DREISSENSIA. 161. 
There is no mistaking this shell. Its triangular boat- 
shape is sufficient to identify it at once. 
It inhabits rivers, lakes, and canals in England and 
Scotland, but it has not yet been found in Ireland. 
It is supposed to have been introduced from Russia 
about 1824. 
This, and indeed all mussels are much appreciated 
by rats. 
Var. I. dtlatéta (Colv.). Broad and flat, beaks pro- 
truding beyond the hinge. 
Var. II. angusta (Col.). Narrower than type. 
“a 
