Established on the second and third molars of each upper jaw, and
three premolars, and one lower molar, portions of the skull and
vertebræ.
This species is, with the exception of _H. princeps_, (Marsh), the
largest species of the genus as yet known. It differs from _H.
princeps_ in the greater proportionate length of the molars, in their
larger size, compared with the bulk of the animal, and in the less
separation of the anterior external conical buttress. The third molar
is the largest; the fold extending from the antero-external lobe
into the valley is very conspicuous. The basal ridge (which is very
strongly marked on the posterior edge), is very feebly indicated on
the exterior. The transverse crests are more oblique in the second
than in the third, but in the latter the valley is deeper and the
crests slightly longer. The anterior conical buttress is of great
size, being larger than the anterior lobe. The premolars have,
as usual, one internal cone; the anterior and posterior external
lobes approach close together, while the accessory fold from the
anterior lobe becomes very prominent, reaching the internal cone and
enclosing a valley between itself and the transverse crest. The basal
ridge does not extend around the inner part of the crown as in _H.
agrarius_.
The only lower molar we have, seems to be a penultimate molar of
the right side. The basal ridge is large anteriorly, very short
posteriorly, but does not appear at all upon the sides, as in _H.
agrarius_.
The remaining bones of the skeleton indicate a rather small animal,
the teeth are therefore proportionately very large.
The occipital condyles are small and sessile; they are much extended
laterally, and the external angles are pointed. In other respects
they resemble the condyles of _Palæosyops_. The zygomatic arch is
slender and does not curve outward strongly. We cannot tell how far
the malar encroaches upon the face. After leaving the maxillary it
becomes much compressed; it has no postorbital process. The maxillary
is of unusual breadth, extends far backwards, and it forms the floor
of the large orbit. The mandible is slender and compressed, with a
large dental canal.
The atlas is small, and has narrow transverse processes, which
are perforated by a large vertebraterial canal. The dorsals have
considerably depressed centra, and the ribs are slender.
_Measurements._
M.
Length of last molar ·025
Breadth of last molar ·030
Length of second molar ·024
Width of second molar ·0305
Length of last (?) premolar .018
Width of last premolar ·0245
Length of second lower molar ·025
Width of second lower molar ·018
From Henry's Fork Divide.