136 The Mollmca of Cambridgeshire 



no further north than Asia Minor and Egypt. It seems to 

 be a species which is dying out in the north, for in England it 

 is found in the Norwich Crag and in the gravels not only of 

 Cambridgeshire but in those of the Humber and Thames and 

 of certain rivers of France, Belgium and Siberia. 



Unio littoralis, Lain., still lives in France, the Iberian 

 Peninsula and North Africa. 



The variety of Unio pictorum described as Ihwwt by 

 Nilsson is now found alive in rivers in northern France. 



Turning from the species which occur only in the Gravels, 

 it is pointed out in Mrs Hughes's paper that near Cambridge 

 there are now living certain common forms which hitherto 

 have not been found in the Pleistocene deposits and therefore 

 perhaps did not enter England till after these were laid down. 

 These are Helicella cantiana, Hygromia rufescens and Helix 

 aspersa, all found in abundance in the district at present. 

 The question of whether the last named was imported into 

 England has been much discussed, but the facts given in a 

 recent paper by Messrs A. S. Kennard and B. B. Woodward 1 

 leave no doubt that though commerce has probably extended 

 its range this species entered the British Isles without the 

 help of man. The authors conclude that it came from south- 

 western Europe over lands now submerged in the Atlantic in 

 the same manner as Geomalacus maculosus entered Ireland, 

 Hygromia montivaga Cornwall and Helix pisana South Wales, 

 Cornwall and the Channel Islands. Helix aspersa is not 

 known as a fossil on the continent of Europe, but it occurs in 

 Pleistocene deposits in Algeria, while in England it is found 

 in Neolithic beds at Hastings, in beds at least pre-Roman at 

 Harlyn Bay in Cornwall, in hill wash at St Catherine's Down, 

 I. of Wight, and in Holocene deposits at Clifden Ilrnipdcii 

 near Oxford. 



Helix pomatia, which lives locally near Shelford, is not 

 known in the Gravels and Mrs Hughes failed to find it with 

 //. iixju'Mi in the Roman pits. In this connection may br 

 1 Proc. Cotteswohl NntnrnUxtS Field Club, xiv., lllO.'i, p. 1 !!. 



