OOLITIC DINOSAURS. 167 



the present work, the materials for a reconstruction of the skull were limited to 

 portions of the mandible and divers teeth therein implanted or detached. 



The diflferences shown by the mandibular specimens were limited to size, the 

 vertical diameter of the deepest part of the type mandible being 3^ inches, while 

 that of the Blenheim specimen gave 4^ inches. But as the teeth, retained in these 

 mandibular pieces, were of the same size, as well as form and structure, there was 

 no ground for predicating distinction of species. 



In the Blenheim specimen I was permitted to expose the germs and portions 

 of the successional teeth concealed in the substance of the mandible. 



Before entering on the description of the first of the present series of fossils 

 which demonstrates cranial characters not hitherto determined, I may premise 

 that existing Saurians show differences in the degree of ossification of the outer 

 wall of the facial part of the skull. 



In Grocodilia it is entire from the relatively small orbit behind to the smaller 

 single nostril in front ; and there is no break in that wall, in modern and Tertiary 

 species, answering to the antorbital vacuity in Liassic genera ; but this opening, 

 recalling the antorbital nostril of IcJithyosaurus, is very small and is margined by 

 the maxillary, lacrymal and nasal bones. 



In existing Lacertians much difference is seen in this character, but in none is 

 the face so completely ossified as in the Crocodiles. The Monitors {Thorides, 

 Tupinamhis) come nearest thereto, the nostril being divided from the orbit by a 

 broad triangular facial plate of the maxillary, supplemented behind by a narrow 

 malo-lacrymal one. In Lacerta the lacrymal enters in larger proportion into 

 the formation of this part of the bony face, and the external nostrils are relatively 

 wider. In Iguana the facial wall dividing the nostril from the orbit is relatively 

 narrower, and the apex of the maxillary process is further removed by a large 

 interposed lacrymal from the nasal bone. But in the Lacertians with a carnivorous 

 dentition {Hydrosaurus, Varanus) the outer bony nostrils are remarkable for their 

 great relative size, especially length ; and the maxillary sends upward and 

 backward a long but narrow pointed plate, which, in Varanus bivittatus, crosses in 

 front of a small lacrymal bone to articulate with the prefrontal. 



Here we attain the cranial modification which forms the best guide to the 

 interpretation of the appearances presented by the fossil, the subject of Plate 87, 

 fig. 1, and restored on a Varanian type in the figure 5. 



But, before entering on this comparative survey, I may note the corresponding 

 degree of resemblance which the skull of Iguanodon presents to the herbivorous 

 and mixed-feeding Lacertians, Ljuana and TJioridcs, with correspondingly adaptive 

 shapes of the teeth. In the relative size of the external nostril Iguanodon Foxii 

 resembles more Tupinamhis than it does Iguana with the larger nostril ; and the 

 side- wall between nostril and orbit is relatively broader and more extensive in Iguana 



