Pliny the Elder [1st century CE] (Natural History, Book 9, 60-62; 9, 74): [Book 9, 60] Purpurae live seven years at most. They stay in hiding like the murex [sea-snail] for 30 days at the time of the rising of the dog-star. They collect into shoals in spring-time, and their rubbing together causes them to discharge a sort of waxy viscous slime. The murex also does this in a similar manner, but it has the famous flower of purple, sought after for dyeing robes, in the middle of its throat: here there is a white vein of very scanty fluid from which that precious dye, suffused with a dark rose color, is drained, but the rest of the body produces nothing. People strive to catch this fish alive, because it discharges this juice with its life; and from the larger purples they get the juice by stripping off the shell, but they crush the smaller ones alive with the shell, as that is the only way to make them disgorge the juice. ... The purple's tongue is an inch long; when feeding it uses it for piercing a hole in the other kinds of shell-fish, so hard is its point. These fish die in fresh water and wherever a river discharges into the sea, but otherwise when caught they live as much as seven weeks on their own slime. All shellfish grow with extreme rapidity, especially the purple-fish; they reach their full size in a year. [Book 9, 61] [Gaius Licinius] Mucianus states that the murex is broader than varieties of the purple, and has a mouth that is not rough nor round and a beak that does not stick out into corners but shuts together on either side like a bivalve shell; and that owing to murexes clinging to the sides a ship was brought to a standstill when in full sail before the wind, carrying dispatches from Periander ordering some noble youths to be castrated, and that the shell-fish that rendered this service are worshiped in the shrine of Venus at Cnidus. Trebius Niger says that it is a foot long and four inches wide, and hinders ships, and moreover that when preserved in salt it has the power of drawing out gold that has fallen into the deepest wells when it is brought near them. ... Purples are taken in a sort of little lobster-pot of fine ply thrown into deep water. These contain bait, cockles that close with a snap, as we observe that mussels do. These when half killed but put back into the sea gape greedily as they revive and attract the purples, which go for them with outstretched tongues. But the cockles when pricked by their spike shut up and nip the creatures nibbling them. So the purples hang suspended because of their greed and are lifted out of the water. [Book 9, 62] It is most profitable for them to be taken after the rising of the dog-star or before spring-time, since when they have waxed themselves over with slime, they have their juices fluid. But this fact is not known to the dyers' factories, although it is of primary importance. Subsequently the vein of which we spoke is removed, and to this salt has to be added, about a pint for every hundred pounds; three days is the proper time for it to be steeped (as the fresher the salt the stronger it is), and it should be heated in a leaden pot, and with 50 pounds of dye to every six gallons of water kept at a uniform and moderate temperature by a pipe brought from a furnace some way off. This will cause it gradually to deposit the portions of flesh which are bound to have adhered to the veins, and after about nine days the cauldron is strained and a fleece that has been washed clean is dipped for a trial, and the liquid is heated up until fair confidence is achieved. A ruddy color is inferior to a blackish one. [Book 9, 74] The purple-fish, the murex and their kind spawn in spring. - [Rackham translation]

Isidore of Seville [7th century CE] (Etymologies, Book 12, 6:50): The murex is a shellfish of the sea, named for its sharpness and roughness. It is called by another name, conchilium, because when it is cut round with a blade, it sheds tears of a purple color, with which things are dyed purple. And from this ostrum is named, because this dye is drawn out from the liquid of the shell. - [Barney, Lewis, et. al. translation]

Aberdeen Bestiary [circa 1200 CE] (folio 77r): The murica is a sea snail, so called from its sharp point and rough surface; it is known by another name, concilium, because when you cut around it with an iron blade, it produces tears which are purple in color, from which purple dye is made; from this comes the other name for purple, ostrum, because the dye is made from the fluid enclosed in the shell (in Greek, ostreon).

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Fish 7.56; 7.62): [Thomas describes the sea-snail under the names murices and purpure.] [Fish 7.56] Murices, as Pliny says, are sea-snails, which wait for the rising of the Dog-star, and come out at a fixed time. They also have a valuable liquid for dyeing clothes. But in sea-snails the color is found only in the white vein: the rest of the body is sterile. This color is squeezed out with their lives because they vomit juice when they are alive. [Gaius Licinius] Mucianus is the author who says, according to Pliny, that a ship with its sails full of winds was stopped by sea-snails clinging to it, as was said of echeneis. It does not have a conical mouth, nor is it round, nor does it have a beak projecting into the corners, but it is closed on both sides like a shell. [Fish 7.62] The purpure as Pliny says, lives for seven years at the most. They hide around the rising of the Dog-star for thirty days. They gather in the spring time and by rubbing force a liquid through their mouths. They have this liquid in the middle of their throats. The purpure shell grows full size in less than a year. [Thomas's description becomes confused at this point; he seems to have added some of the attributes of the pearl, and mixed up some of Pliny's text] But if they pass before they grow, the shell takes away the power of lust, and they can no longer mate or conceive, so as to give birth in time to the precious liquid. Hence the greatest care is taken, so that in the first year the purple shell is pulled off or crushed, so that it does not grow. Clothes of purple are usually dyed with this liquid. This black color is highlighted with a pink color. When the eggs of the sea-snail are returned to the sea, they revive. They are caught by foul odors. - [Badke translation/paraphrase]

Bartholomaeus Anglicus [13th century CE] (Liber de proprietatibus rerum, Book13.29): And some shell fish is called Murice, and have that name of roughnesse and sharpnesse, and have another name, and be called Conchilia. And if they be kitte about with yron, of them drop teares of red colour, and with those teares purple is died, and this coulour and hiew is called Ostrium. For it is taken of the humour of shel fish, as Isidore saith. - [Batman]