PLECOPTERA NYMPHS OF NORTH AMERICA 61 
pronotum, and the meso- and metascutum, a dark brown. Head 
sightly wider than pronotum; eyes and ocelli black; surface 
smooth and sparsely clothed with hairs. Pronotum transversely 
suboval; front and hind margins somewhat convex; hind angles 
more broadly rounded than the front ones; surface somewhat 
rugose, with long hairs around the margin. Meso- and metanotum 
and wing pads covered with hairs; outer margins of wing pads 
broadly rounded. Legs hairy, with a sparse fringe of long, silky 
hairs on the outer margin of the tibiae. 
Abdomen brown, hairy, the segments with a row of short stiff 
hairs on the posterior margin. Cerci rather short and thick at 
the base and tapering to a very slender tip; of about fifteen seg- 
ments, each segment with a whorl of stiff hairs at the tip. 
Deseribed from mature nymphs from Boulder, Colorado, in 
which the genital characters could be plainly discerned. 
Alloperla lamba (?) Needham and Claassen 
Length of body up to 9 mm.; antennae up to 3 mm.; cerei up 
to 2mm. 
General color yellowish brown, with the head darker than the 
rest of the body. 
Head a little wider than prothorax; ocelli small, hind ocelli 
closer to eyes than to each other ; surface smooth, somewhat hairy ; 
antennae with about forty-five segments. Pronotum half again as 
wide as long, suboval; hind angles more broadly rounded than 
front ones; marginal groove continuous all around, darker in 
front and rear, becoming dark brown all around in the maturer 
nymphs; surface hairy, with long thin hairs on the margin. 
Meso- and metanotum and wing pads hairy. Legs flattened, 
hairy, with a fringe of hairs on the outer margin of the femora 
and tibiae, but thinner on the femora than on the tibiae. 
Abdomen brown, hairy. In the more mature nymphs there may 
be seen the darker mid-dorsal line of the developing imago. Cerci 
with about fifteen segments. 
The structure of the genitalia of the nymphs collected by the 
writer in Estes Park, Colorado, on Aug. 9, 1919, indicates that 
they very probably belong to this species. 
Alloperla mediana Banks 
Length of body up to 9 mm.; antennae up to 3 mm.; cerci up 
to 3 mm. 
General color yellowish brown, with no contrasting markings 
