190 Marsh — Cyclopidce and Calanidw of Wisconsin. 



American entomostraca, made his collections in Illinois, south- 

 ern Wisconsin, the Great Lakes, and Montana and Wyoming. 

 Prof Cragin collected in eastern Massachusetts. Prof. Her- 

 rick has collected very widely through the Mississippi valley 

 and the southern states. His reports on the Minnesota Crus- 

 tacea (22, 25, 26) covered a region with a fauna nearly iden- 

 tical with that of Wisconsin. His work of exploration must 

 have been done very thoroughly, for my work in Wisconsin 

 gives me little to add in the way of new species. Because of 

 incomplete descriptions or a lack of figures, it is, in some 

 cases, however, difficult to identify his species. 



In Wisconsin the cladoceran fauna is better known than in 

 any other part of the United States through the well-known 

 work of Prof. Birge, but the copepoda have been almost en- 

 tirely neglected. 



While the number of copepods in a collection from any 

 locality is frequently very large, the number of species is 

 generally small. In pools which are swarming with individ- 

 uals, frequently there are not more than two or three species. 

 In pelagic collections there are seldom more than four to six 

 species. Of diaptomus there is ordinarily only one species in 

 a locality, although two or three species are sometimes found 

 together in pelagic collections. 



Some species ot copepods may be considered strictly pelagic, 

 and some as strictly littoral, while others are found only in 

 stagnant pools. But many species readily adapt themselves to 

 all these conditions, and with little or no change of structure 

 seem to thrive equally well wherever they may be. 



The following may be considered a fairly accurate division 

 of the species according to their habitat: 



