Thyasira sp.
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publication ID |
https://doi.org/ 10.4202/app.2008.0310 |
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persistent identifier |
https://treatment.plazi.org/id/497287A1-F629-7B24-9C3B-FD86FB31F3C6 |
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treatment provided by |
Felipe |
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scientific name |
Thyasira sp. |
| status |
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Fig. 5H View Fig .
Material.—One articulated specimen (though most of the left valve is missing) from the Kanajirisawa site in Obira Town; length 11.7 mm, height 12.4 mm, thickness 6.7 mm, UMUT MM 29540.
Description.—Shell moderate size, thick−walled, triangular in shape, swollen and slightly inequilateral. Umbo prominent, beak slightly prosogyrate, situated at central part of shell. Antero−dorsal margin steeply sloping, making angle with well rounded ventral margin. Posterior area wide; 2 nd posterior fold very strong, posterior sulcus very deep, but without posterior sinus; 1 st posterior fold elevated and sharp, rib−like; submarginal sulcus also deep without marginal sinus; auricle slightly convex and wide. Lunule double; outer lunule wide, bounded by crude ridge; inner lunule small, aubcircular, deeply depressed and bounded by distinct incision. Surface sculptured only by growth lines. Internal features unknown.
Discussion.—This species is unique in having a double lunule, a strongly inflated shell, and a deeply grooved posterior sulcus. These features separate this species from T. tanabei sp. nov. found in the same seep site. Because it is only known from a single specimen with an incomplete left valve, we do not establish a new species for it.
Stratigraphic and geographic range.—Known only from the Cenomanian Kanajirisawa seep site.
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