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



channel, contains representatives of no subgenera which do not occur 

 in Luzon. Only two subgenera (Corasia and Calocochlea) appear 

 to be found there. 



Luzon. — The great size of this island, exceeding as it does in area 

 all the other islands, excepting Mindanao, taken together, and its 

 wide extension to the S. and E., cause it, besides developing a rich 

 fauna of its own, to receive immigrants from subgenera not indigenous 

 to it. Thus there is no group which is not represented on Luzon, 

 with the exception of those peculiar to Mindoro and Luban, but, on 

 the other hand, there is no group (except Pfeifferid) peculiar to it. 

 It is characterized by a rich development of the four subgenera 

 Corasia, Calocochlea, Helicostyla, and Orthostylus ; its neighbour- 

 hood to Marinduque gives it its 2 species of Phengus, to the central 

 group its 2 species of Sypselostyla. Catanduanes, Polillo, and 

 Alabat, the three islands on its eastern side, the fauna of which is 

 well known, present no peculiar features ; the channels separating 

 them from Luzon are shallow, and they are practically a part of the 

 main island. 



Marinduque. — ^This island, although in other respects closely 

 related to Luzon, stands out distinct from it in several respects, and 

 is by no means so closely related to it as the islands just mentioned. 

 The channel separating it from Luzon is deep, and apparently only 

 just fails to exceed 100 fathoms in depth throughout its length. 

 It is the metropolis of the subg. Phengus, 7 out of the 9 known 

 species being found there. No species of Calocochlea, so abundant 

 in Luzon, appears to occur. Orthostylus is abundant, and Sypselo- 

 styla is represented by one species. 



Leyte and Samar. — These two islands, which are separated from 

 one another by a very narrow and shallow channel, are closely related. 

 The San Bernardino channel, which separates Samar from Luzon, is 

 not of great depth, and accordingly no subgenus occurs on these two 

 islands which does not also occur on Luzon. On the other hand, 

 the Surigao passage, which separates Leyte from Mindanao, is, at 

 least in part^ of considerable depth, and we find accordingly that 

 two out of the three subgenera hitherto recorded from Leyte do 

 not occur in Mindanao. Neither of the islands can be said to be 

 well explored. Only Calocochlea and Orthostylus are recorded from 

 Samar, and the same two, together with Sypselostyla, from Leyte. 



Burias and Masbate. — The subgenus Canistrum, so far as our in- 

 formation goes, appears to be peculiar to these two islands. This is 

 the more strange, because the channel separating them from Luzon 

 and from Samar is of no great depth, and the stretch of sea between 

 Masbate and the N. coasts of Negros and Cebu is the largest piece 

 of shallow water in the Philippines, scarcely exceeding 30 fathoms 

 at any point. Eastward of Burias and Masbate the depths are con- 

 siderable, and completely separate these islands from the Tablas- 

 Romblon-Sibu} an group. Ticao does not appear to have been 

 explored. Orthostylus is abundant on Masbate. 



Tablas, Eomblon, Sibuyan. — These three islands, which are 

 separated by very deep water from all their neighbours, are closely 



