Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/875

 apparently the skin. The mandibles are not disturbed, and by their position indicate that the mouth was closed ; but the bones of the upper jaws are not determinable, except the left maxilla, which is in a pretty perfect state ; the praemaxilla, however, has been torn away. The orbit (it) is pretty well preserved, but is removed a little below the natural position.

The contour of the dorsal margin, in front of the dorsal fin, is entirely lost, this region having been forced downwards nearly as far as the centre of the body. Posteriorly, however, the whole form is well preserved, and exhibits the transverse plates and rods in a good state of preservation, the series of lateral (g) and sigmoidal plates (j) being almost complete ; the line of the central lozenge- shaped plates (h) is also quite distinct, with a plate here and there bearing a central ridge. In front this line is thrown suddenly upwards, in consequence of the ruptured condition of the anterior parts. Twenty-eight lateral plates can be counted, and fifteen or sixteen sigmoidal ones along the lower margin ; only ten or eleven can be made out of the dorsal row.

One of the most interesting features in this specimen is the ventral plates (m), which are displayed in a remarkable manner. Without the aid of this specimen it might have been difficult to determine the existence of a double series of these plates, one belonging to each side of the abdomen. Here, however, both sets are most satisfactorily seen, those belonging to the exposed, or left side, being arranged in their natural order, while those of the right side are turned downwards below the ventral margin, so that their outer surface is placed upwards and in the same plane with the similar aspect of the other plates. The lower margins of the two sets are in close contact, the line of junction coinciding with the ventral margin. The plates in both series incline forwards, their pointed extremities being turned backwards ; and the compound columns (n) in connexion with the upper extremities are distinctly displayed, those belonging to the left side taking their usual course upwards in the direction of the head and lozenge-shaped area, those on the right side, or those of the displaced series, passing outwards from the specimen, the columns, like the plates themselves, having been displaced and thrown downwards. And thus we have a satisfactory proof that both the ventral plates and columns are developed in two lateral and distinct series. And furthermore these columns are seen, in the specimen before us, to pass upwards and to become united to the lower anterior lateral plates, notwithstanding that they are much disturbed at this point.

The dorsal fin (ct) has been broken away, only three-quarters of an inch remaining. The anterior basal extension, however, is well shown, as this portion is turned a little towards the observer and has been forced downwards. Consequently the short anterior basal plates, or fin-fulcra, are seen to be arranged in a bilateral series of about twelve. This bilateral arrangement of the fin-fulcra is not, we believe, usual among the ganoids, in which the two lateral halves are commonly united into one piece. Mere traces are observable