UTRECHT MICROPALEONTOLOGICAL BUllETINS

posterior edges are not sharp. The anterior edge is e.xtended antero-basally to
form an anterior process which is undenticulated and may be bent sidewards.
The posterior process is low and tapers gradually in posterior direction. It
carries many subequal denticles which are fused at their bases. The posterior
stretch of the aboral margin is almosTstraight but it curves gradually
downwards in anterior direction. The oral outline of the basal cavity is
nearly straight. The same is true for its anterior outline, which runs very
close to the anterior edge. The tip of the basal cavity penetrates into the base
of the cusp.
The gothodiform element (PI. 6, figs. lOa, b) is quite similar to the
prioniodinaform element. It has a sharp costa to one side of the cusp, which
extends over the base and forms a bulge-like extension of the aboral margin.
The anterior denticles of the posterior process are proclined, like the cusp,
and they may be entirely isolated from each other. The bCl-salsheath is
remarkably thin between the lateral costa and the anterior and posterior
processes.
The oepikodiform element (PI. 6, figs. lla, b) was described by Lindstrom
(1955a) and illustrated by the same author (1971) as part of his multielement
species Gothodus costulatus .. Most of the other elements referred to '
this multi-element species by Lindstrom (1971), form part of a species
described herein as Prioniodus deltatus (LINDSTROM), emend. herein (PI. 8,
figs. 1-9).
The roundyaform element (PI. 6, figs. 12a, b) has a proclined cusp.
Anteriorly it is rounded and the posterior edge of the cusp is sharp.
Antero-Iaterally there are two costae which gradually pass into antero-basal
processes. The posterior process is denticulated with proclined denticles,
which are only fused at their extreme bases. The basal sheath is thin and flat.
It connects the antero-basal and the posterior processes, which therefore are
not true processes as they are not free. The basal cavity is deep, pyramidal
and triangular in cross section. Its tip penetrates into the base of the cusp.
The oistodiform element (PI. 6, figs. 13, 14) is slightly bent sidewards.
The cusp is robust, bladelike, reclined and almost straight. Only the basal
stretch of the anterior edge is recurved and a little extended antero-basally.
The posterior 'edge is reclined and meets the oral edge at an angle of about
50°. The oral edge is straight to slightly convex. It is keeled. The base bulges
on the inner side of the unit. The basal cavity is rather shallow. The aboral
margin is straight posteriorly and curves downwards in anterior direction. At
both lateral sides the ahoral margin shows a sinuous curvature at the point of
its downwards inflexion. The one of the outer side is less prominent than the
other. This oistodiform element is very similar to that of Prioniodus deltatus