Vol. 6^.~] SKELETON OE GOKIOPHOLIS CRASSIDENS. 59 



(5) The lateral temporal fossae and tympanic cavity are greater 

 in G. crassidens than in G. simus. 



(6) Absence of an inter-orbital ridge in G. crassidens ; its presence 

 in G. simus. 



(7) The nasals, anteriorly, in G> crassidens widen till near the 

 constriction, whence they quickly converge to the anterior nares, 

 the posterior border of which is apparently reached. In G. simus 

 they do not broaden, and on reaching the premaxillse rapidly con- 

 tract to an acute point 27 millimetres from the anterior nares. 



(8) In G. crassidens, the hinder extremities of the premaxillse 

 are very blunt, and probably do not extend 29 mm. beyond the 

 anterior nares. In G. simus they are very sharp, terminating 

 where the nasals begin to narrow, 70 mm. from the anterior nasal 

 opening. 



(9) In G. crassidens the surface of the skull is deeply and uni- 

 formly pitted, without any other sculpturing. In G. simus it is 

 neither so uniformly nor so deeply pitted. Moreover, the nasals 

 have a crinkled surface anteriorly and posteriorly, and are almost 

 free from pits, and those that occur are very shallow. The frontal 

 is also crinkled at its juncture with the nasals, while behind this to 

 the orbits it is quite smooth and free from ornamentation. 



(10) In G. crassidens the posterior nares are twice as long as 

 they are wide, and, except their extreme anterior margins, are 

 entirely formed by the pterygoids. In G. simus they are narrower, 

 and a third of their border is formed by the palatines. 



(11) The form of the palatines reveals a remarkable dissimilarity. 

 In G. crassidens the pterygo-palatine suture rises acutely from 



the posterior end of the suture connecting the palatines to the 

 palatal fossa. In G. simus it is nearly horizontal, with a crenated 

 contour. 



In G. crassidens the lateral margins are almost parallel, only 

 slightly expanding as they approach the maxillae. In G. simus 

 they soon commence to dilate, and continue to widen to the maxillo- 

 alveolar border. 



In G. crassidens, the palato-maxillary suture leaves the palatal 

 median suture at right angles, and, keeping horizontal for 31 mm., 

 turns at a right angle, parallel with the median suture until near 

 the pterygo-palatal vacuity, where it doubles back at an acute angle 

 into that fossa. 



In G. simus the course of this suture is quite different. Owen r 

 thus describes it : — 



' The palato-maxillary suture is strongly sigmoid, describing as it leaves the 

 mid-line a convexity forward, then a concavity.' 



In addition to these differences in the skulls, the dimensions 

 of GoniophoUs crassidens are one-third greater than those of 

 G. simus. 



1 ' Monograph of the Fossil Eeptilia of the Wealden & Purbeck Formations ' 

 Suppl. viii (Pakeont. Soc. 1878) p. 8. 



