446 PATAGONIAN EXPEDITIONS : PALEONTOLOGY. 



plane faces, which are not grooved and but faintly striate. The upper 

 premolar is quite large and its valley is rather more distinctly angulate 

 than usual. The first and second upper molars have prominent external 

 pillars, formed by the projection of the anterior lamina ; in m a this pillar 

 is very small and, on the right side, hardly noticeable. The lower pre- 

 molar is not rotated quite so completely as in the type specimen and the 

 valley does not open quite so directly forward, but the difference is not a 

 marked one. The variability of the internal pillar of the lower grinding 

 teeth is well illustrated by this individual ; on the right side of the jaw 

 p T has this pillar distinctly, though not conspicuously, marked, while on 

 the left side there is no trace of it ; m r has no pillar on either side, while 

 on both sides m^ has a small and n% a large one. 



Except in size, the skull differs little from that of P. erutus; as in that 

 species, the periotic is not exposed upon the occipital surface, but in a 

 deep and narrow fossa between the squamosal and exoccipital ; the occiput 

 is considerably higher than in P. ertitus, though the difference is, to some 

 extent, due to the crushing which this specimen of P. puellus has under- 

 gone. On account of this crushing it is difficult to determine the length 

 of the sagittal crest (which appears to be relatively longer than in P. 

 impacttis] and the degree of convexity of the forehead. One peculiarity 

 is, however, quite distinct ; namely, that the notch of the supraorbital bor- 

 der, in front of the postorbital process, is much better defined than in any 

 other species in which this region of the skull is known. The foramen 

 which lies above and in front of the auditory meatus, between the periotic 

 and squamosal, is considerably larger and more conspicuous than in P. 

 erutus. The tympanic bulla is very large, larger than in any other species 

 with which I have been able to compare it. 



The mandible has a high, but thin and laterally compressed, horizontal 

 ramus, on the inner side of which the incisor alveolus forms a hardly 

 noticeable protuberance, much less prominent than in the larger species 

 of the genus. A characteristic feature of this mandible is the abrupt form 

 of the notch in front of p ; forward of this notch the edentulous border 

 rises to the level of the alveolar border, instead of sloping gently to the 

 edge of the incisive alveoli (cf. fig. 4 with figs. 3 and 9, PI. LXVIII). 

 The masseteric crest is proportionately better developed and extends far- 

 ther forward than in the larger species, and the pterygoid crest is also 

 more prominent, making the ventral border of the angle wider and the 



