16 Marsh—On Tivo Neiv Species of Diaptomus. 
of the outer ramus is as broad as long. The second joint is 
armed at tip with two finger-like processes, and both joints are 
armed within with minute hairs. The inner ramus is one-jointed, 
and nearly equal in length to the outer ramus. 
Length of female, 1.2 mm.; male, 1.1 mm. 
This species was found in some material kindly furnished to 
me by Professor E. A. Birge. The collections were made in 
January and February, 1893, in small lakes and ponds in Mis¬ 
sissippi. It was the only Diaptomus in the collections, and was 
found in nearly all of them. It will be noticed that it bears a 
somewhat close resemblance to D. graciloides Sars. 
Diaptomus birgei. Plate 7, Jigs. 4-6. 
Of moderate size. The first segment of the cephalothorax is 
nearly equal in length to the three following. 
The first segment of the abdomen of the female is as long as 
the remainder of the abdomen and the furca. It is much dilated 
in front. The second segment is nearly twice as long as the 
third, and about equal in length to the furca. The second and 
third joints are very closely united. 
The antennae extend to the end of the furca. The right an¬ 
tenna of the male is much swollen anterior to the geniculating 
joint; the antepenultimate joint is produced on its distal end 
into a short, blunt process, which makes very nearly a right 
angle with the longitudinal axis of the joint. 
The outer ramus of the fifth foot of the female is two-jointed, 
the third joint being represented by two spines. The inner 
ramus is one-jointed, hardly as long as the first joint of the 
outer ramus, and armed at the tip with minute setae and two 
rather long spines. 
The basal joint of the right fifth foot of the male is elon¬ 
gated, trapezoidal in form, its greatest breadth being at its dis¬ 
tal extremity. The first joint of the outer ramus is broader 
than long, armed on its inner margin with a broad, thin expan¬ 
sion of the integument. The second joint is elongate, broader at 
base; the lateral spine is situated at about the middle of its 
length, is long and stout, and armed on its inner margin with 
fine serrulations. The terminal hook is slightly angular, and 
