MILIOLIDAE - Acta Palaeontologica Polonica

MILIOLIDAE FROM MIOCENE OF POLAND
121
Pyrgoella cont.roversa (Bogdanowich, 1965)
(pI. XXI, Figs 4a-c, Sa, b, 6a, b; Text-fig. 39/9)
1965. Pyrgo ? controversa Bogdanowich; A. K. Bogdanowich, p. 42, Pl. 3, Fig. 3.
Material. - 50 specimens (CoIl. No. F-174, Sec. No. 437).
Dimensions: L 0.4-0.95; B 0.35-0.85; T 0.3-0.65.
Description. - Test circular-oval, slightly tapering at the top, oval in
cross-section; periphery broadly rounded, chambers broad, embracing
those of the previous whorls entirely and leaving only two last chambers
visible, occasionally also a narrow trace of the third chamber; sutures
flat, poorly visible, with a wide border along the chamber edge; wall
thick; surface smoth, polished; aperture high, somewhat contracted at the
top, filled with a narrow tongue-shaped flap.
Variability. The test shape is variable in cross-section, being irregularly
circular in three-chambered forms (PI. XXI, Fig. 4), irregularly oval in
forms whose third chamber appears only in a narrow slit between the
last two chambers (PI. XXI, Fig. 6), and narrowly oval in forIns with
the last chamber embracing not only the third chamber, but also the most
part of the second chamber (PI. XXI, Fig. 5). The shape of the aperture
and tooth is also variable, from semicircular with a flap of the same shape
to high and narrow, filled with a narrow, tongue-like or even simple tooth
(PI. XXI, Figs 4, 5). Variation in test shape is very likely connected with
dimorphism.
Dimorphism and ontogeny. The sections show a pseudotriloculine
internal structure initially, then biloculine. The specimen sectioned
represent the mega I generation, the P diameter of which is 70 fA. (Textfig.
39/9). In cross-section the chamber shape is semicircular initially,
then sickle-shaped.
Remarks. - This species differs from Pyrgoella ventruosa (Reuss)
from the Miocene of Wieliczka in its less spherical test shape, slight
flattening of the chamber sides, transverse wrinkles present in some
specimens, considerably thicker wall, and oblong tongue-like tooth. The
two forms however seem to be related. ForIns whose third chamber is
distinctly visible are very similar to Miliolinella valvularis (Reuss) from
the Septarien clays of Hermsdorf near Berlin, but differ in the more oval
test, tapering at the top, the narrower and higher aperture, and the tonguelike
tooth. It is conceivable that all the three forms represent an
evolutionary series, from Miliolinella valvularis in the Oligocene through
Pyrgoella ventruosa in the Lower Tortonian to Pyrgoella controversa in
the Upper Tortonian.
Distribution. - Poland: Upper Tortonian (Gliwice Stare, Ligota Zabrska,
Krywald, Zrecze). USSR: Konka (Upper Tortonian) West Precaucasian
region.