|Species||Pleuroacanthites aff. biformis evolutus LANGE|
It is clearly a species of Pleuracanthites, with the characteristic ribbing on the innermost coils. The cross-section of the coils of the holotype is consistently wider than high, suggesting Pl. biformis, but without reaching it in thickness. Lange introduced this new species on the basis of a single small specimen, which makes comparisons to larger cases difficult. The illustration is also not optimal, therefore the classification remains ambiguous and the forms are described as Pl. aff. biformis evolutus. Possibly there is only a microconch of a species already described by Wähner.
* Description according to LANGE 1952, supplemented
The smaller specimen shown here has quite a lot in common with Lange's holotype: the sculpture is also very weak, the coils are wider than high or round.
However, the navel width is much larger, but this may be due to the larger diameter (60mm).
The large specimen is rather badly preserved, but also fits very well to this species from the winding cross-section.
In comparison, Pl. polycyclus and Pl. polycycloides are less thick, whereas Pl. biformis has a much larger Wb .
Both occur above the horizon with Ps. naumanni, probably in the megastoma proaries horizon- contradicting Lange's description ("zone of Ps. calliphyllum").
Dimensions at D= 36mm (according to LANGE):
Nw % v. D: ca. 48%
Wh % v. D: ca. 26%
Wb % v. D: ca. 31%
- 1952 Pleuracanthites biformis evolutus subsp. n. – LANGE S. 93, Taf. 11.4, Abb. 10