434 University of California "Publications in Geology [Vol. 10 



The Pliocene faunas of the Great Basin region clearly represent 

 at least three quite distinct stages : the Ricardo, the Rattlesnake and 

 Thousand Creek, and the Idaho. The Ricardo fauna, including as it 

 does Merycodus, an oreodont, and several other forms of middle 

 Cenozoic type, is certainly older than the Thousand Creek, Rattle- 

 snake, and Idaho, in which these forms do not appear. 



The Thousand Creek and Rattlesnake are evidently of approxi- 

 mately the same stage. In neither fauna is Merycodus represented, 

 and no oreodont remains are known. The antilopine type represented 

 by Merycodus in the Ricardo is expressed in various forms of Spheno- 

 phalos and Ilingoccros. The hipparions of the Rattlesnake and Thou- 

 sand Creek are apparently a more advanced stage than those of 

 Ricardo, and incline toward the Neohipparion rather than the Hip- 

 pariou type. 



If, as seems necessary, the Idaho fauna be included in the Pliocene, 

 it must be considered as representing a much later epoch than any 

 of the other Great Basin stages. The presence of Equus and Cervus 

 and the absence of Pliohippus indicate a stage verging on the Pleis- 

 tocene. 



The three Pliocene stages of the Great Basin province may be 



arranged as follows : 



Idaho Equus-Cervus? zone 



Thousand Creek-Kattlesnake Sphenophalos-Neohipparion zone 



Bieardo Hipparion-Meryeodus zone 



Great Plains Province 



In the Tertiary deposits of the Great Plains region a much larger 

 representation of the Pliocene mammal fauna is found than has been 

 thus far secured in the provinces west of the Rocky Mountains. Two 

 or three occurrences of unusual importance are known and at least two 

 faunal stages are distinguished. 



The Blanco fauna described by Cope 14 from Texas is the most 

 advanced of the well known Great Plains faunas, and the stratigraphic 

 relations of the beds so far as known indicate Pliocene age. 



The list of forms in the Blanco fauna is as follows : 



Blanco Fauna 



Carnivora 



Borophagus diversidens Cope 

 f Amphicyon, sp. 

 Canimartes cumminsi Cope 

 Felis hillanus Cope 



n Cope, E. D., A preliminary report on the vertebrate palaeontology of the 

 Llano Estaeado, 4th Ann. Eep. Texas Geol. Surv., 136 pp., 23 pis., 1893. 



