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 the indigeneity of _Plutellus_. The species according to Dr Eisen show every sign of being genuine inhabitants of California and like certain New Zealand species such as the _Tokea esculenta_ of Benham (referred by Michaelsen to the genus _Megascolides_) were eaten by the natives. If these genera were forms restricted to North America, that is not only with reference to the rest of America but to the world generally, there would be as I think no doubt about the practicability of making a Nearctic region. As it is, it seems to me to suit the facts of distribution better to regard the whole of the land under consideration as forming one great Neogaean region with three sub-regions, the North American, Central American and West Indian, and tropical South American. This region however will not as I take it include the southernmost extremity of South America. Here in Patagonia and in neighbouring islands we have a different earthworm fauna. It is in fact characterised by the sub-family Acanthodrilinae of which it is true some members of the genus _Notiodrilus_ extend further north. I shall however defer this part of the subject until the more easy delimitations of regions are disposed of.