Of the several pearl-yielding mollusks in the Red Sea and on the southeast coast of Arabia, the largest and best known is that called “sadof” by the Arabs, and which has been identified by Jameson as _Margaritifera m. erythræensis_. This is closely related to the large species in the Persian Gulf. It is commonly four or five inches in diameter, and in exceptional instances attains a diameter of eight inches and a weight of three pounds or more. In addition to its size, it is distinguished by a dark green coloring about the edges, and a more or less greenish tint over the nacreous interior surface; this color is darker in the vicinity of Jiddah and Suakin than at the southern end of the sea, or in the Gulf of Aden. This species occurs singly rather than congregated in beds or reefs. Although it is found in depths of fifteen fathoms or more, most of the fishing is in less than five fathoms of water. [Illustration: Persian Gulf and the Red Sea, the pearling center of the world ] The “sadof” yields pearls only rarely, and is sought principally for the shells, which afford good qualities of mother-of-pearl, the pearls furnishing an additional but always looked-for profit to the regular source of income. As in other regions, there is no constant relation between the value of the pearls and the quantity of mollusks taken. The oysters of some reefs are comparatively rich in certain years; while in other seasons or on other reefs the mollusks may be numerous but yield very few pearls. The second species of importance in the Red Sea is similar to the Lingah oyster and is known to the Arabs as “bulbul.” This is much smaller than the “sadof,” averaging less than three inches in diameter. It is collected for the pearls exclusively, the shells being too small for industrial use; but only 3 or 4 per cent. of the individuals yield pearls. It is claimed by writers of authority that it is the red Pinna pearl from this sea that is referred to in the Scriptures under the name _peninim_ as the most precious product, and which has been translated as rubies.[166] The shell is extremely fragile, and the nacreous interior is white tinged with a beautiful red. It is of little importance in the commercial fisheries of the Red Sea at the present time.