Leopecten stearnsii (Dall, 1878)
DALL, W. H. 1878. Fossil molluscs from later Tertieries of California. Proceedings of the United States National Museum, 1: 10-16. [p. 14]
1878 Pecten stearnsii Dall, 1878
Pecten (Pecten) Stearnsii Dall; W. H. Dall, 1898, Contributions to the Tertiary fauna of Florida. Silex Beds of Tampa and the Pliocene Beds of the Caloosahatchie River, Part IV, plate 26, figure 5.
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«Shell moderately large, thin, regular; elegantly radiately ribbed. Upper valve flattened or even a little concave, with about twenty four regularly rounded, vaulted, even ribs, separated by slightly wider channeled interspaces; the whole surface covered with fine, sharp, concentric, regular lamellae, a little looped backward over the top of the ribs, but showing no appearance of reticulation anywhere; ears small, nearly symmetrical, covered with more elevated, crowded, concentric lamellae, especially near the margins; hinge-margin straight, or even a little concave toward the umbo; peripheral margins of the valves strongly and regularly crenulated and interlocking; interior regularly deeply grooved, to correspond with the external ribs; lower valve slightly convex, with about twenty-six regular even ribs, separated by channelled interspaces somewhat narrower than the ribs; the top surface of each rib is flattened with a broad, shallow groove in the middle, with one or two faint riblets on each side of the groove; the whole surface is covered with concentric lamellae, like those of the upper valve, but less sharp, and about twice as crowded. Ears subequal, arched, covered with crowded, elevated lamellae; byssal notch very small. Height of shell, 90 mm; breadth, 100 mm; breadth of hinge-line, 34 mm.; thickness, 15 mm.
This very elegant species, while also showing some general resemblance to P. caurinus Gld., forms a passage toward the section Janira, and differs in many details from any described west-coast species, recent or fossil, so far as figures and descriptions serve to indicate.» WILLIAM HEALEY DALL, 1878
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«The species above Node 6 have one or more costae or grooves on the rib crests. Where one or two grooves are present, the plicae may assume a bicarinate or tricarinate appearance. Node 7 ties together the distinctive rib profiles on the right valves of L. diegensis and its probable fossil precursor (Hertlein and Grant, 1972), L. stearnsi (Dall, 1878), wherein the commarginally lamellate sides of the ribs are undercut beneath the overhanging rib crest. The extinct species L. stearnsi occurs in the middle to late Pliocene and possibly early Pleistocene of southern California (Hertlein and Grant, 1972, p. 179).»
WALLER, T. R. 2007. The evolutionary and geographic origins on the endemic Pectinidae (Mollusca: Bivalvia) of the Galápagos Islands. Journal of Paleontology, 81 (5): 929–950, figs. 1-9. [p. 938]
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Phylogeny of Leopecten; T. R. Waller, 2007, The evolutionary and geographic origins on the endemic Pectinidae of the Galápagos Islands, figure 5.
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«Pecten stearnsii occurs in the Lomita marl (pl. 30, figs. 9, 10) and in the Timms Point silt (pl. 32, figs. 14, 15) and is probably represented in the San Pedro sand by small left valves from localities 58 and 64. Most of the valves from the Lomita marl and Timms Point silt are broken. This species was based on material from upper Pliocene strata in the San Diego formation at Pacific Beach, near San Diego. It is closely related to P. diegensis from moderate depths (14 to 60 fathoms) off the coast of southern California. The fossils reach a slightly larger size than Recent shells and have a few more ribs. On the interior of right (inflated) valves of P. diegensis the projections corresponding to the exterior interspaces are bordered near the margin of the valve by a narrow flange, as on the interior of left (flat) valves. Left valves of P. stearnsii have the interior flange, but on right valves the flange is absent or is weakly developed only near the anterior and posterior ends of the valve. Whether the Recent form is to be assigned specific or varietal rank is a matter of individual preference. If it is assigned varietal rank, it is to be cited as P. stearnsii diegensis, as was done by Grant and Gale, for stearnsii has priority. P. stearnsii survived from the Pliocene into the Pleistocene and then appears to have become extinct. These two forms are more similar to Pecten proper than any other California Pleistocene and Recent species. The right valve, however, is not so inflated as in Pecten proper, the ribs are more angular, and secondary ribs are absent on the main part of the shell and on the ears.»
WOODRING, W. P., M. N. BARMLETTE & W. S. KEW. 1946. Geology and Paleontology of Palos Verdes Hills, California. United States Geological Survey Professional Paper, 207: 1-145, pls. 28-37. [p. 80]
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Pecten stearnsii Dall; W. P. Woodring, M. N. Barmlette & W. S. Kew, 1946, Geology and Paleontology of Palos Verdes Hills, California, plate 30, figures 9, 10; plate 32, figures 14, 15.
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«Description.— Shell of medium size, subcircular, inequivalve, concavo-convex, thin; right valve slightly convex, with about 26 regular, even, square ribs, separated by channeled interspaces somewhat narrower than the ribs; the top surface of each rib is flattened with a broad, shallow groove in the middle, with one or two faint riblets on each side of the groove; whole surface covered with concentric lamellae which are much finer and about twice as crowded as those of the left valve; left valve flattened or concave, with about 24 regularly rounded, vaulted, even ribs, separated by slightly wider channeled interspaces; the whole surface covered with fine, sharp, concentric, regular lamelloo, a little looped backward over the tops of the ridge; ears of this valve concave, with obsolete radiating ridges, and fine, concentric lamellae; ears of right valve subequal, arched, covered with crowded, elevated lamellae; byssal notch very small.
Dimensions.— Alt. 62 mill.; long. 71 mm.; diameter 14 mm.; hinge 25 mm. According to Doctor Dall this is the precursor of P. diegensis, from which it differs by having 5 or 6 more ribs, which in the adult have a conspicuous medial sulcus. P. stearnsii, so far as known, is confined to the Pliocene. It is quite abundant at Pacific Beach, near San Diego, where it is associated with P. healeyi, P. hemphilli, Opalia varicostata, O. anomala, Scala stearnsii, Pecten parmeleei, and other unique forms. In a well at San Juan Capistrano it was found by Watts associated with Turritella cooperi, Venericardia ventricosa, Arca trilineata, Nassa mendica, etc. Two left valves have been found in the Pliocene at Deadman Island, near San Pedro. RANGE.
Pliocene. Temescal Canyon, Santa Monica Mountains, Los Angeles County (Watts, Rivers); San Pedro (Arnold); San Juan Capistrano, Orange County (Watts); Pacific Beach, near San Diego (Hemphill, Stearns, Dall, A6rnold); Third street tunnel, Los Angeles (Hamlin).»
ARNOLD, R. 1906. The Tertiary and Quaternary pectens of California. United States Geological Survey Professional Paper, 47: 1-264, pls. 1-53. [p. 100]
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Pecten (Pecten) stearnsii Dall; R. Arnold, 1906, The Tertiary and Quaternary pectens of California, plate 32, figures 1, 1a.
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