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Gondwanaria japonica (Nakaseko, 1963)

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Sethocyrtis japonica
Shell small, subconical, with the distinct stricture which is divided into two joints or segments, and with apical horn; apical horn very short, conical, triangular; cephalis hemispherical, usually poreless, its length about 0.3 of that of the thorax, and with the columellar at the internal hollow; its columellar thin, rodlike, connected with the apical horn; thorax round conical, the largest diameter at the middle of its own shell, with fairly smooth curved side; its pores fairly small, circular, arranged in regular alternation, similar in form and size, deeply set into the thick wall, and with hexagonal frames; the tiers of the pores six, and about 10 to 12 pores across the widest diameter; aperture simple, smooth, without tooth, and its diameter about 0.6 of that the widest part.
Length of the cephalis, 20µ; of the thorax, 65µ; of the apical horn, 10µ; breadth of the cephalis, 45µ; of the thorax, 88µ; diameter of the aperture, 45µ; of the pores of the thorax, 5-8µ.
Sethocyrtis japonica n.sp. like Lychnocanium nipponicum is one of the most characteristic species in the Neogene formation of Japan, and is abundantly found in the sample. Cephalis and thorax of this species are similar to those of Lychnocanium nipponicum and Theocyrtis redondoensis Campbell et Clark.
Nakaseko 1963
Thorax is nearly conical. Pores irregular, about 7-9 on the half of the equator of the thorax. Naturally lateral feet in some late Miocene individuals are arranged on the abdomen, not on the thorax. Nakaseko has shown the difference from Theocyrtis redondensis (Campbell and Clark): the latter has a nearly global thorax. Th. redondensis might be placed among Calocyclas.
Petrushevskaya 1975











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