6 BULLETIN 85, UNITED STATES NATIONAL MUSEUM. 



genera has been suppressed and becomes almost invisible in some 

 cases. In Pachypsylla it is so small and indistinct that Mr. Stough 

 overlooked it as a sclerite and called it the "Hgamentary process 

 attaching the frons (really the clypeus) ^ to the head." Figure 15 is 

 from a sagital section through the front ocellus and the frons. The 

 suture between the vertex and the frons is very distinct just above 

 the ocellus. The frons is seen to extend downward beneath the 

 genal cones which lie over it and to attach to the clypeus a little 

 farther down (fig. 15). 



A complete and very interesting series may be fomid within the 

 family, showing the suppression of the frons from a large and promi- 

 nent sclerite to a very small one which is little larger than the ocellus 

 attached to it. The variation of the frons in many other groups of 

 the Homoptera is very similar, and there is little doubt but that a 

 comparative study of this sclerite throughout the whole suborder 

 would throw much light on the taxonomy of the group and the rela- 

 tions of the families within the group. 



The gense are very large and comprise the largest part of the head 

 ventrad.2 j^ £,i'i;ia (fig. 20) the genae are two sclerites, lying one 

 on each side of the elongate frons and between the vertex in front 

 and the clypeus behind. In all cases the antennae are attached on 

 the edge of the gense near the vertex. The variation in the form and 

 shape of the head is due mostly to the variability in the form of the 

 gense. From the simple condition as mentioned above for Livia 

 there is a gradual pushing outward of the gense to form two spherical 

 lobes or two conical processes projecting downward or forward. 

 These processes have had various interpretations, and various names 

 have been assigned to them. Some writers have called them frontal 

 cones, or frontal lobes, or frontal processes; Slingerland called them 

 "cones of the clypeus"; Loew and other European writers have 

 called them stirnkeln, and coni frontdles. The writer in previous 

 papers has called them facial cones, a noncommittal term. Stough 

 is inconsistent m recognizing the sclerites from which these cones 

 arise as the gense and yet calling these processes frontal cones, and 

 at the same time calling the clypeus the frons, a sclerite which has no 

 relation to the cones whatever. The term genal cones is applied to 

 these processes in the taxonomic work of the present paper, and, of 

 course, this is the only possible interpretation of them. 



Usually the gense are inferior in position, but in some species of 

 Carsidarinse, notably in Carsidara (figs. 150, 151) a part of the top 

 surface of the head — what appears to be the vertex — is formed by 

 the gense. The vertex consists of a pair of narrow oblique lobes 



1 The parenthesis is my insertion. 



» In all of this discussion the position of the sclerites is described as actually found in the Psyllid head, 

 and not as in the typical or generalized insect. 



