Biology of the Membra cidae of the Cayuga Lake Basin 315 



notiini is inclined to be more or less swollen or flattened and truncate at 

 its distal extremity (Plate xxxii, 13). This is a dependable character, but 

 is unnecessary for systematic diagnosis since other more easily distin- 

 guished characters are always present with it. In the rather remarkable 

 genus OxjThachis the lateral margin of the pronotum is produced in an 

 extended tooth, a character peculiar to the genus and important as a 

 distinctive taxonomic structiu'c. Just below the cephalad end of the 

 episternum is found a triangular frochantin. This piece likewise is a single 

 sclerite without evidence of subdivision. 



The sternum of the prothorax consists of a single transverse bar extending 

 between the coxal cavities (Plate xxxiii, 8). Dorsally this sclerite is 

 smooth, and slightly curved to form the floor of the body cavity. The 

 cephalic edge is also comparatively smooth and articulates with the 

 posterior margin of the head. Ventrally the sternmn is irregular in shape 

 but in the simpler forms is trilobed, the central lobe projecting downward 

 farther than the lobe on either side. 



In summarizing the taxonomic importance of the sclerites of the pro- 

 thorax, it may be observed that the pronotum, because of its variation in 

 form, offers the most valuable characters, not only of the segment, but 

 also, perhaps, of the entire body; the pleural sclerites are doubtless of 

 enough importance to warrant careful study, but, because of the pubescence 

 which is prevalent in this region in most species, they are not suited for 

 superficial examination; the sternum is of practically no importance because 

 of its small size, irregularity of structure, and inconspicuous position 

 between the mouth parts. 



THE MESOTHORAX 



The mesothorax is intimately connected with the metathorax and its 

 dorsal surface is usually completely hidden by the posterior process of 

 the prothorax. The sclerites of the pleura, however, may be distinguished 

 in the mature insect and their extent and position readily verified in 

 prepared material. 



The notum of the mesothorax shows two distinct types, according to 

 whether the scutellum is or is not developed into a posterior prolongation. 

 In by far the greater nmnber of the species of Membracidae the scutellum 

 is simple, rounded, and not at all extended posteriorly (Plate xxxiii, 3); 

 in a smaller number it is prolonged into a strong prong or thorn, which 



