82 
Records of the Geological Survey of India. 
[vol. x. 
PEEISSODACTYLA. 
Hippotherium theobaldi, nobis, 
olim : Sivalhippus. 
In tbe last number of the “ Becords” (p. 31) I described a maxilla of a species of horse 
from the Siwaliks, which I then thought necessary to refer to a new genus, and for which 
I accordingly proposed the name of Sivalhippus; I now find that the specimen must probably 
be referred to Hippotherium, though it presents certain abnormalities which will perhaps 
subsequently render it necessary to make it sub-generieally distinct, in which case the term 
Sivalliippus may be retained for the sub-genus. 
In referring the specimen to a new genus, I was led to believe that the four protruded 
teeth belonged to the premolar series, in which case they would be exceedingly different from 
those of Hippotherium; I now find, after removing some more matrix, that the teeth 
must belong to the milk-molar series, in which case they are like those of Hippotherium in 
form, though they differ in the rate of succession. 
I was led to consider the four teeth as premolars and not milk-molars, because they have 
only just come into wear, and yet behind them there is the alveolus of a fifth tooth, which 
must have been protruded from the jaw; now, in other horses, this fifth tooth, or first true 
molar, would not have pierced the jaw until the milk-molars had been considerably worn 
down, and until their vertical successors were visible in the jaw above them, which is not the 
case in the present specimen ; on the supposition, however, that the visible teeth are premo¬ 
lars, the first molar must have been more worn than they, and must have left a disc of 
pressure against the last of the first series. I now find after further clearing, that the last 
protruded tooth of the specimen does not exhibit any disc of pressure behind, and that, conse¬ 
quently, the fifth tooth, or first molar, could not have been in use, but had merely cut the 
gum; this tooth was therefore newer than the first four teeth, which must consequently be 
milk-molars, and not premolars as at first supposed. 
From the above explanation it will be evident that this species of Hippotherium differs 
from the true Horses, and, as iar as I can gather, from other species of the genus, by the 
unusually early period at which the first true molar appears,—almost as soon as the milk- 
molars are touched by wear and before their vertical successors have shewn in the maxilla. 
In the genus Equus the first true molar does not appear until between the eleventh and 
thirteenth month, when the milk-molars have been greatly worn down, and when their roots 
have been to a great extent absorbed by the premolars. 
The teeth of the present specimen are too large to belong to the milk dentition of H. 
antilopinum, but they may probably be referred to the larger Siwalik species, which H. von 
Meyer identified with the European H. gracile, but which I have found, as already stated 
in my last paper, to differ somewhat from the European species in the form of its upper 
permanent molar series ; this larger species will, therefore, now be known as II. theobaldi. 
The rate of succession of the dental series, together with the unusually large size of th 0 
lachrymal depression in the adolescent maxilla, sufficiently distinguish the species from the 
European H. gracile. The Indian Museum also possesses specimens of the first median 
phalange of the foot of this species, which is extremely different from tlio corresponding 
bone in the European species, or in the smaller Indian H. antilopinum ; there is, therefore, 
no doubt of the very aberrant nature of the larger Indian species, though from the resem¬ 
blance of its upper molars to those of typical forms, I think it best for the present to retain 
it in the genus Hippotherium, and to drop the proposed name of Sivalliippus; the question 
will be more fully discussed ou a subsequent occasion. 
