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Thecosphaera japonica Nakaseko, 1971

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Thecosphaera japonica
Description:— Shell entirely globular, with rough surface and with three concentric spheres; outer shell with moderately thick wall, surface with about 16 pores across the diameter; its pores fairly small, circular, regular, in arrangement, uniform in size and shape, deeply set into the thick wall, with hexagonal frames; secondary inner shell very small, about 0.26 of the outer shell in diameter; its pores small, circular, uniform in size and shape, with rather thick bars; primary inner shell very small about 0.12 of the outer shell in diameter; its pores small subhexagonal, well-spaced, with thin bars; three concentric shells connected by many rodlike radial beams.
Measurements:-Diameter of the outer shell, 130-160µ: of the secondary inner shell 40µ; of the primary inner shell, 15-20µ.
Remarks: — This species is abundantly found in the late Tertiary formations of Japan and is one of the most characteristic species of the district. Also, it is the represented species of the Tj assemblage. The first appearance of this species .seems to be in the upper horizon of the upper Miocene. The faunal exchange between the Tj assemblage represented by this species and the Ta—Ar assemblage is considerably varied, and the boundary of both assemblages can be traced in the Japanese Neogene formation. This species differs from Thecosphaera miocenica in that the surface of the outer shell is more rough, and the pores of the outer shell are smaller in number. This species is distinguished by rough and thick wall from Thecosphaera tochigiensis as described under that species.
Nakaseko 1971











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