_Scales ganoid; fins without fulcra. A series of dorsal spines, to each of which an articulated finlet is attached; anal placed close to the caudal fin, the vent being near the end of the tail. Abdominal portion of the vertebral column much longer than the caudal._ POLYPTERUS.--Teeth rasp-like, in broad bands in the jaws, on the vomer and palatine bones; jaws with an outer series of closely-set, larger, pointed teeth. Caudal fin surrounding the extremity of the vertebral column; ventral fins well developed. A spiracle on each side of the parietal, covered with an osseous plate. A single large gular plate. Air-bladder double, communicating with the ventral wall of the pharynx. [Illustration: Fig. 144.--Polypterus bichir.] This Ganoid is confined to tropical Africa, occurring in abundance in the rivers of the west coast and in the Upper Nile; but it has not been found in the river-systems belonging to the Indian Ocean. It is scarce in the Middle and Lower Nile, and the specimens found below the Cataracts have been carried down, from southern latitudes, and do not propagate their species in that part of the river. There is only one species known, _Polypterus bichir_ (“Bichir” being its vernacular name in Egypt), which varies in the number of the dorsal finlets, the lowest being eight, the highest eighteen. It attains to a length of four feet. Nothing is known of its mode of life, and observations thereon are very desirable. CALAMOICHTHYS.--Distinguished from _Polypterus_ by its greatly elongate form, and the absence of ventral fins. _C. calabaricus_, a dwarf form from Old Calabar. SECOND FAMILY--SAURODIPTERIDÆ. _Scales ganoid, smooth like the surface of the skull. Two dorsal fins; paired fins obtusely lobate. Teeth conical. Caudal heterocercal._ Extinct. _Diplopterus_, _Megalichthys_, and _Osteolepis_ from Devonian and Carboniferous formations. THIRD FAMILY--COELACANTHIDÆ. _Scales cycloid. Two dorsal fins, each supported by a single two-pronged interspinous bone; paired fins obtusely lobate. Air-bladder ossified; notochord persistent, diphycercal._ Extinct. _Coelacanthus_ from carboniferous strata; several other genera, from the coal formations to the chalk, have been associated with it--_Undina_, _Graphiurus_, _Macropoma_, _Holophagus_, _Hoplopygus_, _Rhizodus_. FOURTH FAMILY--HOLOPTYCHIIDÆ. _Scales cycloid or ganoid, sculptured. Two dorsal fins; pectorals narrow, acutely lobate; dentition dendrodont._