Chlamys opuntia (Dall, 1898)
DALL, W. H. 1898. Contributions to the Tertiary fauna
of Florida. Silex Beds of Tampa and the Pliocene Beds of the Caloosahatchie
River. Part IV. I. Prionodesmacea: Nucula to Julia. 2. Teleodesmacea: Teredo to
Ervilia. Transactions of the Wagner Free Institute of Science of Philadelphia,
3 (4): i-viii, 571-947, pls. 23-35. [p. 707, pl. 29, fig. 6]
1898 Pecten (Chlamys) opuntia Dall, 1898
W. H. Dall, 1898, plate 29.
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«Pliocene of San Diego, California; Hemphill and Hamlin.
Allied to P. hericeus var. navarchus Dall, from which it differs by its smaller and not fasciculated radial ribs, more elongated anterior ear, more densely radially costate posterior ear, small size when adult, and by a tendency to be suddenly contracted at the basal margin on the completion of growth, somewhat as in P. pesfelis. Alt. 35, lat. 32.5 mm.» WILLIAM HEALEY DALL, 1898
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«Comments.--The fine, even ribbing on the shell of C. opuntia is distinctive. The holotype is a right valve complete except for a small portion of missing shell at the anterior dorsal edge of the anterior ear. The ribs on the disk have strong, slightly spinose lamellae and imbricated microsculpture. The anterior auricle has 7 lamellose riblets and a moderately wide byssal sinus; the posterior ear has 10 or more fine, lamellose riblets. The shell is equilateral and of about equal length and height.
Geographic rarrge.— Middle California to Baja California Sur. Geologic range.— Miocene to Pleistocene. Occurrence in the Californias.— Miocene and Pliocene: Purisima Formation (Arnold, 1906); Pliocene: Almejas (Minch and others, 1976), Lomita Marl Member, San Pedro (Woodring. 1946), Niguel (J. G. Vedder, written commun., 1978), and San Diego (Arnold, 1906; Hertlein and Grant, 1972) Formations, unnamed Pliocene strata on San Clemente Island (Vedder and Moore, 1976; Susuki and Stadum, 1978); Pliocene and Pleistocene: Fernando (Arnold, 1907b; Moody, 1916: J. D. Mount, written commun., 1971), Merced (Arnold, 1906), Pico (Winterer and Durham, 1962) and Saugus (?) (Waterfall, 1929) Formations.» 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. B26]
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Chlamys opuntia (Dall); E. J. Moore, 1984, Tertiary Marine Pelecypods of California: Propeamussidae and Pectinidae, plate 6, figure 2.
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«Remarks. — Several specimens, mostly single valves, typical of this species, are represented in collections from the San Diego Formation which we studied. A left valve from Loc. 107 (LAM), is 38.4 mm long and 43.6 mm high. Some specimens are more rounded than others. A left valve illustrated by Grant and Gale is 67 mm long and 69 mm high. The fine, uniform, non-fasciculated radial ribs are quite different from any other west American Pliocene species.
Some authors have considered this species to be a member of the Chlamys islandica group. It somewhat resembles some fine-ribbed variants of that group but the San Diego fossil is easily separable by its finer, even ribbing, slightly smaller umbonal angle, generally smaller size and tendency to constriction toward the ventral margin of adult forms. These features serve to separate it from forms of C. rubida and its close relatives. The ribbing and the umbonal angle of C. opuntia are similar to those features on C. hertleini Loel and Corey (345), which was described from beds of early Miocene age. One decided difference in the two species is in the outline of the posterior ears. The posterior ears on C. opuntia slope obliquely downward from the hinge line whereas those on C. hertleini are squarely truncated. Chlamys tamurae Masuda and Sawada (346), compared by its authors with C. opuntia, differs in that the surface of the left valve (and to a less degree the right valve) is folded forming low, broad corrugations. Furthermore, the illustration (see their fig. 12a) shows that the major ribs are divided toward the ventral margin of the right valve, a feature only occasionally present on C. opuntia. In addition to the San Diego Formation in which the type specimen was found, Chlamys opuntia also has been recorded from beds of late Pliocene age north of Simi Valley, in upper Pico beds in Ventura Co., in Temescal Canyon near Santa Monica, in beds encountered in the Third Street Tunnel and elsewhere in Los Angeles, and in the Tijuana-Rosarito Beach area in northwestern Lower California. It also has been recorded from strata at Santa Barbara and in the Lomita Formation near San Pedro. These latter beds have been considered to be of late Pliocene age by some writers and early Pleistocene age by others. Grant (347) considered the Lomita Formation to be of late Pliocene age and he suggested that the sediment was deposited perhaps at depths of 30 to 90 meters (100 to 300 feet) and that the temperature was about 15° to 17° C. (60° to 62° F.)» HERTLEIN, L. G. & U. S. GRANT IV. 1972. The Geology and Paleontology of the marine Pliocene of San Diego, California (Paleontology: Pelecypoda). Memoirs of the San Diego Society of Natural History, Memoir 2, Part 2b. pp. 143-409, pls. 27-57. [p. 193]
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Pecten (Chlamys) opuntia Dall; L. G. Hertlein & U. S. Grant IV, 1972, The Geology and Paleontology of the marine Pliocene of San Diego, plate 30, figures 5, 6.
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«Description.— Shell averaging about 35 millimeters in altitude, slightly shorter than high, subequivalve, equilateral (except for ears), both valves nearly flat until altitude of about 20 to 25 millimeters is reached, when they grow more convex; contracted at basal margin when adult; sides only slightly concave above. Right valve with 40 to 60 subequal, narrow, imbricated, more or less dichotomous ribs, which are separated by channeled interspaces about equal in width to the ribs; hinge line about two-fifths as long as disk; anterior ear much produced, sculptured by about six prominent, sharply imbricated radials, and imbricating incremental lines; byssal notch quite prominent; posterior ear nearly obsolete, radially and concentrically sculptured; whole surface of disk and ears sometimes microscopically checkered or tessellated. Left valve similar to right.
Dimensions.— Alt. 43 mm.; long. 40 mm.; hinge line 16 mm.; diameter 12 mm.; umbonal angle 78°. This species is allied to P. hastatus var. navarchus, from which it differs by its smaller and not fasciculated radial ribs, more elongated anterior ear, more densely radially costate posterior ear, small size when adult, and by a tendency to be suddenly contracted at the basal margin on the completion of growth. P. opuntia is distinguishable from other members of this group by its large number of nearly equal thread-like ribs and small umbonal angle.» ARNOLD, R. 1906. The Tertiary and Quaternary pectens of California. United States Geological Survey Professional Paper, 47: 1-264, pls. 1-53. [p. 118]
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Pecten (Chlamys) opuntia Dall; R. Arnold, 1906, The Tertiary and Quaternary pectens of California, plate 41, figure 2.
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