Miyagipecten alaskensis MacNeil, 1967
MACNEIL, F. S. 1967. Cenozoic pectinids of Alaska, Iceland, and other nothern regions. Geological Survey Professional Paper, 553: iv, 57 p., pls. 1-25. [p. 45, pl. 6. figs. 4, 5]
Miyagipecten alaskensis MacNeil, n. sp.
Plate 6, figures 4, 5 «Description.— Shell of medium size and suborbicular, medium to weakly inflated. Right valve Amusium-like sculpture well developed with two apparent resting stages shown on the holotype. Anterior ear of right valve moderately broad and of moderate length, no well-defined byssal area; byssal notch shallow. Posterior ear of right valve moderately short with a steeply sloping posterior margin. Left valve with numerous small, rounded radial ribs, increasing in number by the addition of intercalary ribs ventrally, the intercalary ribs rapidly becoming as strong as the primary ribs. Microsculpture reticulate or metal lathelike, covering the interspaces and ribs alike. Ears of left valve unknown.
Discussion.— This species is known from the external and internal mold of several right valves and one incomplete external mold of a left valve. It occurs in a hard gravelly sandstone in association with a large unidentified fragment of Patinopecten (Lituyapecten). It is not absolutely celrtain that the two incomplete valves here figured belong to the same species. The ventral half of the internal mold of a specimen with attached valves show that neither valve has internal ribs; the internal mold comes from the external mold of a right valve. The probability is, therefore, that this is not an Amusium, but the possibility exists that the fragment of a ribbed left valve is a Chlamys. No pectinid like this has been reported previously from America. It is presumed to be related to Miyagipecten, although I cannot find a description of a species of that genus that refers to a microsculpture like that of M. alaskensis. M. alaskensis may be closely related to M. saromensis Hasimoto and Kanno (1958, p. 287, pl. 42, figs. 1-5) from the Chirai Formation (middle Miocene) of Kitami Prefecture, nothern Hokkaido. The right valve of M. saromensis has faint radial ribs, unlike the present species, but the radial ribs of the left valve are of similar texture. Types: The holotype (USNM 645049), an incomplete right valve, has an estimated height of about 55 mm, although another incomplete right valve probably was closer to 85 mm. The paratype is numbered USNM 645050. Type locality: Nunatuk north of the east end of the Pinnacle Hills, lat 60º09'40" N., long 140º16'40" W., Malaspina district, Alaska, USGS M1321. The horizon is probably early Pliocene.» FRANCIS STEARNS MACNEIL, 1967
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F. S. MacNeil, 1967, plate 6.
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