Revision of the Early Cretaceous genera Heminautilus Spath, 1927, and Josanautilus Martínez & Grauges, 2006 (Nautilida, Cenoceratidae)

In spite of recent interest, the various species belonging to the genera Heminautilus SPATH, 1927, and Josanautilus MARTÍNEZ & GRAUGES, 2006, have never been the object of a general revision. More than 160 specimens belonging to various species of these two genera were studied, with the aim of identifying the specific characteristics and the stratigraphical and paleogeographical distribution of the various species which compose them, as well as to propose a phylogeny for the group. This study con-firms the non-synonymy of H. saxbii (MORRIS, 1848) and H. lallierianus (ORBIGNY, 1841), establishes that H. tejeriensis MARTÍNEZ & GRAUGES, 2006, and H. verneuilli (VILANOVA, 1870) represent junior synonyms of H. saxbii (MORRIS) and suggests the creation of the species H. ? japonicus sp. nov. The origin of the genus Heminautilus SPATH from Pseudocenoceras SPATH, 1927, proposed by TINTANT and the origin of Jo-sanautilus MARTÍNEZ & GRAUGES from Heminautilus SPATH are both confirmed