NORTH AMERICAN CADDIS-FLY LARV. 
of 18 to 20 strong sete whose bases almost touch, except on the 
median line, where there is a greater space. On each latero- 
anterior angle there is a patch of long, fine hairs, and in the middle 
of the cephalic margin a dense line of short hairs. 
The Thorax.—Prothorax heavily chitinized above and on the 
sides. The area between and in back of the coxal cavities is mem- 
branous, except two narrow spots immediately in front of the 
mesothorax. Mesothorax with a chitinous area which extends 
back over the metathorax as far as the caudal margin of the hind 
coxe. Within this area there is a well-defined, square bearing 
eight sete, figure 149. The sides are not chitinous, except for a 
small black triangle behind each coxa, which bears a circle of 
about twelve sete; the venter is free from heavy chitin, except 
for two narrow yellow spots on the caudal margin. The meta- 
thorax is without heavy chitin above. On the sides the distribu- 
tion of chitinous plates is the same as on the mesothorax; the 
upper mark, however, is not so dark in color as on the preceding 
segment and bears more sete, which are less nearly circular in 
arrangement. The venter differs from that of the mesothorax, 
only in having the chitinous areas near the caudal margins darker 
in color. The front leg, figure 156, is little more than half the 
length of the succeeding legs, but is more robust. It bears three 
stout spurs on the inner angle, next to the tarsus, and one isolated 
spur on the distal margin. On the inner margin of the basal 
segment of the tarsus there is a single row of short stout spines. 
The inner surface of the tibia bears numerous very short spines. 
The inner surface of the femur is sparsely armed with short tri- 
angular teeth. The coxa, on its inner margin, has a few short 
spines and over its entire surface has rows of fine, short hairs 
like those described for the frons. The two succeeding legs (fig- 
ure 153 shows the hind leg), differ from the front leg in being 
longer and less robust, and in having fewer and weaker short 
spines. Each of these legs has but one tibial spur. 
The abdomen is cylindrical and almost uniform in circumfer- 
ence throughout its length. The humps on the first segment are 
not greatly developed. ‘The lateral humps bear an area of short, 
curved spines, whose points are directed forward. The gills are 
distributed on segments 2 to 8, above and below the lateral line, as 
diagrammed in figure 159. The lateral fringe, near the caudal 
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