EXTERNAL ANATOMY OF INSECTS. 695 
those carnivorous genera Dermestes, Anthrenus, Byrrhus, 
&c. In the last-mentioned genus there are cavities in 
the under side of the trunk, in each division of the 
breast, and at the base of the abdomen, to receive the 
legs when folded ; the cove have also a cavity to receive 
the base of the thigh. In the anterior legs this last part 
has a longitudinal one on its wpper side, and in the 
four posterior on the under, which receives the tibia, 
which at the inner edge are straight, and at the outer 
curvilinear, and the ¢arsz are turned up and received by 
the concave part, on the anterior side of the jirst pair 
and the posterior side of the two dast of the tibia, so as 
to lie between it and the body: when the legs are close 
packed, the animal looks almost as if it had none. I 
have observed that when Dytisct repose on the water, 
the posterior legs are turned up and laid over the elytra, 
and curved towards the head. 
vi. Pectines. I must next say a few words upon a re- 
markable organ, which seems in some degree supplemen- 
tary to the legs, by which the Crearor has distinguished 
the genus Scorpio, called from its parallel teeth, set in a 
back, their pecten or comb*. ‘This back consists of two 
or more articulations, is attached by itsanterior extremity 
to the sides of the posterior piece of the mesostethium, 
and is marked by a longitudinal furrow or channel. The 
teeth, which vary in number in the different species, and 
in the same species at different periods of its growth, are 
usually ovato-lanceolate, or obtusangular, furnished on 
their exterior edge with what appears to be a longitudi- 
nal sucker, and supported between their bases, or at the 
2 PratE XXVILI, Fic. 50. 
