North American Species of Diaptomus. 165 



hump. First abdominal segment of the female very char- 

 acteristic of the species, giving to it its name. This seg- 

 ment is provided at the anterior part with short, mucronate 

 lateral processes, and at the posterior part on the right side 

 with a large process bent obliquely backward and moderately 

 acuminate. Besides this an indication of a suture is also 

 often present. The length of this segment, posterior process 

 excepted, is slightly less than the remainder of the abdomen. 

 Furcal rami hardly more than half as long as broad. 



"First pair of antennae of the female always 25-segmented; 

 reflexed, slightly surpass the furcal rami, but do not reach 

 the end of the furcal setae. The antepenultimate article of 

 the prehensile antenna of the male (PI. XXIX., Fig. 4) armed 

 with a medium-sized hook-like process. 



"Fifth pair of feet of female (PL XXIX., Fig. 5) very simi- 

 lar to the corresponding pair of I), siciloides. Outer ramus 

 two-segmented; unguiform process of the second segment 

 slightly curved, almost parallel with the first article ; very deli- 

 cately ciliate within, the last cilia thicker and spine-like. 



"Inner ramus one-segmented, longer than the first seg- 

 ment of the outer ramus ; apex obliquely acuminate and 

 ciliate, and bearing two equal ciliate spines. 



"The right fifth foot of the male (PI. XXIX., Fig. 3) rather 

 slender. First segment of the outer ramus dilated within 

 into a small hyaline lamina. The second segment as long as 

 the first article and the second basal segment together. The 

 marginal spine of the second segment is situated a little 

 below the middle. Terminal hook simply curved. 



"Inner ramus rather broad, acuminate, and short, not 

 reaching to the end of the first segment of the outer ramus. 



' The second segment of the outer ramus of the left foot 

 elliptical or oblong-ovate ; within and toward the apex very 

 delicately aculeate, and bearing two large spines, one of 

 which inclines inward. 



" Inner ramus simple and slender, but long, and extending 

 beyond the middle of the second segment of the outer ramus. 



"Length of female about 1.5 mm. ; of male, 1.3 mm. 



