UTRECHT MICROPALEONTOLOGICAL BUllETINS

flaring and opens to the least convex side of the unit. The basal cavity is
equilaterally triangular in side view. The oral edge may be absent and then
the base is hardly distinct from the cusp. If present, it is highly keeled, just
like the basal stretch of the anterior edge.
The acodiform elements (PI. 5, figs. Sa, b) have sharp antero-lateral, lateral
and posterior edges. These continue over the base and reach the aboral
margin. The facets between the edges are flat or convex outwards. The base
as well as the cusp are well rounded anteriorly as the anterior edge is flexed
sidewards. The basal cavity is an equilateral triangle in lateral view. The
aboral margin is slightly convex outwards between the edges. Like all
elements of this species this one is hyaline and a straight growth axis runs
visibly from the tip of the basal cavity to the tip of the cusp. The cusp is
slightly reclined to erect.
The roundyaform element (PI. 5, figs. 7a, b) is quite similar to the
acodiform element. This unit is bilaterally symmetrical, however; its anterior
side is rounded and both lateral costae are anteriorly located.
The oistodiform element (see PI. 5, fig. 1) was figured and described by
Sergeeva (1963).
Regional occurrence: At Kopingsklint as well as in section 6 this species was
found in the topmost 0.20 m. of the Bruddesta Formation and in the
remaining upper portion of the sequences studied. Near Horns Udde it is
confined to the Horns Udde Formation.
Biostratigraphic range: Triangulodus brevibasis was found in the Triangulodus
brevibasis Assemblage Zone (fig. 15).
Triangulodus subtilis n. sp.
(PI. 5, figs. 8~ 13)
Derivatio nominis: subtilis, Lat. = fine (not coarse).
Holotype: The acodiform element of this multi-element species, PI. 5, figs.
12a, b, cat. nr. T 198-13.
Figured paratypoids: The oistodiform element (PI. 5, figs. 8, 9), the erectscandodiform
element (PI. 5, figs. lOa, b), the drepanodiform element (PI. 5,
fig. 11) and the roundyaform element (PI. 5, figs. 13a, b). Cat. nrs. T198-14
to 18.
Type-stratum: The uppermost limestone bed of member Kk2 at Kopingsklint
section 1; see also sample 13, chart II.
Diagnosis: A Triangulodus species with relatively small and fine elements of
white colour.
Description: So far, the scandodiform or paltodiform elements are unknown
and thus may not exist.