Euvola sanctaecruzensis (Arnold, 1906)
ARNOLD, R. 1906. The Tertiary and Quaternary pectens of California. United States Geological Survey Professional Paper, 47: 1-264, pls. 1-53. [p. 54, pl. 3, figs. 12-13]
1906 Pecten (Pecten) sanctaecruzensis Arnold, 1906
1923 Pecten (Pecten) dickersoni Wagner & Schilling, 1923
1923 Pecten (Pecten) dickersoni Wagner & Schilling, 1923
R. Arnold. 1906, plate 3.
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«Description.— Shell averaging about 50 millimeters in altitude, slightly longer than high, plano-convex, equilateral, rather thin; base regularly rounded; sides only slightly concave above; margins smooth. Right valve quite convex and ornamented with about 12 prominent, perpendicular-sided, slightly convex-topped ribs, separated by flat-bottomed, channeled interspaces about equal in width to thecribs; surface sculptured by small, almostcimperceptible, obsolete, radiating striations and numerous fine sharp concentric lines; hinge line considerably longer than one half length of disk; ears subequal; anterior with shallow byssal notch and fine, sharp concentric lines; posterior similarly sculptured, but rectangularly truncated. Left valve flat, with slight concavity near umbo; lateral areas rather prominent; ribs squarish, with slightly convex tops narrower than those of the right valve and with proportionally wider interpaces; ears subequal, rectangularly truncated, and with surface sculptured by numerous tine, sharp incremental lines.
Dimensions.— Alt. 52 mm.: long. 55 mm.; hinge line 32 mm.; diameter about 13 mm.: unbonal angle 110º. This species is allied to P. bellus and may be its precursor, as it is very similar to the latter in most respects. P. sanctaecruzensis may be distinguished from P. bellus by its fewer rib.s (11 instead of 14) and relatively smaller size when adult. P. sanctaecruensis is so far known only from beds which appear to be transitional from the Oligocene to the lower Miocene. At locality No. 111 (L. S. J. U. Geol. Survey) on Twobar Creek, one-fourth mile above its junction with San Lorenzo River, Santa Cruz County, the type was found associated in a soft sandstone with the following species; Pecten branneri n. sp., Cythera (cf.) vespertina, Tritonium sp. No. 1, Corbula (?) sp.. Yoldia (cf.) impressa, Nucula n. sp. (large, with coarse sculpture), Leda sp. B. and C., Cidaris (?) spines, Callista sp., Tellina (Angulus) sp., Cardium n. sp.. near cooperi, Teredo sp.. Chione (cf.) mathewsoni. One mile southeast of Cowell's asphaltum quarry (locality 30), near Santa Cruz, P. sanctacruzensis is associated with P. peckhami, Nucula sp., Phacoides sp., and Chione sp. The type, a beautifully preserved mold of a left valve, is now in the collection of the department of geology, Stanford University. A small cobblestone containing two right and two left valves of P. sanctacruzensis was found by Miss L. J. F. Hecox, of Santa Cruz, as float in Bear Creek, about 2 miles from the type locality. One of these right valves is figured and serves as a cotype. RANGE.
Oligocene-Miocene. Twobar Creek and Bear Creek. Santa Cruz County (Arnold; Hecox).»
RALPH ARNOLD, 1906
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«Pecten sanctaecruzensis is a potentially valuable species for stratigraphic correlation in California Coast Range basins. Its local stratigraphic range, or teilzone, and position in the provincial foraminiferal chronology are well known (Burchfiel, 1964). Although the record in the Wygal Sandstone Member is the first reported from east of the San Andreas fault, this species also occurs at a locality in the Pleito Formation of the San Emigdio Mountains. It was originally described from "a faulted block of the San Emigdio Formation on Salt Creek" by Wagner and Schilling (1923, p. 253, pl. 45, fig. 1) as Pecten dickersoni. Detailed mapping of this area (Dibblee, 1961) shows that the type locality is in the Pleito Formation of Wagner and Schilling (1923), and study of several topotypes from USGS locality M3747 indicates that the pattern of ribbing and the number of ribs are identical to P. sanctaecruzensis.»
ADDICOTT, W. O. 1973. Oligocene molluscan biostratigraphy and paleontology of the lower part of the Type Temblor Formation, California. United States Geological Survey Professional Paper, 791: 1-48, pls. 1-9. [p. 25]
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Pecten (Pecten) dickersoni, n. sp.; C. M. Wagner & K. H. Schilling, 1923, The San Lorenzo Group of the San Emigdio Region, California, plate 45, figure 1.
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