370 AUSTRALIAN REGION chap. 



whole of the region excepting New Zeahmd and the adjacent 

 islands) is determined by the influence of the Antarctic Drift, 

 which washes the whole of the southern coasts of Australia, and 

 runs strongly northward between Australia and New Zealand. 

 The E. Australian warm current from the north is checked at 

 Sandy Cape by this cold current, and flows off to New Zealand, 

 the western shores of which island are consequently much warmer 

 than the eastern. On the western coast of Australia the An- 

 tarctic Drift has less force, and tropical genera accordingly range 

 some 7 degrees farther south on the western than on the eastern 

 coasts. 



The characteristic genera are Valuta (of which half the known 

 species occur on Australian coasts ^), Cominella^ Siphonalia^ 

 Struthiolaria^ Risella^ Pliasianella^ a number of genera belonging 

 to the Trochidae, e.g. Liotia^ Clanculus, Eiichelus, Thalotia^ 

 Ulenchus, Trochocfjchlea, Zizyjjhiiius^ Bankivia ; Trigonia^ Myo- 

 dora^Myochama^ Solenomya, JEpMppodorita, Anapa, 3IyUtta, Meso- 

 desma, and Chamostrea. Trigonia, originally discovered as a recent 

 form in Sydney Harbour (p. 65), is not peculiar to that locality, 

 occurring also off Cape York, West Australia, and Tasmania. 



(2) The Neozealayiian Suh-region includes New Zealand, with 

 the outlying islands (Chatham, Auckland, and Campbell Is.). 



As many as 455 species (Cephalopoda, 8 ; Gasteropoda, 311 ; 

 Scaphopoda, 2 ; Pelecypoda, 131) have been enumerated by Pro- 

 fessor F. W. Hutton as occurring within the sub-region, of which 

 only 64 are found elsewhere, the proportion of peculiar species 

 being thus nearly 86 per cent. New Zealand therefore is, in its 

 marine, no less than its land Mollusca, greatly isolated. 



The characteristic genera are Antliora, Cryptoconchus, and 

 Vajiganella, which appear to be quite peculiar, Trophon, Comi- 

 nella, Euthria, most of the Trochidae also characteristic of S. 

 Australia, Haliotis, Patella ; Taria, Mesodesma, Mylitta, Zenatia, 

 Standella, and Myodora. 



D. The American Region 



includes the entire coasts of North and South America with the 

 adjacent islands, south of Cape Avinoff on the western, and south 



1 A full account of the distribution of Valuta is given by Crosse, Journ. de 

 Conchyl. (3) xix. p. 263, 



