Stough: the hackberry psylla. 13? 



describe the different parts as I have found them, together with 

 my interpretation as to their homologies. The structure of 

 the notum is not so difficult to determine. Three sclerites are 

 plainly made out (27-3 A). The anterior of these is crescent- 

 shaped, and in life is concealed by the scutellum of the meso- 

 tergum. The dorsal portion of the second sclerite is a small 

 ovate plate, while the third and posterior sclerite is rather 

 broad, its posterior margin somewhat indented and its lateral 

 margins concave. 



The metasternum (27-6; 30-8; 31-1, str) is best developed 

 anteriorally where it is connected with a very light, narrow, 

 median portion between the acetabula, which in turn is con- 

 nected with and almost seems to be a part of the metafurca, mf, 

 of the endoskeleton. Closely connected to the internal pieces 

 of the latter, and separated from the sternum by an obscure 

 suture, is a sclerite whose dorsal end fuses with the other parts. 

 This probably represents the region of the metaepisternum 

 (31-7, es 3). The portion (x) in figure 7 which runs ven- 

 trad and entad to join a part of the metafurca has notches on 

 its ventral edge at x, and with these notches articulates the end 

 of a complex of sclerites extending down the side and across 

 the ventral surface of the segment (27-6 and 31-S). Much 

 difficulty was found in homologizing these sclerites, authorities 

 differing as to the names of some of the parts. Upon tearing 

 loose this complex carrying the metathoracic leg from its at- 

 tachment at X and y (31-S) and examining it under a high 

 power of the microscope, its structure could be made out. It is 

 composed of five sclerites. Entad (somewhat caudad and 

 dorsad) is a more or less crescent-shaped sclerite (fig. 8, str). 

 This I believe to be a part of the sternum. The next sclerite, 

 mer, extad and cephalad, is of a similar shape but bears a blunt 

 projection or tubercle. Authorities differ as to what is the 

 homology of this part. Westwood says : "Beneath, the epimeru 

 of the metathorax are singularly produced behind the place of 

 insertion of the hind legs (which are pushed forwards), and 

 terminated by two strong spurs." Edwards states: "Meso- 

 sternum produced behind into two large, sharp spines." Riley 

 states : "Metasternal processes cylindrical, hardly narrower 

 toward the tip, which is obtuse, not pointed." I find a similar 

 structure in all the Cicadidae which I have examined. In "Les 

 Cicadines D'Europe," translated from the German of Fieber 

 by Reiber (1875), in the discussion of the general structure of 



