80 PARTIAL ORISMOLOGY. 



Kirby and Spenee), generally exceeds the posterior piece in size. In the 

 orders with a free prothorax, this covers it, and it is only visible upon 

 the removal of the latter ; in the rest it occupies the whole central sur- 

 face of the back. In front, at its exterior angles, the corneous ribs of the 

 superior wings articulate, and two corneous ridges, originating at this 

 point and proceeding into the cavity of the thorax, serve for the inser- 

 tion of the muscles which move the wings. In the Hydrocanthari, 

 the mesonoturn is very small, and indicated only by a delicate corneous 

 transverse line (PL IX. No. 2, f. 7, c.) ; it is very large in the Melli- 

 force and Lepidoptera, as well as in the Diptera ; in the dragon flies, 

 (PI. XI. No. 3, f. 1, 2, c, c.), it forms as an obliquely descending bent 

 plate, the anterior portion of the thorax in front of the wings, and 

 therefore does not represent the collar of the Hymenoptera and Diptera 

 (our pronotum), as Kirby and Spence maintain. The posterior divi- 

 sion, the SCUTELLUM (scutcllum), is here seated, as in all, between the 

 wings. This SCUTELLUM (PI. XI. &c. c, c.), is, properly, no separated 

 part ; but, as we have already seen, a mere process of the mesonotum. 

 It is to be observed very distinctly in the Coleoptera, in which it 

 presents itself as a small triangular plate seated between the elytra 

 and the pronotum. In some genera (Macraspis), it attains conside- 

 rable size; indeed in Tetyra and Chelyphus, it almost covers the 

 whole abdomen *. It always extends far backwards, between the 

 posterior wings ; and in many families, it completely covers the third 

 thoracic segment (PI. XIII. No. 4 and 5, c, c. ; PI. XIV. No. 1 and 

 2, c, c.) ; not unfrequently a strong membrane or even a peculiar cor- 

 neous ridge (Cicada, P. XIII. No. 5, f. 1, d, d.} proceeds from the 

 side of the scutellum to the base of the superior wings, and thereby 

 strengthens their connection with the dorsal piece (PI. XIII. No. 4, 

 f. 1, d, d}. This ridge or membrane, Kirby and Spence call the 

 frenum. In many Coleoptera the scutellum appears to be deficient, 

 from its not displaying itself upon the superior surface between the 

 elytra (as in Copris) ; but it is, nevertheless, present, although 

 covered by the elytra and pronotum. These have been called Escu- 

 tellati, wanting a scutellum. 



It is not unusual to find other processes upon the scutellum, as spines 

 and teeth, and which are occasionally found in almost all the orders (Psi- 

 lus Boscli, Stratiomys, Sargus, Reduvius). But we more rarely observe 



I 



* Compare Dalman, Analecta Entomol. p. 32, p. 2, B. 



