In another great group of Devonian Ganoids, we meet with fishes more or less closely allied to the living _Polypteri_ (fig. 105) of the Nile and Senegal. In this group (fig. 106) the pectoral fins consist of a central scaly lobe carrying the fin-rays on both sides, the scales being sometimes rounded and overlapping (fig. 106), or more commonly rhomboidal and placed edge to edge (fig. 105, A). Numerous forms of these "Fringe-finned" Ganoids occur in the Devonian strata, such as _Holoptychius, Glyotoloemus, Osteolepis, Phaneropleuron_, &c. To this group is also to be ascribed the huge _Onychodus_ (fig. 102, d and e), with its large, rounded, overlapping scales, an inch in diameter, and its powerful pointed teeth. It is to be remembered, however, that some of these "Fringe-finned" Ganoids are probably referable to the small but singular group of the "Mud-fishes" (_Dipnoi_), represented at the present day by the singular _Lepidosiren_ of South America and Africa, and the _Ceratodus_ of the rivers of Queensland. [Illustration: Fig. 105.--A, _Polypterus_, a recent Ganoid fish; B, _Osteolepis_, a Devonian Ganoid; a a, Pectoral fins, showing the fin-rays arranged round a central lobe.] [Illusration: Fig. 106.--_Holoptychius nobilissimus_, restored. Old Red Sandstone, Scotland. A, Scale of the same.] Leaving the Ganoid fishes, it still remains to be noticed that the Devonian deposits have yielded the remains of a number of fishes more or less closely allied to the existing Sharks, Rays, and _Chimoeroe_ (the _Elasmobranchii_). The majority of the forms here alluded to are allied not to the true Sharks and Dog-fishes, but to the more peaceable "Port Jackson Sharks," with their blunt teeth, adapted for crushing the shells of Molluscs. The collective name of "Cestracionts" is applied to these; and we have evidence of their past existence in the Devonian seas both by their teeth, and by the defensive spines which were implanted in front of a greater or less number of the fins. These are bony spines, often variously grooved, serrated, or ornamented, with hollow bases, implanted in the integument, and capable of being erected or depressed at will. Many of these "fin-spines" have been preserved to us in the fossil condition, and the Devonian rocks have yielded examples belonging to many genera. As some of the true Sharks and Dog-fishes, some of the Ganoids, and even some Bony Fishes, possess similar defences, it is often a matter of some uncertainty to what group a given spine is to be referred. One of these spines, belonging to the genus _Machoeracanthus_, from the Devonian rocks of America, has been figured in a previous illustration (fig. 102, f).