The separation from S. donar, as introduced by Wähner, is not always comprehensible. Possibly both species are variations of one species. The shape of the shell is essentially identical.
S. pachygaster differs from S. donar by "smaller thickness, more pronounced forward bending of the ribs on the external side, greater thickness of the ribs compared to their height and the width of the interspaces (especially on the external side) and by the earlier onset of rib fission" (cited by Wähner 1884).
* Description according to WÄHNER (1884), supplemented (see also description of Schlotheimia donar).
There are very few outcrops where no rearranged ammonites from the megastoma zone occur in the Fe-Mn crust, i.e. where no "old" S. donar can occur. Therefore, only S. pachygaster is to be expected there. The earlier cleavage of the ribs can be confirmed, although there is not really much comparative material from S. donar.
Specimens of S. donar/ S. pachygaster are very common in the marmoreum fauna. Characteristic compared to other Schlotheimia are the large width of the coils and the numerous ribs.
Dimensions with D= 75mm (according to Wähner):
Nw % v. D: ca. 37%
Wh % v. D: ca. 36%
Wb % v. D: ca. 25-28%
- 1884 Aegoceras donar n.f. mut. pachygaster Suttner – WÄHNER S. 176, Taf. 21.3-6