158 NATURAL SCIENCE [September 
Europe and Asia to hornless ancestors in the Miocene period. It 
was thus clear that they had passed through at least the latest 
stages of their evolution in these regions. In 1850, however, 
Professor Leidy first found a fragment of a rhinoceros in the 
Miocene of North America; and since that time so many remains— 
including several nearly complete skeletons—have been found in 
the United States, that these great quadrupeds are now proved 
to have been at least as abundant in North America as in Europe 
and Asia, during the Miocene and Pliocene divisions of the 
Tertiary period. It is true, indeed, that in North America the 
rhinoceroses never acquired a typical horn, while they became 
extinct before the close of the Pliocene period; but they attained 
a truly remarkable development, and we now know more of the 
characters of the family from the discoveries made in North 
America than from those in Europe and India. 
Professor H. F. Osborn, the well-known Curator of Vertebrate 
Palaeontology in the American Museum of Natural History, New 
York, has just begun to summarise our present knowledge of these 
extinct New World rhinoceroses in the first part of a beautifully 
illustrated quarto Memoir issued by the American Museum (vol. i., 
pt. 3, 1898, pp. 75-164, pls. xiia,-xx., April 22,1898), It appears 
that three distinct groups can now be recognised, adapted for differ- 
ent modes of life. Firstly, there were the Upland or Cursorial 
Rhinoceroses, such as Hyracodon, all agile, slenderly-built animals, 
with three toes, somewhat simulating the three-toed Miocene horses 
with which they were associated. Secondly, there were the Aquatic 
Rhinoceroses, such as Metamynodon, with great tusks, simulating the 
modern hippopotamus of Africa. These were short, heavy animals, 
with four-toed spreading feet, and probably a prehensile lip. Thirdly, 
there were the True or Lowland Rhinoceroses, very abundant and 
doubtless similar in habit to their surviving congeners in Asia and 
Africa at the present day, though, as already remarked, destitute of 
the characteristic horn. These three groups were differentiated in 
North America before the close of the Eocene period, and there is 
already some fragmentary evidence of a similar differentiation in 
Europe, though the materials as yet available for discussion are too 
imperfect to be conclusive, 
The present instalment of Professor Osborn’s Meinoir discusses 
the morphology of the teeth and skull of the Rhinocerotoidea, tracing 
the gradual divergence of the three types, occasionally obscured by 
parallelisms and convergences. The true rhinoceroses, Rhinocero- 
tidae, are then discussed from the points of view of habits, geological 
history, and morphology, while the section ends with a preliminary 
bibliography that will be of much value to students. Then follows 
a detailed account of the hornless rhinoceroses, Aceratheres, collected 
