The lower part of the zone of Didymograptus hirundo, zone 3b ε has been found, forming the upper part of the Lower Didymograptus Shale (3b) at Slemmestad, SSW of Oslo. The development of D. hirundo and some Isograptus species is briefly discussed. A number of biserial graptolites are described from zone 3b ε. The stratigraphical importance of the occurrence of D. hirundo is mentioned.
The Middle Ordovician of the Oslo Region, Norway. 3. Graptolites dating the Beds below the Middle Ordovician.