Io6 Bulletin American Museum of Natural History. [Vol. XIV, 



account has been taken of it, is more constant in a species than 

 any other tooth character hitherto used. 



If the foregoing interpretation of the tooth characters of the 

 genus Eqicus is correct, it seems evident that the synopses for a 

 determination of the species given by Cope have very little value, 

 and no dependence can be placed on them. For convenience of 

 reference one of these synoptic tables is given below.' 



" I. Long diameter of anterior internal lobe of sup. molars not greater than 

 one-third the long diameter of the crown. 

 " Borders of lakes crenate ; internal anterior lobe notched on the inner side so 



as to be bilobate ; crowns a little curved ; large E. crenidens. 



"II. Long diameter of anterior internal lobe more than one-third and not 

 more than one-half the antero-posterior diameter of the crown. 



a Crowns more or less curved. 

 " Crowns wider than, or as wide as, long ; enamel edges little folded. 



E. curvidens. 

 a a Crowns straight or nearly so. 

 ft Diastemata longer. 

 " Crowns nearly square, enamel not very complex ; no facial fossa ; maxillary 



bone produced much beyond m- E. caballus. 



ft ft Diastemata shorter. 

 T No facial fossa. 

 " Crowns nearly square ; enamel not very complex ; maxillary bone little pro- 

 duced behind last molar ; smaller. 



E. hefuionus ; E. hurchelli ; £. qitagga ; E. zebra ; and E. asinus. 

 " Crowns longer than wide on face ; enamel little complicated ; face and max- 



illar}' unknown ; large E. occidentalis. 



" Crowns square ; enamel more folded than in other species ; face and max- 

 illary unknown ; large E. major. 



T A facial fossa. 

 "Crowns nearly square; enamel less complex; maxillary short posteriorly; 



smaller. E. audi tun. 



" III. Long diameter of anterior inner lobe more than half that of crown 

 of molar teeth. 

 " Crowns square; enamel little complex (in Mexican specimens) ; diastemata 



and maxillary behind shorter ; no facial fossa ; large E. excelsus. 



" Crowns square ; enamel little complex ; smallest species E. harcenai." 



The synopsis written by Cope and published in the Journal of 

 the Acad. Nat, Sci., Phila., 1899, Vol. XI, part ii, p. 255, 

 seems likewise to have no standing. 



' Proc. Am. Phil. Soc, Vol. XXII, 1S84, p. 10. 



