l8 THE NON-MARINE MOLLUSCA OF THE RIVER LEA 



Hygromia hispida (Linn) was by far the commonest 

 Helicoid present, but the examples are by no means large, 

 the finest being but 9 mm. in diameter, the average height being 

 5.5 mm. 



Helicigona lapicida (Linn) was not common, and all the 

 examples found were obtained from one patch of shell-marl near 

 the south side of the Lockvvood Reservoir. It is a new discovery 

 for this neighbourhood, though it has been known from the 

 alluvium of the Lea at Canning Town. 



Helicigona arbustorum (Linn) was an extremely common 

 form, and varied much in shape and size, the largest example 

 being 18 mm. in height, and 20 mm. in diameter, whilst the 

 smallest was 13 mm. in height and 16 mm. in diameter. 



Helix aspersa, Miill, was answered for by two examples, 

 both very small, being 25 mm. and 24 mm. in height and 26 

 mm. and 27 mm. in diameter. 



Helix nemoralis, Linn, was very common, the shells being 

 often well preserved, and still retaining their coloration. 



The band formulas noted were : — 

 252 examples 



J) 



It will be noticed that the banded examples are greatly in 

 excess of the unicolorous examples, and that there is a marked 

 tendency for the bands to coalesce, a condition probably arising 

 from some condition in the environment. 



Helix hortensis, Miill, was a new record for these beds. 

 The band formulae observed were : — 



I 2 3 4 5, 12 examples. 



o o o o, 3 „ 



1 (2 3) 4 5, I example. 



1(2 3 4 5). I 

 Balea perversa (Linn). One single example constituted 

 an interesting addition to the fauna of the alluvium of the Lea. 

 The species is extremely rare in the fossil state, being only known 



