1919] Merriam: Tertiary Mammalian Faunas of Mohave Desert 453 



not seem to be identical with any of the Barstow species. The Hypo- 

 hippus-like forms of the Cedar Mountain beds are near the stage of 

 advance in size seen in the species known from the Barstow. Proto- 

 hippine horses are unfortunately very imperfectly known from the 

 Cedar Mountain beds. One form is near the stage of the Barstow 

 Merychippus ; another seems relatively advanced, and may be more 

 progressive than any but the most advanced type known from the 

 Barstow. It is possible that more than one faunal horizon is repre- 

 sented in the Cedar Mountain region, and that the two protohippine 

 horses came from different zones. 



Merycodus is represented in the Cedar Mountain region most 

 commonly by a type corresponding to M. f uroatus, though M. meatus 

 of the Barstow fauna is also present. 



Bhinoceroses are represented in the Cedar Mountain beds, but are 

 not thus far known from the Barstow. 



On the whole the faunal assemblage of the Barstow balances near 

 the stage of evolution of the Cedar Mountain beds. The dissimilarity 

 may be due to the presence in the Cedar Mountain region of some 

 horizons older and some younger than those from which the Barstow 

 fauna has been obtained. A portion of the difference may be due to 

 geographic variation. As the horizontal separation is not large and 

 the environments were presumably not greatly different, the geo- 

 graphic factor may not be sufficient to account for the dissimilarity. 



In general the Barstow and Cedar Mountain faunas are as near 

 to each other as either is to any other known faunal assemblage in the 

 Great Basin Tertiary series. 



RELATION TO TERTIARY FAUNAS OP AMERICA OUTSIDE THE GREAT BASIN 



REGION 



The nearest relationships of the Barstow fauna outside the Great 

 Basin are with the Santa Fe beds of New Mexico. Several types 

 which are among the most important forms of the Santa Fe beds are 

 similar to species in the Barstow fauna. These include Aelurodon 

 wheelerianus, Merychippus calamarius, Procamelus near gracilis, and 

 Merycodus necatus. 



As a considerable distance separates the Barstow geographically 

 from the Santa Fe some difference in fauna is to be expected. It is 

 also possible that the Santa Fe beds represent more than one horizon, 

 or may include beds ranging into stages older or younger than the 

 Barstow. 



