48 BULLETIN 826, U. S. DEPARTMENT OF AGRICULTURE. 



in Hyalop terns 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 very 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 antenna! tubercles, 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, GO. 

 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 

 ab-iupt swelling, but only a gradual one which is not at all prominent, 

 as in Liosomaphis. 



Characters. — Head without prominent antennal tubercles. Antennae 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. Antennse 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. 



