A NEW PHYTOSAUR FROM THE TRIAS OF ARIZONA 147 



supramosal arcade is markedly depressed. The depression of this 

 arcade has not advanced so far as in Machaeroprosopus validus.^ 

 The opening is very inconspicuous in a superior view because of the 

 backward extension of the postorbitaL The opening is directed 

 out and back. It is sHthke, but its length cannot be determined 

 because the outer posterior border is missing. 



SEPARATE BONES OF THE DORSAL ASPECT 



The premaxillae are gradually expanded laterally at the anterior 

 ends for the accommodation of the large terminal teeth. The 

 expanded portion is abruptly down-curved and extends about 

 30 mm. below the palate surface of the rostrum. At the margins 

 of jaw, the premaxillae unite with the maxillae at about the twenty- 

 fifth tooth. From this point the suture extends back and up in an 

 irregular line. At the median line each premaxilla sends back a 

 process to within 45 mm. of the nares. This process and a lateral 

 posterior process extending back the same direction clasp the 

 anterior process of the septomaxilla. 



The septomaxillae are larger than in any other form that the 

 writer has examined. They are united along the median line for a 

 distance of 48 mm. and thence extend forward between the posterior 

 process of the premaxillae a distance of 45 mm. The septomaxillae 

 form a large area about the front and sides of the narial prominence, 

 but their exact posterior extent cannot be determined. It is 

 thought that they make up but a small part of the narial septum. 



The maxilla has its greatest anteroposterior extent along the 

 alveolar margin. In this respect it differs from the University of 

 Wisconsin specimen referred to above. 



The nasals form the posterior, median, and most of the lateral 

 border of the nares. The lower anterior margin extends some 

 distance beyond these openings, essentially as far as the septo- 

 maxillae. Posteriorly they extend about 35 mm. beyond the 

 posterior border of the antorbital vacuity. 



In the shape and extent of the lachrymals and prefrontals there 

 is the normal phytosaur development. 



The parietals differ from those of Machaeroprosopus validus^ in 



I Mehl, op. cit., p. 8, Fig. 2. 



'Ibid. p. II. « 



