NORTH AMERICAN CADDIS-FLY LARVZ. 
on the under side of the proleg near the base there is a chitinous 
hook directed backward, figures 187, 189. 
In a few of the alcoholic specimens examined there are finger- 
like anal gills. It seems probable that anal gills are constant in 
the species, but are protruded in preserved specimens only under 
exceptional conditions. 
Tue Case.—As previously stated, the larva makes no case until 
it begins to prepare for pupation. It then crawls within some 
crevice between large stones and builds a fence-like wall of peb- 
bles about itself. The fence is oval in outline and is many times 
larger than the body of the insect. Inside its inclosure the larva 
spins about itself a close-fitting, parchment-like sheet of silk, 
superficially resembling the puparium of the higher Diptera. 
Here transformation takes place. 
RHYACOPHILA TORVA. 
LarvaL Hasirat.—The half-dozen larvae which have been 
collected in the region were taken in three of the nearby gorges 
leading into the Cayuga Lake Valley. The large number of adults 
occurring in all of the gorges indicates that the species is a com- 
mon one in the swift waters of the region. 
LarvaL Hasirs.—When collected our specimens were not dis- 
tinguished from R. fuscula, which the species probably closely re- 
sembles in habits. 
PrepupaAL Hasits.—The prepual habits of the species were 
not observed. 
Preriop oF EMERGING.—Adults are on the wing during the 
month of June. 
DEscRIPTION OF Larva.—Length, 20 mm. Head, long and 
flat, with parallel sides. 
The Head.—The color of the head is straw yellow, shading 
into brown behind the mouth parts; behind each eye there is a 
jet black subcuticular mark, and the caudal margin is narrowly 
bordered with black, figure 190. The labrum is very weakly chi- 
tinized ; both mandibles have long teeth, much more deeply notched 
than those of R. fuscula; the mandible of the left side is broader 
than that of the right side. 
114 
