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Tsunyidiscus
''Tsunyidiscus'' is a genus of eodiscinid agnostid trilobites. ''Tsunyidiscus'' occurs near the end of the Lower Cambrian, during the late Atdabanian stage period and some collections suggest it may have survived into the Botomian. They are very small (up to 7mm), have eyes, and equal sized head and tail shields, with a narrow dome-shaped glabella and a narrow bullet-shape pygidial axis. It has a thorax of three segments. ''Tsunyidiscus'' is the only genus currently attributed to the family Tsunyidiscidae.〔
== Description ==
Like other Agnostida the body of ''Tsunyidiscus'' is diminutive, the headshield (or cephalon) and tailshield (or pygidium) are of approximately same size, with 3 thoracic segments in-between, each consisting of a horizontal inner portion that abruptly passes into an inclined outer portion (fulcrate). The cephalon has a deeply parabolic outline and maximum width (tr.) usually anterior to genal angle. Glabella extremely narrow, lateral glabellar furrows usually obscure, with rounded and expanded frontal glabellar lobe. The most backward lobe of the glabella (called occipital ring or LO) at least as long as the lobe in front of it (L1), and is usually expanded laterally, may bear sharp, posteriorly directed spine. Long, curved posterior fixigenal spine may be
present. The furrow between those two lobes (SO) is transverse and uninterrupted. The facial sutures are proparian. The free cheeks or (librigena) are ½× as long as the cephalon. The pygidium has a narrow, multisegmented axis (with five, six or more segments). The thorax and pygidial axis segments may carry nodes.〔Whittington, H. B. et al. Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. 1997〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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