A series of teeth from individual Megalosaurs, of different ages, are preserved in the British Museum and in the geological museum at Oxford ; although differing in size, they preserve the characteristic form above described. In one specimen the point of the crown and the trenchant margins have been rubbed down to a smooth obtuse surface ; it seems to have come from the hinder part of the dental series, where the teeth may have been smaller and less sharp, or more liable to be blunted by a greater share in the imperfect act of mastication, than the teeth in advance.
Successional teeth in different stages of growth are shown in the original portion of jaw of the Megalosaur in the Oxford museum. Some, more advanced, show their crowns projecting from alveoli already formed by the plates extending across from the triangular processes before described : vacant sockets, from which fully formed teeth have escaped, occur, generally in the intervals between these more advanced teeth. The summits of less developed teeth are seen protruding at the inner side of the basal interspaces of the triangular plate, between them and the true internal alveolar parapet. There can be no doubt that, in the course of the development of these teeth, corresponding changes take place in the jaw itself, by which new triangular plates and alveolar partitions are formed, as the old ones become absorbed, analogous to those concomi tant changes in the growth and form of the teeth, alveoli, and jaws, which take place in so striking a degree in the elephant. The peculiarity of the Megalosaur, as compared with the crocodiles and lizards which have a like endless succession of teeth, is the deeper position of the successional tooth (fig. 75, c), in relation to the one (a) it is destined to replace, and the great proportion of the tooth which is formed before it is pro truded. The anterior tooth a in this specimen shows at the inner side of its base the commencing absorption stimulated by the encroaching capsule of the successional tooth c below, the crown of which is completed externally, though not consoli dated. On one of the fractured margins of this piece of jaw, a part of the basal shell of an absorbed and shed tooth remains, with part of the root of the successional tooth, which has risen into place, but which shows its base full of matrix, the pulp not having been calcified at that period of the tooth's growth.
In the proportion of the successional teeth which is formed in the formative cavity in the substance of the jaw, the Mega losaur offers a closer resemblance to the mammalian class than do any of the recent or extinct crocodilian or lacertian reptiles. But the evidence of uninterrupted and frequent
succession of the teeth in the Megalosaur is unequivocal ; and this part of the dental economy of the great carnivorous reptile is strictly analogous to that which governs the same system in the existing members of the class. The different forms of the teeth at different stages of protrusion did not fail to attract the attention of the gifted discoverer of the great predatory saurian, in whose words this notice of its dentition may be fitly concluded "In the structure of these teeth we find a combination of mechanical contrivances analogous to those which are adopted in the construction of the knife, the sabre, and the saw. When first protruded above the gum, the apex of each tooth presented a double cutting edge of serrated enamel. In this stage its position and line of action were nearly vertical ; and its form, like that of the two-edged point of a sabre, cutting equally on each side. As the tooth advanced in growth, it became curved. backwards in the form of a pruning-knife, and the edge of serrated enamel was continued downwards to the base of the inner and cutting side of the tooth, whilst on the outer side a similar edge descended, but a short distance from the point ; and the convex portion of the tooth became blunt and thick, as the back of a knife is made thick for the purpose of pro ducing strength. The strength of the tooth was further increased by the expansion of its side. Had the serrature continued along the whole of the blunt and convex portion of the tooth, it would in this position have possessed no useful cutting power ; it ceased precisely at the point beyond which it could no longer be effective. In a tooth thus formed for cutting along its concave edge, each movement of the jaw combined the power of the knife and saw ; whilst the apex, in making the first incision, acted like the two-edged point of a sabre. The backward curvature of the full-grown teeth enabled them to retain, like barbs, the prey which they had penetrated. In these adaptations we see contrivances which human ingenuity has also adopted in the preparation of various instruments of The oldest known beds from which any remains of saurus have been obtained are the lower oolites at Selsby Hi11, and Chipping-Norton, Gloucestershire. Abundant and charac teristic remains occur in the Stonesfield slate, Oxfordshire. Teeth of this genus have been found in the Cornbrash and Bath oolite ; both teeth and bones are common in the \Walden strata and Purbeck limestone. Some of these fossils indicate a reptile of at least 30 feet in length.