Chlamys picoensis (Waterfall, 1929)
WATERFALL, L. N. 1929. A contribution to the paleontology of the Fernando Group, Ventura County, California. University of California Publications, Bulletin of the Department of Geological Sciences, 18 (3): 71-92, pls. 5, 6, text-fig. 1. [p. 83, pl. 5, figs. 2, 4]
1929 Pecten (Chlamys) islandicus picoensis Waterfall, 1929
1929 Pecten (Chlamys) venturaensis Waterfall, 1929
1929 Pecten (Chlamys) venturaensis Waterfall, 1929
L. N. Waterfall, 1929, plate 5.
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«Pecten islandicus Müller, Arnold, U. S. Geol. Surv., Prof. paper 47, p. 113. (Pliocene of Deadman's Island. Not P. islandicus Müller, Recent.)
Type.— No. 31419, U. C. Mus. Pal. Invert. Coll.; U. C. loc. 7100. Paratype.— No. 31417, U. C. Mus. Pal. Invert. Coll.; U. C. loc. 7100. Shell subcircular, somewhat longer than high; valve convex, equilateral except for ears; of medium thickness; sides slightly concave above; base evenly rounded; left valve with about 90 (at basal margin) prominent, square, flat-topped, imbricated, radiating ribs which multiply by division and by intercalation; interspaces generally narrower than ribs, channeled, and minutely reticulated; hinge line over half the length of the shell; anterior ear much produced, nearly twice as long as posterior, sculptured with eleven radiating ribs similar to those on disk; byssal notch distinct, rounded; posterior ear with about eight radiatihg ribs; right valve very similar; judging from the similarity in the two valves of P. islandicus.
Dimensions.— Height 77 mm., length 82 mm., hinge line 44 mm., diameter of left valve 18 mm., apical angle 106 degrees. Occurrence.— Type from top of Pico, U. C. loc. 7100, NW corner Sec. 3, T 3 N, R 21 W, Ventura County, California. Also Pliocene of Deadman's Island.» This differs from the living Pecten islandicus Müller by being relatively longer, and by having a greater apical angle. A specimen in the Voy collection at the University of California, and collected from the Pliocene of Deadman's Island is labeled P. islandicus. This is identical with the type of P. islandicus picoensis n. subsp.»
LOUIS NILES WATERFALL, 1929
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«Holotype.--UCMP 31419; of venturaensis UCMP 31416.
Type locality.— UC 7100. Ventura County, Calif. Upper part of Pico Formation, Pleistocene (may actually be from San Pedro Formation, Pleistocene); of venturaensis, UC 7097, Ventura County, Calif. Upper part of Pico Formation, Pleistocene. Comparison.--"This differs from the living Pecten islandicus Müller by being relatively longer, and by having a greater apical angle." (Waterfall, 1929, p. 84) Grau (1959, p. 76) put C. picoensis in synonymy with C. rubida. MacNeil (1967, p. 28) considered C. picoensis to be more closely related to C. islandica than to C. rubida, and to be more intimately related to the Japanese forms C. chinkopensis Masuda and Sawada (1961), from the Pliocene, and, C. kinoshitai Kubota (1950), from the Holocene. Hertlein and Grant ( 1972, p. 194) said that the radial sculpture on some valves of Chlamys rubida from the San Diego Formation is similar to that of C. picoensis. Comments.— The holotype of C. picoensis is a right valve sculptured with moderately heavy, dichotomous rubs separated by interspaces that are half as wide and in which an interrib may appear when the shell has reached a height of about 30 mm. Imbricated microsculpture is preserved in some of the interspaces. The right anterior auricle has four coarse ribs; the right posterior auricle five somewhat finer ribs. The ventral margin is strongly and abruptly turned in towards the body. The holotype of C. venturaensis is a lelt valve sculptured with rounded ribs narrower than the interspaces and in which an interrib may appear when the shell is about 15 mm high. Imbricated microsculpture is preserved in many of the interspaces. The left anterior auricle has 9 riblets, the left posterior 7 of about equal size. Chlamys picoensis is equidimensional with a wide apical angle which distinguishes it from related species. It presumably does not occur in strata older than Pleistocene but is included here because of the doubt concerning the age of the type locality. Geographic range.— Southern California. Geologic range.— Pliocene? or Pleistocene. Occurrence in California.— Pliocene and Pleistocene: San Pedro (?) Formation (Waterfall, 1929); Pleistocene: upper part of Pico (?) Formation.» 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. B27, B28]
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Chlamys picoensis (Waterfall); E. J. Moore, 1984, Tertiary Marine Pelecypods of California: Propeamussidae and Pectinidae, plate 7, figures 1, 2.
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«In addition to the occurrence of Chlamys rubida in strata of Pliocene age at San Diego, it was reported from Fourth and Broadway in Los Angeles by Willett (361), from the Ventura region by Waterfall (as Pecten (Chlamys) islandicus picoensis and P. (C.) islandicus venturaensis), and from the Ohlson Ranch Group in Sonoma Co. by Peck (362). Nomland (363) reported it as Pecten hastatus hindsii from the Pecten coalingaënsis zone of the Etchegoin Formation. Stewart (364) later reported fragments of "C. cf. C. islandicus (Muller)" from the Acila zone in the San Joaquin Formation in Kettleman Hills, but he did not record C. rubida from that area.»
HERTLEIN, L. G. & U. S. GRANT IV. 1972. The Geology and Paleontology of the marine Pliocene of San Diego, California (Paleontology: Pelecypoda). Memoirs of the San Diego Society of Natural History, Memoir 2, Part 2b. pp. 143-409, pls. 27-57. [p. 195]
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«Pecten (Chlamys) islandicus picoensis Waterfall, 1929, California Univ. Pubs, in Geol. Sci., v. 18, no. 3, p. 83, pl. 5, figs. 2, 4.
Pecten (Chlamys) venturaensis Waterfall, 1929, California Univ. Pub. in Geol. Sci., v. 18, no. 3, p. 84, pl. 6, fig. 4. Pecten (Pecten) islandicus var. hindsii, Grant and Gale, 1931, San Diego Soc. Natl. History Mem., v. 1, p. 163. (In part.) Chlamys rubida, Grau, 1959, Allan Hancock Pacific Exped., v. 23, p. 77. Discussion.-- While this species is closely related to Recent C. islandica and the early Pleistocene subspecies such as C. i. kanagae, it is more intimately related to the
substock of C. chinkopensis (Pliocene) and G. kinoshitai (Recent). The Japanese forms are here regarded as subspecies of G. picoensis. All these forms are less closely related to G. rubida and C. r. hindsii than to C. islandica. Types: The holotype of C. picoensis (UC 31419), a right valve, is smaller than the para type (UC 31417), a left valve; Waterfall gives the dimensions as, height 77 mm, length 82 mm, convexity of left valve 18 mm.
Type locality: Top of Pico Formation, northwest corner sec. 3, T. 3 N., R. 21 W., Ventura County, Calif., UC loc. 7100. The uppermost part of the Pico Formation may be of early Pleistocene age. Other occurrences: Deadman's Island, San Pedro, Calif.» MACNEIL, F. S. 1967. Cenozoic pectinids of Alaska, Iceland, and other nothern regions. United States Geological Survey Professional Paper, 553: iv + 1-57, pls. 1-25. [p. 28]
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