30 



OSBORN: OLIGOCENE, MIOCENE, PLIOCENE EQUIDyE. 



Orinda, San Pablo Bay, California, Merriam, 1913. 



The Orinda formation rests upon the Pinole Tuff fauna, which includes an Hipparion species near H. mohavense of 

 the Ricardo (Merriam, letter Sept. 15, 1917). 



Jacalitos, North Coalinga Region, California, Merriam, 1915. 



Within the limits of the beds mapped as Jacalitos (Arnold Anderson, 1910) remains of Pliohippus have been found. 

 Hipparion occurs only in the lowest levels as described by Merriam {Trans. Am. Philos. Soc, 1915, p. 216). 

 Regarded by Merriam as lower Middle Pliocene. 



Type of Hipparion molle Merriam, 1915.2. 



Rattlesnake, John Day Basin, Oregon. 



The type of Platygonus rex Marsh is recorded from Wilson Springs, Crooked River, south of John Day Valley, Ore. 

 (J. C. M.). Among the referred specimens are Pliohippus supremus Leidy, also the type of Alticamelus alius. 



Type of Pliohippus (Hippidium) spectdns Cope, Type of Hipparion (Hippotherium) sinclairi ^Yortman, 



1880. 1882. 



Ilingoceras Zone, Merriam, 1999. 



Typified by the fauna of Thousand Creek, Nevada, called lower Middle Pliocene. 



Thousand Creek, Nevada. 



This horizon is regarded by Merriam and Matthew as more recent than Snake Creek, Ricardo, or nearer Rattlesnake 

 (Merriam, 1916), as earlier than Blanco. Its characteristic strepsicerine antelopes are Ilingoceras, Sphcnophalus. A 

 rhinoceros related to Teleoccras recorded here may give this horizon an earlier date. Beside its referred Pliohippus 

 fairbanksi is found the 



Type of Hipparion leptode Merriam, 1915.3. 



Pliohippus coalingensis Zone. 



Lower Etchegoin, North Coalinga Region, California, Merriam, 1915. 



Merriam observes (Trans. Am. Philos. Soc, 1915, p. 193) that the lower Etchegoin horizon is characterized by the 

 presence of Pliohippus coalingensis and may be known as the Pliohippus coalingensis zone. This faunal zone near the base 

 of the Etchegoin in the North Coalinga region represents a distinctly more ad\ - anced stage than that of the Jacalitos, 

 according to Merriam. It yields the 



Type of Pliohippus (Protokippus) coalingensis Merriam, 1914. 



Glyptotherium Zone, Middle Pliocene. Astian Stage of Europe. 



This well defined life stage is typified by the fauna of the Blanco formation, Llano Estacado, Texas, containing 

 Glyptotherium, Mcgalonyx, Pliauchenia, Platygonus, and Dibclodon mirificus. This zone is probably later than the Lower 

 Etchegoin of North Coalinga (Merriam, 1916). The important equine types are progressive forms of Pliohippus, three 

 of which were originally referred to Equus by Cope, as follows: 



Type of Pliohippus (Equus) cumminsii Cope, 1893.3. Type of Pliohippus (Equus) simplicidens Cope, 1892. 

 " " " (Equus) minutus Cope, 1893.4. 



