Middle to Upper Ordovician (Darriwilian to Bolindian) graptolite zones of the northern Canadian Cordillera comprise the following: Glyptograptus euglyphus Zone of late Darriwilian (Llandeilo) age, Nemagraptus gracilis Zone of early Gisbornian (late Llandeilo and earliest Caradoc) age, Climacograptus bicornis and Dicranograptus clingani? zones of early to mid-Gisbornian (early to mid-Caradoc) age, Orthograptus quadrimucronatus Zone of Eastonian (late Caradoc) age, and Dicellograptus ornatus zone of Bolindian (Ashgill) age.A prominent biostratigraphic break equivalent to the spiniferus to hians kirki zones (Eastonian) is shown to exist between the clingani? Zone and the overlying quadrimucronatus Zone.Thirty eight common and (or) important species are illustrated, of which one new species, Orthograptus expansus n. sp., is described and figured.

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