THE JUMPING PLANT-LICE OB PSYLLID^ OF THE NEW WORLD. 5 



As a third and very essential method of study serial sections of 

 specimens fixed in various fluids were used. Transverse, sagital, 

 and longitudinal sections were made. 



Figs. 1, 3, 5, 15, 17, 21. 



The head of the members of Psyllidse in the essential parts is not 

 materially different from that of other Homoptera. In appearance 

 it is very variable within the family because of the peculiar pro- 

 longations of the genae or the vertex or some other part of the head. 



The vertex is a large dorsal sclerite comprising usually most or all 

 of the top of the head and divided by a median suture which is 

 always easily visible (fig. 5). At the extreme posterior angles of 

 the vertex are the two posterior ocelli. The surface of the vertex 

 is variable, being sometimes flat, or more often with irregular depres- 

 sions or foveas, or sometimes rounded forward and downward. Its 

 shape also is variable from quadrate to triangular or semicircular, 

 or each of the two lobes may be rhomboidal. 



The /rows has in most cases been overlooked in the Psyllidag and 

 the clypeus erroneously called the frons. In Psylla, Trioza, and 

 many other genera the frons is scarcely visible as a sclerite, but in 

 some species it is very prominent, as, for instance, in PaurocepTiala 

 magnifrons (fig. 16) and Livia, ApJialara, and several other genera. 

 In all cases it is present as a small or large sclerite bearing the anterior 

 ocellus at its base or the end nearest the vertex. In many species of 

 Psylla the ocellus is imbedded between the vertex and the gense 

 and no frons is at first apparent. After careful examination, however, 

 the small sclerite of the frons becomes visible below the ocellus and 

 between and beneath the genal cones (figs. 15, 21). 



The shape and form of the frons is very variable. In Paurocephala 

 magnifrons, a Mexican species (fig. 16), it is a relatively large, con- 

 spicuous, pentagonal sclerite occupying an anterior position on the 

 head (actual, not relative), with the vertex articulating on the two 

 sides, the genas on two sides and the clypeus on the fifth side or apex. 

 The anterior ocellus is at the base, the same relative position as in 

 all the other species. The sutures and sclerites are almost dia- 

 grammatically clear in this species. 



In Livia (fig. 20) BMnocola, Aphalara (fig. 18), Aphalaroida, 

 PaurocepTiala (fig. 16), PauropsyUa, Heteropsylla, some species of 

 Carsidarinae, and others the frons is very distinct but occupies an 

 inferior position on the head and is more elongate and the sutures 

 sometimes less distinct than in the Mexican species mentioned above. 

 In these fonns, too, the anterior ocellus is borne at the base of the frons 

 (the apex of the head), and the frons appears sometimes as the stalk 

 of the ocellus. As stated above, the frons in Psylla and many other 



