Poul 
cornuta’’ in 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. 
Ceriodaphma megops 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 17, and the latest is September 21. Females with summer 
eggs were found in June—September. 
Certodaphnia 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 
