24 LAND AND FRESH-WATER MOLLUSKS. 
brought before it, the valves are at once closed, 
or partially so. On being introduced into the 
aquarium, it at once reconciles itself to its new 
abode, mooring itself by its threads to the stones, 
or the sides of the glass. Young individuals 
are harder to please, exhibiting their dissatisfac- 
tion by their peregrinations, makmg the circuit 
of the aquarium before selecting a resting-place; 
but on finding a suitable spot, they follow the 
example of their seniors and secrete a byssus, 
and there remain fixed for life. 
The present species is now found in bait 
every part of Hurope, in canals, tanks, running 
streams, and rivers, attaching itself by its byssus 
of strong threads to stones, the live shells of Ano- 
don, and the dead ones of their own species, wood 
piles, or brickwork. In docks it luxuriates be- 
neath the floating timber; in canals it abounds — 
beneath the shadow of bridges. It has not yet 
- found its way into Ireland. 
Extinct species of Driessena inhabited the 
fresh waters of the Isle of Wight during the Upper 
Hocene epoch. D. polymorpha is, however, ab- 
sent from the newer Tertiaries of this country. 
‘ 
