| 四环藻属(Tetracyclus Ralfs)中的新化石种和变种(硅藻门Bacillariophyta) |
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| 关键词:Diatom Fossil Taxonomy |
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| Some New Fossil Species and Varieties of the Genus Tetracyclus Ralfs |
| Three new fossil species and three new varieties of the genus Tetracyclus,T.radiatus,T.minutus, T.subdivisium var ellipticus,T.rupestris var. subclypeatus, T.celatom var. minor and T.mucronatus , from the Late Miocene flora of Inner Mongolia, China,are described in this paper.These new species can be distinguished by the shape and number of primary,secondary and tertiary ribs,the length of the central sternum and the shape of the axial area. These new species are apparently endemic to the Chinese fossil flora. Tetracyclus radiatus Li, sp. nov. Plate Ⅰ, figs. 1～6 Synonyms: Tetracyclus japonicus (Petit) Tempere et Peragalla,Li Jiaying [2] ,p.157, pl.II, figs. 1～5. Valves circular, 31～45 μm in diameter; Striae in equidistant rows, slightly radiating at the poles, scattered toward the central face margin 12～15 in 10 μm; Ribs robust, primary, secondary and tertiary; exterding into margin of valve and meeting the sternum 2～3 in 10 μm. Sternum central, bisecting the valve. Three rimoportula present, located margin on the valve mantle; More intercalary bands and septa.; Type locality: Late Miocene flora of Inner Mongolia, China. Locality details held at Institute of Geology, Chinese Academy of Geological Sciences. Holotype: IMS-SZ11-3-02 (1), pl. Ⅰ, fig. 1. Paratype:IMS-SZ11-3-02 (2～6), pl. Ⅰ, figs. 2～6. Tetracyclus minutus Li, sp. nov. Plate Ⅰ, figs. 7～10 Valves circular, 8～15 μm in diameter; Striae in equidissatant rows, radiating at the poles, 28～32 in 10 μm; Ribs robust, primary, secondary and tertiary; exterding into margin of valve and meeting the sternum, 3～4 in 10 μm. Sternum central, bisecting the valve. No rimoportula; More intercalary bands and septa. ; This taxon is similar in shape to Tetracyclus radiatus , but differ in diameter and striae number, no rimoportula.; Type locatity: Late Miocene flora of Inner Mongolia, China. Holotype:IMH4 (2) -3-4, pl. Ⅰ, figs.7～8. Paratype:IMH4 (2) -16-17, pl. Ⅰ, figs. 9～10. Tetracyclus subdivisium var. ellipticus Li, var. nov. Plate Ⅰ , figs. 11 , 13～16 Valves elliptical to almost subcircular, 9～15 μm long, 4～12 μm broad; Primary transverse ribs broad and merging with the axial area, two on the whole valve, 1～2 in 10 μm; sometime one secondary, but no tertiary ribs. Sternum central, narrow and short, slightly thickened internally. Striae in equidistant rows, radiating towards the poles, 30～35 in 10 μm; One rimoportula present, located margin on the valve mantle. This taxon is distinguished by the two divergent central primary and secondary ribs.It differ from Tetracyclus subdivisium in the shape of almost subcircular and more striae on the whole valve. Type locality: Late Miocene flora in Inner Mongolia ,China. Holotype:IMH5-A2-(2)-2, pl.Ⅰ, fig. 11. Paratyepe:IMH5-A2-(2)-2, pl.Ⅰ, figs. 13～16. Tetracyclus rupestris var. subclypeatus Li, var. nov. Plate Ⅰ. figs. 12, 18 Vales broad-elliptical to subcircular, 4.5～9 μm long, 4～7 μm brosd; One primary transverse rib broad and merging with the axial area; No secondary or tertiary ribs. Axial area elliptical lanceolate, almost not thickened internally to form a sternum. Striae radiate, 28～32 in 10 μm, thosenearer the axial area more widely and irregularly spaced. Apical pore field on the mantlle and extending slightly into the marginal lip, striae and areolae 30～34 in 10 μm. One rimopartula present at near the axial end of a polar to subcentral stria. More intercalary bands and septa. This taxon is distingushed by the one central primary rib. It differ from Tetracyclus rupestris in the shape of the valve and striae number. Type locality: Late Miocene flora of Inner Mongolia, China. Holotype:IMH5-A2-(2)-2, pl.Ⅰ, fig.12. Paratype:IMH5-A2-(2)-2, pl.Ⅰ, fig.18. Tetracyclus celatom var. minor Li, var.nov. Plate Ⅱ, figs. 1～13 Valve strongly- slightly constricted in the middle portiom and rounded apices.13～30 μm long, 3～8 μm wide. |
| LI Jia-ying.1999.Some New Fossil Species and Varieties of the Genus Tetracyclus Ralfs[J].Acta Geoscientica Sinica,20(4):439-446. |
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