18S6.] 3D J [Cope. 



For comparison with this specimen I have used five crania of A. equiceps, 

 and one of A. prmtans and A. longicriste each, besides numerous frag- 

 mentary jaws. 



It was found by Mr. J. L. "Wortman in the Ticholeptus beds of Cotton- 

 wood creek, Oregon. 



I give here a list of the species obtained with this one at the locality in 

 question : 



ProtoMppus, 1 sp. Dicotyles condoni Marsh. 



Ilippotherium seversum Cope. Protolabis transmontanus Cope. 



" sindairi Wortman. Merycochcerus obliquidens Cope. 



" occidentale Leidy. Blastomeryx borealis Cope. 



AncMtherium ultimum, Cope. 



The species of the Ticholeptus beds of Montana are the following : 



Mastodon proavus Cope. Cyclopidius emydinus Cope. 



ProtoMppus sejunctus Cope. Pithecistes brevifacies* Cope. 

 Merycoclmrus montanus Cope. " decedens Cope. 



Merychyus zygomaticus Cope. " heterodon Cope. 



" pariogonus Cope. Procamelus vel Protolabis, sp. 



Cyclopidius simus Cope. Blastomeryx borealis Cope. 



This horizon is interesting as that in which the genus Mastodon makes 

 its first appearance in America. It is now shown to be the last which con- 

 tains the genus Anchitherium. See Final Report United States Geologi- 

 cal Survey Territories, Vol. iii, p. 18, where some of the characters of this 

 fauna are pointed out. In the list of the Deep River fauna above given 

 occurs the name 



Merycochcerus obliquidens Cope. 



This is a species hitherto undescribed, which approaches those of Mery- 

 chyus in some respects. As it is established on a mandibular ramus only, 

 although this is nearly entire, it cannot be positively decided to which 

 genus it should be referred, as the generic character is only seen in the 

 presence or absence of lachrymal vacuities. However, in all the species 

 of Merychyus, where the parts are preserved, M. elegans, M. arcnarum, 

 and M. zygomaticus, the first inferior premolar is one-rooted, while in the 

 species of Merycochcerus it has two roots. In the present animal there are 

 two roots. The symphyseal region is very much contracted, so that 

 if there were three inferior incisors they were small. 



This species is smaller than any known species of Merycochcerus, about 



*The absence of caries in the teeth of extinct Mammalia is well known. The 

 type specimen of the Pithecistes brevifacies, however, displays a carious excava- 

 tion on the external side of one of its inferior molars. This feature adds to 

 those which indicate the degeneracy and approaching extinction of this type, 

 as I have remarked in my synopsis of the Oreodontidse, Proceedings American 

 Philosophical Society, 1884, 557. 



