44 THOMAS SAY FOUNDATION 
sternum; and fourth pair similarly located on the. conjunctivae 
between the meso- and metasternum. 
Abdomen brownish; tenth tergite of female triangularly pro- 
duced but not directed upwards, while in the male it is slightly 
more produced and directed upwards; cerei of twenty-five or 
more segments, basal segments very short, apical ones four to 
five times as long as wide; a fringe of hairs on the upper surface 
of the cerci, and each segment ending in a whorl of short hairs. 
Mature nymphs from Boulder, Colorado, in which the genital 
characters of the adults could be readily observed, enabled me to 
identify this species. 
Perlodes tibialis Banks 
(Plate 3, figs. 44-49.) 
Length of body up to 23 mm.; antennae up to 9 mm.; cerci up 
to 11 mm. 
Hairy nymphs, of a light brown color with markings on head 
and thorax; ocelli and eyes small; three pairs of small, single, 
finger-like gills located as follows: one pair at the outer base of 
the submentum, one pair on the lateral margin of the conjunc- 
tivae between the pro- and mesothoracic legs, and one pair on.the 
outer conjunctivae between the meso- and metathoracie legs. 
Head slightly wider than pronotum, thick, yellowish; three 
small ocelli; eyes set far to side of head; frontal M-line distinct ; 
on each side of ocellar triangle an oval mark; epicranial suture 
very distinct; occipital ridge distinct on sides but fading out 
in center; occiput. with an irregular pattern due to the peculiar 
distribution of short brown hairs; antennae of about 70 segments. 
Pronotum nearly twice as wide as long; front and hind mar- 
gins slightly rounded; angles rounded, the hind ones more so 
than front ones; discs with a few inconspicuous rugosites; sur- 
face hairy. Wing pads broadly rounded at apex. Legs with a 
fringe of hairs on femora and tibiae; femora closely beset with 
brown hairs; first and second tarsal segments short, subequal; 
third segment about four times as long as one and two combined. 
Abdomen somewhat flattened; cerei with twenty-five to thirty 
segments, each tipped with a whorl of short spines. 
Mt. Rainier, Wash. 
Perlodes americana Klap. 
Length of body up to 24 mm.; cerci up to 14 mm. 
General color yellowish brown. 
