1913] 



Merriam: New Anchitheriine Horses 



429 



The crowns of the milk molars of the Mohave specimen were 

 apparently somewhat shorter and slightly rougher than those 

 of the permanent molars. As in the permanent dentition, the 

 milk molars show the metaloph connected with the ectoloph, 

 there is no internal or lingual shelf of the cingulum, and the 

 hypostyle is large. On one of the milk molars there is a faint 

 suggestion of crinkling of the anterior side of the outer end of 

 the metaloph. A P 2 from the Mascall Miocene considered by 

 Gidley to represent Archaeohippus differs from the milk molars 

 of the Mohave specimen in showing much greater development 

 of the longitudinal ribs on the outer side of the paracone and 

 metacone. There is a very faint longitudinal rib on the outer 

 face of the paracone in Dm 3 of the Mohave specimen. A longi- 

 tudinal rib is barely perceptible on the outer side of the metacone 

 of this tooth. 



Measurements 



Archaeo- 



Archaeo- 







hippus 



hippus 







ultimus 



ultimus 





No. 19840 



Type specimen 



No. 1689 



Dm 3 , greatest anteroposterior diameter .... 



13 mm. 



P 3 



12 





Dm 3 , transverse diameter 



13.8 



P 3 



16 





Dm 4 , greatest anteroposterior diameter 



13.7 



p.. 



13 





Dm 4 , transverse diameter 



a 14.5 



P 1 



17 





M 1 , anteroposterior diameter measured 









along middle of crown 



13.7 



M 1 



11 





M 1 , approximate transverse diameter meas- 





ured along anterior border 



a 16 



M 1 



15 





M 3 , anteroposterior diameter measured 











along middle of crown 







11 



11 



M 3 , transverse diameter along anterior 











border 







14 



14.8 



a, approximate. 



The form of the cheek-teeth shown in the upper jaw of no. 

 19840 differs from Hypohippus in the greater height of the 

 crown, larger protoconule and metaconule, larger hypostyle, and 

 more abrupt inner wall of protocone and hypocone. Prom 

 Arch aeohipp us no. 19840 differs in its somewhat higher, more 

 rugose crown; larger, more compressed protoconule; much larger 

 hypostyle with posterior cup ; and absence of internal cingulum. 

 Prom typical Parahippus the Mohave specimen differs in absence 



