ON TWO NEW SPECIES OF DIAPTOMUS. 



0. DWIGHT MAESH, 



Professor of Biology, Ripon College. 



I 



Diaptomus mississippiensis. Plate 7, figs. 1-8. 



Of moderate size. The first two segments of the cephalothe- 

 rax are nearly equal in length, and together form somewhat less 

 than half the eephalothorax. 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 



