turtle; and why, I asked, if one formation gives us sauroid fishes, may not another give us chelonian ones? or if in the Lias we find the body of the lizard mounted on the paddles of the whale, why not find in the Old Red Sandstone the body of the tortoise mounted in a somewhat similar manner? The idea originated in error; but as it was an error which not many naturalists could have corrected at the time, it may be deemed an excusable one, more especially by such of my readers as may have seen well-preserved specimens of the creature, or who examine the subjoined prints. (Nos. I. and II.) I submitted some of my specimens to Mr. Murchison, at a time when that gentleman was engaged among the fossils of the Silurian System, and employed on his great work, which has so largely served to extend geological knowledge regarding those earlier periods in which animal life first began. He was much interested in the discovery: it furnished the geologist with additional data by which to regulate and construct his calculations, and added a new and very singular link to the chain of existence in its relation to human knowledge. Deferring to Agassiz, as the highest authority, he yet anticipated the decision of that naturalist regarding it, in almost every particular. I had inquired, under the influence of my first impression, whether it might not be considered as a sort of intermediate existence between the fish and the chelonian. He stated, in reply, that he could not deem it referrible to any family of reptiles; that, if not a fish, it approached more closely to the Crustacea than to any other class; and that he had little doubt Agassiz would pronounce it to be an ichthyolite of that ancient order to which the _Cephalaspis_ belongs, and which seems to have formed a connecting link between crustacea and fishes.[I] The specimens submitted to Mr. Murchison were forwarded to Agassiz. They were much more imperfect than some which I have since disinterred; and to restore the entire animal from them would require powers such as those possessed by Cuvier in the past age, and by the naturalist of Neufchatel in the present. Broken as they were, however, Agassiz at once decided from them that the creature must have been a fish.