1894.] i Zoology. 809 
Limnocalanus macrurus rarely, if ever, comes to the surface, and is 
found most abundantly within.20 meters of the bottom. Nordqvist 
states that he found L. maerurus in Finland, in June, most abundant 
at twelve meters below the surface, where the total depth was 25 to 26 
meters. j 
Pontoporeia and Mysis live at the bottom, and belong to the true 
abyssal fauna. : 
In regard to the diurnal migrations of the pelagic species, I found it 
difficult to fix any exact limits. As has been before stated, they come 
to the surface at night. In the daytime, few of them go below ten 
meters. Daphnia kahlbergiensis, however, seems to be an exception, 
for, apparently, its migrations are limited only by the depth of the 
lake, and sometimes from 40 to 80 per cent are in the last ten meters. 
As a result of these collections, I was led to doubt the value of 
“ Plankton” determinations, at least so far as crustacea are concerned, 
All such determinations must start with the assumption that the life of 
the deeper waters is distributed uniformly. If this were true, succes- 
sive hauls in the same depth of water would contain approximately the 
same number of individuals. This was far from the case in my collec- 
tions. The position in the successive collections varied only as the 
boat drifted very slowly; yet the number of Diaptomi varied from 
291 to 2,966 ; Daphnella from 0 to 122; Daphnia kahlbergiensis from 6 
to 103, and Epischura from 7 to 105. It seems probable that they are 
present in swarms, and that the positions of the swarms are continually 
changing. 
Zacharias, in his last report from the biological Station at Plón, has 
reached the same conclusions, not only in regard to the crustacea, but 
also the other pelagic organisms. “Plankton” determinations, in order 
to have much value, must be almost infinite in number. 
Beginning with the fall of 1894, systematie work of a more detailed 
character will be carried on at Green Lake, as the Trustees of Ripon 
College have made an appropriation for the purpose. 
—C. Dwicur Marsa, Ripon College, Wisconsin. 
Rotatoria of the Great Lakes.—The Michigan Fish Commis- 
sion have issued, as Bulletin No. 3, a list of the Rotatoria found in 
Lake St. Clair and some of the inland lakes of Michigan, prepared by 
Mr. H. S. Jennings. Of the 122 rotifers named in the list, 6 are here 
described and figured for the first time. Strongly swimming forms, 
commonly found in the open water, are designated pelagic ; those found 
among the vegetation of the shores and bottom, littoral. Of the former, 
