32 Annals Entomological Society of America [Vol. VIII, 
The differences which occur between the tentorium of a 
Cicada and a thrips can be largely accounted for in the dif- 
ferences between the head-structures. The head-capsule of a 
thrips is elongated cephalo-caudad while this extension of the 
head-capsule of a Cicada is short. Furthermore in a Cicada 
the clypeus is large and occupies the greater part of the cephalic 
aspect of the head but this is not so in thrips. The invaginations 
of the dorsal arms (i. d.) in thrips are apparently not associated 
with the antennae. This seemingly lost association is undoubt- 
edly due to the excessive cephalic or dorsal growth of the head- 
capsule. The location of the invaginations of the anterior 
arms of the tentorium (i. a.) in thrips resembles the location 
in a generalized insect since they are near the cephalo-lateral 
corners of the clypeus and not near the distal ends of the 
clypeus as in Cicada. 
The following tentorial structures are present in thrips 
which are difficult to account for on the basis of the homology 
with the structures in Cicada. A distinct thickening extends 
along the caudal or ventral margin of the head-capsule between 
the caudal projections (x. and z.). This thickening is present 
in all thrips. In the nymph of Heliothrips the portion of the 
thickening (x.) between the ventral end of the right anterior 
arm (a. a.) and the right posterior arm (p. a.) is wanting. The 
above thickening may be secondary or possibly may be homol- 
ogized with the union of the ventral ends of the anterior and 
posterior arms.of Cicada’ (xc, and’ ze))---In “all the “thrips 
examined, distinct, chitinous, ental projections arise from the 
invaginations of the dorsal arms. These projections are not 
present in Cicada. 
In considering the tentorium of thrips figured in this paper, 
a distinct atrophy of certain portions and parts can be seen. In 
the adult of Heliothrips (fig. 1 and 27) a thickening occurs 
(x. and z.) along the caudo-ventral margin of the head-capsule 
and from this thickening other thickenings (p. a.) arise which 
extend to the caudal projections (c. a.) of the head-capsule. 
Of the anterior arms (a. a.) only the left one is present. The 
left anterior arm is located in a depressed line extending between 
the invagination of the left dorsal arm and the recurrent 
angle on the caudal margin of the front. The dorsal arms 
(d. a.) are wanting and also the posterior arms (p. a.) except 
for a small portion on the caudal projections (c. a.) of the 
