Neithea kochiensis Hayami in Hayami & Kawasawa, 1967
HAYAMI, I. & K. KAWASAWA. 1967. Some Lower Cretaceous bivalves from The Shimantogawa group of south Shikoku. Transactions and Proceedings of the Palaeontological Society of Japan [N. S.], 66: 73-82, pl. 9. [p. 76, pl. 9, fig. 1]
1967 Neithea (Neithella?) kochiensis Hayami in Hayami & Kawasawa, 1967
I. Hayami & K. Kawasawa, 1967, plate 9.
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«Material.— The holotype (GK.H6808) is an incomplete internal mould of right valve from the Dogarano formation of Kakureyashiki (Loc. 2).
Diagnosis.— Large-sized species of Neithea characterized by the right valve with six persistent, round topped, comparatively narrow primary ribs, wide, flattened and finely striated interspaces, and obtuse and subequal auricles. Description.— Right valve large, triangular, subequilateral, higher than long, moderately inflated (holotype, GK.H6808, right in. mould, 72.5 mm. long, 78.5 mm. high, 20.0 mm. thick); umbo submesial, pointed; antero- and postero-dorsal margins of flank a little concave; ventral margin digitated in accordance to the primary ribs; apical angle approximately 80 degrees; primary ribs six in number, persistent, highly elevated, round-topped, comparatively narrow; interspaces wide, flattened, marked with numerous fine radial striae, although secondary riblets are absent at all; both lateral areas narrow, provided with still finer striae; auricles comparatively small, apparently subequal, obtusely truncated; hinge-line unusually short. Left valve unknown. Observations and comparisons.— The present species is now represented only by an incomplete right internal mould. The test is completely eroded away, and the postero-ventral peripheral area broken off. The auricles, the outline of which appears to be nearly completely shown, are obtusely truncated and comparatively small for the genus. Consequently the hinge-line is unusually short for Neithea. In view of the only weakly striated interspaces it must be related to the group of Neithea wrightii for which I proposed subgenus Neithella (HAYAMl, 1965a). All the known species of Neithella are, however, by far smaller than the present species. Moreover, many species of Neithella have comparatively large and anteriorly projected byssal auricle and occasionally effaced or somewhat weakened 1st and 6th primary ribs. Because the present species does not show such a tendency, its subgeneric reference is by no means certain. Some specimens of "Neithea atava" from the Lower Cretaceous of France (D'ORBIGNY, 1847, pl. 442, figs. 1-3; COSSMANN, 1907, pl. 5, fig. 19), Mexico (ALENCASTER, 1956, pl. 2, figs. 5-7) and Trinidad (COX, 1954, pl. 64, figs. 1, 4) have comparable dimensions with the present specimen. As pointed out previously (HAYAMI, 1965a. p. 308), they may belong to a distinct species from the specimens of Neithea atava (RÖMER) from the Lower Greensand of England (WOODS, 1902), which certainly belong to Neithea (Neithella). A species represented by such large specimens of "N. atava", though there have been different understandings about its diagnosis, possesses three-five distinct secondary riblets on each interspace of primaries, being more closely related to the group of Neithea gibbosa than to Neithella. In the large dimensions and flattened interspaces the present new species may recall Neithea (Neithea) kanmerai HAYAMI, 1965, from the Lower Miyakoan (= Aptian) of south-west Japan and some other species belonging to the group of Neithea gibbosa. However, the secondary riblets on each interspace, which are never effaced and typically three in number in the group of N. gibbosa, are absent at all in the present species. It appears somewhat similar to Neithea sexangularis (D'ORBIGNY, 18477) in the mode of surface striae, but differs evidently from the original figures of that species in the more flattened interspaces and the more sharply pointed umbo. Occurrence.— Fine sandstone of the Doganaro formation of Kakureyashiki (Loc. 2), north of Doganaro, Susaki City, TAKEMOTO coll.» ITARU HAYAMI & KEIZO KAWASAWA, 1967
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«N. kochiensis was proposed by Hayami and Kawasawa (1967) based on a poorly preserved inner mould of a specimen that possess no prominent secondary ribs. The feature of secondary ribs of N. kochiensis is possibly a misinterpretation due to its poor preservation. Well-preserved specimens of alleged N. kochiensis were reported by Tanaka et al. (1996), but the rib morphology and distribution pattern of these specimens resembles that of N. atava (Roemer, 1839), a species which displays worldwide distribution inclusive of the Japanese Islands.»
IBA, Y. & S. SANO. 2008. Paleobiogeography of the pectinid bivalve Neithea, and its pattern of step-wise demise in the Albian Northwest Pacific. Palaeogeography, Palaeoclimatology, Palaeoecology, 267: 138-146, figs. 1-6. [p. 139]
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