The tooth which, from its more slender and acuminated form, approaches nearest to the character of those of the Gavial, presents a marked difference, however, from the teeth of any of the recent species of that sub-genus of Crocodilians, as well as from those of the long and slender-snouted extinct genera, called Teleosaurus, Steneosatires, &c. I have described itt, therefore, as indicative of a distinct species, under the name of Crocodiles cultridens. The crown is laterally compressed, subincurved, with two opposite trenchant edges, one forming the concave, the other the convex, outline of the tooth. In the Gavial, the direction of the flattening of the crown and the situation of the trenchant edges are the reverse, the compression being from be fore backwards, and the edges being lateraLt The tooth of the Crocodiles cultridens thus re sembles in form that of the Megalosaur, and perhaps still more those of the Argenton crocodile; but I have not observed any spe cimens of the Wealden teeth in which the edges of the crown were serrated, as in both the reptiles just cited. The teeth of the Cro codiles cultridens also present a character which does not exist in the teeth of the Megalosaur, and is not attributed by Cu vier to those of the Crocodile d'Argenton. The sides of the crown are traversed by a few longitudinal parallel ridges, with regular intervals of about one line, in a crown of a tooth one inch and a half in length : these ridges subside before they reach the apex of the tooth, and more rapidly at the convex than at the concave side of the crown.
Hitherto these teeth have not been found so associated with any part of the skeleton of the same species as to yield further cha racters of the present extinct Crocodilian ; but from the above-mentioned well-marked differences between these teeth and those of all the existing species, it is most probable that the extinct crocodile formed the type of a distinct sub-genus, for which the term Su chosaurus has been proposed.
The second form of tooth having the gene ric characters of those of the crocodile, which has been discovered in the Wealden and approximate strata, is as remarkable for its thick, rounded, and obtuse crown as the teeth of the preceding species are for their slender, compressed, acute, and trenchant character. It consequently approaches more nearly to the teeth which characterise the broad and comparatively short-snouted crocodiles; but it differs from these in one of the same cha racters by which the tooth of the Suchosaurus cultridens differs from those of the Gavials, viz., in the longitudinal ridges which traverse the exterior of the crown. These are, how ever, more numerous, more close-set, and more neatly defined than in the Suchosaurus cultridens. Two of the ridges, larger and sharper than the rest, traverse opposite sides of the tooth, from the base to the apex of the crown ; they are placed, as in the crocodile and Gavial, at the sides of the crown, midway between the convex and concave lines of the curvature of the tooth. These ridges are
confined to the enamel ; the cement-covered cylindrical base of the tooth is smooth. The size of the teeth varies from a length of crown of two inches, with a basal diameter of one inch and a half to teeth of one-third of these dimensions. I have proposed to call this extinct crocodile, with biconcave vertebrae, Goniopholis crassidens.
Development. —In the black alligator of Guiana the first fourteen teeth of the lower jaw are implanted in distinct sockets, the remaining posterior teeth are lodged close together in a continuous groove, in which the divisions for sockets are faintly indicated by vertical ridges, as in the jaws of the Ichthyo saurs. A thin compact floor of bone separates this groove, and the sockets anterior to it, from the large cavity of the ramus of the jaw; it is pierced by bloodvessels for the supply of the pulps of the growing teeth and the vas cular dentiparous membrane which lines the alveolar cavities.
The tooth-germ is developed from the membrane covering the angle between the floor and the inner wall of the socket. It becomes in this situation completely enveloped by its capsule, and an enamel-organ is formed at the inner surface of the capsule before the young tooth penetrates the interior of the pulp-cavity of its predecessor.
The matrix of the young growing tooth affects, by its pressure, the inner wall of the socket, as shown in fig. 573, and forms for itself a shallow recess : at the same time it attacks the side of the base of the contained tooth ; then, gaining a more extensive attach ment by its basis and increased size, it pene trates the large pulp-cavity of the previously formed tooth either by a circular or semi circular perforation. The size of the calcified part of the tooth-matrix which has produced the corresponding absorption of the previously formed tooth on the one side, and of the alveolar process on the other, is represented in the second exposed alveolus of fig. 573., the tooth a having been displaced and turned round to show the effects of the stimulus of the pressure. The size of the perforation in the tooth, and of the depression in the jaw, proves them to have been, in great part, caused by the soft matrix, which must have produced its effect by exciting vital action of the absorbents, and not by mere mechanical force. The resistance of the wall of the pulp-cavity having been thus overcome, the growing tooth and its matrix recede from the temporary alveolar depression, and sink into the substance of the pulp contained in the cavity of the fully-formed tooth. As the new tooth grows, the pulp of the old one is re-• moved ; the old tooth itself is next attacked, and the crown being undermined by the ab sorption of the inner surface of its base, may be broken off by a slight external force, when the point of the new tooth is exposed, as in the fig. 573. b.