But even so the best guarded of the bivalves fall a prey to innumerable enemies, and when we see the strand covered for miles and miles with their débris, we may rest assured that but few of the quondam inmates of these fragmentary shells have died a natural death. Annelides and Sea-snails, crustaceans and star-fishes, strand birds and even quadrupeds, all fatten upon their delicate flesh, and man devours incalculable numbers. [Illustration: Edible Cockle.] In vain the Pholas buries itself in stone, or the cockle in the sand; their security was at an end as soon as man had found out that they were grateful to the palate. The former was reckoned a delicacy by the ancients, and the latter is preferred by some to the oyster itself. So much is certain, that, during the years of famine caused by the potato disease, it preserved the lives of many of the poor Shetlanders and Orcadians. The Razor-Shells, particularly when roasted, and the Clam-Mussels, which are not only a favourite repast of the Greenlander but also of the white bear and arctic fox, are equally reckoned among the most delicate of bivalves. The common Mussel (_Mytilus edulis_), which is found in the littoral zone on almost every rocky shore, is eaten in vast numbers by the coast inhabitants, and carried in enormous masses into the interior of the country; it furnishes an equally cheap and agreeable food, but is not easy of digestion, and sometimes produces symptoms of poisoning, which have been ascribed to the eggs of asterias, on which it feeds during the summer. In the northern countries it is also in great request as a bait for cod, ling, rays, and other large fishes that are caught by the line. In the Frith of Forth alone from thirty to forty millions of mussels are used for this purpose, and in many places they are enclosed in _gardens_, the ground of which is covered with large stones, to which they attach themselves by their byssus or beard. [Illustration: Edible Mussel.]