39 



(Brown), Surrey (Millett), London (Grey), and Essex 

 (Sheppard). 



It is rather singular that this shell has not been dis- 

 covered in Ireland, and, according to Mr. Grey, it is 

 not found in the north of England, and I believe it is 

 not an inhabitant of Scotland. 



In central Europe generally (Forbes), Germany 

 (Pfeiffer), Sicily (Philippi), and in Sweden (Grey). 



Found fossil as far back in time as the oolitic period. 



We are deficient of a very similar-looking shell, a 

 branch of this family, the Paludina Listeri of Forbes 

 and Henley. It is recorded as being found in the 

 Trent in "The History of British MoUusca," but, as I 

 have not met with it, probably the locality may be a 

 considerable distance from Nottingham, and, in which 

 case, of course cannot be included amongst our shells. 

 The chief distinctive difference of Paludina Listeri 

 from Paludina vivipara are, deeper volutions, a white 

 keel, and an open or well-seen operculum. These 

 characteristics are very striking when comparison is 

 made with Paludina vivipara. 



BiTHINIA. 



This is a twisted or spiral shell, much produced in 

 its form, but varying in shape from that of a more 

 ventricosc and stunted form to that of a greater length 

 with little or no increase in ventricosity. The con- 

 volutions are very rounded, and possessing a somewhat 

 horny epidermis. The aperture is nearly egg-shaped, 

 excepting on the upper side, where it is rather angular. 

 The internal rib around the aperture is thickened. 



