526 BRITISH FOSSIL REPTILES. 



smaller, more resemble the serrations which the propounder of the genus Hi/psilophodon 

 erroneously states " are so characteristic of the teeth of Iguanodon."^ 



The tooth, which I have referred, with prol)ahility, to the HyJceomurm, shows the 

 shape of crown on which the Scelidosaurian and Iguanodoiital 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 

 HylcEosatirus in the Palfeontographical Society's volume for 1856^). 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 Ilyloeosaurus. Howsoever this may prove 

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

 Scelidosaurus, Ecldnodon, and Iguanodon, now exemplified by the small skull (PI. 59, 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. 



In this family the skull exhibits a more generalised type of structure than in the 

 existing Crocodiliu and Lacertilia. 



The short, square, massive character of the cranium, and the greater extent of 

 ossification of the rest of its walls, are retained in modern Crocodilia ; but the majority of 

 the characters, as the double or divided external nostrils, the divided frontals, the 

 relatively large orbits, the pterygoids divaricated by intervening basi-sphenoidal pterapo- 

 physes, and the separated palatines, are characters retained by modern Lizards. 

 In the majority of existing Lacertian genera, however, the nasals form a single bone, and 

 the premaxillaries are confluent anteriorly. These bones retain their parial condition in 

 Crocodilia as in Prionodontia. 



The position of the portion of lower jaw — left mandibular ramus — preserved in the 

 block of matrix with the skull, precludes the procedures of exploration requisite for 

 detection of teeth or germs of teeth, with any regard for the safety of the rest of this 

 unique specimen, although the temptation is great, in reference to the alleged absence 

 of an Iguanodontal characteristic, namely, the serrations of the free edge in the teeth of 

 this specimen. Not that the allegation has any real value as to the generic character of the 

 Saurian so represented ; since it is plain that the renmants of the crowns of the upper 

 molars are not such as could show the Iguanodontal serration if it had existed, the 

 apical part being wanting where alone, as a rule, the crown is marginally serrate in the 

 upper molars of Iguanodon Mantelli. In this species, moreover, the serrations are more 

 numerous, and afiiect a relatively greater extent of the margins of the crown in the teeth 

 of the lower jaw than in those of the upper. Hence it might be expected that the 

 mandibular teeth of the small species from the Cowlease Wealden would apply a decisive 



1 ' Quart. Journal Geol. Soc.,' vol. xxvi. 2 p 21. 



