Wikipedia
Fissilobiceras
Fissilobiceras is a smooth, compressed, involute ammonite from the lower Middle Jurassic of Europe, named by Buchman in 1919. It is assigned to the hildoceratoid family, Sonniniidae.
Fissilobiceras is similar to Shirbuirnia, except primarily for being more involute and having complex sutures. More of the inner whorls show in Shirbuirnia and its sutures are simple. Fissilobiceras also has a low keel running along the venter and only a small part of the inner whorls are exposed in the small umbilicus.