Marsh—North American Species of Diaptomus. 413 
and concave on the inner margin. At about one-third of its 
length is a small spine near the inner margin. The lateral 
spine, situated at the beginning of the distal third of the seg¬ 
ment, is slightly curved, and finely denticulate on the inner 
margin. The terminal hook is slender, and equal in length to 
the whole right foot. At slightly less than half its length there 
is an abrupt angle. Distad of the angle, the inner margin of 
the hook is denticulate. The endopodite is one-segmented, 
rounded at tip, and equal in length to the first segment of the 
exopodite. The left fifth foot of the male reaches a little be¬ 
yond the middle of the second segment of the right exopodite. 
The second basal segment is a little longer than wide, and some¬ 
what shorter than the corresponding segment of the right foot. 
The lateral hair is situated at the beginning of the distal third. 
The first segment of the exopodite is about as long as wide, its 
distal end considerably narrower than the proximal. The in¬ 
ner margin is strongly convex and setose. The second segment 
is about twice as long as the first, and is armed at the tip with 
two finger-like processes; the outer of these processes is much 
the larger, and is armed on its inner surface with a minute 
setose pad. The inner process is separated from the main part 
of the segment by a suture. The endopodite is slender, twice 
as long as the first segment of the exopodite, and setose at the 
tip. 
Length of female, 1.1395 mm. Length of male, 1.0248 mm. 
This species was found in collections made in connection with 
the scientific work of the Michigan Fish Commission in Inter¬ 
mediate lake, and in North lake on Beaver island. It also oc¬ 
curred in a collection made by Dr. R. H. Ward in Crooked lake. 
It was associated with D. oregonensis, to which it is closely re¬ 
lated. It is apparently a rather narrowly localized species, for, 
although collections have been made quite generally in the 
Michigan and Wisconsin lakes, it has, so far, been found only 
in these three localities. 
