d4 THOMAS SAY FOUNDATION 
Described from three nymphal skins and one female nymph, 
taken at the same time and place as were the male holotype 
and the female allotype, Yellowstone Park, July 14, 1921. R. 
Muttkowsky. 
Perla bilobata Needham and Claassen 
(Plate 4, figs. 50-54.) 
Length of body up to 9.5 mm. 
General color yellowish-brown, with the pronotal marginal 
oroove dark brown. 
Head wider than pronotum; quite smooth, occipital ridge ab- 
sent; hind ocelli closer to the eyes than to each other; tips of 
antennae broken off in the specimens before me but one partial 
antenna has thirty-eight segments, so that the full number is 
probably near fifty. 
Pronotum about twice as wide as long; transversely oval; mar- 
ginal groove distinct, brown, continuous around entire pronotum, 
and equidistant from the margin all around. Wing pads large 
and only slightly divergent from the body. Legs not much flat- 
tened; with only a sparse fringe of hairs on the outer margin; 
tarsal claws with a distinct basal tooth. 
Abdomen not much flattened ; segments with a fringe of spines 
and a few long hairs on posterior margin; segments of cercl 
tipped with a whorl of long stout hairs. 
Gills absent. 
Mouth parts: labrum at least three times as wide as long, 
covered with hairs and with a fringe of long hairs on the anterior 
margin. Mandibles with four or five unequal teeth followed by a 
fringe of long hairs, and beyond this fringe there is a deep, 
rounded notch. Maxillae with very long stipes; lacinia broad at 
the base, on the inside a large rounded knob, narrowing immedi- 
ately to a long, single, smooth, incurved tooth, the entire sclerite 
devoid of hairs; galea much reduced, hardly a third as long 
as lacinia, and at the apex one long hair; maxillary palpus 
slender and extending somewhat beyond the tip of the lacinia. 
Labium a little longer than wide, and very similar in structure 
to that of P. aestwals; glossae short; paraglossae large, hairy, 
and directed inward; both glossae and paraglossae with small 
papillae at the tip. Hypopharynx broadly rounded and closely 
beset with short stiff hairs. 
Described from two nymphal skins, from specimens reared by 
J. G. Needham, Old Forge, New York, July 13, 1905. 
