Lyropecten miguelensis (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. 79, pl. 22, figs. 1, 1a, 1b; pl. 23, fig. 1]
1906 Pecten (Lyropecten) miguelensis Arnold, 1906
R. Arnold, 1906, plates 22, 23.
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«Description.— Shell averaging about 110 millimeters in altitude, about as long as high, inequivalve, subequilateral, rather thin, and with margins more or less serrate; base rounded; sides slightly concave above, the posterior being slightly longer than the anterior. Right valve more convex than the left, with 17 or 18 prominent rounded ribs, each sculptured by several (10 or 11 at extremity of ribs in type) distinct radiating raised riblets and numerous sharp, minutely wavy, incremental lines; interspaces narrower than ribs, and containing by a prominent radial auxiliary rib, which is ornamented by the incremental sculpture, and toward the periphery of the disk, by two or more radiating riblets as in the large ribs; hinge line somewhat longer than one-half the length of the disk; anterior ear arcuate in front, with small byssal notch, and sculptured by 5 or 6 prominent, rounded, radiating ridges and numerous sharp, concentric lines; posterior ear with 10 or 11 radiating riblets and fine incremental sculpture. Left valve less ventricose than the right, but otherwise similar to it, except that the ribs are slightly narrower and the interspaces relatively broader; ears similar to those of the right valve except that the anterior one lacks the byssal notch.
Dimensions.— Alt. 107 mm.; long. 110 mm.; hinge line 60 mm.; diameter 50 mm. This species is distinguishable from P. estrellanus and others of the same group by its larger size, inequality of valves (which are more or less inequilateral), and radially striate surface from umbo to periphery. It sometimes shows the constrictions common to P. estrellanus. P. miguelensis may be the P. catilliformis of Conrad (Pac. R. R. Rept., Vol. V, Pt. II, p. 83, PI. IX, fig. 83, 1857), but his description is so brief and his figure so poor tliat it is impossible to make anything definite out of it. P. miguelensis is confined to the Miocene (probably lower horizon). The type is a slightly crushed specimen from San Miguel Island. It is the specimen figured, and is now in the collection of the University of California. RANGE
Miocene. San Miguel Island (Univ. of Cal.); Santa Rosa Island (No. 12333, Cal. St. Mill. Bureau); Santa Inez Valley, near Santa Barbara (J. H. Wilson); Santa Inez Mountains, near Santa Barbara, Santa Barbara County (Pac. R. R. Expedition).»
RALPH ARNOLD, 1906
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«Pectens of the species P. (Lyropecten) miguelensis have a widespread distribution in the Vaqueros horizon, Lower Miocene, and are quite abundant in some provinces. The collections at University of California present an interesting evolutionary series within the species. The stratigraphic occurrences are directly related to the evolutionary succession in that the Pectens of the form of P. miguelensis which are found lowest in the Lower Miocene strata present characters which are presumably most primitive; while those forms found in the uppermost zones show highest development of these characters. So far as is known the succession holds true wherever the species is found. It is therefore worthy of consideration as a possible aid in exact correlation of zones and provinces.
The species, as represented in the collection, is a perfectly gradational series from a thin-shelled, low ribbed form with intercalary ribs absent (or faintly developed) to a rugose, heavy-shelled, strongly ribbed form with intercalary ribs of equal height, which is also more inflate or convex. The type specimen, from San Miguel Island, falls about intermediate in the range of these characters, as does the specimen figured by Hertlein from Santa Rosa Island from the "Temblor" horizon (Hertlein), no associated species being named in either case. The faunal association in each case is certainly Vaqueros, as recent collections reveal. By reason of the wide geographic range and stratigraphic importance of the more primitive, earlier form it is thought deserving of varietal designation. The form coming at the other, or upper, end of the series is much less frequent and distinct from the type form and is figured as a variant. This variant, with the intercalary ribs developed to a height equal to the large ribs and the finer radial riblets being obsolete or very faint, is found on the southwest end of Santa Cruz Island, transitional or uppermost Vaqueros horizon; and is abundant in the uppermost zone of the Vaqueros horizon (or transitional to Temblor) in the La Panza region, eastern San Luis Obispo County and in the San Joaquin Hills, Orange County. Range (geographic and stratigraphic).— Pecten (Lyropecten) miguelensis Arnold (type form); San Joaquin Hills, Orange County (abundant in upper part of Vaqueros horizon); southwest end Santa Cruz Island (superform—probably Temblor transitional or upper Vaqueros from associated species which include Tellina ocoyana Conrad), Santa Rosa Island (Arnold, Hertlein), upper part Vaqueros San Miguel Island (Arnold, Hertlein); west Santa Monica Mountains, near top Vaqueros horizon; west Santa Ynez Mountains, Santa Barbara County; upper zone Vaqueros, southern end Santa Lucia Mountains; Adelaida quadrangle, and north San Luis quadrangle; La Panza Mountains, eastern San Luis Oispo County; in upper Vaqueros and Lower Temblor zones (or transitional); between the Nacimiento and San Antonio rivers, Bryson and Bradley quadrangles, and in the type Vaqueros region, Junipero Serra quadrangle. Present in northern Santa Cruz Mountains, head of Corte Madera Creek.» LOEL, W. & W. H. COREY. 1932. The Vaqueros formation, lower Miocene of California I. Paleontology. University of California Publications, Bulletin of the Department of Geological Sciences, 22 (3): 31-410, pls. 4-65. [p. 199, 200]
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Pecten (Lyropecten) miguelensis Arnold; W. Loel & W. H. Corey, 1932, The Vaqueros formation, lower Miocene of California I. Paleontology, plate 29, figures 2, 3; plate 30, figure 2.
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«Plesiotype (No. 4143, C. A. S. type collection), from Loc. 1156 (C. A. S.) about .4 kilometer southeast of spring (near Loc. 1154 C. A. S), east of dike, near top of hill, Santa Rosa Island, California; L. G. Hertlein and E. L. Rixford collectors; Temblor, Lower Miocene.
This fine species occurs abundantly at various localities on Santa Rosa Island and is also present on San Miguel Island. It differs from P. estrellanus Conrad in the details which Arnold [19] stated so well: "This species is distinguishable from P. estrellanus and others of the same group by its larger size, inequality of valves (which are more or less inequilateral), and radially striate surface from umbo to periphery. It sometimes shows the constrictions common to P. estrellanus." The type of P. miguelensis Arnold came from San Miguel Island.» [19] U. S. Geol. Surv. Prof. Paper 47, 1906, p. 79, pl. 22, figs. 1, 1a, 1b; pl. 33, fig. 1.
HERTLEIN, L. G. 1928. Preliminary report on the paleontology of the Channel Islands, California. Journal of Paleontology, 2(2): 142-157, pls. 22-25. [p. 151]
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Pecten (Lyropecten) miguelensis Arnold; L. G. Hertlein, 1928, Preliminary report on the paleontology of the Channel Islands, California, plate 24, figure 1.
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