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oldest type, but the Rhinoceros bad near allies throughout the 

 Tertiary ; and, in view of the continuity of the equine line, it is 

 well worth while to attempt to trace his pedigree. At the 

 bottom of the Eocene, in our Western lake-basins, the tapiroid 

 genus Helaletes is found, represented by numerous small mam- 

 mals hardly larger than the diminutive horses of that day. In 

 the following epoch of the Eocene, the closely allied Ilyracliyus 

 was one of the most abundant animals. This genus was nearly 

 related to the Lophiodon of Europe, and in its teeth and skele- 

 ton strongly resembled the living Tapir ; whose ancestry, to 

 this point, seems to coincide with that of the Rhinoceros we 

 are considering. Strangely enough, the Rhinoceros line, before 

 it becomes distinct, separates into two branches. In the upper 

 part of the Dinoceras Beds, we have the genus Colonoceras, 

 which is really a Hyrachyus with a transverse pair of very 

 rudimentary horn-cores on the nasal bones. In the lower 

 Miocene west of the Rocky Mountains, this line seems to pass 

 on through the genus Dicer atfierium, and in the higher Miocene 

 this genus is well represented. Some of the species nearly 

 equaled in size the existing Rhinoceros, which Diceraikerium 

 strongly resembled. The main difference between them is a 

 most interesting one. The rudimentary horn-cores on the 

 nasals, seen in Colonoceras, are in Diceratherium developed into 

 strong bony supports for horns, which were placed transversely, 

 as in the Ruminants, and not on the median line, as in all 

 existing forms of Rhinoceros. In the Pliocene of the Pacific 

 Coast, a large Rhinoceros has been discovered, which may 

 be a descendant of Diceratherium, but as the nasal bones have 

 not been found, we must wait for further evidence on this 

 point. Returning now to the other branch of the Rhinoceros 

 group, which left their remains mainly East of the Rocky 

 Mountains, we find that all the known forms are hornless. 

 The upper Eocene genus Amynodon is the oldest known 

 Rhinoceros, and by far the most generalized of the family. 

 The premolars are all unlike the molars, the four canines are 

 of large size, but the inner incisor in each jaw is lost in the 

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