1939] 
Immature Trichoptera 
11 
large coxa articulating with the pleurite, a small trochanter 
(always indistinctly divided), a large femur , a tibia, and a 
one-segmented tarsus bearing a movable claw. Usually the 
tibia ends in a spur. In Leptoceridae and some Odontoceridse, 
the middle and hind legs have the femora divided into two, 
the proximal half shorter than, or equalling the distal half. 
In the pupae imaginal structures such as antennae, maxil- 
lary and labial palpi, ocelli, tibial spurs, sternal ligulae and 
genitalia may be studied, in addition to the labral bristles, 
gills and anal processes of the pupal skin itself. All females 
have the maxillary palpi 5-segmented, but the males of some 
families show a reduction in this number. In some families 
in which both sexes have 5-segmented maxillary palpi, the 
terminal segment is secondarily annulated. Labial palpi 
are always 3-segmented. There are 3 ocelli present or none 
are found. The fore tibiae may have as many as 3 spurs, the 
middle and hind tibiae as many as 4 spurs. When no more 
than 2 spurs are present, they are terminal. A third or 
fourth spur is added part way up the tibia. The number of 
spurs is indicated by a spur formula. Thus 1-3-4 indicates 
that the fore tibia bears one (terminal) spur, the middle 
tibia a pair of terminal and a subapical spur(s), the hind 
tibia a pair of terminal and a pair of subapical spurs. The 
labral bristles are used to clean the gratings which allow 
entrance of water into the pupal case. The gills are much 
like those of the larva but often differ in number and ar- 
rangement. The anal processes are extensions of the pupal 
skin which cover the cerci and genitalia and often bear bris- 
tles for cleaning the grating which allows exit of water from 
the pupal case. 
Key to North American Caddis Larvae 
1. Abdomen very much wider than thorax; very minute 
species with all three thoracic segments heavily 
sclerotized above, living in portable silken cases 
which are much larger than the larvae : Hydroptilidse 
Abdomen not much wider than thorax; much larger 
species, never with all three thoracic nota heavily 
sclerotized above in any case-bearing species, the 
cases when present not much larger than the larvae 2 
