Late upper Devonian brachiopods from the West Range limestone of Nevada

Abstract

The West Range Limestone is a nodular argillaceous limestone of early Famennian age underlying a broad area in southeastern Nevada. It contains two brachiopod faunas of which the upper one is described here as the Cleiothyridina reticulata fauna. Eight brachiopod species are recognized and two, Parapugnax bactrianense and Crurithyris fissa are described as new. Three other named species, including Cleiothyridina reticulata, are known at Rhodes Pass, New Mexico, in beds called Percha by Stainbrook, but the Cleiothyridina reticulata fauna has no similarity to the well known Percha-Ouray brachiopod fauna. Age analysis of the West Range brachiopods and conodonts requires a lower, but not lowest, Famennian assignment and the fauna appears to be intermediate in age between the lower Famennian Cyrtospirifer fauna of Merriam and the middle Famennian fauna of the Trident Member of the Three Forks Formation. Three Cleiothyridina species are found to occur in sequence in the Famennian. From oldest to youngest the sequence includes C. angelicoides, C. reticulata, and C. devonica which form a morphologic series showing progressively greater lenticularity and becoming less sulcate.