231 



cornuta" m the backwaters of the Danube at Vienna in April-January. 

 It exhibits a distinct seasonal polymorphism, with a large winter 

 form and a smaller summer one. Data as to relative numbers 

 during the year are not given. Skorikow ('02), in reviewing the 

 investigations on the plankton of Russian waters, reports B. cornuta 

 from the summer plankton of several streams, but expresses doubts 

 as to whether "sie als autopotamische Planktonorganismen anzu- 

 sehen sind oder nicht." Meissner ('03) finds B. cornuta generally 

 in the Volga and its adjacent waters in the summer plankton, with 

 largest numbers in August; and Zykoff ('03) reports it in small 

 numbers from the same stream in May- July. It is not listed by 

 Volk ('03) in the Elbe at Hamburg. 



B. longirostris occurs generally in American waters, though 

 apparently, often in small numbers. Thus Forbes ('82 and '90) 

 reports it in the plankton of Lake Michigan and Lake Superior, and 

 it appears generally in lists of Cladocera from many widely separated 

 smaller bodies of water in this country. Birge ('95 and '97) finds 

 only a few Bosmina (species not stated) in Lake Mendota, but 

 Marsh ('97) reports it (species not given) as perennial in Green 

 Lake, with a maximum in November. His records have also a 

 suggestion of an earlier pulse, in June, in which month there is a 

 sudden rise from a previous minimum. 



This partial survey of the literature of the records of Bosmina 

 in the plankton shows its wide distribution, suggests the probability 

 of great variation, necessitating caution in the description of new 

 species in this genus, and indicates a wide diversity in its seasonal 

 career even in waters with somewhat closely similar environmental 

 conditions. 



Ceriodaphnia me gaps Sars was found singly but once July 25, 

 1896, at 80. 



Ceriodaphnia reticulata Jurine was found in the plankton occa- 

 sionally, and always in small numbers, in April-September. All 

 occurrences appear at temperatures above 66, and the earliest is 

 on April 1 7 , and the latest is September 2 1 . Females with summer 

 eggs were found in June-September. 



Ceriodaphnia rotunda Straus was recorded in 1894-1895, but not' 

 thereafter. Its identification is somewhat questionable, and if 

 correct, this is apparently the first record of this species in North 

 American waters, unless it should appear that C. alabamensis 



