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.