Trilobite traces from the Lower Tremadoc of Tortworth

Summary. The ichnogeneric status of trilobite furrows (Cruziana) and resting excavations (Rusophycus) is discussed and the suggestion (Seilacher, 1970) that these two distinct types of trace should be united under the genus Cruziana is rejected. A variety of trilobite traces is described from the Lower Tremadoc Breadstone Shales of Tortworth, Gloucestershire, including C. semiplicata (Salter), C. tortworthi, sp.nov., C. breadstoni sp.nov., and R. didymus (Salter). The stratigraphic ranges of these and other approximately coeval trilobite traces are assessed and the possibility of using them to distinguish otherwise unfossiliferous Upper Cambrian, Tremadoc and Arenig strata is discussed. This and other material is used to test recent hypotheses seeking to explain the methods by which trilobites produce Cruziana. It is concluded that furrows of C. rugosa and related forms may include markings made by the exites but furrows of C. semiplicata probably do not