NORTH AMERICAN CADDIS-FLY LARVZ. 
The labrum is small, and about half the breadth of the cephalic 
margin of the frons. 
Thorax. —The prothorax, figure 88, on its dorsal surface, has 
ground color of straw-yellow, slightly lighter than the head; it 
is shaded and mottled with dark-brown. 
On the mesothorax the dorsal chitinous plates are mottled 
with dark-brown, except a circular area in each outer caudal 
angle, which is without mottling. 
The metathorax has the median plates slightly separated, sit- 
uated on a single plate-like area that is apparently more heavily 
chitinous than the surrounding integument of the segment. The 
plates of the second pair are uniform brown. The lateral plates 
are brown with dark marks at each end. 
Abdomen.—On the first segment the spacing-humps appear 
as flat, brown, callous areas, which are but slightly raised above 
the surface of the segment; the cone-like form of the humps of 
Halesus is entirely absent. On the ventral surface, behind the 
middle of the segment, there is a pair of chitinous plates, each 
bearing about six sete; in front of the middle of the segment 
there are a few scattered sete. 
The arrangement of gills is shown in figure go. 
DESCRIPTION OF THE CaseE.—The cases of Pycnopsyche 
scabripennis are subject to great variation in form. As a rule, 
the variation is seasonal—almost all of the cases are made on the 
same plan and undergo the same transitional change at the same 
time, but there are often a few specimens to be found that have 
omitted certain changes in their case-making. So one finds great 
numbers of specimens in a locality making cases of the same 
kind, but with careful search it may be possible to find examples 
of other types of architecture. 
The first cases made by the species are usually flat, two-sided 
cases of leaf fragments, figure 93. In making this form of case 
the larva cuts round or oval fragments from sunken leaves. These 
pieces are cemented on the opposite sides of the cylinder in which 
the larva lives. At the cephalic end the upper leaf, or root, pro- 
jects, hood-like, beyond the end of the tube; at the caudal end 
the roof covers the end of the tube, but the floor usually projects 
out even farther. Between the roof and the floor lies the tube in 
which the larva lives. It is made by cementing sides of small 
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