128 The Mollmca of Cambridgeshire 



CLAUSILIIDAE 



Balea perversa (Linn.) (3) 

 Clausilia (Marpessa) laminata (Mont.) 

 Clausilia (Pirostoma) bidentata (Strom.) [= 

 versa Pulteney = ru#osa Drap.] (3) 



SUCCINEIDAE 



Succinea putris (Linn.) (2) (3) (5) 

 Succinea elegans, Risso (3) (5) 



PELECYPODA 



EULAMELLIBRANCHIATA 



DRE1SSENSIIDAE 



Dreissensia polymorpha (Pall.) 

 UNIONIDAE 



Unio pictorum (Linn.) (3) 



Unio tumidm, Retz (l) (3?) 



Anodonta cygnaea (Linn.) (3 ?) 

 SPHAERIIDAE 



Sphaerium rivicola (Leach) 



Sphaerium corneum (Linn.) (3) (5) 



Sphaerium lacustre (Mull.) (3) 



Pisidium amnicum (Mull.) (2 ?) (3) (4) (5) 



Pisidium henslowianum (Shepp.) (3) 



Pisidium subtruncatum, Malm [=fonti>uile Jeff.] (3) 



Pisidium pulckellum, Jenyns (3) 



Pisidium pusillum (Gmel.) [ = fontinale Drap. of 

 Continental authors] (3) (5) 



P'liidium nitidum, Jenyns (3) (5) 



Pisidium obtusale, Pfeitf. (5) 



Compared with the British Isles as a whole the incidence 

 of species of non-marine Mollusca in Cambridgeshire is shown 

 by the following table. 



