The Harps, says Lamarck, are very beautiful shells, and if they were less common, would, on account of their elegant forms and colours, become valuable in a collection. Some species, however, are still considered rare.
The Harps take their name from the fancied resemblance between the regularity and direction of the ribs on the shell, and the strings of a harp. The species are not numerous, not exceeding eight in number.
The Wide-Mouthed Purpura, (Purpura patula.)
This species of Purpura is said to be that which was employed by the Romans in dyeing, but many others of the same family yield a purple colouring-matter. It is nearly three inches in length, and is found in the Atlantic Ocean and the Mediterranean.
The purple colour which this little Molluscous animal produces, was discovered by the inhabitants of the ancient city of Tyre, and was thence called the Tyrian purple. The circumstances which led to the discovery of it are very imperfectly known, but fiction has supplied the want of historical facts, and described its origin with sufficient minuteness of detail. According to one account, the merit of its discovery is due to a dog belonging to a certain Hercules. We are informed that when this dog was accompanying his master along the sea-shore, who was then following the nymph Tyros, the animal seized one of the Purpuræ lying on the sand, and breaking the shell with his teeth, his mouth soon became coloured with the purple juice. The nymph having observed the effect, immediately expressed a strong desire to have a dress dyed of the same beautiful colour; and her lover, no less anxious to gratify her wishes, at last succeeded in discovering a method of applying it to cloth.
This colour was so highly valued by the ancients, that it was either consecrated to the worship of the Deity, or conceived to be fit only for the garments of royalty.
Under the Mosaic dispensation, the stuffs for the service of the altar and the habits of the high-priest were enjoined to be of purple. The Babylonians devoted this colour to the dress of their idols, and most of the other nations of antiquity appear to have done the same thing. Pliny informs us that it was used by Romulus and the succeeding kings of Rome, as well as by the consuls and first magistrates under the republic. The Roman emperors at last appropriated it entirely to their own use, and denounced the punishment of death against those who should dare to wear it, although covered with another colour. This absurd and tyrannical restriction confined the dyeing of the Tyrian purple to a few individuals, and, in a short time, the knowledge of the process was entirely lost.
In the twelfth century, neither the creature that furnished the dye, nor the methods which the ancients employed to communicate to cloths the rich and beautiful purple which it afforded, were at all known; and on the revival of learning, it was even suspected by many, that the accounts which had come down to us respecting this celebrated colour were entirely fabulous.
According to Pliny, the Tyrians removed the finest colouring-matter out of the largest shells, in order to possess it in a more pure state, and to extract it more effectually, but obtained the colour from the smaller by grinding them in mills. He adds, that when the Purpuræ were caught, the receptacle which contained the dyeing-liquor was taken out and laid in salt for three days; and that after a sufficiency of the matter had been collected, it was boiled slowly in leaden vessels over a gentle fire, the workman scumming off from time to time the fleshy impurities. This process lasted ten days, after which the liquor was tried by dipping wool into it, and if the colour produced by it was defective, the boiling was renewed.
Other colouring-matters were employed sometimes to economize, and at other times to vary the effect of the liquors of the Purpuræ. Among these Pliny enumerates Fucus marinus, or Archil, and the Anchusa tinctoria, or Alkanet, both of which are still used as dyes. By these and other means, the purple colour was made to assume a variety of shades, some inclining more to the blue, and others to the crimson.