18907] Geology and Paleontology. 951 
above the angle of this inflection, and is below the middle of the 
coronoid process. There are several small mental foramina. The 
canine tooth is of large size. The fourth premolar is close to it, and 
is one-rooted. Other premolars with compressed crowns, the first 
with a weak posterior cutting lobe. The sectorial has the propor- 
tions seen in Mustela, and possesses a well-marked metaconid. The 
“blade of the heel is external, and there is a low internal basal 
cingulum of the heel only. Tubercular molar small, one-rooted. 
Measurements.—Length of dental series, 47 mm. ; diameter of base 
of canine, 7 mm. ; length of premolar series, 22 mm. ; length of sec- 
torial, 12 mm. ; length of heel of, do, 5 mm. j depth. of ramus at P. 
. q; 13 mm. ; do, at sectorial, 14 mm. 
The depth and thickness of this ramus are identical with those of 
the jaw of the Mustela pennantii, but the length is considerably gi 
Br deni are pachycephalus gen. et. sp. nov. Char. g 
Dental formula: L?; C. 4; P. M. 4; M. 4. Inferior sectorial 2 
wide ar heel, which is as long as the contracted blade; a 
metaconid.— This genus has the dental formula of the typical Mus- 
tele, but it is extremely microdont, having a small sectorial blade 
and wide basin-shaped heel as in the genus Lutra, to which it is evi- 
dently allied. 
Char. specif. — Founded on a left mandibular ramus which lacks the 
portions anterior to the canine, and posterior to the coronoid. 
The sectorial is the only tooth preserved. Posterior border of the 
heel lobulate. P. M. 4 well developed, one-rooted. P. M. with 
the anterior root reduced. P. M. y and , very robust, no. + 
shorter than the sectorial M. „ robust, the root grooved 
on each side. At the P. M. , the ramus is twisted externally. 
The anterior face of the coronoid is as wide as the ramus at 
the sectorial, and the M. is in front of its internal border. The 
dental foramen is behind the base of the coronoid, a little nearer the 
alveolar level than the inferior border of the ramus. Masseteric fossa 
strongly defined in front and below, and with a distinct median 
fundus. 
Measurements —Length of dental series from and exclusive of 
canine, 55 mm.; length of premolar series, 31 mm. ; length of sec- 
torial, 14.5 mm. ; length of heel, 7 mm. ; width of, do, 8 mm.; 
depth of ramus at sectorial, 25 mm. ; width of base of coronoid just 
behind M. y, 14 mm. 
This very robust species represented the otters in the central part of 
North America, during the Loup Fork epoch. Its dimensions were 
