172 Illinois State Laboratory of Natural History. 



Diaptomus birgei Marsh. 



Diaptomus birgei, Marsh,'94, p. 16, PI. I., Fig. 4-6. 

 Diaptomus birgei, Herrick and Turner, *95, p. 79, PI. XLVIL, Fig. 

 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 antennse extend to the end of the furca. The right 

 antenna of the male is much swollen anterior to the geniculat- 

 ing 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 

 distal extremity. The first joint of the outer ramus is broader 

 than long, armed on its inner margin with a broad, thin ex- 

 pansion 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 armed with fine serrulations on its inner mar- 

 gin. The inner ramus is one-jointed, equaling in length the 

 first joint of the outer ramus. 



" The left fifth foot of the male reaches slightly beyond the 

 first joint of the outer ramus of the right. The basal joint is 

 quadrangular, considerably shorter than the right basal joint. 

 The first joint of the outer ramus is about twice as long as 

 broad. The second joint is slightly longer than the first joint ; 

 it is expanded at base, where it is armed with fine hairs, and 



