” was located at about fourteen meters 
below the surface. Probably its location does not change ma¬ 
terially during the summer months. In looking over the collec¬ 
tion of Limnocalanus , I find that during the summer months it 
is found mostly below the fifteen meter level, its distribution 
becoming gradually more general in the fall, and continuing so 
until the late spring. This leads me to infer that the vertical 
distribution of the Linnocalanus varies nearly as the " sprung¬ 
schicht” varies. 
C. brevispinosus did not occur in large numbers in any of the 
serial collections. The largest number obtained at one time 
was 291, on June 6, 1895. In both 1895 and 1896 its occurrence 
was confined almost entirely to the month of June. It was found 
in both May and July, but only in small numbers. At other 
times I have found it in G-reen Lake in August, but it must be 
comparatively rare at that time, for in my serial collections in 
1893 I did not find a single individual. I have found it in the 
Michigan lakes, too, in July and August. 
In regard to its vertical distribution, it appears to be most 
abundant from five to twenty meters in depth. In the upper 
five meters only a few are found, and they do not go below 20 
to 25 meters to any extent. 
