The four sepals are arranged symmetrically, an outer median and an inner lateral pair.
The ventral region of the thoracic skeleton is complex, each segment usually possessing a median sternum with paired episterna (in front) and epimera (behind).
Most of the Chrysomelidae are metallic in colour and convex in form; in some the head is concealed beneath the prothorax, and the so-called "tortoise" beetles (Cassidinae) have the elytra raised into a prominent median ridge.
(Lankester.) x, y, The median antero-posterior axis.
The median and posterior extension of the body of the sternum is a direct outgrowth of the latter, therefore FIG.