The remains of the Ganoid fishes are in a much more perfect state of preservation, so that it is even possible to obtain a tolerably certain idea of the general appearance and habits of some of them, especially of such as were provided with hard carapaces, solid scales, and ordinary or bony fin-rays. A certain proportion of them, as might have been expected, remind us, with regard to external form, of Teleosteous fishes rather than of any of the few still existing Ganoid types; but it is contrary to all analogy and to all palæontological evidence to suppose that those fishes were, with regard to their internal structure, more nearly allied to Teleosteans than to Ganoids. If they were not true Ganoids, they may be justly supposed to have had the essential characters of Palæichthyes. Other forms exhibit even at that remote geological epoch so unmistakably the characteristics of existing Ganoids, that no one can entertain any doubt with regard to their place in the system. In none of these fishes is there any trace of vertebral segmentation. The Palæichthyes of the Old Red Sandstone, the systematic position of which is still obscure, are the _Cephalaspidæ_ from the Lower Old Red Sandstone of Great Britain and Eastern Canada; _Pterichthys_, _Coccosteus_, and _Dinichthys_: genera which have been combined in one group--_Placodermi_; and _Acanthodes_ and allied genera, which combined numerous branchiostegals with chondropterygian spines and a shagreen-like dermal covering. Among the other Devonian fishes (and they formed the majority) two types may be recognised, both of which are unmistakably Ganoids. The first approaches the still living _Polypterus_, with which some of the genera like _Diplopterus_ singularly agree in the form and armature of the head, the lepidosis of the body, the lobate pectoral fins, and the termination of the vertebral column. Other genera, as _Holoptychius_, have cycloid scales; many have two dorsal fins (_Holoptychius_), and, instead of branchiostegals, jugular scutes; others one long dorsal confluent with the caudal (_Phaneropleuron_). In the second type the principal characters of the _Dipnoi_ are manifest, and some of them, for example _Dipterus_, _Palædaphus_, _Holodus_, approach so closely the Dipnoi which still survive, that the differences existing between them warrant a separation into families only.