UTRECHT MICROPALEONTOLOGICAL BUllETINS

of Drepanodus arcuatus PANDER, emend. herein, see PI. 1, fig. 12).
Regional occurrence: At Kopingsklint this species occurs from the top of
member Dk 1 up to the top of member Kk2' In section 6 this species was not
found. Near Horns Udde it occurs from member Dh 1 up to half height
member Kk2'
Biostratigraphic range: This species was found from the Drepanoistodus
numarcuatus/Paroistodus amoenus Assemblage Zone up to and including the
Triangulodus subtilis/Gothodus microdentatus Assemblage Zone (fig. 15).
Paroistodus parallelus (PANDER), emend. VAN WAMEL, herein
(PI. 7, figs. 12-17)
Oistodus parallelus PANDER, 1856, p. 27, PI. 2, fig. 40.
Paroistodus parallelus (PANDER), emend. LINDSTROM, 1971, p. 47, figs. 8, 11.
Drepanodus proteus LINDSTROM, 1955a, p. 556, PI. 3, figs. 18-21; Figs. 2a-f, j.
Paroistodus proteus (LINDSTROM), emend. LINDSTROM, 1971, p. 46, figs. 8, 10.
Oistodus originalis SERGEEVA, 1963, p. 98, PI. 7, figs. 8, 9.
Paroistodus originalis (SERGEEVA), emend. LINDSTROM, 1971, p. 48, figs. 8, 12.
Distacodus expansus (GRAVES & ELLISON). LINDSTROM, 1955a, p. 555, PI. 3, figs. 13-17; Figs.
2g-i.
Remarks: The oistodiform elements (PI. 7, figs. 13, 15, 17) are identical
with Oistodus parallelus PANDER, 1856.
The drepanodiform elements (see PI. 7, figs. 12, 14, 16) were previously
called Drepanodus proteus LINDSTROM, Distacodus expansus (GRAVES &
ELLISON) or Oistodus originalis SERGEEV A, which types often occur
together in the Oland material. According to their original descriptions, the
difference between Drepanodus proteus and Distacodus expansus would be
the absence of lateral costae in the former. There are intermediate variants,
however, with sharp carinae or rounded costae, which intergradation devaluates
this criterion of differentiation. Oistodus originalis SERGEEV A is
rounded antero-basally and lacks an antero-basal flange; its posterior edge
and the oral edge together form a single, evenly recurved line. In the Oland
marerial, the latter forms are present in the lower samples, together with the
other drepanodiform variants. Higher up in the rock-sequence the Oistodus
originalis SERGEEV A-like elements form a larger part of the multi-element
assemblage, which fact might enable the distinction of a multi-element
species Paroistodus originalis (SERGEEV A), emend. LINDSTROM, 1971.
Biometrical data and statistical methods are required to define the boundary
between these two multi-element species. For the time being, Oistodus
originalis SERG EEVA is considered to be part of Paroistodus parallelus
(PANDER), emend. VAN WAMEL,herein.
Scandodiform variants of the drepanodiform elements also occur. These