Pates et al.—Hurdiids from the middle Cambrian of Utah


in the House Range (Elrick and Snider, 2002; Brett et al., 2009; Gaines and Droser, 2010) although they represent a shallower facies (Briggs and Robison, 1984; Brett et al., 2009). The relative global chronostratigraphic ages and polymerid


trilobite biostratigraphy of Radiodonta-preserving units in Utah and British Columbia can be seen in Figure 1.


Results


Taxonomic identifications of new and previously described material are summarized in Table 1. Hurdia victoria Walcott, 1912


101


is described for the first time from the Spence Shale. Hurdia also occurs in the Wheeler Formation. Peytoia occurs in the Wheeler and Marjum formations, but should no longer be reported as present in the Spence Shale.


Hurdia from the Spence Shale Member.—Some of the material interpreted as Hurdia from the Spence Shale comprises appen- dages and mouthparts (Figs. 2, 3); these include both previously


described specimens (Briggs et al., 2008; Daley et al., 2013a, fig. 24) and new material. New carapace material (Fig. 4.1–4.5),


Figure 1. Stratigraphic column showing relative ages of Burgess Shale, Spence Shale, Wheeler Formation, Marjum Formation, and Weeks Formation, with reference to global chronostratigraphic units and polymerid trilobite biostratigraphy. Adapted from Robison et al. (2015).


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