Mr. Owen on the Phascolotherium. 65 



which it separates were to be compared to the contiguous margins of the oper- 

 cular and dentary pieces of a reptile's jaw, it would be seen that the only suture, 

 which in Reptiles is continued from any part of the level of the dental series be- 

 tween these pieces, passes in a totally different direction ; it is the suture which 

 bounds the anterior part of the opercular piece, and which, in all reptiles, runs 

 obliquely downwards and forwards, instead of downwards and backwards. The 

 second impression {d. fig. 2. PI. VI.) in the jaw of the Phascolotherium is much 

 more strongly marked than the preceding ; it is a linear groove continued from the 

 anterior extremity of the fractured base of the inflected angle obliquely downwards 

 to the broken surface of the anterior part of the jaw. Whether this line be due 

 to a vascular impression, or an accidental fracture, I do not offer an opinion ; but 

 this may be confidently affirmed, that there is not any suture in the compound 

 jaw of a reptile which occupies a corresponding situation. And lastly, with refer- 

 ence to the philosophy of pronouncing judgement on the saurian nature of the 

 Stonesfield fossils from the appearances of sutures in the jaws themselves, I would 

 offer one remark, the justness of which will be obvious alike to those who are and 

 those who are not conversant with the details of Comparative Anatomy. 



The cumulative evidence of the true nature of the Stonesfield fossils, afforded by 

 the shape of the condyle, coronoid process, angle of the jaw, different kinds of 

 teeth, with the shape of their crowns, double fangs, and implantation in sockets, 

 reposes on structures which cannot be due to accident, while those which favour 

 the evidence of the compound structure of the jaw may arise from accidental cir- 

 cumstances. 



The dental formula of the genus Phascolotherium is as follows : — 



Incisors 3:1^ ; canines ^—^ ; premolars 3-373 ; molars ^^. 



VOL. VI.— SECOND SERIES. 



