WATER SNAILS. 187 
from a pale yellowish-grey to dark reddish- 
brown; under a high magnifying power the 
surface is seen to be striated spirally; the 
whorls are five in number, convex; the last one 
very large; the aperture is large and oval; the 
inner lip is folded on the columella, forming 
behind it a concealed narrow groove. The length 
is from half-an-inch to an inch; the breadth 
about two-thirds of the length. 
The principal varieties which the shell of this 
species presents, are the following :— 
1. Var. ovata (Pl. X., fig. 118).—The spire 
acute, extremely short; whorls exceedingly 
convex, the last very large; aperture obliquely 
produced, four-fifths of the whole length; shell 
very thin and glossy. It is thus distinguished 
by its ovate form, its dilated aperture, and 
acute spire. It attais a larger size than the 
normal form, and often equals the next species, 
L. auricularia. It is common, and is the form 
usually met with in still waters, especially if of 
great extent ; whereas the smaller and narrower 
form—the type of the species—inhabits running 
waters, small brooks, and splashy pools. 
2. Var. lacustris is an inhabitant of the moun- 
tain lakes in Scotland, Ireland, and North of 
England, and in the Shetlands. It has a small 
glossy thin shell, strongly concentrically wrinkled ; 
the spire is very short, and the aperture is large ; 
