﻿WEALD EN FORMATIONS. 



11 



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

 existing Crocodilia 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 remnants 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 lguanodon Mantelli. In this species, moreover, the serrations are more 

 numerous, and affect 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 

 test, on the assumption that the absence of marginal serrations — all other Iguanodontal 

 characters present — was decisive against a generic relationship with lguanodon. 



Mr. Fox has kindly transmitted to me the portion of the left mandibular ramus, 

 1 inch 7 lines in length, with a depth of 7 lines, where entire, which is the 

 subject of figs. 8 — 11 in PI. II. It includes the sockets and fangs of eight teeth, so 

 closely set as to have necessitated the overlapping arrangement of the crowns, according 

 to the Iguanodontal type, the hind margin of the anterior tooth covering the outer side of 

 the fore margin of the tooth behind, in the lower as in the upper jaws. The proportion 

 of transverse to fore-and-aft diameters of the fractured bases of the mandibular teeth 

 (fig. 8) in this specimen is also Iguanodontal, suggestive of a bruising function. These 

 eight teeth occupy an alveolar extent of 1 inch 3 lines. 



The outer surface of the ramus (ib., fig. 9) is divided into an upper and lower facet 

 by a low, obtuse, prominent angle or ridge extending horizontally, and giving the greatest 

 thickness to that part of the jaw ; a series of five vascular or neuro-vascular foramina 

 extends a little above this ridge. The structure of the outer surface of the ramus, 

 exhibited by the larger jaw of a young lguanodon, also discovered by Mr. Fox, in the 

 same Wealden deposits of the south-west coast of the Isle of Wight, closely accords 



