On Platysiagum sclerocephalum , Egerton, and Palæospinax priscus , Egerton

In the 13th Decade of the Memoirs of the Geological Survey of the United Kingdom, published in 1872, I described the above-named fossil fishes from the Lias formation of Lyme Regis. Since the issue of that publication I have obtained specimens elucidating parts which were defective in the former examples, and which I consider of sufficient importance to warrant description. On referring to the figure of the former ( Platysiagum ), given on plate 6 of the Decade, it will be seen that the dorsal and anal fins are wanting. This also happens with the several specimens described in the text but not figured. These desiderata are furnished by a fine specimen recently obtained. The two extremities are wanting; the remainder of the fish measures 15 1/2 inches in length. It corresponds very closely in size with the larger of the two specimens described in the Decade. The total length of the fish, if restored, would probably be about 22 inches. The vertical diameter of the trunk is very uniform between the occiput and the dorsal fin, and measures 4 inches. This is a singular character in a Sauroid fish, in which family the body is generally fusiform, tapering gradually from the thoracic arch to the commencement of the caudal fin. The dorsal fin which is here preserved is very singular both in position and structure. It is situated 9 1/2 inches behind the occiput, and occupies a position vertically opposed to the interval between the ventral and anal fins, and extends thence nearly