In every modern Dipnoan, Crossopterygian, and ganoid the air-bladder has an effective pneumatic duct.
This preservation of ancient forms in islands appears to me like the preservation of ganoid fishes in our present freshwaters.
Dura Den, a glen near Cupar-Fife, famous for the number of ganoid fossil fishes entombed in its sandstone.
The distinctions between cycloid and ctenoid scales, between placoid and ganoid fishes, are vague, and can hardly be maintained.
The ganoid differs from the Crossopterygian in having the basal elements of the paired fins small and concealed within the flesh.
What most struck me, however, in glancing over the drawers of Mr. Duff, was the character of the ganoid scales of this deposit.
Thus these fishes unite in themselves traits of the shark, lung-fish, and ganoid.
On this, as on other occasions, I was struck by the complex and very various forms assumed by the ganoid scales of the Wealden.
This latter class (including in its highest division frogs and toads) is plainly allied to the ganoid fishes.
Louis Agassiz distinguished four kinds of scales—placoid, ganoid, cycloid and ctenoid.