''Euaptetoceras'' is an evolute hildoceratoid

ammonite Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...

from the lower Middle Jurassic, included in the family

Hammatoceratidae Hammatoceratidae is a family of lower and middle Jurassic ammonites included in the superfamily Hildoceratoidea. Diagnosis Hammatoceratidae comprises genera which are characterized by ribbed evolute shells (all whorls visible), some bearing keel ...

and the subfamility Hammatoceratinae. The genus may be a junior synonym for '' Eudmetoceras'' of Buckman, 1920. The shell of ''Euaptetoceras'' has an evolute, compressed, discoidal shape with a

whorl A whorl ( or ) is an individual circle, oval, volution or equivalent in a whorled pattern, which consists of a spiral or multiple concentric objects (including circles, ovals and arcs). Whorls in nature File:Photograph and axial plane floral ...

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. ''Euaptetoceras'' is found in strata of Europe, Iran, and Argentina.

References

* Arkell ''et al.'', 1957. Mesozoic Ammonoidea; Treatise on Invertebrate Paleontology, Part L (Mollusca 4, Ammonoidea). Geological Soc. of America and Univ. Kansas Press. Jurassic ammonites Fossils of Argentina Fossils of Morocco Hammatoceratidae Ammonitida genera {{ammonitina-stub