Calcareous algae occur in considerable quantity in certain portions of the upper Leadville limestone near Glenwood Springs, Colorado. They include two species of Solenopora, two species of Garwoodia, four species of Ortonella, fragments of Dasycladaceae of the genus Coelosporella, one Girvanella, and at least four unnamed forms of Spongiostroma. None has previously been described from the United States. Three new species—Solenopora glenwoodensis, Garwoodia media and Ortonella coloradoensis—are described; others such as Solenopora similis Paul, Garwoodia aff. Gregaria (Nicholson), Ortonella furcata Garwood, Ortonella cf. kershopensis Garwood, and Girvanella? nicholsoni (Wethered) have been previously described from Great Britain. Remains of other organisms occurring with the algae are tabulated; a few are illustrated to throw light on the conditions of deposition of the limestone.