The upper wings are hard and horny throughout their whole extent, forming a protecting cover to the under pair, and are therefore named elytra. From this circumstance also the name of the order is derived, being compounded of κολεος, a sheath, and πτερα, wings. Where the elytra, or wing-cases, meet, they form a straight sutural line along the back. The under wings, which are the true organs of flight, are membranous and transparent; when at rest they are folded transversely. The mouth is constructed for mastication, and all the parts are very highly developed. Stemmatic eyes have not been observed in the perfect insect, except in the genera Onthophagus, Omalium, and Paussus; but they are the only kinds with which the larvæ are furnished. The prothorax is very freely articulated to the succeeding segment, and the pronotum is so large as to form a considerable part of the dorsal surface. On each side of the pronotum, in the carabideous and aquatic beetles, there is a distinct corneous scale from which the muscles of the coxæ originate, called the smaller or anterior shoulder-blade (omium) by Burmeister. The horns and other prominences frequently rising from the prothoracic case are mere processes or integral portions of its crust, except in one instance, the Harlequin beetle (Acrocinus longimanus), which has a large moveable spine on each side. The only portion of the mesothorax appearing on the surface, is the small triangle named the scutellum; its whole volume, indeed, is comparatively contracted, owing, no doubt, to the elytra which it supports not being
