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 Diaptomi 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 the isolation of partic¬ 
ular species in certain lakes. For example, D. Reighardi oc¬ 
curs in lakes in the Beaver Islands, but not in Lake Michigan 
close by. D. Birgei has been found in but one locality in Wis¬ 
consin; 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 North 
America, distributed as follows. It is to be understood that 
these are simply the known localities, and 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 Northwest Territory. The 
lakes of the eastern United States are unexplored. 
D. albuquerquensis, New Mexico, Mexico, Colorado. 
D. Ashlandi, Idaho, Washington, Great Lakes, Indiana, 
Michigan, Wisconsin, Oregon. 
