Fishes . mall fish of the Lower Carboniferous, thehead mailed, the bodywith small bony scales. Rhipidistia.—In the Rhipidistia the basal bones of the medianfins (axonosts and baseosts) are found in a single piece, notseparate as in the Haplistia. Four families are recognized,HoloptychiidcE, Megalichthyidce, Osteolepida, and Onychodontidce,the first of these being considered as the nearest approach ofthe Crossopterygians to the Dipnoans. The Crossopterygii 229 The Holoptychiida have the pectoral fins acute, the scalescycloid, enameled, and the teeth very complex. Holoptychiusnobilissimiis is a
Fishes . mall fish of the Lower Carboniferous, thehead mailed, the bodywith small bony scales. Rhipidistia.—In the Rhipidistia the basal bones of the medianfins (axonosts and baseosts) are found in a single piece, notseparate as in the Haplistia. Four families are recognized,HoloptychiidcE, Megalichthyidce, Osteolepida, and Onychodontidce,the first of these being considered as the nearest approach ofthe Crossopterygians to the Dipnoans. The Crossopterygii 229 The Holoptychiida have the pectoral fins acute, the scalescycloid, enameled, and the teeth very complex. Holoptychiusnobilissimiis is a very large fish from the Devonian. GlyptolepisIcptopterus from the Lower Devonian is also a notable from the Devonian is known from detached teeth. In the Ordovician rocks of Canon City, Colorado, Dr. Wal-cott finds numerous bony scales with folded surfaces and stellateornamentation, and which he refers with some doubt to aCrossopterygian fish of the family HoloptychiidcB. This fish he. Fig. 163.—Bnsal bone of dorsal fin, IToloptycMus leptopterus (Agassiz). (After Woodward.) names Eriptychiiis amcricanns. If this identification proves cor-rect, it will carry back the appearance of Crossopterygian fishes,the earliest of the Teleostome forms, to the beginning of theSilurian, these Caiion City shales being the oldest rocks in whichremains of fishes are known to occur. In the same rocks arefound plates of Ostracophores and other fragments stillmore doubtful. It is certain that our records in palaeontologyfall far short of disclosing the earliest sharks, as well asthe earliest remains of Ostracophores, Arthrodires, or evenGanoids. Megalichthyidse.—The McgaliclitJiyidcu (wrongly called Rltizo-dontida) have the pectoral fins obtuse, the teeth relativelysimple, and the scales cycloid, enameled. There are numer-ous species in the Carboniferous rocks, largely known fromfragments or from teeth. Megalichtiiys, Strcpsodus, Rhizo-dopsis, Gyroptychiiis, Tristichopterus
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