MILIOLIDAE - Acta Palaeontologica Polonica

MILIOLIDAE FROM MIOCENE OF POLAND 33
and tooth, not to the internal structure. To be sure, this leads to the
separation of two subgenera of Quinqueloculina (see Part I, p. 351), but
certain species remain in the nondescript group "Quinqueloculina sensu
lato". Prell-Miissig (1965) gives more attention to the internal structure,
but states that it is difficult to tell Quinqueloculina from Triloculina.
Thus, she arrives at the conclusion that the triloculine forms that have
a "quinqueradiate" internal structure (later termed "cryptoquinqueloculine"
by Bogdanowich, 1969; see Part I, p. 353), should be included in
the genus Quinqueloculina. Therefore, reverting partly to Williamson's
conceptions from 1858, she pays no attention to the shape of aperture and
the relations between this shape and the internal structure, and within one
genus combines the forms which might be referred to at least three
genera - Quinqueloculina, Cyclojorina and Sinuloculina - and perhaps
also to Varidentella.
The existence of intergeneric transition forms has also been demonstrated
by Hofker (1971), who used the orthogeny of the species "Miliolina
antiqua" Franke from the Albian of Holland and north-western Germany
as an example. Although his studies concern the development of these
forms with time in the layers about 200 m thick, an analogous phenomenon
can be observed in layers of one and the same age or even in a single
sample. Hofker shows that the species studied, numbered by him in the
genus Quinqueloculina, traced from the lowest layer to the highest one,
passes through the genus Sigmoilina into Spirosigmoilina without any
distinct boundaries between them. In consequence, he disputes the value
of these genera and proposes a unit superior to genus, i.e. the "gens", as
a genuine biological unit. Exemplified by "Miliolina antiqua" the "gens"
develops from a certain form and evolves in a definite direction to become
another form different from the initial one. Hofker illustrates this evolutionary
series with sections of the forms mentioned.
An analysis of Hofker's conception calls in question the genera determined
by him, in which he includes the group of forms examined. In view
of the round toothless aperture, the juvenile stage of quinqueloculine
structure and the sigmoiline adult stage, at least two genera, i.e. Quinqueloculina
and Sigmoilina, may be excluded. Spirosigmoilina has not an
aperture at the end of a neck, either. A close analysis will supposedly
show that they belong to still another genus. This, however, is not essential
to our problem, but the fact that intermediate forms can analogously
be observed in series representing the ontogenetic development in several
species of Quinqueloculina derived from a single sample from the Miocene
layers at Korytnica. They, too, comprise quinqueloculine forms together
with massiline ones, the sections of which show intermediate stages
between them (e.g. Q. anagallis, Text-figs 7, 8; Q. buchiana, Text-figs 12,
13; see section "Ontogeny"); nevertheless, they cannot be treated otherwise
than as developmental stages of one species. We can hardly speak about
3 Acta Palaeontologlca nr 1/74