Late Viséan (late Mississippian) ammonoids from the Barnett Shale, Sierra Diablo Escarpment, Culberson County, Texas, USA Author Titus, A. L. D. Korn & Grand Staircase-Escalante National Monument, 669 S. Highway 89 A, Kanab, UT 84741, USA Author Korn, D. J. E. Harrell & Museum für Naturkunde, Leibniz Institute for Evolution and Biodiversity Science, Invalidenstrasse 43, Author Harrell, J. E. L. L. Lambert & Noble Energy Inc., Houston, TX 77070, USA Author Lambert, L. L. Department of Geological Sciences, The University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, USA text Fossil Record 2015 2015-06-04 18 2 81 104 http://dx.doi.org/10.5194/fr-18-81-2015 journal article 298388 10.5194/fr-18-81-2015 49a593d2-44ce-420d-a608-8533ec6745ac 2193-0074 11585625 6C6A1411-F88F-45C2-BA4A-D97C4CD4B415 Girtyoceras Wedekind, 1918 Type species: Adelphoceras meslerianum Girty, 1909 (original designation). Genus diagnosis: Girtyoceratidae with moderately large conch that during ontogeny passes through very different morphological stages: early juveniles are widely umbilicate with crescent-shaped whorl cross section, later thickly discoidal or pachyconic with subangular or rounded umbilical margin. The intermediate stage has rounded flanks and venter and the adult stage is lenticular and oxyconic. Without or with very faint ventrolateral grooves. Suture line with Vshaped external lobe, moderately high median saddle, narrowly rounded ventrolateral saddle, and V-shaped adventive lobe. Remark: For the species composition of the genus and a discussion of the characteristics and limits, see Korn and Titus (2011) .