The incisors are small, arranged in a semi-circle, and have very much compressed fangs, with somewhat procumbent crowns; the canines are small, and form a continuous series with the incisors. There is a diastema between the canine and first premolar; but one which is shorter than in known species of the genus, and which does not indicate the usual curve of the upper border of the ramus.
The molar series, (so far as can be judged from their broken condition), are much the same as in other species; except, perhaps, in the greater relative size of the posterior lobes, and in the more complete closing of the median valley by the junction of the two lobes externally. The ridge which curves downwards and inwards from the external point of the anterior lobe is unusually well developed, and curves across the entire crown. The cingulum is feebly shown; it appears on the anterior and posterior ends of the tooth (first molar) and for a very short distance on the outside of the tooth opposite the median valley; there is no trace of it on the inner side.
Measurements.
| M. | |
| Length of entire molar series (about) | ·080 |
| Length of premolar series | ·033 |
| Length of true molar series (about) | ·047 |
| Fore-and-aft diameter of fang of canine | ·008 |
| Distance between canine alveoli | ·009 |
| Length of diastema | ·115 |
| Length of the first molar | ·015 |
| Breadth of the first molar | ·010 |
| Depth of ramus below last molar | ·0245 |
| Depth of ramus below last premolar | ·0215 |
| Greatest thickness of ramus | ·017 |
| Length of symphysis (about) | ·030 |
Found at Henry's Fork.
Hyrachyus ———— ?
There are three premolars of the upper jaw which we cannot refer to any known species; but they are too imperfect to justify the formation of a new species for their reception.
What appears to be a first premolar is inserted by a single broad fang; it is too much worn to show the characteristic enamel folding, and is peculiarly broad and short. The second premolar shows the usual foldings of Hyrachyus; save that a distinct valley enters the tooth from the posterior edge, running forward to the transverse crest, and inclosed by the curving backwards of the internal cone. The crown is nearly square; the basal ridge is scarcely marked at all.
Measurements.
| M. | |
| Length of first premolar | ·011 |
| Breadth of first premolar | ·016 |
| Length of second premolar | ·012 |
| Breadth of second premolar | ·014 |