WEALDEN DINOSAURS. 527 



test, on the assumption that the absence of marginal serrations — all other Iguanodontal 

 characters present — was decisive against a generic relationship with Iguanodon. 



Mr. Fox has kindly transmitted to me the portion of the left mandibular ramus, 

 1 inch 7 lines in length, with a depth of 7 lines, where entire, which is the 

 subject of figs. 8 — 11 in PI. 60. It includes the sockets and fangs of eight teeth, so 

 closely set as to have necessitated the overlapping arrangement of the crowns, according 

 to the Iguanodontal type, the hind margin of the anterior tooth covering the outer side of 

 the fore margin of the tooth behind, in the lower as in the upper jaws. The proportion 

 of transverse to fore-and-aft diameters of the fractnred bases of the mandibular teeth 

 (fig. 8) in this specimen is also Iguanodontal, suggestive of a bruising function. These 

 eight teeth occupy an alveolar extent of 1 inch 3 lines. 



The outer surface of the ramus (ib., fig. 9) is divided into an upper and lower facet 

 by a low, obtuse, prominent angle or ridge extending horizontally, and giving the greatest 

 thickness to that part of the jaw ; a series of five vascular or neuro-vascular foramina 

 extends a little above this ridge. The structure of the outer surface of the ramus, 

 exhibited by the larger jaw of a young Iguanodon, also discovered by Mr. Fox, in the 

 same Wealden deposits of the south-west coast of the Isle of Wight, closely accords 

 with that shown by the present specimen (compare Bin., PI. 24, fig. 4, with PI. 60, fig. 9). 



In like manner the inner surface of the smaller mandibular fragment (ib., fig. 10) shows 

 a gentle convexity lengthwise and an almost level surface vertically, broken by a longi- 

 tudinal groove near the lower border. 



Concluding that, as in Iguanodon, the germs of successional teeth would lie on this 

 side of the roots of the broken ones which had been in use, and that such germs would 

 have the ' lanceolate and acuminate ' portion of the crown, yielding the required test of con- 

 formity or otherwise in regard to marginal serration, I removed the inner (splenial) plate 

 at parts which exposed three such germs (PI. 60, fig. 11, «, j, d), each demonstrating the 

 character in question. 



The inner side of the crown is traversed longitudinally by the submedial primary 

 ridge, the coronal margin anterior to which shows four acute serrations, with grooves 

 continued from their intervals some way down the surface. The extreme fragility of these 

 precious evidences checked further attempts to expose more of that surface. My inter- 

 pretation of the characters of the mandible and mandibular teeth, so far as they are 

 exhibited by this specimen, is, that they demonstrate a reptile of the genus Iguanodon. 



If the specimen belong to a full-grown individual, the greater relative size and the 

 smaller number of the coronal serrations show it to belong to a distinct species of Iguanodon, 

 for which the name of its discoverer is deservedly to be retained. 



Still may remain the question whether, in the numerous successions of teeth which 

 would ensue dm-ing the acquisition of the magnitude of Iguanodon ManteUi, the number 

 of serrations might not be increased in greater proportion than the increase of the size of 



4 b 



