Six rare trilobites from the Middle Ordovician of the Oslo region are described. The genus Frognaspis, related to the Swedish Ityophorus, is new, and so are the species Frognaspis stoermeri, Pseudosphaerexochus (Pseudosphaerexochus) bulbosus, P. (P.) densigranulatus, and the subspecies Paraharpes ottawaensis similis.
The Middle Ordovician of the Oslo Region, Norway. 18. Rare trilobites of the families Olenidae, Harpidae, Ityophoridae and Cheiruridae.