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, O., "Die Nenia Arten." 



