176 THE INTEGUMENTAL SKELETON OF THE IMAGO. 



cup, this cup articulates with a hemispherical process of the 

 post-scutellum, forming the strong posterior dorso-pleural diar- 

 throsis (4). The inferior process of the rim of the scutellum 

 (6 d) supports the posterior wing-root ; this is the alar process 

 of the scutellum. The anterior and superior process (7) extends 

 forwards on the inner edge of the great alar apophysis and 

 forms its articular head (/j). 



The crescentic rim of the scutellum is united with the post- 

 scutellum by soft syndesmotic integument. 



The Supra-tympanic Fissure (/). — The external surface of the 

 great alar apophysis looks downwards, and forms the anterior 

 part of a triangular inflection of the integument above the great 

 wing-scale. This inflection opens and closes and permits of 

 considerable variation in the capacity of the thoracic cavity ; 

 when closed its superior or anterior half rests upon its posterior 

 or inferior half, in which a complex tympanic mechanism lies, 

 and a minute spiracle opens. These will be described in 

 detail in another chapter. The whole arrangement of the 

 supra-tympanic fissure is similar to the infolded gusset of 

 a pair of bellows — the apex of the fold is just in front of 

 the posterior dorso-pleural diarthrosis. 



The dorso-pleural costa is the inner edge of the floor of the 

 alar fossae. It is prolonged forwards as a sutural ridge, which 

 bifurcates and surrounds the paratreme. 



The presutnral ridge is the inner edge of the presutural 

 sulcus. It joins the two dorso-pleural costse and supports 

 a cup-shaped cavit}' in each, which articulates with the head of 

 the parapteron (77), A pair of small plates, which form the 

 inner wall of the posterior alar fossa, articulate with the 

 scutal portion of the dorso-pleural costa. These I term the 

 ' anterior and posterior parascutum.' 



The Anterior Parascutum (//) is a distinct oblong plate. Its 

 anterior external angle is prolonged in a curved hook {12) 

 — the uncinate process — which embraces the anterior head of 

 the dens, a small sclerite on which the propterj'gium turns 

 when the wing is elevated or depressed. 



The Posterior Parascutum (p) is inseparably fused with the 



