52 



C. HEDLEY. 



and when the cold relaxed, could return to repopulate the 

 former situation (fig. 15). But in South Australia, a 



northern retreat was 

 cut off by the concave 

 coast, so that when 

 locally exterminated 

 by frost there could be 

 no return of' exiles 

 when conditions im- 

 proved. 



Besides the Area, a 

 considerable and varied 

 fauna is supported by 

 the zosteretum. A 

 small carnivorous 



open, on the west it is intercepted by the gasteropod, an active 



Fig. 15. Map of Area retreat during the 

 cold phase. While on the east the route is 



concave coast of the Great Australian Bight. 



scavenger, inhabiting 



a shell half an inch long is Arcularia jonasi (fig. 16). With 



Fig. 16. Arcularia jonasi, a common carnivorous snail 

 of the zosteretum. It is fully extended, in the act of 

 gliding over the mud or weed ; much magnified. 



great energy it glides rapidly over the sand and weed, carry- 

 ing its long siphon so strangely resembling an elephant's 

 trunk, sometimes erect, sometimes arched over its back. 



