SOME CHARACTERS IN THE PERLIDNE* 
By Nathan Banks 
Holliston, Mass. 
Many years ago when I started to classify our Perlidae 
I neglected to study the head, antennae, and legs. In re- 
cent years others have emphasized the importance of 
genitalia and nymphal structure. Species are physiolog- 
ical units, genera are structural units. Reproduction is 
one of the most important physiological processes, so that 
the structure of the genital parts is of great value in 
species. These vary from species to species so that only 
in a general way can they be used for genera. If the 
genus is to be something different from the species, it 
must rest on characters which are not commonly used for 
species. Species reflect adaptation to environment, the 
recent and temporary life. Genera should rest on long- 
inherited structures, of little or no use to the adult, but 
which reflect heredity; characters common to several 
species. 
The wings of Pteronarcys and Isoperla have many dif- 
ferences, but for each genus the wing is efficient ; the great 
number of crossveins in the former genus is not neces- 
sary, they represent inheritance, not use, and so become 
of value in the classification of genera or higher groups. 
Of the several structures that I have observed, the anal 
lobe of the fore wings 1 and a vein (anal brace), arising 
from the under side of the anal cell, and crossing the anal 
lobe seem to me to represent the course of specialization. 
In Pteronarcys the anal lobe is very large and the anal 
brace (vein that crosses it) complete and strong. In 
* Published with a grant from the Museum of Comparative Zoology at 
Harvard College. 
1 This anal lobe is rarely shown in figures of wings. Figure I in Needham 
and Claassen shows the anal area of fore wing but does not indicate the line 
of fold which separates the anal lobe from the rest of the wing. Many 
figures indicate the anal brace but often only partially or incorrectly. In 
the Selys part one, Klapalek on page 6 shows line of fold, in part 2, page 9, 
he shows the anal brace. N. & C. on plates 13 and 16 show the anal brace 
in Perla and Acroneuria. 
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