14 BULLETIN 85, UNITED STATES NATIONAL MUSEUM. 



way between the fork and the apex is an arcuate transverse process 

 connecting the two arms of the furcse; extending from each arm a 

 little further distad is a process connecting with the post-coxal pro- 

 longation of the epimeron; another, a little more proximal of the 

 latter process, unites with the ridge on the internal side of the margin 

 of the epimeron and episternum in front of the coxa (figs. 1, 10, 11). 

 This is the form in several species of Psylla. In other genera there 

 are minor differences, but the principal features of the endo- and 

 exoskeleton are the same. 



The musculature of the thorax, and especially of the metathorax, 

 is very remarkable and interesting, but it will not be discussed here. 

 It scarcely needs to be said that these peculiar developments of the 

 metafurcse and metasternum are for muscle attachment. 



APPENDAGES OF THE THORAX. 



Wings (fig. 395).— The wings, four in number, are membranous, 

 though sometimes the anterior pair is thickened and leathery. The 

 shape is variable from elongate-ovate to rhomboidal. The venation 

 is simple, and presents relatively few striking differences throughout 

 the family. 



The media and cubitus have fused at the base with the radius, and 

 only one principal basal vein is present (R+M + Cu). This divides 

 near the base into either three (Triozinse) or two veins. In the latter 

 case the posterior of the two veins (M + Cu, or the cubital petiole) 

 divides again into the media and cubitus. The upper fork, radius 

 (R) , gives off the radial sector (Rs) about midway in its course to 

 the costa (C). The radius may unite with the costa directly or it 

 may turn near the costa and follow parallel with it for a distance 

 before uniting with it. The space between the costa and radius, in 

 the latter case, is called the pterostigma. The radial sector passes to 

 the apical portion of the wing and is branched only in exceptional 

 cases. 



The medial vein is branched once near its apex, forming M^+j and 

 M3, and the cell thus formed is called the second marginal cell. The 

 cubitus, also, forks once into Cuj and Cug, forming the first marginal 

 cell. The claval suture dividing the clavus and corium is near the 

 base, extending from the base to near the tip of Cuj. Only one anal 

 vein is present, and that is very short and near the base. The veins, 

 and sometimes the membrane, are beset with fine or coarse hairs. 



The venation of the posterior wings is even more simple, the 

 wings themselves being much smaller and more delicate in texture. 

 Rj is wanting, the first vein behind the costa being the radial sector. 

 The media is unforked at the end. The cubitus divides, as in the 

 primary wing, into Cu^ and Cuj. A short anal vein is sometimes 

 present. 



