DERIVATION OF THE FLORA AND FAUNA 317 



+ Tornatellina aperta Odhner. — Mt. A Pacific genus of over 50 species, ranging 

 from E. Ind. and Japan over Micron., Polyn. (inch Hawaii), Melan. (Kermadec 

 Is., N. Caled.) to Austral, and N. Zeal. 



T. bilamellata Anton. Recorded from Oparu I. 



+ T. callosa Odhner. — Mt. 



+ T. conica Anton. — Mt. 



+ T. plicosa Odhner. — Mt. 



T. reclusiaia Petit. — Mf. According to Odhner probably identical with T. iiir- 

 rita Anton. 



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



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



+ Tornatellinops minuta (Anton) Pilsbry et Cooke. — Mt. A Pacific genus of 

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



Zonitidae. 



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

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



Forty-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 occurrence oi Succinea fragilis 

 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 well 

 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), TornatelHna (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 [2^8) 

 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 



