Established on several portions of the head, vertebral column, and
the limbs.
This species may readily be distinguished from the last by its
larger size, the broad nasals with small tuberosities, the stronger
zygomatic arches, and the sub-cylindrical centra of the dorsal
vertebræ.
The _nasals_ are broad and flat for some distance behind the
tuberosities. Although the animal was not adult, the nasal suture
is almost obliterated, and is visible only on the inferior surface;
in this respect it is very different from the _U. leidianum_, in
which the suture persists throughout life; as is shown by the type
specimen, which was past maturity. The tuberosities of _U. princeps_
are lower, broader, and more everted than in the preceding species;
are not divided by a groove, but united together by a low rounded
ridge, to which the surface of the nasals gradually rises from
behind. The portion of the bones anterior is short, stout, and
projects horizontally.
The _median_, or _maxillary_, _projections_ are apparently short and
everted; they are somewhat compressed antero-posteriorly, and enlarge
rapidly downwards. They are transversely oval in section.
The _posterior_, or _parietal_, _projections_ are different from any
that we have yet seen. They are subtrihedral at base and flattened
antero-posteriorly above. The upper margin is regularly arched,
and is the thinnest portion of the process. The posterior face is
perfectly flat, and the parietal crest makes a sharp angle with it,
rising lower down than in _U. leidianum_; the frontal crest is also
lower down than in that species, and the anterior face is strongly
convex. The internal margin is rounded and straight, and does not
show the longitudinal groove marked in the last species.
The _frontal_ has the eminences and depressions common to the members
of the genus; but the superciliary ridge is unusually sharp and
sinuous in outline.
The _squamosal_ is short, stout, and high; is but slightly curved
outwards, but apparently projects somewhat downwards. The malar
articulation is broad and flat, indicating the heaviness of that
bone. As a whole the zygomatic arch is stronger, and probably
shorter, than in _U. leidianum_.
The occipital condyles are proportionately rather small; they are
placed on a long neck and project downwards. They are strongly convex
from above downwards, but scarcely at all so from side to side. The
internal border is slightly emarginate.
The _dorsal vertebræ_ are of about the same proportionate length
as in _U. leidianum_, but are higher and wider; and the centra are
subcircular in section, slightly contracted in the middle. The costal
surfaces are wide and deep, and vertically oval in shape; they are
placed partly on the centra and partly on the neurapophyses. The
transverse processes are short, stout, and tuberous, and raised
high above the centrum. There is a deep notch at the posterior
edge of this process, at its junction with the neurapophysis. The
neurapophyses are trihedral, somewhat low, and very stout, forming a
wide neural canal.
The _ulna_ (Plate VII. Fig. 2) is thick, with a long and rugose
olecranon. The shaft is long and stout; it shows a distinct medullary
cavity. The distal end is small, and shows a low, heavy, styloid
process.
A _metacarpal_ resembles the corresponding bone in _Dinoceras_,
but is rounder and less rugose. There are two faces for carpal
articulations, which meet at an open angle.
_Measurements._
M.
Breadth over nasal tuberosities ·132
Length of nasal tip (anterior to tuberosities) ·033
Circumference of maxillary projection near the tip ·208
Vertical diameter of squamosal ·058
Transverse diameter of ditto at malar articulation ·045
Length of centrum of dorsal vertebræ ·070
Height of ditto ·083
Breadth of ditto below costal surfaces ·097
Breadth of pedicle ·058
Length of transverse process ·056
Extreme breadth of transverse process ·061
Found at Henry's Fork.
Uintatherium robustum. Leidy.
Cont. to Ext. Vert. Faun., p. 96.
A fragmentary skeleton from Henry's Fork.