NO. 13 STAPH YLINIDAE BLACK WELDER 21 



The remainder of the venter is occupied by the membranes lining 

 the coxal cavities (fig. 3 A, cxc) and that connecting the prothorax 

 and the mesothorax (inb). In the lateral parts of this latter membrane 

 and just caudad of the coxal cavities lies the pair of sclerites, the 

 peritremes, bearing the spiracles of the mesothorax. 



The pleural elements appear to have been so far reduced by the 

 approximation of the notum and sternum as to have disappeared en- 

 tirely as separate sclerites. This area normally forms the major ar- 

 ticulation of the coxa (the anterior or dorsal articulation). In the 

 present species the trochantin, whose apical end forms the posterior 

 or ventral articulation, is prolonged around the base and provides 

 also the dorsal articulation. This may be interpreted as an indica- 

 tion that the pleural elements have united with the trochantin and 

 are represented only in that sclerite. 



The trochantin of the prothorax (fig. 3 A, tn, B) is a long narrow 

 sclerite with a lobate projection on the lateral side. This lobe bears 

 the dorsal articulation of the coxa as described above. The cephalic 

 part projects under the anterior margin of the coxal cavity. The caudal 

 part, projecting into the coxal cavity, is more heavily sclerotized and 

 thicker than the rest. It is elevated into a longitudinal ridge which 

 bears a few setae and a series of the minute punctures with setulae. 

 The surface, especially that bordering the ridge, is strigulose. The 

 posteromedian end articulates with the inner edge of the coxa. 



The mesothorax is much shorter than the prothorax or the meta- 

 thorax and is closely united to the latter (fig. 3 A). It is united to 

 the prothorax by a membrane (nib) which is of considerable extent 

 on the ventral aspect, extending to the coxal cavities of the prothorax. 



In this membrane lies the peritreme (fig. 3 A, peri, E) bearing the 

 mesothoracic spiracle (sp). The peritreme is an oblong sclerite, 

 placed transversely, and nearly two and one-half times as wide as 

 long. It is thought to be a secondary sclerotization of the interseg- 

 mental membrane. The spiracle is located in the lateral three-fourths 

 of the sclerite and is similar in appearance to the first abdominal 

 spiracle (fig. 9 D). There are a very few scattered setae on the mem- 

 branous declivity surrounding the sieve processes. At the sides just 

 ventrad and caudad of the spiracles is an area bearing a few minute 

 setae in relatively very large punctures (fig. 3 A, x, F). This area 

 is not differentiated from the remainder of the membrane and is 

 unsclerotized. 



The dorsal aspect of the mesothorax is nearly covered by the pro- 

 jecting caudal edge of the pronotum (fig. 3 A). Its most conspicuous 

 sclerite is the central shield-shaped area (fig. 4 C, A) which is gen- 



