Cyclochlamys falklandica (Dell, 1964)
DELL, R. K. 1964. Antarctic and subantarctic Mollusca: Amphineura, Scaphopoda and Bivalvia. Discovery Reports, 33: 93-250. [p. 181, figs. 1.2, 1.5]
1964 Cyclopecten falklandicus Dell, 1964
R. K. Dell, 1964, figure 1.
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«OCCURRENCE: WS 228, Falkland Islands, 229-236 m, paratype; WS 246, Falkland Islands, 267-208 m, type, paratypes.
DISTRIBUTION: As far as is known, confined to the Falkland Islands.
Shell small, inequivalve, left valve almost equilateral, right valve markedly inequilateral, semi-transparent, the two valves with discrepant sculpture. Left valve sculptured with very fine comparatively widely spaced narrow concentrics crossed by close, rather wavy, microscopic radials. Ears subequal, not strongly divided from disc. Right valve with irregular narrow concentrics, overlaying a microscopic pattern consisting essentially of minutely netted sculpture arranged in radial lines. Posterior ear scarcely marked off from disc, anterior clearly demarcated by a groove; a well-developed byssal sinus. Posterior ear with about four fine radials, situated close to the dorsal margin of valve. Anterior ear with about four radial rows marked mainly by a thickening of concentric sculpture in rows.
Length 5.6 mm; height 5.3 mm (left valve; holotype. B.M. Reg. no. 1962888/1, St. WS 246). Length 4.7 mm; height 4.3 mm (right valve; paratype. B.M. Reg. no. 1962888/1, St. WS 246). Paratypes: B.M. Reg. nos. 1962888/3-8, St. WS 246; 1962889/1, St. WS 228. The type-material consists of two disconnected valves, the left designated as holotype, the right as paratype, from WS 246; other paratypes from St. WS 228. This form does not seem closely related to any described species from Magellan or adjoining regions. It differs markedly in sculpture from subhyalinus Smith, obtained by 'Challenger' off Patagonia in 400 fathoms. In subhyalinus the left valve lacks obvious sculpture, while the right valve is sculptured with definite close concentrics. Cyclopecten (Pecten) pteriola (Melvill & Standen) from off the South Orkneys has the left valve much less equilateral than in falklandicus, and has concentric sculpture consisting of well-marked solid concentric folds (fig. 1, no. 1). The left valve of a specimen in the British Museum presented by Melvill from the South Orkneys is figured here (length 4.7 mm; height 4.5 mm) for comparison. Both falklandicus and pteriola seem best placed in Cyclopecten. RICHARD KENNETH DELL, 1964
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