882 THE AMERICAN NATURALIST. [Vor. XXXIV. 
found in lakes Wingra and Mendota was given in “ List of 
Crustacea Cladocera from Madison, Wis.," by Professor Birge 
in 1875, while Herrick ('81) has described several forms which 
plainly belong to this species. Later observation led to the fact 
that “almost every lake possesses its own variety of D. hya- 
lina” ; and with this in mind Professor Birge, several years 
ago, gave me collections from a number of our lakes, and sug- 
gested that I study the different forms, their relations to one 
another and to the various European types. The material 
was all pelagic and collected from various parts of Michigan 
and Wisconsin. The lakes differ widely in character, from the 
small, reed-bordered Lake Wingra, or shallow Winnebago with 
its sandbars, to lakes like Mendota, of far greater depth, and 
whose shores slope from precipitous bluffs. 
In general, the forms are remarkable for their close resem- 
blance to the varieties of Europe, every variety but one being 
represented here; while several differ widely from any thus far 
described for Europe, but correspond in external appearance - 
to the American representatives of widely different European 
species. Thus, while some European varieties of D. hyalina 
vary in the direction of the Kahlbergiensis, our forms vary to 
correspond with the American species Retrocurva and Brevi- 
ceps. The transitions between the different types are suffi- 
ciently gradual to connect them with the original D. hyalina 
Leydig, thus seeming to confirm what has heretofore been, in 
a measure, assumed by other writers, — that the form first 
discovered is the one from which the others have departed. 
Following is a diagram (Fig. 2) representing the deviations 
from an assumed central form found in Lake Wabasis, Michigan, 
while the table on page 884 gives the principal characters in 
which the varieties are observed to differ. Each variety is 
named from the lake where it occurs. 
