ix] GEOGRAPHICAL DISTRIBUTION 133 



population which appears to be absent from large 

 tracts of Canada will be simply due to involuntary 

 migration. These two views must be left for further 

 development. 



In any case the southern parts of the United 

 States seem to be separable as a distinct region 

 from South America and to be characterised by the 

 sub-family Diplocardiinae, the genus Diplocardia 

 extending as far northwards as the state of Illinois. 

 The distinctness of such a region however from 

 Central America and the West Indies is marred by 

 the abundance of Ocnerodrilus of which Dr Eisen 

 has described so many forms. On the other hand 

 the West Indies are closely allied in their earthworm 

 fauna to tropical South America, sharing with that 

 region several forms of Geoscolecids belonging in 

 both cases invariably to the sub-family Geoscolecinae. 

 The bulk of the latter are undoubtedly tropical South 

 American in range and there is no doubt whatever 

 about the distinctness of this part of the world as a 

 separate region. There is moreover a further puzzle 

 which confronts us who are trying to delimit an 

 American region or regions. In North America are 

 species of the genus Argilophilus which is referred 

 by Michaelsen to the genus Plutellus which comes 

 from the East and at least one species of Megascolides, 

 also an Eastern genus. 



There is at present no doubt to be thrown upon 



