1919] Merriam : Tertiary Mammalian Faunas of Mohave Desert 531 



COMPARISON OP THE RICARDO FAUNA WITH THAT OP THE AMERICAN 

 TERTIARY OUTSIDE THE GREAT BASIN AND PACIFIC COAST PROVINCES 



The faunas outside the Great Basin and Pacific Coast provinces 

 of western North America with which the Ricardo is most closely 

 comparable are the Snake Creek, Republican River, Alachua, and 

 Blanco. 



The Blanco Pliocene fauna of Texas resembles the Ricardo in 

 the absence of horses of more primitive stage than Protohippus, and 

 in the progressive stage of the carnivores and camels. The Blanco 

 horses of the Pliohippus type appear more advanced than those of 

 the Ricardo. Of the known Canidae Borophagus of the Blanco rep- 

 resents a very advanced stage, probably more progressive than any 

 Ricardo form. No machaerodont cats are known in the Blanco, the 

 only representative of the Felidae being a typical FeUs. The only 

 camels of the Blanco are referred to PUauchenia, while the Ricardo 

 forms seem to include Procamclus, PUauchenia, and Altioamelus. The 

 introduction of several edentates, including Glypothcrium and Mega- 

 lonyx, in the Blanco presumably indicates a later stage than the 

 Ricardo, but the difference may be due to failure of southern edentate 

 immigrants to reach California as early as they appeared in Texas. 



The absence from the Blanco of typical aelurodons, machaerodonts, 

 oreodonts, and merycodonts, taken with the presence of a variety of 

 edentates, and general advanced stage of the fauna indicates that the 

 Blanco is distinctly younger than the Ricardo. As the Blanco seems 

 also younger than the Rattlesnake and Thousand Creek, which appear 

 younger than the Ricardo, there is presumably a considerable gap 

 between these two southern faunas of Pliocene age. 



The Snake Creek fauna of western Nebraska contains many 

 elements which correspond closely to those of the Ricardo. In the 

 Carnivora two forms of Aelurodon are represented which are near 

 the stage of evolution of certain species in the Ricardo. With 

 Aelurodon there are, however, at Snake Creek, several Tephrocyon 

 species corresponding to types of the Great Basin Upper or Middle 

 Miocene. The Snake Creek Equidae comprise Protohippus, Plio- 

 hippus, and Ncohipparion of advanced types not less progressive than 

 the Ricardo species. At Snake Creek there is also found abundant 

 representation of the more primitive Merychippus, with Parahippus 

 and Ilypohippus. The remains of Merychippus make up over half 



