North American Species of Diaptomus. 125 



Diaptomus piscinae Forbes. (PL XXII. , Fig. 1-4.) 



Diaptomus piscinas, Forbes, '93, p. 253, PI. XLL, Fig. 22. 

 Diaptomus piscinas, Herrick and Turner, '95, p. 74, PI. V., Fig. 13. 



"A species of medium size and symmetrical proportions, 

 antennae reaching to the tip of the abdomen, cephalothorax 

 broadest about the middle, with four distinct sutures, the 

 posterior lateral angles not produced but armed with two 

 distal spines. 



"The right antenna of the male is without appendage to 

 the antepenultimate joint, and the fifth pair of legs in the 

 same sex has the inner ramus well developed on both the 

 right and left sides. The usual length is 1.75 millimeters, 

 the transverse diameter 0.45 millimeters ; the abdomen with 

 furca is a little more than one third the length of the cephalo- 

 thorax. 



" The fifth pair of legs of the female [PI. XXII., Fig. 2, 4] is 

 without especially marked characters, except that the inner 

 ramus, which reaches to the tip of the principal segment of 

 the outer, is provided with two long, stout, equal seta? more 

 than half as long as the ramus itself. The third joint of the 

 outer ramus is aborted and bears two short, stout spines, 

 and the joint preceding bears a slender spine outside the 

 base of the last. The terminal claw of this joint is simple 

 and nearly straight, viewed in the usual position. 



"In the male the fifth pair of legs [PI. XXII., Fig. 1] has 

 a considerable resemblance to the corresponding append- 

 ages of D. leptopus, from which, however, this species differs 

 by its more slender form and by the absence of the antennal 

 hook. The peduncle of the left leg is quadrate and equal in 

 length to the basal segment of the outer ramus, but is nearly 

 twice as wide. The sides of this latter segment are parallel, 

 the inner terminal angle is broadly rounded and minutely 

 ciliate, and to the outer terminal angle is attached the second 

 segment of the ramus. This segment is a trifle shorter than 

 the preceding and less than half as wide, and bears at its tip 

 a stout, blunt, conical spine, whose length is equal to that of 

 the diameter of the ramus, and within this a long flexible 



