Marsh — ISorth American Species of Diaptomus. 421 



strongly recurved. The Look is denticulate on its inner mar- 

 gin, the distal denticulations being unusually large. The outer 

 angle of the second segment has a small spine. The third seg- 

 ment is short, but distinct, and armed with two spines. The 

 endopodite equals in length the first segment of the exopodite. 

 It is two-segmented, and the distal segment is armed at the tip 

 with three spines, one rather stout and plumose, the other two 

 long and slender. 



The spines of the first basal segments of the male fifth feet 

 are rather small. The second basal segment of the right foot 

 is quadrate, its length being to its width as three to two. The 

 lateral hair is near the middle but on the distal portion. The 

 first segment of the exopodite is very short, its width being 

 about twice its length. The outer margin is prolonged distally, 

 and the inner margin, on the posterior face, bears a hyaline 

 lamella which is much wider at the distal end of the segment. 

 The second segment of the exopodite is twice as long as broad 

 and is quadrate in form. At about a third of its length, on 

 the posterior face, nearer the inner margin, is a small spine. 

 The lateral spine is on the outer distal angle, of medium length, 

 and nearly straight. The terminal hook is as long as the whole 

 right foot exclusive of the first basal segment, is slender, and 

 with a marked angle about midway of its length. The right 

 endopodite is two-segmented, extends something less than one- 

 half the length of the second segment of the exopodite, and is 

 tipped with tw^o small, blunt spines. The second basal segment 

 of the left foot is quadrate, about two-thirds the length of the 

 corresponding segment of the right foot. The lateral hair is 

 near the distal angle. The first segment of the exopodite is 

 long and slender, being nearly four times as long as broad. It 

 is trapezoidal in form, and bears on its inner margin a rounded 

 hyaline projection. The second segment of the exopodite is 

 very slender, and bears two finger -like processes. ISTear the 

 base on the inner margin is a prominent ciliated pad. The 

 endopodite is slender, two-segmented, reaches about midway of 

 the length of the second segment of the exopodite, and is ter- 

 minated by two minute spines. 



