. "Circulocrania is an extinct genus from a well known class of fossil marine arthropods, the trilobites. It lived during the later part of the Arenig stage of the Ordovician Period, approximately 478 to 471 million years ago."@en . . . "Animalia"@en . "Circulocrania"@en . "Circulocrania"@en . "Late Arenig"@en . . "Circulocrania is an extinct genus from a well known class of fossil marine arthropods, the trilobites. It lived during the later part of the Arenig stage of the Ordovician Period, approximately 478 to 471 million years ago."@en . . "Arthropoda"@en . . .