DERIVATION OF THK FLORA AM) FAUNA 317 



+ Tonuxtcllhia apcritx Odhner. — Mt. A Pacilic j^enusofover 50 species, ranijing 

 from \\. Ind. and Japan over Micron., Polyn. (incl. Hawaii), Melan. (Kermadec 

 Is., X. Caled.) to Austral, and .\. Zeal. 



T. bilaiitillaia Anton. Recorded from ( )paru T. 



+ 7'. callvsa Odhner. — Mt. 



+ T. coiiica Anton. — Mt. 



+ T. plicosa Odhner. — Mt. 



7". rcclusiaia Petit. — I\If. .According to ()1)1L\i:r probably identical with 7". liir- 

 rita Anton. 



+ T. trochiforviis (Beck) Pfeiff.— Mt. 



T. trochlearis (Beck) Pfeiff. Oparu I.— Mt. 



+ 'ror)iatelli>iops nii)iuta (Anton) Pilsbry et Cooke. — Mt. A Pacific genus of 

 22 species, reported from Japan, Philipp. Is., Polyn. and N. Zeal. 



Zo)iitidac. 



Hyalinia alliaria Miller. A widely distributed, anthropochorous species.- — Mt. 

 H. cellaria Miller. As the former.— Mt. Mf. 



P"orty-six species are enumerated; of these 6 have been introduced through 

 the human traffic. Of the remaining 40, 35 (87.5 %) are supposed to be en- 

 demic; 13 belong to the two endemic genera. The occnvvQUce o{ Succiuea fragi/is 

 in Hawaii and Juan Fernandez and nowhere else in surprising, and 4 species 

 are credited to Oparu (Rapa) Island, but the distribution is perhaps not too w^ell 

 known. The poverty of Masafuera, where only 5 species have been collected, 3 

 of them restricted to this island, is, I daresay, only apparent. Additional forms 

 have been found later and still await study. On Santa Clara only empty shells 

 of a Masatierran species were found. This islet seems entirely unfit for land-shells. 



Only two well-defined geographical groups are distinguished, to which a 

 third of wider extension is added. 



I. American element. — 8 sp. 



Amphidoxa (2), Radiodiscus (i), Stephanoda (5). 



II. Pacific element. — 23 sp. 



Charopa (3), Fernandezia (11), Tornatellina (8), Tornatellinops (i). 

 III. Austral (or more widespread) element. — 9 sp. 



Punctum (2), Succinea (7, see above). 



Chapter IV. 



Continental and Oceanic islands. 



For a clear distinction between the two main kinds of islands WALLACE [2y8) 

 is as a rule referred to as the leading authority. From a geographic-geological 

 viewpoint an island, usually neovolcanic or coralline, which does not stand upon 

 a continental shelf, is called oceanic. If situated on the shelf there is a strong 



