12 DISTRIBUTION OF QUEENSLAND GASTEROPODA. 



widely over ocean waters is also possessed bj' the sea creatures 

 formerly placed in a separate class as Pteropoda, but now 

 rec^arded as molluscan forms whose life-cvcle has been 

 a-rrested at the free floating marine stage. The Rev. A. 

 H. Cooke.* M.A., states the case as follows : — '" The 

 Pteropoda are a group whose true relations are masked 

 by the special conditions of their existence, which has 

 tended towards the development of certain organs, the so- 

 called ' wings ' and the shell, which give them an apparent 

 symmetry ; this symmetry disappears on a close investi- 

 gation of the internal organs." This author reduces the 

 Pteropoda to a sub-class of the mollusca. 



Recapitulating, the aim of this paper is to show from 

 the distribution of Gasteropods, geographically and 

 geologically, that the shell-fish of the great Indo-Pacific 

 province were almost universally spread through warm 

 temperate and equatorial regions to the end of Eocene 

 times ; but that the north and south barriers, formed by 

 the elevations that produced the Isthmuses of Suez and 

 Panama, limited the range of species to the two oceans 

 that are connected in tropical areas, and by giving rise to 

 modifications of climate in the Atlantic and Mediterranean 

 basins, caused great changes in the character of their 

 molluscan faunas. 



♦Cambridge Natural History, Braehiopods and Mollu.scs, p. 435. 



