Species Geyeroceras subcylindricum (NEUMAYR)

The shells are medium-sized with a characteristic winding cross-section. The umbilical edge is distinct, the flanks flattened. A tight rounding is also observed towards the broadly rounded external side, giving the cross-section a rectangular appearance. Although the flanks do not taper clearly towards each other, the largest winding width is measured near the navel,
The shell is smooth, s-shaped accretion stripes can be observed on the shell in very good condition.
The species is quite common. The stratigraphic level cannot be determined exactly (in the area between the calliphyllum and naumanni/johnstoni horizons).

* Description according to Kment (2000), supplemented


Geyeroceras leptophyllum (HAUER) is particularly similar, but it increases in thickness much faster. It also occurs only in the border area Hettangian/Sinemurian. The trapezoidal winding cross-section is not so clear in G. subcylindricum.
Geyeroceras cylindricum has a very similar winding cross-section, but it is much narrower-billed and also occurs later in the profile.


Dimensions with D= 60mm
Nw % v. D: ca. 18%
Wh % v. D: ca. 50%
Wb % v. D: ca. 44%

  • 1879 Phylloceras subcylindricum n.f. – Neumayr S. 22, Taf, 1.15
  • 1952 Phylloceras subcylindricum Neumayr – Lange S. 83, Taf. 10.2
  • 2000 Geyeroceras subcylindricum Neumayr – Kment S. 193, Taf. 1.6

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    hettangian ammonites

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