Euvola carrizoensis (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. 59, pl. 4, figs. 1, 1a, 1b, 2, 3, 3a]
1906 Pecten (Pecten) carrizoensis Arnold, 1906
R. Arnold, 1906, plate 4.
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«1898. Pecten sp. indet., Dall, Trans. Wagner Free Inst. Sci., vol. 3, pt. 4, p. 706, line 13.
Description.— Shell averaging about 42 millimeters in altitude, longer than high, inequivalve, plano-convex, equilateral, and with smooth margins: base evenly rounded; sides concave above. Right valve convex, ornamented by about 18 or 19 prominent square, flat-topped, medially sulcated ribs; interspaces channeled and slightly narrower than ribs; whole surface sculptured by fine, regular, concentric incremental lines: hinge line less than one-half length ot disk; ears subequal, convex, and ornamented by concentric lines. Left valve flat or slightly concave, ornamented by about 17 prominent, equal, equidistant, narrow, convex-topped ribs, which are separated by flat-bottomed interspaces much wider than the ribs; surface sculptured by numerous fine, regular, wavy, concentric lines; ears concave and sculptured by concentric lines. Dimensions.— Alt. 36 mm.; long. 40 mm.; hinge line 15 mm.; diameter 8 mm.; umbonal angle (left valve) 105°. This species belongs to the group of which P. diegensis is the living member. P. carrizoensis, P. stearnsii, and P. diegensis taken in chronologic order as above may represent a genetic series. The three species are alike in most respects: They are all plano-convex, have squarish, more or less sulcated or longitudinally ridged ribs, convex ears on the right valve, and rather narrow, rounded ribs and concave ears on the left. P. carrizoensis differs from the other two members of the group in the smaller number and less prominence of its ribs and in its relatively much shallower and narrower interspaces. The Pecten mentioned by Dall on page 706 of the Transactions of the Wagner Free Institute as coming from the Miocene deposits near San Diego was compared with the type of P. carrizoensis and found to be of this species. The type locality of P. carrizoensis is at the head of Garnet Canyon, about 12 miles north of the Mexican boundary, in the Carrizo Creek district, San Diego County. The beds in this district contain a fauna diflerent from any of the other known California formations, but from other considerations it is deemed almost certain that the deposits are of Miocene age. Just what horizon the beds represent has not yet been determined. (See list of Carrizo Creek district fossils in Part I, p. 22, and list of Santa Rosalia, Lower California, fossils under P. cerrosensis var. mendenhalli, p. 85.) The type of P. carrizoensis, which was collected by Dr. Stephen Bowers, is now in the collection of Delos Arnold. RANGE.
Miocene. Head of Garnet Canyon, 12 miles north of Mexican boundary, San Diego County (Bowers); Santa Rosalia, Lower California, west of and across the Gulf from Guaymas, Mexico (G. P. Merrill; E. Palmer).»
RALPH ARNOLD, 1906
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«REMARKS: A right valve (incomplete) has a present altitude of 41.2 mm, a left valve is 51.1 mm high. Pecten (Pecten) lecontei Arnold from Cedros Island is very similar except that the left valve is usually entirely concave instead of first concave and then convex as in P. carrizoensis.»
DURHAM, J. W. 1950. Megascopic paleontology and marine stratigraphy. In 1940 E. W. Scripps Cruise to the Gulf of California, Part II. Geological Society of America Memoir 43: 1-216, pls. 1-48. [p. 61]
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Pecten (Pecten) carrizoensis Arnold; J. W. Durham, 1950, Megascopic paleontology and marine stratigraphy, plate 8, figures 1, 3.
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