The Glyptolepis, or carved scale, may be regarded as the representative of a family of the Lower Old Red Sandstone, which, differing very materially from the genera described, had yet many traits in common with them, such as the bare, bony skull, the bony scales, the naked rays, and the unequally sided condition of tail. The fins, which were of considerable length in proportion to their breadth of base, and present in some of the specimens a pendulous-like appearance, cluster thick together towards the creature's lower extremities, leaving the upper portion bare. There are two dorsals placed as in the Dipterus and Diplopterus—the anterior directly opposite the ventral fin, the posterior directly opposite the anal. The tail is long and spreading;—the rays, long and numerously articulated, are comparatively stout at their base, and slender as hairs where they terminate. The shoulder-bones are of huge dimensions, the teeth extremely minute. But the most characteristic parts of the creature are the scales. They are of great size, compared with the size of the animal. An individual not more than half a foot in length, the specimen figured, (see [Plate V.], fig. 2,) exhibits scales fully three eighth parts of an inch in diameter. In another more broken specimen there are scales a full inch across, and yet the length of the ichthyolite to which they belonged seems not to have much exceeded a foot and a half. Each scale consists of a double plate, an inner and an outer. The structure of the inner is not peculiar to the family or the formation: it is formed of a number of minute concentric circles, crossed by still minuter radiating lines—the one described, and the other proceeding from a common centre. (See [Plate V.], fig. 5.) All scales that receive their accessions of growth equally at their edges exhibit, internally, a corresponding character. The outer plate presents an appearance less common. It seems relieved into ridges that drop adown it like sculptured threads, some of them entire, some broken, some straight, some slightly waved, (see [Plate V.], fig. 3;) and hence the name of the ichthyolite. The plates of the head were ornamented in a similar style, but their threads are so broken as to present the appearance of dotted lines, the dots all standing out in bold relief. My collection contains three varieties of this family; one of them disinterred from out the Cromarty beds about seven years ago, and the others only a little later, though partly from the inadequacy of a written description, through which I was led to confound the Osteolepis with the Diplopterus, and to regard the Glyptolepis as the Osteolepis, I was not aware until lately that the discovery was really such; and under the latter name I described the creature in the Witness newspaper several weeks ere it had received the name which it now bears. It was first introduced to the notice of Agassiz, in Autumn last, by Lady Cumming of Altyre. The species, however, was a different one from any yet found at Cromarty.[V]
[V] There are three species of Glyptolepis—G. elegans, G. Leptopterus, and G. microlepidotus.
The Cheirolepis, or scaly pectoral, forms the representative of yet another family of the Lower Old Red Sandstone, and one which any eye, however unpractised, could at once distinguish from the families just described. Professor Traill of the University of Edinburgh, a gentleman whose researches in Natural History have materially extended the boundaries of knowledge, and whose frankness in communicating information is only equalled by his facility in acquiring it, was the first discoverer of this family, one variety of which, the Cheirolepis Traillii, bears his name. The figured specimen ([Plate VI.], fig. 1) Agassiz has pronounced a new species, the discovery of the writer. In all the remains of this curious fish which I have hitherto seen, the union of the osseous with the cartilaginous, in the general framework of the creature, is strikingly apparent. The external skull, the great shoulder-bone, and the rays of the fins, are all unequivocally osseous; the occipital and shoulder-bones, in particular, seem of great strength and massiveness, and are invariably preserved, however imperfect the specimen in other respects; whereas, even in specimens the most complete, and which exhibit every scale and every ray, however minute, and show unchanged the entire outline of the animal, not a fragment of the internal skeleton appears. The Cheirolepis seems to have varied from fourteen to four inches in length. When seen in profile, the under line, as in the figured variety, seems thickly covered with fins, and the upper line well nigh naked. The large pectorals almost encroach on the ventral fins, and the ventrals on the anal fin; whereas the back, for two thirds the entire length of the creature, presents a bare rectilinear ridge, and the single dorsal, which rises but a little way over the tail, immediately opposite the posterior portion of the anal fin, is comparatively of small size. The tail, which, in the general condition of being developed chiefly on the lower side, resembles the tails of all the creature's contemporaries, is elegantly lobed. The scales, in proportion to the bulk of the body which they cover, are not more than one twentieth the size of those of the Osteolepis. They are richly enamelled, and range diagonally from the shoulder to the belly in waving lines; and so fretted is each individual scale by longitudinal grooves and ridges, that, on first bringing it under the glass, it seems a little bunch of glittering thorns, though, when more minutely examined, it is found to be present somewhat the appearance of the outer side of the deep-sea cockle, with its strongly marked ribs and channels, the point in which the posterior point terminates representing the hinge. (See [Plate VI.], fig. 2.) The bones of the head, enamelled like the scales, are carved into jagged inequalities, somewhat resembling those on the skin of the shark, but more irregular. The sculpturings seem intended evidently for effect. To produce harmony of appearance between the scaly coat and the enamelled occipital plates of bone, the surfaces of the latter are relieved, where they border on the shoulders, into what seem scales, just as the dead walls of a building are sometimes, for the sake of uniformity, wrought into blind windows. The enamelled rays of the fins are finished, if I may so speak, after the same style. They lie thick upon one another as the fibres of a quill, and like these, too, they are imbricated on the sides, so that the edge of each seems jagged into a row of prickles. (See [Plate VI.], fig. 3.) The jaws of the Cheirolepis were armed with thickly-set sharp teeth, like those of its contemporaries, the Osteolepis and Diplopterus.[W]
[W] There have been five species of Cheirolepis enumerated—C. Cummingiæ, C. splendens, C. Traillii, C. unilateralis and C. Uragus. The Cheirolepis splendens and C. unilateralis Agassiz regards as doubtful.
PLATE VI.
