1887.] ^"^^ t^oP^- 



A A. Molars with cross-crests (Listriodontoidea). 



Premolars differeut from molars Listriodontidw.. 



AAA. Molars selenodont (with four crescents above). 

 a. Inferior molars with one series of crescents (Merycopotamoi- 

 dea). 



Premolars unlike molars Merycopotcmiid^. 



aa. Inferior molars with two series of crescents. 

 • /?. Superior premolars (except premolar four) with one crest 

 (Cameloidea). 

 y. "Fourth premolar like molars below, with three crests 

 above." 



Two digits only (four? in Agriochcerus) Dicliodontida. 



yy. Fourth premolar entirely different from molars. 

 d. Navicular and cuboid bones distinct from each other. 

 £. Superior incisors present. 



No cannon bone ; a vertebrarterial canal Oreodontidai. 



No vertebrarterial canal ; no cannon bone PoebrotheriidcB. 



No vertebrarterial canal ; a cannon bone Protolahidida,. 



es. No superior incisors (except incisor three). 

 No vertebrarterial canal ; a cannon bone ; superior p. m. iv with external 



and internal crests Camelidw. 



Like Camelidse, but superior p. m. iv a simple cone Eschatiidce. 



80. Navicular and cuboid bones coossifled. 



All premolars but No. iv without internal crescent Tragulidw. 



[il3. Superior premolars 2-3-4 with internal as well as external 

 crest ; a naviculocuboid bone ; no superior incisors 

 (Booidea). 



Superior p. m. ii without internal crescent Mosclddcc. 



Superior p. m. ii with internal crescent. 



Horns permanent, originating distinct from skull Giraffidos. 



Horns permanent, processes of the skull Bovidm. 



Horns periodically shed Cervidm. 



Of the preceding sixteen families, ten are extinct. The six families 

 with living representatives are the Suidae, the Tragulidte, the CamelidiB, 

 the Moschidai, the Cervidae, the GirafHdae and the Bovidoe.* Thus none 

 of the primary divisions, I and II, have recent representatives. But few 

 of them in fact (some Cienolheriidae and Anthracotheriidic) survived the 

 Eocene epoch. Division III is, on the other hand, characteristic of Mio- 

 cene and recent time, except that some specimens of Gelocus of the Tragu- 

 lidse have been found in Upper Eocene beds. Several genera of Tragulidoe, 



* Antilocapra is sometimes separated from the Bovida; as the type of a family, because 

 it is said t« sometimes shed its horny horn-sheath. This character, were it really nor- 

 mal, has no significance sufficient for the establishment of a family division. 



