50 THOMAS SAY FOUNDATION 
ridge of the head, the posterior margin of the pronotum, the 
posterior margin and medical portion of the meso- and metanotum, 
and along the mid-dorsal line of the abdomen. In many nymphs, 
these hairs became coated with a brown slimy ooze and this gives 
the specimens a dirty, fuzzy appearance. 
In the very small nymphs (5 to 7 mm. in length) there are 
only three pairs of gill tufts present. These correspond to the 
three largest pairs in mature nymphs. In these small specimens 
the pronotum bears a fringe of long spines; the meso- and meta- 
notum and the abdomen are covered with long spines as well as 
the femora, which in the young forms are very wide. The oe- 
cipital ridge, however, is very distinct, and this, together with 
the uniformly brown color of the abdomen, makes identification 
of this species possible even in the very young stages. 
This species occurs under stones in the larger streams, but 
the nymphs apparently are able to live in somewhat quieter 
waters than the nymphs of P. immarginata, for mature nymphs of 
P. media have on several occasions been collected from the waters 
of Beebe Lake, on the Cornell University campus, as well as from 
Dwyer’s pond, in Cascadilla creek. It is interesting to note that, 
whereas the adults of the above two species are very similar in 
general appearance and it is at times difficult to separate the 
females, the nymphs are very different in general appearance, the 
nymphs of P. media being dull brown, while those of P. im- 
marginata possess a very striking color pattern. 
P. media is a typical carnivore and probably requires three 
years to complete its life cycle. 
Ithaca, N.Y.; Ogdensburg, N.Y.; Potomac R., Harpers Ferry, 
Md.; Cleveland, Va.; Guelph, Ont. 
Perla immarginata Say 
(Plate 5, figs. 77-82; plate 31, fig. 219.) 
Length of body up to 33 mm.; antennae up to 15 mm.; cerei 
up to 22 mm. 
This is the largest and one of the most beautiful nymphs of 
this genus in the Eastern States. 
It is almost impossible to describe the details of the striking 
yellow and brown, or yellow and blackish color pattern, but the 
photograph (Plate 31, fig. 219) illustrates this very well, and an 
attempt will be made here only to point out some of the more 
striking patterns which aid in identification of this species. It 
