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Show 1901.J MOTHER-OF-PEARL OYSTERS. 377 the nacre. The anterior margin, ventral to the byssal cleft, projects farther forward than in any other variety, so that a perpendicular to the hinge from ils anterior end would cut off about -\ of the valve. Colour greyish yellow or light brown, often resembling that of M. maxima. Radial rows of spots very indistinct and approximating to ground-colour of shell. Inner surface of lip yellowish brown. Nacre silvery white, with a narrow golden or brassy margin. Specimens from the Sandwich Islands and Mazatlan, and occasional Panama examples, together w ith exceptional individuals of M. m. typica, link this form to Linnaeus's species. llanley's name M. mazatlanica takes precedence of Reeve's M. barbata for this variety. It has been referred to Avicula fimbriata Dunker (1852) by Carpenter (1857) ; but the species figured by Dunker (1872), pi. 3. figs. 2 & 6, as his Avicula (Meleagrina) fimbriata, 1852, is certainly distinct from the " Pauama shell" of the trade, and probably represents a Central- American form allied to M. vulgaris or M. sugillata. Geographical Distribution. Panama ; Gulf of California ; Mazatlan ; Vancouver. Specimens from the Sandwich Islands in the British Museum are intermediate between this variety and the type. It is interesting to note that the oceanic variety (cumingi) is the darkest, the Australian and Malay shells are intermediate, and the lightest colours are assumed by shells living on the shores of the great Continents (vars. zanzibarensis, persica, erythrceensis, and mazatlanica). The most extreme of these, i. e. persica and mazatlanica, agree in having the posterior angle of the hinge right or acute. Species 2. MARGARITIFERA MAXIMA, n. sp. Type B.M. No. 1901.2.28.1; Basilaki (Moresby Island), British N e w Guinea, pres. H . Lyster Jameson. Concha margaritifera (ex parte), Lister, 1685, fig. 222 ; 1696, pi. 9 (prae-Linnean). Malacca pearl oyster, Home, 1828, vol. vi. pi. 49. Meleagrina margaritifera (Linnaeus), Kent, 1893, chap. 5, pi. xxxviii. The large white Mother-of-Pearl shell of Australian, Papuan, and Malayan wafers, " Silver-lip," "Gold-lip," &c. It is a singular fact that the largest and most valuable species of Motber-of-Pearl Oyster has passed, hitherto, without a name; having been, no doubt, included by most writers under Linnaeus's species. Saville Kent, who was the first to point out clearly the distinctions between this shell and the " Black-lip," concluded that the more valuable species was the type of Linnaeus's description, and recognized the Black-lip as Avicula cumingii Reeve. Pace (1898) suggested that the Black-lip was the species originally |