20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 28 



directed toward metaconule. Protoconule present but may be weak. 

 In lower molars anterior crest of hypoconid directed toward poste- 

 rior crest of protoconid, and lingual cusps of these teeth with 



prominent styles Eocene AGRIOCHOERIDAE 



(i) Snout not elongate. Canine above and Pi not greatly enlarged. 

 Primary cusp of P* may be twinned. Early forms somewhat 



bunodont but increasingly crescentic in time Protoreodon 



(2) Snout elongate and very broad between the much enlarged canines. 

 Primary cusp of P^ with lingual ridges but not twinned. Upper 



molars transversely broad and not high crested Diplobimops 



c. Upper molars with prominent ribs and styles externally and highly 

 crescentic lingual cusps. Posterior crest of protocone directed lat- 

 erally toward valley between paracone and metacone. Lingual styles 

 of lower molars subdued, but outer cusps highly crescentic, with 

 anterior crest of hypoconid directed lingually toward saddle between 



metaconid and entoconid Leptotragulinae 



(i) P^ and P^ with prominent tritocone. P3 and P4 with posterolin- 

 gually directed crest from apex or near apex of protoconid and 

 well-developed parastylid Leptotragulus 



(2) P^ and P' with weak or no tritocone. P3 and P* with prominent 



metastylid and usually prominent entoconid, but parastylid not 

 separately defined Leptoreodon 



(3) Lower premolars and molars distinctly hypsodont. Metaconid of 



P4 weak though distinct (upper teeth not known) . . .Poabromylus 



Pi is caniniform : AGRIOCHOERIDAE, HYPERTRAGULIDAE, and LEP- 

 TOMERYCIDAE. 



Pi and lower C approximately equal: Homacodontinae (as far as known), 

 OROMERYCIDAE (except Eotylopus), and PoitBROXHERiiNAE. 



Lower C is caniniform: Helohyinae (not verified for Helohyus). 



Upper molars with posterior crest of protocone directed toward hypocone: 

 AGRIOCHOERIDAE and Simimeryx. 



Upper molars with posterior crest of protocone bilobed or bifurcate: ORO- 

 MERYCIDAE, 



Upper molars with posterior crest of protocone directed toward valley between 

 paracone and metacone: Poebrotheriinae and LEPTOMERYCIDAE. 



Protocone of upper molars essentially conical : Homacodontinae, Helohyinae, 

 and Diacodexinae. 



Upper molars with mesostyle distinct : Bunomeryx, Pentacemylus, Mytono- 

 meryx, LEPTOMERYCIDAE, AGRIOCHOERIDAE, OROMERYCI- 

 DAE, and CAMELIDAE. 



Upper molars with mesostyle very weak : Hylomeryx and Antiacodon. 



Upper molars without mesostyle : Homacodon, Mesomeryx, Microsus, Diaco- 

 dexinae, Helohyinae, and HYPERTRAGULIDAE. 



Upper molars with hypocone on M* and M^: Homacodon, Microsus, Antiacodon, 

 Hylomeryx, Mytonomeryx, and Bunophorusf. 



Upper molars with hypocone on M* only (vestige or absent on M^) : Bunomeryx. 



Upper molars without hypocone (vestige or absent on M*) : Mesomeryx, Penta- 

 cemylus, Helohyinae (very small cingular cusp in Helohyus), Diacodexis, 



