48 BULLETIN 826, U. S. DEPARTMENT OF AGRICULTURE. 
in Hyalopterus the cornicles are in the apterous form of fair size and 
not distinctly swollen. 
Specimens of the type of Pergandeidia received from Schouteden 
show that this genus is very close to Hyalopterus and is probably 
almost too close for a Tery distinct genus. The diagnosis given by 
Wilson (1910) for this genus does, not agree with the type species as 
determined by the author of the genus. 
In the specimens examined by the writer the cauda, as will be seen 
in the drawings, is very much longer than the cornicles, bearing about 
the same ratio as seen in Hyalopterus. 
Characters. — Head without distinct antennal tubercle's, antennae of six segments 
armed with subcircular sensoria. Wing venation normal. Cornicles very short, not 
much longer than the cauda is wide at its base, swollen beyond the middle, particularly 
in the alate form. Cauda long and broad, considerably longer than the cornicles. 
Form of the insects elongate, often more or less flat. 
Type (fixed by Passerini, 1860), Aphis pruni Fab. (=A. arundinis Fab.). 
Genus LIOSOMAPHIS Walker. 
Plate VI, NN, 00. 
1868. Liosomaphis Walker, The Zoologist, p. 1119. 
The genus Liosomaphis Walker is related somewhat closely to 
Khopalosiphum. The two genera, however, can be separated on the 
structure of the cornicles. 
In Liosomaphis the cornicles have a very distinct neck near the 
proximal extremity, due to a constriction behind the prominent 
swelling. This is strikingly evident in the apterous form, as well as 
in the alate one. In Khopalosiphum, on the other hand, there is no 
abrupt swelling, but only a gradual one which is not at all prominent, 
as in Liosomaphis. 
Characters. — Head without prominent antennal tubercles. Antennas of six segments 
armed with subcircular sensoria. Wing venation normal. Cornicles elongate, 
distinctly swollen in the middle, and with a constricted neck near the base. 
Structure in both the apterous and alate forms similar. Cauda not as long as the 
cornicles, somewhat narrowly conical. Males usually winged; oviparous females 
usually apterous. 
Type (monotypical), Aphis berberidis Kalt. 
Genus MASTOPODA Oestlund. 
1886. Mastopoda Oestlund, Minn. Geol. Surv. Rept. 14, p. 52. 
The genus Mastopoda Oestlund, like Gillette's Atarsos, is peculiar 
in that the tarsi are atrophied. 
Characters. — Head without distinct antennal tubercles. Antennae of five segments. 
Fore wings with the media twice branched, hind wings with both media and cubitus 
present. Cornicles somewhat long and cylindrical. Cauda short, conical, Aphis- 
like. Legs with the tarsi absent and provided instead with a membranous disk 
which enables the insect to walk inverted on smooth surfaces. 
Type (monotypical), Mastopoda pteridis Oestlund. 
