Phosphatic microfossils etched from Upper Cambrian (Trempealeauan Stage) Limestones of the Whipple Cave Formation, Nevada, and other contemporaneous formations in western North America, are colonies, the individuals of which are arranged irregularly around one or more nuclei. No secondary growth has occurred. During their lifetime, however, the individuals partially filled their chambers with phosphatic matter. The highly differentiated morphology of the colonies is strikingly similar to the living ascidian tunicate Botryllus. Ecological conditions and size range of the fossils are likewise similar to those of the Ascidiacea. If recognized as an ascidian, Palaeobotryllus taylori n.g., n.sp. extends the known occurrence of Tunicata into the Upper Cambrian.