Marsh — North American Species of Diaptomus. 463 



The fifth feet of the male are slender. The first basal seg- 

 ments are armed Avith the customary spines. The second basal 

 segment of the right foot is trapezoidal in form and longer than 

 broad. The rather long lateral hair is situated at about two- 

 thirds of its length. The first segment of the exopodite is 

 quadrate, its length considerably less than its width. The 

 length of the second seginent is somewhat greater than the 

 combined lengths of the second basal regment and the first 

 segment of the exopodite. The lateial spine is situated beyond 

 the middle of the segment. The terminal hook is symmetri- 

 cally curved and is considerably longer than the first two seg- 

 ments of the exopodite. The endopodite is triangular in form, 

 much longer than the first segment of the exopodite, and is 

 sometimes indistinctly tAvo-segmented. 



The second basal segment of the exopodite of the fifth foot 

 of the male has its rather long lateral hair situated almost at 

 the distal angle of the segment. The first segment of the ex- 

 opodite is about as long as broad, its inner and outer margins 

 curved, the inner margin setose on its distal third. The second 

 segment is half again as long as broad, the inner margin ex- 

 panded at the base and at the distal end and setose. The dis- 

 tal end is setose and armed with two finger-like processes. The 

 endopodite is slender, reaches well towards the tip of the 

 second segment of the exopodite, and is setose at the tip. 



Length of female, about 1.187 mm. Length of male, about 

 1.137 mm. 



This species was found in material collected for me by Pro- 

 fessor B. H. Brow^n in Walla Walla, Washington. 



The close relation of this form to D. signicauda is apparent. 

 In the female there are distinctiv^e dift'erences. In the male, 

 however, the structure of the antepenultimate segment of the 

 right antenna and of the fifth foot are so difterent that I think 

 the validity of the species cannot be questioned. The lateral 

 lamella of the antennal segment I have never found in D. sig- 

 nicauda, while it is characteristic of D. wa^hiiigtonensis. The 

 whole male fifth foot is much shorter and stouter in D. wash- 

 ingtonensis, the first segment of the right exopodite has no hya- 



