NORTH AMERICAN CADDIS-FLY LARVZ. 
Key To LArva PHILOPOTAMID2. 
A. Anterior margin of femur without a spur terminated by a 
bristle, anterior margin of clypeus but slightly indented. 
Lateral lobes of labrum but slightly developed.—Philopota- 
mus distinctus (?) 
A.A. Anterior margin of femur with spur terminated by a bris- 
tle, anterior margin of clypeus deeply indented. Lateral 
lobes of labrum well developed. Chimarrha. 
B. Larva orange. Anterior margin of clypeus with deeper and 
more angular incision —C. aterrima. 
B.B. Larva pale yellow. Anterior margin of clypeus with shal- 
lower and more curved incision.—C. socia. 
FAMILY RHYACOPHILIDA:. 
Hapitat.—Rhyacophilid larve are fitted for life only in flow- 
ing water. Representatives of the family may be found in all of 
our streams that flow over a stony bottom and that do not go 
entirely dry during any part of the year. 
Hasits.—Members of the two subfamilies differ widely in 
their larval habits. Members of the subfamily Rhyacophiline 
build no cases until the prepupal stage is reached. They crawl 
actively under or between stones, obtaining a firm hold on their 
support with their well-developed drag-hooks and legs. They are 
active larve that easily crawl about without the protection of a 
case. When their activity is about to cease for pupation, they 
build a strong fence of stones about themselves and in its protec- 
tion undergo pupation. 
Members of the subfamily Glossosomatine build cases of sand 
grains or pebbles. With their cases they crawl slowly over the 
exposed surfaces of stones. They are sluggish larve that cannot 
exist without the protection of a case. Pupation takes place on 
the exposed surfaces of stones, within their cases of sand. 
Before pupation members of both subfamilies spin a sheet of 
silk closely about themselves. This silken cocoon has a strong 
superficial resemblance to the puparia of the higher Diptera. The 
silk of the cocoon is rubber-like in appearance, and even under the 
microscope shows no texture whatever, and no openings for 
transpiration of water are apparent. If taken from water and 
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