258 THE POPULAR SCIENCE MONTHLY 



shown by the presence of many fresh-water moUuscan remains at cer- 

 tain horizons. 



The fauna of the Barstow beds represents a stage in the evolution of 

 Tertiary mammalian faunas previously not distinctly recognized in the 

 Great Basin Province. It seems clearly later than the Middle Miocene 

 life stage well known in the Maseall beds of Oregon and in the Virgin 

 Valley beds of northern Nevada. The fauna is markedly older than the 

 Eattlesnake Pliocene of Oregon and the Thousand Creek Pliocene of 

 Nevada, representing the next described stages following the Middle 

 Miocene in the Great Basin. The fauna of the Barstow beds has few if 

 any species in common with that of the Eicardo formation, and is of a 

 distinctly older type. Its nearest relationships are with the fauna of 

 the Cedar Mountain region of southwestern Nevada, from which it 

 possibly differs somewhat in stage. 



The Second Fauna, the Eicardo Pliocene 



The number of species represented in the Eicardo fauna is approxi- 

 mately equal to that found in the Barstow Miocene and the groups of 

 animals represented are in general of the same type. Comparisons be- 

 tween these two faunas or life stages can therefore be made with some 

 degree of satisfaction. Coupled with the fact that the Mohave and 

 Eicardo faunas comprise an approximately equal representation of 

 similar groups, it is a matter of interest to note the almost complete 

 difference between the species represented in the two, and that with one 

 or two possible exceptions the species of the Eicardo stage represent more 

 specialized or more progressive stages of evolution than the correspond- 

 ing types seen in the Barstow fauna. 



As in the Mohave stage, we find the Eicardo collections consisting 

 mainly of horses and camels, the horses furnishing the most important 

 and most characteristic forms thus far known. 



The Eicardo horses are of at least three types, of which the most 

 common includes one or more species of the genus Hipparion. These 

 are large, three-toed forms with the side-toes reduced and the grinding 

 teeth large. They resemble to some extent one of the small species of 

 the Barstow Miocene, but are much larger; the side-toes are more re- 

 duced ; and the teeth were longer-crowned, heavier, and of more compli- 

 cated structure. The Eicardo Hipparion differs from most of the 

 species referred to this genus in America, and belongs to the true Hip- 

 par-ion tv]>e, which J. W. Gidley considers as characteristic of the 

 Old World, in contrast to a New World form, Neohipparion. Many of 

 the teeth of the Eicardo species are practically indistinguishable from 

 these of Hipparion ricMliofeni, a species abundantly represented in the 

 early Pliocene or late Miocene of China. It has generally been assumed 

 that the Old World horses of the Hipparion type are descended from 



