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Isabelidinium cretaceum
Isabelidinium cretaceum (Cookson, 1956) Lentin and Williams, 1977
Originally Deflandrea, subsequently Isabelia (combination illegitimate), thirdly (and now) Isabelidinium, fourthly Manumiella? This species was retained in Isabelidinium by Bowman et al. (2012, p.54).
Of the original illustrations in the protologue, pl.1, figs.6–7 were considered by Cookson and Eisenack (1960a, p.4) to belong to their new species, Nelsoniella aceras; pl.1, fig.5 was considered by Lentin and Williams (1985, p.231) to belong to Manumiella delicata; thus, only pl.1, figs.1–4 are now considered to belong to this species.
Holotype: Cookson, 1956, pl.1, fig.1; Helby et al., 1987, fig.42L.
Locus typicus: Nelson Bore, Victoria, Australia
Stratum typicum: Late Cretaceous
Original description: Cookson, 1956, p.184: Deflandrea cretacea
Cell always encysted. Theca broadly and bluntly fusiform to almost circular in outline, truncate or slightly concave posteriorly, either concave, rounded, or broadly tapered anteriorly; epitheca sometimes with a minute blunt median projection (Plate 1, Fig. 4); neither transverse girdle nor longitudinal furrow observed; in the region of the cyst one face is plane, the other convex.
The cyst, which is generally crumpled, is large in proportion to the size of the cell, and when fully expanded occupies the greater part of the theca (Plate 1, Fig. 3). A clearly marked, roughly polygonal aperture is present on the convex side of the epitheca.
The membrane of the theca is more or less coarsely granular, that of the cyst is smooth.
Dimensions.--Holotype: theca 55 µm long and 52 µm broad. Range: length of theca 45-65 µm, breadth of theca 43-56 µm.
Affinities:
Cookson, 1956, p.184: Deflandrea cretacea
D. cretacea is of essentially the same type as Deflandrea bakeri Deflandre and Cookson, 1955 (Paleocene Pebble Point Formation, Vic.), and D. bakeri f. pellucida Defl. and Cookson (Nelson Bore, Vic., at 3874 ft), but differs from both in its length, which is only about half that of these forms, and in the absence of a well-marked anterior prominence.
Originally Deflandrea, subsequently Isabelia (combination illegitimate), thirdly (and now) Isabelidinium, fourthly Manumiella? This species was retained in Isabelidinium by Bowman et al. (2012, p.54).
Of the original illustrations in the protologue, pl.1, figs.6–7 were considered by Cookson and Eisenack (1960a, p.4) to belong to their new species, Nelsoniella aceras; pl.1, fig.5 was considered by Lentin and Williams (1985, p.231) to belong to Manumiella delicata; thus, only pl.1, figs.1–4 are now considered to belong to this species.
Holotype: Cookson, 1956, pl.1, fig.1; Helby et al., 1987, fig.42L.
Locus typicus: Nelson Bore, Victoria, Australia
Stratum typicum: Late Cretaceous
Original description: Cookson, 1956, p.184: Deflandrea cretacea
Cell always encysted. Theca broadly and bluntly fusiform to almost circular in outline, truncate or slightly concave posteriorly, either concave, rounded, or broadly tapered anteriorly; epitheca sometimes with a minute blunt median projection (Plate 1, Fig. 4); neither transverse girdle nor longitudinal furrow observed; in the region of the cyst one face is plane, the other convex.
The cyst, which is generally crumpled, is large in proportion to the size of the cell, and when fully expanded occupies the greater part of the theca (Plate 1, Fig. 3). A clearly marked, roughly polygonal aperture is present on the convex side of the epitheca.
The membrane of the theca is more or less coarsely granular, that of the cyst is smooth.
Dimensions.--Holotype: theca 55 µm long and 52 µm broad. Range: length of theca 45-65 µm, breadth of theca 43-56 µm.
Affinities:
Cookson, 1956, p.184: Deflandrea cretacea
D. cretacea is of essentially the same type as Deflandrea bakeri Deflandre and Cookson, 1955 (Paleocene Pebble Point Formation, Vic.), and D. bakeri f. pellucida Defl. and Cookson (Nelson Bore, Vic., at 3874 ft), but differs from both in its length, which is only about half that of these forms, and in the absence of a well-marked anterior prominence.