Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/868

 and articulating lengthwise by notches and points. The fin-rays, which occupy more than half the width of the entire lobe, are rather delicate, jointed, and bifurcated once or twice at the extremities. The rays are longest and are much inclined on the lobes, and become shorter and less inclined in the axis of the fork.

Perhaps the most curious feature in this interesting fish is found in the character and mode of arrangement of the more or less bony plates and rods, regarded by Germar as composing an internal " bony skeleton; " and, indeed, in the general disposition of the component parts there is a strong resemblance to such. On examining them in detail, however, there are one or two anomalous features which render it difficult to work out the homologies of the bones ; and the discrepancies are of a nature to raise the questions, Do, indeed, all these bones really belong to an endo -skeleton ? and may they not in part belong- to an exo-skeleton ? Before, however, entering on these points it will be better to describe the form and arrangement of these peculiar plates and rods. And for the sake of avoiding circumlocution, and to simplify the description, we shall give to the various parts distinct names, referring only occasionally to those in general use, for the purpose of pointing out resemblances.

The plates and rods are arranged in transverse series, of which there are twenty-seven or twenty-eight, extending from the occiput to the root of the tail, reminding one much of the disposition of the transverse flakes of muscle observed on the sides of the body of a fish when the skin has been removed. These transverse series of plates and rods are, for the most part, placed a little asunder, but are at some points in contact, and occasionally seem as if imbricated. They are in contact along the longitudinal middle line, which corresponds to the usual lateral line or the line of the vertebral column. Here there is a chain of lozenge-shaped plates or areas (h) with their angles placed lengthwise and transversely. In the centre of each there is an elongated rounded ridge (fig. 2, h') placed longitudinally; these ridges resemble the mucus-tubes of the lateral line of certain fishes.

These lozenge-shaped areas or plates measure about 1/10 inch across. From either side of each of them there extends a longitudinal transversely elongated plate (figs. 1, 2, g) inclined backwards, the largest of which measures about 1/4 inch in length ; these, which we shall call the lateral plates, are expanded and bifurcated (g') in the direction of the length of the fish at their inner extremities, and thus embrace, as it were, the lozenge-formed areas or plates bearing the ridges already described ; or perhaps this arrangement would be better described by stating that the forks of the opposed plates, meeting on the median line, form the lozenge-shaped areas or plates, to which they give an elevated border. The lateral plates have a boss-like enlargement at the point of bifurcation ; here the plates are narrowest ; hence they widen gradually for some distance, and then, turning backwards, taper to the termination. The margins are abruptly defined, and are slightly elevated into narrow ridges, which die out towards the outer margin. The bifurcations of the adjacent plates are in contact ; and so are the outer terminations. But for the rest.