Camptonectes triadicus Nakazawa, 1952
NAKAZAWA, K. 1952. A study on the pelecypod-fauna of the Upper Triassic Nabae group in the northern part of Kyoto Prefecture, Japan. Part 1. Pectinids and limids. Memoirs of the College of Sience, University of Kyoto [Series B - Geology and Mineralogy], 20 (2): 95-106, pls. 7-10. [p. 96, pl. 7, figs. 1, 2]
1952 Camptonectes triadicus Nakazawa, 1952
K. Nakazawa, 1952, plate 7.
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«Description: – The holotype is repsesented by a left valve. Shell nearly equilateral, suborbicular, moderately convex. Ornament consists of closely-set, fine, slightly punctated or reticulate, often bifurcating striae, curving upwards especially at the posterior side, and crossed by weak concentric growth wrinkles at in intervals.
Anterior ear larger, obtusely triangular, with slightly convex anterior margin, covered by decussate ornament; posterior ear very small, obtusely triangular, ornamented by obliquely divergent striae from disk, without reticulate appearance. (Pl. VII, Fig 1b) Resilifer small, triangular. (Pl. VII, Fig 2) Height almost equal to length. Maximum thickness lying at about 15 mm below the hinge line. Apical angle large. Dimensions of Holotype :
Remarks and Comparison: – Aithough only one left valve could be obtained, judging from its orbicular outline, characteristic ornamentation, and aspect of auricles, this can be safely classified under genus Camptonectes. Bug judglfig from the shapes of several specimens of Minetrigonia hegiensis (Saeki) in the same block, this species laterally elongated by deformation, so that rhe height may exceed the length and the apicai angle smaller than the measurement. The upper margins of both ears do not form a straight level line, but this fact may be likewise caused by deformation.
Thls species resembles jurassic C. Iens (Sow.) (Sowerby, 1818, p. 3, pl. CCV, figs. 2, 3. Arkell, 1928. pp. 94-99, Pl. VII, fig. 1, Pl, IX, figs. 4-7), the type species of the genus, but differs from the latter in its finer and denser striae, weaker and less growth-lines, the decassated ornament of the anterior ear oblique to its upper and anterior margins, and more unequal auricles. The middle portion of the disk is almost smooth as that of C. giganteus Arkell (1928, p. 100, Pl. VII, figs. 2, 3), but in the former the ornament is not preserved, whereas it was originaliy absent in the latter. This is the first Triassic species of Camptonectes, so far as the writer knows. Occurrence: Middle part of N2 bed, Kongoin. (Loc. No. N-102) (Reg. No. JM 10001)» KEIJI NAKAZAWA, 1952
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«1952. Camptonectes triadicus Nakazawa, p. 96, pI. 7, figs. 1, 2.
Type.— Holotype (UK JMlOOOl) from Kongoin, Maizuru, Kyoto Pref. Age and distribution.— Carnian. Nabae group (N2 formation) in Maizuru zone.» HAYAMI, I. 1975. A systematic survey of the Mesozoic Bivalvia from Japan. The University Museum, The University of Tokyo, Bulletin, 10: 1-249, pls. 1-10. [p. 80]
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