1917] Mcrriam: Pliocene Mammalian Faunas 433 



of Caldwell, the bottom of the section furnished material representing 

 a very advanced equine form not distinguished from Equus 

 on the basis of size or of advance in specialization of feet and teeth. 

 This species does not seem to the writer specifically identical with any 

 thus far described in America. It differs from the Pliohippus pro- 

 versus type of the upper Etchegoin Pliocene in the typical equine 

 character of the upper cheek-teeth, as shown by the inner wall of the 

 protocone, the fossettes, and the outer walls of the paracone and meta- 

 cone ; so that it must be included within the genus Equus. On the 

 other hand, it differs from the described Pleistocene forms of Equus 

 in the shorter protocone, which approaches the type of pillar in Equus 

 stenonis of the Old World Pliocene. 



A rhinoceros from exposures considered as Idaho, east of Boise, 

 was referred to Aph clops (Teleoceras) fossigcr. This form represents 

 the late Miocene or Pliocene. Mastodon, mirificus determined by Leidy 

 from a specimen obtained by Clarence King on Sinker Creek is a 

 Pliocene type. The remains of Procamelus might be Miocene or Plio- 

 cene. Horn-cores of antelopes, obtained with rhinoceros material near 

 Boise, represent a Tragocerus-like type known in America only from 

 beds of Pliocene age. Castor is known from the upper Etchegoin of 

 the western border of the San Joaquin Valley in California. A very 

 large machaerodont cat found in an Idaho exposure on the Snake 

 River southwest of Caldwell belongs to a type nearest to Ischyrosmilus, 

 presumed to represent the Tulare stage in Calfornia. 



With our available knowledge of the mammalian fauna of the 

 Idaho, determination of this formation as Pliocene is apparently 

 supported, but beds both older and younger than Pliocene may be 

 included in the localities from which material has been secured. It 

 is highly desirable to have careful collecting work carried on by 

 trained investigators in the bad-land deposits over the entire area 

 presumed to represent the Idaho formation. 



Compared with other faunal assemblages referred to the Pliocene 

 of the Great Basin province, the Idaho fauna of the best known 

 locality in the Snake River region exhibits a relatively advanced stage. 

 The horses find their nearest relatives in the Pleistocene and in the 

 Pliohippus proversus zone of the Upper Etchegoin Pliocene. The 

 deer of the Idaho are possibly related to those of the Upper Etchegoin. 

 The cat is nearest to the ?Tulare Ischyrosmilus. The Idaho stage is 

 evidently later than any other described Pliocene faunal zone of the 

 Great Basin province. 



