332 H. l'. OSBOKN CLASSIFICATION OF THE MASTODON TOIDEA 



on which it was founded, and can not be applied to the bunomastodont 

 gejiotype of Phiomia, which was founded a year later by the same author. 

 There is no question as to the absolute phyletic distinction between these 

 two animals, but until the cutting teeth of Palceomastodon ^ headnelU are 

 known we can not be sure that this animal is directly ancestral to the 

 Mastodontidee, as would appear. 



Schlesinger has added several very important examples of true masto- 

 dons from the Lower and Middle Pliocene of Hungary, to which he gives 

 the name M. tapiroides americanus^ The first appearance of the true 

 mastodon in North America is in the Snake Creek formation. Lower 

 Pliocene of western Nebraska, where a few teeth have been found by the 

 American Museum and Princeton parties, one of which has been selected 

 by Osborn as the type of Mastodon mattheun.^ Its next occurrence is in 

 the Thousand Creek formation of Nevada, Middle Pliocene, represented 

 by two posterior grinding teeth in the collections of the Colorado Museum 

 of Natural History, Denver, and of the University of California, which 

 Osborn has made the type of the species Mastodon meriiami,^ in honor 

 of President Merriam, of the Carnegie Institution. 



These teeth, as well as those of the Low^er Pliocene of Hungary, are 

 readily distinguished from those of M. americanus by their more brachyo- 

 dont character; the crests are low and spreading instead of being tall and 

 narrow. 



Summary 



Eesearch on this group is still in active progress, and from week to 

 week the conclusions both as to phylogeny and as to classification are 

 modified by the discovery of fresh or hitherto undescribed material and 

 by the more careful analysis of the fundamental characters of the differ- 

 ent phyla. 



* Characters examined from an important unpublished memoir bj' Professor Schlesinger, 

 original photographs of which were kindly forwarded to the present author. 



° Amer. Mus. Novitates, No. 10, June 15, 1921. Immediately after the publication of 

 this paper the author learned that the type of Mastodon merriam \ occurred in beds of 

 Middle Miocene age, which makes it geologically older than Mastodon matthewi. 



