Chlamys islandica powersi MacNeil, 1967
MACNEIL, F. S. 1967. Cenozoic pectinids of Alaska, Iceland, and other nothern regions. United States Geological Survey Professional Paper, 553: iv + 1-57, pls. 1-25 [p. 35, pl. 16, figs. 1-2, 4-7]
1967 Chlamys (Chlamys) islandica powersi MacNeil, 1967
F. S. MacNeil, 1967, plate 16.
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«Discussion. This subspecies is closely related to C. i. kanagae. It differs from it by having a more inflated shell and a slight twist to the shell. The riblets of the left valve are smaller, more delicate, and more widely spaced in G. i. powersi, and the riblets of the right valve are correspondingly larger and broader. While both subspecies have fascicular bundles or plications on the left valve, the range of variation differs; C. i. kanagae has variants with fused riblets of moderately broad solid ribs, and even the most weakly fasciculated specimens have a heavier riblet along the crest of the fascicle; G. i. powersi has little or no tendency for the riblets to be fused or enlarged on the fascicles. Both subspecies have similar microsculpture.
While it will not be possible to describe the exact line of descent of this and the other subspecies of C. islandica until the complete range of variation of all intermediate forms is known, it seems fairly certain that this subspecies and C. i. kanagae are two of the oldest known forms that can be included in C. islandica. They are clearly related to the late Pliocene forms here referred to C. cosibensis, C. picoensis chinkopensis, and C. hanaishensis. All these species and subspecies are variable, but it is still not possible to say which variants are more primitive, which are more advanced, which species are successional, or which are coderivatives from older varietal series. This subspecies probably is the closest known fossil relative of C. i. albida (Dall) and C. i. erythrocomata (Dall). Types: The holotype (USNM 645022), a right valve, measures 96 mm in height and 86 mm in length. Two para types (USNM 645023, 645024) are left valves. Three other figures specimens are numbered USNM 645025-645027.
Type locality: Poorly bedded loose sand and gravel forming a fill about 75 ft thick at the head of South Bight, Amchitka Island, Aleutian Islands, USGS D46. Possibly from an upper horizon in the section (middle Pleistocene?).» FRANCIS STEARNS MACNEIL, 1967
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