Azumapecten tugidakensis (McNeil, 1967)
MCNEIL, F. S. 1967. Cenozoic pectinids of Alaska, Iceland, and other nothern regions. Geological Survey Professional Paper, 553: iv + 1-57, pls. 1-25. [ p. 10, pl. 7, figs. 1-11; pl. 8, fig. 1]
1967 Chlamys (Leochlamys) tugidakensis McNeil, 1967
F. S. McNeil, 1967, plate 7.
F. S. McNeil, 1967, plate 8.
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«Description.— Shell of medium to moderately large size; medium inflated, the right valve more inflated than the left valve; dorsoventrally elongate. Anterior ear of right valve elongate and narrow; byssal sinus very broad and deep, byssal area wide with coarse growth lines; posterior ear of moderate size with a nearly vertical, slightly concave posterior margin. Anterior ear of left valve large and broad, anterior margin nearly vertical and slightly convex; posterior ear smaller with a weakly concave posterior margin. Dorsal margins weakly concave, dorsal slopes of right valve narrow with a shallow cleft, dorsal slopes of left valve broad and moderately undercut. Umbonal angle broader in young juvenile stage than in intermediate stage, flaring weakly again in adults. Ribs in juveniles definitely paired on the right valve, single with a well-defined interstitial riblet on left valve. Adult ribs more crudely paired, some paired ribs of equal size, others very unequal. Interstitial ribs rarely present on the right valve of adults; interstitial ribs of left valve nearly as strong as primary ribs in adults. Adult ribs of both valves set with thick, broad, flattened or curved, irregularly spaced spines. Microsculpture consisting of fine raised Camptonectes-like lines that have a fanlike pattern within each interspace and rise along the sides of the adjacent ribs; the juvenile stage of the left valve has a reticulate or metal lathelike microsculpture. Interior of shell weakly corrugated.
Discussion.— Except for C. (?L.) columbiana (Clark and Arnold) (1923, pl. 23) from the Sooke Formation (early Miocene?) of Vancouver Island, British Columbia, no pectinids that have a long ear and a deep byssal notch have been described from the American west coast. C. (?L.) columbiana has much weaker spines on its ribs, and the right valve has fine interstitial riblets. Inasmuch as pectinids of this type are an ancient group, there is no assurance that C. (L.) tugidakensis is descended from C. (?L.) columbiana. Some poorly preserved specimens from the lower part of the Yakataga Formation reported by me as Vertipecten sp. indet. (MacNeil, 1961, p. 236) may belong to this group, but the known specimens are internal molds. Leochlamys-like forms appear to have been in the northwestern Pacific area from early Miocene? through Pliocene time. Types: The holotype (USNM 644871), a right valve, measures height 70 mm, length 60 mm. The paratype (USNM 644872) is a left valve. Other figured specimens are numbered USNM 644873-644881,645052. Type locality: Near the center of the northwest side of Tugidak Island, Alaska, 320 ft below the top of a section computed to be 3,520 ft thick, 56°31" N., 154°42" W., USGS M1494. Other occurrences: 1,900 ft above the base of the Tugidak Island section, USGS M1895; several horizons in the lower 2,500 ft of a section estimated to be nearly 4,000 ft thick, Middleton Island, Alaska, USGS 17746, M1746, M1751, M1754; upper part of Yakataga Formation (horizon probably Pliocene), along south side of Deadfall Creek north of La Perouse Glacier, Lituya district, Alaska, USGS M1851; upper part of the Yakataga Formation (horizon probably Pliocene) in the Chaix Hills, Malaspina district, Alaska, USGS M1878.» FRANCIS STEARNS MCNEIL, 1967
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