48 



Troxell — Hyracliyus and its Subgroups. 



protoloph is entirely severed from the ectoloph by the 

 deep valley running longitudinally. 



The third lower molar is broad on its posterior half. 

 There is a strong basal ridge both fore and aft, the true 

 cingulum, in addition to the sharp ridge running inward 

 from the antero-exterior corner of the crown. 



SlJMMAEY. 



The genus Hyracliyus Leidy, taken as a whole, is made 

 up of a number of groups, each of which, in the writer's 

 opinion, belongs to a single species. H. affinis (Marsh) 

 represents the smallest of these, then in the order of size 

 come H. bairdianus (Marsh) (=H. agrestis Leidy, 

 indet.), and the very large II. princeps Marsh. 



Under the name H. affinis gracilis el new subspecies 

 is described which, because of the completeness of the 

 skeleton upon which it is based, serves admirably as a 

 protype, or reference type, further to establish the group. 

 This specimen has recently been remounted. 



Measurements of Types. 





H. bairdianus 



H. 



H. 



H. 





Cotypes 



Apotype 



gracilis 



affinis 



princeps 





No. 11035 



No. 11.081 



Holotype Holotype Holotype 





mm. 



mm. 



mm. 



mm. 



mm. 



Superior dentition : 













Molar -premolar series, 













length 





94 



74 





f 128 



Molar series, length 



51.8 



53.5 



43.5 



44 



70 



P 4 , width, transverse 





18 



14.5 



14.2 



25 



P 4 , length 





13 



10.5 



11.3 



19.5 



M 2 , width 





21.6 



18.0 



17.3 



30.5 



M 2 , length 





20.3 



16*. 7 



16.7 



25.5 



M 3 , width 



22 



20.4 



17.5 



17.3 



31 



M 3 , length 



18.6 



19 



15.5 



15.2 



26 * 



Inferior dentition : 



No. 11057 











Molar-premolar series, 













length 





?92.5 



78 







Molar series, length 



52.3 



53.7 



45 







P 4 , width 





9.5 



8 







P 4 , length 





13.2 



11.6 







Mi, width 



10.5 



11 



9.6 







M x , length 



15.5 



15.5 



13.6 







M 2 , width 



11.6 



12 



10.2 





17.5 



M 2 , length 



17.5 



18 



15.3 







M 3 , width 



11.7 



12.5 



10.6 





17.5 



Ms, length 



19.3 



20 



12 





28.5 



