530 BRITISH FOSSIL REPTILES. 



two stronger serrations behind the chief or apical one. Smaller serrations mark the hind 

 border of the crown between the above and the end of the basal ridge. 



Thus, all the complexities giving the generic characters of the lower teeth of Igua- 

 nodon are here manifested, as are those of the upper teeth in the skull (PI. 59, figs. 9, 10). 

 The following differences from the larger teeth of Iguanodon Mantelli are of specific 

 value : the defined rise of the basal border of the coronal enamel on both the outer and 

 inner sides of the tooth, especially the latter ; the relatively larger size and smaller 

 number of the marginal serrations ; the larger relative size and more definite median 

 position of the primary longitudinal ridge. 



The latter character, however, is reached in the range of variety to which the teeth of 

 Iguanodon Mantelli are subject, as may be seen in the anterior ' acuminate and 

 lanceolate' tooth in the Purbeck Iguanodon (PI. 59, fig. 8 h), and in the figs. 10, 15, 17, 

 PI. 45, exemplifying the characters of the upper and lower teeth of Iguanodon Mantelli 

 and some of their varieties, due to age, wear, and position in the jaw. 



From the above facts I conclude that the fossils discovered by Mr. Fox, and figured 

 in Pis. 59 and CO, afford the much-needed exemplification of the cranial structure in the 

 genus Iguanodon, and that they contribute to supply characters of the serrident family of 

 Dinosatiria which were not given in the fossil skull of Scelidosaurus Harrisonii, figured in 

 Pis. 46 and 47. The importance of tliis addition to the knowledge of Dinosaurian 

 structures induces me to recapitulate and enforce the passing remarks, offered in the 

 course of my descriptions, on statements which, if true, would leave such addition still a 

 desideratum. 



Serrations of the free edge of the crown, affirmed to be " so characteristic of the teeth 

 of Iguanodon" (Huxley, ut supra, p. 5), are not in any degree characteristic of that genus. 

 They are present in the teeth of older Dinosauria as of contemporary genera. The 

 Liassic Scelidosaur and the Purbeck Echinodon alike manifest the modification. The true 

 generic dental characteristic of Iguanodon is the superaddition to marginal serration of 

 ridged and grooved sculpturing of one of the surfaces of the crown of the teeth ; to wit, 

 the outer one in tlie upper teeth, the inner one in the lower, the sculpturing being in so 

 broad and definite a style that the I'idges can be named. This character, comI)ined 

 with marginal serration, in the molars of the small Dinosaur in question, and this 

 other character of the overlap of the expanded crowns in the one direction above 

 described, are now submitted to impartial Taxonomists as the ground of the reference of 

 the subject of the present section to Conybeare's genus. 



So singular an anomaly in the arrangement of a molar series as the reversal of the 

 order of overlapping at its two extremes might well support a generic distinction, but 

 would need clear and indisputable demonstration for acceptance, Iguanodon Foaii 

 affords no real ground for the ascription of such an anomaly. 



