Inter-tidal Zonation — Beveridge and Chapman 
191 
The consociation attains its best develop- 
ment amidst boulders at the back of the rock 
platform or in more sheltered places. Bostry- 
chia does not appear able to withstand direct 
strong wave action. In general this belt oc- 
curs below the Licbina but above the main 
development of the barnacle zone. 
Under conditions of extreme shade Bostry- 
chia is replaced by Rhizoclonium riparium 
above and Lopbosiphonia macra below. 
Where the shade is rather less intense Calo- 
glossa leprieurii is a common associate. Ento- 
physalis deusta occurs on sunny faces in sum- 
mer and Enteromorpba ramulosa in winter. 
3. Chamaesipho association 
Range: M.H.W.S. to M.S.L. 
Chamaesipbo columna (d) 
Cbamaesipbo brunnea (d) 
Porpbyra columbina ( f-ld ) 
Modiolus neozelanicus (f) 
Elminius plicatus (f) 
Centroceras clavulatum 
The configuration of the rock is important 
in relation to the upward extension of this 
association. Where the wave platform is 
bounded by vertical walls the association oc- 
curs up to the edge, but where the rock is 
sloping the surge of the waves elevates 
the upper limit considerably. Cbamaesipbo 
columna is most abundant from M.H.W.N. 
upwards; below it enters into competition 
with Modiolus and Elminius. Porpbyra co- 
lumbina apparently exists in two forms in 
this association. The first, which is usually 
small, tufted, and light green, occupies a belt 
from H.W.N. to H.W.S., being most abun- 
dant in sheltered and sunny areas. From 
H.W.N. to L.W.N. there is a larger, more 
flaccid, olive-red form, which, however, 
grades into the other form where shading oc- 
curs. The two forms may therefore represent 
sun and shade types. 
4. Modiolus-Chamaesipho columna 
association 
Range: M.H.W.N. to M.L.W.N. 
Cbamaesipbo columna (d) 
Modiolus neozelanicus (d) 
Elminius plicatus ( f— la ) 
Centroceras clavulatum 
(spring and summer) 
Gelidium pusillum (o) 
Apopbloea sinclairii (o) 
Cbaetangium corneum (o) 
Lophosipbonia macra (r) 
The composition of this association varies, 
depending on wave action. One may there- 
fore recognise two fasciations. The principal 
difference is in the greater abundance of El- 
minius plicatus under conditions of moderate 
wave action, whereas where there is strong 
wave action this species is restricted to crev- 
ices and sheltered areas. In places the Modi- 
olus forms a close cover; under these circum- 
stances it appears to be antagonistic to other 
animals and to plants. Only a few algae ap- 
pear capable of attaching themselves to the 
mollusk. 
Although this association is here regarded 
as distinct from the preceding association it 
must be recognised that some workers might 
prefer to regard it as a fasciation of the 
Cbamaesipbo association. It does differ how- 
ever in the co-dominance of the Modiolus, the 
greater abundance of the Elminius under cer- 
tain circumstances, and in the levels it occu- 
pies. It is for these reasons that it is here 
treated as a separate association. 
5. V erm ilia-H ermella association 
Range: M.S.L. to M.L.W.N. 
V ermilia carinifera (d) 
H ermella spinulosa (d) 
Modiolus neozelanicus (o) 
Chamaesipbo columna (o) 
Gigartina alveata (o) 
Gelidium caulacantbeum (o) 
Centroceras clavulatum 
(spring and summer) 
Pleonosporum hirtum (o) 
Caulacantbus spinellus (f) 
