ON BRITISH FOSSIL MAMMALIA. 231 
as a synonym of the species which he subsequently described under the 
name of Equus asinus primigenius*. 
Amongst the numerous teeth of a species of Equus, as large as a horse 
fourteen and a half hands high, collected from the Oreston cavernous fissures, 
I have found specimens clearly indicating two distinct species, so far as spe- 
cific differences may be founded on well-marked modifications of the teeth. 
One of these, like the ordinary Equus fossilis of the drift and pleistocene 
formations, most resembles the existing Hguus caballus in its dental cha- 
racters; the other, in the more complex and elegant plication of the enamel, 
and in the bilobed posterior termination of the grinding surface of the last 
upper molar, more closely approximates the extinct Horse of the miocene 
period which H. v. Meyer has characterized under the name of the Equus 
caballus primigeniust. The Oreston remains differ, however, from this in the 
form of the fifth or internal prism of dentine in the upper molars, and in its 
continuation with the second anterior prism; the fifth prism being oval and 
insulated in the Equus primigenius of V. Meyer. 
The Oreston fossil teeth, which in their principal characters manifest so 
close a relationship with the miocene Equus primigenius, differ like the 
later drift species (4g. fossilis) from the recent Horse, in a greater propor- 
tional antero-posterior diameter of the crown of the second upper molar, and 
also in a less produced anterior angle of the first molar. In neither of the 
fossil species is the entire tooth so much curved as in the extinct Hguus cur- 
videns, nob., the contemporary of the Megatherium in South America. 
The more common species of fossil Horse from the drift formations and 
ossiferous caverns, which differs from the existing domestic Horse in its 
larger proportional head and jaws, resembling in that respect the Wild Horse, 
but apparently differing in the transversely narrower form of certain molar 
teeth, may continue to be conveniently indicated by the name of Eguus 
Jossilis, as Cuvier’s “ cheval fossile” has been translated by M. H. v. Meyert. 
Of this species, the largest bone of an extremity which I have seen, is a se- 
cond phalanx from the upper pliocene deposits at Walton-on-Naze, Essex, 
where it was discovered by Mr. Brown of Stanway; it measures 2 inches 8 
lines in extreme breadth, and 2 inches 4 lines in length. The correspond- 
ing bones from Oreston are smaller. 
The contemporary but distinct species, indicated by the teeth above de- 
scribed from the Oreston caverns, I propose to name Eguus plicidens, on 
account of the characteristic plications of the enamel-island in the centre of 
the molar teeth. I have not yet seen any teeth from British strata having 
the well-marked characters of those of the Equus caballus primigenius of 
M. H. v. Meyer; but the teeth of the extinct slender-legged Horse, trans- 
mitted by Capt. Cautley to the British Museum, are identical with those of 
the above species from the European miocene. 
Tn the more recent or diluvial formations, a fossil species of Equus, smaller 
than any of the preceding, and about the size of the Wild Ass, is indicated 
by molar teeth. Of these I may cite a middle molar of the left side of the 
upper jaw, from the drift overlying the London clay at Chatham; a corre- 
Pine molar from the opposite side of the upper jaw, from the drift at 
esslingland in Suffolk ; and a fifth molar, left side of lower jaw, from a ca- 
vernous fissure at Oreston: all these teeth were in the same fossilized con- 
dition as the associated remains of extinct Mammals with which they had 
clearly been contemporaneous. If we admit the subgeneric separation of those 
species of the genus Hguus, Cuv., that have callosities on the fore-legs only, 
the tail furnished with a terminal brush of long hair, and a longitudinal dor- 
sal line, the last indicated fossil species may be named Asinus fossilis. 
* Palzologica, p. 80. { Nova Acta Acad. Nat. Curios. tom. xvi. p. 448. 
{ Palzologica, p. 79. 
