808 ON THE VOLCANO OF TAAL, 



3. Neritina dubia, Chemnitz, V, 324, figs. 2019 and 2020, and 

 (according to Wood's Index Testaceologicus) iV. dubiosa, 244 ;. 

 JV. Philip^nnarum, Sowerby ; N. reticulata, Quoy ; N. zebroides, 

 Lesson, teste Recluz. This Neritina varies between shining black 

 with minute yellow spots or yellow zigzag diagonal markings, and 

 a distinctly banded form of a great variety of patterns and 

 colours, such as yellow and black, yellow and red, and in the 

 centre of the red lines a black band with minute chevrons. There 

 are also black and white shells of a bi'oad zebra pattern. The 

 aperture is obliquely produced, the columella is broadly enamelled 

 with white, and furnished with minute teeth. The operculum of 

 one large spiral like an argonaut shell with a central ridge, 

 rugose lines of growth and no granulations. On the inner side it 

 is polished, has a broad ridge which terminates spirally in two 

 prominently projecting claws. Found abundantly in one place 

 only on the sands at the exit of the river Pansipit. 



4. Paludina tricarinata, Anton. A diaphanous olive-brown 

 shell, elongately turbinate, slightly i;mbilicate with a pale blue 

 columella. The whorls have three distinct sharp keels, with 

 several smaller intermediate ones and a channel suture. Large 

 quantities of this shell are found in all the rivers and streams of 

 the Philippines. It is a type which belongs to the Asiatic tropical 

 regions, and though several species have been distinguished 

 on minor features, yet they pass into one another in a way that 

 renders identification almost impossible. Generally speaking, all 

 the specimens are distinctly tricarinate, but the intermediate keels 

 vary in their prominence and importance, so that it becomes a 

 matter of opinion whether thei*e are three, four, five, or more. 

 There are considerable numbers — as already stated — at Los Bailos 

 killed by the hot water, and there are others of the same type 

 showing certain variations in the River Pansipit, and along the 

 small streams emptying into the Laguna de Bombon. 



5. Melania aspera, Gmelin. A peculiar, somewhat short 

 species, with distinct tubercles on the upper margin of the whorl, 



