1894.] Zoology. 809 



Limnoealanus 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. macrurus in Finland, in June, most abundant 

 at twelve meters below the surface, where the total depth was 25 to 26 

 meters. 



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 

 u 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 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 Plon, 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, systematic 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. Dwight Marsh, 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, 



