36 Annals Entomological Society of America [Vol. VIII, 
biting type of mouth. The arrangement of the parts of the 
mouth-cone, the presence of maxillary and labial palpi and 
other characteristics in Thysanoptera show this close similarity. 
The labium of the nymph and adult of thrips is similar 
(fig. 60 and 61). The entire convex, caudal area of the mouth- 
cone is the labium. From a caudal view it is distinctly tri- 
angular in outline, with the apex at its distal end and from a 
ventral or lateral view it is convex. The labium is attached 
along its lateral margins to the triangular, palpus-bearing 
sclerites (mx. s.) while its dorsal margin is united with the ventral 
membranous portion of the prothorax. It is composed of 
two distinct sclerites separated by a transverse suture (s.). 
The proximal piece is the submentum (sm.) and the distal 
piece is the mentum (m.). The mentum has at its distal 
end a membranous area which gives rise to a pair of small, 
two-segmented palpi (lb. pl.). The distal margin of the 
mentum possesses two small, chitinous projections considered 
by Hinds as paraglossae (pr.). 
Heliothrips femoralis.—The labium of Heliothrips (fig. 60) 
corresponds to the general description. The dorso-ventral 
length of the labium is about the width of the submentum. 
The ectal surface of the labium is slightly reticulated. 
Cephalothrips yucce.—The labium of Cephalothrips (fig. 61) 
corresponds to the general description. The mouth-cone of 
Cephalothrips is short, consequently the dorso-ventral length 
of the labium is less than one-half the width of its submentum 
(s. m.). The submentum is heavily chitinized along its proxi- 
mal margin as indicated in the figure.. The mesal portion of 
the suture (s.) between the submentum and the mentum is 
obsolete, but its lateral ends show distinctly. The two pro- 
jections or paraglossae at the distal end of the labium are united 
and form a lip-like structure over which the movable, paired, 
piercing organs pass. This lip is indicated by shading in 
figure 8. 
MAXILLAE.—A pair of asymmetrical, triangular, palpus- 
bearing sclerites (mx. s.) are situated on the lateral sides of the 
clypeus and labrum in the mouth-cone of the Thysanoptera 
(fig. 1 and 8). The palpi (mx. pl.) of these pieces are usually 
two- or three-segmented. A comparison of these palpus- 
bearing sclerites with similar sclerites in Cicada shows that 
