170 University of California Publications in Geology [Vol. 9 



assemblage of forms from the Cedar Mountain certainly seems more ad- 

 vanced than the Middle Miocene of the Great Basin, though it may 

 approach it more closely than does the Barstow fauna. 



Compared with the Upper Miocene fauna of the Barstow beds the 

 Cedar Mountain fauna is distinguished especially by the absence of 

 large aelurodons, and by the presence of rhinoceroses with Merycodus 

 furcatus as the most common merycodont. Other differences, as 

 the absence of Merycochoerus and Dromomeryx from the Cedar Mount- 

 ain, and the absence of certain rodents as Dipoides from the Barstow, 

 may be due to the chances of collecting. 



Aside from the differences mentioned above, the Cedar Mountain 

 and Barstow faunas have in general a similar aspect. The presence 

 in the Cedar Mountain of a form of Tephrocyon ; the occurrence in 

 both faunas of a very progressive type of Hypohippus, an advanced 

 MerycMppus, and a protohippine form more specialized than typical 

 Merychippus, indicate that the faunas are not widely separate in 

 stage of development. It seems evident that the Cedar Mountain is 

 nearer the Barstow than to any other faunal stage thus far known 

 in the Great Basin, and is therefore probably of Upper Miocene age. 



The presence of rhinoceroses and of Merycodus furcatus in the 

 Cedar Mountain in the same association as in the Santa Fe Upper 

 Miocene, whereas they are both absent from the Barstow, may be due 

 to geographic variation or difference in environment. It is possibly 

 due to slightly earlier stage of evolution of the Cedar Mountain fauna. 

 The collections from the Barstow beds are the largest thus far brought 

 together in the southwestern portion of the Great Basin, but as yet 

 neither rhinoceroses nor Merycodus f urcatus appears in the abundant 

 material. 



Compared with the Ricardo fauna, the mammals of the Cedar 

 Mountain beds lack the advanced aelurodons, while the horses and 

 camels are generally much more primitive. The presence of Dipoides, 

 Mylagaulus, and one rather advanced horse in the Cedar Mountain 

 beds would seem to show a relatively advanced stage; but Dipoides 

 and Mylagaulus are both known in the Upper Miocene of America, 

 although not as yet obtained in the Barstow. while the progressive 

 horse may not be more specialized than one form in the Barstow beds. 



Unless it be true that there is in the Cedar Mountain region a 

 series of beds somewhat younger than those from which the principal 

 fauna has been obtained, there is good reason for considering the 

 fauna of these beds as considerably older than that of the Ricardo. 



