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Abstract
New material of Irvingella from central Sweden includes a cranidium of Irvingella major which is associated with fragmentary olenid trilobites that represent the Parabolina brevispina Subzone of the P. spinulosa Zone. This affords a direct correlation between the olenid trilobite zonation of Baltica and the Irvingella major Zone at the base of the Sunwaptan Stage in Laurentia. Several topotypic cranidia of Irvingella suecica Westergård confirm the features of that species but do not provide a direct indication of its position within the olenid zonal succession.
Acknowledgements
We are grateful to Phil Crabb of the Natural History Museum for taking the photographs of trilobites and to Kevin Webb for assisting with making up figures 3, 7 and 8. Adrian Rushton thanks Professors S.R. Westrop and B.D.E. Chatterton for discussion of Irvingella. Our manuscript benefited from constructive remarks from the referees P. Ahlberg, Lund, and E.N.K. Clarkson, Edinburgh.