PLECOPTERA NYMPHS OF NORTH AMERICA — 23 
. First and second tarsal segments very short, subequal, to- 
gether less than half as long as third; labrum three to four 
times as wide as long; labial palpi slender and reaching far 
beyond the tip of labium, which is 2-lobed (i.e., glossae are 
much reduced) ; mandibles slender and without a molar; 
body mostly flattened; carnivores; all strikingly colored 
Peruse DELON O NETO ab... er an 6G leds: PERLIDAE 0 (p. 41) 
First and second tarsal segments together about as long as 
third or at least more than half as long; labrum not very 
much wider than long; labial palpi stout and usually not 
reaching beyond the tip of labium, which is 4-lobed, (i.e., 
olossae and paraglossae are subequal) ; mandibles with a 
molar; body not brightly colored; more or less cylindric; 
under 1 inch in length when fully grown; herbivores 16. 
. Only two distinct ocelli present; copious gill tufts under 
CUNOTED SS. oh dupe ie ey0n 2 erlie  eaiet ce AR ai ne ay eka ago 6 
Pieecaoce le with or without gillg 01.2. 2454... eee ee fi 
. Two ocelli set very close together ; caudal gills present ; oceipi- 
tal ridge present ; lacinia of maxilla bidentate .......... 
gs 2S a are eee ea Neoperla (p. 66) 
Two ocelli separated by several diameters of a single ocellus ; 
caudal gills and occipital ridge absent; lacinia unidentate 
1 ny RM eR ARR on eae Atoperla (p. 78) 
. With branched filamentous gill tufts on the under side of the 
SOM e LoL UOaDASeEROM LNG ACLS fo vet «at cis eds ce ete eee 8 
Without branched gill tufts; in some nymphs there are, how- 
ever, small, single, inconspicuous gill protuberances.. 11 
. Head very long; eyes small and set far forward so that the 
distance from the posterior border of the eye to the hind 
margin of the head is much greater than the diameter of 
the eye; gills much branched and about as long as the 
front femora; small caudal gills........ Perlinella (p. 79) 
Head shorter; distance behind the eyes less or at. most not 
much greater than the diameter of the eye; gills usually 
mideushorier than theiront femora... 52.5.6 «<a 9 
. Mature nymphs not over half an inch in length; body usu- 
ally freckled with small brown dots; cerci almost as long 
as body and composed of about 25 long segments; second 
tooth of lacinia very large and not followed by a fringe of 
WER WS, S 3 SANE A Site en ae are Cee enna Perlesta (p. 76) 
Mature nymphs usually much more than half an inch in 
leneth; body concolorous or with yellow and brown pat- 
tern, but not freckled; cerci usually of more than 30 seg- 
