is a little less than -fa of an inch wide ; and from this we infer that more than one-half of this fin is wanting. In this specimen it would probably be a little short of 4 inches long. There are twenty-four or twenty-five rays at the base of this elongated portion, including the short anterior plates or fulcra ; and 1| inch up only seven or eight can be counted. Very little is to be seen of the narrow posterior portion of the fin, there being only a slight trace of a few rays.
The pectoral fins (c) are in a pretty perfect condition, occupying their natural position immediately behind the posterior angle of the gill-covers, one partially overlying the other. At the root of one of them there are two flat curved bones, which may perhaps be respectively the scapula and coracoid. Arising from these are the brachials (o'), to the number of fourteen or fifteen; they are about ^ of an inch long, and are delicate and flat, thicker than the fin-rays, with the extremities obtuse ; and there are two simple rays, composed of many joints, to each brachial.
The remains of both the ventral fins (cl) are seen in front of the ventral plates, the edge of the belly being turned a little upwards. Two elongated bones, nearly ^ of an inch long, lie in contact with them, and have their anterior ends a little enlarged and nodulous. These are probably the pelvic bones, to which the fins were attached, the thickened extremities having all the appearance of articular surfaces. The mere casts of these bones are observed in connexion with the specimen ; but the bones themselves are present on a fragment of the slab that was split off from the specimen.
The enlarged portion of the anal fin (6) is pretty well displayed, immediately behind the ventral plates ; but the narrow posterior part is scarcely traceable.
The tail is well developed ; but half of the upper lobe is wanting. The under lobe shows distinctly the numerous short joints of which the rays are composed, as well as their terminal bifurcations. This lobe is lg inch long. The scales (<?) and marginal plates, or fulcra (/), are well preserved on the upper lobe.
The last specimen (Pl. XLIII. fig. 4) we have to describe is the largest of the four ; it is 5 inches in length and 2 inches deep. The head is much crushed ; but the orbit (u), the narrow elongated gill- plates (s), and jaws (p, q) are all determinable, though much injured. The ventral plates are confused and broken ; they occupy, however, their natural position ; and a few of the compound columns are present and can be traced to the anterior lateral plates. The great abdominal rods (o) are also conspicuous, inclining backwards, the lower wide extremities in contact with the last ventral plate and the upper extremities leaning against and, as it were, pushing backwards the lateral plates in the immediate vicinity of the abdomen.
The lateral plates (cj) and rods (i) are well preserved ; and the series of lozenge-shaped areas (7t) form a distinct line from end to end, displaying better than any of the other examples the elevated central ridges. The plates on the shoulder (/) are also beautifully preserved in regular order, and exhibit, in great perfection, the ridges resembling mucus-tubes ; and the whole series of the sig-
