﻿14 



FOSSIL REPTILIA OF THE 



it bends in from its broadest part, are conspicuous. Minute, short, irregular, longi- 

 tudinal, linear risings of the enamel may be seen with the pocket lens in part of the 

 interspaces of the longer and plainer ridges. The crown expands to its extreme fore- 

 and-aft breadth about one third of its length from the fang. 



The enamel on the inner side of the crown (ib. fig. 15, magn.) begins by a like 

 definite rise from the level of the fang, but this runs straighter across before bending up 

 to the margins of the expanding basal part of the crown. The continuation to the hinder 

 border is more prominent and its termination is more abrupt, giving a slightly angular 

 contour to that border, and making the surface of the crown between the border-ridge and 

 the primary longitudinal ridge a little concave transversely. The basal rising subsides more 

 quickly and completely upon the anterior border, which describes a gentle convex curve, and 

 does not rise so as to render the inner surface of the crown between it and the primary 

 ridge concave. Thus, the inner and outer sides of the crown being determinable by their 

 difference of sculpturing, the fore and hind borders are shown by the above specified 

 characters, and the detached tooth can be referred, as in the case of those of the larger Igua- 

 nodon, by like characters to its own ramus or side of the jaw ; this, in the present tooth, 

 is the right one. The inner side of the crown of this tooth of Iguanodon Foxii, as in the 

 lower teeth in situ, has one chief median primary longitudinal ridge, increasing in strength 

 from its origin at the basal rising of the enamel to the apex of the crown. On the front 

 facet a short secondary ridge begins, next the primary one, near the apex of the crown, and 

 terminates in the point or ' serration ' next to that of the primary ridge. Another secondary 

 ridge begins at the base of the crown, and runs nearly parallel with the primary one. 

 The margin of the crown, anterior to this ridge, shows the usual smaller serrations. On 

 the hind facet two secondary ridges commence at the up-bent part of the basal one, run 

 parallel with the primary ridge, gaining in prominence and breadth, and terminate in the 

 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. I, 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. I, fig. 8 b), and in the figs. 10,15, 17, 

 Plate VII (' Monograph on the Genus Iguanodon,' Supplement No. 2, Pal. vol. for 1858), 

 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. 



