Olivbe. — Mollusca of the Kermadec Islands. 563 



Land Formations. 



The numerous small animals and fungi living under stones and leaves 

 in forest, and subsisting mainly on decaying vegetation, constitute a bio- 

 logical communitv distinct from but coterminous with the forest formation 

 which gives rise to it. On Sunday Island eight small molluscs are found 

 in this situation. On the trunks of trees eight other species are found ; but 

 this habitat is practically an extension of that on the ground, one species 

 (Helicarion kermadecensis) being found in both. All the land molluscs 

 found at Sunday Island are small, but this is, no doubt, due to the means 

 of transportation available for them to reach the group — namely, on floating 

 logs or other accidental means. 



One land mollusc, Assiminea nitida, affected open rocks wetted by fresh 

 water, which habitat was also shared by some crustaceans and cryptogamic 

 plants. 



Littoral Rock- Formations. 



Several communities of plants (algae) and animals are to be distinguished 

 in the marine littoral belt. Certain ecological adaptations are easily observed 

 when the whole belt is examined. For instance, the size of animals is found 

 to increase from high- water mark downwards. In other words, the more 

 water any station receives during the day, the greater the variety and 

 abundance of life found therein ; consequently, more food is available, and 

 therefore larger animals are found. A second and more important though 

 scarcely less obvious generalization is that the higher up above low-water 

 mark an animal lives the more it is protected from desiccation by a calcareous 

 shell or chitinous test. In the Kermadec Group rocks between tide-marks 

 support a fauna and flora much poorer in species and individuals than the 

 .corresponding belt in New Zealand, and this I presume to be the result of 

 its greater degree of insolation. In New Zealand I have observed that the 

 line between the submerged and emerging belts is much more pronounced 

 in the north' than it is in the south. 



Bock Belt. — Rocks about and above half-tide mark support no algae 

 except crustaceous species, and in places small filamentous species, which, 

 by harbouring mud, form a kind of slime. Molluscs, however, are fairly 

 numerous. Near high-water mark are small species hiding in crevices of 

 rocks, as Melarhaphe unifasciata, Tectarius feejeensis, Siphonaria amphibia 

 ■ — all able to live for more than half their time out of water. The 

 Siphonaria by sticking close to the rock retains a drop of water, while 

 Tectarius and Melarhaphe when withdrawn within their opercula are capable 

 of living without water for days. 



Lower down, where the rocks are exposed from about six to fifteen hours 

 daily, are found plentifully Cellana craticulatus, C. hedleyi, Siphonaria 

 raoulensis, Neothais smithii, Flaxiphora mixta, Nerita melanotragus, Hinea 

 brasilianus, and less commonly Pinclada vulgaris, Melina nucleus, Sym- 

 pharochiton themeropis, Onithochiton oliveri, and Nerita plicata — al' able to 

 conserve moisture by pressing close to the rock surface, or withdrawing 

 within opercula or shelly valves. 



Corallina Belt. — On rocks just above low- water mark considerable areas 

 are covered by a dense growth, about 15 mm. tall, of the alga Corallina 

 officinalis. This harbours, besides much sand and many worms, a lar^e 

 number of small bivalves of the species Lasaea miliaris and Septifer biio- 

 cularis. 



