PLECOPTERA NYMPHS OF NORTH AMERICA = 55 
Perla expansa Banks 
Length of body up to 16 mm.; antennae up to 6.5 mm.; cercl 
up to 8 (?) mm. 
The nymphs of this species resemble very closely those P. balo- 
bata, but are larger in size and differ in a few details of struc- 
ture. General color yellowish with a narrow brown marginal 
eroove around the pronotum. Head much wider than pronotum ; 
maxillae extending far out beyond the outer margin of the eyes, 
ereatly accentuating the width of the head; hind ocelli about 
as close to the eyes as to each other; occipital ridge absent. 
Pronotum transversely oval, almost twice as wide as long; mar- 
sinal groove dark and continuous around entire pronotum. Legs 
slender, with a distinct but rather feeble fringe of fine hairs; 
tarsal claws with a small basal tooth. Abdomen not much flat- 
tened; each segment with fine spinules on the posterior margin. 
Gills absent. 
Mouth parts very similar to those of P. bilobata, but the lacinia 
narrows down more gradually in expansa than in bilobata, is uni- 
dentate and devoid of any hairs; galea feeble and very short. 
The sexes are readily distinguished in the more mature nymphs 
by the developing genital structures. 
Identification of this species was made possible by a study of 
the genitalia of both male and female nymphs which were col- 
lected in the Big Thompson River, Estes Park, Colorado, August 
4, 1921 (P.W.C.), and from Tolland, Colorado (G.S.D.). 
Perla hastata Banks 
(Plate 3, figs. 33-38; plate 15, fig. 188; plate 33, fig. 230.) 
Length of body up to 25 mm.; antennae up to 10 mm.; cerci 
up to 14 mm. 
The nymphs of this species are readily recognized by the 
variegated pattern of yellow and brown, absence of gills, large 
head, which is much longer and wider than pronotum; and 
especially by the two transversely oblong mottled areas on the 
large occiput of the head. Body not much flattened. 
Head at least half again as long as the pronotal disc and much 
wider; the cardo and stipes of the maxillae very long, and thus 
the maxillae protrude on the sides of the head so as to be plainly 
visible from above, accentuating the width of the head; ocelli 
set close together in a small triangle, the hind ocelli half again 
as close to each other as to the eyes; eyes small; occiput long, 
and on each side with a large transverse mottled area completely 
