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Deflandrea belfastensis
Deflandrea belfastensis Cookson and Eisenack, 1961
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, 1961, pl.11, fig.4
Locus typicus: Belfast No. 4 Bore, Victoria, Australia
Stratum typicum: Senonian
Original description: Cookson and Eisenack, 1961, p.71
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 Ám, breadth 63 Ám, internal body 48x56 Ám. Range length 94-120 Ám, breadth 54-68 Ám.
Affinities:
Cookson and Eisenack, 1961, p.71: 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, 1961, pl.11, fig.4
Locus typicus: Belfast No. 4 Bore, Victoria, Australia
Stratum typicum: Senonian
Original description: Cookson and Eisenack, 1961, p.71
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 Ám, breadth 63 Ám, internal body 48x56 Ám. Range length 94-120 Ám, breadth 54-68 Ám.
Affinities:
Cookson and Eisenack, 1961, p.71: 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.