LIMNORIA LIGNORUM. 353 
to drag itself along. It turns rapidly, using chiefly the 
caudal plates, which it uses as oars; sometimes also it 
propels itself by a sudden movement of the tail, back- 
wards, to the distance of an inch or more, through the 
water. 
It appears that, notwithstanding the extent and im- 
portance of its ravages upon structures, affecting the 
interests of mankind in a very extensive manner, it was 
not noticed until about the year 1811, when Dr. Leach 
announced it, as a new and highly interesting species, 
sent to him by Robert Stevenson, Esq., the celebrated 
engineer, and as occurring in the greatest abundance at 
the Bell Rock lighthouse on the Scotch coast, erected 
by that gentleman, burrowing into the old woodwork, 
which it perforated in a most alarming manner, entering 
into it to the depth of several inches by boring in every 
direction, generally in straight lines, avoiding, however, 
the knots of the timber, round which it works. 
Many kinds of wood, including old oak, are devoured 
by the Limnoria, although it was generally found in other 
timbers, especially Memel fir. Mr. Stevenson saw it 
attack oak, black-birch, and other woods; indeed, teak 
was the only wood exposed to its ravages which was not 
perforated. Its mode of attack is very similar to that of 
the common Anobium in the timber of houses, &c., which 
is so often mistaken for dry rot, the chief difference 
being that the action of the waves wash away the outer 
and harder annual layers, in consequence of all the soft 
intervening spaces being eaten away, whilst the inner 
ones, as well as the knots of the branches, stand out 
in relief—consequently the surface of the wood soon 
becomes gradually rotten and reduced in its dimensions, 
It is by means of its mandibles that it forms its 
burrows in the wood, which evidently forms its support, 
VOL. II. iN ss 
