810 ON THE VOLCANO OF TAAL. 



of this type are not so much distinguished by colour as by the 

 presence of a double membranaceous periostraca, to which the 

 different species are indebted for their characteristic patterns. 

 B. ciimingii, Fir., and B. leaii, Pfr., and a few others belong to 

 another type. In this the shell is inflated, mostly shining white 

 with only a very thin single periostraca. About 80 species have 

 been collected, each, with the exception of about half a dozen^ 

 confined to its particular island. Some live on the branches of 

 trees, but a few, such as B. elongatulus, Pfr., and B. panayensis, 

 Pfr., burrow underground. These are transparent and horny 

 (Reeve Elem. Conch. 1860). I found a very great resemblance 

 in type between the Philippine land shells and those of Borneo. 



EXPLANATION OF PLATES. 



Plate xviii. — Map of y. Luzon with Lake Bombon. 

 XIX. — Map of Volcano Island, Taal. 



