GENERIC CLASSIFICATION OF APHIDIDAE. 17 
Genus UNILACKNUS Wilson. 
Plate II, E-G. 
1819. U.nilachnus Yv'ilson, Ent. News, v. 30, p. 5. 
The genus Unilachnus Wilson appears to be a connecting link 
between this subtribe and the Euiachnina. In some respects the 
genus is very suggestive of that subtribe. The form is elongate and 
the cornicles are reduced. They are armed, however, with hairs and 
are not so reduced as in the Euiachnina. The ocular tubercles here 
are very rudimentary, almost absent, and in this regard, too, the genus 
suggests the Euiachnina, but it seems to belong in this subtribe. 
Characters.- — Form elongate; cornicles somewhat reduced; ocular tubercles small; 
media of fore wings simple. Antennas of six segments moderately armed. 
Type, Lachnus parvus Wilson. 
Subtribe PTEROCHLORINA. 
The genera belonging in the subtribe Pterochlorina are in some ways 
more primitive than those of the Lachnina, but in other respects some 
of them are more specialized. The radial sector of the fore wings is still 
curved and in some genera quite elongate. This is much nearer the 
early type of wing than is the wing of the Lachnina where the radial 
sector is short and has migrated almost to the tip of the wing. Of 
course, the distinct curving of this vein found in some of the genera 
is an advance on the slightly curved elongate vein usually met with 
in the fossils, but to our mind the location and character of this vein 
are much more primitive than in the Lachnina. The stigmal area and 
the sexual forms appear considerably more primitive than in the 
Anoecina, the specialization of which has been in a different direction 
from that of the Lachnina. The male of Stomaphis is, however, an 
exception. 
Characters. — Head often divided; antennas of six segments, armed with hairs and 
sub circular sensoria. Fore wings with radial sector somewhat curved and not close 
to the tip of the wing. Cornicles on broad hairy cones. Males usually winged. 
Key to the Genera of the Pterochlorina. 
1. Stigma extending along costal margin almost to the tip of the wing. -Longistigma. 
Stigma not so extending 2. 
2. Beak extremely long, very much longer than body; antennas covered 
• with very tine, short hairs Stomaphis. 
Beak normal in length; antennas with rather stout hairs, often quite 
long Pterochlorus. 
Genus LONGISTIGMA Wilson. 
Plate II, H-L. 
1909. Longistigma Wilson, Can. Ent., v. 41, p. 385. 
1909. Davisia Del Guercio, Redia, v. 5, p. 185. 
The genus Longistigma Wilson can be distinguished at once by the 
shape of the stigma which is drawn out at the tip to an acute point 
which extends almost to the tip of the wing. The t}^pe species is 
141613°— 20— Bull. 826 2 
