Marsh—North American Species of Diaptomus. 457 
The spines of the first basal segments of the fifth feet of the 
male are rather long and slender. The second basal segment 
of the right foot is about twice as long as broad, and convex on 
inner and outer margins. The lateral hair is situated at about 
two-thirds of its length. It bears a small tubercle on the pos¬ 
terior surface, near the inner margin, at about one-third its 
length. The first segment of the right exopodite is twice as 
long as wide, convex on the outer margin and concave on the 
inner; the second segment is three times as long as wide, 
strongly concave on the inner margin and convex on the outer. 
The lateral spine is near the outer distal angle, is of medium 
length and slightly curved. The terminal hook is stout, nearly 
as long as the segment, bent sharply at about the middle. It is 
denticulate on the inner margin. The endopodite is rudimen¬ 
tary, being represented by a short, curved process. 
The left foot, in length, does not reach the end of the first 
segment of the exopodite of the right foot. The second basal 
segment of the left foot is trapezoidal in form, three-fourths as 
long as the corresponding segment of the right foot. The lat¬ 
eral hair is at about two-thirds its length. The first segment 
of the exopodite is one-half as wide as the second basal seg¬ 
ment, is twice as long as wide, with rounded apical angles; the 
inner distal angle is setose. The second segment is less than 
two-thirds the length of the first, is concave on the inner mar¬ 
gin and convex on the outer. It is armed at the tip with a 
stout finger-like process at the outer angle, and a slender curved 
process at the inner angle. The process at the outer angle is 
finely denticulate on the inner margin, and the process at the 
inner angle is setose. The inner margin of the second segment is 
setose. The endopodite is two-segmented and nearly equals in 
length the exopodite. The first segment is slender. The sec¬ 
ond segment is oval, crenate on the inner margin, and setose at 
the tip and on the inner and anterior surfaces. 
Length of female, 1.47-1.58 mm. Length of male, 1.30- 
1.33 mm. 
This was found in Wigwam pond, Nantucket. 
Pearse’s paper containing the description, of which the above 
is nearly a verbatim copy, modified only to correspond to the 
