A NEW MYLODON. 321 



squamosal process, is slightly less than the width between the rounded supra- 

 orbital processes. The heavy occipital crests meet the strong sagittal crest 

 on the braincase in a slightly overhanging ridge, which passes anteriorly into 

 tl>e smooth surface of the frontal region, with a poorly defined prolongation to 

 the blunt supraorbital angle. The sides of the braincase are nearly vertical and 

 their surface is much roughened for the attachment of the temporal muscles. 

 Anterior to the orbit the rostrum is broader and nearly square, with much less 

 elongation than in Paramylodon. The tips of the nasals, though slightly dam- 

 aged, seem to have been convexly rounded, and did not project beyond the sides 

 of the muzzle. The latter is slightly inflated and smooth. 



The outhne of the nasal opening, viewed from in front, is a trapezoid, of 

 which the base, formed by the bones of the palate, is parallel to the top, which 

 is formed by the nasals. The width of the base is nearly double that of the top, 

 so that the sides (i. e. the maxillaries) converge dorsally. There is no indica- 

 tion of a bony nasal septum. 



The posterior view of the skull is almost horseshoe-shaped in outline, with 

 the convexity dorsal. The extreme narrowness of the braincase is here empha- 

 sized by the fact that the extreme height of this occipital face is considerably 

 greater than the width, whereas in the Colorado skull, as in Paramylodon, this 

 face is much wider than high, so that its outline is nearly a semicircle. A strong 

 median ridge extends from the upper lip of the foramen magnum dorsally to the 

 lambdoid ridge which forms tlie boundary of the posterior face of the skull. 

 On each side between the condyle and the lambdoid ridge is a triangular depres- 

 sion, whose surface is marked by several small ridges, for the attachment of the 

 digastric muscle. The foramen magnum, as in Paramylodon, looks downward 

 as well as backward, and about one half the surface of the condyles is ventral. 



In ventral view, (Plate 2, fig. 3) the palate is seen to be long, contracted 

 posteriorly and expanded anteriorly with its greatest width just in front of the 

 first tooth. In contrast to the form of palate shown by Mylodon robustus, 

 that of the present species is produced some 50 mm. anterior to a line joining 

 the front edges of the first teeth, and is long, narrow, and very slightly expanded 

 anteriorly, instead of being broad, blunt, and with widely divergent sides. The 

 interpterygoid fossa is extremely deep and narrow. Its walls are parallel, and 

 anteriorly converge to form a pointed arch. The pterygoids are likewise parallel 

 to the long axis of the skull and diverge but little ventrally in contrast to those 

 of the Colorado skull and Paramylodon, in which the pterygoids flare widely 

 apart. 



