82 University of California Publications in Geology [ VoL - 10 



collections. Moropus occurs only in the former fauna, while Meryco- 

 choerus(f) and Dromomeryx are found only in the latter, hut the 

 collections are not sufficiently large to make the absence of a form 

 from one fauna and its presence in the other significant. Merycodus 

 is present in the collections from both localities, but the material is too 

 scanty to allow an accurate comparison. 



Of the horses, the species from the Phillips Ranch horizon has much 

 smaller and much more primitive cheek-teeth than either of the forms 

 in the Cache Peak fauna. The horse astragali from the Phillips Ranch 

 horizon are all of a smaller type, while there are in the collections from 

 the upper horizon astragali of a larger type as well. 



The evidence of the camel material is not emphatic, but the larger 

 size of most of the camel teeth and foot parts in the Cache Peak fauna 

 tends to confirm the view that this assemblage represents a more 

 advanced stage. 



The Phillips Ranch fauna is quite certainly considerably older and 

 less advanced than the assemblage from the Cache Peak horizon. 



In considering the relations of the Phillips Ranch and Cache Peak 

 faunas to other groups it seems desirable to compare them with faunas 

 known from neighboring areas. In the Mojave Desert the Ricardo 

 fauna, known from considerable collections to be of approximately 

 lower Pliocene age, occurs about twenty miles to the northeast ; the 

 Barstow fauna, also well represented by material and of approxi- 

 mately upper Miocene age, is found about eighty miles to the east. 

 In the southern San Joaquin Valley on the opposite side of the south- 

 ern Sierra a meager collection obtained in the Tejon Hills is of ap- 

 proximately very late Miocene or lower Pliocene age. 



The species of Merychippus found in the Phillips Ranch fauna is 

 very different from any species found in the Barstow upper Miocene 

 collection, being much more primitive. The camels do not permit of 

 an exact comparison because of scantiness of the Phillips Ranch 

 material, but they appear to be different. The species of Merycodus 

 may be the same as that from Barstow, but with the material at hand 

 a certain determination cannot be made. 



The horse material from Phillips Ranch resembles still less any of 

 the horses found in the Ricardo fauna, being much more primitive. 

 It is likewise less advanced than the horse species obtained in the 

 Tejon Hills in the southern San Joaquin Valley. 



The Phillips Ranch fauna certainly represents a stage of evolu- 

 tionary development much earlier than the Barstow, Ricardo and 

 Tejon Hills faunas. 



