New species of Fusulinidae described from the late Pennsylvanian part of the Gaptank Formation, west Texas, include: Triticites celebroides, T. acutuloides, T. moorensis, T. marathonensis, T. confertoides, T. asperoides, T. elegantoides, T. cameratoides, T. capaxoides, T. nealensis, and Triticites sp. A. For the first time a species of Waeringella is reported from the formation. Within the formation eight fusulinid assemblage subzones are recognized in this part of the Range Zone of Triticites. They are in ascending order the Assemblage Subzones of (1) T. celebroides, (2) T. collus, (3) T. joensis, (4) T. acutuloides, (5) T. moorensis, (6) T. turgidus, (7) T. cameratoides, and (8) T. nealensis. The oldest subzone correlates with the lower part of the Linn Subgroup, Kansas City Group (middle Missourian), Midcontinent region, and the Brownwood Shale Member, Graford Formation, Canyon Group, central Texas. The youngest subzone correlates with the Speck Mountain Limestone Member, Thrifty Formation, Cisco Group, central Texas, and probably also with the lower or middle part of the Wabaunsee Group, Virgilian Series, Midcontinent region. No major depositiositional break in the sequence occurs between the lowest and highest of these assemblage subzones.

Four lithologic facies within the formation contain different associations of fusulinid species. A shallow-shelf limestone facies has many species with thickly fusiform tests, such as Triticites beedei Dunbar & Condra, T. cullomensis Dunbar & Condra, T. elegantoides n. sp., and T. capaxoides n. sp. A shelf-edge limestone facies has few species but includes thickly fusiform species and elongate species, such as T. cameratoides n. sp., Triticites sp. A, T. joensis (Thompson), and T. tenuis Merchant & Keroher. A deeper water limestone facies has many species of fusulinids with closely coiled early volutions and fusiform to elongate fusiform tests, such as T. asperoides n. sp., T. acutuloides n. sp., T. confertoides, n. sp., and T. comptus Ross. A thin-bedded impure limestone facies has many species with elongate and irregular tests, such as T. celebroides n. sp., T. collus Burma, T. neglectus Newell, T. plicatulus Merchant & Keroher, and T. marathonensis n. sp