The creature’s cranial buckler, which was of great size and strength, might well be mistaken for the carapace of some Chelonian fish of no inconsiderable bulk. The cranial bucklers of the larger Dipterians were ample enough to have covered the corresponding part in the skulls of our middle-sized market-fish, such as the haddock and whiting; the buckler of a _Coccosteus_ of the extreme size would have covered, if a little altered in shape, the upper surface of the skull of a cod, but the cranial buckler of _Asterolepis_, from which the accompanying wood-cut was taken, (fig. 27,) would have considerably more than covered the corresponding part in the skull of a large horse; and I have at least one specimen in my collection which would have fully covered the front skull of an elephant. In the smaller specimens, the buckler somewhat resembles a laborer’s shovel divested of its handle, and sorely rust-eaten along its lower or cutting edge. It consisted of plates, connected at the edges by flat squamous sutures, or, as a joiner might perhaps say, _glued_ together in _bevelled_ joints. And in consequence of this arrangement, the same plates which seem broad on the exterior surface appear comparatively narrow on the interior one, and _vice versa_; the occipital plate, (_a_,) which, running from the nape along the centre of the buckler, occupies so considerable a space on its outer surface, exhibits inside a superficies reduced at least one half. Like nine tenths of its contemporaries, the _Asterolepis_ exhibits the little central plate between the eyes; but the eye orbits, unlike those of the _Coccosteus_, and of all the Dipterian genera, which were half-scooped out of the cranial buckler, half-encircled by detached plates, were placed completely within the field of the buckler,—a circumstance in which they resemble the eye orbits of the _Pterichthys_, and, among existing fish, those of the sea-wolf. The characteristic is also a distinctive one in Cuvier’s second family of the Acanthopterygii,—the “fishes with hard cheeks.” A deep line immediately over the eyes, which, however, indicated no suture, but seems to have been merely ornamental, forms a sort of rudely tatooed eyebrow; the marginal lines parallel to the lateral edges of the buckler were also mere tatooings; but all the others indicated joints which, though more or less anchylosed, had a real existence. So flat was the surface, that the edge of a ruler rests upon it, in my several specimens, both lengthwise and across; but it was traversed by two flat ridges, which, stretching from the corners of the latero-posterior, _i. e._ parietal, plates, (_b_, _b_,) converged at the little plate between the eyes, while along the centre of the depressed angle which they formed, a third ridge, equally flat with the others, ran towards the same point of convergence from the nape. The three ridges, when strongly relieved by a slant light, resemble not inadequately an