Fia. 212. — Diagram to illustrate the development of the skull and molar teeth in the 

 camel tribe, in ascending geological order. A, ^Protylopus petersoni, Uinta Eocene. 

 B, ^Poebrotherium wilsoni. White River. (After Wortman.) C, jProcamelua gracilis, 

 upper Miocene. (After Cope.) D, Lama huanacus, the modern Guanaco. 



^99) 



