THE LAND GASTROPODA IN THE NORTH ATLANTIC REGION 165 



since the subgenera in question occur also in South and Central America. 

 The alternative of a North Atlantic dispersal is certainly out of the question 

 for the essentially warm-temperate to tropical genus Strobilops. 



A similar distributional pattern and history is also shown by the richly 

 differentiated, preponderantly tropical genus Gastrocopta as well as by 

 Pupoides whose origin, however, may be American. There are no indications 

 that the latter genus has ever lived in Europe, 



Some further genera, which may be characterized as chiefly Pantropical, 

 have a distribution which is difficuh to understand without assuming a 

 trans-Atlantic dispersal. As an example, the subterranean-dwelling Cecilioides 

 may be mentioned. It is represented by different subgenera in Europe and 

 America, the European one having advanced as far north as the southern Baltic. 



However, it must be admitted that all these genera, by their very extensive 

 distribution and their good qualifications for passive dispersal, show rather 

 vague indications of faunal history. Stronger evidence for trans-Atlantic 

 dispersal is given by the American genera Gastrodonta and EitgJandina. 

 The former genus shows affinities to Jamdus of Madeira and the Canary 

 Islands, which was widely distributed in Europe during the Tertiary. Euglan- 

 dina, along with several tropical American genera, is related to Poiretia in the 

 Mediterranean territory. These genera suggest a trans-Atlantic dispersal, but 

 it must have been remote, perhaps in the Mesozoic. 



To conclude, there are no facts which unambiguously indicate that the 

 southern element in the land gastropod fauna, which Europe and North 

 America have in common, has followed the North Pacific route. The alterna- 

 tive, a trans-Atlantic dispersal within the warm latitudes is, on the contrary, 

 difficult to reject. But the nature of this dispersal yet seems enigmatic. 



The evidence is too scattered to support assumptions of any kind of land 

 bridge. Rather it points to factors facilitating the passive dispersal, e.g., by the 

 presence of interjacent islands. The idea that the Macaronesian archipelago 

 once offered a connecting link can be rejected. When regarding their gastropod 

 fauna it appears to be, as already emphasized, a decided derivative of the 

 Early Tertiary Mediterranean and west European fauna. Probably this has a 

 bearing on the occurrence of Jamdus too. 



The arguments for a connection between tropical Africa and South 

 America, which have been brought forward, can be ignored here. They have 

 no bearing on the actual problem, because the European land gastropod 

 fauna always has been so profoundly isolated from the tropical African one. 

 Besides, South America has relatively few groups in common with Africa, its 

 main affinities being Australian and East Asiatic. 



However, these problems will not be discussed further here, as they refer to 

 a faunal element of only peripheral importance in connection with the North 

 Atlantic biota. It has seemed justified to draw attention to them because 

 otherwise there would be the danger of overstressing the importance of the 



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