SINOPA, Leidy.
A genus of small carnivorous animals, which Dr. Leidy regards as
intermediate between the recent _Canis_ and the extinct _Hyænodon_.
Owing to the fragmentary condition of the remains found, no
satisfactory generic definition has been given.
From the portion in our collection, we are able to throw some further
light upon the genus, summing up the generic characteristics thus:
Small carnivores, which have the last upper premolar as sectorial
(thus differing from _Hyænodon_), the other premolars simple and
conical.
The sectorial is shorter, antero-posteriorly, than the preceding
tooth; has a short blade of a single lobe, and a large cusp developed
from the posterior part; a cingulum surrounds the entire crown. The
_lower_ sectorial has the blade of a single lobe, and with a short
heel.
Sinopa rapax, Leidy.
Proceedings of Ac. Nat. Sc., 1871, p. 115.
In addition to the molars of the lower jaw, described by Dr. Leidy we
have what corresponds to the third and fourth premolars of the fox,
their dental formulas being probably the same.
The third premolar is small and pointed; differing from the
corresponding tooth in the fox, (1) in its being less compressed, (2)
in its shorter antero-posterior diameter, (3) in the straighter and
more nearly equal margins, and in (4) the absence of a posterior heel.
The tooth is inserted by two fangs, as in _Canis_ and _Hyænodon_. The
posterior shows a rudiment of a third, which is connate with its
entire length above the alveolus. There is an indistinct cingulum
around the entire crown.
The fourth premolar has a very curious shape. The blade of this tooth
resembles the crown of the third, but is smaller. It is inserted by
three fangs, the disposition of which is opposite to that in _Canis_,
the internal, being on the same transverse line as the posterior
external, instead of the anterior, as in _Canis_. From the internal
fang arises a sharp cusp, which is nearly as large as the blade of
the tooth, the two are connate at base. The anterior face of the
crown is much worn, and there is a small anterior heel formed by the
basal ridge. The cingulum is complete all around.
The _maxillary_ does not show the outward bulge at the third
premolar, which is so marked in the fox. The alveolus is straighter,
and the palatine plates are comparatively thicker and flatter. The
infraorbital foramen is oval, and not so much compressed as in the
fox, to which it corresponds very nearly in position, though situated
slightly forward as in _Hyænodon_.
_Measurements._
_Upper Jaw._ M.
Length of third premolar ·007
Breadth of third premolar ·004
Length of fourth premolar ·007
Breadth of fourth premolar ·007
_Lower Molars_, from Dr. Leidy.
Length of last premolar ·0075
Length of first molar ·009
These exhibit nearly the same proportionate size as in the gray fox.
_Genus_ ----. _Species_ ----.
_Sacrum_ (Plate IX., Fig. 8).--This peculiar sacrum is composed
of only one true vertebra; there may have been one or more
pseudo-sacrals, but this is not certain.
The centrum is very long, strongly depressed, and straight on the
inner margin, not curved as in the sacrum of most mammals. The
anterior articular face is much depressed, and is one third larger
than the posterior. The neural canal is low and subtriangular,
resembling very much that of _Canis_. The pleuropophysial plates for
articulation with the ilia are large and stout. The laminæ are heavy
and concave on their upper side, supporting a very long, stout spine,
which is retroverted and decidedly tuberous at the end.
The pedicles are deeply notched behind; and on the fore part, just
inside the metapophyses, there is a deep fossa.
The chief features of this sacrum are decidedly carnivorous; but to
what genus or family it should be referred we are unable to say.
It has some of the characteristics of _Canis_, but the length
and retroversion of the spine, as well as the size of the
centrum, prevent this classification. In the general form of the
pleuropophysial plates it approximates to the _seals_; while in its
angle and curvature, it partakes of the character of the _Ursidæ_.
The chief point of interest in this fossil centres in the fact that
it was found only a few feet from the brain cast that is described
below.
_Measurements of Sacrum._
M.
Length of centrum ·031
Long diameter of anterior articular face ·024
Long diameter of posterior articular face ·017
Width of neural canal ·019
Height of neural canal ·011
Length of neural spine ·036
Extreme width of sacrum ·052