stough: the hackberry psylla. 135 



labium, which is imbedded in a membranous fold between the 

 former, most of the prosternal region, leaving the prosternum 

 to develop mostly on the sides. The "collar," already described 

 as a chitinized process holding the labium to the thorax, may 

 be of the nature of the apophyse as seen in the endoskeleton of 

 the mesothorax. 



Mesothorax. — The mesothorax is next in complexity of 

 structure, naturally being larger and more complex than the 

 prothorax, as it bears, besides one pair of legs, the fore wings. 

 The tergum is composed of three sclerites (34-2, and 27-3, A, 

 B), Edwards thus describes the mesotergum of the Psyllidse: 

 "Mesonotum large, generally suborbicular ; a portion of its 

 area in front in the shape of a broadly truncate triangle (the 

 dorsulum) , separated from the remainder by a distinct suture, 

 and a small crescent-shaped piece projecting from the middle 

 of its hind margin (the scutellum) , also marked off by a 

 suture." 



The dorsulum {27-S A and 1) is in shape an equilateral 

 triangle, truncate at its angles, with the edges of the lateral 

 truncations notched. The posterior margin is not straight, but 

 produced on each side into a small projection midway between 

 the median line and the edge of the sclerite. The anterior third 

 of the dorsulum is covered by the posterior edge of the prono- 

 tum (fig. 3 A). 



The mesonotum (27-S A and 1, mm) is the largest sclerite 

 of the thorax, ovate, convex, and about twice as wide 

 as long, with anterior margin almost straight and posterior 

 margin deeply convex. The sclerite is laterally narrowed to a 

 blunt, notched point, which is best seen in lateral view (fig. 1). 



The scutellum (figs. 3 A and B, sen, and 1) is, viewed from 

 above, ovate, twice as wide as long, lateral edges rounded, an- 

 terior margin slightly concave and posterior convex and hol- 

 lowed out at the median line. The structure of the pleurum 

 of the mesothorax is exceedingly complicated and the sutures 

 are all indefinite. The structure of the same is shown (partly 

 diagrammatic) in figure 1. The suture between the meso- 

 sternum and the sclerite just dorsad could generally be made 

 out. This latter sclerite I take to be the mesoepisternum, es 2. 

 The mesoepimeron, es 2, is a very irregular, much folded scle- 

 rite intimately connected with the inwardly extending endoskel- 

 eton (fig. 2, es 2 and eytd) . These pleural sclerites are so folded 



2-Univ._Sci. Bull.. Vol. V. No. 9. 



