UNIVALVES. 
55 
brown spiral bands on the last whorl, and two 
upon each of the two preceding whorls ; the 
shell is also finely striated longitudinally * 
whorls six, rather convex, with a well-defined 
suture; aperture oval, peristome continuous, 
umbilicus represented by a narrow slit behind 
the inner lip ; the operculum horny, rather thick. 
Length an inch and a half, and one inch broad. 
The body is a dark grey, or brown speckled 
with yellow. The young shells are sometimes, 
at least, clothed with a downy epidermis, rising 
into short spines round the middle of each 
whorl,—disappearing much on dying. 
In the timber docks on the Thames, and in the 
various canals about London, this species is very 
abundant, and in fine condition. Following the 
ramifications of our system of water-roads, the 
species inhabits the Kent and Avon canals, the 
canals of Gloucestershire, Staffordshire, &c.; but 
is by no means restricted to such habitats, for 
it is found in many of the slow rivers in the 
midland and southern counties of England. It 
occurs in the river Ouse and Barnsley Canal, at 
Wakefield, in Yorkshire, which are probably its 
northern limits. Dead shells of this species and 
of some southern forms are frequently introduced 
with the ballast into localities where it is not 
indigenous. 
M. Joly, after keeping several individuals of 
