Marsh — North American Species of Diaptomus. 437 



denticulate ou its inner margin. The eudopodite is one-seg- 

 mented, 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 

 eudopodite 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 jSI^ew Lisbon, Wisconsin. 

 \"ery 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 Kichmond, 

 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 



