MATTHEW, CLIMATE AND EVOLUTION 225 



we have any satisfactory evidence, the diflFerent races or most of them 

 appear to have originated in the Holarctic region and spread to the 

 southward. The most primitive division, the zalambdodonta, includes 

 four families, the Centetidge of Madagascar, Chrysochloridse of South 

 Africa, Potamogalidge of West Africa and Solenodontidge of Cuba. Fossil 

 zalambdodonts are found in the late Miocene in South x4.merica, in the 

 early Oligocene (and recently in the Basal Eocene) in Xorth America. 

 These indications are in conformity with the derivation of the group 



Pig. 12. — Distribution of Soricidw (right to left shading) and of Talpidce (left to right 



shading) 



The less specialized Soricidse are more widely dispersed, the highly specialized Talpidae 

 limited to Holarctica. Ancestral types of both are found in the Tertiary of Europe and 

 North America, but the evidence as to their phylogeny is very scanty. 



from very ancient Holarctic ancestors, the modern zalambdodonts being 

 the last surviving remnants of a dispersal from the north in early Ter- 

 tiary or possibly pre-Tertiary times. But the evidence is too slight to 

 be conclusive. 



The hedgehogs are more clearly of Palsearctic origin, the most primi- 

 tive survivors being the East Indian Gymnura and Hylomys, while the 

 most progressive genus, Erinaceus, is Palsearctic and is preceded in the 



