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-hyposto mal 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 gr oups are found in late Lower to mid Middle Cambrian rocks of North Ame rica, Siberia, Asia and Australia, and rare examples occur in South Am erica and Antarctica. Oryctocephalids are typical of deposits in outer shelf and slope areas, in which completely or partially articulated e xoskeletons are characteristic. Arrangements of sclerites in such spec imens of Oryctocephalus burgessensis are considered to result from bur ial events, not from manoeuvres during exuviation. Compaction and tect onic distortion of specimens in these fine-grained elastic rocks rende rs questionable some of the characters used in taxonomy.