UTRECHT MICROPALEONTOLOGICAL BUllETINS

Remarks: The aSSOcIatIOnof the oistodiform and suberectiform elements
with the drepanodiform-, acodiform- and the scandodiform elements is a
little speculative, due to the sporadic presence of the two first mentioned
elements.
The oistodiform, suberectiform and scandodiform elements of this species
have not been described earlier.
The oistodiform element (see PI. 3, figs. 5 and 6) is either almost straight
or it may be slightly bent sidewards. The base is laterally compressed and its
aboral margin is evenly curved, convex in aboral direction. The oral edge is
rather short, it is keeled and convex upwards. The basal cavity is relatively
deep and its oral outline is convex upwards. The tip of the basal cavity is
situated rather far anteriorly and only a small and shallow extension runs
anterior of it. The cusp is relatively wide and a carina is present to both
lateral sides, the one at the inner side being slightly more pronounced. The
anterior and posterior edges are sharp and evenly curv~d, convex outwards.
The angle between the posterior edge and the oral edge varies between
20° _50° and the angle between the anterior edge and the aboral margin is
variable too. The anterior and posterior basal angles are rounded.
The suberectiform element (see PI: 3, figs. 7a, b) is wide antero-posteriorly
and it is laterally compressed. It may be slightly bent sidewards. No distinction
between cusp and base can be drawn; there is no oral edge. The basal
cavity is shallow and triangular in side view. Its tip is very sharp and points
anteriorly and upwards. To the outer side of the unit the base can flare a
little and its aboral margin can have an indentation. The cusp is blade-like,
with keeled anterior and posterior edges. These are both recurved. The
growth axis is accompanied by a rounded costa on either sides of the cusp.
Lindstrom's (1971) description of the drepanodiform element (see Pl. 3,
fig. 8) is fully adequate.
In the scandodiform elements (see PI. 3, figs. 9a, b) the cusp is bent
sidewards. The basal sheath is convex to the outside of the unit and its
aboral margin may be inflected. In side view, the outline of the basal cavity
is quite similar to that of the drepanodiform element.
Nothing needs to be added to the original description of the acodiform
element (see PI. J, figs. lOa, b). As the antero-basal costa of the acodiform
elements usually is very faint, it can be difficult to distinguish these elements
from the scandodiform elements.
Lindstrom (1971) put Drepanodus numarcuatus LINDSTROM, Drepanodus
amoenus LINDSTROM and ~Oistodus purallelus PANDER together in
one multi-element species called Paroistodus numarcuatus (LINDSTROM).
However, according to the data available now, the stratigraphic ranges of