Marsh — North American Species of Diaptomus. 465 



than broad. The lateral hair is situated at about two-thirds 

 of its length and is rather long. The first segment of the ex- 

 opodite is trapezoidal in form, and its length and width are 

 about equal. It bears a thin hyaline lamella resembling that 

 in signicauda, but it is more pointed at the distal end. This 

 hyaline lamella is not inserted on the inner margin, but on the 

 posterior surface, so that as viewed from some directions only 

 the distal end is visible, although it really extends the whole 

 length of the segment. The second segment of the exopodite 

 is somewhat shorter than the combined lengths of the first seg- 

 ment and the second basal segment. The lateral spine is sit- 

 uated proximad of the middle of the segment. The terminal 

 hook is symmetrically curved, and is somewhat longer than the 

 two segments of the exopodite. The endopodite is broad, acu- 

 minate, nearly equaling in length the first segment of the exo- 

 podite. The second basal segment of the left fifth foot of the 

 male has the rather long lateral hair siituated almost at the 

 distal angle of the seginent. The first segment of the exopodite 

 is slightly longer than broad, has its inner and outer margins 

 curved, and is setose on the distal third of its inner margin. 

 The second segment is nearly three times as long as broad, and 

 has the inner margin expanded near the base and setose. It 

 terminates in two finger-like processes, one of which is much 

 larger than the other. The endopodite is long and slender, 

 reaching two-thirds the length of the second segment of the 

 exopodite. 



Length of female, 0.93 mm. Length of male, 0.9 mm. 



This form was found in material collected by Mr. Chauncey 

 Juday in Twin lakes, Colorado, and the name is given in rec- 

 ognition of the many collections which Mr. Juday has had 

 the kindness to send to me. The species in most respects 

 bears a very close resemblance to D. signicauda. The male 

 fifth foot differs in the proportions of the segments, the form 

 of the lamella of the first segment of the right exopodite, the 

 position of the lateral spine on the second segment of the same 

 exopodite, and in the form of the segment and the terminal 

 processes of the second seg-ment of the left exopodite. The 

 30— S. & A. 



