596 EXTERNAL ANATOMY OF INSECTS. 
except at their base, are armed with little teeth, alter- 
nating with each other like the cogs of a mill-wheel. In 
apterous beetles the elytra are often connate, or have 
both sutures as it were soldered together. The margin* 
or external edge of the elytra is generally formed by a 
bead or ridge, which, except in the case of the truncated 
ones, in which it is straight, curves more or less from 
the base to the apex; this ridge is often recurved so as 
to form a kind of channel between it and the disk of the 
elytrum, as may be seen in the Dynastideé ; in some there 
are two parallel ridges, as in Copris ; in Silpha the mar- 
gin is dilated ; in Heleus and Cossyphus it is remarkably 
so and recurved, so that, in conjunction with that of the 
prothorax which is similarly circumstanced, it gives the 
animal some resemblance to a small model of a barge. 
Though the margin of elytra is most commonly intire, 
yet in some beetles, as Gymnopleurus Illig., a sinus is 
taken out of it; in Cetonia it often projects at the base, 
and in Cryptocephalus in the middle, into a lobe; in 
Phoberus it is denticulated, and in many Buprestes more 
or less serrulated; sometimes it terminates before it 
reaches the apex of the elytrum in a tooth, as in many 
Carabi. The epipleura” or side-cover is that part of 
the organ in question, below the margin, with which it 
usually forms an angle, being more or less inflexed, that 
covers the sides of the body. It varies in different tribes, 
being sometimes obsolete, as in the weevils; in the 
Capricorn beetles it is very narrow; in Carabus, &c., 
dilated at the base; in many Heteromerous beetles, 
as Blaps, Pimelia, &c., it is very wide and conspicuous; 
in Cossyphus it stands out a little from the abdomen, so 
* PrLare X. Fic. 1. c. > Pate XXVIII. Fic. 6—8. a!". 
