13 



pools and gulfs, the latter freely exposing itself to the surf and 

 relying on its pectoral disc to hold on to the rocks. The more con- 

 spicuous echinoderms are the sea-urchin Evechinus chloroticus and the 

 starfishes Asterina regularis, Asterias scabra, and Pentagonaster pul- 

 c helium. Of especial interest is the fauna which is found within the 

 hollowed-out bases of Durvillea. Here are found Siphonaria zealandica, 

 various Crustacea and worms, and the chitons Plaxiphora egregia and 

 Onithochiton neglectus. 



Corallina-Hormosira Association. Between tide-marks there is 

 developed, especially in rock-pools, an association in which th,e 

 branched coralline Corallina officinalis and the brown alga Hormosira 

 Banksi are often fairly well mixed. The distribution of these two 

 algae is determined by the amount of water present, Hormosira 

 affecting drier situations than Corallina, so that frequently Corallina 

 will grow on the floor of a pool, with Hormosira fringing the water- 

 line and exposed during the recess of the tide. Hormosira Banksi 

 sometimes, especially on level rocks, forms a pure association. The 

 animals associated with Corallina and Hormosira include Turbo 

 smaragdus, Cerithidea tricarinata, Melaraphe unifasciata, and, in 

 pools, blennies and shrimps. 



Porphyra Association. Conspicuous on rocks between tide-marks 

 is an association of Porphyra laciniata. It forms large patches about 

 half -tide. The thallus is like that of the sea-cabbage (Ulva), but of 

 a pale-greenish colour. It has a shining appearance when dry, and 

 the tips suffer a good deal from wilting during exposure to the 

 atmosphere. 



Barnacle Association. The chief animal association on rocks 

 between tide-marks is that which occupies a belt over a yard in 

 vertical width just above the brown-algae formation. The rocks are 

 to a large extent covered with the sessile barnacle Chamaesipho 

 columna. With it are associated a number of (usually small) molluscs 

 Cellana denticalata, C. ornata, Siphonaria obliquata, Monodonta 

 coracina, Lepsiella scobina, Sypharochiton pellisserpentis, and many 

 others. The association is in all respects comparable with similar 

 associations on the Australian coasts, but the species are, with the 

 exception of one or two only, entirely different. Within Wellington 

 Harbour the barnacle association is present, but on the more exposed 

 rocks gives way to an association of mussels. 



Zostera Association. Extensive areas of intertidal flats in Wel- 

 lington Harbour are covered with a sward of the grass-wrack Zostera 

 tasmanica. With it occurs an assemblage of molluscs, including 

 herbivorous species such as Turbo smaragdus, Monodonta corrosa, 

 and M. aethiops, and a number of carnivorous forms, including 

 Cominella adspersa, C. lurida, and C. maculosa. The shell locally 

 called " cockle " (Antigona stutchburyi] is abundant just below the 

 surface of the mud. 



Monodonta- A mphibola Association. On mud-flats where Zostera 

 does not grow, a number of molluscs are found, mostly identical with 

 those living among the Zostera. Of especial interest, however, is 

 the presence of the Amphibola crenata. This is a member of the 

 pulmonate or air-breathing order of gastropods which has returned 

 to a life in the water. So dependent now is it on a continuous supply 

 of moisture, which while the tide is out it gets from the moist mud, 

 that it is unable to live for any length of time if kept without water. 



W. R. B. OLIVER. 



