10 GASTEOCOPTA. 



and in exactly the same stage of evolution, evidently indi- 

 cating a late Tertiary dispersal over this area. 



Excepting the Australian Australbinula, all of the highly 

 specialized Gastrocoptoid groups, such as Hypselostoma, Im- 

 mersidens, Ch&naxis, and the more complex Albinulas, are in 

 eastern Asia and North America. There seems no reason 

 (and certainly there is no evidence) for believing that any of 

 them arose in parts of the world remote from their present 

 areas. 



The chiefly middle and South American and African dis- 

 tribution of the typical (acarus and servilis) group of Gas- 

 trocopta is somewhat problematic, and is perhaps traceable 

 to an earlier radiation than the groups considered above. It 

 does not connect readily with the other stocks. In Polynesia 

 the extraordinarily wide distribution of G. pediculus and 

 lyonsiana, seems>to me explicable only by the supposition that 

 the former was carried by the Polynesian islanders ; it occurs 

 also in Micronesia, Melanesia and the East Indies. G. lyon- 

 siana may have been spread later, by nineteenth-century 

 commerce. 



SUBDIVISIONS OF GASTROCOPTA. The species will be grouped 

 geographically in the following account, as this is more con- 

 venient in practical use than a strictly systematic sequence. 



I. North American and West Indian species (nos. 1 



to 25). 

 II. South American species (nos. 26 to 37). 



III. East Asiatic species, Japan to Indo-China (nos. 38 



to 45). 



IV. Species of Western Siberia and Europe (nos. 46 



to 64). 



V. African and Mascarene species (nos. 65 to 76). 

 VI. Species of Ceylon, India and the Malay Peninsula 



(nos. 77 to 85). 

 VII. Insular species, East Indies, Melanesia, Micronesia, 



Polynesia, Hawaii (nos. 86 to 94). 

 VIII. Australian species (nos. 95 to 106). 



