506 University of California Publications in Geology [Vol. ll 



might indicate its affinity with Pliohippus. This specimen was asso- 

 ciated with the type specimen of M. intermontanus from locality 1401 

 in the Barstow syncline. 



The characters of this tooth are near those of M. inter montanus, 

 but it differs from that form in greater width and its much more 

 compressed and anteriorly longer protocone. 



The form represented by no. 21423 (figs. 80, 81) may be a species 

 distinct from M. intermontanus or may be a more advanced stage of 



80 



Figs. 80 and 81. Protohippus ? or Pliohippus?, sp. Superior cheek-tooth, no. 

 21423. Fig. 80, outer view; fig. 81, occlusal view. Barstow Miocene, Mohave 

 Desert, California. 



Fig. 82. Protohippus or Pliohippus?, sp. Superior cheek-tooth, no. 21424, 

 natural size. Barstow Miocene, Mohave Desert, California. 



that species. Specimen no. 21423 represents the maximum of advance 

 of the Equidae in the Barstow fauna. It differs from all three of 

 the Pliohippus forms of the Ricardo. It is smaller, and less advanced 

 than Pliohippus fairbanksi. It differs from P. tantalus in the smaller 

 fossettes, and is also somewhat smaller and apparently less advanced. 

 A single tooth from the Ricardo, representing a form near Pliohippus 

 mirabilis is smaller in cross-section than no. 21423 from the Barstow 

 fauna, but the Ricardo specimen is considerably worn and may orig- 

 inally have been the longer crowned and more progressive of the two. 



Two other upper cheek-teeth, nos. 21424 and 21425, from localities 

 in the Barstow represent forms near that seen in no. 21423 described 

 above. No. 21424 (fig. 82) is little worn and is the longest molar 

 found in the Barstow. The pattern of the crown and of the protocone, 

 so far as known, suggests that of no. 21423. No. 21425 is a much worn 

 tooth and may represent Merychippus intermontanus. 



