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, pis. xik.-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 Mctamynodon, 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 Memoir 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 



