Marsh—North American Species of Diaptomus . 437 
denticulate on its inner margin. The endopodite is one-seg- 
rnented, conical in form, slightly exceeds in length the first seg¬ 
ment of the exopodite, and is setose at tip. 
The left fifth foot of the male reaches slightly beyond the 
first segment of the right exopodite. The second basal segment 
is quadrate, considerably smaller than the corresponding seg¬ 
ment of the right foot. The lateral hair is situated near the 
distal end of the segment. The first segment of the exopodite 
is twice as long as broad, narrowing to the distal end. The 
outer margin is curved, and the inner has a rounded elevation 
at its middle. The second segment is slightly longer than the 
first. It is setose, especially on its inner surface. It is ter¬ 
minated with a long finger-like process, which is apparently 
jointed, and a slender falciform process on the inner side. The 
endopodite is one-segmented, slender, conical, setose at the tip, 
and extends to nearly one-half the length of the second segment 
of the exopodite. 
Length of female, 1.31 mm. Length of male, 1.22 mm. 
The original description of this species was from material 
collected by Professor Birge near Hew Lisbon, Wisconsin. 
Very few individuals were found, but as it seemed so distinct 
in its characteristics from any other American species, there 
was no hesitation in describing it. As time went on, however, 
and no other specimens were found, although the state of Wis¬ 
consin was pretty thoroughly explored, it became a question 
whether it were not an abnormal form. It was something of 
a relief to the author, therefore, when the identical form was 
found in material collected by Mr. Chauncey Juday in Wino¬ 
na lake, Warsaw, Indiana. In Mr. Juday’s collections it 
was present in considerable numbers, associated with D. ore - 
gonensis. The two species were easily separated, as D. Birgei 
is distinctly larger than D. oregonensis. 
In the fall of 1904 I collected the species at Richmond, 
Indiana, and, just as I was finishing the preparation of this 
report, I found it in material collected by Professor H. S. 
Pratt at Cold Spring Harbor, Long Island. It is not likely 
that it occurs in many other Wisconsin localities, for pretty 
