MILIOLIDAE - Acta Palaeontologica Polonica

MILIOLIDAE· FROM MIOCENE OF POLAND 117
Tortonian, Baden, Nussdorf, Vienna Basin. Czechoslovakia: Lower Tortonian,
Zidlochovice.
X Pyrgo inornata (d'Orbigny, 1846)
(pl. XXII, Fig. 3a, b; Text-fig. 39/5, 6)
1846. Biloculina inornata d'Orbigny; A. d'Orbigny, p. 266" PI. 16, Figs 7-9.
1867. Biloculina bulZoides d'Orbigny var. truncata gracilis Reuss; A. E. Reuss, PI. 2,
Fig. 2.
1868. Biloculina tenuis Karrer; F. Karrer, p. 133, PI. 1, Fig. 5.
1952. Pyrgo inornata (d'Orbigny); A. K. Bogdanowich, p. 168, PI. 25, Figs 3, 4.
1956. Pyrgo inornata (d'Orbigny); A. Sulimski, p. 74, Pl. 2, Fig. 2a-c.
Material. - About 200 specimens (ColI. No. F-170, Sec. No. 436a, b).
Dimensions: L 0.4-1.3; B 0.2-0.95; T 0.25-0.9.
Description. - Test oval, tapering towards the aperture and expanded
at the base; chambers inflated, usually semicircular in cross-section, lower
part of penultimate chamber narrowing downwards and truncate; periphery
broadly rounded; chamber sides narrow at the top, broader at the
base and somewhat sloping; sutures distinct; surface smooth, polished;
aperture small, semicircular, with a low transverse-quadrangular tooth
of variable width and with small lateral processes.
Variability and ontogeny. The test shape is variable and oscillates
between regularly oval and narrowly oval. The convexity of the
penultimate chamber is also variable; it usually occurs in the central
portion, but is occasionally displaced upwards, with the lower portion of
the chamber flat. Such specimens morphologically resemble Pyrgo
oblonga (d'Orbigny). The specimens sectioned represent the micro generation,
with the proculus diameter 10 fl, and the mega II generation, the
proculus of which is very large, its diameter being 320 1J. (Text-fig. 39/5,6).
The internal structure of the micro generation is initially irregularly
triloculine, later biloculine, that of the mega II generation is biloculine
throughout.
Remarks. - This species differs from Pyrgo oblonga (d'Orbigny, 1839)
in the more regular shape of the test, which does not taper so much at
the top and expand at the base. P. tenuis (Karrer, 1868) from the Miocene
of Kostej probably represents the juvenile stage of P. elongata, the test
of which may have a similarly elongated and flattened shape. P. bulloides
truncata gracilis, figured by Reuss (1867) from the Miocene of Wieliczka,
does not differ from P. inornata from Baden. The topotypes of P. inornata
from Baden are identical with those from the Miocene of Poland, but they
are more flattened than the specimen in d'Orbigny's illustration. As both
more or less inflated forms occur in our material, the convexity of the
test has been assumed to be exponent of intraspecific variability. From
P. clypeata (d'Orbigny, 1846) P. inornata differs distinctly in its more