6 THOMAS SAY FOUNDATION 
present in the submentum, the coxae, the ventral side of the 
femora, and the first eight abdominal sternites. In the abdomen 
several tufts arise from each ventral abdominal commissure and 
extend to the posterior margin of the segment.’’ (Plate 29, fig. 
211.) In the following genera tracheal gills are absent: Isogenus, 
Clioperla, Paraperla, Kathroperla,? Isoperla, Alloperla, Chloro- 
perla, Perlomyia,? Leuctra, Capnia, Allocapnia, Capnura,? and 
certain species of Taeniopteryx, Nemoura and Perla. Perlodes 
possesses two or more small, fleshy, finger-like gills. In P. ameri- 
cana, which possesses only one pair, they are attached to the outer 
base of the submentum. P. tibialis has, in addition to the gills on 
the submentum, two pairs on the pleural conjunctivae of the 
thorax and P. signata has three pairs of thoracic gills in addition 
to the pair on the submentum. In Peltoperla arcuata five pairs of 
single, long, pointed, gill filaments may be seen to protrude from 
under the large sternal plates of the thorax where they are at- 
tached to the soft integument at the base of the legs.° 
Of the genus Taeniopteryx; 7. mvalis, T. maura, and T. par- 
vula each possesses three pairs of coxal gills. These gills are three- 
segmented and occur as single filaments attached, one to the coxa 
of each leg. In certain of the species of Nemoura (JN. venosa, N. 
sinuata, ete.) we find tracheal gills in the cervical region.* These 
gills have been called prosternal tracheal gills by Wu (57) and 
he describes them as follows for NV. venosa and N. sinuata: ‘‘ Hach 
gill consists of two tufts of hair-like gill filaments, the number 
of which varies with the species. In N. venosa, each tuft is com- 
posed of five to six filaments. In N. sinwata, there are five to six 
vill filaments in each outer tuft, and about fifteen in each inner 
tuft. A gill trachea extends downward to the base of each gill 
from the longitudinal trunk near the anterior margin of the 
prothorax. This gill trachea divides into many branches, each of 
which enters one of the gill filaments and subdivides into a large 
number of tracheoles. Loops are formed by these tracheoles in the 
gill-filament at its distal end.’’ 
The nymphs of the following genera possess copious gill tufts 
underneath the prothorax, and in some of the species gill tufts 
are found also on some of the abdominal segments, while in others 
*The nymphs of Kathroperla, Perlomyia, and Capnura are not known, 
but when they are discovered they will doubtless be without gills. 
*Uéno (56) reports a species, from Japan, of Peltoperla which possesses 
no gills whatsoever. 
*Imms (11) says, ‘‘in Nemoura, for example, they [gills] assume the 
form of lamellate outgrowths on the pronotum.’’ In all the nymphs of 
Nemoura which I have seen these gill filaments are cylindrical. 
