semiconical

Animal unknown but supposed to be closely allied to the Belemnite. Shell internal, oblong, semiconical, with the apex inflected towards the ventral aspect, and enlarged into an obtuse umbo, pierced by a pore on the ventral surface; the anterior part hollowed into a deep semiconical cavity extending to the pore, and having the inner surface covered by two calcareous sheaths, one within the other, continued over the ventral surfaces of, and enveloping, a series of transverse septa, perforated by a ventral siphon.

1877, Frederic Erasmus Edwards, Searles Valentine Wood, “Cephalopoda”, in A Monograph of the Eocene Cephalopoda and Univalves of England, volume I, Palaeontographical Society, page 38