1004 MALAYSIAN LAND AND FRESHWATER MOLLUSCA, 
heat. All these conditions are found pre eminently in the region 
I have specified, and perhaps in no country of the world are they 
more favourably united for the development of terrestrial mollusca. 
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- 
evei’, that some types are very wide-S| >read, such for instance, as 
the forms of which Helix citrina L., and Bulimus perversus L., are 
the types. 
It is highly probable that we have in the Malay Peninsula 
and its islands the remains 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 suV)-kingdom a fauna of great anthjuity. The 
circumstances also favour the restriction of species, because the 
land is so broken up into islands. Thus si>ecific peculiarities 
become propagated and I’estricted. 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 
