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 subterminal bristle without, and 
several terminal ones. Tip of last segment with two stout, curved, claw-like set®, 
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 subterminal 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 setfe, all of which are soft. Two of these, on the short inner lobe, are much 
longer and stouter than the others, and project directly backward. The base of this 
lobe bears two plumose setae 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 leugth springing together from the inner side of the apex. 
The.second 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- 
fourtlis the length of the third and about two-tliirds 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 set;e. The series of teeth with numerous accessory smaller teeth and spines, 
and two transparent lamellae — slender, but as long as the teeth themselves — inserted 
