UTRECHT MICROPALEONTOLOGICAL BUllETINS

member Kk 1 up to the top of member Kk 2. In section 6 it is confined to the
top of member Ka- d 2' Near Horns Udde it was only found in the top portion
of member Kk 2.
Biostratigraphic range: Paracordylodus gracilis was found from the upper
part of the Drepanodus arcuatus Assemblage Zone up to and including the
basal portion of the Protopanderodus rectuslOepikodus evae Assemblage
Zone (fig. 15).
Genus Paroistodus LINDSTROM, 1971
Type species: Oistodus parallelus PANDER, 1856.
Definition: "Paroistodus includes drepanodid conodonts with drepanodiform
and oistodiform elements. The basal cavity tends to become inverted
anteriorly. Drepanodiform elements tend to develop a sharp, low costa on
each side. Base of oistodiform elements is roughly square in side view and
does not extend very far anteriorly" (op. cit. Lindstrom, 1971, p. 46).
Remarks: In addition to drepanodiform and oistodiform elements, slightly
asymmetrical forms with a basal cavity opening to one side (= scandodiform
elements) are also part of the species of this genus.
Paroistodus amoenus (LINDSTROM)
(PI. 7, figs. 8-11)
Drepanodus amoenus LINDSTROM, 1955a, p. 588, PI. 2, figs. 25, 26; Fig. 4b.
Oistodus parallelus PANDER. LINDSTROM, 1955a, p. 579, PI. 4, figs. 27-29; Fig. 3N, not PI. 4, figs.
26,30,31; Fig. 30.
Paroistodus numarcuatus (LINDSTROM) pars, emend. LINDSTROM, 1971, p. 46, fig. 8.
Remarks: The oistodiform element (see PI. 7, figs. 10, 11) is very similar to
that of Paroistodus parallelus (PANDER) (see PI. 7, figs. 13,15,17). In the
former the basel cusp proportion is relatively smaller, the angle between the
posterior and the oral edge is larger and the antero-basal part of the base is
seldom inverted.
As shown in figs. 8 and 9 of PI. 7, the base of the drepanodiform elements
is roughly triangular or quadrangular in lateral view. Usually, the lower parts
of the anterior and posterior edges are prominently keeled. This is an
important feature to differentiate the form species Drepanodus amoenus
LINDSTROM from Drepanodus sculponea LINDSTROM or from Drepanodus
proteus LINDSTROM. In the drepanodiform elements the anterior stretch of
the aboral margin may be open. In these forms the basal cavity flares and
may open to one side (= scandodiform elements). The latter types resemble
the form species Scandodus pipa LINDSTROM (= the scandodiform element