MILIOLIDAE - Acta Palaeontologica Polonica

MILIOLIDAE FROM MIOCENE OF POLAND 29
of ribs or striae, or their presence only in some specimens of a given
species. There are only few species which have little varying morphological
characters, e.g. Quinqueloculina regularis (Text-fig. 21/1, 2), Q. pygmaea
(Text-fig. 21/3, 4) or Siphonaperta ovalis (Text-fig. 34/3). Cycloforina
contorta is one of the most variable species as regards morphology.
The periphery of its chambers has two longitudinal edges, which are
sharp in typical forms but may be rounded to a various degree in other
specimens (Text-fig. 26). Similarly, Cyclojorina vermicularis may have an
angular truncate periphery or a more rounded one without any signs of
the angles (Text-fig. 32). The ribs on the chamber surfaces in Lachlanella
incrassata may be either well or ill developed (Text-fig. 33/1, 2). Sigmoilopsis
foeda may be regularly oval or S-shaped (PI. XV, Figs 3, 4) and
Triloculina intermedia has either keeled chambers or their edges are
rounded (PI. XXIII, Fig. 1), etc. Great variation in shape is especially
frequent in Sarmatian species, like Varidentella reussi (Text-fig. 49),
Cycloforina karreri ovata (Text-fig. 30) or some species of Articulina
(e.g. A. problema, A. multibullata and A. sarmatica).
Some attention should also be given to the variation in the shape of
the aperture and tooth, especially in such genera as Cycloforina, Miliolinella,
Pyrgo, Pyrgoella and Varidentella. In Cycloforina the variable
shape of the aperture occurs in the species that have the last chamber
unextended and as a result the aperture may be round with a narrow
tooth or slightly flattened at the base with a somewhat broader square
tooth (e.g. in Cycloforina suturalis, C. toreuma, C. predcarpatica and
C. stomata). In Miliolinella the shape of the tooth is differentiated and it
assumes the form of a fairly broad or narrow apertural plate, e.g. in
M. valvularis (PI. XX, Figs 4, 5). This is also true of Pyrgoella, whose
apertural plate may be narrowed so much as to become a tongue-shaped
tooth, as in P. controversa (PI. XXI, Figs 4-6). In Pyrgo the variation
of the apertural shape can be seen particularly well in P. amphiconica
(PI. XX, Figs 6-8), in which the width of aperture may be nearly equal
to the diameter of the test. The most variable shape of the aperture and
tooth is observed in the genus Varidentella, whose aperture ranges from
a transverse slit with a broad tape-shaped tooth to a large semicircular
opening with a short square tooth (e.g. in Varidentella sarmatica or
V. latelacunata).
ONTOGENY
The ontogenetic stages can be observed in transverse sections, which
show the shape of the chambers from the juvenile stage to the adult one,
whereas the structure of the aperture and tooth in an early stage is
exposed by the removal of the external chambers.