572 EXTERNAL ANATOMY OF INSECTS. 



drangular, and the lateral ones roundish ; in the Asilida 

 and most others of this Order, with the postscutellum, it 

 forms a segment of a circle a , sometimes armed with a 

 pair of spines, as in Stratyomis F., and is what has been 

 usually regarded as the real scutellum, though, as I have 

 endeavoured to show, not correctly b . 



10. Postscutellum . The postscutellum bears the same 

 relation to the postdorsolum that the scutellum does to the 

 dorsolum, but it is seldom, if ever, a distinct piece. In the 

 Coleoptera it is represented by the longitudinal narrow 

 channel that terminates the postdorsolum towards the 

 anus d : this usually figures an isosceles triangle with the 

 vertex truncated or open; but ii Copris the triangle is 

 equilateral. In the other Orders it is little more than 

 the central posterior point of the postdorsolum e . 



11. Postfrcenum f . The part now mentioned is much 

 more important than the preceding one, and must not be 

 passed over so cursorily. In the Coleoptera it usually 

 presents itself under the form of two large and usually 

 rather square pannels, the disk of which is convex, but 

 the rest of their surface unequal, which are situated one 

 on each side of the postscutellum & ; under the anterior 

 outer angle of these is the socket or principal attachment 

 of the secondary wings, and their basal margin is at- 

 tached to their outer side ; posteriorly behind the vertex 

 of the postscutellum the postfrcenum is crowned with a 

 ridge or bead, below which it descends vertically or 

 obliquely to the adomen ; this ridge often turns upwards, 



* Plate IX. Fig. 19, 20. t . b See above, p. 558—. 



c Plates VIII. IX. u. J Plate VIII. Fig. 3 u'. 



e Ibid. VIII. Fig. 12. u. Plate IX. 7- W. 

 1 Plates VIII. IX. v , s Plate VIII. Fig. 3. v. 



