PLECOPTERA NYMPHS OF NORTH AMERICA — 89 
line; surface covered with fine hairs, and posterior margins with 
a fringe of spinulose hairs; cerci composed of about thirty-five 
segments, each with a whorl of short spines on the posterior 
margin; the cerci are devoid of long hairs. 
Gills. Ten pairs of much-branched, filamentous gills; two small 
pairs at the outer base of the prothoracic legs; one on the outer 
conjunctivae between the pro- and mesothorax; two pairs at the 
outer base of the mesothoracic legs; one pair on the outer con- 
junctivae between the meso- and metathoracic legs; and one pair 
of large caudal gills. Some of these gills are so closely crowded 
that superficially the nymph appears to have only six pairs of 
gills, including the anal gills. 
Mouth parts. Labrum about three times as wide as long; an- 
terior margin with a fringe of long hairs. Mandibles slightly 
asymmetrical, each with five distinet teeth, of which the first, 
second, and fourth are the largest ; beyond these teeth is a fringe 
of long hairs. Maxillae: lacinia bidentate, with the second tooth 
a little more than half as long as the first; following the second 
tooth there is a fringe of long hairs; galea distinctly two-seg- 
mented, shorter than the lacinia, and at the tip with a small 
eroup of hairs; maxillary palpus extends considerably beyond 
the tip of the lacinia. Labium: submentum very broad; glossae 
small, triangular; paraglossae large and fleshy, directed inward 
at the tips, and bearing a series of long hairs. 
This species is quite common in the swift-running streams of 
the Western States. 
Logan R., Utah; Provo R., Utah; Estes Park, Colo.; Boulder, 
Colo.; Yellowstone National Park; Pecos, N. Mex.; Jocko R., 
Mont. 
Acroneuria ruralis Hagen 
(Plate 24, fig. 203; plate 32, fig. 223.) 
Length of body up to 24 mm.; antennae up to 11 mm.; cerci up 
to 25 mm. 
The nymphs of this species are readily recognized by their 
uniform light brown to chestnut brown color, their very broad 
pronotum, with wide, flaring flanges ; antennae not more than half 
as long as the body; cerci extremely long, equaling or surpassing 
the entire body. 
Head a little narrower than pronotum, uniformly brown, ex- 
cept for somewhat lighter areas around the ocelli and eyes; eyes 
small, black, and set forward some distance from the postero- 
