﻿10 



FOSSIL REPTILIA OF THE 



Four 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. I, 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 ( % ). 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 (10) 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 (' Monograph of a Fossil Dinosaur,' &c, PI. V, fig. 3 J ) shows the teeth 

 of the two genera to be modifications of the same type. The exterior surface of the 

 crown in Scelidosaurus (PI. II, 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. I, figs. 9, 10) of the present Monograph exemplify the 

 rule of the generic type : the first-cited figure of the two former Monographs shows the 

 variety more approaching the type of the geologically older Dinosaurian {Scelidosaurus). 



The molars of the Purbeck Dinosaur {Echinodon, PI. II, fig. 22) repeat the pattern of 

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

 smaller, more resemble the serrations which Professor Huxley states " are so characteristic 

 of the teeth of Iguanodon." 2 



The tooth, which I have referred, with probability, to the Hylceosaurus, shows the 

 shape of crown on which the Scelidosaurian and Iguanodontal patterns have been 

 superinduced ; it expands from the base to two lateral angles, whence the sides converge 

 to a third apical angle. If the converging borders of the terminal half of the crown had 

 originally been notched or serrate, those projections had been worn away by use, in the 

 tooth figured (' Monograph on the Fossil Reptilia of the Wealden Formations : Genus 

 Hylceosaurus' in the Palaeontographical Society's volume for 1856 s ). I may remark, also, 

 that this tooth is a mandibular one, and that a nearer approach to the serrident type may 

 have been shown in the maxillary teeth of the Hylceosaurus. Howsoever this may prove 

 to be, the conformity of cranial structure, as of fundamental tooth-type, between 

 Scelidosaurus, Echinodon, and Iguanodon, now exemplified by the small skull (PI. I, fig. 9), 

 makes it convenient to associate the genera in a section of Dinosauria, which may be 

 termed ' Prionodontia,' i. e. serrident, or saw-toothed. 



1 Pal. Soc. vol. for year 1859. 2 Loc. cit., p. 5. 3 P. 21. 



