CRETACEOUS CROCODILES. 201 



chodon, the interspaces between the longer ridges widening as they approach the 

 apex. The teeth of the Polyptycliodon never offer any approach to opposite trenchant 

 edges of the crown : but this part, presenting throughout its extent a transverse section 

 of an almost circular form, {Crocodilia, PL 26, fig. 7, PI. 29, fig. 3,) is slightly and regu- 

 larly bent lengthwise, and is invested with a moderately thick layer of true enamel, of 

 which substance the ridges are wholly composed, the surface of the outermost layer 

 of dentine being quite smooth, (PI. 29, fig. 4.) The teeth of the Polyptychodon may 

 be distinguished at once from those of the Mosasaiirus or Pllosaurus by the absence 

 of the less convex, or almost flattened facet of the crown, which is divided by strono- 

 ridges from the remainder of the crown. 



■'o'- 



PoLYPTYCHODON coNTiNuus, Otoen. Plate 29, figs. 4, 5, 6. 



'Odontography,' vol. ii, p. 19. 



The first evidence of this species was a single tooth, which was discovered by 

 W. H. Bensted, Esq., of Rock Hall, near Maidstone, September 16th, 1834, in what 

 is called the ' Trigonia-stratum ' of Shanklin Sand, in the Kentish Rag Quarries near 

 that town, this stratum being a member of the Lower Green-sand Formation. The 

 tooth in question (PI. 29, figs. 5 and 6,) has a crown upwards of three inches in leno-th, 

 and one inch four lines in diameter across its base. The compact dentine has been 

 partially resolved by decomposition into a series of superimposed thin hollow cones 

 fig. 6, and the short and wide conical pulp-cavity is confined to the base, and 

 beginning of the fang, which has been broken away. The cavity of the crown of the 

 tooth in Hypsodon would seem to have been always much larger, as it is in many other 

 predatory fishes in which the teeth are more rapidly shed and renewed than in the 

 Crocodilian Reptiles. In the Collection of Henry Catt, Esq., of Brighton, is preserved 

 tlie crown of a nearly equally fine specimen of the Polypty chodon continuus, from the 

 Chalk of Sussex: this specimen is figured of the natural size in PI. 29, fig. 4. A portion 

 of the ridged enamel has scaled ofi", exposing the smooth surface of the dentine which 

 it protected. The teeth of this species of Poly pity chodon differ from those supposed to 

 have belonged to PoiJdIopleuron, in the ridges of the crown being more numerous and 

 close set, and in the transverse section being circular instead of elliptical. 



Gigantic Fossil Saurian from the Lower Green-sand at Hythe. 



Crocodilia, Plates 27, 28. 



'Proceedings of the Geological Society of London, June 16th, 1841.' 



I propose to describe these remarkable and highly interesting fossils under the . 

 present section, on account of the identity of the Formation in which they were dis- 

 covered, with that of the tooth qI Polypitychodon continuus above described, and because 



