GENERIC CLASSIFICATION OF APHIDIDAE. 47 
Cylindrical but extremely short, not as long as wide. Cauda very short and rounded, 
not Aphis-like; anal plate rounded. 
Type (monotypical), Crypto siphum artemisiae Buckt. 
Genus HYSTERONEURA Davis. 
1919. Heteroneura Davis, Can. Ent., v. 51, p. 228. 
1919. Hysteroneura Davis, Can. Ent., v. 51, p. 263. 
Characters. — Head without prominent antennal tubercles. Antennae of six seg- 
ments armed with subcircular sensoria. Fore wings with the media twice branched. 
Hind wings with the cubitus absent. Cornicles somewhat tapering or subcylindric, 
cauda Aphis-like; anal plate rounded. 
Type (monotypical), Aphis setariae Thos. 
Genus HYADAPHIS Kirk. 
Plate VI, A A, BB. 
1904. HyadapMs Kirkaldy, The Entomologist, v. 37, p. 279. 
1863. Siphocoryne Passerini, Aphididse Italics, p. 8 (not Siphocoryne , 1860). 
As indicated under the discussion of Siphocoryne, Passerini set 
xylostei as type of his genus in 1863. Nymphaeae had, however, 
been set in 1860, so Kirkaldy gave Hyadaphis to Passerini's 1863 
conception, of which genus xylostei becomes the type. Xylostei has no 
caudal horn and is quite similar in general appearance to a Khopalo- 
siphum. We may separate the two genera, however, on the cauda, 
which in xylostei, particularly in the apterous form, is very large, fully 
as long as the cornicles, and broad, quite unlike that of nymphaeae- 
Several other species which have generally been considered in the 
same genus with xylostei possess a distinct caudal projection on the 
abdomen. One of these has been made the type of Cavariella so that 
such species will be removed from our conception of Hyadaphis. 
Characters. — Head without prominent antennal tubercles; antennae of six segments 
which are rather abundantly armed with tuberculate sensoria. Wing venation normal. 
Cornicles somewhat swollen but not prominently so. Cauda, particularly in the 
apterous form, large, as long as the cornicles, and broad. Males usually winged; 
oviparous females apterous; summer forms usually feeding on the Umbelliferse. 
Type (fixed by Kirkaldy, 1904), Aphis xylostei Schrk. 
Genus HYALOPTERUS Koch. 
Plate VI, ER-WW. 
1854. Hyalopterus Koch, Die Pflanz. Aphid en, p. f6. 
1917. Hayhurstia Del Guercio, Redia, v. 12, p. 208. 
ApMs pruni Fab. was set as the type of this genus in 1860 by 
Passerini. In 1917 Del Guercio erected the genus Hayhurstia. 
There is little difference between the two as will be seen by examining 
the drawings given herewith. The cauda in Hayhurstia is slightly 
narrower than that in Hyalopterus. It is the writer's opinion that 
the two represent only one genus. 
Two other genera may be mentioned here. They are Brachycolus 
Buckt. and Pergandeidia Schout. Specimens of the type species of 
Brachycolus show that this genus is quite similar to Hyalopterus, 
but it differs in the cornicles. In Brachycolus the cornicles are very 
small, almost mere rounded swellings in the apterous form, whereas 
