UTRECHT MICROPALEONTOLOGICAL BUllETINS

Remarks: Throughout the Oland sections, the oistodiform element remained
very constant in· shape, whereas both the ozarkodinaform element (= the
Prioniodina inflata-like elements, Pl. 4, figs. 18~20) and the multiramiform
elements (= the elements of the Periodon transition series of Lindstrom
1964; see for instance Pl. 4, figs. 15-17) underwent considerable changes in
shape.
The older forms of the ozarkodinaform elements had a short and undenticulated
base (Pl. 4, fig. 18). They also lacked the oulodus-like bending,
described by Lindstrom (1964). The anterior process was hardly developed
and undenticulated. The illustrations of plate 4, figs. 18 to 20, show the
gradual change to the ozarkodinaform elements described as Prioniodina
inflata LINDSTROM, 1955.
The early forms of the multiramiform elements were hardly denticulated
if at all (Pl. 4, fig. 15). The basal sheath was higher and the cusp wider and
flatter, compared to the later forms (Pl. 4, figs. 16 and 17). The change to
the more conspicuously denticulated forms was very gradual.
Biometrical and statistical data probably will enable the distinction of
several species within this lineage. For the time being, they are all placed in
one multi-element species.
Regional occurrence: At Kopingsklint the species occurs from the top of
member K k2 up to and including the top portion of the Bruddesta Formation.
In section 6 from member Ka- d 1 up to and including the lowermost
portion of the Horns Udde Formation. Near Horns Udde from the top of
member K k2
up to a level at about 2.80 m. over the base of the Bruddesta
Formation.
Biostratigraphic range: Periodon flabellum was found from the Triangulodus
SlAbtilis/Gothodus microdentatus Assemblage Zone up to and including the
lower portion of the Triangulodus brevibasis Assemblage Zone (fig. 15).
Genus Pravognathus STAUFFER, 1936
Type species: Heterognathus idoneus STAUFFER, 1935.
Definition: "Base thin, long, slender, straight or slightly arched and twisted
just anterior to the middle; lintler side of base with narrow groove extending
entire length,. slightly widening and deepening beneath the arch or beneath
the more prominent denticles; the upper edge of base bears 2, 3 or 5, possibly
more, large, long, pointed, orally flattened, aborally rounded denticles on
the arched or twisted portion; these may incline in various directions. Anterior
limb or portion of base bears 4 or 5, possibly more, denticles of decreasing
size; posterior limb bears 10 to 12, possibly more, small laterally flattened,