PLECOPTERA NYMPHS OF NORTH AMERICA 47 
better known, especially in the genus Perla, in order to arrange 
the species in more natural groups. 
Key to the Nymphs of Perla 
Th, WETAMS WPe SST? Bee een lube ieee ali ad Oia ee a a 2 
LES. BA OBISNAN ES. fur gos 3k oe ale, eR a 4 
Pee alert SepTOSeN iinks. «cee ae ts eas ok capitata (p. 47) 
COEERTRO EN, GU] REA GI) eR aaa petals an ROU ce ae en 3 
3. Almost uniformly brown; abdomen not banded with yellow 
and brown; no yellow spot in the ocellar triangle ........ 
37 2. cepa IEE RO Se ee sg media (p. 48) 
Briehty patterned with yellow and brown or black; abdomen 
banded with yellow and brown; a yellow spot in the ocel- 
| PEPE 01g ERE Go se gene tee, Oo ea ummarginata (p. 50) 
4. Lacinia composed of a single long tooth; galea very small, less 
PreaMeatisaslON OAs ACINIO@ Aas A. eke sos Siena eve 9) 
Lacinia bidentate; galea at least half as long as lacinia... 6 
5. Western; length of mature nymphs 16 mm.; a narrow dark 
line around margin of pronotum ........ expansa (p. 5d) 
Eastern; length 10 mm.; apparently no dark line around 
TUT eS oes ae bilobata (p. 54) 
6. Oceiput of head, each side, with a roundish mottled area 
Nouncdedsbyeardarkemeinaroin, 05... <2 ues hastata (p. a 
DONE: ESL oot qycchsebe peas ea ace 6 ee naa ae 
7. Head with a wide dark transverse band; pronotum aie 
in center and dark all around; abdomen banded with yel- 
low and brown or yellow and black ...... verticalis (p. 57) 
SIL). (SLOP Yo Slag i teeth oe ae A eae aestivalts (p. 53) 
Perla capitata Pictet 
(Frontispiece; plate 31, fig. 220.) 
Length of body up to 28 mm.; antennae up to 11 mm.; cerci 
up to 14 mm. 
These brightly colored yellow and brown or yellow and black 
nymphs are easily recognized by the two dark transverse bands 
across the head, the two dark transverse bands on the femora, the 
presence of caudal gills and the yellow and dark banded abdomen. 
Head a little narrower than pronotum; occipital ridge dis- 
tinct ; hind ocelli at least twice as close to each other as to the eyes; 
the wavy dark transverse band which passes through the ocellar 
triangle extends backward in the middle to the hind ocelli, or 
slightly beyond, but usually bears a V-shaped yellow area between 
