i8 HOMOPTERA 



of an enormous number of species, that the posterior structures are inclined to be more constant than 

 the anterior; the posterior process, for this reason, is found to be available as a generic character, while 

 the more variable dorsal and suprahumeral structures are suitable for the separation of species. 



The sclerites of the prothorax are not complicated. The pleuron is joined directly to the notum 

 without intervening sclerites. Two distinct lateral sclerites are found, the episternum and the 

 epimeron. The notum projects downward between these sclerites in a triangular extension, the 

 cephaHc margin of which is hollowed out to form a fossa for the eye. Both episternum and epimeron 

 are roughij triangular in shape as seen from a side view, the apex of the triangle pointing upward and 

 the base forming part of the coxal cavity. Neither sclerite is subdivided but the episternum in some 

 forms shows a slight indentation at the cephalo-ventral margin which suggests a coalescence. The 

 pleural suture is not prominent, and is very short since the prolongation of the notum in this region 

 forms a separating ridge which extends almost to the lateral margin of the segment. In certain 

 foliaceous forms, as represented for example in many species of the Membracina, this part of the lateral 

 notum is inclined to be more or less swoUen or flattened and truncate at its distal extremity. Tiiis is 

 a dependable character, but is unnecessary for systematic diagnosis since other more easily dis- 

 tinguished characters are always present with it. In the rather remarkable genus Oxyrhachis the lateral 

 margin of the pronotum is produced in an extended tooth, a character pecuhar to the genus and 

 important as a distinctive taxonomic structure. Just below the cephalic end of the episternum is 

 found a triangular trochantin. 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. 

 Dorsally this sclerite is smooth and articulates with the posterior margin of the head. Ventrally 

 the sternum is irregular in shape but in the simpler forms is trilobed, the central lobe projecting 

 downward farther than the lobe on either side. 



The Mesothorax. — The mesothorax is intimately connected with the metathorax and its 

 dorsal surface is usually completely hidden b^' 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 

 number of species of Membracida the scutellum is simple, rounded, and not at all extended posteriorly ; 

 in a smaller number it is prolonged into a strong prong or thorn, which shows a wide range of shapes 

 and positions. As has been noted, this difference serves as a distinction between the subf. Centroiina and 

 the other subfamilies. VVhile this is a valuable and reliable character, it is unfortunate that it must 

 be chosen as a primary distinctive structure of so large a group as a subfamily, since its determination 

 often necessitates the destruction of the specimen. 



The mesonotum usually shows three rather distinct areas, but these areas are apparently not 

 separate sclerites since from the earliest nymphal stages they are evidently fused. In the adult, 

 however, the regions are set ofF from one another b}' infoldings, or grooves, which may warrant the 

 application of the usual names to these parts. The scutum is uniformly smooth, poorly developed and 

 weakly chitinized. Being covered by the pronotum it is not in reality an external sclerite at all and 

 is not functional as far as protection is concerned. The scutellum when present iorms the second 

 region of the mesonotum, and, as been often noted, develops to form a thick, heavy process ; when 

 undeveloped, the scutellar region is indicatedby a mere transverse fold. Both scutum and scutellum 

 are often entirely membranous. Posterior to the scutellum is a third area, separated from the scutellum 

 by a narrow band of connective tissue. This is probably homologous with the (i pseudonotum » as 

 described by Snodgrass (1909). Snodgrass has found that in certain Hemiptera the mesopseudonotum 



