WEALDEN DINOSAURS. 525 



have broken the teeth, at that time cemented to their sockets. Howsoever that may be, 

 displacement is obvious, and no inference can be drawn as to the original relative position 

 of the crowns of these anterior teeth. As it is, the anterior edge of the crown of the 

 third molar does not overlap in the slightest degree the posterior edge of the crown of 

 the tooth before it ; the reverse is the case if any overlap at all can be predicated. In 

 the undisturbed molars the hind edge of each tooth projects a little beyond the fore 

 edge of the one behind it. This is the characteristic arrangement of the upper or 

 maxillary teeth of Iguanodon. It is exemplified in the specimen figmed in Din., 

 PI. 45, fig. 2, in the undisturbed upper teeth, there marked m, n, o. The overlap by the 

 anterior edge of the crown in the anterior four maxillary teeth of the posterior edge of the 

 tooth in front, and the reverse arrangement in the rest of the maxillary series, may be 

 a character of Jlj/jjsilojj/iodo/i, Huxley, but is not one of the present nor of any previous 

 evidences of Iguanodon. In the small species discovered by Mr. Fox, as in the large type 

 of the genus, the maxillary grinders not merely seem to overlap, but do so, in the way 

 and degree exemplified in fig. 9, PI. 59, and in fig. 2, PI. 45. 



Eour or five teeth may have occupied the alveolar interspace between the foremost 

 of the series of ten maxillary teeth and the second tooth from the premaxillary one, i 

 (PI. 59, fig. 9). Sixteen teeth of the pattern characteristic of the upper molars of 

 Iguanodon would thus occupy the extent of the alveolar border of the upper jaw 

 preserved behind the pointed tooth(j). The maxillary is broken away behind such 

 sixteenth molar. The small Iguanodon may, therefore, have resembled the large one, in 

 number or ' formula,' as in the characteristic and peculiar generic pattern, of its teeth. 

 The arrow (lo) points to the tooth which is the subject of the magnified view (fig. 10). 

 A comparison of this figure with a similar magnified view of an upper molar of 

 Scelidosaurus {Din., PI. 46, fig. 3 ') shows the teeth of the two genera to be modifications 

 of the same type. The exterior surface of the crown in Scelidosaurus (PI. 60, fig. 21) 

 has a median and two marginal longitudinal elevations or ridges. The marginal ones 

 diverge with the expansion of the crown, and end in points at its extreme breadth, rather 

 more than half way between the base and apex of the crown. This apex and the points 

 of the marginal ridges define a triangle, the converging sides of which are notched or 

 serrate. The hollows between the medial and marginal ridges are smooth in Scelidosaurus, 

 the anterior hollow is usually ridged in Iguanodon. In this genus the ' secondary ' ridges 

 are more feeble than the primary ones, and are plainly the seat of variety, as in the 

 instances above cited. The upper molars of the small Iguanodon (PI. 59, figs. 9, 10) 

 exemplify the rule of the generic type : fig. 2, PI. 45, shows the variety more approaching 

 the type of the geologically older Dinosaurian {Scelidosaurus). 



The molars of the Purbeck Dinosaur {Ecldnodon, PI. 60, fig. 22) repeat the pattern of 

 those of Scelidosaurus, but the marginal serrations, being more numerous and relatively 



1 Pal. Soc. vol. for year 1859. 



