386 Wisconsin Academy of Sciences, Arts, and Letters, 



generally speaking, the species of this genus adapt themselves 

 to variations of climate only to a limited extent. 



Third, if climatic conditions tend to produce new species, 

 the more recently developed species would be in the south un- 

 der warmer temperature conditions, and in the west where 

 isolation as well as climate comes in as an important factor. 



Some emphasis should be placed on the effect of isolation, 

 for experience shows that the distribution of Dlaptomi is 

 brought about largely, if not entirely, by actual water carriage. 

 It is, of course, possible that birds and winds may carry the 

 animals or their eggs in some cases, but this is not an ordinary 

 method. This is shown by the fact of tlie isolation of partic- 

 ular species in certain lakes. For example, D. Beighardi oc- 

 curs in lakes in the Beaver Islands, but not in Lake Michigan 

 close by. D. Birgei has been fomid in but one locality in Wis- 

 e-onsin; this also is true of D. siciloides, which is found only 

 in Cedar lake, Washington county. There may be other local- 

 ities for these species, but Wisconsin has been pretty thorough- 

 ly explored without finding them. 



DISTRIBUTION OF SPECIES. 



I have recognized thirty-four species of Diaptomi in j^orth 

 America, distributed as follows. It is to be understood that 

 these are simply the known localities, &nd it is possible in 

 many cases that the distribution is much wider. Anything 

 like thorough collections have been made only in Illinois, Mich- 

 igan, Wisconsin and Indiana. Many collections have been 

 made in the states in the Mississippi valley, and scattered col- 

 lections in the mountain regions of the West. The immediate 

 vicinity of Lincoln, Nebraska, has been explored by the De- 

 partment of Zoology in the University of Nebraska. I have 

 only one set of collections from the ISTorthwest Territory. The 

 lakes of the eastern LTnited States are unexplored. 



D. alhuquerquensis, New Mexico, Mexico, Colorado. 



D. Ashlandi, Idaho, Washington, Great Lakes, Indiana, 

 Michigan, Wisconsin, Oregon. 



