This animal is much smaller than the Teredo navalis, and differs from it in shape, being about one-sixth of an inch in length and very much like a woodlouse, whereas the teredo has more the shape of a worm. The Limnoria appears to be furnished with a small mouth and a few strong teeth, with which it bites the softer particles of the wood, entirely avoiding the knots and the harder parts. It is said never to attack teak, and to confine its operations almost entirely to fir timber, whereas the teredo attacks mahogany, teak, and other hard woods. Mr. Stevenson found that Memel timber was destroyed by the Limnoria at the Bell Rock at the rate of about one inch inwards per annum* It appears to extend its depredations to a higher point above low water than the teredo.

479. There is also another animal of the same class as the Limnoria, but far more destructive, which was detected in timber taken from the sea at Trieste, called the Chelura terebrans, or wood boring shrimp; it was first observed as an inhabitant of the British Seas, several years ago, by Mr. Robert Hall, of Dublin, and in January, 1847, it was described by Mr. Mullins in a paper read before the Institution of Civil Engineers of Ireland, as being very injurious to the timber piles of the jetty in Kingstown Harbour, near Dublin.‡

480. Smeaton describes a kind of worm which he had observed in Bridlington piers. The wood of these piers he says is destroyed by a certain species of worm differing from the common worm whereby ships are destroyed. "This worm appears as a small white soft substance, much like maggot; so small as not to be seen distinctly without a magnifying glass, and even then a distinction of its parts is not easily made out. It does not attempt to make its way trough the wood longitudinally or along the grain, as is the case with the common ship worm, but directly, or rather a little obliquely, inward. They do not appear to make their ay by means of any hard tools or instruments, but rather by some species of dissolvent liquor, furnished by the juices of the animal itself. The rate of progression," he was informed, "is, that a three-inch oak plank will be destroyed in eight years by action from the outside only."*

* ' Account of the Bell Rock Lighthouse.'

† ' Min. Proc. Inst, of Civil Engineers,' 1849-50.

Fir appears also to be more rapidly destroyed by this worm than oak.

None of these worms can live except where they have the action of the water at every tide, nor do they live in the parts covered with sand.

481. A species of Pholas (Pholas striata) is another animal which is very destructive, not only to timber but to stones, clay, etc, when submerged in water. It makes its attack in a similar manner to the teredo, by burrowing when young the entrances of the holes being only about one-fourth of an inch in diameter. The animal increasing in size as it advances forms a larger hole, until it arrives at maturity,-when it ceases to bore. It derives its sustenance from the water, and never bores so far that it cannot reach the water with its proboscis.†

482. The Lepisma is also a destructive little animal in the East Indies; it begins to prey on the wood as soon as it is immersed in sea water. The unprotected bottom of a boat has been known to be eaten through by it in three or four weeks.

483. The following Table by Mr. Stevenson shows the result of exposing different kinds of timber to the attacks of the Limnoria terebrans at the Bell Rock in 1814, 1821, 1837, and 1843.

* Smeaton's 'Reports.'

† Wilcox, ' Papers on Naval Architecture,' vol. i., p. 154.