408 C. GORDON HEWITT. 



chitinous apodemes project into the thoracic cavity. The 

 lateral regions of the pronotum are in contact with the 

 humeri and the prothoracic episterna. The humeri (/iw.) are 

 a pair of strongly convex sclerites situated in the antero- 

 lateral region of the thorax. They are bounded above by the 

 prescutum of the mesothorax, internally and below by the 

 episterna of the prothorax, and externally by the lateral plate 

 of the mesosternum and the anterior thoracic spiracle. Its 

 inner concave surface serves for the attachment of the muscle 

 of the prothoracic coxa. The episterna (eps/) (epitrochlear 

 sclerites of Lowne) are comparatively large sclerites forming 

 the lateral regions of the prothorax. They overhang the 

 attachments of the prothoracic limbs. The internal skeleton 

 of the prothorax consists of the two stout hollow apodemes — 

 the hypotremata mentioned previously. They arise from the 

 postero-lateral edges of the presternum, and run obliquely 

 across the ventral edge of the anterior thoracic spiracle 

 where the hypotreme divides, the posterior branch runs up 

 the posterior margin of the spiracle, between the lateral plate 

 of the mesosternum and the peritreme (the chitinous ring 

 surrounding the spiracle), the anterior branch fuses with the 

 prothoracic episternum. 



The Mesothorax. — The notum of the mesothorax occu- 

 pies the whole of the dorsal side of the thorax. It is com- 

 posed of the four sclerites to which Audouin (1824) gave the 

 name of prescutum, scutum, scutellum, and postscutellum. 

 The prescutum (prs.) forms the anterior part of the dorsal 

 region of the thorax. Its anterior portion bends down almost 

 vertically to unite with the pronotum. The anterior edge of 

 the prescutum is inflected after the pronotal suture, and is 

 produced in the median line into a small bifurcating process. 

 The prescutum is bounded laterally by the humerus and a 

 membranous strip — the dorso-pleural membrane. The scutum 

 {se.) is the largest of the mesonotal plates. It occupies the 

 whole of the median dorsal region of the thorax. Anteriorly 

 it is bounded by the prescutum, laterally by the alar membrane 

 and the lateral plate of the postscutellum, and posteriorly by 



