of the Genus Stenomylus. 



323 



the typical tylopod contemporaries of the Protomeryx type, 

 fed on a generalized diet, and retained their brachydont den- 

 tition, and while the long-limbed Oxydactylus gronp were 

 feeding on leaves and shrubbery, and likewise retained their 

 brachydont dentition, that there arose another group of upland 

 tylopods which took up the grazing habit, and these developed 

 the hypsodont dentition. These then represent a separate branch 

 of the Tylopoda, which must have had its beginning in the 

 later part of the Oligocene, being derived from Poebrotherium, 

 which genus Stenomylus resembles in most of its characters. 

 This group of tylopods seems to have flourished greatly during 

 the lower Miocene, especially during the Lower Harrison, out- 

 side of which horizon it has not been found. I see no especial 

 affinity to Oxydactylus other than that common to all Tylopoda. 

 The affinities may be graphically indicated as follows : 



Protomeryx 



Middle 

 Miocene 



Alticamelus 



Lower 



Miocene 



Oxydactylus- 



Protomeryx 



Stenomylus 



Upper 

 Oligocene 



Paratylopus 



Middle 

 0] igocene 



Paratylopus 



Poebrotherium 



Poebrotherium 



The Lower Harrison beds then will show three types of 

 Tylopoda, each presumably in a different type of habitat , the 

 Stenomylus in the upland, the Protomeryx near or in the val- 

 leys where a considerable variety of vegetation flourished, and 

 the Oxydactylus in the intermediate country and probably 

 feeding on leaves and twigs of trees. 



Collectors in the Lower and Upper Harrison beds can not 

 but be greatly impressed by the great variety of tylopods which 

 occur in these beds, there being beside the already known spe- 

 cies certainly as many more indicated by the great variety of 

 toe and isolated bones found. The Lower Miocene seems to 

 be the period of especial luxuriant development for all types 

 of camel-like forms. 



Amherst College. 



