UTRECHT MICROPALEONTOLOGICAL BUllETINS

flat ones; while the base can be laterally compressed to widely flaring
sidewards. The robust forms with rounded cusps and rather wide bases were
described as Drepanodus cf. subarcuatus by Lindstrom (1955a). The laterally
compressed units were called Drepanodus deltifer by this author.
The variation in the shape of the oistodiform element (see PI. 2, fig. 7) is
wide too; almost erect (= Scandodus varanguensis VIIRA) to strongly reclined
forms (= Oistodus inaequalis PANDER) may occur together. The
oistodiform elements of Drepanoistodus inaequalis strongly resemble comparable
elements of Drepanoistodus inconstans emend. herein (see PI. 3,
fig. 11). The latter elements have a more pronounced rounded costa to the
innerside of the cusp and they have a parapet-like extension of the base to
this side.
The scandodiform elements (see PI. 2, figs. 11, 12) are asymmetrical
variants of the drepanodiform elements. They have one prominent carina
and the base opens to one side of the unit. These forms take an intermediate
position between the drepanodiform and the acodifoim elements (= Acodus
tetrahedron LINDSTROM, see PI. 2, fig. 13 herein). Other scandodiform
elements are slightly bent sidewards, with the basal sheath of the outer side
extended in aboral direction (see PI. 2, fig. 12 and Machairodus ensiformis).
The suberectiform element (see PI. 2, fig. 8) was described earlier as
Drepanodus bisymmetricus VIIRA and as Drepanodus pristinus VIIRA. It is
a bilaterally symmetrical unit, without a sharp distinction between the base
and the cusp. The basal cavity is wide sidewards and its tip penetrates into
the basal portion of the erect cusp. In side view the outline of the basal
cavity is concave posteriorly and convex anteriorly. The aboral margin is
faintly sinuous and slightly extended in antero-aboral direction. It is indented
where the two lateral carinae meet the aboral margin. The cusp is
sharply pointed and it has a lanceolate cross section. The lack of anterolateral
costae enables differentiation of these suberectiform elements from
those of Drepanoistodus acuminatus (PANDER) (see PI. 2, figs. 3a, b) and of
the suberectiform elements of Drepanoistodus inconstans (LINDSTROM)
(see pI. 3, fig. 12).
Regional occurrence: At Kopingsklint this species occurs from the base of
member Da-d 2 ,up to the top of member Kk 1. In section 6 this species was
not found with certainty. Near Horns Udde it occurs from member D h 1 up
to and including part of member Kk 2.
Biostratigraphic range: Drepanoistodus inaequalis was found from the
Cordylodus rotundatus Assemblage Zone up to and including the Prioniodus
deltatus Assemblage Zone (fig. 15).