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Again, vast as is the number of undoubtedly Ganoid fossil Fishes, and great as is their range in time, a large mass of evidence has recently been adduced to show that almost all those respecting which we possess sufficient information, are referable to the same sub-ordinal groups as the existing 'Lepidosteus', 'Polypterus', and Sturgeon; and that a singular relation obtains between the older and the younger Fishes; the former, the Devonian Ganoids, being almost all members of the same sub-order as 'Polypterus', while the Mesozoic Ganoids are almost all similarly allied to 'Lepidosteus'.
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 Mesozoic Lepidosteidæ, again, have, at most, biconcave vertebræ, while the existing Lepidosteus has Salamandroid, opisthocoelous, vertebræ. So, none of the Palæozoic Sharks have shown themselves to be possessed of ossified vertebræ, while the majority of modern Sharks possess such vertebræ.
Its true alliance with the Lepidosteus of the early geological ages became clear to him only later in his study of the fossil fishes. He then detected the reptilian character of the type, and saw that from the articulation of the vertebrae the head must have moved more freely on the trunk than that of any fish of our days.
Adams would have liked to begin afresh with the Limulus and Lepidosteus in the waters of Braintree, side by side with Adamses and Quincys and Harvard College, all unchanged and unchangeable since archaic time; but what purpose would it serve? A seeker of truth or illusion would be none the less restless, though a shark!
Again, vast as is the number of undoubtedly Ganoid fossil Fishes, and great as is their range in time, a large mass of evidence has recently been adduced to show that almost all those respecting which we possess sufficient information, are referable to the same sub-ordinal groups as the existing Lepidosteus, Polypterus, and Sturgeon; and that a singular relation obtains between the older and the younger Fishes; the former, the Devonian Ganoids, being almost all members of the same sub-order as Polypterus, while the Mesozoic Ganoids are almost all similarly allied to Lepidosteus.
Not only for its own novelty and variety, but for its bearing on the geographical distribution of animals, the fauna of this great sheet of fresh water interested him deeply. On this journey he saw at Niagara for the first time a living gar-pike, the only representative among modern fishes of the fossil type of Lepidosteus.
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