Gyr`a·can'thus (jĭr`ȧ*kăn'thŭs) noun [ New Latin , from Greek gyro`s round + 'a`kanqa spine.] (Paleon.) A genus of fossil fishes, found in Devonian and carboniferous strata; -- so named from their round, sculptured spines. Found on http://www.encyclo.co.uk/webster/G/71