MILIOLIDAE - Acta Palaeontologica Polonica

MILIOLIDAE FROM MIOCENE OF POLAND 139
Variability. The shape of test is variable from oval to circular.· The
terminal portion of the last chamber may be sometimes more or less
inclined towards the penultimate one, the test being then circular in shape
and the middle chambers having an oblique position. The terminal portion
of the last chamber does not adhere closely to the test wall in some specimens,
being somewhat deflected from the surface terminally; thus the
aperture has the shape of a transverse slit at the end of the last chamber
which is surrounded with a thickened border and lacks the tooth.
Dimorphism and ontogeny. The specimens sectioned represent the
microspheric generation, with a proloculus 20-40 ~ in diameter and a
megalospheric I generation, with a proloculus 80 l-l in diameter. A turn
lmm
Fig. 47. Morphological variability and internal structure of Varidentella georgiana
sp. n., Lower Sarmatian, Machow 290 borehole, depth 26-27 m: 1-micro generation,
typical form, turn of coiling axis visible in the ontogeny; 2 - mega I generation,
rounded form showing oblique position of central chambers, turn of coiling axis
visible in the ontogeny; 3 - micro generation, juvenile stage irregular triloculine,
then quinqueloculine; 4 - micro generation, juvenile form with irregular chamber
arrangement; a front view, b apertural view, c (except no. 2) - cross-section,
no.2-longitudinal section.
of the coiling axis appears distinctly after a few juvenile chambers (Textfig.
47).
Remarks. - This species approaches morphologically to Varidentella
reussi (Bogdanowich), but differs in having a characteristic aperture and
definite regular striae which are not wrinkles like those in gerontic
specimens of V. reussi. It differs from Recent Triloculina fichteliana
d'Orbigny from Cuba and from Recent T. webbiana d'Orbigny from the
Canary Is. in more elongated shape and in having a low tape-shaped
tooth in the aperture. From Recent T. suborbicularis d'Orbigny (not