in botany, a genus of mosses belonging to the cryptogamia algae. The character is taken from this circumstance, that they are covered with a simple capillary filament or down, resembling soft dust. There are 15 species, all natives of Britain, growing upon rotten wood, old walls, &c.

Byssum, a fine thready matter produced in India, Egypt, and about Elis in Achaia, of which the richest apparel was anciently made, especially that wore by the priests both Jewish and Egyptian. Some interpreters render the Greek Βύσσος, which occurs both in the Old and New Testament, by fine linen. But other versions, as Calvin's, and the Spanish printed at Venice in 1556, explain the word by silk; and yet byssus must have been different from our silk, as appears from a multitude of ancient writers, and particularly from Jul. Pollux. M. Simon, who renders the word by fine linen, adds a note to explain it; viz. "that there was a fine kind of linen very dear, which the great lords alone wore in this country as well as in Egypt." This account agrees perfectly well with that given by Hesychius, as well as what is observed by Bochart, that the byssus was a finer kind of linen, which was frequently dyed of a purple colour. Some authors will have the byssus to be the same with our cotton; others take it for the linen of Ephesus; and others for the lock or bunch of silky hair found adhering to the pinna marina, by which it fastens itself to the neighbouring bodies. Authors usually distinguish two sorts of byssus; that of Elis; and that of Judaea, which was the finest. Of this latter were the priestly ornaments made. Bonfrerius notes, that there must have been two sorts of byssus, one finer than ordinary, by reason there are two Hebrew words used in Scripture to denote byssus, one of which is always used in speaking of the habit of the priests, and the other of that of the Levites.