326 Illinois State Laboratory of Natural History. 



In the above numbers Minnesota takes the lead with 82 

 species, owing to the extended study of the microscopic forms 

 by Prof. C. L. Herrick. Massachusetts with 48 and Wisconsin 

 with 34 owe much to the study of the Cladocera by Prof. E. A. 

 Birge. Illinois with 30, to which might properly be added 

 most of the 15 of Lake Michigan, shows the careful research 

 of Prof. S. A. Forbes. Other states owe their relatively high 

 rank to the elaborate monograph of the Astacidae, by Dr. 

 Faxon, that has recently appeared. The contrast between the 

 States above mentioned and others shows the nature of the 

 work for future investigators. When we consider that twenty- 

 seven of the above States and territories do not exceed ten 

 species (seventeen not exceeding five), and add Delaware, 

 Nevada, Arizona, and Indian Territory, from which no species 

 have been reported, we can begin to realize how meagrely the 

 group has been studied. There ought to be a response by some 

 one, or by many, from all these neglected regions. 



Of the seven orders the Copepoda* Ostracoda and Clado- 

 cera, including all the microscopic forms, have been studied 

 only in the eastern half of the United States, if we except six 

 species reported from Colorado by Chambers. In sharp con- 

 trast with this ; 20 of the 34 Phyllopoda are known only west 

 of the Mississippi River. Of the 17 Amphipoda four extend to 

 Colorado, five to the Southern States, while the remainder seem 

 confined to northern waters. The Isopoda and Decapoda are 

 more uniformly distributed, and with the PTiyllopoda extend 

 to the Pacific coast. 



The largest genera are Cambarus, with 50 species, Cyclops 

 with 21 species, Daphnia with 15 species, Porcellio with 15 

 species, Cypris with 11 species, all the rest falling below 10. 

 Forty-one of the 88 genera are represented by a single species. 



In the preparation of this list the compiler has been 

 greatly aided by kind-hearted zoologists who have furnished 

 copies of their papers, cited references, corrected synomymies, 

 and otherwise contributed to the completeness of the list. 

 Their generosity entitles them to public thanks by the compiler 

 and by all who may use this list when published. Their names 



*This remark does not properly apply to the parasitic forms, as 

 some species have been reported from the Pacific coast. 



