2 BULLETIN 823, U. S. DEPARTMENT OF AGRICULTURE. 
The present work was undertaken in the hope of remedying such 
a condition to some extent at least. The genera of the world have 
been studied. Many workers have lent material and the large col- 
lections of the National Museum and Bureau of Entomology have 
been drawn upon. In the National Museum collection a large per- 
centage of types has been available. To the study of preserved 
material have been added embryological, anatomical, and biological 
investigations that a better understanding of the natural relationships 
might be gained. 
Besides many aphidologists in this country and abroad, who have 
given helpful suggestions and many of whom have read and criticized 
the manuscript, the writer is indebted to Dr. A. L. Quaintance, of 
the Bureau of Entomology, for the facilities for conducting many of 
the biological investigations which to a large extent have laid the 
foundation for the systematic treatment here given. 
Superfamily APHID OIDEA. 
There appear to be two distinct families in the superfamily Aphi- 
doidea. These are the Aphididae and the Phylloxeridae. The present 
paper deals only with the Aphididae. 
Members of the Phylloxeridae differ markedly from forms belong- 
ing to the Aphididae. In the first place their biologies are quite 
different in that parthenogenetic oviparous forms occur during the 
summer. In the Aphididae only the sexed females which are pro- 
duced in the fall are normally oviparous. 
In structure the two families are separated at once by the formation 
of the stigma of the forewing. The wing itself seems very little 
different in an Adelges or Phylloxera from that in some of the special- 
ized genera of the Aphididae. An examination of the freshly emerged 
wing, however, as has been pointed out by Dr. Patch, shows that the 
stigma in the Phylloxeridae is formed by the radial sector and the 
stigmal vein is the media. In the Aphididae, on the other hand, 
the stigma is formed by radius 1 and the stigmal vein is the radial 
sector. The two families may thus be separated as follows: 
Key to the Families of the Aphidoidea. 
Summer parthenogenetic oviparous forms produced: Stigma formed by 
the radial sector Phylloxeridae. 
Only sexual oviparous forms produced : Stigma formed by radius x Aphididae . 
A word of explanation in regard to the name Phylloxeridae may 
be necessary. The genus Chermes was erected by Linnaeus in 1758 
and in 1862 was replaced by Psylla Geoffroy. For this genus Chermes 
jicus L. was set as type by Lamarck in 1801. Ficus, therefore, be- 
comes ipso facto the type of Chermes, and Chermidae the family 
name of the " jumping plant-lice." The family name for the aphi- 
doidcan group, therefore, is derived from the genus Phylloxera 
Boyer (1834). 
