The oldest organism yet discovered in the most ancient geological system of Scotland in which vertebrate remains occur, _seems_ to be the _Asterolepis_ of Stromness. After the explorations of many years over a wide area, I have detected none other equally low in the system; nor have I ascertained that any brother-explorer in the same field has been more fortunate. It is, up to the present time, the most ancient Scotch witness of the great class of fishes that can in this case be brought into court; nay, it is in all probability the oldest _ganoid_ witness the world has yet produced; for there appears no certain trace of this order of fishes in the great Silurian system which lies underneath, and in which, so far as geologists yet know, organic existence first began. How, then, on the two relevant points—bulk and organization—does it answer to the demands of the development hypothesis? Was it a mere fœtus of the finny tribe, of minute size, and imperfect, embryonic faculty? Or was it of at least the ordinary bulk, and, for its class, of the average organization? May I solicit the forbearance of the non-geological reader, should my reply to these apparently simple questions seem unnecessarily prolix and elaborate? Peculiar opportunities of observation, and the possession of a set of unique fossils, enable me to submit to our palæontologists a certain amount of information regarding this ancient ganoid, which they will deem at once interesting and new; and the bearing of my statements on the general argument will, I trust, become apparent as I proceed. THE RECENT HISTORY OF THE ASTEROLEPIS. ITS FAMILY. It had been long known to the continental naturalists, that in certain Russian deposits, very extensively developed, there occur in considerable abundance certain animal organisms; but for many years neither their position nor character could be satisfactorily determined. By some they were placed too high in the scale of organized being; by others too low. Kutorga, a writer not very familiarly known in this country, described the remains as those of mammals;—the Russian rocks contained, he said, bones of quadrupeds, and, in especial, the teeth of swine: whereas Lamarck, a better known authority, though not invariably a safe one,—for he had a trick of dreaming when wide awake, and of calling his dreams philosophy,—assigned to them a place among the corals. They belonged, he asserted, as shown by certain star-like markings with which they are fretted, to the Polyparia. He even erected for their reception a new genus of Astrea, which he designated, from the little rounded hillock which rises in the middle of each star, the genus _Monticularia_. It was left to a living naturalist, M. Eichwald, to fix their true position zoologically among the class of fishes, and to Sir Roderick Murchison to determine their position geologically as ichthyolites of the Old Red Sandstone.