THE MOLLUSCA. 139 



Planorbis contortus (Twisted Coil-shell). In many ditches on 

 the Moss. The whorls are very closely coiled and very 

 narrow, the upper surface rather flat, the underneath 

 deeply concave. 



Limnceus pereger (Puddle Mud-shell). In every ditch, pond, 

 and stream, where it may be commonly found crawling 

 about the bottom. 



Limnceus stagnalis (Lake Mud-shell). Fine specimens may be 

 found in ditches in Birkdale Park, and in ditches on the 

 Scarisbrick-road and on the Moss. It is a handsome 

 shell, light brown, an inch and a half high, the body 

 whorl large and open, the spire of six or seven volutions 

 tapering to a fine point. 



Limnceus glaber. Also found in Birkdale ditches, but very rare. 



Limnceus truncatulus (Ditch Mud-shell). Not uncommon in 

 most ditches on the Moss, generally at the surface of the 

 water, close to the side. Shell dark brown, about a 

 quarter of an inch high. 



Limnceus palustris (Marsh Mud-shell). Rather common in 

 ditches on the Moss, in Birkdale, and in the neighbour- 

 hood of Churchtown. Shell dark brown, about three- 

 quarters of an inch high, body whorl longer than broad, 

 the spire gradually tapering to a point 



Ancylus fluviatulus (Common River Limpet). Very rare. 

 Found on stones in a stream on the Moss. The shell is 

 about a quarter of an inch in diameter and height, cone- 

 shaped, with the apex curved backwards and near one 

 end. Semi-transparent, light greenish horn colour; inside 

 blueish white, shining. 



