540 EXTERNAL ANATOMY OF INSECTS. 
form a sinus or angle*. In certain Acride@ there are 
only two of these lines or ridges, but notched or toothed ; 
and in some of the genus first named only one °; in Lo- 
custa Dux and affinities the prothorax has several trans- 
verse channels or rather folds‘, with corresponding 
ridges on its internal surface. 
6. With respect to the clothing of the prothoraz, I have 
not much to say: in Coleopterous insects this part is com- 
monly naked; but in some genera, as Byrrhus, Anthrenus, 
Dermestes, and many weevils (2thyncophora) it is partially 
or totally covered with hairs or scales. In the other tho- 
racic Orders it is usually naked, but in some Newroptera, 
the Myrmeleonina, &c., it is hairy ; and in the Libellulina 
it is fringed posteriorly with hairs. 
7. As to its relative proportions, the prothorax is some- 
times rather wider than the rest of the trunk and the 
head, as in Onitis, Pasimachus, &c.; it is considerably 
narrower in Colliuris and Odacantha ; and of the same 
width in those Scarit¢de with striated elytra’. Again, 
it is sometimes of the same width with the elytra, but 
wider than the head, as in Hydrophilus, Dytiscus, &c. ; 
in some instances it is of the same width with the head, 
and narrower than the elytra, for instance in Anthia and 
Brachinus. In most Coleoptera it is longer than the 
head and shorter than the elytra; but in Manticora, the 
vesicatory beetles, &c., it is shorter than either. In 
Gnoma ? Giraffa*, it is nearly as long as the elytra; in 
many Staphylinide, Atractocerus, &c., longer; in Pha- 
neus carnifex, bellicosus, &c., it is longer than the elytra 
and the rest of the body. With regard to itself, it is 
* Prate XIII, Fie. 17. ® Prare VIII. Fic. 10. 
* Thid. 4 Linn. Trans. vi. t, xxi. f. 10. * bid. f. 8. 
