20 



THE NON-MARINE MOLLUSCA OF THE RIVER LEA 



Copenhagen, who kindly identified the species for us, informs us 

 that it is now living in Siberia, Finland, and Northern Scandi- 

 navia, ^vhile it occurred in Denmark solely in deposits of the 

 Oak-period ( = Bronze-age). Up to the present we have noted 

 it from the dried "Thames mud" of the Embankment on the 

 site of the New Scotland Yard (in which it is probably a derived 

 fossil), from the Holocene gravels at the same spot and at the 

 Houses of Parliament ; from Betteridge Road, Fulham ; Kew,. 

 Staines, and Clifton Hampden, Oxfordshire. It will be noted 

 that these are all connected with the Thames river system. 

 Why a form, which was abundant within comparatively modern 

 times, should have become totally extinct, is indeed an interest- 

 ing problem, for which we can offer no solution. (Fig. 2.) 



Planorbis fontanus, Lightft., forms another new record 

 for these beds. 



2- 3- 



FIG. 2. PIANORBIS STRCEMIT, WEST. 

 FIG. 3. PISIDIUM SUPINUM, A, SCHM. 

 Both ffiagnijied four diameters. 



No less than 9 species of Pisidium were obtained, of which 

 the most noteworthy is P. supinum, A. Schmidt, a form w^hich 

 has hitherto been undetected in these islands. For its identifi- 

 cation we are again indebted to Mr. A. C. Johansen. The 

 examples are large, but are by no means so fine as those which 

 occur in the Pleistocene of Grays. We are of opinion that this 

 form will eventually be found to have been widely distributed in 

 England during Pleistocene and Holocene times, though as yet 

 it has not been detected living. (Fig. 3.) 



CONCL USIONS. 

 We have now a list of 73 species of Mollusca from the 

 Alluvium of the River Lea, 70 coming from the older 



