8 BULLETIN 85, UNITED STATES NATIONAL MUSEUM. 



The mandibular and maxillary setae are attached near the base of 

 the clypcus and pass out along the labium. They are very long, 

 often very much longer than the labium. 



The eyes are lai^e and usually more or less hemispherical, project- 

 ing laterad from the side of the head. The facets are relatively very 

 large. In Livia (fig. 20) the eyes are peculiarly flattened, and are 

 pecuHar, too, in having a tubercle (pre-ocular tubercle) projecting 

 partly into their front margin. This resembles very much an ocellus 

 and may possibly be some kind of a sense organ. There are three 

 ocelli, as mentioned above; two on the vertex and one on the frons. 



The antennse are nearly always ten-segmented, rarely nine- and 

 only abnormally eleven-segmented. They are attached to the genae 

 near the margin of the vertex, sometimes near the lateral margin of 

 the genae, and sometimes more toward the front. The first two 

 segments are always larger and shorter than the following joints. 

 The third is nearly always the longest, the others each being shorter 

 than the preceding one. The terminal segment is thickened a little 

 and bears two thick setae of unequal length. In some genera (Pauro- 

 spylla and others) these setae are half as long as the antennae. Scat- 

 tered over the surface of the intermediate segments are hairs, probably 

 sensory, which in some species, Homotoma species for instance, are 

 very abundant. There are also a considerable number of sensory 

 areas of various kinds, some being simple differentiated rings or pits, 

 and others being of a rather complicated structure. Further study 

 of these undoubtedly will bring to light many interesting forms of 

 sensory apparatus. The living psyUid moves the antennae rapidly 

 and almost continually; sometimes the movement is so rapid that 

 it might well be called vibration. 



Figs. 1-4, 6-12. 



In proportion to the rest of the body the thorax of the Psyllidae is 

 very large. It has become specialized by the habits of leaping of 

 the insect, and is not only large and strong but some of the sclerites 

 are most remarkably developed. This is true especially of the meso- 

 and metathorax. 



The prothorax is short. The notum consists of a single sclerite 

 wliich is arched over behind the head. The extent to which it reaches 

 downward on each side varies in the different genera. In Livia it is 

 large and extends down laterad to the forecoxae (fig. 3), while in 

 Psylla and Trioza it extends only about halfway down toward the 

 coxae (figs. 1, 4, 6-8). Near each lateral extremity, in most species, 

 is a foveal impression which sometimes is very prominent. The 

 lateral extremity may be more or less swollen and knoblike, as in 



