Proterovaginoceras Temporal range: Darriwilian ~466–463.5 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Subclass:	Nautiloidea
Order:	†Endocerida
Family:	†Endoceratidae
Genus:	†Proterovaginoceras Reudemann, 1905
Type species
Proterovaginoceras belemnitiforme (Holm, 1885)
Species
P. belemnitiforme (Holm, 1885) P. incognitum (Schröder, 1882) P. rapidum Fang, 2022[1]
Synonyms
P. belemnitiforme Endoceras belemnitiforme Holm 1885 P. incognitum Dideroceras amplum Balashov 1968 Dideroceras brevispiculum Balashov 1968 Dideroceras kundense Balashov 1968 Dideroceras longispicum Balashov 1968 Dideroceras pribalticum Balashov 1968 Endoceras duplex Wahlenberg 1821 Orthoceras duplex Wahlenberg 1821 Schmidtoceras estonicum Balashov 1968 Schmidtoceras kundense Balashov 1968 Vaginoceras endoseptum Chang 1957

Proterovaginoceras (Ancient Greek for "earlier shield horn") is a medium to large sized^[ambiguous] 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:^[2]

• Loobu Formation, Estonia
• Abastu Formation, Iran
• Pivorjaiskaja Formation, Lithuania
• Huk and Stein Formations, Norway
• Gillberga, Holen and Komstad Formations, Sweden
• China