648 EEPOET— 1888. 



racteristic fossils of eacla groiip, stress was laid on tlie gradual approximation of 

 various groups to the living Mammalia. The definitions are the following : — 



Divisions. Chaeacteeistics. 



1. Eocene, or that in which the higher Extinct orders. 

 Mammalia (Eutheria) now on the earth Living orders and families, 

 were repressented by allied forms belonging to Xo living genera, 

 existing orders and families. 



Oligocene. 



2. Meiocene, in which the alliance be- Living genera, 

 tween fossil and living Mammals is closer No living species, 

 than before, 



3. rieiocene, in which living species of Living species few. 

 Mammals appear. Extinct species predominant. 



4. Pleistocene, in which living species of Living species abundant. 

 Mammals preponderate. Extinct species present. 



Man present. 



5. Prehistoric, or that period outside Man abundant. 



history in which Man has multiplied ex- Domestic animals present, 

 ceedingly on the earth and introduced the Wild Mammals in retreat, 

 domestic animals. One extinct Mammal. 



6. Historic, in which the events are re- Records, 

 corded in history. 



These definitions are of more than European significance. The researches of 

 Leidy, Marsh, and Cope prove that they apply equally to the Tertiary strata 

 of North America. The Wasatch Bridger and Uinta strata contain representa- 

 tives of the orders Cheiroptera and Insectivora, the sub-orders Artio- and Perisso- 

 dactyla, and the families Vespertilionidfe and Tapiridae ; but no living genera.' 

 The Mammalia are obviouslj- in the same stage of evolution as in the Eocenes of 

 Europe, although there are but few genera, and no species common to the two. 



The White River and Loup Fork Groups present us with the living genera 

 Sciui-us, Castor, Hystriv, Rhinoceros, Dicotyles, and others ; but no living 

 species, as is the case with the Meiocenes of Europe. In the Pleiocenes of 

 Oregon the first living species appear, such as the Beaver, the Prairie Wolf, and 

 two Rodents {Thomomys clusius and T. tal/joides), while in the Pleistocene river 

 deposits and caves, from Eschscholtz Bay in the north to the Gulf of Mexico in the 

 south, there is the same grouping of living with extinct species as in Europe, and 

 the same evidence in the glaciated regions that the Mammalia occupied the land 

 after the retreat of the ice. 



If we analyse the rich and abundant fauna yielded by the caves and river 

 deposits both of South America and of Australia, it will be seen that the Pleisto- 

 cene group in each is marked by the presence of numerous living species in each, 

 the first being remarkable for their gigantic extinct Edentata, and the second for 

 their equally gigantic extinct Marsupials. 



The admirable work of Mr. Lydekker allows us also to see how these definitions 

 .apply to the fossil Mammalia of India. The Meiocene fauna of the lower Sivaliks 

 has yielded the living genera Hhinoceros and Manis, and no living species. 



The fauna of the Upper Sivaliks, although it has only been shown, and that 

 with some doubt, to contain one living Mammal, the Nilghai (Boselaphus trago- 

 cnmelus), stands in the same relation to that of the Oriental Region, as that of the 

 Pleiocenes of Europe to that of the Palaearctic Region, and is therefore Pleiocene. 



' The genus Vesjyerugo has not been satisfactorily determine<l. — Cope, Report of 

 Geol. Surrey of the Territories. Tertiary Vertelrata, I., 1 884. 



