JAVA AND BORNEO 



309 



It seems not impossible, from the point of view of the land 

 Mollusca only, that the Sunda Islands may at one time have 

 stretched much farther into the Bay of Bengal, prolonged, per- 

 haps, into what are now the Andaman and Nicobar groups, 

 while Cejdon and the western side of the Deccan, united into 

 one continuous piece of land, and possibly separated from N. India 

 by a wide stretch of sea, extended farther eastward in a long 

 island, or series of islands. 



Java, from its Mollusca, does not appear to hold the compara- 

 tively isolated position which its mammals and birds seem to 

 indicate. Borneo, on the other hand, is more Siamese than Java 

 or Sumatra in respect of a group whose metropolis is Siam, 

 namely, the tubed operculates ; for while that section is repre- 

 sented by 3 species in Sumatra and only 2 

 in Java, in Borneo it has as many as 19, 

 Rhiostoma not occurring in the two former 

 islands at all. Alycaeiis^ Lagochilus^ Pupina^ 

 and Cyclophorus are found throughout, but 

 Hyhocystis (Malacca, 1 sp.) does not quit the 

 mainland. Borneo is remarkably rich in 

 land operculates, especially noticeable being 

 the o,ccurrence (11 sp.) of OpistJiostoma 

 (Fig. 208), a most extraordinary form of 

 land shell (Ceylon, Siam), of Diplommatina 

 (17 sp.), and Raphaulus. The occurrence 

 of a single Papuina (Moluccas eastward) 

 is very remarkable. 



Amphidromus is a genus characteristic 

 of the great Sunda Islands, attaining its ^^• 

 maximum in Java (12 sp.). The Indian Glessula still has 

 one species each in Sumatra, Java, and Borneo. One species 

 of Streptaxis'^ occurs in Malacca, but Unnea (3 sp.) reaches as 

 far east as Borneo and the Philippines. Parmarion, Helicarion^ 

 Ariophanta^ and other groups of the Naninidae are well repre- 



FiG. 208.— A, Opisthostoma 

 Cookei E. A. Smith, 

 Borneo ; B, Opistho- 

 stoma grandispinosum 

 G.-A., Borneo. Both 



1 Streptaxis is a remarkable instance of a mainland genus. Although abundant 

 in the Oriental, Ethiopian, and Neotropical regions, it never seems to occur on 

 any of the adjacent islands, except in the case of Trinidad (1 sp. ), which is prac- 

 tically mainland. Omphalotropis, on the other hand, is the exact reverse of 

 Streptaxis in this respect, occurring all over Polynesia and the Malay Is., as far 

 west as Borneo, as well as on the Mascarenes, but never, save in a doubtful case 

 from China, on the mainland of Asia, Australia, or Africa. 



