1919] Merriam: Tertiary Mammalian Faunas of Mohave Desert 477 



The crowns of the milk molars of the Barstow 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. A P 2 

 from the Mascall Miocene, considered by Gidley to represent Archaeo- 

 hippus, differs from the milk molars of the Barstow specimen in 

 showing much greater development of the longitudinal ribs on the 

 outer side of the paracone and metacone. There is a very faint longi- 

 tudinal rib on the outer face of the paracone in Dm 3 of the Barstow 

 specimen. A longitudinal rib is barely perceptible on the outer side 

 of the metacone of this tooth. 



Measurements 



Arehaeo- 



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 4 



13 





Dm 4 , transverse diameter 



ali.5 



P 4 



17 





M 1 , anteroposterior diameter measured. 





along middle of crown 



13.7 



M 1 



11 





M 1 , approximate transverse diameter 











measured along anterior border 



al6 



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. 



In the lower jaw specimen, no. 19764 (fig. 33), the cheek-teeth are 

 brachyodont, without evidence of cement covering. The crowns of 

 the molars and premolars are slightly rugose, and tend to be some- 

 what higher than in the average Tlypohippus. P 4 is considerably 

 larger than M 1 in both anteroposterior and transverse diameter. The 

 metaconid and metastylid show a distinct tendency to separate at the 

 summit, the separation being more marked than in typical Hypo- 

 hippus, and less advanced than in typical Parahippus. The entostylid 

 is well developed. The cingulum is well shown on the anterior and 

 posterior sides of the crown, but shows no distinct shelf on the outer 

 and inner sides. 



The dentition of specimen 19764 differs from the lower teeth 

 referred to Archaeoliippus by Gidley in the absence of external and 

 internal eingula, and apparently also in the proportions of the 

 premolars. 



