Cephalaspis

Cephalaspis, a genus of fossil fishes occurring, among the earliest of the class, in Upper Silurian and Old Red Sandstone deposits. It is the type of the family Cephalaspidae of the sub-order Placodermata, of the ganoids. It has a persistent notochord, but ossified peripheral elements of the vertebrae, a heterocercal tail, a dorsal fin, rhomboid scales, and a head-shield with distinct bone-cells. It is named from its cephalic shield, with its posterior angles produced into long "cornua."