In the second specimen the cusps are all low, and the crests prominent, giving the molars something of the appearance of Opisthotomus. This difference is probably sexual.
Measurements.
| M. T. No. 1. | M. T. No. 2. | M. T. No. 3. | |
| Length of entire molar series | ·038 | ···· | ·032 |
| Length of premolar series | ·017 | ···· | ·0125 |
| Length of true molar series | ·021 | ···· | ·0195 |
| Fore-and-aft diameter of canine | ·003 | ·005 | ·0065 |
| Length of last molar[1] | ·008 | ···· | ·005 |
| Width of last molar | ·004 | ···· | ·003 |
| Length of second molar | ·007 | ·007 | ·0072 |
| Width of second molar | ·005 | ·006 | ·005 |
| Length of last premolar | ·0055 | ···· | ·007 |
| Length of penultimate premolar | ·004 | ···· | ·005 |
| Depth of jaw at second molar | ·012 | ·012 | ·0095 |
| Thickness of jaw at second molar | ·0065 | ·009 | ·004 |
[1] In measurements of teeth we use the word length to mean antero-posterior diameter, and width to mean transverse diameter.
Specimen No. 1 was found at Cottonwood Creek, and specimen No, 2 at Henry's Fork, Wyoming.
HYOPSODUS, Leidy.
Pr. Ac. Nat. Sc., 1870, p. 110.
Lower teeth: I. 3, C. 1, Pm. 4, M. 3, in uninterrupted succession. Last molar has cusps in opposing pairs; the antero-internal cusp on all the molars is single; the last molar has a heel, and the last premolar has an inner cusp. The true molar cusps are all high and simple.
Hyopsodus paulus, Leidy.