The Middle Ordovician of the Oslo Region, Norway. 19. The trilobite family Odontopleuridae.

For the first time all of the Norwegian Middle Ordovician odontopleurid material has been revised and it has been shown that specimens from the Upper Chasmops Limestone (4bð), which were formerly referred to the Swedish species Apianurus furcata, belong to a new species, A. thorslundi. This and a second new species, A. abietinus from the Upper Chasmops Shale (4bγ), are closely related to other apianurinid species from Sweden, Estonia, and Virginia. Isolated exoskeletal parts of Primaspis and Diacanthaspis have affinities with Caradocian species from Britain and Virginia, and one more complete new species, Primaspis multispinosa, is described from the older Ogygiocaris Series (4aα). A series of measurements which are helpful when describing apianurinid cranidia are defined. All new species have been illustrated with the aid of stereoscopic photographs.