T y p e s p e c i e s. Ammonites listeri SOWERBY, 1812; by subsequent designation (Foord and Crick 1897: 226; see also ICZN (1956): Opinion 420, p. 150).
D i a g n o s i s. Genus of the family Gastrioceratidae with thickly discoidal, pachyconic and globular conch with moderate and wide umbilicus; umbilical shoulder nodose. Ornamentation ranging from simple transverse lirae to reticulate pattern in some species. Suture line with a high median saddle between the attenuated prongs of the ventral lobe; lateral lobe generally nearly symmetrical and becoming attenuated on mature specimens (after Mapes et al. 1997).
S p e c i e s i n c l u d e d. G. adaense MILLER et OWEN, 1944, Oklahoma (USA); G. angustum PATTEISKY, 1964, Rhenish Mountains (Germany); G. araium MCCALEB, 1968, Arkansas and Oklahoma (USA); G. attenuatum MCCALEB, 1968, Arkansas and Oklahoma (USA); G. carbonarium (BUCH, 1832), Rhenish Mountains (Germany); G. circumnodosum FOORD, 1903, Leinster (Ireland); G. coronatum FOORD et CRICK, 1897, Lancashire (England); G. crassum WEDEKIND, 1914, Rhenish Mountains (Germany); G. depressum DELÉPINE, 1937, Heerlen (the Netherlands); G. fittsi MILLER et OWEN, 1944, Oklahoma (USA); G. formosum MCCALEB, 1963, Arkansas (USA); G. glenisteri NASSICHUK, 1975, Canadian Arctic Archipelago (Canada); G. kahrsi WEDEKIND, 1914, Rhenish Mountains (Germany); G. kenadsae DELÉPINE, 1941, Béchar Province (Algerian); G. kutejnikovense POPOV, 1979, Donets Basin (Ukraine); G. liratum NASSICHUK, 1975, Canadian Arctic Archipelago (Canada); G. listeri (SOWERBY, 1812), Yorkshire (England); G. lupinum POPOV, 1979, Donets Basin (Ukraine); G. magoffinense WORK et al., 2012, Kentucky (USA); G. matsumotoi NISHIDA et KYUMA, 1982, Akiyoshi (Japan); G. melvillensis NASSICHUK, 1975, Canadian Arctic Archipelago (Canada); G. occidentale MILLER et FABER, 1892, Kentucky (USA); G. stenolobum DELÉPINE, 1941, Atlas (Morocco); G. stenumbilicatum RUAN et ZHOU, 1987, Ningxia (China); G. weristerense DEMANET, 1943, Liège (Belgium); G. wongi GRABAU, 1924, Ningxia and Gansu (China).
S t r a t i g r a p h i c r a n g e. Late Bashkirian to early Moscovian.