1915] The Head and Mouth-Parts of Thysanoptera 27 
CLYPEUS AND LABRUM.—The clypeus and labrum are the 
mesal pieces on the ventral aspect of the mouth-cone. 
Heliothrips femoralis (fig. 1 and 13).—The adult and nymph 
show no marked differences in the form of the clypeus and 
labrum. The clypeus (cl.) is the large asymmetrical piece, 
and the convex piece at its distal end is the labrum (Ir.). Garman 
and other workers have considered the area cephalad of the 
line f as the clypeus and the area ventrad of this line as the 
labrum. With this interpretation one meets with considerable 
difficulty 1n homologizing the parts in the two suborders. 
If the line f is a suture, it can not be the clypeo-labral suture, 
but must be the proximal margin of the clypeus. The area 
between this so-called suture and the front is a broad hyaline 
membrane (me.). In safranin-stained material, it is slightly 
colored while in sagittal sections stained in haematoxylin it 
shows a decided blue tinge. The above interpretation of the 
line f may be correct, but a better interpretation seems to be 
that it marks the point where the heavily chitinized, proximal 
end of the clypeus becomes more or less membranous, and thus 
permits the dorsal and lateral movements of the mouth-cone. 
The line f is located in a deep fold from which point the mouth- 
cone extends in a caudo-ventral direction in the adult and 
cephalo-ventrad in the nymph. A distinct line or suture 
(s.) can be seen extending from the recurrent angle on the front 
poOpeae lett alateral end: of the: dine if... Dhis/suture is’ the left 
lateral margin of the clypeus and shows distinctly in the nymph 
of Heliothrips (fig. 13) and in the adult of Thrips physapus 
(fig. 3). This evidence supports the interpretation that the 
entire area from the front to the small convex labrum is the 
clypeus. Garman’s drawing of Limothrips cerealium shows 
clearly the above clypeal and labral areas even tho he interprets 
the parts differently. 
The clypeus (cl.) is an asymmetrical triangle with its right 
latero-cephalic angle decidedly more cephalad than its left 
latero-cephalic angle. The left margin of the clypeus is a 
comparatively straight line from the front to the labrum and 
nearly parallel with the meson, while the right margin in the 
adult is a curved line and extends at a decided angle to the 
meson from the labrum to the point of attachment of the right 
caudal projection with the head-capsule. This unique asym- 
metry is characteristic of all the Terebrantia examined. 
