Nippononectes Tashiro, 1982
TASHIRO, M. 1982. A new pectinid genus Nippononectes from the Cretaceous of Japan. Memoirs of the Faculty of Science, Kochi University [Series E - Geology], 3: 1-6, pIs. 1, 2. [p. 1]
«Family Pectinidae Rafinesque, 1815
Subfamily Chlamydinae Korobkov, 1960 Genus Nippononectes Tashiro, nov. Type species:— Chlamys (s. l.) tamurai Tashiro, 1976; Upper Campanian, Southwestern Japan.
Diagonosis:— Shell small to medium in size, roundly ovate, inequivalve; test thin; umbo located nearly midpoint of valve length; byssal notch deep in right valve with several ctenolia; external surface ornamented with two sorts of ribs; one is radial ribs, spinose generally on ventral part, more numerous on left valve than in right valve; the other ribs are divaricate striae; ears ornamented in the same way as the disk; two pair of cardinal crurae present; a pair of crurae on either sides of resilifer; the other pair of cardinal crurae below the hinge line, parallel to cardinal axis; inner surface smooth; inner margin smooth.
Remarks:— This new genus is characterized by Camptonectes-like divaricated striae and Camptochlamys-like radial ribs on the surface. The divaricated striae are very abundant and developed on entire surface of the valve. The radial ribs are round-topped, delicate but distinct, generally narrower than their interspaces, crowded on both lateral parts of the valve, and stronger and less numerous than the divaricated striae.
Camptonectes Agassiz (in Speden, 1972) which is a cosmopolitan genus of the Jurrasic and Cretaceous, resembles this new genus in its divaricate striae, but differs in its less developed radial ribs. This is similar to Camptochlamys Arkell (1930), of the Triassic pectinid, in the narrow radial ribs, but differs clearly in its divaricated striae. A possibility of a new genus in the Family Pectinidae for Chlamys (s. l.) tamurai Tashiro has already been suggested in my previous studies (Tashiro, 1976; 1978). The comparison of Chlamys (s. l.) tamurai s. l. Tashiro with the similar species in Eburneopecten Conrad (see, Speden, 1972), Micronectes Ichikawa and Maeda (1958), Radulonectites Hayami (1957) and Palliolum Monterosato (Abbot, 1955), was made in detail in Tashiro (1978). List of species and subspecies:--
Chlamys (s. l.) tamurai Tashiro, 1976 (Chlamys (s. l.) tamurai tamurai Tashiro, 1978); Upper Campanian (Hetonaian K6b) of the Himenoura Group, Kyushu, and the Izumi Group, Shikoku; Maastrichtian (Hetonaian K6c) of the Izumi Group, Izumi Mountaines. Chlamys (s. l.) tamurai immodesta Tashiro, 1978; Lower Santonian (Urakawan K5b) of the Himenoura Group, Kyushu. Nippononectes monobensis, n. sp.; Middle Turonian and Upper Turonian (Gyliakian K4b) of the Kajisako Formation, Monobe Area, Shikoku. Nippononectes kozaii, n. sp.; lower Lower Cenomanian (Gyliakian K4a) of the Fukigoshi Formation (Tashiro, Matsuda, Kozai and Katto, 1982) = ("Hagino Formation" at and near the Nagase Dam site in the Monobe Area, by Katto and Suyari, 1956), Shikoku. Nippononectes eleganus, n. sp.; Lower Aptian (Miyakoan K3a) of the Hibihara Formation (= Kaminiro Formation), Shikoku. Distribution:— Lower Aptian to Maastrichtian (Miyakoan to Hetonaian); South-western Japan.»
MASAYUKI TASHIRO, 1982
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Chlamys (s. l.) tamurai, sp. nov.; M. Tashiro, 1976, Bivalve faunas of the Cretaceous Himenoura Group in Kyushu, plate 6, figures 1-7.
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Nippononectes sp.; G. W. Kendrick & A. V. Vartak, 2007, Middle Cretaceous (Cenomanian) bivalves from the Karai Formation, Uttattur Group, of the Cauvery Basin, south India, figure 11.K
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«Remarks
The genus Nippononectes was erected by Tashiro (1982) for four small, Early Aptian to Maastrichtian Japanese pectens. The original generic diagnosis is: "Shell small to medium in size, roundly ovate, inequivalve; test thin; umbo located nearly midpoint of valve length; byssal notch deep in right valve with several ctenolia; external surface ornamented with two sorts of ribs; one is radial ribs, spinose generally on ventral part, more numerous on left valve than in right valve; the other ribs are divaricate striae; ears ornamented in the same way as the disc; two pair of cardinal crurae [sic] present; a pair of crurae [sic] of either sides of resilifer; the other pair of cardinal crurae [sic] below the hinge line, parallel to cardinal axis; inner surface smooth; inner margin smooth".
"The new genus is characterised by Camptonectes-like divaricated striae and Camptochlamys-like radial ribs on the surface. The divaricated striae are very abundant and developed on entire surface of the valve. The radial ribs are round-topped, delicate but distinct, generally narrower than their interspaces, crowded on both lateral parts of the valve, and stronger and less numerous than the divaricated striae" (Tashiro 1982). In all available characters, the present species agrees well with Tashiro's genus, of which it would appear to be a south Indian Cenomanian representative. Of the Japanese species, it most resembles (RV) Nippononectes tamurai (Campanian-Maastrichtian), differing in its larger apical angle, larger posterior auricle (RV) and fewer, wider, commarginal costellae. In view of the discrepant sculpture of the valves on the Japanese species, the LV of the Odiyam species, when found, may differ in this respect from the RV. Western Australian occurrences of Nippononectes have been reported (as Nipponectes, err.) from the Maastrichtian Miria Formation and Santonian Gingin Chalk by Darragh and Kendrick (1991: 58- 62, fig. 12C, F). From these, the south Indian species differs in its wider apical angle, larger posterior auricle (RV) and fewer, much wider antimarginal costellae; in essential sculpture of the RV, these species appear to be congeneric and suggest a wideranging presence for Nippononectes throughout the Late Cretaceous.» KENDRICK, G. W. & A. V. VARTAK. 2007. Middle Cretaceous (Cenomanian) bivalves from the Karai Formation, Uttattur Group, of the Cauvery Basin, south India. Records of the Australian Museum, Supplement 72: 1-101, figs. 1-20. [p. 58, 59]
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