1004 MALAYSIAN LAND AND FRESHWATER MOLLUSCA, 



heat. All these conditions are foimd preeminently in the region 

 I have specified, and perhaps in no country of the world are they 

 more favourably united for the development of terrestrial mollusc;^. 



Soil also has a remarkable influence. Some species prefer 

 granite formations; but the predilection of land mollusca for 

 limestone rocks is very striking. In the Malay Peninsula there is 

 quite a number of small isolated limestone outliers in the form of 

 hills and table-lands, mostly of a precipitous character. These are 

 all distinguished by an abundance of genera and species of land- 

 shells. The restricted habitat of some is most remarkable, and 

 each patch of limestone seems to have its own species. It has 

 been remarked by various naturalists how few means of dispersal 

 the land-shells have, and thus it is that we find each island with 

 its own fauna, no matter how small it is. Some of these species 

 are peculiar and exceptional types. It must be admitted, how- 

 ever, that some types are very wide-spread, such for instance, as 

 the forms of which Helix citrina L., and B^dimns perversus L., are 

 the types. 



It is highly probable that we have in the Malay Peninsula 

 and its islands the I'eniains of a very ancient continent. None 

 of the younger formations have any place except in Sumatra and 

 Borneo. At any rate there are no rocks which would justify the 

 supposition that the region has been completely submerged within 

 modern geological times. For these reasons, therefore, we have in 

 the molluscan sub-kingdom a fauna of great anti(|uity. The 

 circumstances also favour the restriction of species, because the 

 land is so broken up into islands. Thus specific peculiarities 

 become propagated and restricted. It may be said, in keeping 

 with this, that though the species or varieties of the region are 

 very numerous, yet the types are comparatively few. I take here 

 the opportunity of noting that though I give a list of all the 

 species enumerated by various authors known to me, I am very 

 far from endorsing their views as to the value of the specific 

 distinctions in any case. Probably the number of species, and 

 even the genera, will admit of extensive reduction hereafter. In 



