late viséan (late mississippian) ammonoids from the barnett shale, sierra diablo escarpment, culberson county, texas, usa

Mid-Carboniferous strata of the Barnett Shale in the Sierra Diablo region are deep water, offshore sediments deposited in the Marathon Foreland Basin. These strata contain a remarkably complete ammonoid record spanning from the Late Viséan to the middle Atokan (Moscovian). Late Viséan strata are referred to as the "Folks Member" of the Barnett Shale and locally yield numerous ammonoids. Three assemblages can be recognized, which contain, from oldest to youngest, Goniatites eganensis and Girtyoceras hamiltonense (Goniatites eganensis Zone), Goniatites multiliratus and Girtyoceras meslerianum (Goniatites multiliratus Zone), and Choctawites cumminsi and Pachylyroceras cloudi (Choctawites cumminsi Zone). We erect the new genera Choctawites and Uralyroceras to accommodate, respectively, the North American species "Goniatites choctawensis Shumard, 1863", "G. kentuckiensis Miller, 1889" and "G. cumminsi Hyatt, 1893", and Uralian species formerly attributed to Pachylyroceras. For the material of "Pachylyroceras cloudi" of the South Urals, the new species name Uralyroceras arquatum is proposed.