Argopecten ventricosus eldridgei (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. 87, pl. 25, figs. 3, 3a, 3b, 4, 4a, 5, 5a, 6]
1906 Pecten (Plagioctenium) eldridgei Arnold, 1906
R. Arnold, 1906, plate 25.
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«Description.— Shell averaging about 20 millimeters in altitude, nearly as high as long, equivalve, somewhat oblique (the posterior portion being the longer), very thick and heavy, very ventricose, and with serrate margins; base unequally rounded; sides somewhat concave above and sloping at a moderately steep angle. Right valve with 19 or 20 small, rather low but sharply defined, squarish ribs; interspaces about one-half as wide as ribs, channeled, and with flat bottoms; surface of disk ornamented by numerous sharp concentric lines which loop back over the ribs; more or less prominent constrictions, indicating interrupted growth, are common on most specimens; hinge line equal to about three-fourths length of disk; anterior ear slightly longer than posterior, deeply notched, and ornamented by 3 or 4 prominent radiating ridges and numerous imbricating incremental lines; posterior ear rectangularly truncated and ornamented by 8 or 10 radiating ridges and incremental sculpture. Left valve similar to right, except that the ribs are slightly narrower and more rounded; ears similar to those of right valve except that the anterior one is not as deeply notched. Hinge similar to that of P. circularis except stronger and with the auricular crura much more highly developed. Adductor impressions very deep.
Dimensions.— Alt. 20 mm.; long. 21 mm.; hinge line 1.5 mm.; diameter 15 mm. This species is similar in many respects to P. circularis, but is characterized by its smaller size, greater ventricosity, thicker and heavier shell, deep adductor impressions, and more or less prominent constrictions. It sometimes attains an altitude of 45 millimeters, as shown by fragments collected at the type locality. P. eldridgei appears to be confined to the oil-bearing strata of the San Joaquin Valley, which are probably San Pablo or upper Miocene in age. The type, which is figured and is now in the United States National Museum, was collected in the hills south of the Dabney water wells, McKittrick district, Kern County. Named in honor of the late Mr. G. H. Eldridge, of the United States Geological Survey. RANGE.
Miocene (upper). McKittrick district, Kern County (Eldridge): Buena Vista and McKittrick, Kern County (Watts).»
RALPH ARNOLD, 1906
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«Comments.— The holotype is a small, inequilateral left valve with closely spaced, subrounded ribs and shallow interspaces; looped, concentric lamellae cross both the ribs and the interspaces near the ventral margin. The left anterior auricle is deeply notched.
Geographic range.— Middle to southern California. Geologic range.— Miocene to Pliocene. Occurrence in California.— Miocene and Pliocene: Etchegoin Formation; Pliocene: Cascajo Conglomerate Member, San Joaquin Formation (Woodring and others, 1940).» 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. B36]
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Argopecten circularis eldridgei (Arnold).; E. J. Moore, 1984, Tertiary Marine Pelecypods of California, plate 9, figure 11.
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«The base of the San Joaquin formation is placed at the base of a unit consisting of conglomerate and sandstone, generally blue, here designated the Cascajo conglomerate member. Cascajo Hill, on the west flank of South Dome, is the type locality of the Cascajo conglomerate. The average thickness of the Cascajo is 50 feet, but at places it is considerably greater. Throughout the Kettleman Hills the Cascajo and underlying sandstones are relatively resistant rocks and form a series of hills and ridges.
In northern South Dome the Cascajo contains the small pecten Aequipecten circularis eldridgei. On the basis of the occurrence of this fossil, which has not been found at other horizons in the outcrop section, it is suggested that the Cascajo is equivalent to sand and gravel that unconformably overlie Miocene shale near McKittrick, [52] on the west border of the San Joaquin Valley 50 miles southeast of the Kettleman Hills, the type locality of A. circularis eldridgei. If this correlation is correct, the widespread deposition of gravel in the Kettleman Hills at the horizon of the Cascajo appears to be the result of deformation in the adjoining Coast Ranges. Should this small pecten be found at other horizons the suggested correlation would be less certain. Even in that event the base of the Cascajo might be considered an appropriate horizon for drawing the base of the San Joaquin formation in the Kettleman Hills. The Cascajo conglomerate disappears below the surface in the saddles between the three anticlines in the Kettleman Hills and the correlation of strata assigned to this member in the three anticlines is not entirely satisfactory. The correlation rests on the occurrence of sandstone and conglomerate in an appropriate part of the section and on the occurrence of fossils at scattered localities. The fossils in Middle and North Domes do not include, however, A. circularis eldridgei but do include fragments of a larger Aeguipecten, probably related to A. circularis impostor of the Pecten zone. (...)
A. circularis eldridgei (Arnold) (pI. 24, figs. 10-13), found only in the Cascajo conglomerate of South Dome, is smaller than A. circularis impostor and has a thicker shell. The Cascajo specimens are smaller and less inflated than specimens from the type locality near McKittrick, where they occur in strata suggested in the present report as representing the equivalent of the Cascajo. This small pecten was heretofore recorded only at the type locality. (W. P. W., R. S.)»
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. 49, 91]
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Aequipecten circularis eldridgei (Arnold); W. P. Woodring, R. Steward & R. W. Richards, 1940, Geology of The Kettleman Hills oil field California, plate 24, figures 10-13.
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«Shell small, both valves very convex, thickened, sculptured with 19 to 20 low, squarish ribs.
Dimensions (from Arnold): Altitude, 20 mm.; longitude, 21 mm.; length of hinge, 15 mm.; diameter of the two valves, 15 mm. Type specimen: In the U. S. National Museum, No. 164,850. Type locality: In the hills south of Dabney water wells, McKittrick district, Kern County, "upper Miocene." Pliocene: Etchegoin formation of the southeastern end of the San Joaquin basin, at the type locality (Arnold), and between McKittrick and Midway (Pack).
The original reference of this species to the Miocene created an enigma, for the species from which it is most likely to have been derived, deserti and circularis, are not known so far north as California in the Miocene. Pack, however, has identified it in Etchegoin beds not far from the type locality; and it is probable that the type locality also is Etchegoin. P. eldridgei appears to be a stunted, brackish-water derivative of deserti, most like the typical form; and it is not at all surprising to find it in beds that are approximately equivalent in age to the beds in which the varieties of deserti are found. Even the typical variety of deserti, from the Imperial formation, may be of approximately equivalent age.»
GRANT IV, U. S. & H. R. GALE. 1931. Catalogue of the marine Pliocene and Pleistocene Mollusca of California and adjacent regions. Memoirs of the San Diego Society of Natural History, 1: 1-1036, pls. 1-32, text figs. 1-15. [p. 214, 215]
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