Ordovician odontopleurid trilobites from Estonia and Latvia

All available type and other odontopleurid material from Estonia and Latvia is described and figured. This includes the new species Acidaspis aviensis from the Upper Ordovician Porkuni Stage (FII) and Middle and Upper Ordovician (D1-FIa) material belonging to at least 3 new species of Diacanthaspis. However, because of the incompleteness of this latter material, no specific names are given to it.