and from the scaly base the rays diverge like the radii of a circle, and terminate in a semicircular outline. The ventrals are placed nearer the tail, says Agassiz, than in any other ganoid fish. (See Plate X., fig. 2.) But no such description can communicate an adequate conception to the reader of the strikingly picturesque appearance of the _Holoptychius_, as shown in Mr. Noble's splendid specimen. There is a general massiveness about the separate portions of the creature, that imparts ideas of the gigantic, independently of its bulk as a whole; just as a building of moderate size, when composed of very ponderous stones, has a more imposing effect than much larger buildings in which the stones are smaller. The body measures a foot across, by two feet and a half in length, exclusive of the tail, which is wanting; but the armor in which it is cased might have served a crocodile or alligator of five times the size. It lies on its back, on a mass of red sandstone; and the scales and plates still retain their bony color, slightly tinged with red, like the skeleton of some animal that had lain for years in a bed of ferruginous marl or clay. The outline of the occipital portion of the specimen forms a low Gothic arch, of an intermediate style between the round Saxon and the pointed Norman. This arch is filled by two angular, pane-like plates, separated by a vertical line, that represents, if I may use the figure, the-dividing astragal of the window; and the under jaw, with its two sweeping arcs, or branches, constitutes the frame. All of the head which appears is that under portion of it which extends from the upper part of the belly to the snout. The belly itself is thickly covered by huge carved scales, that, from their massiveness and regular arrangement, remind one of the flags of an ancient stone roof. The carving varies, as they descend towards the tail, being more in the ridged style below, and more in the tubercled style above. So fairly does the creature lie on its back, that the ventral fins have fallen equally, one on each side, and, from their semicircular form, remind one of the two pouch holes in a lady's apron, with their laced flaps. The entire outline of the fossil is that of an elongated ellipsis, or rather spindle, a little drawn out towards the caudal extremity. The places of all the fins are not indicated, but, as shown by other specimens, they seem to have been crowded together towards the lower extremity, like those of the _Glyptolepis_, an ichthyolite which, in more than one respect, the _Holoptychius_ must have resembled, and which, from this peculiarity, presents a brush-like appearance--the head and shoulders representing the handle, and the large and thickly clustered fins the spreading bristles.[AP] [Footnote AP: There are now six species of _Holoptychius_ enumerated--_H. Andersoni_, _H. Flemingii_, _H. giganteus_, _H. Murchisoni_, _H. nobilissimus_, and _H. Omaliusii_.]