46 THOMAS SAY FOUNDATION 
Wing pads long, rather slender, and pointed. Legs long, quite 
slender and fringed with long hairs; tarsal claws with a small 
sharp basal tooth. 
Abdomen moderately flattened; posterior border of each seg- 
ment with a fringe of very small spinules. Gills absent. 
Mouth parts: labrum at least three times as wide as long; hairy 
on the surface, and with a fringe of long hairs on the anterior 
margin. Mandibles asymmetrical, each with five unequal teeth 
followed by a fringe of long hairs. Maxillae: lacinia bidentate, 
the second tooth about half as long as apical one, followed by a 
series of long hairs; galea cylindric and reaching a little beyond 
the base of the second lacinial tooth; maxillary palpus about as 
long as lacinia. Labium about as wide as long; glossae small, and 
at the apex a small membranous tubercle; paraglossae large, 
hairy, and also tuberculate at the tip; labial palpi extending con- 
siderably beyond paraglossae. Hypopharynx broadly rounded 
and at the tip closely beset with very fine spinules. 
A mature female nymph, without locality label, ready to 
emerge, has enabled me to identify the species with some degree 
of certainty. However the nymphs have been in alcohol so long 
that the bodies are rather badly shriveled and the color pattern 
eannot be observed clearly. 
Genus PERLA Geoffroy 
The limits of this genus are not easy to define, for it is made 
up of a rather heterogeneous group of species. The known nymphs 
fall into two rather distinct groups. The first of these groups 
(capitata, media and immarginata) possess copious gills, a very 
distinct occipital ridge, and the body is considerably depressed. 
These species are typical of Perla sensu str., and agree with the 
descriptions of the known European Perla nymphs. 
The second group (bilobata, expansa, verticals and aestivalis) 
possesses no gills, the occipital ridge is absent and the body is 
more cylindrical. These nymphs fall under the subgenus Hemi- 
melaena Klap. Perla hastata Bks., which is here included in the 
genus Perla, was originally assigned to Isogenus by Banks, and 
I am rather inclined to believe that the nymphs, and possibly the 
adults, are more typical of Isogenus than of Perla. However, I 
Shall not attempt in this paper to revise or change the nomen- 
clature of any of the genera from that adopted by Needham and 
Claassen (27). It is evident that some changes will have to be 
made as soon as the immature stages of the various species are 
