Whatever theory we may conceive or adopt respecting the origin of species, it is undeniable but that Acanthodes—a genus of fossil fishes—has maintained a noble struggle for life. Known to occur first of all in the Lower Devonian or Old Eed Sandstone, it has been found also in the Middle Division of that great system, and again in the coal-measures, and finally disappears in the Lower Permian—the Roth-todt-liegende or Lower Dyas of German authors.

In the accompanying table we have endeavoured to put into accessible and readable shape the particulars of its occurrence, so far as known to us, among the rocks.

We first detected the occurrence of Acanthodes in the Lower Devonian or Old Red Sandstoue at Farnell, in the county of Forfar, Scotland, in the summer of the year 1857. From investigations since made, it now appears that an abundant flush of Acanthodian life ushered in the morning of the vast period embraced by the Old Red Sandstone. Along with the genus Acanthodes there occur also several other genera of the Acanthodian family, such as Climatius, Parescus, and some unnamed. The genera Climatius and Parescus were first founded upon and described by Agassiz, in his great work, from spines, but since the perfect forms have turned up in our northern rocks, it has been found necessary to remove them from among the Cestraciont Placoids into the Acanthodian family of the Ganoids, that is to say, provided we adhere to the classification of Agassiz.