322 A NEW MYLODON. 



The mandible, in comparison with that of the latter genua, is of especial 

 interest. The coronoid process is smaller, and the ramus, instead of tapering 

 strongly towards the symphysis is of nearly the same depth at tliat point as at 

 the level of the last molar, which is in correlation with the less elongated rostrum. 



Certain of the cranial bones and the teeth require further mention. 



The nasals are broad anteriorly, with a combined width of 70 mm. at the 

 nasal orifice but taper rapidly back to about the level of the orbit, where, on 

 account of the nearly complete disappearance of the median boundary through 

 fusion and by reason of a slight crushing of the frontals, their outlines cannot 

 be traced. Apparently, however, there is little if any indication of a posterior 

 expansion such as Brown figures in Paramylodon. 



The malar s (Plate 3, fig. 7) or jugal bones are complete and separate. Proba- 

 bly they were but loosely articulated with the maxillaries. Tlie upper anterior 

 portion is concavely rounded to form the lower border of the orbit. The ascend- 

 ing wing of the bone has a deep notch for the reception of the squamosal process. 

 In the South American Mylodon robustus the portion of bone dorsal to the notch 

 is produced backward so that the distance from its tip to the point of the notch 

 is nearly twice that from the tip of the bone forming the ventral side of the 

 notch to the same point. This bone is not described for any of the North Ameri- 

 can species nor for Paramylodon, but in our specimen it presents the noteworthy 

 difference that the bony wings forming the sides of the notch are of nearly cciual 

 length, the dorsal only some 10 mm. longer than the ventral portion. The 

 descending portion of the malar is similar to that of M. robustus in general form 

 but is narrower and longer, with a wider concavity between it and the ascending 

 portion. Its anterior margin is also much less bowed out. 



The premaxillarics were evidently united, but were only loosely articulated 

 with the maxillaries by a short stem which fitted into a deep median cleft between 

 them at their anterior end. The lateral wings of the premaxillaries bevel over 

 the dorsal surface of the tips of the maxillaries, but are wholly separate from 

 them. The cleft for the reception of this articulating stem of tlie premaxillaries 

 extends posteriorly as a broad V for about 31 mm., or nearly one half the dis- 

 tance from tlie tip of the maxillary to the first tooth. It is apparently mucli 

 deeper in the Colorado skull and in Paramylodon, extending nearly to the 

 level of the large oval tooth (the second in Mylodon). The greatest median 

 length of the premaxillaries is 54 mm., their combined width 96. The tips are 

 thickened and shghtly concave below as if for aiding the prehensile power of 

 the hps. 



