In the Mergui Archipelago, which is within the territory of lower Burma and under the jurisdiction of the government of British India, patches of pearl-oyster reefs are scattered over an area roughly computed at 11,000 square miles, taking 97° 40′ as the western boundary. They occur principally in the strong tidal passages among the islands. The bottom is formed largely of porphyritic granite interspersed with sand and thinly covered with corals, coral cups, the long whip-like black coral (_Antipathes arborea_), and other submarine animal and vegetable growths.[163] These constitute a home most favorable to the growth and development of molluscan life. Of the several species of pearl-bearing mollusks occurring in the Mergui Archipelago, by far the most important is the “mok,” or large Australian pearl-oyster (_Margaritifera maxima_). The shell attains a maximum size of about thirteen inches in diameter, and the nacre is of a milky or silvery color. This species occurs in its two varieties of “golden lip” and “silver edge,” the former being in greater abundance. The “silver edge” shell is the more valuable owing to its uniformity of coloring, and the pearls found therein are of superior luster and orient. The “pate goung,” or Lingah pearl-oyster (_Margaritifera vulgaris_), is similar to that of the Gulf of Manaar. It is circular in shape and measures about two and one half inches in diameter. The nacre is silvery, with slight yellowish tinge. Many of the pearls from this species are of a silvery color, but most of them are yellowish or golden. The fishery for this mollusk is of little importance compared with that for the larger pearl-oyster, which is the species referred to in Mergui when not otherwise mentioned. The pearl fisheries of Mergui originated with the Selangs or Salangs, a nomadic race of maritime gipsies, the last remnants of whom live among the three thousand islands of this group. They are supposed to be of Malay descent; but their early history is unknown, and they are rapidly passing away in the conflict of existence with the neighboring peoples. Probably in no part of the world are the pearl fisheries prosecuted by a more primitive class of men. With their women and children, they live mainly in roomy dug-out boats; but during the southwest monsoon they erect temporary shelters on the shore, these consisting of a few frail sticks, supporting coverings of braided mats, and floors of bamboo strips.