4 PKOCEEDINGS OF THE NATIONAL MUSEUM vol.66 



loosed to view. Other teeth dropped out of the alveoli in the upper 

 jaws after the skull was covered with sediments as several were 

 found in the matrix. The outer surface of the maxilla is worn, 

 more so in some places than in others. Nevertheless, it appears that 

 the anterior alveoli in the maxilla are separated from the outer sur- 

 face by a very thin plate, hardly more than 15 mm. in thickness. 

 The lateral border of the maxilla overhangs the alveoli more notice- 

 ably posteriorly than anteriorly. The alveoli in the maxillae agree 

 in size with those for the coiTesj)onding teeth in the mandibles. At 

 least eight alveoli are present in the distal end of each maxilla 

 and a complete skull may have carried 18 or more teeth in each jaw. 

 From the inferior margin, the maxilla curves upward to the pre- 

 maxilla in a gradual curve which becomes more pronounced as the 

 maxilla attains a greater depth posteriorly. Apparently, the hori- 

 zontal plate-like inwardly projecting portions of the premaxillae 

 do not roof the mesorostral gutter to the extremity of the rostrum, 

 but this can not be stated with any degree of certainty for although 

 they taper raj)idly their extremities are clearly mutilated. The 

 maxillae gradually increase in breadth toward the base of this sec- 

 tion of the rostrum and then appear to suddenly expand as would 

 be expected in a skull characterized by a lateral constriction of the 

 extremity of the rostrum. From a lateral view the maxillae in- 

 crease in depth as they approach the base; whereas the premaxillae 

 decrease. 



The mesorostral gutter extends the full length of the rostrum. 

 Its distal extension is made up entirely by the premaxillae which 

 meet mesially on the floor in a linear suture. Posterior to the third 

 pair of alveoli is the distal extremity of the vomer which contributes 

 the floor of the gutter for most of its length, and on each side is 

 mortised into the ventral extensions of the premaxillae and they in 

 turn are applied to the inner borders of the maxillae. From its ex- 

 tremity posteriorly, the vomer increases in width and eventually 

 gains a position on the walls. The dorsal wall or roof of the 

 vomerine gutter is formed, as mentioned above, by the overhanging 

 l)late-like portions of the premaxillae. From the level of the third 

 pair of alveoli posteriorly, the premaxillae retain a nearly uniform 

 breadth. 



Mandibles. — Since this specimen projected from the face of the cliff 

 and was exposed to the action of the elements for 35 years at least, it 

 IS not surprising that the inferior surfaces of the mandibles should 

 exhibit evidence of considerable erosion. From a ventral view, 

 numerous branching canals are now visible, although they are filled 

 with matrix, which afforded passage for nerves and blood vessels. 

 In places, this wear has amounted to an inch or more in thickness. 



