THE PHYTOSAURIA OF THE TRIAS 131 



OPENINGS OP THE DORSAL SURFACE OF THE SKULL 



The external nares are situated on a prominence at the beginning 

 of the rostrum and rise fully 18 mm. above the level of the general 

 surface of the cranial roof. The thin, vertical, median septum 

 separating the nares does not rise to the same height as that of the 

 posterior and lateral borders and thus the nares are given the 

 appearance of a single opening with rounded posterior and acute 

 anterior border. In length they are about 62 mm. and the greatest 

 width of the seemingly common opening is 40 mm. The anterior 

 border is about even with the anterior borders of the antorbital 

 vacuities and 590 mm. from the tip of the rostrum. The region 

 about the anterior border of the nares is somewhat abraded, and the 

 sutures are not distinguishable. No. septomaxillae have been dis- 

 tinguished, but as they are present in another specimen to be 

 described later they probably have about the same position here 

 and form the anterior border of the nares. 



The antorbital vacuities are large, oval in outline, with rather 

 acute anterior and posterior extremities. Their greater diameter 

 is fully 130 mm. and the lesser diameter about 55 mm. Their size 

 is accentuated by an abrupt depression or excavation of the bone 

 along their posterior and upper borders. 



The large orbits are somewhat elongate antero-posteriorly, about 

 89 mm. long and 55 mm. wide. Their planes are directed outward 

 and a little less upward, perhaps. The interorbital width is about 

 68 mm. Only a narrow bar, not over 9 mm. in width, separates 

 the orbit from the lateral temporal fenestrae. 



The sides of the lateral temporal fenestrae form rough parallelo- 

 grams with unequal diagonals. The greater diagonal is 171 mm. 

 and the lesser, which is almost perpendicular to the plane of the 

 palate, is about 113 mm. The greatest width of these openings is 

 about 87 mm. There is an excavation for a short distance about 

 their lower anterior borders similar to that of the upper posterior 

 border of the antorbital vacuities. 



The supratemporal fenestrae are oval in outline with an antero- 

 posterior diameter of 84 mm, and a width of 46 mm. Their plane 

 is directed upward. They are peculiar in that they are closed 

 behind by a well-developed parieto-squamosal arcade that lies in 



