UTRECHT MICROPALEONTOLOGICAL BUllETINS

Genus Oistodus PANDER, emend. VAN WAMEL, herein
Type species: Oistodus lanceolatus PANDER, 1856.
Synonyms: Oistodus PANDER, 1856, p. 27.
Oistodus PANDER, emend. LINDSTROM, 1955a, p. 572.
Oistodus PANDER, emend. LINDSTROM, 1971, p. 35.
Remarks: According to Lindstrom's (1971) last redefinition of the genus,
only hyaline conodonts should be included. However, hyaline specimens of
the type species often occur together with partially white or almost entirely
white individuals. Furthermore, the symmetry transitions characteristic for
Oistodus lanceolatus PANDER emend. LINDSTROM, 1971, appear to be
present in an entirely white coloured conodont species i.c. Oistodus papiliosus
n. sp.. As a consequence, it is suggested to redefine the genus Oistodus
as:
A multi-element genus including both hyaline and white conodonts with
symmetry transitions from simple forms without any lateral costa (oistodiform
elements), through forms with a strongly developed costa on one side
(triangulariform elements), to symmetrical forms with two antero-Iateral
costae and no anterior edge (deltaform elements).
Oistodus lanceolatus PANDER. emend. VAN WAMEL, herein
(PI. 1, figs. 15-17)
Oistodus lanceolatus PANDER, 1856, p. 27, Pi. 2, figs. 17-19. LINDSTROM, 1955a, p. 577, Pi. 3,
figs. 58-60.
Oistodus lanceolatus PANDER, emend. LINDSTROM, 1971, p. 38.
Oistodus triangularis LINDSTROM, 1955a, p. 591, Pi. 5, figs. 45, 46.
Oistosus delta LINDSTROM 1955a, p. 573, Pi. 3, figs. 3-9
Remarks: In all elements of this species hyaline specimens were found
associated with identical individuals, partially or almost entirely composed
of "white matter". In most casses, the "white matter" is confined to the cusp.
The triangulariform elements may have one or two additional costae, usually
running postero-laterally of the main costa (see PI. 1, fig. 16).
Regional occurrence: At Kopingsklint the species occurs in the basal 2.40 m.
of the Bruddesta Formation. In section 6 from the base of member Kk3 up
to a level at 3.00 m. above the base of the Bruddesta Formation. Near Horns
Udde from the base of member K k3 up to a level at 2.30 m. above the base
of the Bruddesta Formation.
Biostratigraphic range: Oistodus lane eo latus was found from the Oistodus
lanceolatus/Prioniodus deltatus Assemblage Zone up to and including part of
the Microzarkodina flabellum Assemblage Zone (fig. 15).