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Show 574 DR. GWYN JEFFREYS ON THE MOLLUSCA OF THE [June 17» SILICULA FRAGILIS \ Jeffreys- (Plate XLV. figs. 6, 6 a.) B O D Y clear white ; foot axe-shaped. S H E L L ensiform or obliquely oblong, inequilateral, compressed, thin, glossy, nacreous, and semitransparent: sculpture extremely fine and numerous but irregular concentric striae, which are only observable with a magnifying glass ; there are also occasional lines of growth : colour white, under a pale brownish-yellow epidermis : margins nearly straight at the back on the anterior side, rounded at the other side, extended and wedge-shaped at the anterior side, the extremity of which is truncated, with a slight notch or indentation in the middle, gradually curved in front: beaks placed near the smaller end, at about one third the length of the back; they are small, rather prominent, and calyciform : lunule well defined, lance-head- shaped, and elongated: ligament none: cartilage and pit oblique: hinge-line long, nearly straight on the anterior side, and gently curved on the other side : hinge-plate rather narrow: teeth elongated, four on each side, somewhat like the lateral teeth in Tel- Una, but overlapping one another, and not continuous : they are of different lengths, those at each end being the shortest and strongest: inside polished and iridescent, microscopically fretted towards the front margin : scars inconspicuous. L. 0*15, B. 0*3. 'Porcupine' Exp. 1869: St. 16, 28. A. More or less angulated or pointed at the longer end. 1. LEDA PERNULA, Muller. Arca pernula, Mull, in Beschaft. Berl. Ges. naturf. Fr. iv. p. 57 (1779). L. pernula, B. C. ii. p. 158; v. p. 173 : G. 0. Sars, Moll. reg. arct. Norv. t. v. f. 1 a-d. ' Porcupine' Exp. 1869 : St. 4, Loch Torridon. 1870: Atl. 1, 2, 6, 9. One perfect specimen (but dead) and several valves of different sizes, all being more or less smooth or destitute of concentric strice. Distribution. Arctic Ocean in the N. Atlantic southwards to the Cattegat on the east and Maine on the west, Novaya Zemblia, Behring Strait; 5-210 fms. Fossil. Post-tertiary or " glacial." N. lat. 82°, N.E. America, Archangel, Scandinavia, Great Britain and Ireland; 0-1360 ft. Being variable in shape and sculpture, this species has many synonyms. 2. LEDA MINUTA, Muller. Arca minuta, Mull. Zool. Dan. Prodr. p. 247- L. minuta, B. C. ii. p. 155, pi. iv. f. 2; v. p. 173, pi. xxix. f. 6. 'Porcupine' Exp. 1869 : St. 1, 23a, 25, North Channel, the Minch, Little Minch, near Belfast. 1870 : Atl. 2, 9 (valves only, and perhaps semifossil). Distribution. Arctic seas in both hemispheres, to the Cattegat 1 Brittle. |