Vertipecten popofensis MacNeil, 1967
MACNEIL, F. S. 1967. Cenozoic pectinids of Alaska, Iceland, and other nothern regions. United States Geological Survey Professional Paper, 553: 1-57, pls. 1-25. [p. 39, pl. 1, fig. 1; pl. 2, figs. 1, 3, 5, 6, 8]
1967 Vertipecten popofensis MacNeil, 1967
F. S. MacNeil, 1967, plates 1, 2.
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«Description.— Shell of medium size and moderately thin. Left valve more inflated than right valve, especially near the beak. Anterior ear of left valve larger than posterior ear, anterior margin weakly S-shaped, posterior ear with a convex margin, ears of right valve not well known, anterior ear broad with a broad byssal area. Left valve sculpture consists of moderately broad rounded ribs over most of the disc; the ribs become smaller and weakly beaded posteriorly. Weaker interstitial ribs present in some interspaces on the disc and in most posterior interspaces. Right valve with low rounded to flattened ribs and interspaces of nearly equal width; posteriormost ribs weak and irregular. Reticulate or metal lathelike microsculpture present on ears, the upper part of the disc, and persisting to the margin on the posterior part of the shell, posteriorly having a diagonal strike as in Camptonectes.
Discussion.— Although the material on which this species is based is fragmental and the fragments belong to different individuals, it is presumed that the fragments all belong to the same species. Several nearly complete internal molds are present in the same collections. The shell of this species is thin for a pectinid of this size, a factor contributing to the rarity of large pieces of test; the fragments figured were freed from matrix in the laboratory. The test apparently crumbled and was lost on free specimens collected in the field. Vertipecten popofensis is probably most closely related to two Miocene species, V. fucanus (Dall) from the Astoria Formation of Washington and V. bowersi (Arnold) (= V. nevadanus (Conrad)) from the Temblor Formation of central California (for both see Arnold, 1906). This group of Vertipecten has moderately strong to strong ribs; the ribs of the right valve are broadly rounded or flat topped. V. porterensis (Weaver) (see Clark and Arnold, 1923, pl. 24, fig. 1), from the Blakeley Formation of Weaver (1912) (late Oligocene and early Miocene) of Washington, appears to belong to a different group of Vertipecten, a group that is more primitive morphologically and that retains more of the characters of the ancestral Chlamys. V. porterensis is more closely related to V. lachenbruchi and may be derived from that species. The oldest known Vertipecten, V. yneziana (Arnold) (see Weaver and Kleinpell, 1963, pi. 30, fig. 7; pl. 31, figs. 1, 4), and V. sespeensis (Arnold) (ibid., pl. 29, fig. 10; pl. 30, fig. 1), both from late Eocene or early Oligocene beds of southern California, may also represent two groups; V. sespeensis the group of V. porterensis, and V. yneziana the group of V. fucanus. V. popofensis occurs in association with Acila shumardi (Dall), Ostrea tigiliana Slodkewitsch, Arca cf. A. merriami (Van Winkle), and numerous other probably undescribed species. A fragment of a pectinid (pl. 1, fig. 1) from the upper part of the Tokun Formation (Eocene and Oligocene) in the Katalla district, Alaska, may be referable to V. popofensis. The specimen is an internal mold with a little shell material adhering; it does not show the external character of the ribs. The horizon in the Oligocene from which this fragment was obtained may be older than the horizon of the type of V. popofensis. The species of Vertipecten here described are the first undoubted Vertipecten to be reported thus far from Alaska. Some internal molds from the Yakataga district reported previously (MacNeil, 1961, p. 236) may be a Chlamys related to Chlamys tugidakensis, here described. Vertipecten may have originated in Alaskan waters. Types: The holotype (USNM 645037), an incomplete left valve, measures 48 mm in its longest preserved dimension; it is a half-grown specimen. The paratype from the same locality (USNM 645038), a large fragment of the disc of a left valve, would have a restored length of about 90 mm. Two paratypes and two figured specimens are numbered USNM 645039, 645041, 645051. Type locality: An unnamed formation within the Acila shumardi zone (middle Oligocene), seacliff near the northwest corner of Popof Island, Shumagin Islands, Alaska, USGS 3563. Other occurrences: Same horizon, northeastern Unga Island south of West Head, USGS 5037. Doubtful occurrence: Upper part of Tokun Formation, "Split Creek, 100-200 yards above branch that heads against the Bedwood Creek divide," Katalla district, USGS 4323.» FRANCIS STEARNS MACNEIL, 1967
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