Species of Deiracephalus Resser, 1935, are rare elements in most Guzhangian (upper Marjuman) trilobite faunas of Laurentian North America, and are characterized by striking cephalic spinosity that includes very long genal and occipital or preoccipital glabellar spines. Almost all previous reports of the genus have assigned sclerites to two species, Deiracephalus aster (Walcott, 1916) and Deiracephalus unicornis Palmer, 1962. However, new material from the Shallow Bay Formation of western Newfoundland and restudy of type material from the southern Appalachians show that as many as eight species are present, although not all of them are sufficiently well known to be formally named. Deiracephalus aster and D. unicornis are restricted to their respective holotypes from the Conasauga Formation of Alabama; new species from the Shallow Bay Formation are Deiracephalus narwhali, Deiracephalus rhinocerotis, Deiracephalus dynastoides, and Deiracephalus phanaeus. Deiracephalusunicornis, D. narwhali, D. rhinocerotis, and a poorly known species from Nevada all possess preoccipital glabellar spines, and form an informal “unicornis group” of species. This group occurs high in the traditional Crepicephalus Zone (latest Guzhangian) and offers a potentially important means of biostratigraphic correlation. Species with occipital spines are older than the unicornis group and extend down into the Cedaria Zone as used traditionally in North America.

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