460 REV. A. H. COOKE ON [May 17, 



species of Amphidromus are known from the Philippines (Sumatra 5, 

 Java 15, Borneo 6) ; of these two get no farther north than Balabac, 

 another occurs on Palawan, while two others are met with in Min- 

 danao, and one of these has penetrated as far as Bohol and S. Leyte^. 

 A detailed survey of some of the principal genera common to the 

 Philippines and the neighbouring islands will be given below. 



It would seem as if the connection which probably at one time 

 existed between Palawan, Busuanga, and Mindoro was not directly 

 across the present Mindoro Strait, where the depth is extreme. The 

 Cuyos Is. appear to have shallow water to the W., and decidedly 

 deeper water to the E. ; thus their connection is with Palawan now. 

 Again, the water shallows rapidly towards the S.E. end of Mindoro 

 Strait, and is broken by islets and submarine banks, which extend 

 from the S. point of Mindoro towards Panay and also towards 

 Busuanga ; the water, however, between these banks and islets is deep, 

 being generally over 100 fathoms, and often more. The water off 

 the N. and W. sides of Panay has not been very accurately surveyed, 

 but is in all probability extremely deep. It would thus seem probable 

 that any connection which may have existed between Mindoro and 

 Busuanga (and a consideration of the very remarkable Helicidse of 

 both islands makes such a connection extremely probable) followed 

 the line of shallower water at the E. end of the Mindoro Strait, and 

 possibly extended some distance eastward towards Panay. 



It will now be interesting to examine the Land-MoUusca of these 

 two ridges, with a view of discovering whether or not they belong to 

 the Philippine fauna. 



Unfortunately, our knowledge of the Land-Mollusca of the Soo-loo 

 ridge is meagre in the extreme. We know that Basilan, Lampinigan, 

 and Malanipa are, by their Gochlostylce, closely related to Mindanao. 

 We know also that one species of Gochlostyla (lais, Pfr.) occurs on 

 Soo-loo Is. Tawi-tawi^ is quite unexplored. The MoUusca of 

 Bongao, the last island at the Borneo end of the chain, are known. 

 Eleven species in all are enumerated, five of which show distinct 

 relations with Borneo. 



The following species are known to occur on Basilan : — 



Gochlostyla zamhoangee, H. & J. Also occurs in Mindanao. 



Xesta mindanaensis, Semp. „ Mindanao. 



Ghloritis sanziana, H. & J. ,, Mindanao. 



Ohhina rota, Brod. „ Bohol, Siquijor, &c. 



Rhysota semiglobosa, Pfr. „ Phihppines generally. 



Macrochlamys crelristriata, Semp. Also occurs in Mindanao. 



Microcystis myops, Semp. & Dbrn. „ Philippines 



[generally. 

 Trochomorpha metcalfei, Pfr. Also occurs in Philippines generally. 

 Stenogyra panayensis, Pfr. „ Phihppines generally. 



Pupina ottonis, Dohrn. „ Mindanao. 



^ Am;ph. maculiferus, Sowb. ; see Semper, Reisen, II. iii. p. 148. 



* The ' Samarang ' anchored off the island, but did not make a landing. 



