Amussiopecten vanvlecki Arnold, 1907
ARNOLD, R. 1907. New and characteristic species of fossil mollusks from the oil-bearing Tertiary formations of Santa Barbara County, California. Smithsonian Miscellaneous Collections, 59 (4-4): 419-447, pls. 50-58. [p. 428, pl. 53, figs. 1, 2]
R. Arnold, 1907, plate 53.
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«DESCRIPTION.― Shell averaging about 70 millimeters in altitude, length and height about equal, outline circular; both valves convex, the right slightly more so than the left, equilateral, thin; base regularly rounded; sides only very slightly concave above; margins smooth. Right valve somewhat convex, the region of greatest convexity being just below the beak; surface ornamented with 13 or 14 rather prominent ribs, these being quite rounded in the younger stages of growth, but gradually becoming flatter and lower toward the periphery; interspaces rounded near umbos, but shallower and flatter below; equal, fine, sharp, raised incremental lines, separated by interspaces as wide as the lines, cover the surface of the disk and ears; hinge line longer than half length of disk; ears subequal, anterior with shallow byssal notch; posterior rectangularly truncated. Left valve slightly less convex than right, flat to concave immediately below umbo; ribs regularly rounded throughout entire length, becoming flatter and sometimes almost obsolete toward the periphery; minute sculpture as in right valve; ears flat, the anterior one showing two or three faint radial riblets. Interior of both valves reflecting the external ribbing very prominently.
DIMENSIONS.― Longitude 70 mm.; altitude, 64 rnm.; diameter (approximate), 12 mm. NOTES.― This species appears to be most 'closely related to P. sanctaecruzensis Arnold, which occurs in the Oligocene and lowest Miocene of the Santa Cruz Mountains. It is distinguishable from the latter by its larger size, flatter disks, less elevated ribs, and by the prominent reflection of the external ribbing on the interior of the disk. This last is one of the most prominent, unique, and interesting characteristics of P. vanvlecki. Named in honor of Mr. Robert Van Vleck Anderson, of the United States Geological Survey. TYPE.― Cat. No. 165,305, U. S. N. M. (right valve). PARATYPE.― No. 165,306, U. S. N. M. (left valve). LOCALITY.― Mouth of Ballard Canyon, 2 miles south of Santa Ynez, Santa Barbara County, California; locality No. 4478. HORIZON.― Vaqueros formation, lower Miocene.» RALPH ARNOLD, 1907
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«Comments.— Flabellipecten? hawleyi was placed in synonymy with A. vanvlecki as an immature form by Masuda (1971b, p. 210-211). The left valve holotype of F.? hawleyi is almost flat and has 18 narrow, round ribs separated by slightly wider interspaces. Both auricles are smooth, but the rest of the shell bears imbricated, concentric lamellae. The left valve paratype of A. vanvlecki is somewhat convex and has 13 ribs; the anterior auricle has three faint riblets. I believe that F.? hawleyi is not an immature form of A. vanvlecki and concur with Hertlein and Grant (1972, p. 178) in tentatively assigning it to Flabellipecten.
Geographic range.— Southern California to Baja California Sur. Geologic range.— Oligocene and Miocene. Occurrence in the Californias.— Oligocene and Miocene: Soda Lake Shale Member, Vaqueros (Vedder, 1973) and Vaqueros (Arnold, 1907b; Loel and Corey, 1932; Dibblee, 1950; Avila and Weaver, 1969) Formations; Miocene: Branch Canyon Sandstone (Vedder, 1968), Buttonbed Sandstone Member, Temblor Formation (Addicott, 1972), Isidro (Stump, 1979), Obispo Formation (Hall, 1973), Painted Rock Sandstone Member, Vaqueros Formation (Vedder, 1973), and Saltos Shale Member, Monterey Shale (Vedder, 1973).» MOORE, E. J. 1984. Tertiary Marine Pelecypods of California: Propeamussidae and Pectinidae. United States Geological Survey Professional Paper, 1228-B: iv + B1–B112, figs. 1-2, pls. 1-42. [p. B70]
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Amussiopecten vanvlecky (Arnold); E. J. Moore, 1984, Tertiary Marine Pelecypods of California, plate 29, figure 5; plate 30, figure 1.
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«Comparison:— Pecten (Pecten) hawleyi was described by HERTLEIN (1925) from the same formation containing P. vanvlecki, and was based upon one small left valve and one small, poorly preserved right valve. However, according to the re-examination of type specimens (Stanford University Type Coll. Nos. 19, 20) it seems that P. hawleyi is a synonym of P. vanvlecki, that is to say, P. hawleyi has features characteristic of P. vanvlecki, such as slightly inflated left valve with rounded radial ribs that tend to become flatter and lower towards ventral margin. distinct, raised, regularly spaced incremental lines and distinct paired internal ribs. Thus, it appears that P. hawleyi represents an immature form of P. vanvlecki. Also P. hawleyi was recorded by LOEL and COREY (1932) from the Vaqueros Formation at Santa Ynez Mountains in Southern California. However, according to the writer's study of their type specimens (Museum of Paleontology, Univ. Calif. Berkeley, Coll. Nos. 31718, 31719), the left valve can be identified with P. vanvlecki but the right valve can be considered to be referable to Aequipecten andersoni (ARNOLD).
Pecten vanvlecki has frequently been confused with Pecten (Amusium) lompocensis Arnold (1906), described from the Temblor Miocene in Southern California, as already pointed out by Loel and Corey (1932), but the former is easily distinguishable from the latter by its rather thick shell, squarish, low, flatly round-topped radial ribs tending to become obsolete towards the ventral and lateral margins, paired internal ribs developed at lower part and larger and angulated auricles.» MASUDA, K. 1971. Amussiopecten from North America and Nothern South America. Transactions and Proceedings of the Palaeontological Society of Japan, n. s., 84: 205-224 [210-211]
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Amussiopecten vanvlecki (Arnold, 1907); K. Masuda, 1971, Amussiopecten from North America and Nothern South America, pl. 25, figs. 1a-b, 2, 3, 4.
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«This distinctive species has sometimes been reported as P. lompocensis Arnold (1906), a Temblor Pecten (Amusium) but is easily distinguishable from that species by its prominent, fiat, and wide ribs; P. lompocensis being without prominent radial surface ribs. Both species are usually found poorly preserved, as casts, but even in that condition their ribbing is different in that P. vanvlecki has raised rib molds while in P. lompocensis the interior riblets are represented by grooves in the cast.
It should be noted that P. vanvlecki varies somewhat in the width and number of ribs. Specimens from near Nojoqui Creek, ten miles west of the type locality and in the same zone, commonly have as many as 17 or 18 well developed ribs. Geologic range.— Confined to Vaqueros horizon, Lower Miocene. Distribution.— Oak Ridge (Torrey Canyon), Ventura. County; western Santa Ynez Mountains, Santa Barbara County; present, Santa Cruz Island, Santa Lucia Mountains, and western foothills (a "reef bed") from northern San Luis Obispo quadrangle, and Nipomo across southwest Paso Robles quadrangle to central western Adelaida quadrangle, San Luis Obispo County. Present in Santa Cruz Mountains.» LOEL, W. & W. H. COREY. 1932. The Vaqueros formation, lower Miocene of California I. Paleontology. University of California Publications, Bulletin of the Department of Geological Sciences, 22 (3): 31-410, pls. 4-65. [p. 195]
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Pecten (Pecten) vanvlecki Arnold; W. Loel & W. H. Corey, 1932, The Vaqueros formation, lower Miocene of California I. Paleontology, plate 20, figures 3, 5.
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