570 DR. GWYN JEFFREYS ON THE MOLLUSCA OF THE [June 17, 



Idas argenteus, Jeffreys. (Plate XLV. fig. 3.) 



Idas 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. 



S 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 Ire- 

 land, S.W. and S. France, Podolia, Vienna Basin, Transylvania, 

 Italy, Cyprus and Rhodes ; 0-600 ft. 



Several obsolete synonyms. 



•^ 3. Arca nodtjlosa, Huller. 



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 the North Atlantic and Mediterranean, I am con- 

 vinced 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 



