148 MAURICE G. MEHL 



and not to their absence, as the septomaxillary bones are apparent 

 in the specimen of A. gracilis. In all probabihty the region about 

 the anterior border of the nares in many of the phytosaurs was 

 always more or less cartilaginous. In many of the specimens that 

 the writer has studied, either from figures or from the original, this 

 anterior border is ill defined, extending forward in a sort of slit. In 

 A. gracilis the septomaxillae evidently unite along the median line 

 and form the anterior border of the nares. Their extent in front 

 of the nares along this line is 45 mm. What part they take in the 

 median septum in separating the nares cannot be determined. 

 Their greatest width is about 27 mm. on a line through the anterior 

 border on the nares. In front the premaxillae dovetail into them 

 and form their anterior border. The nasals meet the premaxillae 

 far forward along the lateral border of the septomaxillae and form 

 the lateral boundaries of those elements. The relations of these 

 various elements are diagrammatically shown in Fig. 4. 



The rostrum in this species is much more slender than that of 

 A. grandis. From the tip to the anterior border of the nares is a 

 distance of 670 mm., or about 610 mm. to the anterior border of 

 the antorbital vacuity. In A. grandis these measurements are 

 650 mm. and 585 mm. respectively. The width of the rostrum just 

 back of the terminal expansion is 34 mm., at about midlength 

 44 mm., and at a point 140 mm. in front of the antorbital vacuity, 

 56 mm. These respective measurements in A. grandis are 42 mm., 

 65 mm., and 94 mm. In the latter species the rostrum, seen in a 

 lateral view, tapers down much less abruptly from the cranium 

 proper than in the former. The terminal expansion of A. gracilis 

 starts abruptly at a distance of 68 mm. from the end of the hori- 

 zontal portion, increasing from a width of 34 mm. to 51 mm. This 

 width it maintains, with only a very slight increase, to the tip. 

 The extremity is bent abruptly downward and extends approxi- 

 mately 44 mm. below the ventral surface of the rostrum. The ros- 

 trum as a whole is curved, concave upward, but this is probably a 

 result of deformation. As seems to be the usual case in phyto- 

 saurian remains, most of the teeth have dropped from the alveoli. 

 Only the first, second, and fourth of the right premaxilla teeth are 

 preserved in this specimen but these are entire and well preserved. 



