120 The Mollusca of Cambridgeshire 



The wide range of variation here seen is of course not 

 without parallel in the case of many other animals and plants, 

 but the facts are given in some detail as they show the ease with 

 which useful information may be obtained from common forms 

 within a restricted area, and an instance like this furnishes 

 a good starting-point for a systematic enquiry by anyone to 

 whom variation is of interest. Dealt with more fully and the 

 enquiry extended to others of the small water-courses of 

 the neighbourhood, with regard held also to their individual 

 features and past and present connections, a study of the 

 local variation of this Limnaea might well yield an instructive 

 result. 



Mr B. B. Woodward has pointed out 1 that the Pleistocene 

 gravels of Barnwell contain many apparent intermediates 

 between Limnaea peregra and L. auricularia, while many 

 of the former are the inflated form named variety wata by 

 older writers. 



Passing to terrestrial species it will be found that the 

 Backs are a fairly good hunting-ground, and here among 

 moss and grass roots in the damper spots several of the 

 Vitreas are common, such as V. alliaria, V. crystallina, 

 V. nitidula, and with them Zonitoides nitidus. Vitrea cellaria 

 occurs more frequently under stones. Of the Helicidae 

 Hygromia hispida (among grass roots in the damp) and Val- 

 lonia pulchella may be found fairly abundantly. 



Sheep's Green and Coe Fen also have several of the above 

 species, Vitrea nitida, for instance, occurring numerously near 

 water. Agriolimax laevis is also an inhabitant of these 

 pastures 



The Botanic Garden is a fairly good locality for the 

 commoner forms, and the writer is indebted to Mrs Hughes 

 for the record of Testacella haliotidea from this part of 

 Cambridge. It was probably introduced from Kew about 

 twenty years ago. Vitrea lucida is also found in the Garden 



1 " Notes on the Pleistocene Land and Freshwater Mollusca from the 

 Barnwell Gravels," Froc. Geol. Assoc., x., 1888, p. 355. 



