North American Species of Diaptomus. 141 



The pool from which they were taken was particularly rich 

 in decaying vegetable material and received the drainage of a 

 pasture in which cattle and horses were allowed to graze. 

 The water literally swarmed with Volvox; and Diaptomus, 

 Cyclops, and insect larvae were very abundant. The food sup- 

 ply was practically inexhaustible and the specimens taken 

 were unusually large. 



Diaptomus shoshone Fokbes. r (Pl. XXVI., Fig. 1-3.) 



Diaptomus shoshone, Forbes, '93, p. 251, PI. XLIL, Fig. 23-25. 

 Diaptomus shoshone, Herriek and Turner, '95, p. 61, PI. V., Fig. 11. 



"A very large and robust species. Thorax broadest in 

 front, across the maxilla?, tapering gradually, with little con- 

 vexity, to the posterior third. In the female the angle of the 

 last segment is bifid, both projecting points being minutely 

 spinose at tip. The first segment of the abdomen (PL XXVI. , 

 Fig. 1) is laterally expanded, the expansion of the left side 

 with a minute spine at the apex, behind, that on the right 

 produced at the same point into a small, prominent, rounded 

 tubercle, 0.03 millimeter in length, about as broad as long, 

 making this first segment somewhat unsymmetrical. This is 

 not merely a modified cuticular appendage, but is penetrated 

 by the hypodermis. Egg-mass very large, obovate (narrowest 

 forward). 



"Eight antenna of male robust, the last two joints without 

 special appendages, antepenultimate with a very long inartic- 

 ulate process at its outer apex, extending beyond the tip of 

 the penultimate and to the middle of the last segment. The 

 margins of this process are smooth, but it is broad and 

 emarginate at the tip. 



" The fifth pair of legs in the male resemble the correspond- 

 ing appendages of Diaptomus stagnalis, but differ notably in 

 detail. The left ramus of the right leg is borne at the inner 

 terminal angle of the second joint ; is longer than the joint 

 following ; is armed at the apex with a few small acute spines ; 

 and bears upon its outer margin, near the tip, a broad fas- 

 cicle of delicate hairs. The basal joint of the outer ramus is 

 two thirds the length of the second joint of the peduncle, 



