20 HOMOPTERA 



irregular plate tused with the presternum anteriorly and extending almost to the coxal cavities poste- 

 riorly. Its lateral margins unite with the ventral edges of the episterna. The sternellum is always more 

 or less distinct. Its lateral arms form the anterior edge of the coxal cavities and its central disk 

 separates these cavities. The central disk often bears 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. 

 No other segment of the thorax is so well developed ventrally as the mesothorax, and no other shows 

 anj' indication of subdivision in the sternum. 



The Matathorax. — 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 sclerite 

 forming the entire dorsal surface of the segment. No subdivisions have been found and the entire 

 piece is relatively smooth. The metanotum is more strongly chitinized than the mesonotum, probablj' 

 due to the fact that this segment is less protected by the pronotum in most forms. The lateral extrem- 

 ities of the sclerite are slightly bent outward and bear two wing processes, an anterior notal wing 

 process and a posterior notal wing process. Of these the anterior is the better developed. The pleuron 

 consists of an episternum and an epimeron. homologous to those of the mesothorax but differing in 

 position with reference to the body axis. In the metathorax the sclerites appear to be twisted out 

 of position, so that instead of being side by side, as in the normal condition, they are in an oblique 

 Hne, with the episternum clearly below the epimeron and the pleural suture extending more or less 

 ventro-caudad rather than perpendicularly. The pleural sclerites are distinctly set off from the meta- 

 notum by the wing cavity, the only connection being the interscleritic membrane. The metathorax 

 agrees with the mesothorax in showing no traces of paraptera. It would appear that one of the 

 distinctive structural characters of the family is the absence of these supporting sclerites. The epi- 

 sternum is subquadrangular and inclined to be prolonged at its ventral angle. In certain forms of the 

 sf. Membracina a small sclerite, apparently derived from the episternum, is found just cephalad of this 

 sclerite, but this has been noted in only a few species even of that subfamily. A divided episternum, 

 however, would not be an unnatural condition, as evidenced by the structure of the mesothorax. The 

 epimeron isdistinctly divided into two sclerites, the larger being cephalo-ventrad of the smaller. Aside 

 from a slight shifting in position throughout the subfamilies, the epimeron is a constant and uniform 

 structure. It may be mentioned that the pleura of both the meso- and metathorax are much inclined 

 to pubescence in the Membracida. In certain genera of the Cenirotina this region is usually covered 

 also with a hairy white excrescence, which in the adult insect completely hides all anatomical structures. 

 These white tomentose patches are remarkabl}- persistent and do not rub off easily. They have been 

 used, in fact, and apparently with success, as systematic characters, and are very distinctive in certain 

 species. The nature and function of the deposit is unknown, but its presence in many forms entirely 

 precludes the use of scleritic structure for taxonomic purposes. This same woolly covering, described 

 by various authois in various terms but often designated as « cretaceously sericeous », is also commonly 

 found on the exposed scutellum. In fresh specimens it is generally snow-white in color and is a most 

 attractive decoration. In the genus Oxyrhachis both the meso- and the metapleura are extended to 

 form short, blunt teeth. Such developments are, however, rare in the family. 



A striking development of the pleura which is characteristic of the Membracidas is found in 

 the mesothoracic episternum. This is the episternal hook. This hook arises from near the upper 



