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XVII. On Fossil Remains of Equines from Central and South America referable to 
Equus eonversidens, Ow., Equus tau, Ow., and Equus arcidens, Ow. By Pro- 
fessor Owen, F.R.S. &c. 
Received November 17, 1868, — Read February 4, 1869. 
Having examined the dental characters of existing species of the Horse-kind so far as 
seemed requisite for the determination of the Equine remains found in the Cavern of 
Bruniquel*, I have been enabled, on the same basis of comparison, to deal with other 
Equine fossils, and propose to communicate in the present Paper the results of this 
labour in elucidation of those which have reached me from some American localities. 
In the account of the Mammalian Remains brought from South America in the ‘Voyage 
of the Beagle,’ I described and figured an upper molar tooth as belonging to a species 
of Equusf ; and this tooth, having been found by Mr. Darwin imbedded in the quartz 
shingle of cemented pebbles at Punta Alta in Bahia Blanca, together with remains of 
Megatherium, Megalonyx, Mylodon, and Scelidotherium, I concluded not to be a tooth 
of a horse imported by Europeans into South America, but to have belonged to an Equine 
species which had coexisted with those large Megatherioids and had, with them, become 
extinct a prehistoric period. An Equine upper molar tooth of similar pattern, included 
in the collection of fossils from the same ‘ Voyage,’ was labelled as having been found 
in red argillaceous (postpliocene V) deposits at. Santa Fe, in the province of Entre Rios, 
Buenos Ayres and this tooth being associated in the series with parts. of Mastodon and 
Toxodon confirmed me in the above conclusion 
In the Monograph of 1840, above quoted, I did not feel, however, that I had sufficient 
grounds for differentiating the species to which the two detached fossil teeth had be- 
longed from Equus caballus , the upper molars of which seemed to differ from the fossils 
chiefly in a slight superiority of size, with some seemingly unimportant modifications of 
the complex but characteristically Equine enamel-folds. 
But improved practice and attention to detail in the course of my work on ‘ Odonto- 
graphy ’ led me to appreciate the value of the latter indications, and to note a greater 
degree of curvature of the entire tooth, and also a greater relative antero-posterior dia- 
meter of the crown as compared with Equus caballus. I accordingly pointed out the 
distinctive character of these teeth as those of Equus curvidens in that work § ; and I 
entered the specimens, Nos. 1030 & 1031, as of an Equus curvidens in my ‘Catalogue 
* Ante, pp. 535-557. 
t The Zoology of the Voyage of H.M.S. ‘ Beagle,’ pt. i. Fossil Mammalia, 4to, 1840, p. 108, pi. xxxii. fig. 13. 
t Tom. cit. p. 109. § Odontography, p. 575 (1842). 
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