Marsh—North American Species of Diaptomus. 421 
strongly recurved. The hook 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, hut 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 two 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. Hear 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. 
