Land-snails 373 



l^y an external rib. Moderately common. F. 'pmilla 

 and P. angustior differ from all the rest in having 

 sinistral shells, i.e. the mouth opening faces our 

 left side as we look at it. P. imsilla is one- m^ 

 fourteenth of an inch, the mouth triangular- ^^ 

 oval, with six or seven teetli, and a strong antiva-tujo 

 yellowish-white rib both inside and outside. It 

 is very local, but has been reported from north Devon, 

 Oxfordshire, Notts, Derbyshire, west Yorks, Durham, 

 Northumberland; Ayrshire; and County Londonderry. 

 P. angustior is only one-sixteenth of an inch, and pro- 

 portionately narrower than imsilla) the mouth more 

 triano-ular and narrow, with four or five teeth, and a 

 rib as in the previous species. It occurs at the roots 

 of grass in wet places, but is very local. Its recorded 

 stations are in Derbyshire, Yorks ; Sutherland ; County 

 Londonderry, Sligo, Galway west, Cork south. 



It is to be presumed that the teeth, which are so 

 important a character of these shells, serve a practical 

 purpose in keeping out minute insect enemies which 

 frequent the same situations. 



The Tree Snail {Balea i^erversa) is the sole British 

 representative of its genus. It is not greatly unlike 

 a Buliminus. The animal is much the same, 

 though its teeth and their arrangement on the 

 radula are different. There is a central tooth 

 with 20 laterals on either side in each row, and 

 the number of rows is 130— a total of 5330. 

 The shell is club-shaped, thin and glossy, coiled 

 to the left as in P. lyusilla ; yellowish brown 

 in colour. The mouth is somewhat pear-shaped, 

 without teeth, except that occasionally full-grown 

 specimens are found with a small one near the 



