| Species | Pleuroacanthites biformis (SOWERBY & CANAVARI) |
| Author | CANAVARI SOWERBY |
| Group | Psiloceraten |
| Horizon | atanatense-horizon pachygaster-horizon seebachi-horizon curviornatum-horizon |
| Zone | marmoreum-zone megastoma-Zone |
| Stage | Upper Hettangian Middle Hettangian |
Description
Pleuracanthites biformis increases in width most rapidly compared to all related species. Already on the first coils the cross-section is much wider than high. This weakens with increasing size, but the species always appears particularly thick and is somewhat reminiscent of Lytoceras.
The characteristic bulges can still be clearly seen on the inner coils and attenuated even on larger specimens. In the very small specimen shown here, the ratio Wb:Wh = 2:1. Several such very thick small specimens were found together with Alsatites proaries, which WÄHNER also describes as a finding horizon. Larger specimens are very rare in our area.
WÄHNER notes that the shell shape and sculpture of Pl. biformis varies greatly. There are wider and narrower forked and more or less strongly ribbed specimens. A separation into two different species did not seem advisable to him because there are all kinds of transitions.
* Description according to WÄHNER 1884 + 1894, supplemented
Compare
The closest resemblance to the more closely forked specimens is Analytoceras articulatum, which also occurs alpine. In Analytoceras, however, there are more clearly defined and deeper constrictions on the inner coils instead of bulging undulations. The following coils in Analytoceras are as good as smooth with old mouth margins at regular intervals. The sculpture is much more strongly and irregularly developed in Pleuracanthites.
WÄHNER goes into great detail on the differences in the lobe line within the genus Pleuracanthites and in comparison to Analytoceras.
Dimension
Dimensions with D= approx. 90mm:
Nw % v. D: ca. 51%
Wh % v. D: ca. 26%
Wb % v. D: ca. 28%
Literature
- 1884 Pleuracanthites biformis Sow. (Canav.) – WÄHNER S. 245, Taf. 3.2, 4.1-3, 9.3-4
- 1952 Pleuracanthites biformis (Sow.) Canavari – LANGE S. 93
- 2021 Pleuroacanthites biformis (SOWERBY) – KMENT S. 269, Fig. 10.4
