632 



PATAGONIAN EXPEDITIONS: ZOOLOGY. 



Australia by way of the Gondwana continent, leaving isolated genera by 

 the way in Madagascar, the Seychelles, Ceylon and the Moluccas. To 

 this Palaeozoic and early Mesozoic land the South African Endodoutidce, 

 Peripatits, etc., may also belong. The evidence for an isthmus connecting 

 South Africa and Antarctica, as sketched by Forbes, Ortmann and some 

 other palaeogeographers, seems unsubstantial. Nothing in the distribution 

 of non-marine mollusks lends it support. 



Fig. 38. 



Showing sources of the South and Middle American mollusk faunas. Early Mesozoic and 

 earlier migrations in heavy lines, late Mesozoic lighter lines, Tertiary and later migrations in dotted 

 lines. 



The rather large size of the fresh-water mussels and Bulimulida pre- 

 cludes the idea of their distribution as adult organisms except by actual 

 land connection. Some embryonic UnionidcB are probably carried by water 

 birds, but we do not know that this is the case with Diplodon ; moreover 

 only short distances can be so traversed, since unionid embryos are known 

 to die quickly out of water. It is hardly conceivable that Bulimulid eggs, 

 which are smooth and not viscid, should be so carried. The same is true 



