PLECOPTERA NYMPHS OF NORTH AMERICA 51 
will also be necessary to point out something of the limits of 
variation in color pattern within the species. 
The pattern on the head varies somewhat, but normally there 
is an oval white spot in the center of the dark mark which covers 
the ocellar triangle. There is always a long, dark elongate mark 
on each of the femora. This mark extends about two-thirds of 
the length of the femur, and at the distal end there may be seen 
on the inner side (sometimes on both sides) another small dark 
blotch. The abdomen is alternately barred with yellow and black 
or yellow and brown, the basal half of each segment being dark 
and the caudal half light. Here is to be found considerable varia- 
tion, for in the darker specimens the entire segments are some- 
times almost equally dark, but I have never yet seen a nymph 
of this species in which the tenth tergite was not yellowish at the 
apex, and in most most nymphs this yellow color cuts into the 
basal dark band in a V-shaped manner. 
Head slightly narrower than the pronotum; the occipital ridge 
very prominent; epicranial suture distinct; hind ocelli closer to 
each other than to the eyes; antennae more than half as long 
as body and made up of about ninety segments. 
Pronotum almost twice as wide as long; somewhat widened 
posteriorly ; hind angles much more broadly rounded than front 
ones; front margin nearly straight, hind margin slightly concave 
in the center; surface feebly pilose, and the margin with a fringe 
of very short spinules; marginal groove distinct in front and be- 
hind, and more or less continuous around the entire pronotum. 
Meso- and metanotum, including wing pads, with scattered 
hairs and the margins of the wing pads with a fringe of fine 
spinules. 
Abdomen flattened; tergites with a fringe of spinules on the 
posterior margin; surface with scattered short hairs and with 
longer hairs along the mid-dorsal line. This line of long hairs 
is especially noticeable-in the half-grown and smaller nymphs 
where these hairs are especially thick on the caudal segments. 
The cerei are about three-fourths as long as the body and are 
composed of fifty or more segments, each segment terminating in 
a whorl of short spines. On the inner dorsal margin the cerci 
bear a fringe of long fine hairs, which are longest near the base 
of the cerci. 
The legs are much flattened and bear a thick fringe of long, 
fine, whitish hairs on the outer margin. 
Ventral surface of body quite uniformly yellowish. Seven pairs 
