ISLANDS ADJACENT TO THE PHILIPPINES 



315 



Islands adjacent to the Fhilippines. — The Philippines are 

 connected with Borneo by two distinct ridges or banks of eleva- 

 tion, which enclose between them the Soo-loo or Mindoro Sea. 

 There can be little doubt that these ridges represent the 

 ancient highway of transit, by which Indo-Malay species passed 

 into the Philippines. The depth of the sea on either side is 

 profound, ranging from an average of about 1000 fathoms west 

 of Palawan to 2550 off the south-west coast of Mindanao. 



It appears that the fauna of the Soo-loo ridge is definitely 

 Philippine up to and including Bongao, Sibutu, and Bilatan, the 

 last islands at the Bornean end of the ridge. On these are found 

 two species of Cochlostyla and an Ohhina. 



The Palawan ridge may also be described as more or less 

 Philippine throughout. One species of Cochlostyla occurs on 

 Balabac, just north of Borneo, and two on Palawan, but these 

 are perhaps counterbalanced by the definitely Indo-Malay Amphi- 

 dromus and 02nsthopoms (1 sp. each). At the northern end of 

 the ridge, on Busuanga and Calamian, the Philippine element 

 predominates. 



Eepresentatives of two remarkable groups of Helix (Camaena 

 and Phoenicohms) occur along the Palawan ridge and in Mindoro. 

 The Fhoenicohius find their nearest allies in the curious small 

 group known as Ohha, from N. Celebes, the Camaena possibly in a 

 type of Helix {Hadra) occurring in New Guinea and N.E. Australia. 

 The only other Helix from the whole of the E. Indies which 

 bears any resemblance to the Fhoenicohius group is H codonodes 

 Pfr., which is peculiar to the Nicobars. A few forms assigned to 

 Camaena also occm- in Further India and Siam. It would 

 appear possible, therefore, that these two isolated groups are a 

 sort of survival of a fauna which perhaps had once a much 

 more extended ransje. 



