1879.) Extinct American Rhinoceroses and their Allies. 77 
The earliest species of the toothless or African series is the 
Atelodus pachvgnathus of Wagner, whose characters have been so 
well worked out by Gaudry in his great work on the Fossil Fauna 
of Attica. That species sometimes presents a single small incisor 
or canine tooth in the mandible! From what has preceded it is 
also apparent that the generally most specialized type of rhinoc- 
eros, the genus Ca/odonta, has become entirely extinct. Its three 
species yet known, were confined to Europe and Northern Asia, 
and the most formidable of them extended its range with the 
hairy mammoth within the Arctic circle. The Celodonta anti- 
quitatis (the wooly rhinoceros) was evidently the most effectively 
armed of the family, as it had two horns, which, judging from the 
character of the surface of the skull to which they were attached, 
must have been of unusual size. To provide further against the 
shocks incident to their use in combat, the nareal septum was 
ossified, thus becoming a-solid support to the nasal bones, etc., on 
which they stood. . 
It remains to look backwards, and to discover, i€ possible, the - 
probable origin of the family in that of its earliest known genus, 
Aceratherium, A late survivor of this ancestral type is seen in 
the genus Zaladis Cope, of which one species, the Z. sivalensis, 
has been discovered by Cautley and Falconer in the late Tertiary 
of Hindostan. In this form, according to Falconer, there are 2 
incisors and ¢ canines. The early type, which corresponds most 
nearly with this genus, and which preceded the Aceratheria in 
time, is the genus Amyzodon Marsh, which has left a species in 
the Uinta or Upper Eocene of Utah. Here the incisors are 2 and 
the canines }. - This formula is intermediate between that of Acer- 
atherium and that of the Eocene tapirs, where the normal num- 
bers $ + prevail. According to Marsh, Amynodon further differs 
in the primitive condition of the premolars above, which, as in the 
Lophiodontide, differ from the molars in their greater simplicity. 
Thus it is probable that tapiroid animals, probably Lophiodontide, 
gave origin to the R/znocerid@, as Marsh has suggested. And it is 
further altogether probable that the general type of dentition pre- 
sented by the ‘Riinoceride, Lophiodontidae, etc., which I have 
named the palzotheriodont, took its origin from the type which 
is intermediate between it and the bunodont, viz: the symboro- 
dont, as I have pointed out in an essay on this subject.” 
1 The large tooth of the mandible described by the older authors as an incisor, has 
been regarded as a canine by Gervais, Subsequently Marsh adopted the same view. 
The Homologies and Origin of the Molar Teeth of Mammalia, etc. Journal 
wfeease DRA, tQea nn 13-14. 
