THE MOLLUSCS. 295 



In the genus Lymncea the shell is conic oval, or 

 elongated, the spiral turning from left to right or dextral. 



There are eight British species. Those commonly met 

 with are Lymncea peregra (Fig. 4) or the Wanderer, 

 Lymncea stagnalis (Fig. 5), and Lymncea palustris (Fig. 7). 

 There are fourteen varieties of this mollusc. 



The genus Ancylus (Fig. 8) is at once distinguished by 

 its shell being hood-shaped. There are two species : 

 Ancylus fluviatilis shell semi-oval or curved towards the 

 front like a Phrygian cap, not glossy, of a yellowish-grey 

 or horn colour found abundantly on stones and rocks in 

 shallow rivers and streams ; and Ancylus lacustris, found 

 chiefly on the under side of the leaves of water-lilies and 

 other aquatic plants ; shell oblong, obliquely twisted to the 

 left, glossy, greyish horn -colour. 



In the genus Neriiina there is only one species, Neritina 

 fluviatilis shell semi-globose, cornea above slightly com- 

 pressed towards the spire, almost concave below, yellowish- 

 brown with zig-zag bands. It is found in rivers and 

 streams and ponds having a gravelly bottom. Both trout 

 and grayling are very fond of this mollusc. 



Of the Land Snails, there are two which often come 

 under our notice out of the vast number comprised in the 

 three families Limacidce, Testacidce, and Helicidce. 



The Helix aspersa has a reddish-brown shell with a 

 single white band commonly known as the Garden Snail. 



HELIX ASPERSA. 



It is found in woods and gardens, and is one of the shells 

 forming the kuchen midden of the thrush, this bird bein^ 

 extremely fond of the animal itself, as well as of the 

 Helix memoraltS) which is also found in woods, hedges, 



