164 PLANT LICE. 
for the abnormal vegetable growths or galls they produce and 
in which they live; others are peculiar on account of the form 
and the abundance of their excretions. The species form two 
sections, the Pemphigini and the Schizoneurini. 
In the Pemphigini the rather short feelers are six-jointed, 
rarely five-jointed, the third joint being longest; the eyes are 
large, though sometimes absent in the apterous forms enclosed 
in the galls. The species are very similar in form, but the galls 
they make are of such peculiar shape and so constant in form and 
position on the various parts of the woody plants on which they 
occur that we can distinguish the different species by the galls. 
We have three genera in our state, which can be recognized as 
follows: 
Fic. 144—Pemphigus populi-transversus Ril.—After Riley and Monell in Bull. U.S. 
Geol. and Geog. Survey. 
A. Hind wings with two discoidal veins......... PEMPHIGUS. 
AA. Hind wings with only one discoidal vein. 
Be; Antenne 6=jomtedey: She. fascias tate on. Semele TETRANEURA. 
BECAME I5-jGiMted nin none a ero nec tte HORMAPHIS. 
The genus Hormaphis is represented in Minnesota by H. 
papyracee Oest., which according to Prof. Oestlund is found on 
the under side of the leaves of the paper birch, corrugating them 
between the veins, forming long folds in which the lice are packed 
as closely as it is possible for them to be, and at the same time 
be able to reach the leaf with the beak. Being also abundantly 
covered with a flocculent substance, especially the apterous form, 
they undoubtedly find a good protection between the plications 
of the leaf. 
