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This genus has never yet been found in either of the two higher divisions of the Old Red Sandstone, and confirms Sir R. Murchison's previous suspicion that the rocks in which it occurs belong to the Lower "Old Red," or agree in age with the Arbroath paving-stone. The Devonian fish were referred by Agassiz to two of his great orders, namely, the Placoids and Ganoids.
If we except the Placoids already alluded to, and a few other families of doubtful affinities, all the Old Red Sandstone fishes are Ganoids, an order so named by Agassiz from the shining outer surface of their scales; but Professor Huxley has also called our attention to the fact that, while a few of the primary and the great majority of the secondary Ganoids resemble the living bony pike, Lepidosteus, or the Amia, genera now found in North American rivers, and one of them, Lepidosteus, extending as far south as Guatemala, the Crossopterygii, or fringe-finned Ichthyolites, of the Old Red are closely related to the African Polypterus, which is represented by five or six species now inhabiting the Nile and the rivers of Senegal.
The Archegosaurus, which we have figured, and the Anthracosaurus, are forms which appear to have existed in great numbers in the swamps and lakes of the age. The fish of the period belong almost entirely to the ancient orders of the ganoids and placoids. Of the ganoids, the great megalichthys Hibberti ranges throughout the whole of the system.
It will be necessary to enter more at large than in my preceding volumes into the resources of Canada, and, for this end, Geology and other scientific subjects must be introduced; but, as I dislike exceedingly that heavy and gaudy veil of learning, that embroidered science, with which modern taste conceals those secrets of Nature which have been so partially unfolded, I shall not have frequent recourse to absurd Greek derivations, which are very commonly borrowed for the occasion from technical dictionaries, or lent by a classical friend; but, whenever they must occur, the dictionary shall explain them, for I really think it beneath the dignity of the lights of modern Geology to talk as they do about the Placoids and the Ganoids, as the first created fishlike beings, and of the Ctenoids and the Cycloids as the more recent finners.
They form a great contrast to the fish of the secondary strata, as, with the exception of the Placoids, they are all Teleosteans, only one genus, Pycnodus, belonging to the order of Ganoids, which form, as before stated, the vast majority of the ichthyolites entombed in the secondary are Mesozoic rocks.
As the rays and sharks both belong to the order of placoids, it appears that the shark is not particular about preying on his kindred. "Are sharks plenty here?" I inquired. "Indeed they are!" said Pecetti: "I wonder we have not had our lines cut by them. I have caught half a dozen in an hour's time right here. I think I can show you one very quick."
Underlying all its divisions and subdivisions, is the average expression of the type in the past and present; the Placoids and Ganoids, with their combination of reptilian and fishlike features, characterizing the earlier geological epochs, while in the later the simple bony fishes, the Cycloids and Ctenoids, take the ascendancy.
"More than fifteen hundred species of fossil fishes, which I have learned to know, tell me that species do not pass insensibly one into another, but that they appear and disappear unexpectedly, without direct relations with their precursors; for I think no one will seriously pretend that the numerous types of Cycloids and Ctenoids, almost all of which are contemporaneous with one an other, have descended from the Placoids and Ganoids.
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