Bactritida

The order Bactritida comprises fossil cephalopods dominated by the genus Bactrites intermediary between the ancestral nautiloids and derived ammonoids and belemnoids. The including Bactritoidea is equivalent in terms of description and content.

Diagnosis
Bactritids have shells that vary from orthoconic (straight) to cyrtoconic (gently curved) which may be short (breviconic) or elongate (longiconic), with variable apical angles. The siphuncle, the tube running through the chambers, is narrow and always in contact with the ventral wall. Septal necks are either orthochoanitic, straight, or cyrtochoanitic, outwardly flared and point to the rear as characteristic of the Nautiloidea. Sutures always have a V-shape ventral lobe, more characeristic of the Ammonoidea.

Taxonomy
The Bactritida, and by implication the Bactritoidea, includes two families, the:


 * Bactritidae comprising genera with straight to moderately curved elongate shells with a small apical angle, and


 * Parabactritidae comprising both short and elongate genera with a somewhat large apical angle.