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Isabelidinium bakeri
Isabelidinium bakeri (Deflandre and Cookson, 1955) Lentin and Williams 1977; Emendation: Stover, 1974, p.169–170, as a "revised description" for Deflandrea bakeri.
Originally Deflandrea, subsequently Isabelia (combination illegitimate), thirdly (and now) Isabelidinium, fourthly Alterbia (combination illegitimate).
Yun, 1981, transferred this species to Alterbia Lentin and Williams, 1976. Lentin and Williams, 1985, retained it in Isabelidinium.
Holotype: Deflandre and Cookson, 1955, pl.4, fig.1
Paratype: Deflandre and Cookson, 1955
Locus typicus: Victoria, Australia
Stratum typicum: Paleocene-Early Eocene
Original description: Deflandre and Cookson, 1955, p.251: Deflandrea bakeri
Cell generally but not always encysted. Theca widely fusiform, somewhat obliquely truncated posteriorly; transverse girdle faint, neither hollow nor shallow, sometimes quite indistinct, dividing thr theca into two unequal parts. Longitudinal furrow not observed. Epitheca larger than hypotheca, widely conical or bell-shaped, surmounded by a short more or less bluntly pointed, slightly thickened prominence. Hypotheca like a frustum or a cone, sometimes with two unequal very short horns and occasionally a third submedian conical expansion, sometimes with a lower angle simple or one of the two rounded. In lateral view the encysted cells have an asymetrical outline with, at the level of the cyst, one face plane and the other convex. This convexity does not seem to exsist in the rare non-encysted examples that have been examined. The cyst also causes a slight frontal enlargement.
The cyst is ellipsoidal, more or less regular when viewed from front, more asymmetrical in lateral view. The encysted cells have a rather regular polygonal aperture on the convex side of the epitheca. Membrane of the theca more or less strongly and irregular punctate, except in the region of the transverse girdle, where it is generally smooth.
Dimensions: Range - theca, length 87-108 µm, breadth 54-69 µm; cyst, length 41-50 µm, breadth 50-56 µm.
Originally Deflandrea, subsequently Isabelia (combination illegitimate), thirdly (and now) Isabelidinium, fourthly Alterbia (combination illegitimate).
Yun, 1981, transferred this species to Alterbia Lentin and Williams, 1976. Lentin and Williams, 1985, retained it in Isabelidinium.
Holotype: Deflandre and Cookson, 1955, pl.4, fig.1
Paratype: Deflandre and Cookson, 1955
Locus typicus: Victoria, Australia
Stratum typicum: Paleocene-Early Eocene
Original description: Deflandre and Cookson, 1955, p.251: Deflandrea bakeri
Cell generally but not always encysted. Theca widely fusiform, somewhat obliquely truncated posteriorly; transverse girdle faint, neither hollow nor shallow, sometimes quite indistinct, dividing thr theca into two unequal parts. Longitudinal furrow not observed. Epitheca larger than hypotheca, widely conical or bell-shaped, surmounded by a short more or less bluntly pointed, slightly thickened prominence. Hypotheca like a frustum or a cone, sometimes with two unequal very short horns and occasionally a third submedian conical expansion, sometimes with a lower angle simple or one of the two rounded. In lateral view the encysted cells have an asymetrical outline with, at the level of the cyst, one face plane and the other convex. This convexity does not seem to exsist in the rare non-encysted examples that have been examined. The cyst also causes a slight frontal enlargement.
The cyst is ellipsoidal, more or less regular when viewed from front, more asymmetrical in lateral view. The encysted cells have a rather regular polygonal aperture on the convex side of the epitheca. Membrane of the theca more or less strongly and irregular punctate, except in the region of the transverse girdle, where it is generally smooth.
Dimensions: Range - theca, length 87-108 µm, breadth 54-69 µm; cyst, length 41-50 µm, breadth 50-56 µm.