Reviews — Prof. A. Gaudry — The Evolution of Mammalia. 223 



and Lamantin; and Pugmeodon is intermediate between tlie Lamantin 

 and HaUtherium. Zewjlodon the author is inclined to place nearer to 

 the Seals than the Whales, chiefly on the form of its skull. 



The Pachyderms form a large group, and the resemblances of 

 extinct to living species are very marked. The Rhinoceros was 

 preceded by Acer other ium, Pal(^otherium and Paloplotherium ; and 

 the distinction between these types is shown chiefly in the skull and 

 in the dentition. Acerotherium . is essentially a Rhinoceros without 

 horns, and consequently with smaller nasal bones ; and the fossil 

 species of Rhinoceros show all intermediate conditions of this region 

 of the skull. The incisors of Acerotherium in America are three pairs, 

 as in Palceotherium, and this number is also found in the Rhinoceros 

 Sivalensis of India, so that there is a passage from a complete incisive 

 dentition in this type, through various species of Rhinoceros to 

 animals in which the incisors are lost. The author deals with the 

 difficulty of molar teeth by accepting the view held by some 

 anatomists of this country, that they are really compound teeth 

 formed by the blending together of several simple teeth, which are 

 now indicated by the denticles. The Tapirs are similarly traced to 

 Lophiodon of the Eocene, by means of the American genus Hyrachyus ; 

 and the relation of the teeth of Lophiodon to those of Rhinoceros is 

 fully indicated. The Pigs are traced in the genus Sus to the Middle 

 Miocene. Sus LocTcarti is nearly allied to Hyotherium, and this genus 

 is closely allied to Palceochcerus, which resembles the Peccary of 

 South America. Palceochcerus passes to Chceropotamus, and this genus 

 is closely related to Dichobune. 



The Ruminants are discussed chiefly as to their horns and teeth, 

 and the modifications of the extremities. Unlike the Pachyderms, 

 which abound chiefly in the older Tertiaries, the Euminants 

 flourish most in the later periods. The earliest known genera are 

 Xiphodon, Dichodon, and Amphimeryx. Most of the older American 

 Euminants, like Xiphodon, possess some of the characters of Pachy- 

 derms. In France Gelocus and Dremotherium exemplify this point. 

 In the Upper Miocene all the chief ruminant types are developed. 

 The older forms, such as Oreodon, are without horns. The first 

 Antelopes have the horns very small, and they appear to have de- 

 veloped gradually, becoming relatively large in Antelope recticornis 

 of the Lower Pliocene. Antlers also developed gradually, just as 

 they grow in complexity in the life of existing Deer. In the 

 Middle Miocene the genus Dicroceras has antlers with two prongs, 

 in the Upper Miocene the antler has three prongs, and it is only in 

 the Pliocene and Post-Tertiary that antlers attain the complexity 

 seen in existing species. Since the fossil antlers are always attached 

 to the skull, the author suggests that they may have been permanent 

 in the older types, and subsequently became deciduous, and remarks 

 that at first only the upper portion of the antler was shed, long 

 pedestals remaining attached to the frontal bones. 



The earlier Euminants, Oreodon, Dichodon, and Xiphodon, have 

 canines and incisors in the upper jaw like Pachyderms. An 

 elaborate examination of the molar teeth, however, fails to suggest 



