Euvola coalingaensis (Arnold in Anderson, 1905)
ANDERSON, F. M. 1905. A stratigrafic study in the Mount Diablo Range of California. Proceedings of the California Academy of Sciences [3th Series], Geology, 2 (2): 155-248, pls. 13-35. [p. 197, pl. 18, figs. 94-98]
1905 Pecten coalingaënsis Arnold in Anderson, 1905
F. M. Anderson, 1905, plate 18.
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«Shell moderate in size, the largest having a diameter of 2¼ inches; inequivalve, radially ribbed; lower valve convex, upper concave.
Arnold's description of this species is not yet published, but as the specimens here figured are from his type locality and have been identified by Dr. Arnold, there is no doubt about the correctness of the determination. They have been referred by Arnold to the Miocene of the Kreyenhagen ranch, but the true horizon is that of the Etchegoin Beds, which are probably Pliocene. Occurrence.— This species is common in the Etchegoin Beds of the Mount Diablo Range, at the Kreyenhagen ranch on Zapata Chino Creek.» FRANK MARION ANDERSON, 1905
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«Pectinidae.— The genus Pecten, represented by P. coalingaensis Arnold (pl. 13, figs. 1, 2, 17, 18; pl. 16, fig. 4), is characteristic of the Pecten zone and was found in place only in that zone. A specimen collected at an Acila zone locality may have been derived from older alluvium. On 150 valves of this species the number of ribs ranges from 15 to 23, but three-fourths of the inflated valves have 19 to 21 ribs, and three-fourths of the flatter valves have 18 to 20 ribs. The nearest living relative of P. coalingaensis is P. cataractes Dall, from the Gulf of California. The living species may be distinguished from P. coalingaensis by the presence of secondary radials in the interspaces on the flatter valve. All of 150 valves of P. coalingaensis lack secondary radials except 5, which have a radial in one or two interspaces, but only 1 of 29 left valves of P. cataractes lack the radials, and that valve is small (height, 22 millimeters). P. coalingaensis and its allies may be distinguished from P. bellus Conrad, a fossil species from Santa Barbara, and its allies, by the greater number of ribs, the greater inflation of the inflated valve, and the shorter internal channels corresponding to the external ribs on the flatter valve. The cross section of the ribs of the inflated valve also differ in the two groups: P. bellus has square-topped ribs, whereas P. coalingaensis has round-topped ribs. P. coalingaensis was treated as a variety of P. bellus by Grant and Gale, but a close relationship seems very doubtful. The two groups are evidently distinct in the living Japanese fauna, P. bellus being represented by P. laqueatus Lischke [26] and P. coalingaensis being represented by P. puncticulatus Dunker, [27] which does not have secondary radials on the flat valve. The two specimens of P. puncticulatus available differ from P. coalingaensis in having fewer large ribs on the flatter valve and small ribs at the dorsal margins of the disc. The inflated right valve of the Japanese species has slightly flatter ribs. P. vogdesi, from the Pleistocene at San Pedro, may be a connecting form between P. coalingaensis and the living P. cataractes. The two specimens of P. vogdesi examined lack the secondary radials on the flatter valve, thus resembling P. coalingaensis. According to Grant and Gale, [28] however, P. vogdesi and P. cataractes cannot be consistently distinguished from each other by this character. Pecten auburyi Arnold, from the Pliocene of the Puente Hills, near Los Angeles, and P. lecontei Arnold, from the Pliocene of Cedros Island, Lower California, apparently lack secondary ribs on the flat valve and according to figures are probably very closely related to P. coalingaensis. Two other forms described from Pliocene strata on the Lower California mainland are also probably related to P. coalingaensis: P. heimi Hertlein, which evidently lacks secondary ribs on the flat valve; and P. hartmanni Hertlein, the flat valve of which has not been described. (R. S.).»
[26] Lischke, C. E., op. cit.. vol. 2, p. 157, pl. 12, figs. 1-2,1871. Reeve, L. A., Conchologia Iconlca. Pecten, pl. 30, fig. 135 (?), 1853.
[27] Pilsbry, H. A., New and hitherto unfigured Japanese mollusks: Acad. Nat. Sci. Philadelphia Proc., vol. 43, p. 473, pl. 19, figs. 1-3, 1892. [28] Grant, U. S., IV, and Gale, H. R., op. cit. (San Diego Soc. Nat. History, Mem., vol. 1, p. 229. WOODRING, W. P., R. STEWARD & R. W. RICHARDS. 1940. Geology of The Kettleman Hills oil field California. United States Geological Survey Professional Paper, 195: 1-170, pls. 1-57. [p. 90, 91]
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Pecten coalingaensis Arnold; W. P. Woodring, R. Steward & R. W. Richards, 1940, Geology of The Kettleman Hills oil field California, plate 13, figures 1, 2, 17, 18; plate 16, figure 4.
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