WEALDEN FORMATIONS. 43 



delicate rugous structure, in a well-defined border, concave toward the root. The 

 opposite side of the crown, flattened below and concave above, has the enamel smooth, 

 except at the base, where it is rugous, and is extended nearly half an inch lower down 

 the crown, where it terminates by a border convex toward the root. 



The margins of the crown are obliquely abraded toward the concave side of the 

 crown, and, near the base of the straighter border, there is an oblique depression. 



The root is subcylindrical, and shows the remains of a pulp-cavity : it appears as 

 if it had been implanted in a complete alveolar cavity ; but the unequal extent of the 

 enamel on the two sides of the crown indicates a corresponding inequality in the 

 outer and inner alveolar walls of the jaw which supported this tooth. Assuming the 

 thecodont mode of its implantation, it would in this respect resemble the teeth of 

 the Crocodiles, and of certain Enaliosaurs and Dinosaurs. 



The shape of the crown of this tooth, especially the degree of compression of the 

 crown and its expansion above the root into opposite borders, which become 

 trenchant, accords best with the characters of the teeth in the carnivorous Sauria. 

 Of such teeth as have hitherto been discovered in the Wealden strata, those that have 

 been referred to the Hylaosauriis* make the nearest approach to the form of the 

 tooth in question ; but, besides the difference of size, the crown has a more 

 symmetrical shape in Hylceosaurus, and its broadest part is nearer the apex : the 

 opposite worn margins which converge to the tip are both relatively shorter and 

 thicker, and are not obliquely abraded so as to be trenchant, as they are in the larger 

 Wealden tooth here described. It is a tooth of allied form to that of the Hylaosaurus, 

 and, like it, was implanted by a cylindrical fang, apparently in a distinct socket : 

 the few specimens that have been discovered of the teeth ascribed to Hylaosaurus 

 appear to have been broken from the socket, not to have been naturally shed so as to 

 show the traces of absorption ; and the same is the case with the larger tooth in 

 question. 



The difference of form between the tooth of the Megalosaurusj; and the present 

 large piercing and cutting tooth is too obvious and strongly marked to need 

 particularising ; and it departs still further, both in shape and mode of implantation, 

 from the tooth of the Iguanodon.;J: 



The present tooth, therefore, indicates a reptile equal in size to any of those above 

 cited from the Wealden strata, but of a distinct genus : and vertebral evidence has 

 been adduced, in the present ' Monograph,' of at least two genera — independently of 

 Streptospondylus — of large Wealden reptiles equally distinct from those originally 

 made known by Buckland and Mantell. 



The tooth in question may, very probably, belong to either Cetiosaurus or 

 Pelorosaurus. Future discoveries of teeth or of jaws with teeth, associated with the 



* 'Monograph on Wealden Reptiles,' part iv, 18J6, p. 21, Tab. VIII, figs. C — 9. 

 t Ibi<'., part iii, 185G, p. 21, Tab. XI and XII. X Ibid., part i. 



