GENEKIC CLASSIFICATION OF APHIDIDAE. 35 
Characters. — Cornicles present, truncate in form, often sculptured. Antennae of 
six segments (with the exception of the dimorph) armed with oval sensoria and promi- 
nent hairs. Fore wings with the media twice branched; hind wings with both 
media and cubitus present. Cauda and anal plate rounded. 
Forms living upon the foliage of trees. Sexes not strikingly different from the 
other forms, possessing beaks and feeding. Males winged, oviparous females with 
the ovaries normally developed, thus laying several eggs. Small lamellate or hairy 
dimorphic forms produced in summer. 
Type (monotypical), Periphyllus testudo Van der Hoeven {—testudinatus Thorn- 
ton). 
Genus NEOTHOMASIA, n. n. 
Plate IV, Y, Z. 
1910. Thomasia Wilson, Can. Ent., v. 42, p. 386. 
Wilson erected the genus Thomasia with populicola Thos. as 
type, and his description appeared in December, 1910. The same 
name had, however, been used for a genus of Diptera, the description 
of which appeared in September, 1910. A new name, Neo thomasia, 
therefore, is necessary for Wilson's genus. 
Characters. — Cornicles present; antennae of six segments armed with sub circular 
sensoria and prominent hairs. Fore wings with the media twice branched, hind wings 
with both media and- cubitus present. Cauda and anal plate both rounded. 
Forms living in colonies upon the leaves or bark of trees; no dimorphic forms pro- 
duced; sexual' forms not markedly different from the viviparous ones. Oviparous 
females laying several eggs. 
Type (monotypical), Chaitophorus populicola Thos. 
Genus SIP HA Pass. 
1860. Sipha Passerini, Gli Afidi, p. 29. 
This genus and Atheroides are distinct from the other genera in 
the subtribe by possessing five-segmented antennae instead of six- 
segmented ones. The genus has not been much confused excepting 
by Thomas's placing of rubifolii. For a time some workers in this 
country were led to conceive of the genus as indicated by that spe- 
cies which in reality belongs in the Aphidini. 
Characters. — Cornicles present, truncate, short, almost mere rings. Antennae of 
five segments armed with large circular sensoria. Body form flat, entire insect cov- 
ered with rather long stout hairs. Fore wings with the media twice branched, hind 
wings with both media and cubitus present. Cauda knobbed, anal plate rounded. 
Forms living upon the leaves of grasses usually in moist localities, sometimes even 
submerged, the water appearing to affect them little. 
Type (fixed by Passerini, 1860), Aphis ghjceriae Kalt. 
Subtribe PTEROCOMMINA. 
The subtribe Pterocommina is composed of bark-feeding insects, 
some of which retain quite primitive characters. It is the writer's 
opinion, however, that they are, as a group, more specialized than 
the Chaitophorina, but closely related.. This is indicated by the 
development of the cornicles met with in the species. Like the 
