1006 MALAYSIAN LAND AND FRESHWATER MOLLUSCA, 



Some of the peculiai' genera of this region have extraordinary 

 organs which are not seen elsewhere. Thus Opisthoporus is a 

 depressed shell furnished with a little open tube behind the mouth. 

 Pterocychs has an almost similar tube formed by a notch in the 

 peristome at its junction with the superior whorl, an arrangement 

 which is slightly modified in an allied genus named Spiraculum. 

 Alycceus has the last whorl swollen, constricted and strongly 

 twisted near the mouth. All these species have peculiar opercula 

 composed of a calcareous spiral series of concentric plates. In 

 the family Pupininse there are the strongest modifications of the 

 last whovl which becomes twisted and constricted in the most 

 erratic manner. In Opisthostoma it is elevated vertically in the 

 air like an elephant's trunk. In Hybocystis we have a very 

 peculiar torra of land-shell, of which a full description is given 

 at the end of the list. It is an approach to Megalomastoma, and 

 may be said to be confined to Burmah and the Malay Peninsula. 



As the limits of the region here dealt with are so little explored, 

 no such things as sub-provinces can be made, unless it be in the 

 way of considering each island a sub-province in itself. It is 

 obvious to any one who considers the size and extent of any of the 

 islands, that only a very small portion of them can have been 

 well explored for their molluscan fauna. The total number of 

 known species or varieties, amounting as it does to scarcely 

 400, can only be considered as an instalment of the actual census. 

 The large island of Borneo alone might be expected to furnish 

 such a number, when we remember how the climate, soil, and 

 vegetation of this region favour the development of the molluscan 

 fauna. Yet the species of Borneo can scarcely be said to be known 

 at all. 



In dealing with the genera and species of the various authors, 

 it has already been stated that the specific or generic value in any 

 individual case is a matter for which the authors themselves are 

 alone responsible. Yet it must be borne in mind that the difli- 

 culty of dealing with some of the larger genera renders sub-division 

 of some kind absolutely necessary. Thus in the immense genus 



