Marsh — North American Species of Diaptomus. 423 



two segments, the third segment being represented by two 

 spines. The second segment is prolonged into the customary 

 hook, which is very finely denticulate on the inner margin. 

 The endopodite slightly exceeds in length the first segment of 

 the exopodite, is delicately hairy at the tip, and is armed with 

 two rather short terminal spines. 



The first basal segments of the male fifth feet are armed with 

 large spines. The second basal segments are rudely trapezoidal 

 in form with the inner margins curved, and wdtli the lateral 

 hairs situated at about one-third the length of the segments from 

 the distal ends; the segment of the right foot is considerably 

 larger than that of the left. The first segment of the exopo- 

 dite is quadrate, its length and breadth being nearly equal. It 

 bears upon the outer distal angle a rounded hyaline lamella, 

 and another rounded hyaline lamella projects on the posterior 

 surface from the distal part of the segment; this lamella pro- 

 jects slightly over the second segment of the exopodite. The 

 second segment is much shorter than the combined length of the 

 first segment and the second basal segment. The lateral spine 

 is situated at about three-fourths its length. The terminal hook 

 is falciform, and about a third longer than the two segments of 

 the exopodite. The endopodite is slender, hairy at the tip, and 

 slightly exceeds in length the first seginent of the exopodite. 

 The two segments of the left exopodite are rudely oval in form, 

 about equal in lengtli. The inner margin of the terminal seg- 

 ment and the distal third of the inner margin of the first seg- 

 ment are ciliate. The second segment bears two short finger- 

 like processes. The left endopodite is slender, reaching nearly 

 half the length of the second segment, and is indistinctly two- 

 segmented. 



Length of male, 1.195 mm. jSTot enough mature females 

 were secured to get an average of lengths. 



This species was found in material collected by Mr. Russell 

 T. Congdon in Glen lake, Saskatchewan. 



The noticeable peculiarities which distinguish this from other 

 forms are the elongated female abdomen, without lateral spines, 

 and the hyaline lamellae of the first segnnent of the exopodite 

 of the right male fifth foot. 



