356 THE CANADIAN NATURALIST. [Sept. 



the Horse-kind, the requisite and much-needed basis of compari- 

 son for the determination of other fossils of the Solidunj^ulate 

 group, and he devotes the present paper to the elucidation of 

 those which have reached him from Central and South America. 



" In a subsequent paper be commences by referring to the type- 

 specimens of teeth, from two localities in South America, on which 

 he founded the species E. curvidens, describing it (in 184-0) ' as 

 one co-existing with the Megatherium, Toxodon, &c., in that 

 continent, and which had become extinct at a pre-historic period.' 



" He then proceeds to describe more complete evidences of the 

 dentition of an allied extinct Horse discovered by Don Antonio 

 del Castillo, mining engineer, in newer Tertiary deposits of the 

 Valley of Mexico. Besides repeating the originally described 

 characters of the curvature of the grinder with a certain resem" 

 blance of enamel-pattern to the grinding-surface of the E. curvi- 

 dens, they show a greater degree of curvature of tbe alveolar 

 series of the upper jaw, with corresponding greater convergence 

 of the right and left molar series toward the fore part of the 

 palate, than in any previously described species of Equus. 



" Deciduous teeth of the Equus conversidens from the same 

 deposits of the Valley of Mexico are described. Having deter- 

 mined these corroborative and distinctive characters of aboriginal 

 and now extinct American horses, the author remarks, ' It is 

 unlikely, seeing the avidity with which the Indians of the Pampag 

 have seized and subjugated the stray descendants of the European 

 horses introduced by the Spanish ' Conquistadors ' of South 

 America, and the able use the nomad natives make of the multi- 

 tudinous progeny of those war-horses at the present day, that any 

 such tameable Equine should have been killed off or extirpated by 

 the ancestors of the South-American aborigines.' If, therefore, 

 the fossil Equine teeth do belong, as the author deems that he 

 has proved, to a species distinct from Equus caballus, Linn., 

 the circumstances of their discovery, and the fact of the extinc- 

 tion of such (curvident and conversident) species of Horse would 

 point to some other cause than that of man's hostility to so 

 useful an animal, and such doubt as to extinction by human 

 means may then be extended to the contemporaries of the Equus 

 curvidens and E. conversidens, viz , Megatherium, Mylodon, 

 Toxodon, Nesodon, Macrauchenia, Gli/ptrjdon, Mastodon, &c.' 



" The author next proceeds to describe fossil teeth from the 

 upper and lower jaw, discovered by Don A. del Castillo in the 



