Mixtipecten amuriensis (H. Woods, 1917)
WOODS, H. 1917. The Cretaceous Faunas of the North-eastern Part of the South Island of New Zealand. New Zealand Geological Survey, Paleontological Bulletin, 4: 1-41, pls. 1-20. [p. 26, pl. 12, figs. 2-9]
1917 Pecten (Aequipecten) amuriensis H. Woods, 1917
H. Woods, 1917, plate 12.
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«Description.— Right valve ovate, slightly convex, somewhat inequilateral; height and length equal or nearly equal; outline rounded, with the umbonal region pointed. Antero-dorsal margin slightly concave or nearly straight; postero-dorsal margin slightly convex. Ears large; the anterior elongate triangular, with a few radial ribs; byssal sinus deep. Posterior ear obtusely triangular, with radial ribs crossed by regularly spaced concentric linear libs. Shell apparently nearly smooth, but with faint radial ribs which are stronger near the posterior ear than elsewhere.
Left valve ovate, nearly equilateral, moderately convex. Ears large, triangular, with radiating ribs. Ornamentation consists of mimerous narrow strong radial ribs, separated by broad flat or slightly concave interspaces, which are crossed at intervals by fine linear concentric ribs. Remarks.— Although the two valves described above have not been found united in any case, it seems probable that they belong to the same species, since they occur abundantly in the same beds, and in some cases are found close together on the same block of rock. The surface of the right is not perfectly preserved, so that the exact character of the ornamentation cannot be determined; but on one specimen linear and concentric ribs, like those on the left valve, are seen. Associated with the specimens just described are several left valves (Plate XII, figs. 10, 11) having the same form, but usually with more numerous radial ribs, which are sometimes alternately large and small; and the fine concentric ribs are not generally visible, but in one specimen they are seen near the umbo. It seems probable that this is not more than a variety of P. amuriensis; some of the apparent differences may be due to imperfect preservation. Affinities.— The form of the right valve is similar to that of P. subaratus Nilsson,* from the Senonian of Sweden, but the radial ornamentation appears to be much less well developed, and on the left valve of that species the radial ribs are more numerous, and concentric ribs appear to be absent. The ornamentation of the left valve is somewhat similar to that of P. tesselatus Hennig,† from the Senonian of Sweden. Distribution.— Amuri Group (calcareous conglomerate), east and West wings of Amuri Bluff (5, 6, 13) ; perhaps also black grit, east wing of Amuri Bluff (8).» * Hennig, Revis. Lamellibr. Nilsson's " Petrific. Suecana " (1897), p. 46, pl. iii, figs. 16, 17.
† Bihang. Svenska Vet. Akad. Handl., vol. xxiv (1899), p. 10, pl. i, figs. 5, 6. HENRY WOODS, 1917
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«12. Genus MIXTIPECTEN nov.
Type: Pecten (Aequipecten) amuriensis Woods. Shell small, right valve almost flat, left well inflated; ears large, subequal, not ascending, joining disc without channel; byssal notch very deep. Sculpture: right valve almost smooth, with a few weak radials at extremities; left valve with many narrow but strong primary radials with wide flat interspaces which are sometimes traversed by a secondary radial, and which have somewhat irregular, spaced, concentric ridges.»
MARWICK, J. 1928. The Tertiary Mollusca of the Chatham Islands including a generic revision of the New Zealand Pectinidae. Transactions and Proceedings of the New Zealand Institute, 58 (4): 432-506, figs. 1-148. [p. 456]
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