OrirvER.— Marine Littoral Plant and Animal Communities. 499 
Zealand is a form of Avicennia officinalis, not extending south of latitude 
38° S. Animals living a semi-terrestrial existence here are Amphibola 
crenata, Potamopyrgus antipodum, Phytia ornata, Helice crassa, and certain 
amphipods. The same forms live in similar situations in salt marshes. 
But a more direct route over a sandy beach might be taken by such 
within their shells during the retirement of the tide, but seal themselves 
up behind their opercula, and attach the peristome of their shells to the 
rock by means of a mucilaginous secretion. An interesting summary of the 
habits of Littorinoids in this connection is given by Hedley (1915, p. 33). 
The New Zealand members of this family, Melaraphe unifasciata and 
M. cincta, have already been mentioned as advancing up the rocky coast 
to beyond the lower limit of land vegetation. More success, however, 
appears to be achieved by gasteropods in crossing the rocky shore where 
patches of succulent plants are found beyond high-water mark. At Island 
Bay, Cook Strait, occurs a plant-formation consisting chiefly of a low dense 
growth of Selliera radicans and Triglochin striatum, where soil has collected 
in hollows among the rocks well beyond the reach of the tides. By search- 
ing carefully among this, Marinula filholi and Acmella neozelanica may 
be found in abundance. The former, however, is a pulmonate occurring 
between tide-marks. 
OCEAN CURRENTS. 
The shores of New Zealand are washed by at least two distinct ocean 
currents. The Antarctic drift current, which has a general set towards 
the north-east, affects chiefly the southern and eastern coasts as far north 
as Jackson’s Bay on the west and Banks Peninsula on the east. From 
Jackson’s Bay the current flows southward along the coast and through 
Foveaux Strait. Drift from the south of New Zealand has been cast 
up on the Chatham Islands; there are certain points of agreement, too, 
between the fauna and flora of the same two localities. This current 
appears to be pushed off shore by a current, presently to be described, 
passing through Cook Strait from the west. The second ocean current 
