Orthocones were a type of enormous mollusc in the early Palaeozoic. They could be found in the Silurian Period.
During the Ordovician, many orthocones are believed to have reached 3m or more (Cameroceras may have reached 9m long).
Humeoceras was one of a few species surviving into the Silurian.
The thick shell gives the orthocone 30% armour against conventional attacks.