Zygochlamys seymouri (Marwick, 1928)
MARWICK, J. 1928. The Tertiary Mollusca of the Chatham Islands including a generic revision of the New Zealand Pectinidae. Transactions of the New Zealand Institute, 58 (4): 432-506. [p. 457, fig. 23]
1928 Chlamys seymouri Marwick, 1928
J. Marwick, 1928, figures 22-27.
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«Shell large, thin, compressed, subcircular, slightly oblique. Apical angle acute, widening with age. Ears very unequal, anterior sinus deep. Sculpture: right valve with about 18 narrow primary ribs with very wide concave interstices with 8 and 10 or even more, scaly riblets of which two are often stronger than the others, these two appear on the sides of the primaries about 10 mm. from apex and the others follow later, their relative strength corresponding with their time of appearance; anterior ear with 4 scaly radials; posterior with 8. Left valve with about 20 narrow primaries, the wide concave interstices with two secondaries sometimes almost as strong as the primaries, each secondary interspace with 3 to 7 scaly riblets of irregular strength; anterior ear with about 15 spaced scaly radials of which 6 are stronger than the others, posterior with about 10.
Height 77 mm., length 73 mm., thickness (1 valve): 10 mm. Localities: 1176, Momoe-a-toa; (?) Whenuataru Peninsula. Remarks: Sometimes the primaries are smooth and much stronger than the interstitial riblets, giving the shell a resemblance to C. delicatula which, however, has more ribs. At other times the strength of the ribbing is very regular, making the shell look like a large C. radiata. Small specimens are often indistinguishable from C. radiata except by the vertical outer edge of the left anterior ear. C. seymouri is a development of C. chathamensis in which there are many additional secondary riblets, all the radials having strong scales.» JOHN MARWICK, 1928
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«Stratigraphical age and distribution. Earliest Pliocene (early Opoitian; Fig. 25). P. seymouri is the oldest known species of Psychrochlamys and is known only from the Momoe-a-Toa Tirff at Cape Young, N coast of Chatham Island, New Zealand (Fig. 22). It occurs together with very abundant Sectipecten allani Marwick, 1928, uncommon Talochlamys aff . gemmulata (Reeve, 1853), common Mesopeplum (Mesopeplum) dendyi (Hutton, 1902), rare M. (Borehamia) aff. crawfordi (Hutton, 1873), and very rare M. (Borehamia) toaense (Marwick, 1928) (CampbelI et al.,1993).
Remarks. Psichrochlamys seymouri is similar in size to Late Pliocene P. delicatula delicatula and Pleistocene P. delicatula instar, with an only slightly narrower umbonal angle, and a comparable auricular asymmetry but it has a much deeper byssal notch (Fig. 34) and very much finer radial sculpture than seen in these younger taxa.» JONKERS, H. A. 2003. Late Cenozoic-Recent Pectinidae (Mollusca:Bivalvia) of the Southern Ocean and neighbouring regions. Monographs of Marine Mollusca, 5: i-viii + 1-125 pp, 17 pls. Backhuys Publishers, Leiden. [p. 54]
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Psychrochlamys seymouri (Marwick); H. A. Jonkers, 2003, Late Cenozoic-Recent Pectinidae (Mollusca: Bivalvia) of the Southern Ocean and neighbouring regions, plate 10, figures a, b.
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