Rare to abundant silicified polyplacophoran faunas occur in the late Wolfcampian Bird Spring Formation and the Leonardian Pequop and Loray Formations in Nevada, the Leonardian Arcturus Formation in Utah, and the early Leonardian Ft. Apache Limestone Member of the Supai Formation in Arizona. The faunas associated with the polyplacophorans are dominated by molluscs. New species include Gryphochiton distinctus, Acutichiton gracilis, A. nevadensis, and Arcochiton richardsoni. Traces of color patterns are present on Arcochiton richardsoni.

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