PLATE XCIX. 



This aquatic snail is rather scarce ; it has been lately found in the 

 Thames, near Greenwich. Petiver says his were found in the rivu- 

 lets about Peterborough House, Westminster. 



Da Costa mistook this for the Helix complanata of Linnaeus ; it is 

 evidently the Helix contorta of that author, who veiy minutely de- 

 scribes it in the Fauna Suecica. 



