472 University of California Publications in Geology [Vol. ll 



advanced cheek-teeth on which the enamel may have a thickness of 

 8 mm. or more. On one specimen there is a trace of enamel on the 

 tusk. 



EQUIDAE 



Remains of forms representing the Equidae are the most abundant • 

 fossils in the exposures of the Barstow syncline. Especially at one 

 horizon, known as the Merychippus bed, in the upper portion of the 

 section referred to by Baker 27 as the Fossiliferous Tuff member, 

 scattered bone fragments and teeth are common. At least five 

 species are known, two anchitheriine and three protohippine forms. 

 The brachyodont forms comprise a large species of Hypohippus, 

 possibly of the subgenus Drymohippus 28 recently described from the 

 Tertiary beds near Mina in southwestern Nevada, and a smaller form 

 near Parahippus. 20 The protohippine forms include advanced species 

 of Merychippus and a form presumably near Protohippus. 



The brachyodont horses are very rare. A single jaw fragment 

 of Hypohippus is known, and the number of skeletal elements referred 

 to this group is relatively very small. Of the Parahippus-like form 

 only two specimens are known, one representing the upper, the other 

 the lower dentition. The collections of horse specimens from the Bar- 

 stow syncline consist mainly of Merychippus, with a small percentage 

 of more advanced forms evidently close to Protohippus. 



HYPOHIPPUS, near AFFINIS (Leidy) 



This genus is represented in the collections from the Barstow 

 syncline by a fragment of a lower jaw with M 1 and M 2 from locality 

 2060, a fragment of an upper molar from locality 2058, and a few 

 limb bones from localities 1398 and 2056. 



The molars (fig. 28) in the lower jaw fragment, no. 21215, repre- 

 sent a very large species comparable in size to Hypohippus affinis of 

 the Upper Miocene in the Great Plains region, or approximately com- 

 parable with H. nevadensis of the Stewart Valley beds in southwestern 

 Nevada. Unfortunately the lower teeth of H. nevadensis of the 

 Stewart Valley beds in southwestern Nevada are not certainly known. 

 The dimensions correspond very closely with teeth from the Upper 

 Miocene of Big Spring Canon, South Dakota, described by Matthew 



27 Baker, C. L., Univ. Calif. Publ., Bull. Dept. Geol., vol. 6, p. 346, 1911. 



28 Merriam, J. C, Univ. Calif. Publ., Bull. Dept. Geol., vol. 7, p. 420, 1913. 

 Mlbid., p. 427, 1913. 



