Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/874

 most protuberant at the muzzle ; behind, it is angulated near the centre, the posterior margin of the operculum (s) determining the form ; the jaws (p, q) are nearly perfect, and are closed, showing that the mouth shuts upwards ; the maxilla is wanting, only the impression of it remaining, indicating its form and position. The brow, orbit (u), gill-cover, and clavicle (r) are all in their natural positions, no considerable disturbance of these parts having taken place.

The pectoral fin (c), though in disorder, occupies its proper situation immediately below the angle of the operculum, near the longitudinal centre ; and one of the ventral fins (d) is well displayed at the ventral margin in connexion with the lower extremity of the clavicle. It is narrow, and its pointed extremity inclines backwards as far as the posterior extremity of the second ventral or thoracic plate ; it is upwards of half an inch in length. Little more than half an inch remains of the elongated portion of the dorsal fin (a) ; and mere traces are perceptible of the narrow posterior division. The narrow backward portion of the anal fin is scarcely distinguishable ; but the large anterior member (b), though not entire, is distinct about the middle of the ventral margin and a little behind the ventral plates. The tail-fin is almost perfect, exhibiting both the general outline with the lobes spread and the surface- characters. The upper lobe, which is a little longer than the under, is about an inch long.

The transverse series of plates and rods are much disturbed over the whole surface, though in places they are partially in order and show the same surface-characters as are displayed in specimens in which these parts are more perfect ; and, as in them, they are covered with black enamel-like matter. The ventral plates (m), however, are arranged in complete order along the ventral margin, from the base of the ventral fin to a little in front of the anal, overlying each other apparently forwards; but on closer examination they are seen to imbricate backwards, and to give off from their upper extremities the peculiar compound columns (n) already described, which, extending upwards in parallel order, incline towards the head. The anterior ones are the shortest, and appear to terminate near to the margin of the clavicle. A few of the posterior pass above the angle of the operculum and can be seen to join with the lateral plates of this region, notwithstanding that they are much disturbed. The large posterior abdominal rods (o) occupy their usual position, sloping backwards from the last ventral plate.

The specimen (P1, XLIII. fig. 2) next to be described is highly instructive, though it is in many parts much disarranged. The head, in particular, has greatly suffered, the upper margin being entirely obscured by the opercula(s), which have been torn from their natural positions and turned upwards and forwards ; their lower extremities are placed close together, and project in front of the brow. They lie with the external surface uppermost, their anterior margins approximating. That belonging to the right side has carried along with it the pectoral fin (c), which is beautifully displayed, in an expanded state, almost complete. The left pectoral is distinctly seen in its natural position, though much injured, and overlain by a thin film of