IX.] CHARACTERISTICS OF THE FAUNA. 311 



have united Dr Sclater's Palaearctic region and Nearctic region ; 

 for although the species of North American Rhopalocera are 

 seldom identical with those of northern Asia and Europe, still the 

 genera are the same with scarcely an exception, except a few 

 representatives of South American genera, which have no more 

 right to be considered Nearctic species than the similar chance 

 representatives of African 1 forms in North Africa or south-west 

 Europe, or of Indian forms in south-east Europe, have to be con- 

 sidered Palaearctic species." 



On the other hand, North America differs remarkably from the 

 eastern half of the Holarctic region as regards its land molluscs. 

 Thus the Rev. A. H. Cooke 2 writes, that " no district in the world 

 of equal extent is so poor in genera, while those which occur are 

 generally of small size, with scarcely anything remarkable either in 

 colouring or form. The elongated land-shells (Clausilia, Bull- 

 minus] so characteristic of Europe are entirely wanting, but a few 

 Bulimulus, of Neotropical origin, penetrate Texas, and from the 

 same sources come a few species of Glandina (as far north as 

 South Carolina), Holospira (Texas), and Helicina" Probably this 

 poverty is largely due to the unsuitableness of the greater part of 

 North America to molluscan life ; aided by the circumstance that 

 land-molluscs are just the creatures that would have been unable 

 to pass over from Asia by way of Bering Strait. The batrachians, 

 again, which differ most remarkably in their distribution from 

 mammals, are not indicative of the unity of the Holarctic region, 

 the American types being very different from those of the Eastern 

 Hemisphere. 



According, however, to Mr F. E. Beddard 3 , " the earth-worms 

 offer the best evidence of any group in favour of the Holarctic 

 region." 



Although during the Plistocene era even subsequently to the 

 passing away of the glacial period elephants, rhino- 

 ceroses, and hippopotami abounded over the greater tics ^he 

 part of Europe, while species of the two former 

 groups ranged as far north as Siberia, and macaques 



1 The author obviously means Ethiopian. 



2 Cambridge Natural History Mollusca, p. 339 (1895). 



3 Appendix, No. 5, p. 80. 



