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''Placoparia'' is a genus of trilobites of average size (up to 6 cm) that lived during the late Lower to the early Upper Ordovician on the paleocontinents Gondwana, Avalonia and Laurentia, now the Czech Republic, France, Germany, Morocco, Portugal, Spain and Wales. Its headshield (or cephalon) is semi-circular to rectangular with rounded frontal corners. It lacks eyes, but eye ridges are present. The fact that the facial sutures are opisthoparian (with sutures in ''Pliomera'' gonatoparian) is an exception in the otherwise proparian Cheirurina. The thorax has 11 or 12 segments, with the axis slightly wider than the ribs (or pleurae) to its sides. The tips of the pleurae are free, which associates with an old-fashion radiatior of the central heating. The axis in the small tailshield (or pygidium) consists of four rings and a minute endpiece. The four pleurae end in spatulate spines that fit to corresponding indentations in the cephalon. == Distribution == * ''P. borni'' has been found in the Middle Ordovician of the Czech Republic, France, Spain and Portugal (Llandeilo, Dobrotivian). * ''P. cambriensis'' is known from the Lower Ordovician of Morocco (Arenig), Wales (Upper Arenig and lower Llarvirn), and the Lower and Middle Ordovician of Spain, Portugal, France and the Czech Republic (Llarvirn). * ''P. tournemini'' is present in the Middle Ordovician of Spain, Portugal and France (Llandeilo, Dobrotivian). * ''P. zippei'' occurs in the Middle Ordovician of the Czech Republic (Llandeilo, Dobrotivian) and Morocco (Llandeilo), and a comparable form in Germany (Llarvirn). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Placoparia」の詳細全文を読む スポンサード リンク
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