163 
to a satisfactory analysis of the genus in our waters. Brachionus 
contains by virtue of variation in the hard parts of its lorica most 
excellent material for the study of the problem of variation, and its 
rapid multiplication makes possible a correlation with seasonal and 
environmental changes not often afforded. 
Evidence has accumulated in the various papers of Schmarda, 
Ehrenberg, Barrois, v. Daday, Anderson, and others who have dealt 
with the microscopical fauna in tropical regions, that this genus 
attains its greatest development in the warmer waters. It is there- 
fore not strange that Skorikow (’96) finds the genus well represented 
in the warm and shallow waters of Russia, and that the plankton of 
the Illinois River and its backwaters should contain a large and 
varied representation of the genus. 
For convenience in treatment I have arranged the individuals of 
Brachionus under the following species, without, however, intending 
to indicate thereby that they have equal claims for specific recogni- 
tion. The most of these include one or more varieties, and in desig- 
nating the varieties I have taken those forms—for example, in 
Brachionus bakeri—whose descriptions most closely fit the predomi- 
nant varieties in our waters, designating them often without com- 
plete consideration of all synonymic possibilities. In some cases 
several possible varieties have been included under one head. The 
following is the list of species with the varieties which have been 
thus separately enumerated. 
Brachionus angularts Gosse, 
% oF var. bidens Plate 
bakert Ehrbg. 
= “var. bidentatus Anderson 
2 os “ brevispinus Ehrbg. 
cluntorbicularis Skorikow 
< * ‘““ melhemt Barrois and v. Daday 
obesus “ > * 
rhenanus Lauterborn 
tuberculus Turner 
budapestinensts v. Daday 
militaris Ehrbe. 
mollis Hempel 
a pala Ehrbg. 
(12) 
