1915] The Head and Mouth-Parts of Thysanoptera - 25 
asymmetrical clypeus are the mesal pieces on the ventral 
aspect of the mouth-cone. The compound eyes are located 
at the latero-cephalic corners of the head-capsule, and the 
ocelli when present are between the compound eyes on the 
dorsal aspect of the head. 
Heliothrips femoralis (fig. 1, 2, 5, 7, 12, 13, and 19).—A line 
extending between the vertex and the mouth-cone on the head 
of a nymph of Heliothrips has a dorso-ventral position, while a 
similar line on the head of an adult has a cephalo-caudal 
direction. The position of this line or axis in the nymph 
suggests a similarity to the position of the head of an orthopteron 
(Acrididae), while the position of the head of the adult is similar 
to the position of the head of an homopteron (Cicada). 
_ The head-capsule of the nymph is non-reticulated and 
slightly chitinized, while that of the adult is highly reticulated 
and heavily chitinized. The mouth-cone of the nymph occupies 
more than one-half of the cephalic aspect of the head-capsule 
and extends ventro-cephalad, while in the adult it is com- 
paratively smaller and projects ventro-caudad. 
Two similar caudal projections (c. a.) arise from the ventro- 
caudal margin of the head-capsule of the nymph and extend 
for a short distance as narrow pieces between the maxillary 
sclerites (mx. s.) and the submentum (sm.). In the adult 
of Heliothrips the caudal projections (c. a.) differ from those 
of the nymph in that they are decidedly asymmetrical. The 
left projection is broadly joined to the head-capsule while the 
broad right projection has a narrow, neck-like attachment. 
This striking asymmetry is possibly due to the excessive 
lateral extension of the clypeus toward the right side. The 
asymmetry of the caudal projections of other adult Terebrantia 
such as Thrips physapus Linne (fig. 3 and 6) is not as prominent 
as that found in Heliothrips. The caudal projections articulate 
along their dorsal sides against certain sclerites of the prothorax. 
The asymmetry of the head-capsule of the nymph and adult 
is very evident in a frontal view (fig. 1 and 13). About half-way 
between the meson and the left side of the head-capsule on the 
ventral margin of the front there is a decided recurrent angle 
which is very distinct in the adult. The thickenings, depres- 
sions, and invaginations on the frontal area of the head will be 
discussed under the internal head-skeleton. 
