North American Species of Diaptomus. 159 



first caudal segment of the female is very characteristic of the 

 species (in the male it is of the ordinary form) and, unlike 

 that of D. signicauda, surpasses in length the rest of the 

 abdomen. This segment is provided at the anterior part on 

 both sides with a short and mucronate lateral process, and at 

 the posterior part with a large triangular process extending 

 almost directly toward the right, with apex slightly acumi- 

 nate. F ureal rami rather short, not twice as long as broad. 



" First pair of female antennae 25 -segmented, almost reach- 

 ing the base of the furca. The antepenultimate article of the 

 prehensile male antenna (PI. XXXI., Fig. 1) armed with an 

 almost straight and rather slender process reaching almost 

 to the middle of the penultimate article, and provided with- 

 out with small teeth. 



" Outer ramus of the fifth pair of feet in the female (PL 

 XXXI., Fig. 5) two-segmented; the unguiform process of the 

 second segment slightly curved, robust, moderately ciliate 

 within and at the middle part, last cilium broad, spine-like. 

 Third segment wanting, produced into two short spines, the 

 outer half as long as the inner. 



"Inner ramus one-segmented, almost equal to the first seg- 

 ment of the outer ramus ; apex obliquely acuminate, pro- 

 vided with two rather long subequal spines. 



" Second segment of the outer ramus of the right fifth foot 

 of the male (PI. XXXI. , Fig. 4) very long, longer than the 

 first segment and the basal segment taken together. Margi- 

 nal spine of this segment inserted above the middle. Termi- 

 nal hook slightly curved, inner margin ciliate. 



" Inner ramus curved, ovate, broad, pointing inward, with 

 mucronate apex, barely reaching to the end of the first seg- 

 ment of the outer ramus. 



" First and second segments of the outer ramus of the 

 left foot ciliate within, the second one obovate, hirsute toward 

 the apex, and bearing two short spines one of which points 

 inward. 



" Inner ramus one-segmented, slender, equal to the first 

 segment of the outer ramus." 



"Length of female about 1.5 mm. ; of male 1.4 mm. 



