GANOID, a name applied to fishes with rhombic bony scales covered on the outer surface with a layer of ganoine, a vitreous substance. It is now known that ganoid scales differ considerably in structure, and that the ganoids are not a natural group. Most fishes with ganoid scales are extinct, but the gar-pikes (Lepidos teus) survive in the fresh-waters of North America, and the Polypteridae in the rivers of Africa. (See FISHES.)