Lissoceras

Lissoceras is an involute, smoothly or finely vetrolaterally ribbed ammonite with a blunt, un-keeled venter included in the Haploceratidaefamily that lived from the Lower Bajocian to Middle Oxfordian ages in what is now Europe, south Asia, and southern Alaska.
Lissoceratoides, once considered to be a subgenus of Lissoceras, is indistinguishable morphologically from it.