Marsh — North American Species of Diaptomus. 4Y5 



tepenultimate segment bears a recurved, hook-shaped process, 

 which is about one-half the length of the penultimate segment ; 

 on the outer surface of this hook, and extending down the seg- 

 ment, is an inconspicuous hyaline lamella. 



The first basal segments of the female fifth feet are armed 

 with long and rather slender spines. The lateral hairs of the 

 second basal segment are short and weak. The exopodite con- 

 sists of three segments. The first segment is more than twice 

 as long as its width. The second segment has a small spine 

 'on the outer distal angle; its inner margin is only slightly 

 curved and is finely denticulate. The third segment is dis- 

 tinct and bears two spines, of which the inner is the longer. 

 The endopodite is shorter than the first segment of the exopo- 

 dite, and is one-segmented, or indistinctly two-segmented; its 

 tip is setose, two of the setae being especially prominent, but 

 hardly large enough to be called spines. 



The spines of the first basal segments of the male fifth feet 

 are long and acute. The second basal segment of the right 

 foot is rectangular and longer than broad ; the lateral hair is 

 near the distal end of the segment; on the inner margin, about 

 midway of its length, is a prominent hyaline projection with 

 a semi-elliptical outline. The first segment of the exopodite is 

 short, its length being to its breadth as one to one and one-half ; 

 on the posterior surface is a ridge running from the inner 

 margin to about the middle of the segment. The second seg- 

 ment of the exopodite is slightly longer than the combined 

 length of the second basal segment and the first segment of the 

 exopodite; the outer margin is angular; the lateral spine is 

 stout, slightly sigmoid, and is situated just beyond the angle 

 near the end of the proximal half of the segment ; on the pos- 

 terior surface of the segment, nearly opposite the distal edge 

 of the lateral spine, is a curved transverse ridge extending 

 nearly across the segment. The terminal hook is strongly 

 curved, falciform, slightly longer than the rest of the exopo- 

 dite and the first basal segment, and is finely denticulate on 

 the inner margin. The endopodite is one-segmented, about 

 twice as long as the first segment of the exopodite, and is se- 

 tose at the tip. 



