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The brachiopod fauna of the Keyser Limestone within a 50-mile radius of the type section at Keyser, West Virginia, is described. Thirty-three species representing 26 genera are recognized in the fauna; six species are new: Rhynchospirina martinensis and R. newcreekensis, Delthyris hynd-manensis, Nanothyris boucoti, Rhynchotreta? hancockensis, and Mach-aeraria whittingtoni.

A new name, the New Creek Limestone, is proposed for the rock-stratigraphic unit referred to as the Coeymans Limestone in Maryland and West Virginia. The type section is at New Creek, West Virginia.

The two faunal zones of the Keyser, the Eccentricosta jerseyensis Zone in the lower part and the Meristella praenuntia Zone in the upper part, are redescribed, and use of the "subzone" terminology previously employed for the formation is discouraged. The name, Meristella praenuntia Zone, is proposed to replace the inappropriate, older name, Favosites helderbergiae praecedens Zone, for the upper Keyser zone.

On the basis of the brachiopods, the E. jerseyensis Zone is correlated with the Decker Formation in New Jersey, the Rondout Formation in south-eastern New York and the Cobleskill Limestone in central New York. The M. praenuntia Zone cannot be correlated with certainty with any other formations.

The age of the Keyser Limestone is concluded to be Late Silurian and Early Devonian. The M. praenuntia Zone contains the brachiopod genera, Meristella, and Nanothyris and the subgenus Kozlowskiellina (Megakozlowskiella) which are known only in post-Silurian rocks in other areas and suggest an Early Devonian age for the upper part of the Keyser. Halysitid corals, known only from pre-Devonian rocks, are found in the E. jerseyensis Zone and indicate a Late Silurian age for the lower Keyser. The boundary between the Silurian and Devonian is concluded to lie within the Keyser Limestone near the faunally and lithologically gradational boundary between the two zones.

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