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Show 570 DR. GWYN JEFFREYS ON THE MOLLUSCA OF THE [June 17, IDAS ARGENTEUS, Jeffreys. (Plate XLV. fig. 3.) Ldas argenteus, Jeffr. in Ann. & Mag. N. H. Nov. 1876, p. 428. 'Porcupine' Exp. 1870, Atl. St. 16. Distribution. 'Valorous ' Exp.; 1450 fms. Family VII. ARCID^E. 1. ARCA BARBATA, Linne. A. barbata, L. S. N. p. 1140: Poli, Test. utr. Sic. ii. p. 135, t. xxv. f. 6, 7: B. C.ii. p. 183; v. p. 176. 'Porcupine' Exp. 1870: Atl. St. Gibraltar B. Distribution. Atlantic coasts of France from Quimper to Rochelle, Cadiz, Mogador, throughout the Mediterranean and Adriatic; 2-100 fms. Fossil. Miocene and Pliocene. S.W. and S. France, Vienna Basin, Galicia, Transylvania, Volkynia, Italy, Morea, Cyprus and Rhodes, Madeira. 2. ARCA LACTEA, Linne. A. lactea, L. S. N. p. 1141: B. C. ii. p. 177; v. p. 175, pi. xxx. f. 5. 'Porcupine' Exp. 1870: Atl. St. Vigo B., 36, Tangier B., Gibraltar B.; Med. 50, 55, Adventure Bank. Distribution. Berwick B. and Oban southwards to Mogador, and eastwards to the Morea, Adriatic, Red Sea, Senegal, Canaries; 0-150 fms. Fossil. Miocene, Pliocene, and Post-tertiary. England and Ireland, S.W. and S. France, Podolia, Vienna Basin, Transylvania, Italy, Cyprus and Rhodes ; 0-600 ft. Several obsolete synonyms. 3. ARCA NODULOSA, Muller. A. nodulosa, Mull. Zool. Dan. Prodr. p. 247 : B. C. ii. p. 180 ; v. p. 176, pi. c. f. 2. 'Lightning' Exp.: St. 2, 4, 5. 'Porcupine' Exp. 1869: St. 13, 14, 51, 61, 65. 1870: Atl. 3, 9, 16, 17 a, 24, 26-29 ; Med. 45, 55, 58, Adventure Bank. Distribution. Loffoden Isles to the iEgean, Adriatic, Josephine Bank, Canaries, G. Mexico; 10-700 fms. Fossil. Pliocene and Post-tertiary. Norway, S. France, Italy; 0-100 ft. Having carefully examined and compared more than one hundred specimens from tbe North Atlantic and Mediterranean, I am convinced that A. scabra of Poli is merely a coloured variety of the present species. Some specimens are oval, others oblong ; the angle of the hinge-line on either side is of different degrees of acuteness or obtuseness; and the texture and sculpture are finer or coarser according to the nature of the locality and sea-bottom. Specimens from the Gulf of Mexico are undistinguishable from Norwegian. In |