ECHINUS, in architecture, a convex moulding, under the abacus of a column capital, so called from its resemblance, in form, to a sea urchin (Greek Ex vos, echinos). It is universal in both Greek and Roman Doric orders, in which it usually has a profile of circular or elliptical curvature ; occasional Roman examples have a cyma recta, double curved (see CYMA) profile. The convex moulding between the volutes of the Ionic order is also termed an echinus, as is any similar form in a capital of any style. (See ORDER.)