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Show 1901.] MOTHER-OF-PEARL OYSTERS. 381 Species 5. MARGARITIFERA CARCHARIARUM, n. sp. (Text-fig. 92.) Type B.M. 1901.2.28.48; Sharks Bay, pres. A. van Noorden, Esq. " Sharks Bay shell " of Mother-of-Pearl markets. Shell flat as in M. margaritifera, in outline suggesting a small example of Al. maxima, but differing in the relatively greater size of the rostrum and the more vertical posterior margin of the nacre. Anterior teeth very abortive, in grown examples only-represented by a slight uuevenness on tbe inner surface of the hinge. Lateral teeth represented by a tiny lamina or elongated Text-fig. 92. Margaritifera carchariarum, nat. size. facet just posterior to the ligament. The posterior angle of the nacre, where its margin meets the hinge-line, is a right angle. There is no marked sinus in the hinder margin, but a slight notch. The hinge is nearly as long as the antero-posterior measurement of the nacre, the ratio of measurements being the following :- Hinge : length (ant.-post.) of nacre : depth (dors.-vent.) of nacre : : 60 : 70 : 75. Average specimens measure about 8-10 cm. in diameter. The hinge is relatively longer than in M. sugillata. In the latter species the anterior margin of the nacre, ventral to the byssal notch, projects considerably forwards. The lappet-like lip processes are crimped as in M. sugillata, |