THE UPPER TRIASSIC OF WESTERN TEXAS. 



23 



The posterior part of the outer surface of the jaw is largely formed by the angular; 

 it is marked in its posterior portion by a very coarse sculpture, which changes to a 

 coarse radiating pattern anteriorly and gradually dies out near the anterior third of 

 the jaw. No suture can be made out between the angular and the surangular, and it 

 is not certain that the surangular appears on the outer side, as it is figured in Eryops 

 by Broom. The sutures between the angular, dentary, postsplenial, and splenial are 

 all clear and distinct. Near the posterior end of the jaw there is a deep linear depression 

 devoid of sculpture; this may mark the position of the suture between the angular and 

 surangular, but no traces of the suture could be made out in or near the depression. 



Fig. 5. — Outlines of intcrclavicles, all, except D, from University of Michigan. 



A. No. 7368. B. No. 7448. C. No. 3814. D. Metoposaurusfrassi Lucas. E. No. 7266. 

 F. Posterior portion, No. 7367. G. Posterior portion, No. 7366. H. Posterior 

 portion, No. 7374. 



Viewed from above, the posterior end of the jaw shows two distinct halves which 

 seem to meet as distinct bones at the posterior end; these may be the angular and the 

 surangular or the surangular and the prearticular. Just posterior to the elevation of 

 t he surangular on the posterior edge of the supra-Meckalian opening there is apparently 

 a distinct element represented by an egg-like mass of bone between the two separate 

 halves described above. This may be the articular, as no other trace of that bone can 

 be found. 



A second jaw (No. 7503, University of Michigan), also from Sand Creek, is com- 

 plete, but badly rotted by gypsum. The sutures can not be traced, but the Meckalian 



