Proterovaginoceras (Ancient Greek for "earlier shield horn") is a medium to large sized endocerid (endocone-bearing orthoconic nautiliod) from the Early and Middle Ordovician included in the family Endoceratidae. Proterovaginoceras has a straight shell with a circular cross section, straight sutures, and a ventral to central, nanno-type, siphuncle which fills the entire apical part of the shell. Septal necks are macrochoanitic, up to two camerae (chambers) long; connecting rings, one chamber in length line the inside of the necks. Endocones are long and slender, fill the entire bulbous, nanno-end, of the siphuncle. Proterovaginoceras was named by Reudemann in 1905. Dideroceras Flower 1950 and Chisloceras Gortani 1934 are probably synonymous equivalents. Distribution Fossils of the genus have been found in: Loobu Formation, Estonia Abastu Formation, Iran Pivorjaiskaja Formation, Lithuania Huk and Stein Formations, Norway Gillberga, Holen and Komstad Formations, Sweden China References Further reading O. K. Bogolepova, B. Kröger, M. Falahatgar and M. Javidan. 2014. Middle Ordovician cephalopods from the Abarsaj area, northern Iran. GFF - Geological Society of Sweden 136(1):34-37 B. Kröger. 2014. Middle Ordovician cephalopod biofacies and palaeoenvironments of Baltoscandia. Lethaia B. Kröger. 2012. The 'Vaginaten': the dominant cephalopods of the Baltoscandian Mid Ordovician endocerid limestone. Geologiska Föreningen i Stockholm Förhandlingar 134(2):115-132 H. Mutvei. 1997. Siphuncular structure in Ordovician endocerid cephalopods. Acta Palaeontologica Polonica 42(3):375-390 J. Laskovas, V. Marcinkevicius, and J. Paskevicius. 1993. The Stratigraphy and Structure of Ordovician Rocks of the South - East Part of the Baltic Basin (Druksiu Area). Geologija, Detailed Stratigraphy (14)81-98 Tiechert,C. 1964. Endoceratoidea. Treatise on Invertebrate Paleontology, Part K. Endoceratoidea, Actinoceratoidea, Nautiloidea. Geological Soc. of America and Univ Kansas Press External links Proterovaginoceras in the Paleobiology Database Nautiloids Darriwilian Ordovician cephalopods Ordovician animals of Asia Paleozoic Iran Fossils of Iran Ordovician animals of Europe Paleozoic Estonia Fossils of Estonia Paleozoic Lithuania Fossils of Lithuania Ordovician Norway Fossils of Norway Ordovician Sweden Fossils of Sweden Fossil taxa described in 1905 Ordovician China