Marsh — North American Species of Diaptomus. 419 



to tlieir breadth as one and one-half to one; they are ciliate on. 

 both inner and outer margins. 



The first pair of antennae in the female are 25-segmented,. 

 and reach about to the furca. The antepenultimate segment 

 of the right antenna of the male bears an unguiform process, 

 slightly longer than the penultimate segment. 



In the female fifth foot, the exopodite is three-segmented. 

 The first segment is somewhat elongate, its length being nearly 

 three times its width. The second segment is prolonged into 

 the customary hook. The hook is arcuate, denticulate on the 

 inner margin, the last tooth being the largest. The segment 

 bears a small spine at its outer distal angle. The third seg- 

 ment is small but distinct, and bears two small spines. The 

 endof)odite is one-segmented, about equal in length to the first 

 segment of the exopodite, and bears at the tip two unusually 

 long spines which are ciliate at base. 



In the male, the second basal segment of the right foot is 

 quadrate, longer than wide, and bears the lateral seta a little 

 beyond the middle. The first segment of the exopodite is 

 quadrate and short, being only about one-half the length of the 

 second basal segment. The second segment is rectangular, 

 rather less than twice the length of the first ; the lateral spine 

 is situated at the distal angle, and about midway of tlie inner 

 margin there is a minute spine. The terminal hook is long, 

 equaling the whole right foot exclusive of the first basal seg- 

 ment, is sigmoid, and slender towards the apex. The endo- 

 podite is small, barely reaching the middle of the second seg- 

 ment of the exopodite, is imperfectly two-segmented or one- 

 segmented, and bears a spine at the apex. 



The left fifth foot of the male reaches about t-o the middle 

 of the second segment of the exopodite of the right foot. The 

 second basal segment is longer than broad, shorter than the cor- 

 responding seginent of the right foot, is concave on the outer 

 margin and convex on the imier; the lateral hair is situated 

 at about three-fourths of its length. The first segment of the 

 '^xopodite is twice as long as wide, nearly as long as the second 

 basal segment. The second segment is about equal in length 



