Argopecten nerterus Woodring, 1982
WOODRING, W. P. 1982. Geology and paleontology of Canal Zone and adjoining parts of Panama. United States Geological Survey Professional Paper, 306-F: 1-759, pls. 83-124. [p. 597, pl. 123, figs. 1-2, 4]
1982 Argopecten nerterus Woodring, 1982
W. P. Woodring, 1982, plate 123.
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«Moderately large, height and length subequal, generally slightly inequilateral, posterior end slightly longer than anterior. Convexity moderate and subequal, right anterior auricle slightly longer than posterior; left auricles subequal. Ribs generally low to very low, exceptionally of moderate height, crest arched; ribs wider than interribs or of about same width; 19 to 23 (generally 20 or 21) on both valves. Concentric sculpture generally in form of growth threads of irregular spacing and strength, extending across ribs and interribs, exceptionally on parts of some valves consisting of uniformly spaced fine lamellae. Flanks narrow, indistinctly set off from disk. Radial sculpture of right anterior auricle moderately stronger than that of posterior. Radial sculpture of left auricles moderately weak or absent. Byssal notch moderately narrow, moderately deep. Ctenolium short or absent. A pair of moderately strong cardinal crura.
Length 46 mm, height 43.6 mm, convexity 7.2 mm (type). Length 51.5 mm, height (incomplete) 45.5 mm (estimated restored height 50 mm), convexity about 5 mm (largest specimen). Type (right valve): USNM 647131; paratype (left valve) USNM 647132. Type and paratype locality: 188 (USGS 16946, Río Piña road, 0.9 mile (1.4 k) southwest of Gatun Dam spillway bridge, Canal Zone), Toro limestone member of Chagres sandstone. This low-ribbed, moderately convex, generally slightly inequilateral species is abundant in the Toro limestone member of the Chagres sandstone westsouthwest of Gatun Dam. The collections from localities 188 to 188e, inclusive, in that area, contain 110 valves, ranging in length from 7.8 to 51.5 mm. None is articulated. It is rare elsewhere in the Toro and also in the Chagres proper. The ribs of five valves, one of which is illustrated (pI. 123, fig. 4.), are somewhat higher than those of the typical form, but others are more or less gradational. Druid Wilson called my attention to his collection from Olsson's Unit A (USGS 22704, road-metal pit on Florida highway 80 west of Belle Glade), which consists of low-ribbed scallops of the size of Argopecten nerterus; the low-ribbed Argopecten from that locality were identied by Waller (1969, p. 65) as A. gibbus. Some are very slightly inequilateral. All are, however, slightly more convex than the fossils from Panama and have a shallow byssal sinus and very weakly sculptured right anterior auricle. Occurrence: Toro limestone member of Chagres sandstone (late Miocene or early Pliocene), localities 187,188, 188a, 188b, 188c, 188d, 188e. Chagres sandstone proper (late Miocence or early Pliocene), localities 201, 202 (fragment, identification doubtful)». WENDELL PHILLIPS WOODRING, 1982
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