THE PHILIPPINES 313 



sian element, and a remarkable development of individual char- 

 acteristics. 



The principal indigenous feature is the profuse abundance 

 of the genus Cochlostyla^ a group of large and elegant land shells, 

 partly helicoid, partly bulimoid in shape, many of the species 

 of which are covered with a curious hydrophanous epidermis. 

 They are in the main of arboreal habits, living in the tops of the 

 enormous forests which cover the greater part of the islands. 

 As many as 247 species, belonging to 15 sub-genera, have been 

 described. 



The distribution of the sub-genera of Oochlostyla on the 



Fig. 210. — Co chlosUj la (Chry- Fig. 211. — Oochlostyla (Ortho- 



salis) mindoroensis Brod., stylus) Po7'tei 'Reeve, LiWzon. 



Mindoro, Philippines. x §. 



different islands of the Philippine group affords important 

 evidence on the geological relation of the islands to one another. 

 Thus we find Orthostylus and Hyp^elostyla occurring in the 

 central islands and S. Luzon, but not in Mindanao or Mindoro ; 

 we find Chrysalis peculiar to Mindoro, Prochilus to Mindoro 

 and the Cuyos, Ptychostyla to Luban, all these being sub-genera 

 of very marked characteristics. Six out of the fifteen sub-genera 

 are entirely absent from Mindanao, although occurring on the 

 islands in the immediate vicinity. The little group Tablas- 

 Romblon-Sibuyan are entirely deficient in certain sub-genera 

 which occur on the islands surrounding them on all sides.^ 

 1 A. H. Cooke, P. Z. S. 1892, pp. 447-469. 



