1913] 



Merriam: New Anchitheriine Horses 



433 



stage of evolution are near Archaeohippus, from which it is dis- 

 tinguished in the upper molariform teeth hy absence of eingula 

 on the protocone side, by higher cusps, and by a slightly more 

 advanced stage of development of the protocone and hypostyle, 

 though the metaloph is not more advanced in the Mohave form. 

 From the imperfectly known lower teeth of Archaeohippus it is 

 distinguished by the absence of external eingula, and evidently 

 also by proportions of the premolars. The absence of eingula 

 on the protocone side of both upper and lower molars may have 

 some significance in considering the stage of evolution, or may 

 concern only the matter of immediate relationship. 



The Mohave type represented by specimens no. 19840 and 

 19764 is evidently related to Parahipj)us in most characters, 

 though distant from the typical form. The absence of a crochet 

 in the upper teeth, and the very slight separation of metaconid 

 and metastylid columns in the lower teeth, indicate a relatively 

 undeveloped stage. "Whether this form is too primitive to be 

 included in Parahippus will he determined most clearly when 

 better material is available for study. 



Some significance may attach to the fact that this form, 

 having a certain resemblance to Parahippus, but being relatively 

 primitive, occurs in strata which were presumably deposited in 

 a later period than the time of maximum development of the 

 genus Parahippus. On the other hand, the Mohave form, being 

 somewhat more advanced than Archaeohippus in most respects, 

 and occurring in strata presumably younger, might be considered 

 a product of modification from Archaeohippus. It is interesting 

 to note that in the development of the crochet, in which one 

 would expect advance, the Mohave form is more primitive than 

 the Middle Miocene Archaeohippus. 



The Mohave type strongly suggests Anchitherium, from 

 which it seems to be separated by its slightly larger protoconule, 

 separation of metaconid and metastylid columns of the lower 

 teeth, and reduction of the cingulum on the outer side of the 

 lower cheek-teeth and inner side of the upper cheek-teeth. 

 Anchitherium is, moreover, doubtfully represented in America. 

 Ancliitheriumf f ) zitteli of China approaches the Mohave form in 

 certain characters, but seems clearly separable. 



