North American Species of Diaptomus. 135 



margin with a cushion-like protuberance densely covered with 

 minute hairs. This segment is produced into two spines, 

 forming a forcipate structure. The inner spine is slightly 

 shorter than the main part of the segment, thick, incurved, 

 and movable, and armed on its outer margin and on the distal 

 third of the inner one with minute hairs. The outer spine is 

 immovable, ending in a blunt point, and its curve is rather 

 more pronounced than that of the inner one. 



Inner ramus of left fifth foot one-segmented, straight, and 

 armed with minute hairs at the apex. It is about three times 

 as long as broad and reaches beyond the middle of the second 

 segment of the outer ramus. 



First basal segment of the fifth foot of the female (PI. XXV., 

 Fig. 1,-2") subquadrate, slightly longer than broad, bearing 

 a short thick spine near the outer distal angle. The distal 

 segment is also subquadrate and bears the usual delicate hair. 

 Outer ramus two- jointed, the first segment oblong, about 

 twice as long as wide ; second segment in the form of a thick 

 incurved hook, with a broad, quadrate basal portion. The 

 hook is about three times as long as its greatest breadth, the 

 distal fourth of the inner edge armed with a variable number 

 of teeth (8-15). Third segment wanting, represented by two 

 spines ; the outer short, thick, about one third the length of 

 the segment ; the inner rather longer and more slender, sin- 

 uously curved, and about half as long as the second segment. 



Inner ramus of fifth foot of female straight, one-segmented, 

 about four times as long as broad ; armed at the tip with two 

 smooth spines of almost equal length and but slightly curved. 

 The tip of the ramus is delicately hairy. 



Length of female 1.4-2.12 mm; of male l.-2."mm. 



Breadth of female .4-.43 mm; of male .3-.33 mm. 



The synonymy of this species is almost as complicated as 

 that of D. leptopus. First described by Dr. Forbes (76), it 

 was next described under two different names (D. sanguineus 

 and D. minnetonka) by Herrick ('84). I am also led to 

 believe very strongly that Herrick's D. armatus is nothing 

 but a variant of D. sanguineus. The descriptions and figures 

 (Herrick, '82, p. 223, Fig. 1, a and b) seem to me to be 



