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

 camel tribe, in ascending geological order. A, \Protijlopus petersoni, Uinta Eocene. 

 B, ]Poebrotheriumwilsoni,WhiteRiveT. (After Wortman.) C, fProcamelus gracilis, 

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



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