ON TWO NEW SPECIES OF DIAPTOMXJS. 
C. DWIGHT MARSH, 
Professor of Biology , Ripon College. 
Diaptomus^ mississippiensis. Plate /, figs. 1-3. 
Of moderate size. The first two segments of the cephalothe- 
rax are nearly equal in length, and together form somewhat less 
than half the cephalothorax. The last segment of the cepha- 
lothorax is armed behind with two minute spines. 
The first segment of the abdomen of the female is as long as 
the remainder of the abdomen and the furca; it is dilated later¬ 
ally and in front, and bears two prominent lateral spines, the 
right spine being considerably larger than the left. The second 
segment is somewhat shorter than the third, and the third and 
the furca are of about equal length. 
The antennae reach beyond the furca. The right antenna of 
the male is swollen anterior to the geniculating joint, and the 
antepenultimate joint is without armature. 
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, a little longer than the first joint of the 
outer ramus, and armed at the tip with minute setae and two 
rather long spines. 
In the right fifth foot of the male the basal joint is dilated on 
the inner margin. The first joint of the outer ramus is slightly 
broader than long. The second joint is elongated, quadrangu¬ 
lar, with the lateral spine situated at the distal end. The ter¬ 
minal hook has the symmetry of the curve broken by two rather 
abrupt angles, and its inner margin is armed with fine serru- 
lations. The inner ramus is one-jointed, and reaches about half 
the length of the second joint of the outer ramus. 
The left fifth foot of the male reaches to about the middle of 
the second joint of the outer ramus of the right. The first joint 
