The Pinna, or Sea-wing, is contained in a two-valve shell, weighing sometimes fifteen pounds, and emits a beard of fine long glossy silk- like fibres, by which it is suspended to the rocks twenty or thirty feet beneath the surface of the sea. In this situation it is so successfully attacked by the eight-footed Polypus, that the species perhaps could not exist but for the exertions of the Cancer Pinnotheris, who lives in the same shell as a guard and companion. Amoen. Academ. Vol. II. p. 48. Lin. Syst. Nat. Vol. I. p. 1159, and p. 1040. The Pinnotheris, or Pinnophylax, is a small crab naked like Bernard the Hermit, but is furnished with good eyes, and lives in the same shell with the Pinna; when they want food the Pinna opens its shell, and sends its faithful ally to forage; but if the Cancer sees the Polypus, he returns suddenly to the arms of his blind hostess, who by closing the shell avoids the fury of her enemy; otherwise, when it has procured a booty, it brings it to the opening of the shell, where it is admitted, and they divide the prey. This was observed by Haslequist in his voyage to Palestine. The Byssus of the antients, according to Aristotle, was the beard of the Pinna above mentioned, but seems to have been used by other writers indiscriminately for any spun material, which was esteemed finer or more valuable than wool. Reaumur says the threads of this Byssus are not less fine or less beautiful than the silk, as it is spun by the silk-worm; the Pinna on the coasts of Italy and Provence (where it is fished up by iron-hooks fixed on long poles) is called the silk-worm of the sea. The stockings and gloves manufactured from it, are of exquisite fineness, but too warm for common wear, and are thence esteemed useful in rhumatism and gout. Dict. raisonne art. Pinne-marine. The warmth of the Byssus, like that of silk, is probably owing to their being bad conductors of heat, as well as of electricity. When these fibres are broken by violence, this animal as well as the muscle has the power to reproduce them like the common spiders, as was observed by M. Adanson. As raw silk, and raw cobwebs, when swallowed, are liable to produce great sickness (as I am informed) it is probable the part of muscles, which sometimes disagrees with the people who eat them, may be this silky web, by which they attach themselves to stones. The large kind of Pinna contains some mother-pearl of a reddish tinge, according to M. d'Argenville. The substance sold under the name of Indian weed, and used at the bottom of fish-lines, is probably a production of this kind; which however is scarcely to be distinguished by the eye from the tendons of a rat's tail, after they have been separated by putrefaction in water, and well cleaned and rubbed; a production, which I was once shewn as a great curiosity; it had the uppermost bone of the tail adhering to it, and was said to have been used as an ornament in a lady's hair.