In a short paper on the nomenclature of the Old Red Sandstone Fishes published in this Magazine for November, 1888, I expressed the opinion “that the scattered teeth and fragments of jaws known as Dendrodus and Lamnodus belong to fishes at present known to us by their scales as species of Holoptychius and Glyptolepis.” The family terms “Holoptychiidæ” and “Dendrodontidæ” I consider absolutely synonymous. On the other hand, the Rhizodontidæ (Gyroptychius, Tristichopterus, Rhizodus, etc.) present a somewhat different form of tooth-structure, and one which is, in the main, identical with that which, in so many Stegocephalous Amphibia, is called “labyrinthodont.”