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 Green 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. 



