192 Marsh — Cyclopidoe and Calanidm of Wisconsin. 



adapt themselves to change of environment with little percep- 

 tible change of structure. Thus Cyclops pulchellus Koch, is a 

 common pelagic form of the larger lakes, and seems well adapted 

 to its environment, but I have found it in Rush Lake, a reed- 

 covered, shallow body of water, in which we would hardly 

 .expect to find any distinctive pelagic fauna. 



It is to be noticed that the American species of Diaptomus 

 are distinct from those of Europe, and that they are, in some 

 cases, quite limited in their distribution. 



The pelagic species are generally colorless, and the body and 

 appendages are more elongated than in the littoral forms. 

 When a species occurs both in shallow and in deep water, the 

 same difference is noted, the pelagic forms in some cases form- 

 ing well marked varieties. 



The species of shallow water and stagnant pools are fre- 

 quently highly colored, but the color is generally of little 

 value in distinguishing species. Quite generally all the cope- 

 poda and cladocera of a pool have the same prevailing color, 

 while the same species under other conditions of environment 

 may be entirely colorless. This was noticed by Herrick in 

 1883 (25 p. 385.) Certain species, however, seem to have a 

 coloration peculiarly their own, — like the purple tips of the 

 antennae in Diaptomus leptopus. The specimens of Cyclops 

 modestus which I have found, have possessed a distinct purple 

 tinge, very different from the colors of the species with which 

 they were associated. 



In the synonomy of species I have followed the European 



authors. It seems to me next to an impossibility to identify 



the species of Koch and Baird, for their descriptions are of no 



• value whatever. All that is left for one to do is to accept 



them as defined by later authors. 



It has not been my aim to add to the already sufficiently 

 numerous descriptions of "new species, " but rather to make 

 more clear the descriptions already given, to indicate the 

 proper synonymy, and to reduce the number of specific names 

 rather than to increase them. In doing this, I know I have 

 laid myself open to criticism, for it is, perhaps, presuming too 

 much to revise another author's descriptions. My only excuse 



