356 ZOOLOGICAL GEOGRAPHY. [part in. 



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 distril)ution. A squirrel (Sciurus 

 hangkcmvs) 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. ]\Iore curious are the two species of 

 Pitta peculiar to Banca ; one, Pitta mcgarhynclius, is allied to 

 the P. hrachyurus, which inhabits the whole sub-region and ex- 

 tends to Siam and Cliina, but differs from it in its very large bill 

 and differently coloured head; 'the other, P. langhanus, is allied 

 to P. cncullatus, which extends from Nepal to INIalacca, and to 

 P. sordidus, wliicli 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 tliis 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 into 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 roclcs 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 tlie 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 ti'acts as Borneo or Suma- 

 tra, subjected to more varied conditions of soil, climate, 

 vegetation, food, and enemies, would preserve, almost or quite 



