In the _Osteolepis_,—an animal the whole of whose external head I have, at an expense of some labor, and from the examination of many specimens, been enabled to restore,—the cranial buckler (fig. 12) was divided in a more arbitrary style; and we find that an element of uncertainty mingles with our inferences regarding it, from the circumstance that some of its lines of division, especially in the frontal half, were not real sutures, but formed merely a kind of surface-tatooing, resorted to as if for purposes of ornament. The cranial buckler of the _Asterolepis_ exhibited, as I shall afterwards have occasion to show, a similar peculiarity;—both had their pseudo-sutures, resembling those false joints introduced by the architect into his rusticated basements, in order to impart the necessary aspect of regularity to what is technically termed the coursing and banding of the fabric. We can however, determine, notwithstanding the induced obscurity that the buckler of the _Osteolepis_ was divided transversely in the middle into two main parts or segments,—an occipital part, C, and a frontal part, A; and that the occipital segment _seems_ to include also the parietal and mastoid plates, and the frontal segment to comprise, with its own proper plates, not only the nasal plate, but also the representative of the anterior part of the vomer. All, however, is obscure. But in our uncertainty regarding the homologies of the divisions of this dermal buckler, let us not forget the homology of the buckler itself, as a whole, with the upper surface of the true cranium in the osseous fishes. Though frequently crushed and broken, it exists in all the finer specimens of my collection as a symmetrically arranged collocation of enamelled plates, as firmly united into one piece, though they all indicate their distinct centres of ossification, as the corresponding surface of the cranium in the carp or cod. The lateral curves in the frontal part immediately opposite the lozenge-shaped plate in the centre, show the position of the eyes, which were placed in this genus, as in some of the carnivorous turtles, immediately over the mouth,—an arrangement common to almost all the Ganoids of the Lower Old Red Sandstone. The nearly semicircular termination of the buckler formed the creature’s snout; and in the _Osteolepis_, as in the _Glyptolepis_ and the _Diplopterus_, it was armed on the under side, like the vomer of so many of the osseous fishes, with sharp teeth. Some of my specimens indicate the nasal openings a little in advance of the eyes. The nape of the creature was covered by three detached plates, (9, 9, 9, fig. 13,) which rested upon anterior dorsal scales, and whose homologies, in the osseous fishes, may possibly be found in those bones which, uniting the shoulder-bones to the head, complete the scapular belt or ring. The operculum we find represented by a single plate (8) which had attached to it, as its sub-operculum, a plate (13) of nearly equal size, (see figs.