896 



572. 



Teeth in different stages of formation from one 

 alveolus of the Gavial: a is the base partly 

 absorbed by the pressure of b, the successional 

 tooth ; below which is figured c, the germ of the 

 next tooth to follow. 



Amongst the remains of Oocodilians which 

 are scattered through the Tilgate strata, the 

 most common ones are detached teeth, from 

 the difference observable in the form of which, 

 Dr. Mantell has observed, that " they appear 

 referable to two kinds, the one belonging to 

 that division of crocodiles with long slender 

 muzzles, named Gavial, the other to a species 

 of Crocodile, properly so-called, and resembling 

 a fossil species found at Caen."* 



Dr. Mantell has obligingly communicated 

 to me figures of well-preserved specimens of 

 both the forms of teeth alluded to, the exact- 

 ness of which I have recognised by a com- 

 parison with the specimens themselves in the 

 British Museum. 



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, Steneosaurus, &c. I have 

 described itf, therefore, as indicative of a 

 distinct species, under the name of Crocodilus 

 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 lateral. 



* Wonders of Geology, 1839, vol. i. p. 386. 

 t Odontography, pi. Ixii. A., figs. 9, 10. 

 % The tooth attributed by M. Deslongchamps 

 to the Poikilopleuron, agrees in form with those of 



TEETH. 



The tooth of the Crocodilus 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- 

 codilus 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 AV 

 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 Suchosaurtis 

 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- 



the Gavial, and differs in the characters cited in the 

 text from those of the Crocodilus cvltridens. 



