INTRODUCTION. 
xiii 
and comprising Eosiren, ZevgJodon, and Prozeuglodon. It seems probable that some 
of tliese last, like the genera included in section 1, are of endemic origin, having 
originated from land-mammals inhabiting the region. 
In the first section it will be noticed that all the genera belong to the Ungulata, and 
with one exception to that subdivision of the order to which the name Subungulata 
has been given — a group in which the feet have not undergone any extreme 
specialisation. The exception to this is Geniohyus, which is an Artiodactyl and 
should perhaps be placed in the second section. 
Among the Subungulates, by far the most striking of the new forms is Arsinoitherhim, 
the first remains of which were found by Mr. Beadnell towards the end of 1900. 
Subsequently a great quantity of remains of one of the species, A. zitteli, w-ere collected, 
including skulls of various ages, and nearly all the other parts of the skeleton (see 
text-fig. oG, p. GO), so that the structure of this extraordinary mammal is now almost 
completely known, so far as this is possible from the bones alone. 
In its general appearance Arsinoitherium zitteli must have been somewhat like a large 
and heavily built Rhinoceros (see p. xxviii) : on the head there were two pairs of horns, 
the great anterior nasal horns projecting forwards and upwards, and a much smaller pair 
situated over the orbits. Both these horns, unlike those of Rhinoceros, are bony out- 
growths of the skull, but most likely the anterior pair at least were covered Avith horny 
sheaths, much like those of the Cavicorn Ruminants. The muzzle was very narrow, 
so that probably the animal did not graze, but browsed on low bushes and herbage, 
grasping its food by means either of a prehensile tongue or possibly of a mobile upper 
lip. In correlation with the great weight of the skull, the occipital condyles are large 
and the ridges for the attachment of muscles prominent ; from the form of the 
occipital condyles and the forward slope of the occipital surface, it appears that the 
head could be moved freely up and down. The dentition is complete, and the teeth, 
which form closed series on either side of both the upper and lower jaws, possess 
extraordinarily high crowns, especially for an animal of such an early period. The 
molars, which differ very widely from the premolars, consist of two very high transverse 
crests, and it is very difficult to imagine from what type of low-crowned tooth they 
were derived ; it is, however, possible that they may have originated from a tooth 
resembling the molars of the Hyracoidea, in Avhich a gradual increase in the height of 
the croAvn has been accompanied by the infolding of the outer wall till the crown is 
divided into an anterior and a posterior column, lire possibility that Arsinoitheriidte 
may have been descended from the same ancestral stock as the Hyracoidea is supported 
c 
