1938 ] 
New Genus of Perlidx 
137 
Hesperoperla obscura sp. nov. 
In general structure much as in H. pacifica. Body brown 
to almost black, venter pale through the middle, some 
yellowish on head, anterior margin of head a little more 
projecting than in H. pacifica ; sculpture of pronotum as in 
H. pacifica; last dorsal segment gently, evenly rounded ; the 
ventral plate of female with a distinct median emargination. 
Fig. 1. a — Hesperoperla, mesosternal grooves; b — Hesperoperla 
obscura, ventral plate; c — Acroneuria, mesosternal grooves. 
Wings less distinctly yellowish than H. pacifica , venation 
similar. 
Expanse 48 to 50 mm. 
From Laggan, Alberta 22 July (Osburn coll.). 
In H. pacifica Bks. the ventral plate of the female is 
rounded and entire ; the head and pronotum more yellowish. 
Type, M. C. Z., no. 23223. 
I believe that these grooves from the inner ends of the 
slits of the meso- and metanotum have an important bearing 
on the classification of the Perlidse. They are present mostly 
in the old genus Perla, now much divided. In our fauna 
they are in Perla, Acroneuria, Togoperla, and Banksiella; 
in Asia they occur in Tylopyge, Oyamia, Kaminuria, 
Mesoperla, Niponiella, Kalidasia, and, Schistoperla. 
They are not present in Isogenus, Clioperla, Hydroperla, 
Perlesta, Isoperla, Perlinella, nor in Paraperla which I pro- 
pose to put in a separate tribe, the Isogenini. They are not 
present in the Cloroperlini (Alloperla and Chloroperla) , 
nor in the Peltoperlini, but are evident, though sometimes 
fainter, in the Neoperlini. The Peltoperlini have the middle 
part of the metasternum very much broader than in the 
other groups. 
