320 W. D. FUNKHOUSER 



The sternum of the mesothorax indicates by its sculpture a development 

 from three distinct sclerites, but even in the nymphal forms these sclerites 

 are not clearly distinguished. For the sake of convenience in description 

 the areas may be given the usual terms of presternum, sternum, and 

 sternellum, altho it is not at all certain that the regions so designated 

 are strictly homologous with the same sclerites in other insects. The 

 entire sternum is roughly shield-shaped (Plate xxxiii, 8) and in the mature 

 insect shows an anterior fold, a central plate, and a rather distinct posterior 

 piece consisting of a thin arm partly encircling the coxal cavity on each 

 side with a lobed central extension. The presternum is very indistinctly 

 set off from the sternum, and indeed in very few cases can the faint lateral 

 lines that are believed to represent sutures be determined. The sclerite 

 can be distinguished, however, l)y the ventral lobe which is produced 

 downward just behind the presternum. The central sternum is a flat, 

 irregular plate fused with the presternvim anteriorly and extending almost 

 to the coxal cavities posteriorly. Its lateral margins unite with the 

 ventral edges of the episte'rna. The sternellum is always more or less 

 distinct. The lateral arms form the anterior edge of the coxal cavities 

 and the central disk separates these cavities. The central disk bears in 

 many forms a median protuberance, or tooth, which extends directly 

 ventrad. The coxal cavities are not completely closed by the sternal 

 plates of the mesothorax. 



Because of the fact that the notum of this segment projects farther 

 cephalad than the anterior line of the sternum, and because the pleural 

 sclerites are turned under the overhanging edge of the lateral margin of 

 the notum, a strictly ventral view of the mesothorax shows much more 

 than the sternum (Plate xxxiii, 9). No other segment of the thorax is 

 so well developed ventrally as the mesothorax, and no other shows any 

 indication of subdivision in the sternum. 



THE METATHORAX 



The metathorax is a narrow segment closely fused with the mesothorax 

 but weakly joined to the abdomen. In general structure it conforms to 

 the preceding segment but none of the areas are so well developed. 



The notum, as in the mesothorax, is an arched saddle-shaped scknitc^ 

 forming the entire dorsal surface of the segment (Plate xxxiii, 10). No 

 subdivisions have been found and the entire piece is relatively smooth. 



