288 University of California Publications in Geology [Vol. 12 



A comparison of these five interesting and somewhat similar faunas 

 of the Eden, Rattlesnake, Chanac-Etchegoin, Thousand Creek, and 

 advanced stage of the Snake Creek shows: {!) Prosthennops. The 

 Eden species is more progressive than the Snake Creek, and perhaps 

 less so than the Thousand Creek, while a larger peccary species from 

 the Eden, more closely resembling Platygonus, suggests a similar 

 form known only from the Blanco. (2) Procamelus and Pliauchenia. 

 Pliauchenia merriami of the Eden is of more advanced type than any 

 of the evidently earlier Snake Creek camels, which alone are repre- 

 sented in a manner sufficient for comparison. (3) Prohoscidea. Re- 

 mains occur in all four horizons, but the material is too scanty for 

 fixed reference. (4) The twisted-horn division of the Antelopinae. 

 Represented in the Thousand Creek and suggested in the Rattlesnake, 

 this is absent from the Snake Creek as from the Etchegoin-Chanac and 

 the Eden. (5) Ehinocerotidae. The Rhinoceroses are as yet unknown 

 from the Eden alone of these mid-Pliocene horizons, though likewise 

 unrecognized in the earlier Ricardo where their presence would be 

 expected. (6) An important difference in the Eden in comparison 

 to these other formations occurs in the absence of Hipparion. (7) 

 Pliohippus. Species are present in all four formations. Among the 

 Eden Pliohippus forms there is one that greatly resembles P. spectans 

 of the Rattlesnake ; another of more advanced equine characters than 

 any occurring in the four former horizons; while the Pliohippus 

 mirahilis type of the Snake Creek and of the Ricardo and the P. fair- 

 hanslii of the Ricardo, Rattlesnake, and perhaps of the Etchegoin and 

 Chanac, are not represented. This presence of an advanced and inter- 

 esting form of Pliohippus among more generalized Pliohippus types, 

 such as P. spectans, and the ab.sence of more primitive equine forms 

 is taken to indicate a relative lateness in the Eden fauna. It is on 

 these advanced characters of the Pliohippus forms, the added evidence 

 of a later stage suggested through the absence of Hipparion, and the 

 general progressive characters of the fauna as a whole that the writer 

 has proposed the correlation of the Eden fauna with those of other 

 Pliocene horizons shown in attached table, in which the correlation of 

 the Ricardo, Etchegoin and Chanac, Rattlesnake, and Snake Creek 

 follows that already proposed by Professor Merriam. 



San Timoteo. — The horses of the overlying San Timoteo, as 

 described and discussed at length in the text, are perhaps more 

 like Pliohippus cumminsii and Pliohippus simplicidens (Cope) of 

 the Blanco, which are unfortunately but poorly represented for 



