A revision of the Bajocian Lissoceratinae is presented. The study of more than 500
lissoceratins from different sites of the Western Tethys (Northwest European, Sub-Mediterranean
and Mediterranean bioprovinces) within the Tethys-Panthalassa Realm provided data
useful to implement the systematics of these almost neglected, never deeply analysed
ammonites. Two genera, Lissoceras Bayle and Semilissoceras n. gen., are described
with 16 species, among which eight new species (four dimorphic, three macroconchiate
and one microconchiate): L. submediterraneum, L. maizetense, L. ovale, L. sturanii,
L. maerteni, S. ellipticum, S. turgidulum and S. costellatum. The neotype of L. oolithicum
is established. The microconchiate genus Microlissoceras is regarded as the junior
synonym of the macroconchiate Lissoceras. Taxa are discussed according to four groups
that gather taxa sharing common morpho-structural features. They roughly relate to
successive biochronostratigraphical intervals within the Bajocian Stage and are headed
by species largely known in literature: S. semicostulatum (Buckman) with suboval to
compressed whorl section and rectiradiate ribs on the outer half flank; L. oolitbicum
(d'Orbigny) with subtriangular to ovate whorl section, large and depressed ventral
saddle, large suspensive lobe; L. baugi Sturani with ovate to globular whorl section,
narrow lobe E and suspensive lobe; and L. psilodiscus (Schloenbach) with highly compressed
whorl section, high ventral saddle and narrow lobe E. The phyletic relation of Lissoceras
and Semilissoceras to the Aalenian-Bajocian Bradfordia-group is discussed, regarding
Semilissoceras as the known stem-taxon of the subfamily Lissoceratinae.