the plates are divided by a lanceolate space. The tapering distal or outer extremities of the lateral plates are united each to a stoutish rod (i), which at the point of union is cylindrical and somewhat enlarged. These are slightly arched backwards and inclined considerably in the same direction ; their outer extremities are a little widened, flattened, and grooved longitudinally ; and, suddenly contracting, they turn forwards, and each becomes joined to the inner pointed extremity of a sigmoidal ridge-like plate (j), which rises boldly up, and which, inclining much forward, terminates in a recurved sharp point a little within the general margin of the fish. The sigmoidal ridges gradually widen in the centre, where there is a longitudinal groove ; and they, as well as the rods, are divided from each other by a considerable space. Such is the general appearance of these sigmoidal ridges or plates ; but on closer examination the ridges are found to be formed of the turned-up edges of wide flat sigmoidal plates (j'), which extend from ridge to ridge.
Such is the description of the transverse series of plates and rods of the posterior half of the body, numbering sixteen or seventeen corresponding to the caudal vertebrae, to which the lozenge-shaped areas and lateral plates have a strong resemblance. On the anterior half the dorsal members of the transverse plates and rods are somewhat modified. The central lozenge-shaped plates bearing the ridges and the elongated lateral plates are continued to the occiput unaltered in character, or only slightly changed in form. Below, or towards the ventral margin, the sigmoidal ridges or plates seem to be replaced by a series of seven large thoracic or ventral plates (m), which are arranged along the margin of the body, those of the two sides meeting on the median line, where doubtless they formed a sharp edge. They are 3/8 inch long, and about 1/8 inch wide.
They appear to imbricate forwards, and are of an irregular ovate form, with the posterior margin thin and somewhat flattened, and the anterior or overlapping margin thickened, grooved, and a little shouldered above. We say appear to imbricate forwards ; but in the most perfect specimens there are indications that they are really imbricated backwards, the groove of the anterior margin receiving the thin posterior border of the preceding plate ; and the appearance to the contrary seems to be owing to dislocation. Both extremities of the plates are drawn out, the lower one being considerably prolonged, pointed, and directed backwards. The upper extremities are directed upwards and forwards, and are produced into widish columns (n) (the ribbon-shaped organ of Germar), the two or three anterior of which, increasing in length backwards, terminate immediately behind the clavicle. The posterior ones pass upwards, and are united to the outer extremities of the lower lateral plates near the occiput. These columns, which are divided by narrow spaces, present a very peculiar appearance. Each of them is composed of numerous, narrow, much elongated plates or rods, with pointed extremities, which, overlapping each other considerably, give to the whole a sort of twisted look. They are probably, however, in a disturbed state. About seven of the lower lateral plates next the occiput are
VOL. XXVI. — PART I. 3 A
