Nippononectes tamurai (Tashiro, 1976)
TASHIRO, M. 1976. Bivalve faunas of the Cretaceous Himenoura Group in Kyushu. Paleontological Society of Japan, Special Papers, 19: 102 p., pls. 1-12, text-figs. 1-23. [p. 52, pl. 6, figs. 1-7]
1976 Chlamys (s. l.) tamurai Tashiro, 1976
M. Tashiro, 1976, plate 6.
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«Material:— Holotype, KE 2239, from loc. S4; paratypes, KE 2107, 2110-2, from loc. S7; paratypes KE 2108-9, from Himezuka of Dogo, Matsuyama city, Ehime Pref.
Description:— Shell roundly ovate, a little inequilateral, inequivalve, weakly inflated, nearly as long as high or slightly higher than long; test thin; hinge line nearly straight; anterior margin slightly concave; ventral margin semicircular; posterior margin straight; umbo a little posterior to a midpoint of valve length; apical angle about 75º; anterior ear larger than posterior; posterior ear obliquely truncated; byssal notch deep in right valve and ctenolia about 5; external surface ornamented with two sorts of ribs; one is radial ribs which are narrower than their interspaces, spinose on ventral part, stronger and more numerous on left valve than in right valve, generally crowded on anterior and posterior parts of the disk; the other is divaricate striae which are fine and numerous, about 10 or more in a distance of 5 mm on ventral margin of mature specimens, irregularly sinuated and frequently bi- or tri-furcated on ventral part; growth lines generally weak but fairly distinct on ventral part, especially of left valve; ears ornamented in the same way as the disk; two pairs of cardinal crurae present; a pair of crurae on either sides of resilifer short and weak; the other pair of cardinal crurae below the hinge line elongated, parallel to cardinal axis; auricular crura not present; inner surface smooth; inner margin smooth.
Remarks:— This species resembles species of Camptonectes AGASSIZ (in SPEDEN, 1972) in having divaricate striae on the disk, but differs in having radial ribs on the disk. Chlamys (Camptochlamys) inspecta KIPARISOVA (1961) from the Triassic of North Boctoka, resembles this species in having the radial ribs and fine striae which appear on the interspaces of the radial ribs. However, a network structure is shown in Chlamys (Camptochlamys) inspecta by the striae crossing the concentric striae. Micronectes bellaturus ICHIKAWA and MAEDA (1958) is discriminated from this species by regularly spaced concentric ribs and a smaller valve.
Occurrence:— Locs. S4, S7; Member U-IIb; Lower Hetonaian (Upper Campanian), also found in black siltstone of the basal formation of the Izumi Group at Himezuka of Dogo, Matsuyama city, Ehime Pref. (Upper Campanian).»
MASAYUKI TASHIRO, 1976
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