6 CLASSIFICATION OF THE ALEYKODIDJS. 
The vertex is rounded in most forms and often possesses a median 
longitudinal ridge or marking. In some forms, however, as in the 
genera Udamoselis and Didleurodicus, it is produced into a large 
cone-shaped structure. This prominence between the insertions of 
the antennae in both of these genera seems to point to their close 
relation. 
The f rons is rounded when viewed from the side and when viewed 
from the front it is somewhat U-shaped, the bottom of the U forming 
the suture between it and the clypeus. Its upper edges extend back- 
ward. Below the clypeus is the labium, which is trapezium-shaped. 
The edges of this, as well as those of the clypeus, are slightly turned 
back so that as the structure lies on the labium there will be a better 
situation for the setae. Below the labrum is a triangular sclerite, 
the epipharynx. All of these sclerites are somewhat united into an 
elongate triangular structure which, together with the setae, remains 
attached to the head and is easily separable from the labium. 
The labium is inserted in the base of the head on what is apparently 
a projection of the thorax. It is of considerable length and is com- 
posed of three segments. The relative length of these segments seems 
to vary in the different forms. Near its proximal end the labium is 
bent strongly caudad and appears to be grooved for its entire length. 
At the base this groove is wide, but more centrally it becomes nar- 
rower. The first (proximal) segment is much the longest and is 
narrow. It is in many forms, armed with a few scattered hairs. 
The second segment is thicker and shorter and the sutures separating 
it from the first are not well defined. This has no doubt given rise to 
Marlatt's statement that the labium is two-segmented. 9 The third 
segment is short in Aleyrodes, while in Aleurodicm it is considerably 
longer. It is more heavily chitinized than the others and tapers 
distad. It is covered with numerous hairs and its tip is bilobed. 
Each of these lateral lobes is armed with three pegged-spiked taste 
sensoria situated close together (PI. II, fig. -i). It is noteworthy that 
very similar lobes and the same number of similar pegged sensoria 
occur on the labium of the Psyllidae. The labium in that family is 
also bent on its proximal part. 
The maxillary and mandibular, sclerites are present below the 
frons, the lower extremity of the former becoming projections. The 
seta', four in number, constitute two pairs. Those of the inner or 
maxillary pair are closely pressed against each other and sometimes 
for this reason appear as only one. The outer or mandibular setae 
i certain extent Inclose the maxillary ones. 
Tn his excellent paper on (lie hackberry Psylla, Stougfa has pointed 
out the very great similarity between the inouthparts in this family 
and those of the Psyllid®. He says: 10 
The monthparts, exclusive of the labium, are almost Identical with, though 
htr^<T than, those of the Alenrodids which I have examined. The same 
