Euaptetoceras is an evolute hammatoceratid ammonite

Ammonite

Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct subclass within the Molluscan class Cephalopoda which are more closely related to living coleoids Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct...

 from the lower Middle Jurassic, included in the family Hammatoceratidae and the subfamility Hammatoceratinae. The genus may be a junior synonym for Eudmetoceras

Eudmetoceras

Eudmetoceras is an extinct genus from a well-known class of fossil cephalopods, the ammonites. It lived during the Jurassic Period, which lasted from approximately 200 to 145 million years ago....

of Buckman, 1920.

The shell of Euaptetoceras has an evolute, compressed, discoidal shape with a whorl section higher than wide. The inner whorls have long primary ribs while the outer whorls become smooth. The venter, which is the outer rim, is narrowly to sharply rounded and its suture is rather complex. Eudmetoceras is found in strata of Europe, Iran, and Argentina.