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. 



Br'achionus angularis Gosse, 



var. bidens Plate 

 bakeri Ehrbg. 



" var. bidentatus Anderson 

 " brevispinus Ehrbg. 

 " cluniorbicularis Skorikow 

 " melhemi Barrois and v. Daday 

 " obesus " 

 " rhenanus Lauterborn 

 " tuber culus Turner 

 budapestinensis v. Daday 

 militaris Ehrbg. 

 mollis Hempel 

 pala Ehrbg. 



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