1 I 8 Bulletin American Museum of Natural History. [Vol. XIV, 



of E. caballus; (2) the occipital region seems to be narrower 

 transversely, and the muzzle, judging from the front portions of 

 lower jaws in the collection, seems to be proportionally shorter. 



(12) Equus conversidens Oiven. 



Type Locality. — Valley of Mexico. 



Type. — A portion of the upper jaw of the right side containing the full 

 molar-premolar series. . 



Authors description. — In describing the specimens to which he gave the 

 name E. conversidens, Owen considered the following to be the distinguishing 

 characters: They correspond closely in "size, curvature, and pattern of the 

 grinding-surface of the upper molar teeth, with Equus curvidevs. . . . 

 There is " a curved convergence of the two series of upper grinders towards the 

 fore part of the palate to a degree exceeding that in other Equines. 

 The last molar, m-, is relatively smaller than in any old-world Equines. 

 The first premolar, p-, resembles in the minor production of the anterior lobe 

 that tooth in Eqiius asiniis, Equus quagga, and differs in this respect from E- 

 caballus. The grinding-surface, however, retains, as in Equus aff. caballo, Ld., 

 and in E. curvidens, the general conformity of character of enamel-folding so 

 remarkable in all the modern and in the European Pleistocene Equine species 

 hitherto described. . . . But the most distinctive character of the upper 

 grinders of E. conversidens is their disposition in the jaw, denoted by the 

 nomen triviale of the extinct Mexican horse ; and to the character of the curva- 

 ture of the molar series of alveoli may be inferentially added a concomitant 

 modification of the shape of the upper jaw itself, involving that of the lower 

 one." 



Measurements. 



8 j Antero-posterior diameter 30 m 



( Transverse " 25 ' 



3 j Antero-posterior " 25 ' 



' Transverse " 25 ' 



■^ J Antero-posterior " 22 ' 



( Transverse " 21 ' 



3 j Antero-posterior " 19 ' 



( Transverse " 18 ' 



The principal character upon which Owen based this species is 

 undoubtedly an unnatural feature, not, however, due to distortion, 

 as suggested by Cope,' but rather to a placing together of upper 

 jaws of opposite sides of two different individuals. The writer 

 was led to this conclusion by a careful comparison of the corre- 

 sponding teeth of the opposite sides as shown in Owen's figure of 

 his type specimen. (S ee Plate XXI, which is a reproduction from 



' Proc. Am. Phil. Soc, 1884, p. 13. 



