THE PHYTOSAURIA OF THE TRIAS 143 



though its outer, anterior, and inner margins are normally represented by the 

 highly sculptured squamosal, postorbital, and parietal. The median posterior 

 portion of the parietal seems to end suddenly over the occiput, and the parieto- 

 squamosal arcade appears to be lacking. In fact. Marsh has stated (1896) 

 that "the skull of Belodon [Phytosaurus] shows that the supratemporal openings, 

 characteristic of the true crocodillians are wanting." 



Again, in characterizing the Phytosauria, McGregor says:^ 

 "Post-temporal (parieto-squamosal) arcade greatly depressed, re- 

 duced, and covered by muscles." In Angistorhinus grandis, how- 

 ever, this is not the condition. A comparison of the posterior view 

 of A . grandis with that of Mystriosuchus planirostrus (Figs. 5 and 6) 

 will serve well to show the differences. In the former the post- 

 temporal arcade is well developed and borders the supratemporal 

 vacuities in the same plane that extends over the roof of the cra- 

 nium. The posterior extension of this parieto-squamosal arcade 

 forms an overhanging shelf that in a dorsal view hides all the bones 

 of the posterior side of the skull. The parietals seem to have a com- 

 paratively small lateral and downward expansion on the posterior 

 surface and but slight contact with the supraoccipital. The 

 squamosals, on the contrary, send down broad, platelike extensions 

 from the posterior borders of the supratemporal vacuities that con- 

 nect broadly with the supraoccipital at their inner edges. They 

 form the upper and outer borders of the post-temporal vacuities 

 and connect broadly with the upper inner ends of the opisthotics. 

 As the specimen is now prepared, a large fenestra pierces this ele- 

 ment on either side of the skull just over the post-temporal vacuity. 

 This opening is, however, undoubtedly due to the abraded condi- 

 tion of the bone as the matrix beneath indicated an uninterrupted 

 bone surface. The lateral, downward-directed angles or hooklike 

 processes of the squamosals, mentioned above, extend some 23 mm. 

 below the lower borders of the opisthotics. The boundaries of the 

 supraoccipital are not distinct; it seems to be a small, approximately 

 triangular element forming a considerable portion of the upper 

 border of the foramen magnum. Its greatest width is probably 

 not over 31 mm. The exoccipitals and opisthotics are thoroughly 

 co-ossified. The exoccipitals form the lateral and probably most of 



^ Ihid., p. 92. 



