ON THE ORIGIN OF CLAUSILIA 
349 
land connection between eastern Asia and Central America 
as suggested by Dr. von Ihering.* The American species 
all belong to the sub-genus Nenia, being extremely like the 
Pyrenean Clausilia pauli. So far only a single species is 
known from the West Indies, while the genus has not 
yet been discovered in Central America (Fig. 19). No 
trace of Clausilia, either recent or fossil, has been met with 
in North America or in northern Asia. If we assume that 
Clausilia passed across the Atlantic Ocean to the West Indies 
and thence to South America, it should have traversed Central 
America. It may still be found in Guatemala, or it may 
recently have become extinct. At any rate, I think it passed 
from Central America to the western or Pacific land bridge con¬ 
necting Guatemala with Ecuador. The latter state, together 
with northern Peru, must be looked upon as the centre of 
dispersal of the South American species of Clausilia. Over 
fifty Clausilias are now known from South America.f A few 
are found northward of Ecuador as far as the province of 
Bogota in Colombia. The great mass, however, is confined to 
the highlands of Ecuador and Peru. South of Bolivia the 
genus is unknown. Is there any possible explanation for the 
presence of this isolated colony of mountain snails in western 
South America except by migration on a former land connec¬ 
tion from Europe or eastern Asia ? A dispersal of the ances¬ 
tral Clausilia in early Tertiary times to South America by 
means of either land bridge is possible, but I greatly favour 
the Atlantic one (compare Fig. 14). It also explains the 
presence of a species of Clausilia in Portorico better than the 
other theory. 
Besides this instance of discontinuous distribution, we more 
over have a large number of others exhibiting ancient rela¬ 
tionship between the faunas of the west coasts of North and 
South America. These will be more fully dealt with when we 
come to the consideration of the Chilean fauna. I may only 
mention one example, that of the three very closely related 
genera of scorpions, Hadrurus, Hadruroides and Caraboc- 
tonus. The first inhabits California, having spread from there 
* Ihering, H. von, “ Verbreitung der Heliciden,” p. 450. 
t Boettger, 0., “ Die Nenia Arten.” 
