TAVA AND BORNEO 



JO9 



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

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

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

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

 while Ceylon and the western side of the Deccan, united into one 

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

 a wide stretch of sea, extended farther eastw^ard in a long island, 

 or series of islands. 



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

 tively isolated position wdiich its mammals and birds seem to 

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

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

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

 sented by 3 species in Sumatra and only 2 

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

 BJiiostoma not occurring in the two former 

 islands at all. Alycaeus, Lagochilus, Pupind, 

 and Cydoi^horus are found throughout, but 

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

 mainland. Borneo is remarkably rich in 

 land operculates, especially noticeable being 

 the occurrence (11 sp.) of Opistliostoriut 

 (Fig. 208), a most extraordinary form of 

 land shell (Ceylon, Siam), of Dip)lomniatina 

 (17 sp.), and Rapliaidus. 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 Ennea (3 sp.) reaches as 

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

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



' Strcidaxis 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 practically 

 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. 



Fig. 208. — A, Opistliostoma 

 Cookei E. A. Smith, 

 Borneo ; B, Opistlio- 

 stoma grandispinosuiii 

 G.-A., Borneo. Both 

 x8. 



