Charophyte oogonia and ostracods from formations of Lower Cretaceous age of the Rocky Mountain region are described and illustrated. The charophyte genera Atopochara Peck, heretofore known only from the Trinity of Texas and Oklahoma, Clavator Reid and Groves, and Perimneste Harris, heretofore known only from the Purbeck of England, are common in strata of Lower Cretaceous age in the Rocky Mountain region. The Ostracoda consist mostly of representatives of the fresh-water genera Cypridea Bosquet and Metacypris G. S. Brady. Two of the ostracod species occur also in the Trinity of Texas and Arkansas, and the entire ostracod fauna bears a close resemblance to Upper Purbeck-Wealden of England. The absence of known Lower Cretaceous microfossils in the Morrison is considered good evidence of the Jurassic age of the Morrison formation.