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



ter given by Cope as the one by which E. cretiidens could be dis- 

 tinguished, that of the crimping of the enamel of the lakes; the 

 comparatively complex folding of the enamel, all prevent the 

 identification of this tooth with that species. Its grinding-surface 

 is much weathered and the enamel foldings of the lake borders 

 are so obliterated that they cannot be made out and appear to be 

 very simple. This evidently led Cope to the belief, as shown in 

 his figure and description, that the tooth pattern was very simple. 

 A section (Fig. 27 A^) made about three-fourths of an inch below 

 the grinding-surface shows very plainly the true character of the 

 enamel foldings. 



Although in this tooth, as seems characteristic of the genus, 

 there seem to be no characters which can be said to be of 

 definite specific value, its great size, which exceeds by at least 5 

 mm. any other Equus tooth of which record has been made, and 

 the relatively small area of the cement lakes or fossettes mark it 

 as evidently distinct from any species hitherto described; hence 

 a new name seems necessary. The size suggests the name E. 

 giganteus. 



The measurements are as follows: 



■px- . f • J- r ( Antero-posterior 41.5 mm. 



Diameter 01 grinding-surface -I ^ • t j 



( Transverse 36 " 



Diameter where section ( Antero-posterior 40 " 



was made ( Transverse 39 



Length of crown 100 " 



The tooth had evidently been only slightly worn by use, hence 

 the difference in transverse diameter when the cut was made. 

 The length of the tooth compared with its other measurements 

 shows a comparatively short crov/n. 



Summary and Conclusions. 



The general results of this systematic comparison may be 

 summed up as follows: 



E. curvidens. — A South American horse, indeterminate. North 

 American specimens referred to this species erroneously. 



E. major. — Absolutely indeterminate; a nomen tiudum. 



E. americanus. — A preoccupied name, replaced by E. complicatus. 



E. FRATERNUS. — Southeastern United States, probably a valid 

 species, but still imperfectly known. It represents a very 



