510 EXTERNAL ANATOMY OF INSECTS. 



the pectens of scorpions ; and that they are connected 

 with the respiration a . 



4. We are next to say something upon the shape of 

 the jprothorax. The forms of the thoracic shield, espe- 

 cially in the Coleoptera, are so various, that it would be 

 endless to aim at particularizing all ; but it may be use- 

 ful to notice a few of the most remarkable. The pro- 

 thorax of Moluris, a darkling-beetle, approaches the 

 nearest of that of any insect to a spherical form, from its 

 remarkable convexity ; in the wheel-bug (Reduvius ser- 

 ratus) it is compressed, and longitudinally elevated into 

 a semicircular serrated crest : it is crested, also, in many 

 Locustce and Acridce, in some having two parallel ridges; 

 but, generally speaking, its surface is more depressed. 

 In Necrodes it is nearly circular, in Blatta petiveriana 

 semicircular, in Nilion and some CoccinellidcE crescent- 

 shaped, in Carabus obcordate, in Cantharis and Sagra 

 approaching to a square, in Languria to a parallelogram ; 

 in many Cimicidce, Belosto?na, &c, it is triangular, with 

 the vertex truncated; it is trapezoidal in Elater, in Ateu- 

 chus rather pentagonal, and exhibiting an approach to 

 six angles in some other beetles b : but the prothorax 

 most singular in form is that of some species of M. La- 

 treille's genus Helceus c , as H. perforatus, Brownii, &c. : 

 in these its anterior angles are producted, and curving 

 inwards, lap at the end one over the other, so as to form 

 a circular orifice for the head, which otherwise would be 



a Organisation Exterieure des Ins. 177- 



h A subgenus, related to Lebia (Hexagonia K. MS.) and some Ci- 

 micidce, are so circumstanced. 

 c Regne Animal in. t. xiii.y*. 6. 



