49 

 HYRACHYUS, Leidy. 



Proc. Ac. Nat. Sc., 1871, p. 229, et sqq. 



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 exter- 

 nally. 



a. With anterior conical buttress larger than ante- 

 rior lobe. 



a. Buttress separate, and no fold from 



anterior lobe H. princeps. 



ft. Buttress united, and quite large fold 



from anterior lobe H. imperialis. 



b. With anterior conical buttress smaller than an- 

 terior lobe. 



ex. Tooth large H. eximius. 



ft. Tooth smaller H. agrarius. 



c c. Cingulum only on outer side of first molar, but- 

 tress 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. 



