Mylodon harlani, from Rock Creek, Texas. 345 



Mandible. 



Portions of the lower jaws of at least three individuals are 

 present, to which arbitrary numbers have been assigned as 

 before, based largely upon distinctions of size. Of these at 

 least three portions could have come from one jaw and 

 represent an old animal of greater size and indicated jaw power 

 than the Rancho La Brea specimen, the relative depth of the 

 ramus at the hinder margin of the posterior alveolus being 

 108 ,nm for the Texan form to 10O5 mm for the Californian. 

 Opposite the anterior limit of the third alveolus the disparity 

 is still more apparent, the latter measuring 80 mm and the 

 former 99 mm . The least thickness of the California mandible 

 is 33 mm and of the Texan 43 mm . The anteroposterior 

 diameter of the alveolus of the fourth tooth is 55'5 mm for the 

 first and 62 mra for the second. The symphysis of the Texan 

 form is much more robust, but the outline of the muzzle is not 

 preserved, though that of the California type is slenderer than 

 in M. robustus. 



As a further distinction between the California and Texas 

 forms the third alveolus shows a distinct ridge on its outer wall 

 in the latter which is lacking in the former type, and that on 

 the inner wall is more pronounced. The tooth of the Texas 

 form, therefore, would be somew r hat quatrefoil in section, 

 that of the California jaw having but two columns, an outer 

 and an inner one. The hinder wall of the posterior alveolus 

 in the Texas form is nearly at right angles to the long axis of 

 the jaw ; in the California type it is more oblique. The trilo- 

 bate character of the last lower molar which Brown* makes a 

 distinguishing feature of Paramylodon is very distinctly seen 

 in the smaller ramus No. 10267, but very faintly indicated in 

 the larger 10264. The ridge on the external wall of the 

 penultimate alveolus is, on the contrary, absent in the smaller 

 jaw. Otherwise, except for size< the two jaws approximately 

 agree, the distinctions being mainly those of age. 



A comparison with the California jaw and that of the type of 

 Paramylodon shows a curious complex of agreement and dis- 

 agreement. 



The large Texan jaw has a penultimate tooth which is unique, 

 while the ultimate one agrees with that from California. In 

 the smaller Texan jaw both teeth are like those of Paramy- 

 lodon, whereas the Californian jaw shows a Paramylodon-\\ke 

 penultimate tooth, while the hinder one resembles more nearly, 

 except for its oblique hinder face, that of the larger Texan 

 type. 



I have before me for comparison also a cast of the type of 

 Mylodon harlani, which is somewhat smaller than the larger 



* Brown, B., op. cit., p. 569. 



