28 Illinois State Laboratory of Natural History. 



been used for the separation of species by our most emineni 

 workers. 



I have made a vigorous effort to obtain authentic examples 

 of all the species considered; and while I have been in 

 general successful, f have been forced in the case of Herriek's 

 species to depend wholly upon the collections to which I have 

 had access myself, and the identifications of other men who 

 have collected in Herriek's localities. 



The collections which I have had an opportunity to study 

 in the preparation of this paper are those of the Illinois 

 State Laboratory of Natural History, extending over a period 

 of more than twenty years ; several made under the auspices 

 of the l". S. Fish Commission in Wisconsin and in the far 

 West ; collections made in Florida by Mr. Adolph Hempel and 

 in Manitoba by Prof. L. S. Ross, of Drake University, Iowa, 

 and kindly loaned me by these gentlemen ; and all of the col- 

 lections made at the Lllinois Biological Station at Havana, 

 Illinois. This material is from the following states : Massa- 

 chusetts, Florida, Ohio, Indiana, Michigan, Wisconsin, Illi- 

 nois, Kentucky, Iowa, Missouri, Minnesota, Idaho, Wyoming, 

 Washington, and Oregon, and from Manitoba, in the Domin- 

 ion of Canada. 



The localities represented by these collections are widely 

 distributed and of great variety. They extend from the 

 New England states in the northeast to Florida in the south- 

 east, to Manitoba on the north and to Washington and Oregon 

 in the northwest, and from the sea-level in Massachusetts 

 and Florida to some of the highest lakes in the Rocky and 

 Sierra Nevada Mountains. In these collections are Cyclops 

 from small temporary points of a few weeks' duration, from 

 the greatest lakes and rivers in the world, and from a great 

 number and variety of situations intermediate in character. 

 They have been made in every season -of the year; and 

 although the southwestern part of the United States is not 

 represented, they probably contain nearly all of the American 

 species of the genus. 



The results published in this paper do not, however, repre- 

 sent an exhaustive study of the distribution of the species 



