Pemphigus monophagus, n. sp.

Described from holotype and 16 paratypes from gall on Populus balsamiferae at 8,200 feet elevation, August 17, 1924, in Rocky Mountain National Park, Colorado.

The Gall. A more or less globular gall composed of leaf blade located at the base of the leaf with nearly circular opening on the under side closed by a thickened portion of the petiole that lays in a plane almost parallel to the blade of the leaf. The opening may be at the right or left of midrib. In a gall open on the right side of the midrib the thickened part of the petiole bends sharply to the left; then from a point near where the petiole passes into the midrib there is an abrupt bend to the right. Thus the thickened parts form a letter S. When the gall opens on the left of the midrib the S is backwards. There is usually a shallow furrow passing over the gall near its middle suggesting a double gall.

Taxonomy.-This species is placed in the genus Pemphigus because of the great structural similarity. In the number of generations and the sequence of forms it differs from the typical Pemphigus. There are but four generations, three of which, the fundatrix, fundatrigenia and sexupara, all develop in the same gall. Observations lead to the conclusion that all of the young of the fundatrix develop into apterous viviparae, these in turn producing the sexuparae. Further study may place this species in a new genus since it resembles Pemphigus much as Cornaphis does Asiphum. What appears to be this species was taken by J. J. Davis on August 5, 1913. near Flat Head Lake in Montana. Material received from R. Glendenning collected at Lillooet and Merrit, B. C., on Populus trichocarpa also appears to be this species.

- Asa Maxson: (1934) Four new pemphigids from Colorado (Aphidae: Homoptera)^©