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Isabelidinium cooksoniae
From Fensome et al., 2019:
Isabelidinium cooksoniae (Alberti, 1959b, p.97, pl.9, figs.1–6) Lentin and Williams, 1977a, p.167. Holotype: Alberti, 1959b, pl.9,
fig.2. Originally Deflandrea, subsequently Australiella, thirdly Isabelia (combination illegitimate), fourthly (and now) Isabelidinium. Taxonomic junior synonyms: Deflandrea (as Isabelidinium) belfastensis and Isabelidinium bujakii, according to Fensome et al. (2009, p.39). Age: Late Cretaceous.
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Original description, Alberti, 1959: Deflandrea cooksoni n. sp. (Taf. 9 Fig. 1-6)
Derivatio nominis: In honor of Mrs. Dr. I. Cookson, Melbourne.
Holotype: The specimen preserved in specimen no. Oeb/S 1 and shown on plate 9, fig. 2.
Locus typicus: Oebisfelde (Altmark) borehole
Stratum typicum: Upper "Senon".
Diagnosis: Carapace flattened, its outline elongated, pentagonal-rounded to oval, often slightly deviating from this. The shoulder-shaped epithet, approximately the length of the hypotheca, is extended into a small, slightly distinct apical horn. The transverse furrow is usually absent, if present, very shallowly indented. Usually only one antapical horn, often oblique to the longitudinal axis of the carapace. The inner body is elliptical, its longitudinal axis perpendicular to that of the carapace, causing a bulge in the carapace, which fits tightly to the inner body. The carapace membrane is granulated, that of the inner body is rough.
Additions: One of the two anta-apical horns may be completely or partially reduced. At the level of the completely reduced lateral horns, the carapace is sometimes slightly notched; a transverse furrow is rarely present. The archeopyle is trapezoidal-rounded. The apical horn has an opening at its free end.
Differential diagnosis: The outline of the epi- and hypothalamus and the antapical horn, which is oblique to the longitudinal axis, distinguish it from the Australian species Defl. pellucida Cookson & Eisenack. Compared to all other species of the genus, Defl. cooksoni n. sp. is well characterized.
Dimensions of the holotype: Length 72 μm, width 48 μm. In other specimens, the length varies between 68 μm and 96 μm, and the width between 40 μm and 54 μm.
Material: Over 40 specimens
Occurrence: Upper "Senon" of the Oebisfelde region (Altmark)
Isabelidinium cooksoniae (Alberti, 1959b, p.97, pl.9, figs.1–6) Lentin and Williams, 1977a, p.167. Holotype: Alberti, 1959b, pl.9,
fig.2. Originally Deflandrea, subsequently Australiella, thirdly Isabelia (combination illegitimate), fourthly (and now) Isabelidinium. Taxonomic junior synonyms: Deflandrea (as Isabelidinium) belfastensis and Isabelidinium bujakii, according to Fensome et al. (2009, p.39). Age: Late Cretaceous.
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Original description, Alberti, 1959: Deflandrea cooksoni n. sp. (Taf. 9 Fig. 1-6)
Derivatio nominis: In honor of Mrs. Dr. I. Cookson, Melbourne.
Holotype: The specimen preserved in specimen no. Oeb/S 1 and shown on plate 9, fig. 2.
Locus typicus: Oebisfelde (Altmark) borehole
Stratum typicum: Upper "Senon".
Diagnosis: Carapace flattened, its outline elongated, pentagonal-rounded to oval, often slightly deviating from this. The shoulder-shaped epithet, approximately the length of the hypotheca, is extended into a small, slightly distinct apical horn. The transverse furrow is usually absent, if present, very shallowly indented. Usually only one antapical horn, often oblique to the longitudinal axis of the carapace. The inner body is elliptical, its longitudinal axis perpendicular to that of the carapace, causing a bulge in the carapace, which fits tightly to the inner body. The carapace membrane is granulated, that of the inner body is rough.
Additions: One of the two anta-apical horns may be completely or partially reduced. At the level of the completely reduced lateral horns, the carapace is sometimes slightly notched; a transverse furrow is rarely present. The archeopyle is trapezoidal-rounded. The apical horn has an opening at its free end.
Differential diagnosis: The outline of the epi- and hypothalamus and the antapical horn, which is oblique to the longitudinal axis, distinguish it from the Australian species Defl. pellucida Cookson & Eisenack. Compared to all other species of the genus, Defl. cooksoni n. sp. is well characterized.
Dimensions of the holotype: Length 72 μm, width 48 μm. In other specimens, the length varies between 68 μm and 96 μm, and the width between 40 μm and 54 μm.
Material: Over 40 specimens
Occurrence: Upper "Senon" of the Oebisfelde region (Altmark)