146 MEMOIRS OF THE CARNEGIE MUSEUM 
line to the root of the zygomatic process, thence obliquely back to meet the fronto- 
nasal suture. 
There is a strong swelling on the side of the muzzle, plainly indicating the direc- 
8 § I 
tion of the root of the incisor. The muzzle is broadest across this swelling. ‘The 
naso-premaxillary suture converges backward, making the nasals narrower poste- 
riorly than anteriorly. 
THe Manprsre. Plate X VIL, figs. 1, 4. 
The lower jaws are very heavy. ‘The ascending ramus occupies more than half 
of the entire length of the mandible. The coronoid process takes its origin on the 
exterior side of the ramus, opposite the posterior part of pg; thence ascending in a 
gentle backward slope to near the summit, which is rapidly curved posteriorly, and 
terminates in a thin, rounded, and transversely compressed point. There is rela- 
tively a deeper and larger fossa separating the alveolar border from the coronoid 
process than in the beaver. In the fossil, the alveolar border is abruptly elevated 
above the diastema in front. Anteriorly, the jaws are united by a strong symphysis. 
On the chin is a strong process, similar to that in the beaver. The external face of 
the ramus is irregularly convex, the internal somewhat concave below the molar 
series. The angle is greatly deflected outward, and the inferior portion descends 
more below the border of. the horizontal ramus than it does in the beaver. In S. 
fossor this angle terminates in a strong postero-lateral process. This process is very 
similar to that in Aplodontia, with somewhat less inferior and exterior development. 
The alveolus of the incisor terminates posteriorly in a heavy, rounded protuber- 
ance on the external face of the ascending ramus below the condyle, similar to what 
is seen in S. peninsulatus. The deep fossa above this protuberance is similar in the 
two species, so far as can be judged from the type of S. peninsulatus. The form of 
the condyle also agrees with Cope’s description: it ““is subglobular, and has con- 
siderable more external than internal articular surface” (Tertiary Vertebrata). 
With the exception of the less developed inferior process on the chin, the ap- 
parently more rounded anterior face of the incisor, the comparatively heavier femur 
and much longer tibia, the type of S. peninsulatus agrees closely with S. fossor. The 
skull, which Cope associates with the lower jaw, and the hind limbs of S. peninsu- 
latus, figured on Plate 68, figs. 18, 18a, 18) (Tertiary Vertebrata), is distinctly dif- 
ferent from S. fossor in having less expansion across the zygomatic arches, and pos- 
sessing apparently a much shorter tube on the otic bulla, and a somewhat longer 
muzzle. 
The skull figured and described as 8. pansus (Bull. Am. Mus. Nat. Hist., Vol. 
