GANGED FISHES, an order of fishes founded by Agassiz on the character of the scales of certain fossil fishes, which are bony and lustrous, now regarded as a group-name for a rather heterogeneous series of low and chiefly extinct fishes. They are distinguished from the Clasmobranchs by their scales, their possession of true bone and of an air-bladder, and from the teleosts or true fishes by the pos session of a spiral valve and a contractile bul bus arteriosus and the absence of decussation in the optic nerves. (See IornivoLocr). The ganoids were most numerous in Palaeozoic and early Mesozoic times, and few and diverse are the surviving forms, which include the paddle fishes and sturgeons, the gar-pikes, the mud fishes of the African rivers and a few others, all elsewhere described. In this group fall some of the most famous fossil fishes of palaeontolog.y, described by Hugh Miller in his 'Old Red Sandstone' and otherwise introduced long ago to the public. The berry-bone (Coc costeus), the seraphim (Pterichthys) and the Asterolepis also had a bony shield, the flexible trunk having scales in Pterichthys, being naked in Coccosteus. The anterior limbs, or pectoral fins, of Pterichthys were long, covered with closely fitted plates and had a complex joint connecting them with the thorax. The gar-pikes of the American lake region are the modern representatives of the Lepidotus, tEchmodus, etc., of Mesozoic strata and of the Carbon
iferous Palcroniscus. Polypterus, the type of this group, is confined to the Nile and a few other African rivers. The group is most abun dant in the Paleozoic strata, Dipterus, Osteo lepis, Holoptychius, Phaneropleuron, being Old Red Sandstone genera; Rhizodus, Megalichthys with rhomboidal scales, Strepsodus with cycloid scales, Carboniferous. The ccelacanths range from the Carboniferous to the Chalk forma tions, and are the only members of the order in which the tail is homocercal.
The Ganoids are not a homogeneous group. The Crossopterygii, whose sole extant repre sentatives are Polypterus (see Bicnni) and Calamoichthys from equatorial Africa, stand close to the common origin of the other Ganoid stocks, the teleosts, or ordinary bony fishes, and the dipnoi. The Chandrostei, in cluding the sturgeons and spoon-bills, stand later palmontologically and in their degree of specialization, but show some interesting re semblances to the sharks and rays. Still later in their degree of development and definitely on the track of teleost evolution are the Holostei, of which the bow-fin and gar-pike survive.