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THK NON-MARINE MOLLUSCA OF THE RIVER LEA 



size and in their composition. Occasionally all traces of 

 molhisca had vanished, whilst in others only a few still 

 remained ; but as a rule they were very abundant and well 

 preserved. Many were coated with calcareous matter, com- 

 pletely covering the shell. This condition is also met vvith in 

 some of the Irish lakes where the dead shells are drifted ashore. 

 It is also found in the Holocene deposits of the Thames, and in 

 the Pleistocence High Terrace Gravel at Swanscomb, Kent. 

 It has been suggested that the primar}- cause of this incrustation 

 may be the coating of algoid growth that invested the 

 test during the life of the animal. As a rule, more aquatic forms 

 were present in these marls than terrestial, although occasionally 

 the reverse condition prevailed. We obtained 66 species, of 

 which 1 8 have not hitherto been recorded from these beds, whilst 

 four, before observed, were not found by us : — 



LIST OF SHELLS FROM SHELL-MARL. 



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Agriolimax agresfis (Linn.) 

 Vitvea crystaUina (Miill.) 

 alliavia (Miller) 

 cellar} a (MiilL) 

 nitidnla (Drap.) 

 radiatida (Alder) 

 iiitida (Midi.) 

 fiilva (Midi.) 

 Avion ater (Linn.) 

 Punctum pygmceuni (Drap.) 

 Pyrainidula rotundata (Mull.) 

 Hygvomia graniilata (Alder) 



„ hispida (Linn.) 

 VaUonia pnlchella (Miill.) 

 Helicigona lapicida (Linn.) 



,, avbustovum (Linn.) 



Helix aspersa, Miill. 

 ,, nemoralisj Linn. 

 ,, Jiorfensis, Miill. 

 Cochlicopa Inhrica (Miill.) 

 Pupa muscorum (Linn.) 

 Vertigo antivertigo (Drap.) 



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Vertigo pygmo'a (Drap.) 

 Balea perversa (Linn.) 

 Clatisilia laniinata (Mont) 

 hidentata (Strom) 

 piitris (Linn.) 

 Snccinea elegans, Risso. 

 Carychium iniiiiniuin, Mvill. 

 A ncylus fliiviatilis ( M till .) 

 Velletia lacnstris (Miill.) 

 LimncFa auric nl aria (Linn.) 

 pereger (Miill.) 

 palustris (Miill.) 

 trnncatula (IMiill.) 

 stagnalis (Linn.) 

 Planorhis corneus (Linn.) 

 albns, IMiill. 

 strcemii. West. 

 11 a utile us (Linn.) 

 carinatus, Miill. 

 inarginatus, Drap. 

 vortex (Linn.) 

 spirorbis, Miill. 



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