562 Transactions. 



Polynesian Element. 



This is undoubtedly the largest element in the molluscan fauna of the 

 Kermadecs. The figures given above include several species which I have 

 in the literature at my disposal found recorded from Australia only ; but 

 most of them are tropical species, and no doubt extend to Polynesia as 

 well. According to the table, over two-fifths of the Kerrnadec Mollusca 

 are also found in Polynesia. But to estimate this element correctly there 

 should be included all those endemic species of Polynesian affinities, and 

 this would bring the proportion up to about two-thirds. 



New Zealand Element. 



Under this head I include one-eighth of the total number of molluscs 

 known from the Kermadecs. Of these, twenty-three extend also to Aus- 

 tralia, and, in addition, there are fifteen other New Zealand species dis- 

 tributed over the headings " Pelagic " and " Polynesian," thus making 

 forty-six species common to the Kermadecs and New Zealand. 



Pelagic Molluscs. 



These are species which frequent the surface of the open ocean. They 

 form about one-eighth of the total known molluscan fauna of the Kerma- 

 decs, a proportion which is evidently due to the situation of the group in 

 a wide tract of ocean. Included are several Cephalopods and Pteropods, 

 Recluzia, Atlanta, and four species of lanthina, besides some species found 

 in floating logs and coconuts. 



Summary. 



The Mollusca of the Kerrnadec Islands appear to be derived from two 

 sources ; that is, there appear to have been two main streams of migration 

 — one, by far the larger, from Polynesia, and another from New Zealand. 

 A highly peculiar group, typified by Scutellastra kermadecensis, may be taken 

 as evidence of a first period of dispersal along a continental shore-line, but 

 the bulk of the species, including all the terrestrial forms, indicate a later 

 period synchronous with the existence of the present islands when no con- 

 nection existed with other lands. 



Ecology. 



Although one of the most interesting branches of biological study, very 

 little can be written under this head. A few remarks on the dependence 

 of marine animals on the supply of water and food, quite obvious to the 

 casual observer, interspersed among brief descriptions of the molluscan 

 formations is all that I will attempt. These formations may conveniently 

 be arranged, at least for my present purpose, in four series — namely, land, 

 littoral rocks, sea-bottom, and surface of ocean. In abstracting the mol- 

 luscan element in a formation, or, as I would prefer to call it, " biological 

 community," one cannot get a correct view of the inter-relations of organisms, 

 because the whole community really consists of every plant and animal 

 living in and responding directly or indirectly — that is, through other 

 plants or animals — to the same habitat. Defined by such considerations, 

 two or more formations may be found in the same area. For instance, in 

 the littoral belt, the group of organisms found living under stones is quite 

 d-'stinct from that found on their upper surfaces. The habitats are different, 

 and few species are common to both. 



