AQUATIC INVERTEBRATE FAUNA OF WYOMING AND MONTANA. 245 



The terminal segment of the palp of the first maxilla is a little more than a 

 fourth the length of the basal, the latter with one subterininal bristle without, and 

 several terminal ones. Tip of last segment with two stout, curved, claw-like setse, 

 and four or five smaller, softer ones. Outer lobe of maxilla proper reaching to tip 

 of first segment of palp, nearly equaling it in diameter, also with two curved claws, 

 shorter but much stouter than those above mentioned, three-fourths as long as the 

 lobe itself. Besides these, two smaller setae and three or more subterininal ones, two 

 of which are smooth, like the terminal group, and one strongly plumose. A single 

 plumose seta also springs from near the base of the concave surface of this lobe. 

 The second and third lobes similarly armed at tip, but with a larger number of 

 curved setae, all of which are soft. Two of these, on the sliort inner lobe, are much 

 longer and stouter than the others, and project directly backward. The base of this 

 lobe bears two plumose setee about as long as those just mentioned. The length of 

 the inner lobe is half that of the outer, the middle one being intermediate. 



The second maxilla with about twelve terminal setae, which diminish in length 

 inward, most of them slightly plumose, and two long slender setae, one springing from 

 the middle of the inner margin and the other from the base. Palp thick, slender 

 ovate, twice as long as the masticatory lobe, fringed with a soft silky pile, and bearing 

 three more or less plumose setae at its tip, the middle one of which is the longest. 

 Branchial lobe very small, semicircular, with three fully developed plumose setae 

 nearly as long as the palp, and two much shorter ones, one delicate and smooth, the 

 other stout and plumose. 



The basal segment of the second antenna trigonal, with one moderately long hair 

 beneath, and two of similar length springing together from the inner side of the apex. 

 The.secoud segment subcylindrical, with two hairs diverging from the middle of the 

 outer side of the apex, the under one of which is very short and weak, about as long 

 as the third segment is wide, while its companion reaches about to the tip of that 

 segment. On the inside of the tip of the second segment is another hair, similar to 

 the above, and of about the same length. The third segment bears, at the union of 

 its basal with its middle third, on the under side, set beyond a slight tooth-like pro- 

 jection, a jointed olfactory club, whose length is about two-thirds the diameter of the 

 segment. Otherwise this segment bears no hairs except at the tip, where, upon its 

 inferior angle, is one long, stout hair, reaching beyond the tip of the last joint, and 

 upon its inner surface a fascicle of five plumose hairs, the four longer of which are 

 curved and parallel, while the fifth is short and straight. The third segment is slightly 

 longer than the second and about two-thirds as thick. The fourth segment is three- 

 fourths the length of the third and about two-thirds its diameter, slightly enlarged 

 at the middle, where it bears, on the under side, a group of three long hairs, and upon 

 the upper side two shorter ones. At the tip of this segment are a group of three 

 long plumose hairs and a stout, curved, concave, acute claw,, nearly three times the 

 length of the last segment, doubly dentate on both edges. At tip of last segment the 

 usual strong, curved, bidentate claws, five in number, three of equal length, as long 

 as the two last segments of the antenna, and two others about half that length. 



Mandible with a row of six dark corneous teeth, more or less bifid, the series 

 continued in an irregular cluster of tooth-like spines, and terminating in two highly 

 plumose setae. The series of teeth with numerous accessory smaller teeth and spines, 

 and two transparent lamellae slender, but as long as the teeth themselves inserted 



