AQUATIC INVERTEBRATE FAUNA OF WYOMING AND MONTANA. 251 



Diaptomus shoshone, n. sp. (Plate XLII. Figs. 23-25.) 



A very large and robust species. Thorax broadest in front, across the maxillae, 

 tapering gradually, with little convexity, 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 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 cuticnlar appendage, but is penetrated by the hypodermic. Egg mass very 

 large, obovate (narrowest forward). 



Right antenna of male robust, the last two joints without special appendages, 

 antepenultimate with a very long inarticulate process at its outer apex, extending be- 

 yond 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 of the male reseinble the corresponding appendages of Diap- 

 tomus 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 fascicle of delicate hairs. The basal joint of the outer ramus is 

 two-thirds the length of the second joint of the peduncle, and without hairs or spines 

 of any description. The second joint of this ramus is about equal in length to the 

 second joint of the peduncle, and bears at its outer margin, close to the tip, the usual 

 stout seta, which is two-thirds as long as the joint to which it is attached. The ter- 

 minal claw is not regularly curved, but is nearly straight for the basal three-fourths. 

 The left leg is biramose, the inner ramus straight, slender, extending about to the 

 middle of the second joint of the outer, and armed at its tip. The second joint of this 

 ramus is as long as the first, if measured from the tip of the apical spine. This spine, 

 seen from behind, is stout, conical, rather blunt, and has opposed to it withiu, pro- 

 jecting from the inner angle of the segment, a stout, curved seta, slightly plumose on 

 it's distal half. Between these, but more closely applied to the outer spine, is a hemi- 

 spherical cushion-like elevation, set with small, short spinules. On the basal half of 

 the inner margin of this terminal segment is also a much larger hemispherical cushion, 

 but with longer and more slender hairs, while the terminal half of the inner margin of 

 the segment preceding is also moderately inflated and covered with delicate hairs. 



The antennae of the female are 25-jointed, as usual, and reach to the base of 

 the abdomen. The legs of the fifth pair closely resemble those of stagnalis, but 

 have the terminal setae of the inner rami much less developed. This ramus is a 

 little shorter than the basal joint of the outer ramus, and of about half its diameter. 

 It bears at its tip two stout setae equaling the ramus itself in length, plumose under a 

 high power, and has, in addition, at its inner tip and on the inner margin adjacent, a 

 patch of delicate hairs and spines. The second joint of the outer ramus is as long as 

 the first, if measured to the tip erf its terminal claw. The latter is nearly straight, 

 very slightly recurved. This joint bears a single spine at its outer distal angle, just 

 within which is the rudiment of the third segment of the ramus, which bears two 

 spines similar to the above, the inner of which is the longer, the outer itself being 

 longer than the adjacent spine of the second joint. Adults of both sexes are blood- 

 red throughout, except the egg sac of the female, which is purple. 



