UNIVALVES. 
61 
eighths of an inch long, by a quarter broad, 
composed of three whorls, the last one exces¬ 
sively disproportionate; the spire very short, 
and as if lateral. A polished brownish-green 
horny epidermis covers the shell; in dead shells 
the beautiful spots or bands of white purplish- 
brown or pale brown are seen to perfection, for 
in fresh shells this colouring is much hidden by 
the epidermis, but may be seen by the aid of a 
magnify in g- glas s. 
The species is common in all the larger rivers 
where the bottom is stony, and in canals upon 
stones. It does not occur in the north of Ire¬ 
land, and is rare in Scotland, but is recorded 
from Loch Stennis, in the Orkneys. 
The animal is rarely to be seen in motion : it 
crawls slowly, with the shell slightly raised; the 
long, slender divergent tentacles, the large black 
eyes, placed on short stalks at the base of the 
tentacles, are then shown; the skin is covered 
with stiff silky hairs. 
The lingual teeth (see fig. 9) the central 
tooth (a) is minute; the first lateral tooth is 
Fig. 9.—Teeth of Neritina fluviatilis (Loven). 
