A NEW MYLODON. 323 
The palate is much roughened and pitted, with a narrow rounded ridge 
passing down the center from the level of the front of the first tooth to a point 
opposite the back of the penultimate molar. A similar ridge, but apparently 
of less extent, seems to be indicated in the Colorado skull, beginning on a level 
with the second tooth. The maxillopalatal suture extends forward to the 
level of the penultimate molar, and the palatal bone itself is smooth. A large 
foramen is present at each side behind the last molar. 
The pterygoids in side view are very large and extend some 75 mm. below 
the general outline of the palate. In this respect they resemble those of Paramy- 
lodon and differ conspicuously from those of Mylodon robustus and the Colorado 
skull in which the pterygoids extend but slightly below the general ventral out- 
line. Their interior surface, except for a narrow roughened rim, is smooth, 
but the exterior bears many small bony ridges for muscle attachments. There 
is a broad shallow concavity in the posterointernal part of each. 
What appears to be the tympanic bone is a narrow horseshoe-shaped element 
fused solidly with the os petrosum on each side. Posterior to this is a roughened 
depression 15 to 20 mm. in diameter for the reception of the articulating process 
of the stylohyal. The foramina for the eleventh and twelfth nerves are internal 
to this depression and slightly posterior to it. The latter is the larger, about 
15 mm. in diameter. 
The occipital condyles have the characteristic bordering ridge, said to be 
absent in Paramylodon. Their ventral surfaces are set obliquely to the frontal 
plane and constitute more than half the articulating area. In ventral view the 
transverse diameter is much greater than the longitudinal, 59 and 42 mm. re- 
spectively. In the Colorado skull the length of the condyles seems to be greater 
in proportion to the width. 
Teeth.— There are five teeth in the upper and four in the lower jaw on each 
side. The upper series measures 160 mm. in alveolar length, the lower 156; 
the toothrows in both jaws converge towards the posterior end of the palate. 
The last upper tooth is but 21 mm. from the level of the posterior narial opening, 
a distance equal to about two thirds of its own length. In the Colorado skull 
the last tooth is much farther from this opening (58 mm.) nearly twice its own 
length. 
The first upper molar is the smallest, slightly oval in outline, and a trifle 
recurved. Its crown therefore is directed posteriorly, and this appearance is 
further enhanced by a slight bevel due to contact with the anterior part of the 
crown of the first lower molar. Its diameters at the alveolus are:— longitudinal, 
