1892.] THE LAND-MOLLUSCA OF THE PHILIPPINES. 457 



Bay in the N. and lUana Bay in the S., appears to me to represent the 

 original channel of separation \ Oorasia occurs all over the island ; 

 its appearance and development must therefore have preceded the 

 separating of the western portion. But Calocochlea and Eudoxus, 

 the latter of vrhich is almost peculiar to Mindanao, occur only in 

 the N. and E. (e. g. smaragdina is found from Mainit in the extreme 

 N. to Davao on the S.E. coast), and are not recorded from any 

 point west of the narrow isthmus. Again, the section of Chloritis 

 of which H. spinosissima, Semp., quieta, Reeve, and sanziana, H. 

 & J., are well known examples, is almost peculiar to Mindanao, but 

 is only found in the district to the W. of this peninsula, and does not 

 appear to have penetrated the main portion of the island. 



One species of Corasia {samboangce,^. & J.) is recorded from 

 the island of Basilau (S. of Mindanao) ; the species is not peculiar, 

 and occurs also on Mindanao. 



Mindoro. — The general relations of this island are very remarkable, 

 and cause it to stand out as by far the most isolated of the whole 

 Philippine group. A glance at the map might incUne us to regard 

 it as a link between Luzon and Panay, with close relations to the 

 former island, and with no cause for especial individuality. Mindoro, 

 however, is incomparably the most isolated of all the Philippines. It 

 contains one, possibly two, absolutely peculiar subgenera, which are 

 very well marked, and of which the nearest relations appear to be with 

 Sypselostyla. In other words, the relations of Mindoro, are, so far, 

 but only very remotely, with Panay. At the same time, however, 

 no existing subgenus appears to be common to the two islands. 

 Probably further exploration may detect Chloreea^ Corasia, and 

 Calocochlea on Panay ; but that would not bring its relationship to 

 Mindoro at all closer, since these subgenera are known from almost 

 every island. With Luzon Mindoro has, excluding the three sub- 

 genera universally prevalent, only one subgenus {Helicostyla) in 

 common. All the species, however, are peculiar to Mindoro. 

 Through this subgenus Mindoro appears also related to the Tablas- 

 Romblon-Sibuyan group, and also to the Cuyos Is., but not to Panay. 

 Accina, Eudoxus, Orthosfi/lus, Pliengus, Canistrum, and Hypselostyla 

 are completely absent. Cochlodryas, however, is common to Min- 

 doro and Burias only. 



Cuyos Is. — These islands are very imperfectly known, but what 

 little information we have tends to relate them with Mindoro, and 

 not with Panay or Palawan. If Cuming's authority is to be trusted, 

 the only two subgenera which occur in the Cuyos (Helicostyla and 

 Prochilus) are common to Mindoro, but do not occur either on Panay 

 or Palawan. 



Luban. — This little island, lying almost between Luzon and 

 Mindoro, must have been, in all probability, isolated for a long time. 

 It contains one well-marked subgenus, Ptychostyla, which is quite 

 peculiar. Deep water surrounds the island on every side. 



^ Most atlases, even the most recent, erroneously represent this isthmus as 

 traversed by a lofty range of mountains. 



