380 Wisconsin Academy of Sciences, Arts and Letters. 



cera. Doubtless more careful and prolonged collecting would disclose 

 new species in both bodies of water, but the larger lake is certainly- 

 poorer in number of forms, especially the littoral species. The pelagic 

 forms are, of course, more abundant in the larger lake, and one variety- 

 has been found in Lake Mendota which Lake Wingra does not possess. 



This single locality has yielded a number of species, comparing not 

 unfavorably with the fauna described from England, Denmark or Russia. 

 No European country shows more than 100 species; so that more than 

 one-half of the probable fauna of Wisconsin has been found here. That 

 so large a fraction of the entire fauna should belong to one locality will 

 not appear strange when the similarity of the fauna to that of Europe is 

 considered. If the species of Cladocera have so wide a range as appears 

 from Sar's observations on Australian Cladocera, and from my work 

 here, it is not probable that many species are strictly local. We should 

 expect to find any given species over a large extent of country in suita- 

 ble localities. This expectation has been realized in many cases. As 

 conspicuous instances I may note the occurrence of Drepanothrix 

 dentata, Euren, in Wisconsin, the finding of Dunhevedia setiger, Birge, 

 in Hungary by Daday, and the occurrence of Ilyocryptus longiremis, 

 Sars, in Wisconsin and in Australia. No doubt some species are strictly 

 local, confined to a small area, or the product of life-conditions existing 

 there and not elsewhere. But the chance that this is true in any given 

 case is small, and all well marked species should be looked for in every 

 suitable locality. We should expect also that a locality especially favor- 

 able to the development of the Cladocera would contain a very large 

 fraction of the fauna of the region. 



The subjoined list also shows the value of long and careful collecting 

 in one locality, and the impossibility of justly estimating the Cladocera 

 of a lake from a single visit. The different forms behave much like the 

 plants of a locality. Some species are present throughout the season. 

 Some can be found only for a few days. Some come in the spring and 

 disappear early, while others belong to the latter part of the open season. 

 Of the nearly sixty species found in Lake Wingra I have never found 

 more than thirty as the result of a single day's work. It is clear that a 

 list of Cladocera compiled from a flying visit to a locality and containing 

 from six to twenty species, has no claim to represent the fauna of that 

 locality. Only careful collecting at intervals throughout an entire sea- 

 son can give even an approximate idea of the number of species 

 present. 



I may add that a single specimen was found in Lake Wingra, belong- 

 ing to the genus Anchistropus, Sars, and apparently not to the species 

 emarginatus, Sars. It was accidentally destroyed before it could be 

 carefully studied. 



