Lyropecten terminus (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. 77, plate 23, figs. 2, 2a]
1906 Pecten (Lyropecten) estrellanus var. terminus Arnold, 1906
R. Arnold, 1906, plate 23.
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«Description.— Shell averaging about 70 millimeters in altitude, somewhat longer than high, ventricose, subequivalve, equilateral; margins coarsely serrate. Right valve with about 15 prominent, squarish ribs, separated by narrower channeled interspaces, in each of which runs a prominent intercalary; surface of ribs and interspaces obsoletely radially striate; hinge line more than one-half length of disk; ears subequal, the anterior strongly radially ribbed, the posterior with finer sculpture: byssal notch deep and rather narrow. Left valve similar to right, except that the ribs are relatively narrower.
Dimensions.— Alt. 70 mm.; long. 75 mm.; hinge line 43 mm.; diameter 32 mm. This variety is distinguishable from the typical form by its fewer and broader ribs, relatively longer hinge line, and finer obsolete radial striation; and from var. catalinae by its fewer ribs and greater convexity. The type of P. var. terminus is from tihe upper Miocene or San Pablo horizon of Monterey County, and is now in the collection of the University of California. RANGE
Miocene (upper). Monterey County (University of California).»
RALPH ARNOLD, 1906
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«Description. — Valves equal, flat to moderately convex. Beaks project slightly, equally, beyond hinge line. Auricles unequal, costate, and lirate. Byssal notch deep. Hinge length about half shell length. Right-valve rectangular ribs 14-15, one riblet in juvenile interspaces, four or more costae in adults. Left-valve ribs 13-14 (a few 12), rectangular in profile, of equal prominence and spacing. Leftvalve interspaces wide, with four to five or more costae, as in L. crassicardo; L. terminus has no key or raised ribs, no nodes. Large specimens commonly measure 12-14 cm high; one individual from the Salinas Valley is 16 cm high, 17.6 cm long.
Variability. — Fine sculpture varies between juveniles and adults, right and left valves; rib counts vary by one, rarely two ribs. Juvenile right valves have one prominent riblet per interspace (as in L. estrellanus), adults have four or more radial striae. Rib widths and moderately convex valve profiles are consistent characters. Comparative notes. — Articulated specimens are rare; single, worn specimens are hard to distinguish from L. estrellanus except by their lower rib count and left-valve fine sculpture. Phylogenetic affinities. — Lyropecten terminus is morphologically closest to L. estrellanus and probably its direct descendant. Disarticulated valves of both species are found in beach deposits that may be reworked. Lyropecten terminus is relatively rare and restricted geographically geographically to the southern Salinas Valley and San Joaquin Valley near Coalinga. It may be an abnormally low-ribbed variant of L. estrellanus that lived later than L. estrellanus s.s. in progressively shallower basins in central California.» SMITH, J. T. 1991. Cenozoic Giant Pectinids from California and the Tertiary Caribbean Province: Lyropecten, "Macrochlamis", Vertipecten, and Nodipecten species. United States Geological Survey Professional Paper, 1391: v + 1-155, figs. 1-18, pls. 1-38. [p. 66]
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Lyropecten terminus (Arnold, 1906); J. T. Smith, 1991, Cenozoic Giant Pectinids from California and the Tertiary Caribbean Province, plate 22, figures 2, 3.
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