OLIVER.— Marine Littoral Plant and Animal Communities. 503 
Notoacmea pileopsis and Atalacmea unguis-al Both agree in having 
thin shells, that of Atalacmea being almost transparent. N. pileopsis occurs 
at high-tide mark, Atalacmea near low- ar elated animals, 
The bright-green algae Ulva rigida, C. etomorpha Darwinii, Caulerpa sedoides, 
and C. Brownii flourish in the most brightly illuminated situations, and, 
moreover, present the maximum amount of chlorophyll-bearing tissue 
to the light—Ulva by its wide wavy thalli, Chaetomorpha and Caulerpa 
by having the green layer only on the outside of turgid segments of 
elongate or branched thalli. (Plate 49, fig. 1.) Rock-pools perhaps afford 
a test as to light-enduring qualities, for here the air-drying factor does 
ing in full ht in such situations is Corallina 
voiding ; Corallina and Hormosira are 
morpha appear to be light-seeking. 
A difference is noticed in the colour of Corallina and Amphiroa 
corresponding to the degree of exposure to ight: species | Y 
situations are full-coloured, while those exposed to bright light are always 
much paler. In the same plant the col 
on the outside branches to a deeper shade of re 
branches, which receive less light. P i. 
'The shells of Brachyodontes maorianus are brown when living in shaded 
positions, such as under stones ог under the base of Lessonia, but when 
exposed to full light are of the normal bluish-black colour. Siphonaria 
be but the shade form of the darker S. zelandica. 
tering action on 
light passing through it; in other ed 
different degrees according i 
are absorbed more quickly 
pigments with which t ' 
assumed to be related to the varying qua 
