Gastropods from the Lower Cretaceous of Vorarlberg, Austria. A ...

KOLLMANN: Gastropods from the Lower Cretaceous of Vorarlberg. A systematic review 31
Description. Shells large, side of spire slightly convex. Whorls strongly to moderately
concave, bulging abapically. Sutures narrow canaliculate. Selenizone situated in the
middle of whorl, flat, accompanied by strong rib on each side. Besides ribs limiting the
selenizone, sculpture consisting of 6 spiral ribs on inner whorl face and 7 ribs on outer
whorl face, all noded at intersection with delicate collabral ribs.
Last whorl strongly bulging. Periphery acute. Base almost flat, anomphalous, in holotype
with strong, bent growth lines and traces of spiral threads. Paratypoid (P 15438) with
densely spaced spiral threads. Aperture resembling low parallelogram, columella oblique.
Remarks. High conical specimens with concave whorls as well as broad conical specimens
with shallow concave whorls are included in this species. They agree by their
sculpture, their anomphalous condition, flat base and low aperture. HEIM, BAUMBERGER
& FUSSENEGGER, lit. cit., determined a comparatively broad specimen (VN: P 10382) as
P. neocomiensis. This species has a broad umbilicus and the selenizone is positioned on
an angulation. Its systematic position is therefore in Bathrotomaria.
Pyrgotrochus cf. concavus n. sp.
Plate 1, Figure 13
1879 Pleurotomaria pseudoelegans PICTET & CAMPICHE - VACEK, p. 741
1933 Pleurotomaria Favrina LORIOL - HEIM, BAUMBERGER & FUSSENEGGER, p. 204
Material. GBA: 1879/01/76. 2 specimens from the Breiterberg, close to Bad Haslach,
reference material to VACEK, 1979; reference material to HEIM, BAUMBERGER &
FUSSENEGGER, 1933, from the debris at the Breiterberg (VN, P 10383)
Dimensions.
H H (est.) B LW A
GBA/1 36.0 41 39.4 21.5 60°
GBA/2 24.3 25.7 15.3 60°
Description. Shells broad trochiform, whorls moderately concave. Selenizone flat, with
lunulae, positioned in middle of whorl between two ribbons. Sculpture consisting of
approximately 8 spiral threads on the inner whorl face and 15 on the outer whorl face,
forming nodes at the intersections with irregular collabral ribs. Sculpture in some parts
weak or totally lacking. Periphery bulging, acute in the internal mould.
Base slightly convex. In larger specimen basal shell not preserved, central hole filled by
calcite. Smaller specimen anomphalous. Aperture resembling parallelogram.
Remarks. The sculpture is almost the same as in Pyrgotrochus concavus n. sp. and the
overall morphology of the shell falls within the variability of this species. The deposition
of calcite in the central hole of the larger specimen shows that the shell was anomphalous.
The most striking difference to P. concavatus n. sp. is the higher aperture. The
preservation is not good and the two shells are therefore described with open nomenclature.
Distribution in Vorarlberg. Kieselkalk Formation, Gemsmättli Member