14 Envin H. Barbour 



feet. The opposite is true of the later equines. The ancestral 

 horses fall into four groups, each including its quota of genera. 

 The fossil horses are assembled under the divisions : ( i ) Hyraco- 

 theres ; (2) Anchitheres (3) Protohippines ; and' (4) Equines, the 

 later horses. 



Ancestral horses had cementless, short-crowned, brachydont 

 teeth, while later members of the branch had partly cemented 

 crowns of considerable length, sub-hypsodont ; and the more recent 

 members had very long, cemented crowns, hypsodont teeth. 



It is an interesting fact that in the same bed with Hypohippus 

 matthezui, simple and complex, short-crawned, and long-crowned 

 teeth were found intermingled. This emphasizes the fact that the 

 old and less advanced forms of equids persisted and mingled with 

 the new and more advanced types. 



In Anchithcrinm, Mesohippiis, Hypohippus, and closely related 

 forms, the transverse crests of the teeth are generally distinct and 

 perfect. In Hypohippus matthezci, the metaloph is continuous 

 w^ith the ectoloph. This cross crest runs obliquely forward, then 

 obliquely backward and meets the ectoloph at the mesostyle. The 

 styles are well developed, and the parastyle is bold and strong. 

 The fosettes are very deep, and the bounding walls nearly vertical. 

 The protoloph runs obliquely forward and outward by a sigmoid 

 curve to the anterior border of the tooth. It is entirely discon- 

 nected from the ectoloph in the premolars, but gradually becomes 

 more connected in the first molar. The teeth are fully adult, 

 though not old, with the outer crest and cross crests worn. The 

 teeth, especially those of the left side, show pronounced cement 

 reinforcement half way up the crown, and all are etched by 

 " Daimonelix fibers." 



Measurements of the teeth of Hypophippus ]\Iatthewi : 

 Pm I. Missing. Represented by an alveolar scar and root. 

 Pm 2. Antero-posterior diameter along outer border, 38 mm. 



Diameter tlirough hypoconule to front of tooth, 31 mm. 



Greatest transverse diameter, 36 mm. 



Extreme height of crown, 30 mm. 

 Pm 3. Antero-posterior diameter along outer border, 37 mm. 



Diameter through hypoconule to front of tooth, s~ mrn- 



Greatest transverse diameter, 41 mm. 

 198 



