80—14 INDIAN TERTIARY AND POST-TERTIARY VERTEBRaTA. 
to such variation in size, 1 that it would seem that this ground of distinction will 
not hold ; and we are, therefore, driven to depend on the characters of the teeth 
themselves. This renders the task of indicating precise specific characters one of 
great difficulty, as there are such extremely insignificant differences between the 
teeth of all the species of the genus. 
Between the four middle upper molars of H. aniilopinum figured here, and 
the corresponding teeth of H. gracile, I cannot find any crucial point of distinction, 
and they might, as far as I can judge, be referred to the same species. Almost the 
only difference seems to be that in the Indian form the anterior s pillar ’ is more com- 
pletely enclosed in the cement, and is hence less conspicuous on the inner surface. 
In the upper milk-molars a few points of difference can he detected between 
the European and Asiatic forms. In the former 2 the plications of the central 
enamel islands are less complex than in the latter ; while the anterior i pillars ’ 
are less completely embraced in the crowns of the teeth in the former. In the 
second milk-molar of H. gracile both the ‘ pillars ’ are connected with the 4 crescents 1 
by isthmuses of dentine, while in the corresponding tooth of H. aniilopinum both 
are completely isolated. Eurther, in the same tooth of the latter there is a distinct 
infold of enamel from the inner side of the produced anterior angle* which is 
entirely wanting in the corresponding tooth of the former. 
The mandible of the Indian form is decidedly more curved interiorly than 
that of the European form. 
It will be seen, therefore, that the points distinguishing H. aniilopinum from 
II. gracile are extremely slight, and it is not improbable that von Meyer’s identifi- 
cation of the two may be correct. It appears to me best, however, seeing that there 
are some minute points of difference, to retain, at all events for the present, the 
two specific names, though it may be doubted whether the two forms should be 
ranked as races or species. 
American hippotheres. — All the American species of the genus seem to be 
distinguished by the simpler structure of the enamel folds. Should any of them, 
which is extremely unlikely, turn out to be the same as the Indian species, the 
name of the latter has the priority of all. 
Distribution Remains of this species have been obtained throughout the 
sub- Himalayan Siwaliks, but not from Sind or Burma. An atlas of a small species 
of horse in the Indian Museum from Perim Island has been referred by Dr. Eal- 
coner, with considerable probability of correctness, to the present species. It is 
uncertain whether the liippotherian teeth from China in the British Museum, 
mentioned by M. Gaudry in the passage already quoted, should be referred to this 
or the next species. 3 
1 Compare fig. 7, pi. XXXIV of “ Animaux Fossiles et Geologie de l’Attique,” with fig. 9 of pi. V, of “ Ani- 
maux Fossiles du Mont Leberon.” 
2 See “ Animaux Fossiles du Mont Leberon, ” pi. V, fig. 7. 
3 These teeth are referred to in the “Quarterly Journal of the Geological Society of London.” Vol. IX, p. 354. 
