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Show •J ' LIGHTNING' AND 'PORCUPINE' EXPEDITIONS. 35 ' Porcupine ' Exp. 1870 : Atl. St. 24, 27, 28, 28 a, 30 ; Med. Adventure Bank. Distribution. North Japan (St. John) ! This species may be known by the flattened apex and the remarkable semicircular pad on the umbilicus, which is proportionally much smaller than in N. josephinia. It is possible, however, that the present species may be a southern, and therefore a smaller, form or variety of N. affinis. The operculum in the Japanese specimens is calcareous. It is also possible that m y N. spheroides from the 'Valorous' Expedition (1750 fathoms) may be the young of the present species. 16. NATICA AFFINIS, Gmelin. Nerita affinis, Gmel. ed. L. S. N. p. 3675 (ex Mull. Zool. Dan. Prodr. no. 2956). Natica affinis, B. C. iv. p. 229 ; v. p. 215, pi. cii. f. 3; G. O. Sars, Moll. reg. arct. Norv. p. 159, t. 21. f. 14 a, 14 b. 'Lightning' Exp. St. 5. 'Porcupine' Exp. 1869: St. 39, 65, 89. Distribution. Circumpolar and arctic seas in the Atlantic and the Pacific, Iceland, Faroe Isles, between the Hebrides and Faroes, Norway, Labrador, Gulf of St. Lawrence, N e w England, Siberia, Sea of Okhotsk, Aleutian I. (Dall), North Japan (v. Schrenck and Lindholm); 1-1255 fms. Fossil. Pliocene: Red Crag (S. V. Wood). Post-tertiary: Glacial beds in Greenland, Siberia, Iceland, Scandinavia, British Isles, Palermo (Dr. van Geuns), Russia, and N. America ; 0-1360 ft. The difference of level in Great Britain extends to 1840 ft., viz. from the Shetland sea-bed, 480 ft., to Moel Tryfaen, 1360 ft. Synonyms. N. clausa, Broderip and Sowerby ; N. septentrionalis (Beck), Moller; and as a variety, N. occlusa of S. V. Wood and N. russa of Stimpson. Prof. G. O. Sars considers N. affinis and N. clausa distinct species, chiefly because of a difference in size and in the radula. But in his figure of the larger form, which he names clausa (t. 21. f. 12 b), the umbilicus is shown as quite open and without any callosity. It has been said that even the good Homer occasionally becomes sleepy ! The present species is not N. affinis of Von d. Busch. The animals or soft parts of the typical form and the variety occlusa or russa were described by me in my notices of the ' Valorous ' Expedition. A specimen of the former is an inch and three tenths long, and nearly as broad. As to the greater size of Invertebrata from Arctic seas, Mr. Norman remarks, in his " Notes on the Oceanic Copepoda from Nares's Arctic Voyage : " - " With respect to size, we find here, as in so many other instances among the Invertebrata, an extraordinary development of the Arctic specimens, which are at least six times the size of those from the Irish coast' and measure five millimetres in length, exclusive of the antennae." |