. Animal Life and the World of Nature; A magazine of Natural History. A Dental Plate of a Sharp-Toothed Kay. each tooth, which finally assumes a distinctly cuspidate form in the teeth at the apex of the jaw. Evidently this type of dentition is intended for a diet very different from that of ordinary sharks, which feed by tearing off large masses of flesh and swallowing them whole. As a matter of fact, the Port Jackson shark feeds chiefly upon shelled molluscs, for crushing which the pavement- like teeth of the hinder part of the jaws are admirably adapted. Crushing-teeth of a type very similar
. Animal Life and the World of Nature; A magazine of Natural History. A Dental Plate of a Sharp-Toothed Kay. each tooth, which finally assumes a distinctly cuspidate form in the teeth at the apex of the jaw. Evidently this type of dentition is intended for a diet very different from that of ordinary sharks, which feed by tearing off large masses of flesh and swallowing them whole. As a matter of fact, the Port Jackson shark feeds chiefly upon shelled molluscs, for crushing which the pavement- like teeth of the hinder part of the jaws are admirably adapted. Crushing-teeth of a type very similar to those of the Port Jackson shark are very common in the Oolites and Lias, but, as already mentioned, are of much larger size, many of them measuring fully an inch and a half across. Before leaving this part of my subject, attention may be directed to the extreme beauty of the dentition of the Port Jackson shark, especially the crushing portion. A reproduction of this might, I think, be introduced with excellent effect into ornamental architecture. Nearly allied in structure to the hinder crushing-teeth of the Port Jackson shark are those of the Carboniferous genus Orodus, two of which are shown in Fig. 6. The name Orodus signifies " mountain-tooth," and has been applied to the members of this group owing to the rugged and centrally-elevated form of the teeth. Before leaving the dentition of the sharks, a few lines must be devoted to certain very remarkable extinct types which display some of the most beautiful spirals to be met with in nature. The best-preserved specimens are obtained from strata—corresponding roughly in age with the upper portion of our own Carboniferous system—in the Government of Perm. Eussia, and the sharks to which they belonged have been named Helicoprion. One of these specimens is shown in the accompanying figure (7). It is supposed to be a single transverse row of teeth from either the upper or lower jaw. During life the individual teet
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