16 Marsh — On Two New 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 I, Jigs. J/.-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 



