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Show 572 DR. GWYN JEFFREYS ON THE MOLLUSCA OF THE [J Say's description of A. transversa and the figures lately given by Binney and Tryon, as well as from specimens which Mr. Dall has kindly sent me, I am inclined to consider it either the same as the present species or at most a variety of it. In Weinkauff's collection of Algerian shells is a specimen three and a half inches long, with 32 ribs, the usual number being 28. A monstrosity in the same collection was named by M . Crosse A. weinkauffi. There are several other synonyms. 7. ARCA OBLIQUA, Philippi. A. obliqua, Phil. Moll. Sic. ii. p. 43, t. xv. f. 2 : B. C. ii. p. 175; v. p. 1 75, pi. xxx. f. 4. ' Lightning ' Exp.: St. 5. ' Porcupine' Exp. 1869 : St. 14, 15, 25, 65. 1870 : Atl. 2, 3, 24, 25, C. Sagres, 26-30, 36; Med. 45, 55, 58, Adventure Bank, off Rinaldo's Chair. Distribution. Bergen and Shetland to the ^Egean, Azores; 30- 600 fms. Fossil. Pliocene. S. France, Calabria, and Sicily. Having now reexamined a great number of recent and fossil specimens from various localities, I must separate this from the next species for the following reasons:-A. obliqua is not merely much smaller, but it is shorter (measured from the beak to the front margin), and more sharply angulated on the anterior side ; the strise are nodulous ; and the teetb are more numerous, and straight instead of being set obliquely on the anterior side, as in A. glacialis. Both species are somewhat inequivalve. Some specimens of A. obliqua have the inside of the front margin regularly and closely denticulated. 8. ARCA GLACIALIS, Gray. A. glacialis, Gray in Suppl. App. Parry's first voyage, p. ccxliv; Torell, Spitzb. Moll. t. ii. f. 7, a, b. ' Porcupine' Exp. 1869 : St. 23 a, 89. Valves only, and perhaps semifossil relics of the last glacial epoch. Distribution. Arctic seas in both northern hemispheres, Iceland, and G. of St. Lawrence ; 25-1622 fms. Fossil. Post-tertiary. Scandinavia, Maine ; 0-240 ft. Not A. glacialis of Mighels. 9. ARCA PECTUNCULOIDES, Scacchi. A. pectunculoides, Sc. Ann. Civ. due Sic. vii. p. 82 (1833) : B. ii. p. 171 ; v. p. 175, pi. xxx. f. 3. ' Lightning ' Exp. : St. 2, 5, 7. ' Porcupine' Exp. 1869 : St. 1, 6, 14, 15, 17, 23, 25, 61, 62, 65, off Lerwick. 1870 : Atl. 1, 2, 3, 6, 8, 9, 12, 13, 14, Setubal B., 24 -34 ; Med. 45, Cartagena B., 55, Benzert Road, Adventure Bank, off Rinaldo's Chair. Distribution. Davis Strait to G. of St. Lawrence and Halifax. |