Ranking next to _Margaritifera vulgaris_ in extent of pearl production is the _Margaritifera margaritifera_, which is widely distributed about the tropical inshore waters of the Pacific and Indian oceans. It is very much larger than the Lingah oyster, good specimens measuring seven or eight inches in diameter, and the nacreous interior is usually of a darker color. In addition to its yield of pearls, the shell of this species is of value in the mother-of-pearl trade, and contributes largely to the economic results of the fisheries. Indeed, in several regions the shell is of more value than the pearls, which represent only an incidental yield. As Jameson notes, the color and markings of the shell, though extremely variable, generally suffice to distinguish this species. The ground color of the exterior ranges through various shades from yellowish brown to very dark brown. Its characteristic markings consist of from ten to eighteen radial rows of white and yellow spots, running from the umbo, or hinge, to the margin. Several varieties of _Margaritifera margaritifera_ are recognized. The type species occurs along the north coast of Australia, from Brisbane on the east to Sharks Bay on the west; on the New Guinea coast; at Formosa; and about many of the islands of the Pacific. The well-known “black lip shell” of Australian waters is of this species; it shows a greenish black on the margin of the nacre. The yield of this is very small compared with that of the large pearl-oyster of Australia. [Illustration: SHELL OF PEARL-OYSTER WITH ATTACHED PEARL (_Margaritifera margaritifera mazatlanica_) From Costa Rica ] The _Margaritifera margaritifera_ occurs on the eastern coast of Arabia in two varieties, which differ somewhat from the type species. These have been designated by Jameson as _M. margaritifera persica_ and _M. margaritifera erythræensis_. These are much larger than the Lingah shell of the Persian Gulf, but are smaller than the Australian species. The percentage of pearls in them is less than in the Lingah species, but from a commercial point of view this is to some extent offset by the greater value of the shell. The _M. m. persica_ is more numerous in the gulf than the _M. m. erythræensis_, and large quantities of the shell are marketed in Europe. Formerly the shipments were made principally by way of Bombay, hence the shell is known in the mother-of-pearl trade as “Bombay shell.” The exterior is of a light grayish or greenish brown color, with yellowish white radial bands. The nacre has a slightly roseate tint, and the margin is greenish yellow. The pearls found herein are more yellowish in color and attain a larger size than those from the Lingah oyster.