1947] 
Banks — Characters in the Perlidce 
271 
The head of Perlodes , when viewed from above, shows 
the side behind each eye somewhat swollen before it be- 
gins to slope inward. Behind the eye of Isogenus the 
side is, at first straight, then slopes inward ; in Hydroperla 
it is less distinct, since the head is shorter behind the eyes, 
but in ebria and gravitansCt) the side is plainly promi- 
nent before sloping. The last two species, when viewed 
from below, show a somewhat globose area behind the 
eye. In many species the side behind eye is convex, but 
it begins to slope at the eye. Perlinella and Calliperla 
show the side somewhat swollen before the slope. 
Femora. 
The femora have on their lower edge a row of short, 
fine hairs or the hairs may have above them a row of 
stouter bristles, or the hairs may be more numerous and 
spreading up on the lower part of the femur, and with 
bristles interspersed or in a row. Those with the row 
of short fine hairs are the genera Perlodes (and subgen- 
era), Iso genus, Hydroperla, Clioperla and Isoperla, the 
other genera have bristles besides the hairs. In the 
Perla and Chloroperla sections there are always bristles 
on the femora, either in a row or among the hairs. 
In shape the femora may be very long and slender, with 
nearly parallel sides, but in many of the genera with 
bristles among the hairs (Perlesta, Neoperla, Calliper- 
linae) the femora are shorter, broader, and the upper edge 
convex. 
Wings. 
Needham and Claassen in the table to species of Perla 
use the position of the cubito-anal cross-vein to divide 
the genus in two sections, one in which this cross-vein is 
placed its length beyond the end of anal cell, and the other 
where the cross-vein is at end of cell or only a trifle be- 
yond. In general it would be better to divide whether 
the cross-vein is at or before end of anal cell, or plainly 
beyond. The amount beyond varies a bit in some species. 
It is plainly beyond in Iso genus, Hydroperla, Perlodes, 
Perlinella. In Pteronarcys this vein is much beyond end 
of cell, so we may consider this a primitive character. 
