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 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 next 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 
Rumina 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 
