Duplipecten parki (Marwick, 1942)
MARWICK, J. 1942. Some Eocene Mollusca from New Zealand. Transactions of the Royal Society of New Zealand, 72: 268-279, pls. 23-25. [p. 270, pl. 23, figs. 7, 10, 13]
1942 Lentipecten parki Marwick, 1942
J. Marwick, 1942, plate 23.
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«Shell fairly large, almost equilateral and equivalve except for the ears. Dorsal margins slightly concave, apical angle increasing from about 110° to about 125°. Surface smooth, but having extremely fine, regular, concentric grooves, about 12 per mm. Ears subequal, relatively very long, those of the left valve with a remarkably straight dorsal margin and almost rectangular corners, those of the right valve with a strongly but irregularly serrate dorsal margin. Right anterior ear with a moderately deep byssal notch which, however, does not form a radial groove or ridge. Both ears of the right valve set on a plane oblique to that of the disc ahd separated from it by a step or ramp which gets rapidly broader distally. Internally, the hingemargin is narrow, and quite intersected by the resiliary pit.
Height, 55 mm.; length, 57 mm.; inflation (1 valve), 8 mm. Localities: Hampden Beach (type); G.S. 2572, Waihao Downs; G.S. 164, Greensands, Kakahu (Bortonian Stage); G.S. 2873, Ten Mile, Greymouth, near top of Island Sandstone (? Tahuian).
This shell is, of course, very like the widespread Miocene L. hochstetteri (Zitt.), and has been so identified (under the synonym P. huttoni Park) in most lists of Hampden mollusca. The two species are easily distinguished by their ears. In the left valve; the ears of hockstetteri (Plate 23, fig. 12) have a much shorter dorsal margin having, at its extremities, obtuse angles of about 120°. The long, straight dorsal margin of the ears of L. parki (Plate 23, fig. 13) forms with the anterior and posterior vertical margins an approximate right angle. In the ears of the right valve the dorsal margin is straighter and the distal angles are rounded and obtuse in hochstetteri (Plate 23, fig. 9), but they are sharp and subrectangular in parki (Plate 23, figs. 7, 10). Further, the bysal notch of parki is considerably deeper, but the shallow sinus of hochstetteri forms a low radial bulge.
If the ears are missing difficulty may be met in identifying the disc of parki as distinct from hockstetteri, but the very fine regular concentric grooves are better developed in parki. Another item for distinguishing parki is the well defined step or ramp on the right valve, separating the ear from the disc. The holotype of L. waikaoensis consists of a fairly complete, ribbed left valve and a smooth right valve with much damaged ears. These were collected by J. A. Thomson, together, and appeared to belong to one individual. If the relationship of the valves is as supposed, then parki must be closely related to waihaoensis, because their right valves are indistinguishable. No ribbed left valves have been found at Hampden, though smooth ones are not uncommon; but at Waihao Downs both smooth and ribbed left valves occur. Further, there are differences in the strength of the ribs. It may be that a gradation exists at Waihao between the smooth and the ribbed, but more material is required to throw light on this question. The absence of any ribbing on the Hampden shells justifies their systematic recognition.» JOHN MARWICK, 1942
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«4. Duplipecten Marwick, 1928; Maxwell (in Beu & Maxwell 1990: 101, pl. 5d; Maxwell 1992: 64-65, pl. 3d-f) demonstrated that the late Middle and Late Eocene species D. parki (Marwick, 1942), although included in Lentipecten by Marwick (1942), is not a particularly close homeomorph of Lentipecten. It has the opposite relative valve inflation to L. hochstetteri, the auricles are set off from the disc by deep, undercut grooves, quite unlike the very shallow, obscure grooves of other Lentipecten homeomorphs (including Victoripecten), the proximal part of the disc, in particular, is sculptured with fine but obvious, regular commarginal ridgelets, and the hinge has a very different appearance as the teeth are much less obvious than in Lentipecten and the interior of the dorsal margin is dominated by large, thick, valve-abutting surfaces. D. parki is apparently descended from the slightly earlier Bortonian D. waihoaensis (Suter), which has obvious, low, wide radial costae developing relatively late in ontogeny on the LV disc.»
BEU, A. G. & T. A. DARRAGH. 2001. Revision of southern Australian Cenozoic fossil Pectinidae (Mollusca: Bivalvia). Proceedings of the Royal Society of Victoria, 113: 1-205, figs. 1-67. [p. 122]
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