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Leptodinium arcuatum

Leptodinium arcuatum Klement, 1960, p.48, pl.6, figs.5–6. Emendations: Gitmez, 1970, p.270; Sarjeant, 1984a, p.163–164.

Holotype: Klement, 1960, pl.6, figs.5-6; Sarjeant, 1984, pl.1, figs.1-2, text-fig.4; Jan du Chene et al., 1986, pl.67, figs.9-12
Paratypes: Klement, 1960
Locus typicus: Scherstetten 1 Well, SW Germany
Stratum typicum: Middle Oxfordian
Translation Klement, 1960: LPP

Original description: Klement, 1960, p. 48
Diagnosis: A Leptodinium species of a squat figure, mostly broader than long. Epitheca calotte-shaped. Hypotheca definitely polyhedrical, with a trapezoid outline. Girdle-furrow spiral, displacement of the ends around three times its width. Longitudinal furrow relatively narrow, its course winding from the first apical plate down to the antapex.
Description (annotated): The plate pattern and structural characteristics of L. arcuatum grossly correspond to those of L. subtile. The general appearance, however, is determined by the apical, broadly spread, arch-shaped rounding of the epitheca and the clearly polyhedrical hypotheca in the form of a blunt pyramid. The squat shell is broader than long. The sutures bear low to middle-broad, smooth-rimmed septa, which may be reduced or absent on the ventral side of the eiptheca. Pattern and form of the plates correspond to those of L. subtile. The epithecal plates are convex. Archaeopyle precingular (P3). The ends of the spiral girdle-furrow show a remarkably high displacement of up to 3 times the width. The girdle-furrow appears to be sunk between the flanking septa, and stands out in outline. The longitudinal furrow streches in a narrow, winding course from the first apical plate down to the antapex, without showing a further differentiation.
Sizes: holotype L:B (including septa): 74:77 Ám. Paratypes: 72:77 Ám, 70:77 Ám. Septa around 4 Ám.

Emended diagnosis: Gitmez, 1970, p. 270
A Leptodinium having a relatively large, subspherical shell. Tabulation: 4", 1a, 6"", 6C, 5""", 1p and 1""""; plates bordered by delicate, high crests. Cingulum helicoid, laevorotatory; sulcus long, extending on the epitract and hypotract for nearly equal lengths and broadening on the hypotract. Surface of the shell very finely granular or smooth. A large precingular archaeopyle forms by loss of plate 3"".
Description: The subspherical shell is divided by the laevorotatory cingulum into two parts. The epitract is approximately hemispherical, the hypotract is in the form of a truncated cone. The crests are thin and high; their distal edge is always smooth.
The crests separate the four apical plates at the apex: plate 1" and 3" are smaller than plates 2" and 4". Precingular plates are large, only plate 6" is somewhat reduced to accommodate intercalary plate Ia, which is long. Five well-developed postcingular plates are present, plate 5""" being smaller than the other postcingular plates. Posterior intercalary plate 1p is placed between the plates 1""" and 1"""". The antapex is occupied by a single antapical plate 1"""". The sulcus is long, extending between the apex and the antapex and broadening posteriorly.

Emended diagnosis: Sarjeant, 1984, p.163-164
Cyst proximate, acavate. Ambitus broadly ovoidal to rounded-hexagonal or almost lozenge-shaped, somewhat broader than long. Epitract and hypotract of comparable size; epitract almost hemispherical, hypotract approaching the form of a truncated cone. Parasutures marked by crests of moderate height, entire to undulose, rarely fenestrate. Paratabulation 2pr, 4", ?0a, 6"", 6c, 5""", 1p, 1pv, 1"""". Cingulum of moderate breadth, forming a laevorotatory spiral whose two ends differ in anteroposterior position by 1 1/2 times its width. Sulcus short and fairly broad, confined to the central portion of the ventral surface and widening laterally to its junction with 1""". Typically it is not divided into paraplates but exhibits flagellar marks. Paraplate lpr is small and circular, wrapped around on its left ventral flank by 2pr. Paraplate 4" is somewhat longer than 6"", both paraplates being of quadrate shape. Their mutual boundary is long and intersects the right lateral boundary of 1" at the level of its junction with the sulcus. Phragma thin and punctate, the punctations of variable size and density. Archaeopyle single-plate precingular, Type P (3"" only); operculum free.
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