C. The Australian Region
includes the Australian coast-line from about Swan R.[388] (lat. 32° S.) to Sandy Cape (lat. 25° S.), Tasmania, New Zealand, and the adjacent islands (except Lord Howe’s I.).
(1) The Australian Sub-region proper (which consists of the whole of the region excepting New Zealand 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 Antarctic 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 Voluta (of which half the known species occur on Australian coasts[389]), Cominella, Siphonalia, Struthiolaria, Risella, Phasianella, a number of genera belonging to the Trochidae, e.g. Liotia, Clanculus, Euchelus, Thalotia, Elenchus, Trochocochlea, Zizyphinus, Bankivia, Trigonia, Myodora, Myochama, Solenomya, Ephippodonta, Anapa, Mylitta, Mesodesma, 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 Neozealanian Sub-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, 134) have been enumerated by Professor 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 Anthora, Cryptoconchus, and Vanganella, which appear to be quite peculiar, Trophon, Cominella, 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 of Cape Cod on the eastern coast, the portions north of these points belonging to the Arctic Sub-region.
(1) The Aleutian Sub-region consists of the islands of Yesso and Saghalien, with the adjacent shores of the Sea of Okhotsk to Cape Lopatka, the Aleutian Is., and the west American coast from about Cape Avinoff (lat. 60° N.) to St. Jean de Fuca Straits.