| UPPER JAW. | M. |
| Length of entire dental series | ·275 |
| Length of incisor series | ·375 |
| Length of diastema between canine and incisors | ·018 |
| Fore-and-aft diameter of canine | ·019 |
| Transverse diameter of canine | ·015 |
| Length of diastema between canine and premolars | ·0145 |
| Length of premolar series | ·083 |
| Length of first premolar | ·016 |
| Width of first premolar | ·009 |
| Length of second premolar | ·021 |
| Width of second premolar | ·017 |
| Length of third premolar | ·022 |
| Width of third premolar | ·022 |
| Length of fourth premolar | ·024 |
| Width of fourth premolar | ·027 |
| Length of true molar series | ·106 |
| Length of first molar | ·031 |
| Width of first molar | ·031 |
| Length of second molar | ·037 |
| Width of second molar | ·040 |
| Length of third molar | ·038 |
| Width of third molar | ·041 |
| LOWER JAW. | M. |
| Length of entire molar series | ·202 |
| Length of premolar series | ·081 |
| Length of true molar series | ·121 |
| Length of second premolar | ·024 |
| Width of second premolar | ·0125 |
| Length of third premolar | ·022 |
| Width of third premolar | ·014 |
| Length of fourth premolar | ·0235 |
| Width of fourth premolar | ·0155 |
| Length of first molar | ·030 |
| Width of first molar | ·017 |
| Length of second molar | ·038 |
| Width of second molar | ·021 |
| Length of third molar | ·053 |
| Width of third molar | ·024 |
Found at Henry's Fork Divide.
This may eventually prove to be a species of Telmatherium, (Marsh); but the description given by him of that genus is so brief and uncharacteristic that it might apply to any of the allied genera. Indeed, Dr. Leidy has regarded it as a synonym of Palæosyops.
HYRACHYUS, Leidy.
Proc. Ac. Nat. Sc., 1871, p. 229, et seq.
A genus of tapiroid mammals, which is thus defined: "Lower Jaw: Third molar with two crests; four premolars, third and fourth with one transverse and one longitudinal crest. Upper Jaw: Seven molars, first without interior heel; premolars with two transverse crests." (Cope.)
Synopsis of Species.
| I. | Long diastema between lower canines and molars. | |||
| A. | Lower jaw with six molars | H. nanus. | ||
| B. | Lower jaw with seven molars. | |||
| a a. Upper molars with complete cingulum. Enamel wrinkled. | ||||
a. The last molar with two external lobes on nearly the same transverse line. | H. intermedius. | |||
| b. Last molar with the external lobes on the same longitudinal line. | H. modestus. | |||
| b b. Upper molars with cingulum incomplete externally. | ||||
| a. With anterior conical buttress larger than anterior lobe. | ||||
| α. Buttress separate, and no fold from anterior lobe. | H. princeps. | |||
| β. Buttress united, and quite large fold from anterior lobe. | H. imperialis. | |||
| b. With anterior conical buttress smaller than anterior lobe. | ||||
| α. Tooth large. | H. eximius. | |||
| β. Tooth smaller. | H. agrarius. | |||
c c. Cingulum only on outer side of first molar, buttress separated by a ridge from anterior lobe, fold from this lobe very prominent. | H. implicatus. | |||
| II. | Short diastema between lower canines and molars. | |||
| A. | Descending ridge from antero-external point of lower molar extends entirely across the crown of the tooth anteriorly. | H. crassidens. | ||