North American Species of Diaptomus. 177 



" Outer ramus of the fifth pair of feet in the female Inarticu- 

 late ; unguiform process of the second segment almost parallel 

 to the first segment, slightly curved within and minutely ciliate 

 on the inner margin, the last cilia spine-like. Inner ramus 

 simple and slender, about equal to the first segment of the 

 outer ramus ; armed at the outer margin and near the apex 

 with two medium- sized spines ; apex obtuse and finely hairy. 



"Eight fifth foot in the male slender and of medium size. 

 First segment of the outer ramus with a small hyaline lamella 

 near the inner apical angle. Second segment comparatively 

 small and strongly curved ; the outer marginal spine at about 

 the middle. Terminal hook slightly sigmoid; inner margin 

 smooth. Inner ramus minute and simple, not reaching the 

 end of the first segment of the outer ramus. 



" Second segment of the outer ramus of the left foot of the 

 same pair almost triangular ; inner margin slightly sinuate 

 and ciliate and armed with two obtuse processes (one apical, 

 the other lateral). Inner ramus indistinctly two-segmented 

 extending about to the middle of the second segment of the 

 outer ramus ; minutely hairy within and at the apex. 



"Length of female 1.9 mm.; of male 1.8 mm."* 



" This Diaptomus is distinguished from all its related forms 

 by the large lateral lobes of the last thoracic segment. These 

 lobes, seen from above, are acuminate, but seen from the side, 

 the posterior extremity is obtuse and armed with two spines. 



" The first abdominal segment is remarkable on account of 

 its long, strong, pointed processes. 



" The female of this species slightly resembles 1). ambiguus 

 Lillj., from Behring Isle, but the lateral projections of the 

 first abdominal segment are wanting in the latter. ]>. tyrrelli 

 differs from most other American species in the absence of a 

 prolongation on the antepenultimate article of the male pre- 

 hensile antenna. 



"The first specimens of this copepod were collected in 

 Summit Lake, in the Eocky Mountains, at a height of 5,300 

 feet, and sent to Herr S. A. Poppe by Mr. J. B. Tyrrell, of 

 Ottawa, Canada. 



*Lilljeborg's description from de Ouerne et Richard, "89b. 



