Java, from its Mollusca, does not appear to hold the comparatively 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 represented 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. _Alycaeus_, _Lagochilus_, _Pupina_, and _Cyclophorus_ are found throughout, but _Hybocystis_ (Malacca, 1 sp.) does not quit the mainland. Borneo is remarkably rich in land operculates, especially noticeable being the occurrence (11 sp.) of _Opisthostoma_ (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. [Illustration: FIG. 208.--=A=, _Opisthostoma Cookei_ E. A. Smith, Borneo; =B=, _Opisthostoma grandispinosum_ G.-A., Borneo. Both × 8.] _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_[369] 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 represented. _Hemiplecta_ and _Xesta_ are abundant and large, while the _Rhysota_ of Borneo contain some huge sinistral forms. _Rhodina_ is a remarkable form from Malacca, whose exact generic position is not yet settled. _Clausilia_ has a few species on all the islands, the last occurring on Ternate, and a single _Papuina_ (Moluccas and N. Guinea) occurs in Borneo. The _Island of Celebes_ marks the beginning of a distinct decrease in the Indo-Malay element. The Naninidae lose ground, in proportion to the Helicidae, _Macrochlamys_, for instance, being represented by only one species, and _Hemiplecta_ by four. Other characteristic genera of the Indian region dwindle, such as _Amphidromus_, _Clausilia_, the tubed operculates, and _Cyclophorus_, while _Sitala_, _Kaliella_, _Glessula_, and _Plectotropis_ disappear altogether. Comparing the total numbers of Naninidae and Helicidae from Sumatra to New Guinea, we obtain this interesting result:-- Sumatra Java Borneo Celebes Moluccas N. Guinea _Nanina_ (all genera) 26 32 51 22 36 40 _Helix_ (all genera) 7 11 13 14 55 91 It will be noticed that the proportion of Naninidae to Helicidae, which has been nearly 4 to 1 in Sumatra, falls to 3 to 1 in Java, and rises again to 4 to 1 in Borneo (showing the essentially continental character of the island); in Celebes it further falls to 3 to 2, while in the Moluccas the scale turns and _Helix_ has the advantage by about 8 to 5, and in N. Guinea by more than 2 to 1.