50 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 1 1 



7. The sponge "geminates" occurring on the two sides of tropical 

 and subtropical America have not arisen by convergent evolution under 

 the influence of similar conditions, because the conditions in areas vi^here 

 "geminates" occur are widely different. 



8. The sponge fauna of the Gulf of California and the West Indies 

 are closely related. Fifty-eight per cent of the sponges in the Allan 

 Hancock Foundation from the Gulf are either identical with, or "gemi- 

 nates" of, West Indian forms. 



9. The major portion of the sponge fauna of the Gulf of California 

 arose as an "off branching" from the West Indian stock probably in the 

 late Miocene period when the portal of Tehuantepec across Mexico was 

 open. 



10. A large portion of the present sponge fauna of the coast of Cali- 

 fornia proper probably arose as an extension of the fauna of the Gulf of 

 California. Forty-eight per cent of the sponge genera from the Gulf in 

 the Allan Hancock collection are identical with, or "geminates" of, forms 

 from the coast of California proper. 



11. There is some evidence that the coast of California may repre- 

 sent, for sponges, a transition zone between the tropical, or subtropical, 

 and temperate regions. 



12. The sponge fauna of the Gulf of California is intermediate 

 between that of the West Indies and that of the coast of California 

 proper. "Geminate species" occurring in the latter region arise either 

 because California forms are identical with Gulf forms, which in turn 

 are "geminates" of sponges from the West Indies or because the Gulf 

 sponges, which are "geminates" of California forms, are identical. 



