instrument like the _teredo_, but is supposed to possess some species of dissolvent liquor, furnished by the juices of the animal itself. Dr. Coldstream was of opinion that the animal effects its work by the use of its mandibles. From ligneous matter having been found in its viscera, some have concluded that it feeds on the wood, but since other molluscs of the same genus, _Pholas_, bore and destroy stonework, the perforation may serve only for the animal’s dwelling. The _limnoria_ seems to prefer tender woods but the hardest do not escape: teak and greenheart are about the only woods it does not attack. The rate at which the _limnoria_ bores into wood in pure salt water is said to be about one inch in a year; but instances have occurred in which the destruction has been much more rapid. At Lowestoft Harbour, square 14 inch piles were in three years eaten down to 4 inches square. At Greenock, a pile 12 inches square was eaten through in seven years. It is stated that a 3-inch oak plank, 12 feet long, would be entirely destroyed in about eight years. Joists of timber have been found at Southend Pier, 2 feet and 3 feet below high-water mark, where they had made rapid destruction. The _limnoria_ almost always works just under neap tides; it cannot live in fresh water, and whilst it is destroying the surface of a pile, the _teredo_ is attacking the interior: sometimes the former is found attacking the same timber as the Chelura. As with most of these creatures, the male _limnoria_ is smaller than the female, being about one-third her size. The female may be distinguished by the pouch in which the eggs and afterwards the young are carried. About six or seven young are generally found in the pouch. The WOOD-BORING SHRIMP (_Chelura terebrans_) is a crustacean that nearly rivals the _teredo_ itself in its destructive powers. It makes burrows into the wood, wherein it can conceal itself, and at the same time feast upon the fragments, as is proved by the presence of woody dust within its interior. Its tunnels are made in an oblique direction, not very deeply sunk below the surface, so that after a while the action of the waves washes away the thin shell, and leaves a number of grooves on the surface. Below these, again, the creature bores a fresh set of tunnels, which in their turn are washed away, so that the timber is soon destroyed in successive grooved flakes.