ISLANDS ADJACENT TO THE PHILIPPINES 



315 



Islands adjacent to the Philippines. — 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 i-epresent the ancient 

 highway of transit, by which Indo-Malay species passed into the 

 Philippines. The depth of the sea on either side is profound, 

 ranofino- from an averaofe 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 rids^e. 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 Opisthoporus (1 sp. each). At the northern end of 

 the ridge, on Busuanga and Calamian, the Philipjjine element 

 predominates. 



Representatives of two remarkable groups of Helix ( Camaena 

 and Phoenicohius^ occur along the Palawan ridge and in iMindoro. 

 The Phoenicohius 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 Phoenicohius group is H. 

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

 assigned to Camaena also occur 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 range. 



