Sharks are formidable from their muscular strength and the numerous rows of teeth with which their expansive and powerful jaws are armed: they may be considered as the most destructive and voracious of all the inhabitants of the deep. Their stomachs, which are of enormous capacity, are generally found filled with a mixed collection of substances, some of which seem calculated to try the strength of their digestive powers. It does not appear that their sense of smell always guides them in procuring food, as paper, canvas, or indeed any thing thrown overboard which they are capable of swallowing, is greedily devoured by them. To decide correctly on the _habitat_, or extent of range, taken by any particular species, is difficult, and requires a numerous collection of facts. Frequent mistakes are made in this respect; as in the instance of the _Squalus cornubicus_, or porbeagle shark, whose _habitat_ was supposed to be confined to the British coasts, but which I have since discovered has been found, although rarely, inhabiting the coasts of New Zealand. The teeth of sharks vary in different species. Blumenbach observes, that “in most of the sharks the mouth is furnished with very numerous teeth, for the supply of such as may be lost. The white shark has more than two hundred, lying on each other in rows, almost like the leaves of an artichoke. Those only which form the front row have a perpendicular direction, and are completely uncovered. Those of the subsequent rows are, on the contrary, smaller, have their points turned backwards, and are covered by a kind of gum. These come through the covering substance, and pass forward, when any teeth of the front row are lost. It will be understood, from this description, that the teeth in question cannot have any fangs.”[89] The shark, no doubt, sheds its teeth at certain periods, and the posterior rows are to supply, in succession, the places of those so lost, as, in a number of jaws that I have examined of different species, the second row may frequently be seen in a perpendicular direction, advancing to supply the place of the first. With respect to such teeth having fangs, those of most species have merely rudiments of them, excepting the squalus cornubicus, or porbeagle shark, which has two distinct fangs to every tooth, and they may be seen in the second and third, as well as in the first rows. The posterior rows having their points turned backwards, prevent their prey, when seized, from escaping. The teeth of the shark are used by the Polynesian natives, fixed in rows, as knives. They are attached also to their spears, are used for cutting themselves on occasions of joy or grief, and were employed, previously to the introduction of European knives, for the ornamental carving of their weapons, domestic utensils, &c.