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Isabelidinium belfastense
Isabelidinium belfastense (Cookson and Eisenack, 1961) Lentin and Williams, 1977
Taxonomic senior synonym: Deflandrea (now Isabelidinium) cooksoniae according to Fensome et al. (2009, p.39).
Originally Deflandrea, subsequently Isabelia (combination illegitimate), thirdly Isabelidinium.
Holotype: Cookson and Eisenack, 1961a, pl.11, fig.4; Helby et al., 1987, fig.41D.
Locus typicus: Belfast No. 4 Bore, Victoria, Australia
Stratum typicum: Senonian
Age: Late Cretaceous.
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G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Isabelidinium belfastense (Cookson and Eisenack, 1961) Lentin and Williams, 1977a. According to Cookson and Eisenack (1961a), this species has convex sides in the middle region slanting slightly towards both apex and antapex. There is a short blunt apical horn, which may end in a short solid process. The antapex is broadly truncate or slightly concave with 2 short, laterally placed, approximately equal blunt horns. There is no indication of a cingulum. Surface of pericyst distinctly and coarsely granular in the apical and antapical regions, smooth in the vicinity of the endocyst. Size: overall length 94-120 µm, width 54-68 µm.
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Original description: Cookson and Eisenack, 1961, p.71: Deflandrea belfastensis
Shell considerably longer than broad, sides convex in the middle region slanting slightly towards both apex and antapex. At the apex there is a short but decided bluntly-pointed horn which occasionally ends in a minute solid process which may be turned inwards. The antapex is broadly truncate or slightly concave with 2 short laterally placed, approximately equal, blunt horns. There is no indication of a girdle, longitudinal furrow or tabulation. The surface of the shell is distinctly and rather coarsely granular in the apical and antapical regions smooth in the vicinity of the internal body.
The internal body is oval to nearlv circular in surface view, its longer axis being perpendicular to the longitudinal axis of the shell. It does not extend to the lateral margins of the shell but projects prominently on the ventral surface. The pylome is rather large and hoof-shaped.
Dimensions: Type--length 109 µm, breadth 63 µm, internal body 48x56 µm. Range --length 94-120 µm, breadth 54-68 µm.
Affinities:
Cookson and Eisenack, 1961, p.71: Deflandrea belfastensis
This species is closely related to D. bakeri Deflandre and Cookson (1955). It differs from this species in (1) the narrower shape of the shell and its more sloping sides, (2) the more constant and stronger development of the apical horn, (3) the more prominent antapical horns, (4) the complete absence of a girdle which Deflandre and Cookson mention as being developed in D. bakeri. D. belfastensis is the older species and it seems likely that D. bakeri was derived directly from it.
D. belfastensis also seems close to D. cretacea Cookson. The general build and ornamentation is the same but in D. cretacea the apical and antapical horns are only occasionally slightly represented and the shell is considerably less elongated.
Taxonomic senior synonym: Deflandrea (now Isabelidinium) cooksoniae according to Fensome et al. (2009, p.39).
Originally Deflandrea, subsequently Isabelia (combination illegitimate), thirdly Isabelidinium.
Holotype: Cookson and Eisenack, 1961a, pl.11, fig.4; Helby et al., 1987, fig.41D.
Locus typicus: Belfast No. 4 Bore, Victoria, Australia
Stratum typicum: Senonian
Age: Late Cretaceous.
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G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Isabelidinium belfastense (Cookson and Eisenack, 1961) Lentin and Williams, 1977a. According to Cookson and Eisenack (1961a), this species has convex sides in the middle region slanting slightly towards both apex and antapex. There is a short blunt apical horn, which may end in a short solid process. The antapex is broadly truncate or slightly concave with 2 short, laterally placed, approximately equal blunt horns. There is no indication of a cingulum. Surface of pericyst distinctly and coarsely granular in the apical and antapical regions, smooth in the vicinity of the endocyst. Size: overall length 94-120 µm, width 54-68 µm.
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Original description: Cookson and Eisenack, 1961, p.71: Deflandrea belfastensis
Shell considerably longer than broad, sides convex in the middle region slanting slightly towards both apex and antapex. At the apex there is a short but decided bluntly-pointed horn which occasionally ends in a minute solid process which may be turned inwards. The antapex is broadly truncate or slightly concave with 2 short laterally placed, approximately equal, blunt horns. There is no indication of a girdle, longitudinal furrow or tabulation. The surface of the shell is distinctly and rather coarsely granular in the apical and antapical regions smooth in the vicinity of the internal body.
The internal body is oval to nearlv circular in surface view, its longer axis being perpendicular to the longitudinal axis of the shell. It does not extend to the lateral margins of the shell but projects prominently on the ventral surface. The pylome is rather large and hoof-shaped.
Dimensions: Type--length 109 µm, breadth 63 µm, internal body 48x56 µm. Range --length 94-120 µm, breadth 54-68 µm.
Affinities:
Cookson and Eisenack, 1961, p.71: Deflandrea belfastensis
This species is closely related to D. bakeri Deflandre and Cookson (1955). It differs from this species in (1) the narrower shape of the shell and its more sloping sides, (2) the more constant and stronger development of the apical horn, (3) the more prominent antapical horns, (4) the complete absence of a girdle which Deflandre and Cookson mention as being developed in D. bakeri. D. belfastensis is the older species and it seems likely that D. bakeri was derived directly from it.
D. belfastensis also seems close to D. cretacea Cookson. The general build and ornamentation is the same but in D. cretacea the apical and antapical horns are only occasionally slightly represented and the shell is considerably less elongated.