THE UPPER TRIASSIC OF WESTERN TEXAS. 



77 



prominent and rugose, with a deep, irregular groove marking the position of the suture. 

 Between the tubera is a sharp angulation marking the line between junction of the 

 basioccipital and the basisphenoid, and along this the suture between the two bones is 

 easily traced. On the sides of the basioccipital, just posterior to the basisphenoid suture, 

 there is a shallow groove running upward and backward. Between the tubera and 

 basipterygoid processes on either side are the large openings of the foramina for the 

 internal carotid arteries. These foramina run upward and inward and open a little to 

 either side of the lower end of the hypophysial cavity. The cavity is triangular in 

 section above, but contracts rapidly below; it is surprisingly small and shallow. The 

 basipterygoid processes are well developed and point outward and downward, with a 

 smooth, flat, oval face for the pterygoid. The sphenoidal rostrum is broken away in 

 all of the specimens, but was evidently vertical, narrow, and of great extent. In none 

 of the specimens is there any suggestion of a composite structure, i. e., an upper (pre- 

 sphenoidal) and a lower (parasphenoidal) portion, such as described and figured by Huene. 



Fig. 30. 



A. Basicranial region, left side, No. 7261, U. of Mich. 



B. Lower side of same 



X0.6. 



No. 7257 is the largest of the specimens, being nearly twice the size of No. 7474 

 and the least well preserved. It has lost the occipital condyle and parts of the tubera 

 and basipterygoid processes. The anterior lower part of the basioccipital is still in 

 position, and clean breaks show (he suture between it and the basisphenoid. The 

 whole basisphenoid is shorter and higher than in the other specimens. The basipterygoid 

 processes are shorter and less well developed; they pointed more directly backward, 

 and on the inner posterior corner of the base of each there is a prominent rugosity, which 

 on the left side has the form of a pit with elevated edges. The space between the basi- 

 pterygoid processes is marked by two prominent rugose ridges, which converge forward 

 and unite at the origin of the sphenoidal rostrum. It would appear that this space 

 between the processes was almost vertical instead of slanting rather steeply upward and 

 forward, as in the other specimens, but as this would make the sphenoidal rostrum rise 

 vertically in the skull it is probable that the position of the occipital condyle was different 

 from that it occupies in the other specimens. This specimen is so much larger and so 

 different from the others and from any described form that it indicates, in all probability, 

 a new species, but it seems undesirable to give a new name to such imperfect material, 

 especially as the large size suggests the possibility that the peculiar features may be 

 due to advanced age. 



