Two genera of fossil fresh-water algae, Pediastrum and Botryococcus, and several specimens tentatively referred to Tetraedron, are recorded from lacustrine fluviatile sediments of the late middle Miocene Mascall formation from the John Day basin, Oregon, and from strata equivalent in age or somewhat younger from the Blue Mountains to the NE., and the Stinking Water basin to the S. The fossil Pediastrum and Botryococcus are compared with the living species, P. boryanum, P. duplex, and B. braunii on the basis of gross morphology. Specimens referred to Pediastrum are the first record of this genus in North American Tertiary sediments.

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