MOLLUSCAN AFFINITIES 273 



true that another group of Clausilia, known as Garnieria, from 

 tropical and eastern Asia also approaches the American group 

 closely. Yet the fact that no Clausilia, either fossil or recent, 

 has ever been discovered in northern Asia or North America, 

 although many species, as I remarked, thrive in high altitudes 

 and cold climates, speaks strongly against the supposition of 

 the ancestors of the West Indian and South American stock 

 having wandered through Asia and North America to these 

 regions. The geographical distribution of Clausilia thus 

 offers one of the most cogent arguments in favour of a direct 

 land bridge between the Mediterranean and the Antillean 

 regions. Opponents of this view may urge that Clausilia is 

 merely represented by a single species in the West Indies, 

 while none are known from Central America. We. may explain 

 this curious circumstance by the fact that the West Indies 

 were submerged probably before the newly immigrated Clau- 

 silias had time to gain possession of the higher eminences, 

 so that most of them would have been destroyed. In Central 

 America fewer traces of European affinity have been detected 

 than in western North America or western South America, 

 because in the latter 1 regions the faunas remained more or less 

 isolated for long periods, while the great rush of South 

 American invaders, combined with climatic changes, swept 

 all before them in Central America. Why Clausilia has suc- 

 ceeded in reaching western South America without attaining 

 western North America will be discussed in the neixt chapter 

 but one. 



Dr. Simroth suggests that the ancestors of the American 

 Bulimulidae, at least the group of Orthalicinae, may be of 

 European origin, while I venture to think that the curious 

 Bumina decollata, which is supposed to be a human importa- 

 tion in Cuba, may be indigenous there, since it is now known 

 to have lived unchanged in the Mediterranean region since 

 Oligocene times. In view of my remarks in previous chapters 

 on the relationship of the North American snake Tropido- 

 notus, of the crayfish Potamobius, of the slugs belonging 

 to the family Arionidae, of the glass snake, of all that remark- 

 ably European assemblage of animals in the south western 

 States, of the snail Adelopoma in Guatemala and numerous 

 other instances, such; as the range of the flamingoes, it need 



L.A. T 



