356 
ZOOLOGICAL GEOGRAPHY. 
[PART 111. 
Banco ,. — We must, however note the fact of peculiar species 
occurring in Banca, a small island close to Sumatra, and thus 
offering another problem in distribution. A squirrel ( Sdurus 
bangkanus) is allied to three species found in Malacca, Sumatra, 
and Borneo respectively, but quite as distinct from them all as 
they are from each other. More curious are the two species of 
Pitta peculiar to Banca ; one, Pitta mcgarliynchus , is allied to 
the P. brachyurus , which inhabits the whole sub-region and ex- 
tends to Siam and China, but differs from it in its very large bill 
and differently coloured head ; the other, P. bangkanus , is allied 
to P. cucullatus , which extends from Nepal to Malacca, and to 
P. sordidus , which inhabits both Borneo and Sumatra as well as 
the Philippines. 
We have here, on a small scale, a somewhat similar problem 
to that of Java, and as this is comparatively easy of solution we 
will consider it first. Although, on the map, Banca is so very 
close to Sumatra, the observer on the spot at once sees that the 
proximity has been recently brought about. The whole south- 
east coast of Sumatra is a great alluvial plain, hardly yet raised 
above the sea level, and half flooded in the wet season. It is 
plainly a recent formation, caused by the washing down iuto a 
shallow sea of the debris from the grand range of volcanic 
mountains 150 miles distant. Banca, on the other hand is, 
though low, a rugged and hilly island, formed almost wholly of 
ancient rocks of apparently volcanic origin, and closely resem- 
bling parts of the Malay Peninsula and the intervening chain of 
small islands. There is every appearance that Banca once 
formed the extremity of the Peninsula, at which time it would 
probably have been separated from Sumatra by 50 or 100 miles 
of sea. Its productions should, therefore, most resemble those of 
Singapore and Malacca, and the few peculiar species it possesses 
will be due to their isolation in a, small tract of country, sur- 
rounded by a limited number of animal and vegetable forms, and 
subject to the influence of a peculiar soil and climate. The 
parent species existing in such large tracts as Borneo or Suma- 
tra, subjected to more varied conditions of soil, climate, 
vegetation, food, and enemies, would preserve, almost or quite 
