46 RAMBLES IN SEARCH OF SHELLS. 



of land and fluviatile mollusca. Of the remaining 

 species, the flattened coil-shell, P. comj)lanatus ; the 

 keeled ditto, P. carinatus ; and the white ditto, 

 P. albus, will be the most easily recognized. The 

 shell of couiplanatus (PL VI., fig. 3) may be dis- 

 tinguished from that of carinatus (PI. VI., fig. 2) 

 by its narrower and more rounded whorls, as well 

 as by the keel being placed below, instead of in or 

 towards the middle of the periphery. It is usually 

 larger and thicker than that species, and is much 

 more plentiful, as well as more generally diffused. 

 The greyish white colour of rdbiis (PI. VI., fig. 1) 

 renders it sufficiently conspicuous, and on this 

 account it is not difficult to select it at once from 

 amongst a number of its congeners. 



