382 W. B. DAWKINS OK THE CLASSIFICATION OF THE 



The orders, families, genera, and species in the above table, when 

 traced forward in time, thus fall into the shape of a genealogical tree, 

 with its trunk hidden in the Secondary period, and its branchlets 

 (the living species) passing upwards from the Pliocene — a tree of 

 life, with living mammalia for its fruit and foliage. Were the ex- 

 tinct species taken into account, it would be seen that they fill in 

 the intervals separating one living form from another, and that they, 

 too, grow more and more like the living forms as they approach 

 nearer to the present day. 



It must be remembered that in the above definitions the fossil 

 marsupials are purposely ignored, because they began their specia- 

 lization in the Secondary term, and had arrived in the Eocene at 

 the stage which is marked by the presence of a living genus — the 

 Didel/pliys^. Each of the above groups of mammalia will be taken 

 separately, beginning with the Eocene period. 



4. The Eocene Mammalia of Britain and France. 



The Mammalia which lived in Eocene Britain and France fall 

 naturally into three groups — (1) the Lower or Pre-nummulitic, 

 (2) the Middle or the IvTummulitic, and (3) the Upper or Post- 

 nummulitic. . In determining the British species in the accompany- 

 ing lists, I have used the works of Prof. Owenf, and have to 

 acknowledge the valuable aid of Mr. William Davies, of the British 

 Museum, in which collection, and in the Woodwardian at Cam- 

 bridge, most of the specimens are preserved. Those of Erance, 

 obtained principally from the works of Professors Gervais and 

 Gaudry :|:,have for the most part been checked by me in the Jardin des 

 Plantes in Paris and other French collections. 



4 a. Principal Eocene Mammalia of Britain. 

 LOWER EOCENE. 

 Marsupialia. 

 Didelphys colchesteri, Ow. Woolwich and Eeading beds, Kyson. 



Ungulata Perissodactyla. 



Hyracotherium leporimim, Ow. Woolwich and Reading beds, Kyson. 



cuniculus, Ow. Woolwich and Reading beds, Kyson. 



Coryphodon eocasnus, Ow. London Clay, Harwich. 

 Pliolophus vulpiceps, Ow. London Clay, Harwich. 



MID EOCENE. 



Ungulata Perissodactyla. 

 Lophiodon minimus, Ow. Bracklesham. 



* r=:Peratherium of Gervais. In the view in the text, I am following 

 Gaudry. 



t * Palaeontology ' and * British Fossil Mammalia.' 



I Gervais, ' Paleontologie Fran9aise,' 4to, 1859; Gaudry, * Sur les Enehaine- 

 ments du monde animal,' 8vo, 1878. 



