18 CONTENT SO PA BONE CAVE. 



The premaxillary bones with incisor teeth of several individuals accompany 

 the mandibles just described, and some of them probably belong to this species, 

 and others to the A. quadrans. I cannot detect any difference in the two which 

 are best preserved, and which correspond to the two individuals represented 

 by molar series, and symphyses with inferior incisors. The section of the pro- 

 duced pair of premaxillary bones is triangular near the middle. That of the 

 lateral walls is greatly convex, and the median line below is keeled for a short dis- 

 tance. Immediately behind the keel is a narrow fossa. The section near the base 

 of the incisors is subquadrate, and there is a deep longitudinal median fossa just 

 behind the base of the teeth, whose fundus appears to receive a foramen. 



The symphyses above mentioned are long and acuminate. The union of the 

 inferior surface continues posterior to the point of divergence of the dental ridges, 

 forming the bottom of a large fossa. The section of the anterior or beak-like 

 portion of the symphysis is subtriangular, the sides approaching each other upwards, 

 but separated by a broadly obtuse median ridge. Near the middle of the length a 

 slight enlargement is visible in both the specimens. The inner face of the incisor 

 teeth is more strongly convex than the external. 



MEASUREMENTS. 



M. 

 Length of beak of symphysis . . . . . .090 



Diameter of beak at middle | vertical - 025 



(.transverse .... .023 



. ,. . . . (vertical .014 



" of inferior incisors < 



(. transverse . . . . .014 



The most complete mandible includes the right ramus with all the alveoli, the 

 entire symphysis with the right incisor tooth in place. The molar alveoli are empty. 

 The posterior alveolus is as wide as long, as in the typical specimen, and is in form 

 about a quarter of a circle. The third and second alveoli are similar in form, but 

 a little more quadrate, and the second is materially the smallest of all. The third 

 is much longer and a little wider than the second. The symphyseal beak is more 

 attenuated than in the specimens just described, and its superior middle line is 

 more angular, giving a roof-shaped section. The incisor tooth is exposed on its 

 external side for almost the entire length of this rostrum, to a point 17 m " u 

 anterior to the divarication of the alveolar ridges. The cutting edge of the incisor 

 is transverse. The lateral fossa is below the second and part of the first molar. 

 This is anterior to the position which it occupies in the mandibles described under 

 A. latidens and A. quadrans. This fact, in connection with the slight difference 

 in the form of the symphyseal rostrum, has led me to question the propriety of 

 the reference of the animal to the A. latidens. The fourth molar evidently has 

 the form characteristic of that species, rather than that of the A. quadrans. 



