BIVALVES. 
23 
completely established on the beds of gravel in 
the river Avon, at Evesham, and also in the canal 
between Warwick and Birmingham, and in the 
canals near Wednesbury, in Staffordshire. He 
remarked that, as its propagation was so aston- 
ishingly rapid, it would become in a few years 
one of our commonest British shells. This has 
proved so true, that not only has it found its way 
throughout England, literally paving with its 
shells the beds and sides of our navigable rivers 
and canals, but it has even taken up its quarters 
in the water-pipes of London, Manchester, &c. 
The Zebra Mussel made its appearance in the 
neighbourhood of Gloucester a few years after 
the opening of the Gloucester and Berkeley Canal, 
and has increased in numbers to such an extent, 
that it may be said to line the banks from the 
edge of the water to a considerable depth, 
throughout its entire length of sixteen miles. It 
appears in every available inch of space, from 
the water-line to the depth of fifteen or sixteen 
feet, upon the dock walls at Gloucester. 
It is very tenacious of life and exceedingly 
prolific, provided the locality is favourable. 
This mollusk is evidently sensible to light, 
which it would usually avoid, as exemplified in 
its occurrence in such prodigious numbers in 
water-pipes. If when the animal is at rest, with 
the shell partly open, an object is suddenly 
