No. 494] 



THE TERTIARY MAMMALS 



1 1 1 



whose origin has been until now an insoluble enigma, indi- 

 cates the method we should follow, and the necessity for 

 searching for the centers of dispersion of each branch. 



A preliminary work at least is possible at our present 

 stage of knowledge; it is to establish for each region 

 whose paleontologic exploration is sufficiently advanced, 

 the part which pertains to each of the two factors deter- 

 mining faunal changes: (1) Evolution of the local fauna 

 (autochthonic evolution), (2) Immigrations from adistant 



I shall attempt to analyze these facts for the Tertiary 

 faunae of Europe, where this distinction has never been 

 established in a systematic manner. 



I. Thanetian or Lower Londinian stage (deposits of la 

 Fere, Cernay, Billy, Chalons-sur-Vesle in France; of 

 Erquelines in Belgium). 



1. Local Evolution.— X single instance, Neoplagiaxlax 

 (Multituberculata), which may perhaps have been de- 

 rived, in spite of the great gap of the Cretaceous, from 

 Plagiaulax of the Purbeck, but may also have migrated 

 from North America. 



2. Migrations of North American Origin, -Introduc- 

 tion into Europe of several families of Creodonta: Oxy- 

 claenidae (Procynictis = Chriacus), Aretocyonidae (Conas- 

 pidotherium = Claenodon), Mesonychidae (Dissacus) ; and 

 of the Condylarthra (Euprotogonia). 



3. Migrations of unknown origin of the Insectivora 

 (Adapisoricidae), of the (?) Artiodactyla (Pleuraspido- 

 theriidaa), of the aberrant Primates of the group Plesi- 

 adapidae, of the Perissodactyla (Hyracotheriidae or Pre- 

 equidae), of the Amblypoda (Coryphodon). 



II. Sparnacian or Upper Londinian stage (deposits of 

 Soissons, Guny, Muirancourt, Saron near Ste Maxence, 

 Laon, Upper Cernay, Meudon, Vaugirard, Sezanne, in 

 France ; Dulwich and Croyden (Woolwich beds) in Eng- 

 land. Fauna unfortunately still very scanty. 



1. Local Evolution,— Continuance of Amblypoda (Co- 

 ryphodon, and of Hyracotheriidae (f Pachynolophus ) . 



