| Species | Geyeroceras cylindricum (SOWERBY) |
| Author | SOWERBY |
| Group | Phylloceraten |
| Horizon | rotiformis-horizon subsalinarius-horizon atanatense-horizon |
| Zone | rotiformis-zone marmoreum-zone |
| Stage | Lower Sinemur Upper Hettangian |
Description
The shells are predominantly quite small with a characteristic winding cross-section. The umbilical edge is distinct, the parallel flanks flattened. A tight rounding is also observed to the broadly rounded external side, giving the cross-section a rectangular appearance. The width of the navel is very small.
The housing is smooth.
The species is very common and occurs first in the first limestone bank of the Adnet Fm. (Lienbacher Member) above the marmoreum crust. Possibly it reaches even further up. For the time being a cylindricum ammonite horizon is used as level.
* Description according to Kment (2000), supplemented
Compare
The species differs from other Geyeroceras by the very narrow navel.
Other narrow-branched phyllocerates do not have a rectangular cross-section.
Dimension
Dimensions with D= 30mm
Nw % v. D: ca. 11%
Wh % v. D: ca. 52%
Wb % v. D: ca. 36%
Literature
- 1993 Geyeroceras cylindricum Sowerby – Rakus & Lobitzer S. 923, Taf. 1.1-2, Taf. 2.1
- 2000 Geyeroceras cylindricum Sowerby – Kment S. 194, Taf. 2.1
