Article: Oryctocephalid trilobites from the Cambrian of North America

Type and additional specimens of species of Oryctocephalus, Lancastria and Oryctocara are described. Oryctocephalidae have a rostral-hypostomal plate, and hence belong in the Order Corynexochida. Characteristic of the family is the development of lateral glabellar furrows as pits situated inside the axial furrow, and the absence of a border on the pygidium. Two subfamilies are used: Oryctocephalinae, having genal and pleural spines; Oryctocarinae lacking such spines. Species of both groups are found in late Lower to mid Middle Cambrian rocks of North America, Siberia, Asia and Australia, and rare examples occur in South America and Antarctica. Oryctocephalids are typical of deposits in outer shelf and slope areas, in which completely or partially articulated exoskeletons are characteristic. Arrangements of sclerites in such specimens of Oryctocephalus burgessensis are considered to result from burial events, not from manoeuvres during exuviation. Compaction and tectonic distortion of specimens in these fine-grained clastic rocks renders questionable some of the characters used in taxonomy.