HASEMAN, GEOGRAPHICAL D I ST RIB VTION IN 80 UTH AMERICA 81 



ican coasts. The writer looked carefully along the coast south of Iguape 

 for Aporrhais pespelecani and was unable to find this form either living: 

 or dead. The few dead shells of this species known from a seaport have 

 little significance, because peddlers and sailors are known to be great dis- 

 tributers of shells. The writer picked up one valve of Lucina jamai- 

 censis (?) on a sand bar below the Urubu-punga waterfalls of the Alto 

 Eio Parana, which is several hundred miles from the seacoast, but this 

 shell had evidently been dropped there by an Indian. 



A very important factor in the distribution of the marine mollusca of 

 the Atlantic Ocean is the tropical condition which existed in the North 

 Atlantic during the Eocene. This would have given excellent oppor- 

 tunities for exchanges of forms between the African-European and 

 American coasts. These ancestors of the existing forms would have been 

 pushed south again when the climate of the North Atlantic became 

 cooler. As a result of this, many resistant ancestral forms living in 

 similar environments and evolving along rather definite lines would pro- 

 duce a great similarity between the coasts of the South Atlantic. 



Furthermore, it is not impossible that some young forms of land 

 gastropods could have been carried with tropical plants to the eastern 

 hemisphere just as Litorina litorea has probably been imported in some 

 way to the American coast. 



After a long detailed study of the living and fossil Tertiary mollusca, 

 von Ihering has recently concluded that Archhelenis, the land-bridge 

 between Africa and South America, began to disappear in the Cretaceous 

 but continued to exist in the Tertiary. Ortmann (1910) used the same* 

 data and arrived at a different conclusion, namely, that Archhelenis had 

 disappeared before the beginning of the Tertiary; but neither of these 

 authors has taken into consideration the effects of similar tropical en- 

 vironmental complexes along the African and South American coasts on 

 the ancestral stock from which the existing species have evolved. When 

 this is done and the cosmopolitan forms are eliminated and when due 

 allowance is given possible larval and adult distribution by ocean cur- 

 rents, floating debris and boats, then no land-bridges are needed to ex- 

 plain the distribution of marine mollusca. 



Only static studies have been made, and until some dynamic work has 

 been done the evidence derived from the mollusca is not a safe peg to 

 hang a theory on. 37 



37 The brachiopoda appear to me to offer even less evidence, because many almost cos- 

 mopolitan genera have existed during various past ages. This is all the more true when 

 certain similar forms are known to exist in similar environments. So it appears that 

 extensive land-bridges like Archhelenis will have to rest on evidence derived from geology 

 and continental faunas and floras. 



