566 
PROFESSOR OWEN ON FOSSIL REMAINS OF EQUINES 
versidens. I now proceed to the description of some fossil Equine upper molars which 
show a curvature exceeding as much that in Equus curvidens (Plate LXII. fig. 16) as 
do the teeth in that species as compared with the upper molars of the Horse or Ass. 
The teeth of Equus arcidens (Plate LXII. figs. 3 & 7) compete in this respect with those 
of the extinct South- American pachyderm for which the term Toxodon was devised to 
express that character ; and it may be remarked that both Toxodon and Nesodon resemble 
Equus in the great length of the crown of the grinding-teeth before the development of 
any roots, if such occur at any age in Toxodon . 
The following are the circumstances under which I became cognizant of the present 
remarkable extinct species of South- American Horse. 
I received from Her Britannic Majesty’s Minister at Monte Video a letter of the date 
of May 29th, 1867, referring to the discovery of some fossil mammalian remains and 
their transmission to the British Museum, in which the Hon. Mr. Lettsom writes, 
“ Since that case was packed I have received four more teeth from the spot where the 
remains in Boxes 2 and 3 were met with, viz. the * Arroyo Gutierrez.”’ 
This 4 Arroyo’ is a brook falling into the 4 Arroyo Negro;’ and the spot where the teeth 
and other fossils were found is ten leagues south of Paysandi, in the Republic of Monte 
Video. 
The other fossils referred to are parts of a Megathere and Glyptodon. The 4 four 
teeth ’ subsequently received by Mr. Lettsom and transmitted to the British Museum 
(Plate LXII. figs. 1-8) present a character of the grinding-surface having a general 
conformity to that in the Equus neogceus (fig. 9) and Equus principalis (fig. 10) of 
Lund. Assuming those Brazilian cave-fossil teeth also to have participated with the 
present ones from the Megatherian deposits of Monte Video in the degree of curvature, 
they may well indicate a section of extinct Equines having affinities, in the direction hinted 
at by the acute Danish naturalist, to certain more singular extinct American forms of 
Ungulates. Both the present and the Brazilian species above cited differ in a marked 
and unmistakable degree, in the pattern of the grinding-surface of the upper molars 
(as doubtless also of the lower ones), from Equus curvidens , Equus conversidens, Equus 
tau, as well as from Equus macrognathus (Weddell) (Plate LXII. fig. 11) and Equus 
Devillei* (Gervais), represented by figures (unfortunately of half the natural size) in 
* Of Equus Devillei, Gerv. (op. cit. pi. vii. fig. 11), Professor Gervais appears not to have received any upper 
molars : he records that, whereas the lower molar series of E. macrognathus (ib. fig. 4) has a longitudinal ex- 
tent of 0-195“ (=7" 7"'), that of E. Devillei only gives 0-160“ (=6" 4'") — and that they have a rather different 
disposition of the internal enamel-fold (of the lower molars), which seems from the figure (copied in fig. 17, 
Plate LXII.) to be less deep and less expanded in the antero-posterior direction than in E. macrognathus. In 
this respect both species, and a fortiori Equus Devillei, differ from E. tau. With respect to the “ Eq. curvidens 
de Buenos Ayres,” cited by M. Gervais (op. cit. p. 34), I may remark that, as yet, I have not received any 
evidence of that extinct species of Horse from the Province of Buenos Ayres. The specimens on which the 
species was founded were obtained at Bajada de Santa Fe, in the Province of Entre Rios, and at Bahia Blanca, 
on the confines of Northern Patagonia. The species from Buenos Ayres so called by Burmeister (op. cit. 
1867) has upper molars more resembling those of Equus principalis, Ld., and of E. arcidens, Ow. 
