NORTH AMERICAN CADDIS-FLY LARVZ. 
The Thorax—The chitinous shield of the pronotum is ex- 
tended forward in thorn-like form at each cephalic corner. In 
color the pronotum is deep mahogany-brown, with a broad, lighter- 
brown line on each side of the median suture. 
PSILOTRETA FRONTALIS. 
162. Larva. Head and thorax. 164. Larva. Frons. 
163. Larva. Labrum. 165. Case. 
The shield of the mesonotum is deep mahogany-brown, with 
a lighter line on each side of the median suture, which, in some 
specimens, ends at about the middle of the sclerite, and in other 
specimens extends back to the caudal margin of the shield. 
The metanotum, figure 162, bears a broad, brown, transverse 
plate near the cephalic margin, behind which there is a pale, nar- 
row, transverse plate; on each side of the erate there is an 
elongate brown plate. 
The Abdomen.—On the first segment all three spacing-humps 
are represented by obtuse mounds. The gills of the subdorsal 
and subventral series are well developed, occurring in tufts of 
from five to twenty-five filaments behind the cephalic margin of 
the segment. The lateral series of gills is represented by a few 
weak filaments on the first three or four gill-bearing segments, 
or is entirely wanting. The drag-hooks are stout, with heavily 
chitinized supports on the prolegs. 
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