UTRECHT MICROPALEONTOLOGICAL BUllETINS

navis/P.crassulus Zone (figs. 15 and 19).
The upper part of Lindstrom's Prioniodus evae Zone, in which Prioniodus
evae is scarce or absent, can be correlated approximately with the middle
part of the Prioniodus navis/P.crassulus Zone of N.W. bland (charts II, III
and IV). In fig. 19, Lindstrom's entire Prioniodus evae Zone then seems to
be correlative with the uppermost part of Tjernvik's Zone of Plesiomegalaspis
planilimbata together with Tjernvik's Zone of Megalaspides dale carlicus
and possibly with part of his zone of Plesiomegalaspis estonica, i.e. with
the uppermost portion of the Swedish Zone of Didymograptus balticus
together with the Zone of Phyllograptus densus and possibly with part of the
Zone of Phy IIograptus angustifolius elongatus.
Lindstrom (1971, fig. 1) himself correlated his Zone of Prioniodus evae
with the Swedish Zone of Phyllograptus densus together with the Zone of
Phyllograptus angustifolius elongatus, or to the upper part of his Billingen
Substage. According to Lindstrom (1971, p. 30), the upper boundary of this
substage is marked "by a bed containing brightly coloured discontinuity
surfaces and amphora-shaped borings". Obviously, Lindstrom meant what
was called "the Flowery Sheet" in this paper, and the fact should be
remarked, that on bland Oepikodus evae was not found higher than a level
at about 1.20 m. below "the Flowery Sheet" (chart III).
In Lindstrom's next younger Baltoniodus triangularis Zone, Baltoniodus
triangularus (= elements referred to Prioniodus navis emend. herein) is the
leading new element and Microzarkodina flabellum is another diagnostic
species. Furthermore, Drepanoistodus forceps (= part of Drepanoistodus
forceps emend. herein) and Protopanderodus rectus would be abundantly
present. As the base of the Baltoniodus triangularis Zone is characterized by
the first appearance of Baltoniodus triangularis, this boundary must be
correlated with the base of the Prioniodus navis/P.crassulus Assemblage Zone
(figs. 15 and 19). This implies, that the upper portion of LindstrQrn's.
Prioniodus evae Zone and the basal portion of his Baltoniodus triangularis
Zone show overlap in our zonation (fig. 19). Baltoniodus triangularis would
be succeeded by Baltoniodus navis (= part of Prioniodus navis emend.
herein) according to Lindstrom (1971, p. 31), the latter species being characteristic
for his Zone of Baltoniodus navis. The upper boundary of the latter
zone is marked by the first appearances of Paroistodus originalis (= part of
Paroistodus parallelus emend. herein), and of Oistodus brevibasis (= element
of Triangulodus brevibasis emend. herein), both species being typical for
Lindstrom's next younger Zone of Paroistodus originalis. This indicates, that
the upper boundary of the Baltoniodus navis Zone is correlative with the
upper boundary of the Microzarkodina flabellum Zone of N.W. bland. Thus