Sphyrna zygaena;is a species of hammerhead shark, family Sphyrnidae, so named because of the distinctive shape of the head, which is flattened and laterally extended into a hammer shape (called the "cephalofoil"), without an indentation in the middle of the front margin (hence "smooth"). Polyurethane cast of an original private collection. Size. 5in.12.5in.