1889.] RELATIONSHIPS OF PALAWAN ISLAND. 227 



inquiry into the physical geography of the group and the relationship 

 of the mammalian fauna ; and they appear to me to be, when taken 

 together, of sufficient weight to justify the inclusion of these islands 

 definitely as an integral portion of the Boruean group in the 

 western sub-area of Indo-Malaya, and this notwithstanding the 

 probability that future research may show that in some classes of 

 animals the Philippine element preponderates, and that many of 

 the small low islets immediately confronting the Philippines on the 

 eastern margin of the Bornean bank, such as the Cuyos, no longer 

 retain any trace of their original western element. 



If the origin of the Palawan fauna here suggested be the true 

 one, then the highlands which are still wholly unexplored, and which 

 attain to an elevation of between 6000 and 7000 feet, will probably 

 be found to exhibit a yet more marked predominance of Bornean 

 forms than is presented by the low country. 



The islands of Cagayan-Sulu and Sibutu, which have been treated, 

 like Palawan, as belonging to the Philippines, should be regarded 

 similarly as natural component portions of the Bornean group. 

 They are both situated on the edge of the fringing submarine 

 bank of north-eastern Borneo. The first named has been visited 

 by Dr. Guillemard, who obtained a small collection of the birds, 

 comprising 15 species, and who pointed out ^ that, judging from 

 the position of the island and the character of its avifauna, it should 

 be regarded as related to the Bornean instead of, as heretofore, to the 

 Philippine group. The only [.eculiar species obtained was Mixomis 

 catjaijuneiisis, a representative form of M. borneensis. The Island 

 of Sibutu has never been visited by a naturalist, and although of 

 small extent it is of interest in view of its close proximity to the 

 southern extremity of the Philippine Archipelago. Dr. Guillemard, 

 again, was the first to show ' that this island should probably be 

 considered as an outlying portion of Borneo ; and as his remarks 

 contain all the information about it, I cannot do better than quote 

 them, premising that the Tawi-Tawi Islands, of which, in pohtical 

 geography, Sibutu is one, form the south-western extension of the 

 Sulu Archipelago, which is admittedly Philippine in the character 

 of its fauna. Dr. Guillemard says : — " West of Tawi-Tawi the level 

 of the sea-bottom completely changes, depths of 100 fathoms or 

 more being obtained close in-shore, while in the fairway of the 

 Strait (the Sibutu Passage) Captaiu Chimmo was unable to get 

 bottom at 500 fathoms. The distance across the Strait is about 

 18 miles, and the surveys hitherto made seem to show an equally 

 precipitous slope of the eastern banks of Sibutu Island. We are at 

 present without exact information as to the soundings between 

 Sibutu and Borneo, one point of which, Tanjong Labian, is distant 

 only 20 miles ; but as many islets, reefs, and sand-cays are known 

 to intervene, it is almost certain that they are not of any great 

 depth. This Sibutu Passage thus seems to be the natural delimita- 

 tion of the PhiUppine Archipelago, and though of the only two 

 species (of birds) obtained, or said to have been obtained, from 

 1 P. Z. S. 1885, p. 418. - P. Z. S. 1885, p. 250. 



