Middle Oxfordian representatives of the genera Lithacoceras Hyatt, 1900, and Liosphinctes Buckman, 1925, from the Polish Jura Chain

Abstract

The genera Lithacoceras (with its three subgenera: Lithacoceras s.s., Larcheria and Discosphinctes) and Liosphinctes are described from the Oxfordian  (Plicatilis and Transversarium Zones) of the Polish Jura Chain. Sexual dimorphism is recognized in both genera. Apparent similarity of macroconchs of these genera is interpreted in terms of homeomorphy. It is also supposed that the majority of Upper Oxfordian/Kimmeridgian forms of Lithacoceras sensu Geyer (1961) are homeomorphs of this genus and really belong to Liosphinctes. The Oxfordhm and Tithonian Lithacoceras faunas supposedly represent two waves of invasion from the Tethyan areas.