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Allocotoceras is an endocerid from the Lower Ordovician (upper Canadian) of Australia (Tasmania), included in the Endoceratidae, based on small, straight or gently curved siphuncles.
Septal necks, according to Teichert, 1964, are holochoantic, reaching to the previous septum. Endocones are described as having a dorsal wedge, or process, making the internal opening, or endosiphocone, simicircular in cross section. In this sense Allocotoceras seems to resemble the genus Najaceras.
References
Allocotoceras Wikipedia(Text) CC BY-SA