The stratigraphy and lithology of the lower portion of the Carboniferous found at McCoy, Colorado, are described, and the megafauna and microfauna are listed. One new genus and four new species of ostracodes, and eleven new species and three new varieties of foraminifera are described. Splendid specimens have enabled the authors to emend the genus Deckerella, show the method of growth of the genus Bradyina, and determine the presence of septal pores and very strong chomata in several species of Fusulininae. The genus Ulrichia is much restricted.