660 THE BRIDGER FAUNA. 



fourth articulates with the two inner cuneiforms, and has a small lateral con- 

 tact with the ectocuneiform. The phalangeal articulations of the lateral 

 metatarsals are but little unsymmetrical. The median ungual phalange is 

 wide and flat, and has proximal lateral processes. The latter ungual pha- 

 langes are unsymmetrical, and have but one, an external proximal process. 



The above general characters are derived from the study of one almost 

 perfect skeleton of H. eximius. 



The aflinities they displa}^ are most rhinocerontic, then tapirine, and 

 least equine, of the perissodactyle families. The unsymmetrical form of 

 the external wall of the superior molars is represented among living types 

 by the Bliynocerontidce only, while the transverse crests of the inferior mo- 

 lars are shared by that family and the Tajnndce. The form of the sternum 

 is rhinocerontic, while the first are much like thosfe of the tapirs. In the 

 articulation of the lumbar vertebrae Hyrachyus is rather more equine. 



Species. — Eight species of this genus have been distinguished by Messrs. 



Scott, Spier, and Osborne,^ in a satisfactory way. I add another to the list, 



and copy their analytical table almost entire: 



I. A long diastema between lower canines and molars. 

 aa Superior molars surrounded by a cingulum ; enamel wrinkled. 

 Last molar with two external lobes in nearly the same transverse line. .H. intermedins. 

 Last molar with two external lobes in nearly the same longitudinal line. .fl^. modestus. 

 aa Superior molars with cingulum complete externally only. 

 fi With anterior cingular cusp larger than anterior lobe. 



Ciugular cusp separate and no ridge from anterior lobe H. princeps. 



Cingular cusp nnited with anterior lobe by a crest H. imperiaUs. 



(i[i With anterior cingular cusp smaller than anterior lobe. 



Teeth and jaws larger -S. eximius. 



Teeth and jaws smaller , E. agrarius. 



II. Inferior diastema short. 

 No cingula or additional lobes of superior molars; inferior molarr. with strong anterior 



cingulum S. impUcatus. 



II. Inferior diastema unknown. 

 a No internal cingulum on superior molars ; the anterior crest with a distinct me- 

 dian lobe. 



A strong internal projection of the external wall; enamel smooth; an internal ledge. 



T. amarorum. 



The Triplopus amarorum is mentioned here for comparison with the spe- 

 cies of this genus. It resembles them in some portions of its skeleton. 



' Paleontological Report of the Princeton Scientific Expedition of 1877-1878, p. 49. 



