Lituyapecten yakatagensis (Clark, 1932)
CLARK, B. L. 1932. Fauna of the Poul and Yakataga formations (upper Oligocene) of southern Alaska. Geological Society of America Bulletin, 43: 797-846, pls. 14-21, 1 fig. [p. 807, pl. 15, fig. 8; pl. 16, fig. 1]
1932 Pecten (Patinopecten) yakatagensis (Clark, 1932)
B. L. Clark, 1932, plates 15, 16.
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«Type.— Number 30381, University of California Museum of Paleontology invertebrate Collection, University of California Locality 3859.
Paratype.— Number 30382, University of California Museum of PaIeontology Invertebrate Collection, University of California Locality 3859. Shell fairly large, left valve nearly flat, right valve only slightty inflated, apical angle about 125 degrees. Left valve sculptured by about 28 narrow, flat-topped, T-shaped ribs; tops of wider ribs grooved; surface also covered by fairly prominent concentric laminae which cross the narrow ungrooved ribs without any break, while on the grooved ribs the laminae are developed only on each side of the groove, appearing as low spiny processes. Ears imperfect on the specimens at hand; apparently they were large and broad and covered by fine radiating ribs broader and not so high as on left valve; sides of the ribs slope down rather steeply, but not distinctly T-shaped as in left valve; the tops of these ribs, especially below the center of the valve, are broadly concave or grooved; interspaces flat-bottomed. Surface of the shell smooth except for incremental lines; posterior ear on specimen at hand entirely gone; anterior ear somewhat imperfectly preserved but shows that it had a well-developed byssal notch and that the surface was sculptured by at least three fairly prominent radial ribs. Dimensions of type: a left valve broken laterally, height about 79 millimeters; length approximately 75 millimeters. Occurrence.— University of California Locality 3859. Pecten yakatagensis of all the species referable to the subgenus Patinopecten is unique. Most of the species in this group have the ribs on the left valve acutely rounded, rather than grooved or imbricately sculptured; the Alaskan species has squared, grooved, T-shaped ribs with imbricating lamellae. The right valve of the other species of Patinopecten, eg. Pecten coosensis Shumard, Pecten turneri Arnold, Pecten healeyi Arnold, Pecten caurinus Gould, etcetera, has the squared, usually T-shaped, grooved ribs. lt is very possible that Pecten yakatagensis should be placed in a new section.» BRUCE LAWRENCE CLARK, 1932
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«Remarks:— This species was originally described by CLARK (1932) from the Tertiary of the Yakataga District. Subsequently, MACNEIL (1961) re-examined this species and gave a detailed description of it. The characteristic features of the present species are its medium-sized, sub orbicular shell sculptured with 26 to 31 radial ribs which are sub rounded in juveniles but become flattened or bear a median groove in adults, and the well-defined dentic1es on both sides of left valve. Moreover, the present species is characterized by having two rows of frills or flanges on the radial ribs of the central parts of the left valve, but the both ribs of the anterior and posterior margins have only a single frill. The inters paces have rarely a scalelike interstitial rib let.
This species is rather similar to Patinopecten (L.) lituyaensis MACNEIL, 1961, but differs by having a large number of radial ribs. In addition, the radial ribs on the left valve of the latter sometimes have or bear a strong third beaded riblet on some of the middle ribs. Localities:— 7011-68, medium-grained sandstone, about 420 meters above the base of the Yakataga formation in the Duktoth Mountains, the lower part of the Yakataga formation; 81001, float specimens in the upper reaches of Poul Creek; 80503, fine-grained sandstone, Yakataga formation. Reg. No. TUE 8418.» KANNO, S. 1971. Tertiary molluscan fauna from the Yakataga District and adjacent areas of southern Alaska. Paleontological Society of Japan, Special Papers, 16: 1-154, pls. 1-18. [P. 53, 54]
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Patinopecten (Lituyapecten) yakatagensis (Clark), 1932; S. Kanno, 1971, Tertiary molluscan fauna from the Yakataga District and adjacent areas of southern Alaska, plate 3, figures 1, 2; plate 6, figure 3.
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