OCR Text |
Show 374 DR. H. L. JAMESON ON THE [Apr. 16, variable, generally suffice to distinguish this species. The groundcolour is pale yellowish brown, green, olive, reddish grey, dark brown or black. It is characteristically marked with about 10-18 radial rows of white or yellow spots, running from the umbo to the margin, which may be so large as to fuse and form radiating bands, or may be completely suppressed. The interior of the lip approximates to the ground-colour of the shell, and shows indistinct lighter markings corresponding to the distal ends of the radial rows of spots. The nacre is highly iridescent, often somewhat steely in lustre, with a marginal band of dark metallic green, bronze, or brassy yellow iridescence. Average specimens measure 10-18 cm. in diameter, but larger dimensions are at times acquired, especially by Polynesian examples, which sometimes almost rival M. maxima in size and weight. Variation in this widely distributed species is so great that the above specific characters will by no means be found to cover every specimen. I find it necessary to break it up into several geographical races, which, although they intergrade, differ markedly from one another. Var. a. M. margaritifera ( ? tgpica). The original locality of Linnaeus's type specimens in the Linnean Society's collection is not known. Linnaeus gives " in utriusque indice oceano" as the distribution of his Mytilus margaritiferus. One of his specimens, a right valve, is obviously East Indian, probably from the Malay Archipelago, as it agrees in all respects with the " Black-edged Banda " shell of the trade. The other is apparently a Red Sea example, as it is quite indistinguishable from trade samples from that locality. Linnaeus's description iu the Mus. Reg. Ulr. is more applicable to the former than the latter specimen ; so I feel inclined for the present to regard the Black-edged Banda shell as representing the type of Linnaeus's species, and to group the geographical varieties round it. Australian aud N e w Guinea shells do not show sufficient differences to warrant m e in separating them from the type by a distinct name, although their racial characters are enough to cause them to be distinguished in the Mother-of-Pearl markets. Australian, N e w Guinea, and Malayan examples are characterized by dark greenish or brownish ground-colour, with well-defined radial rows of white spots which do not as a rule fuse to form regular striae. The margin of the nacre is usually dark green, bronze, or smoky, but not so marked as in Polynesian examples. The form of the shell is usually that described for the species generally. Geographical Distribution. Australia, all along N. coast (Australian Black-lip); E. coast as far south as Moreton Bay (specimens from Moreton Bay, Mus. Cuming, B.M.), W . coast to about 29° S., Coasts of N e w Guinea and the adjacent Islands ("New Guinea Black-lip " ) , N e w Britain, the Solomon Islands, & c , and probably every suitable locality in the Western Pacific. |