Marsh—North American Species of Diaptomus. 425 
as long as wide. The hook of the second segment is moderately 
curved, and finely denticulate on the inner margin. The third 
segment is represented by two spines, of which the inner is the 
longer. The endopodite is slender, slightly exceeding in length 
the first segment of the exopodite. It is setose at tip and hears 
two rather long terminal spines. It is commonly composed of 
one segment, but sometimes has two. 
The male fifth feet are of moderate length. The spines of 
the first basal segments are slender and rather long. The sec¬ 
ond basal segment of the right foot is longer than wide, and its 
inner and outer margins are convex. The lateral hair is short, 
and situated at the beginning of the distal fourth. The first 
segment of the exopodite is as long as broad, and somewhat pro¬ 
duced at the distal outer angle. From the posterior surface 
near the internal distal angle extends a hyaline lamella. The 
second segment is more than twice as long as its width, is 
strongly convex on the outer margin, and slightly concave on 
the inner. The distal end is about one-half as wide as the 
proximal. The lateral spine is slightly curved, about half as 
long as the segment and situated near the beginning of the 
distal third. The terminal hook is slender, falciform, sym¬ 
metrically curved, somewhat less in length than the rest of the 
right foot. The endopodite is slender, either one- or two-seg¬ 
mented, and considerably longer than the first segment of the 
exopodite. The second basal segment of the left foot is quad¬ 
rate, slightly longer than broad, with the lateral hair situated 
at the beginning of the distal fourth. The first segment of 
exopodite is longer than wide, its inner surface strongly curved 
and setose. The second segment is twice as long as wide. The 
inner margin has two setose convexities, the distal one being 
continuous with the rounded end of the segment. This segment 
is terminated by two finger-like processes, the inner being shorter 
and more slender. The left foot reaches to about the middle 
of the second segment of the right exopodite. The endopodite 
is long and slender, reaching about two-thirds the length of the 
second segment of the exopodite. It is composed of either one 
or two segments, and is setose at the tip. 
