MILIOLIDAE - Acta Palaeontologica Polonica

MILIOLIDAE FROM MIOCENE OF POLAND 89
Description. - Test rhomboid-oval, subtriangular in cross-section,
periphery subacute; chambers narrow with flattened sides, arcuate, of
uniform width, middle chamber large and prominent, fifth chamber
clearly visible; sutures distinct, slightly depressed; surface with thick
longitudinal, sometimes slightly oblique or sinuous, interrupted grooves
cutting the wall in such a fashion that the ridges arising between them
make the impression of ribs; wall thick, dull; aperture circular, at the end
of the poorly developed neck, and with a short tooth widening at the end.
Variability. Most of the specimens are triangular in cross-section,
having the periphery subacute. There occur also specimens with the lower
part of chambers dilated and truncate, and thus having the periphery
angular in cross-section. The periphery only rarely remains angular
throughout and in old specimens (Text-fig. 32/1); in other specimens it
passes slowly into a normal, subangular periphery towards the end of the
chambers, which gives the test the appearance of being irregularly bent
as figured by Karrer.
Dimorphism and ontogeny. All specimens sectioned belong to the micro
generation; PD 20-30 fl. The sections show that some specimens with the
subacute periphery have it angular in the earlier chambers (Text-fig.
32/2, 4) and vice versa, those with the angular periphery may have it
lmm
4b_~65b
.--'"'-....-~J'-.°k£'c ~c ~c ~5C
Fig. 32. Morphological variability and internal structure of Cycloforina vermicularis
(Karrer); Lower Tortonian, Karsy; micro generation; 1 - form with angular chamber
edges; 2 - form with truncate chamber edges; 3 - forms with subacute chamber
edges; a front view, b apertural view, c cross-section.