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Family Muricidae — Part 3

Sub-family PURPURINAE

SHELL bears nodules but no varices; columella flattened, spread out; canal short, or a mere notch; operculum oblong, with lateral nucleus. A large sub-family whose boundaries cannot be definitely set at present.

Genus PURPURA, Brug.

Shell oblong-oval, last whorl large; spire short; aperture large, ovate, ending in short, oblique canal or notch; columella flattened; outer lip simple; operculum horny.

A carnivorous genus, living from the water line to twenty-five fathoms' depth in all parts of the world. Recent species, fifty-seven; fossil species, forty, Tertiary.

By the recession of the tide these mollusks are left out of water twice a day for several hours. They breathe air which passes over a small quantity of water retained in the branchial cavity. They are amphibious, as well as carnivorous; and well protected by their strong shells against injury by the waves and by predatory birds and mollusks. Altogether, they are adapted to succeed in the race for life.

The common name of this genus has a long and interesting pedigree, which takes us far back into ancient history. The "Tyrian purple," famous because used solely for dyeing garments to be worn by emperors and kings, was obtained by crushing these mollusks in mortars or in pot holes along the rocky coasts of Tyre and other Mediterranean ports. Pliny says that 111 Purpurae to 200 Buccina, pounded together, produced the richest shade of purple. The animals of large species were removed from their shells.

The colouring matter is not contained in the shell, but in a vein or sac on the back of the body. Its use to its owner is the same as the ink of the common squid. A jet of ink colours the water, and enables the pursued to escape from an enemy. We can understand how hard and tedious was the process of obtaining this dye in quantities.

The complex art of blending the juices to produce the desired play of colouring was known only in ancient Tyre, and this secret was lost when the city was destroyed. Meanwhile the cochineal bug and modern coal tar dyes have supplied cheaper materials.

"In the reign of Augustus one pound of wool dyed with Tyrian purple sold for about pounds 36 sterling." Six pounds of liquor were required to one pound of wool. Consequently fabrics when dyed often cost their weight in gold.

The Princely Purple (P. Persica, Linn.) is the type of this genus. It is oval, with a short spire; its brown surface is regularly spirally grooved, and wound with a narrow band of white, dotted with brown. A row of nodules encircles the upper whorls. Columella reddish yellow; aperture wide, pinkish or bluish within; lip thin, with five interrupted brown lines crossing the inner margin. Length, 3 to 5 inches.

Habitat.--Philippines.

The Open-mouthed Purple (P. patula, Linn.) is like the preceding in size, colour scheme, wide columella and gaping aperture. The spire is depressed, however, and the spiral ridges are much stronger, and irregularly tubercled. The lip is fluted, and marked with the dark brown that alternates with white on the outer surface. The columella is reddish chestnut, with a dark brown semi-lunar patch at the top. The sculpture is much sharper in young than in adult specimens.

Habitat.--Gulf of California, Philippines, West Indies.

The Chocolate Purple (P. chocolatum, Duclos), with deep chocolate exterior, knobbed along the square shoulders, and closely ridged on the thick lip, is described as a very active mollusk. The early Peruvians must have used the mollusk as food, judging by the piles of shells found near the tombs at Arica. Length, 3 1/2 inches.

Habitat.--Peru.

Another large species which Reeve calls P. gigantea, is connected by intermediate forms with P. consul, Lam. Spire is sharp; whorls encircled with fine brown lines; shoulders square, tuberculated; columella broad, flat, orange-red; aperture orange; lip margin ridged. Length 2 1/2 to 5 inches.

Habitat.--Philippines.

The large species were commercially important in the earliest times because they yielded more of the precious dye than the smaller kinds.

The Rock Purple or Dog Winkle (P. lapillus, Linn.) is one of the best known inhabitants of northern rocky coasts on both sides of the Atlantic. P. saxicola, Val., of the west coast, is probably the same. This species has attained its remarkable geographical range by variations which adapt it to changed conditions of life.

The collection of P. lapillus made by Cooke in Great Britain alone exhibits nineteen distinct forms. Large size, prolonged spire and small mouth characterise those found on protected coasts where food is plenty and attachment to the rocks an easy matter. A low spire, a large mouth, small size and a thick shell belong to forms taken in exposed situations where food is scarce. The most strikingly banded and brightly coloured shells are found on veined and coloured rocks, the dullest in estuaries and sheltered bays.