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Trilobita - Asaphida - Asaphidae
It was misspelled as Ptychocephalus by Sepkoski (2002); it was corrected as Ptyocephalus by Fortey (1975), Jell and Adrain (2003) and Peters (2003).
It was assigned to Isotelinae by Fortey (1975); to Asaphida by Sepkoski (2002); and to Asaphidae by Jell and Adrain (2003) and Peters (2003).
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If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.